When an erase voltage is applied to the sources of data erasable and rewritable memory cells each having a floating gate, the erasure characteristics of the memory cells can be improved by controlling the rise time of the erase voltage or by increasing the erase voltage stepwise. In test mode, no row lines are selected by a row decoder and further the sources of the respective memory cells are set to ground level. Under these conditions, in case there exists an overerased memory cell, this cell is turned on due to depletion, so that it is possible to detect the presence of the overerased memory cell on the basis of change in potential of the column line connected to this turned on memory cell. A differential amplifier is used to detect the change in potential of the column line. In the test mode, the potential of the column lines is compared with a reference potential applied to a dummy column line, and a source bias generating circuit applies a test potential suitable for test to the respective sources of the cells, to shift the threshold level of the respective cells in a positive direction, for instance. By applying this test potential to the cells, it is possible to detect the pseudo-threshold level shifted in the positive direction; that is, to detect the overerased status of the memory cell more properly.

An EEPROM (Electrically Erasable and Programmable Read Only Memory) which can electrically erase stored data and further rewrite new data therein has been widely used more and more for control apparatuses or as IC cards (memory cards ), because data can be erased easily in response to electric signals under the condition that the EEPROM is kept mounted or assembled on a board.
A memory cell structure as shown in FIGS. 1 to 4 has been so far known as the EEPROM suitable for a large capacity. FIG. 1 is a plan view showing a pattern of the memory cell; FIG. 2 is a cross-sectional view taken along the line A--A' in FIG. 1; FIG. 3 is a cross-sectional view taken along the line B--B' in FIG. 1; and FIG. 4 is an equivalent circuit thereof.
As depicted in these drawings, a gate oxide film 18 with a thickness of about 100 angstrom is formed on a region enclosed by a field oxide film 20 formed on a P type substrate 13. A floating gate 11 of a first poly silicon layer is formed via the gate oxide film 18. Further, a control gate 12 of a second poly silicon layer is formed on the floating gate 11 via an insulating film 19. The insulating film 19 is of three-layer structure, for instance such as O--N--O (oxide-Nitride-Oxide). The thickness of the insulating film 19 is about 200 angstrom in oxide film conversion. The control gate 12 is used as a word line of the memory cell. Further, another insulating layer 21 is formed on the control gate 12.
In addition, a source 14 and a drain 15 formed of an N+ type diffusion layer are formed on the P type substrate 13 and on both the sides of the floating gate 11 and the control gate 12. A contact hole 16 is formed open in the insulating layer 21 at such a position as to correspond to the drain 15. Further, a data line 17 of an aluminum layer is connected to the drain 15 through the contact hole 16.
The memory cell constructed as described above can realize the function corresponding to an equivalent circuit as shown in FIG. 4, in which D denotes the drain 15; S denotes the source 14; and CG denotes the control gate 12, respectively.
The operation of the memory cell thus constructed will be described hereinbelow.
To erase date, an erase voltage of 12 volts, for instance is applied to the source 14 with the drain kept floated. Further, the control gate 12 is set to 0 volts. Under these conditions, a relatively high erase voltage is applied between the floating gate 11 and the source 14 via the thin gate oxide film 18. Electrons in the floating gate 11 are emitted into the source 14 on the basis of Fowler-Nordheim tunnel effect, with the result that data is erased.
To write data, on the other hand, a voltage of about 6 volts is applied to the drain 15; a voltage of 0 volts is applied to the source 14; and a voltage of 12 volts is applied to the control gate 12. As a result, impact ionization occurs in the vicinity of the drain 15, so that electrons are injected into the floating gate 11 to write data therein.
Further, to read data, a voltage of 1 volt is applied to the drain 15; a voltage of 0 volts is applied to the source 14; and a voltage of 5 volts is applied to the control gate 12. Therefore, it is possible to obtain data "0" or data "1" on the basis of the presence or absence of electrons in the floating gate 11.
FIG. 5 shows a circuit configuration of the conventional semiconductor memory device using the memory cells constructed as described above, in which a flash type 8-bit EEPROM of byte structure is shown in particular by way of example.
in FIG. 5, the memory cells are arranged in a matrix pattern of m-rows and n-columns. The sources of these memory cells 30 are all connected in common to a terminal SS. The control gates of these memory cells 30 are connected to the row lines WL1 to WLm, respectively for each row. The drains of these memory cells 30 are connected to the column lines DL1 to DLn, respectively for each column.
Further, the terminal SS is connected to a source voltage control circuit 37, to which a high supply voltage is supplied through an external high voltage supply terminal Vpp. The row lines WL1 to WLm are connected to a row decoder 31. The column lines DL1 to DLn are connected to common junction points N-1 to N-8 via enhancement type column select transistors 33-1 to 33-n, respectively. Outputs of a column decoder 32 are applied to the gates of the column select transistors 33-1 to 33-n through column select lines CL1 to CLn, respectively.
Data writing enhancement type load transistors 34-1 to 34-8 are connected between the common junction points N-1 to N-8 and the external high voltage supply terminal Vpp, respectively. Written data Din*1 to Din*8 are inputted to written data control circuits 35-1 to 35-8 through external terminals, respectively. The inverted written data /Din*1 to /Din*8 (/D denotes an inversion signal of D) are inputted from the written data control circuits 35-1 to 35-8 to the gates of these load transistors 34-1 to 34-8, respectively.
Further, an output SW of a high voltage switching circuit 36 is supplied to the row decoder 31 and the column decoder 32. A high voltage is supplied to this switching circuit 36 through the external high supply voltage terminal Vpp.
Further, data reading sense amplifiers 38-1 to 38-8 including a load transistor, respectively are connected to the common junction points N-1 to N-8. Output circuits 39-1 to 39-8 for outputting data to the external terminals are connected to these sense amplifiers 38-1 to 38-8, respectively.
In a source voltage control circuit 37, an erase signal Erase is inputted to the gates of series-connected P type transistor 37A and N type transistor 37B, respectively. The output of the common-connected drains of these P and N type transistors 37A and 37B is inputted to the gates of series-connected P type transistor 37D and N type transistor 37E through the source and drain of an N type transistor 37C, respectively. The common-connected drains of these P and N type transistors 37D and 37E are connected to the terminal SS and also to the gate of the P type transistor 37F. The drain of the P type transistor 37F is connected to the gates of the P and N type transistors 37D and 37E, respectively. The source of the P type transistor 37A and the gate of the N type transistor 37C are connected to the supply voltage Vcc, respectively. The sources of the P type transistor 37F and the P type transistor 37D are connected to the external high supply voltage terminal Vpp.
The operation of the circuit configured as described above will be described hereinbelow.
To write data, a voltage of 12 volts is supplied to the external high supply voltage terminal Vpp. Upon application of 12 volts to the external high supply voltage terminal Vpp, the high voltage switching circuit 36 outputs 12 volts to the column decoder 32 and the row decoder 31 as the output SW, respectively. At the same time, one memory cell 30 for each output bit; that is, a sum total of 8 memory cells 30 for 8 output bits are selected on the basis of the column select lines CL1 to CLn and the row lines WL1 to WLm selected in response to address signals, respectively.
Here, the assumption is made that a voltage of 12 volts is applied to the selected line (e.g., WL1) of the row lines WL1 to WLm and another voltage of 12 volts is applied to the selected line (e.g., CL1) of the column select lines CL1 to CLn.
Here, when the written data Din*1 to Din*8 are at "0", the written data control circuits 35-1 to 35-8 (to which a high voltage is applied from the external high supply voltage terminal Vpp, respectively) output voltages of about 9 volts as the written data/Din*1 to Din*8, respectively, so that the load transistors 34-1 to 34-8 are turned on, respectively. Accordingly, a voltage of about 6 volts is applied from the external high supply voltage terminal Vpp to the selected lines of the column lines DL1 to DLn via the load transistors 34-1 to 34-8 and the column select transistors 33-1 to 33-n, in order to write data in the corresponding memory cells 30. On the other hand, when the written data Din*1 to Din*8 are at "1", since the written data/Din*1 to/Din*8 are at "0", the load transistors 34-1 to 34-8 are all turned off, so that no voltage is applied to the drains of the selected memory cells 30 without writing data therein.
To erase data, a high voltage of about 12 volts is supplied from the external high supply voltage terminal Vpp to the terminal SS via the source voltage control circuit 37, in order to set all the column select lines CL1 to CLn and the row lines WL1 to WLm to "0" volts, so that all the memory cells are erased simultaneously.
Further, in this case, the erasure is made by applying an erase signal Erase to the source voltage control circuit 37. However, in response to the erase signal Erase, the P type transistor 37A is turned off and the N type transistor 37B is turned on. Therefore, the P type transistor 37D is turned on through the N type transistor 37C and simultaneously the N type transistor 37E is turned off, so that the external high supply voltage Vpp is outputted to the terminal SS. At the same time, the external high supply voltage Vpp is applied to the gate of the P type transistor 37F to turn off the P type transistor 37F.
Further, to read data, the data writing load transistors 34-1 to 34-8 are always tuned off, and the output SW of the high voltage switching circuit 36 is set to Vcc (5 volts). The data "1" or "0" of the memory cells 30 selected by the column decoder 32 and the row decoder 31 are sensed and amplified by the sense amplifies 38-1 to 38-8, and then outputted to the external output terminals via the output circuits 39-1 to 39-8, respectively.
As described above, in the conventional semiconductor memory device, since the external high supply voltage Vpp is applied to the device through the source voltage control circuit 37 when data are erased, the following problems arise:
FIGS. 6A to 6C are waveform diagrams for assistance in explaining the data erasure operation, in which FIG. 6A shows the waveform of a voltage outputted from the terminal SS in response to the erase signal Erase; FIG. 6B shows the tunnel current characteristics of when a bias voltage is applied to the sources of the respective transistors of the memory cells 30; and FIG. 6C shows the load characteristics of the P type transistor 37D of the source voltage control circuit 37, respectively.
As shown in FIG. 6A, when the erase signal Erase changes to "1" in the data erasure mode, the high voltage supplied from the source voltage control circuit 37 to the terminal SS rises sharply up to 12 volts. This rise time is as fast as 1 .mu.sec or less.
In the data erasure mode, a voltage of zero volts is applied to the control gates of the memory cells 30 to obtain the floating drains thereof, and further an erase voltage is applied to the sources thereof from the source voltage control circuit 37. In this case, the tunnel current I of the transistor of the memory cell 30 changes according to the source voltage Vs, as shown in FIG. 6B. In more detail, under the condition that electrons are injected into the floating gate of the memory cell 30 and the gate is kept at a negative potential, the tunnel current flows between bands on the basis of the source voltage lower by this negative voltage, as shown by the line T in FIG. 6C. At this time, when a tunnel current i1 ampere flows between bands, electrons are extracted from the floating gate at the intersection Q between the load line R of the P type transistor 37D and the vertical line T.
With the advance of data erasure, the potential at the floating gate rises. Therefore, the current between bands decreases gradually, so that the operating point changes from the point Q to 12 volts along the line P.
In this case, however, before the source voltage reaches 12 volts, if current flows by a cause (e.g., breakdown current) other than the leak current, there exists a problem in that the source voltage will not rise up to 12 volts and therefore the tunnel current also stops.
In other words, in the data erasure, when the source voltage of the memory cell 30 rises sharply, current between bands flows, with the result that the erasure characteristics deteriorate.
Another problem will be described hereinbelow.
As already explained, the erasure of data from the memory cell is achieved by extracting electrons existing in the floating gate 11 to the source side 14 by applying a high voltage of 12 volts to the source 14. That is, tunnel current flows due to an electric field generated between the floating gate 11 and the source 14, so that data is erased.
Therefore, there exists a problem in that the erasure characteristics differ according to dispersion in the electric field. There are various factors of causing the dispersion in the electric field, for instance such as the dispersion of the gate insulating film 18, an overlap length (as shown by X.sub.js in FIG. 3) of the floating gate 11 and the source 14, etc. Accordingly, even if a voltage is applied to the source 14 for a predetermined time, since there exist various memory cells of high electric field and memory cells of low electric field, a difference in erasure characteristics occurs between the memory cells, so that there exists a distribution in the erasure status; that is, there exist various cells of high erasure speed and low erasure speed.
FIG. 7 shown the erasure characteristics, in which the abscissa designates the voltage Vg of the control gate 12 and the ordinate designates the current Id of the drain 15. This graph shown in FIG. 7 indicates that there exists a distribution in the thresholds of the memory cells from which data are erased; that is, there exists an erasure distribution between the high erasure speed cells and the low erasure speed cells. Therefore, where the memory cell LSI is erased, if the erasure operation is kept executed until the lowest erasure speed cell can be erased, there exists a problem in that the high erasure speed cell is overerased and thereby the leak current flows under the condition that the voltage Vg of the control gate 12 is kept at 0 volts. Once the overerasure occurs, the threshold voltage of the memory cell becomes negative; the depletion occurs; the cell is turned on and the current flows even if the control gate 12 is at 0 volts, with the result that a leak current inevitably flows.
FIG. 8 is a circuit diagram for assistance in explaining the operation of the memory cell LSI in which an overerased memory cell exists. In FIG. 8, the row decoder 23 determines access to the row lines WL1 to WLm. The column decoder 22 determines access to the column lines BL1 to BLn. A number of memory cells Ml1 to Mln and Mm1 to Mmn are arranged in a matrix pattern in the vicinity of the intersections between the row lines WL1 to WLm and the column lines BL1 to BLn. Here, the assumption is made that the memory cell Mmn is overerased into depletion status. The data reading sense amplifier SA is connected to the column lines BL1 to BLn.
In the circuit configuration as described above, the assumption is further made that the column decoder 22 selects the column line BLn and the row decoder 23 applies a voltage of 5 V to the row line WL1 and a voltage of 0 V to the row line WLm to select the memory cell Mln in which data "0" is written. Under these conditions, no current flows through the bit line BLn. However, since a leak current I- flows through the non-selected overerased memory cell Mmn, in spite of the fact that the control gate thereof is at 0 V, the sense amplifier SA erroneously read the data in the memory cell Mln as "1". In other words, if an overerased memory cell exists along the selected column lines BL1 to BLn, a leak current flows through the overerased cell, irrespective of the fact that the overerased cell is selected or not by the row lines WL1 to WLn, with the result that the sense amplifier SA always reads "1". Namely, it is impossible to correctly read the data from the memory cells connected to the column lines BL1 to BLn on which an overerased memory cell exists.
Accordingly, it is very important to check whether the memory cells are overerased into depletion status or not, in order to secure the reliability of the operation of the memory cell LSI. In the ordinary EEPROM, it is necessary to guarantee the number of data rewriting operations beyond 10.sup.4 to 10.sup.5 times, when the memory cells are used as a memory card. After data have been rewritten repeatedly by the above-mentioned times, since electrons are trapped in the oxide film, the data rewriting characteristics deteriorate gradually. On the other hand, if the data are rewritten by the above-mentioned 10.sup.4 to 10.sup.5 times, the test time is excessively long and also meaningless. Therefore, it is very important to determine the margin in the overerasure test.
The conventional methods of testing the overerasure are disclosed in U.S. Pat. Nos. 4,841,482 or 4,860,261, respectively. In these methods, the potential of the word lines is floated about 0.5 V, for instance to get a margin of the test for checking whether the overerasure status occurs or not. In other words, the flow of the leak current is tested under the above-mentioned condition (the word line potential is floated by 0.5 V), in order to obtain a margin of 0.5 V. This is because the non-selected word lines are set to 0 V in the actual data reading operation.
However, the conventional methods involve the following problem: when the memory cell LSIs are manufactured, the threshold levels of the memory cell LSI distribute from 2 V to 3 V in the erasure operation. On the other hand, there exists a close relationship between the threshold level of the erased memory cell and the access time of the same memory cell. When the data is erased down to a lower threshold level, since a large operating current can be obtained in the data read operation, it is possible to operate the cell at a higher speed. Here, the threshold level on which data is determined to be erased is assumed to be 2.5 V, by considering that the threshold level distribution of the memory cells is about 2 V and by anticipating that the margin thereof is 0.5 V. In this case, however, the erasure threshold levels of the acutely manufactured memory cell LSI chips distribute up to about 3 V. Therefore, if an LSI having the 3 V threshold distribution is manufactured and erased at 2.5 V in the erasure test, since a leak current flows, the LSI chip becomes defective. In other words, when the erasure operation is made at a lower threshold voltage, defective chips increase and thereby the manufacturing cost increases. In contrast with this, if the erasure level is set to a higher threshold level under consideration of the high threshold distribution chips, since sufficient operating current cannot be obtained in the data reading operation, thus raising another problem in that the operation speed is low.
As described above, in the conventional semiconductor memory device, since the memory cells cannot be erased at the lower threshold level, the memory cells are not suitable for high speed operation, and further it has been difficult to improve the operation margin.
Further, FIG. 9 shows a circuit for monitoring the threshold level Vth of the conventional LSI chip. In the threshold level (Vth) measuring test mode in FIG. 9, the signal Icell is set to "1" to turn on a transistor 101 and off a transistor 102, so that a sense amplifier circuit 103 is disconnected from the bit lines of the memory cells MC, and an I/O pad 104 is connected to the bit lines BL of the memory cells MC. As described above, a voltage is applied from the I/O pad 104 to the drains of the memory cells MC, and an external supply voltage Vpp is applied to the gates thereof via a row decoder 105. Further, the potential of the selected word lines WL is changed by changing the external supply voltage Vpp.
Here, a Vpp/Vcc switching circuit 107 switches the supply voltages Vpp and Vcc, and supplies the external high supply voltage Vpp to one terminal of a P channel transistor 105A (the final stage buffer circuit) of the row decoder 105 in the data write operation and the supply voltage Vcc thereto in data read operation. Further, a transistor 108 switches the output of the Vpp/Vcc switching circuit 107 and the external supply voltage Vpp or vice versa in the threshold level (Vth) measuring test mode. Here, the reason why an output of a booster circuit 109 is applied to the gate of the transistor 108 is to prevent the drain voltage applied to the memory cells MC from dropping by the threshold level Vth. In FIG. 9, the circuit includes a column decoder 110, transistors 111 selected by the column decoder 110, a memory cell array 112 and an output circuit 113.
The problems involved in the conventional circuit shown in FIG. 9 will be described hereinbelow.
Here, the assumption is made that after the threshold level distributes between 0 and V2 volts after erasure as shown in FIG. 10. At this time, the external supply voltage Vpp is changed to change the voltage applied to the gate of the memory cells MC. However, if the external supply voltage Vpp drops below the threshold level of the P channel transistor 105A of the row decoder 105, the P channel transistor 105A is turned off, so that the word line WL (1) changes to a floating status, thus it being impossible to apply a reliable voltage to the gates of the memory cells MC.
In other words, when the threshold level Vth of the P channel transistor 105A is V1, it is impossible to measure the threshold distribution of the memory cells whose threshold levels lie between 0 and V1 volts shown in FIG. 10. That is, the threshold distribution of the overerased cells cannot be measured, thus raising a serious problem in evaluation of the memory cell LSI.
As described above, in the conventional memory device, it has been difficult to erase the device so that the threshold levels of the memory cells become appropriate value, and in addition it has been impossible to measure the threshold levels appropriately.

Non-volatile semiconductor memory device


A framework for performing aggregation methods on hierarchical data objects is described herein. A data aggregation request is received, the request including a tree of nodes to aggregate, an aggregation method, and a filter criteria. A configuration table is used to identify previously generated aggregation hierarchies that correspond to the received request, and a mapping of attributes of the received nodes to attributes of the previously generated aggregation hierarchies. For each node in the tree of nodes, when a corresponding node in the previously generated aggregation hierarchy is identified, attribute values from the corresponding node are used to create a node in a target aggregation hierarchy. When a corresponding node does not exist, but corresponding child nodes do exist in the previously generated aggregation hierarchy, the aggregation method is applied to the corresponding child nodes and the result is used to create a node in the target aggregation hierarchy.

Performing data aggregation methods on hierarchical data can be challenging, particularly on large volumes of data, and on data stored in a relational database. Hierarchical data, in which entities are described as a tree, or with a parent/child relationship, is not easily described or queried with Structured Query Language (SQL). Moreover, such calculations tend to be resource intensive, particularly at scale.
Therefore, there is a need for an improved framework that addresses the abovementioned challenges.


A new and distinct Rhododendron cultivar named ‘HOLDEN52’ is disclosed, characterized by colorful rose-pink flowers with definite white and light pink patterning. Plants are heat tolerant to USDA zone 9 and cold hardy to Zone 5. Resistance to Phytophthora root rot has been observed. Plants have a dense, mounded habit and dark green, glossy mature foliage. The new cultivar is a Rhododendron, suitable for ornamental garden purposes.

The new cultivar is a product of a planned breeding program. This new variety, hereinafter referred to as 'HOLDEN52', was discovered as a seedling, resulting from the crossing of an unpatented, unnamed Rhododendron hyperthyrum with the pollen parent Rhododendron hybrida 'Henry's Red', unpatented. The cross resulting in the new variety occurred during 2005. The new variety was selected by the inventor during of 2010 at an arboretum in Madison, Ohio.
After identifying the new variety as a potentially interesting selection, the inventor first organized propagation of 'HOLDEN52' by vegetative cuttings Fall of 2007 at the same arboretum in Madison, Ohio. The inventor continued controlled testing and propagation, assessing stability of the unique characteristics of this variety. Multiple generations have been reproduced and have shown that the unique features of this cultivar are stable and reproduced true to type.


This invention generally relates to a composition and its production method useful for developing drugs/vaccines and/or therapies against a variety of degenerative diseases in humans. Particularly, the present invention teaches the essential steps of production and purification processes necessary for producing small hairpin-like RNA (shRNA) compositions, such as microRNA precursors (pre-miRNA) and short interfering RNAs (siRNA), which are useful for treating human ageing related diseases, such as, but not limited, Alzheimer's diseases, Parkinson's diseases, osteoporosis, diabetes, and cancers. The novelty of the present invention is to create an artificially enhanced adaptation environment for prokaryotic cells to adopt eukaryotic pol-2 and/or pol-2-like promoters for transcribing desired ncRNAs and/or their precursors without going through error-prone prokaryotic promoters, so as to improve the productive efficiency and reading fidelity of the shRNA transcription in the prokaryotic cells. The resulting shRNAs, preferably pre-miRNAs and siRNAs, are useful for developing therapeutic drugs against human degenerative diseases, particularly through a mechanism to induce CD34-positive stem cell expansion and/or regeneration.

Stem cells are like a treasure box containing numerous effective ingredients useful for stimulating new cell growth/tissue regeneration, repairing and/or rejuvenating damaged/aged tissues, treating degenerative diseases, and preventing tumor/cancer formation/progression. Hence, it is conceivable that we can use these stem cells as a tool for novel drug screening, identification and production. As a result, the drugs so obtained will be useful for developing pharmaceutical and therapeutic applications, such as a biomedical utilization, device and/or apparatus for research, diagnosis, and/or therapy, and a combination thereof.
MicroRNA (miRNA) is one of the main effective ingredients in human embryonic stem cells (hESCs). Major hESC-specific miRNA species include, but not limited, members of the miR-302 family, miR-371˜373 family, and miR-520 family. Among them, the miR-302 family has been found to play a functional role in tumor suppression (Lin et al., 2008 and 2010). MiR-302 contains eight (8) familial members, including four (4) sense miR-302 (a, b, c, and d) and four (4) antisense miR-302* (a*, b*, c*, and d*). These sense and antisense members are partially matched and can form double-stranded duplex, respectively. Precursors of miR-302 are formed by miR-302a and a* (pre-miR-302a), miR-302b and b* (pre-miR-302b), miR-302c and c* (miR-302c), and miR-302d and d* (pre-miR-302d) with a link sequence in one end (stem loop), respectively. In order to activate miR-302 function, miR-302 precursors (pre-miR-302s) are first processed into mature miR-302s by cellular RNase III Dicers and further form RNA-induced silencing complexes (RISCs) with certain argonaute proteins, subsequently leading to either RNA interference (RNAi)-directed degradation or translational suppression of targeted gene transcripts (mRNAs), in particular oncogene mRNAs (Lin et al., 2008, 2010 and 2011).
MiR-302 is the most abundant ncRNA species found in hESCs and induced pluripotent stem cells (iPSCs). Our previous studies have shown that ectopic overexpression of miR-302 beyond the level found in hESCs is able to reprogram both human normal and cancerous cells to hESC-like iPSCs with a relatively slow cell cycle rate (20-24 hours/cycle) similar to that of a morula-stage early human zygote (Lin et al., 2008, 2010 and 2011; EP 2198025; U.S. Ser. No. 12/149,725; U.S. Ser. No. 12/318,806; U.S. Ser. No. 12/792,413). Relative quiescence is a defined characteristic of these miR-302-induced iPSCs, whereas hESCs and other previously reported four-factor-induced (either Oct4-Sox2-Klf4-c-Myc or Oct4-Sox2-Nanog-Lin28) iPSCs all showed a highly proliferative cell cycle rate (12-15 hours/cycle) similar to that of a tumor/cancer cell (Takahashi et al., 2006; Yu et al., 2007; Wernig et al., 2007; Wang et al., 2008). To disclose this tumor suppression effect of miR-302, we have identified the involvement of two miR-302-targeted G1-checkpoint regulators, including cyclin-dependent kinase 2 (CDK2) and cyclin D (Lin et al., 2010; U.S. Ser. No. 12/792,413; U.S. Ser. No. 13/964,705). It is known that cell cycle progression is driven by activities of cyclin-dependent kinases (CDKs), which forms functional complexes with positive regulatory subunits, cyclins, as well as by negative regulators, CDK inhibitors (CKIs, such as p14/p19Arf, p15Ink4b, p16Ink4a, p18Ink4c, p21Cip1/Waf1, and p27Kip1). In mammals, different cycling CDK complexes are involved in regulating different cell cycle transitions, such as cyclin-D-CDK4/6 for G1-phase progression, cyclin-E-CDK2 for G1-S transition, cyclin-A-CDK2 for S-phase progression, and cyclin-A/B-CDC2 (cyclin-A/B-CDK1) for entry into M-phase. Hence, our studies suggested that the tumor suppression function of miR-302 results from co-suppression of the cyclin-E-CDK2 and cyclin-D-CDK4/6 pathways during G1-S transition.
Although miR-302 is useful for designing and developing novel anti-cancer drugs/vaccines, its production is problematic because natural miR-302 can only be found in human pluripotent stem cells such as hESCs, of which the resource is very limited. Alternatively, synthetic small interfering RNAs (siRNA) may be used to mimic pre-miR-302; yet, since the structure of a pre-miR-302 is formed by two mis-matched strands of miR-302 and miR-302*, those perfectly matched siRNA mimics can not replace the function of miR-302*, of which the sequence is totally different from the antisense strand of siRNA. For example, the antisense strand of siRNA-302a mimic is 5′-UCACCAAAAC AUGGAAGCAC UUA-3′ (SEQ.ID.NO.1), whereas native miR-302a* is 5′-ACUUAAACGU GGAUGUACUU GCU-3′ (SEQ.ID.NO.2). As miR-302 function results from both of its sense miR-302 and antisense miR-302* strands, previous reports using those siRNA mimics have shown different results from native miR-302 function. On the other hand, our recent discovery of iPSCs may provide an alternative solution for pre-miR-302 production (EP 2198025; U.S. Ser. No. 12/149,725; U.S. Ser. No. 12/318,806). Nevertheless, the cost of growing these iPSCs is still too high to be used for industrial production.
Alternatively, the use of prokaryotic competent cells may be a possible approach for producing human microRNAs and their precursors. However, prokaryotic cells lack several essential enzymes required for eukaryotic microRNA expression and processing, such as Drosha and Dicer. Also, prokaryotic RNA polymerases do not efficiently transcribe small RNAs with high secondary structures, such as hairpin-like pre-miRNAs and shRNAs. In fact, there is no true microRNA encoded in bacterial genomes and bacteria do not naturally express microRNA. As a result, if we can force the expression of human microRNAs in prokaryotes, the resulting microRNAs will most likely remain in their precursor conformations similar to pri-miRNA (a large primary cluster of multiple pre-miRNAs) and/or pre-miRNA (one single hairpin RNA). Despite all of the above problems, the real challenge is how to force the expression of human microRNAs in prokaryotes. To overcome this major problem, our priority application U.S. Ser. No. 13/572,263 has established a preliminary method; yet, it is currently not sure whether these prokaryote-produced microRNAs (pro-miRNA) will possess the same structures and functions as their human counterparts. Also, the pro-miRNAs so obtained may be contaminated with bacterial endotoxin, which is not suitable for direct use in therapy.
As learning from current textbooks, every ordinary skill person in the art knows very well that prokaryotic and eukaryotic transcription machineries are different and hence not compatible to each other. For example, based on current understandings, eukaryotic RNA polymerases do not bind directly to a promoter sequence and require additional accessory proteins (cofactors) to initiate transcription, whereas prokaryotic RNA polymerases form a holoenzyme that binds directly to a promoter sequence to start transcription. It is also a common sense that eukaryotic messenger RNA (mRNA) is synthesized in the nucleus by type-II RNA polymerases (pol-2) and then processed and exported to the cytoplasm for protein synthesis, whereas prokaryotic RNA transcription and protein translation take place simultaneously off the same piece of DNA in the same place. This is because prokaryotes such as bacteria and archaea do not have any nucleus-like structure. Accordingly, these differences make a prokaryotic cell difficult or even impossible to produce eukaryotic RNAs using eukaryotic promoters.
Prior arts attempt at producing mammalian peptides and/or proteins in bacterial cells, such as U.S. Pat. No. 7,959,926 to Buechler and U.S. Pat. No. 7,968,311 to Mehta, used bacterial or bacteriophage promoters. For initiating expression, a desired gene was cloned into a plasmid vector driven by a bacterial or bacteriophage promoter. The gene must not contain any non-coding intron because bacteria do not have any RNA splicing machinery to process the intron. Then, the vector so obtained was introduced into a competent strain of bacterial cells, such as Escherichia coli (E. coli), for expressing the transcripts (mRNAs) of the gene and subsequently translating the mRNAs into proteins. Nevertheless, the bacterial and bacteriophage promoters, such as Tac, Lac, T3, T7, and SP6 RNA promoters, are not pol-2 promoters and their transcription activities tend to be an error-prone process which causes mutations. In addition, Mehta further taught that glycerol/glycerin might be used to increase the efficiency of bacterial transformation; yet, no teaching was related to enhancement of RNA transcription, in particular pol-2 promoter-driven prokaryotic RNA transcription. Due to lack of possible compatibility between eukaryotic and prokaryotic transcription systems, these prior arts were still limited by the use of prokaryotic RNA promoters for gene expression in prokaryotes.
Due to the problems of system incompatibility and possible endotoxin contamination, there was previously no means for producing human pre-miRNA/shRNA-like drugs in prokaryotes. Also, a pre-miRNA/shRNA is sized about 70˜85-nucleotides in length which is too large and costly to be made by a RNA synthesis machine. To overcome these problems, the present invention provides a novel breakthrough—By adding some defined chemicals mimicking certain transcriptional cofactors, we can create a novel adaptation environment for prokaryotic cells to use eukaryotic pol-2 and/or pol-2-like promoters for transcribing desired pre-miRNAs and shRNAs without going through error-prone prokaryotic promoters. The advantages are: first, cost-effective mass production due to the fast growth of bacteria; second, easy handling because of no need for growing dedicate hESCs or iPSCs; third, high fidelity productivity in terms of pol-2 promoter-driven RNA transcription; fourth, high purity of desired microRNAs due to lack of true microRNA in prokaryotes; and last, no endotoxin, which can be further removed by certain chemical treatments. Therefore, a method for producing human pre-miRNAs and/or shRNAs in prokaryotic cells without the problems of system incompatibility and endotoxin contamination is highly desirable. Furthermore, the drugs so obtained may present novel therapeutic effects other than the currently known function of a microRNA.

This patent is subject to a terminal disclaimer.

Use of microRNA precursors as drugs for inducing CD34-positive adult stem cell expansion

WJWU & LYNN INSTITUTE FOR STEM CELL RESEARCH


A catalyst for lowering NOx concentration in an exhaust gas is disposed in an exhaust gas passage of an engine. The catalyst composed of a catalyst layer formed on a substrate. A NOx absorber that absorbs NOx when an oxygen concentration in the exhaust gas is high and releases NOx when the oxygen concentration drops, and a precious metal for reducing NOx are supported on a support material as catalyst components, and the NOx absorber includes Ba, K, Sr, and Mg. By lowering the oxygen concentration in the exhaust gas and raising a temperature of the NOx absorber when sulfur component is absorbed excessively in the NOx absorber, it is possible to regenerate the catalyst from the S poisoning.

The present invention relates to a device for purifying an exhaust gas, a method for purifying an exhaust gas, a catalyst for purifying an exhaust gas, and a method for manufacturing the catalyst, arranged in such a manner that a NOx (nitrogen oxide) absorber that absorbs NOx in an excess oxygen atmosphere is disposed in an exhaust gas passage of an engine or the like, thereby making it possible to remove NOx from exhaust even in a lean air-fuel ratio condition.
Generally, there has been a known arrangement to dispose, in an exhaust gas passage of an engine, a NOx absorber that absorbs NOx in an exhaust gas when an air-fuel ratio mixture is lean, and hence, when an oxygen concentration in the exhaust gas is high, and releases NOx when the oxygen concentration drops, thereby purifying released NOx by means of reduction.
However, in a case where fuel or engine oil contains a slight amount of sulfur component (S), when the sulfur component are burned and exhausted, a conventional NOx absorber absorbs SOx (sulfur oxide) more readily than NOx in an exhaust gas, and further, once it has absorbed SOx, it hardly releases SOx even when the oxygen concentration in the exhaust gas drops. As a result, an amount of absorbed SOx increases with a lapse of time while the NOx absorption ability gradually deteriorates.
In regard to a problem of the S poisoning (sulfur poisoning), Japanese Patent Laid-Open Publication No. 6-142458 describes that combining Ba serving as a NOx absorber with at least one of alkali metal, Fe, Ni, Co, and Mg and supporting the combination on a substrate is advantageous in improving resistance to the S poisoning of Ba, and that in the case of a combination of Ba and K, SO2 in the exhaust gas is incorporated in the form of complex sulfate with Ba and K, and when the oxygen concentration drops, the complex sulfate decomposes or is reduced at low temperatures to BaO and K2O that are active to NOx, which provides an advantage in improving resistance to the S poisoning of Ba. It should be noted, however, that the Ba support amount per 1 L (an apparent volume, and the same applies to the description below) is 13.7 to 27.4 g and the K support amount per 1 L is 0.39 to 7.8 g of the substrate.
However, when the K support amount is too little, the NOx absorption ability is not improved, and when the K support amount is increased to improve the NOx absorption ability, HC is not purified adequately in an atmosphere with reductants (excess oxygen ratio xcexxe2x89xa61), that is, during a theoretical air-fuel ratio combustion operation or a rich combustion operation of the engine. The reason for this is not obvious, but it is assumed that a great deal of K is placed in the periphery of precious metal and prevents HC from approaching in close proximity to the precious metal.
Japanese Patent Laid-Open Publication No. 7-51544 describes that when a combination of at least two kinds of alkaline-earth metal is supported on a substrate as a NOx absorber, the NOx absorber incorporates SO2 in the exhaust gas as complex sulfate and the complex sulfate readily decomposes at low temperatures when the oxygen concentration drops, thereby providing an advantage in improving resistance to the S poisoning of Ba. It should be noted, however, that, in the case of a combination of Ba and Mg, the Ba support amount per 1 L of the substrate is 41 to 69 g and the Mg support amount per 1 L is 2.4 to 4.8 g, and in the case of a combination of Ba and Sr, the Ba support amount per 1 L of the substrate is 41 to 69 g and the Sr support amount per 1 L is 8.7 to 42 g.
Also, Japanese Patent Laid-Open Publication No. 10-118494 describes that, in regard to a NOx purifying catalyst for purifying NOx by means of reduction in an excess oxygen atmosphere, by supporting Pt and Rh as catalytic metal on an alumina substrate and by also supporting Sr or Mg in addition to K having high affinity to NOx, it is possible to achieve high NOx purifying performance even in the presence of SOx. It is preferable to arrange in such a manner that, in the case of a combination of K and Sr, the K support amount per 1 L of the substrate is 20 to 40 g and the Sr support amount per 1 L is 0 to 50 g, and in the case of a combination of K and Mg, the K support amount per 1 L of the substrate is 5 to 20 g and the Mg support amount per 1 L is 0 to 5 g.
Also, Japanese Patent Laid-Open Publication No. 10-274031 describes that SOx absorbed in the NOx absorber is detached by injecting fuel in an expansion stroke of an in-cylinder direct injection engine and thereby raising a temperature of the exhaust gas.
The object of the present invention is to control absorption of sulfur component in an exhaust gas by the NOx absorber.
Another object of the present invention is to improve the heat resistance of the NOx absorber.
A further object of the present invention is to achieve a balance between NOx purifying performance during a lean combustion operation after being exposed to a high temperature atmosphere and HC purifying performance during a theoretical air-fuel ratio combustion operation or a rich combustion operation by adequately setting the K support amount.
Still another object of the present invention is to regenerate deteriorated NOx absorption ability of the NOx absorber resulted from absorption of sulfur component in the exhaust gas by causing the NOx absorber to detach the sulfur component, and more particularly to make an arrangement of the NOx absorber such that it can readily regenerate by detaching the sulfur component when predetermined sulfur detaching means is activated.
The present invention provides a catalyst for purifying an exhaust gas, disposed in an exhaust gas passage of an engine, for lowering NOx concentration in an exhaust gas containing NOx, sulfur, and oxygen, the catalyst including:
a substrate; and
a catalyst layer formed on the substrate by supporting, on alumina, a NOx absorber that absorbs NOx when an oxygen concentration in the exhaust gas is high and releases NOx when the oxygen concentration drops, and a precious metal for reducing NOx,
which is characterized in that the NOx absorber includes Ba, K, Sr, and Mg.
According to the invention, deterioration of the NOx absorption ability of the NOx absorber caused by the S poisoning can be suppressed, and the heat resistance of NOx absorber can also be improved. The reason for this is not obvious, but it is assumed as follows.
Firstly, it is assumed that the elements (K, Sr, and Mg) other than Ba are more susceptible to the S poisoning than Ba, and for this reason, the S poisoning of Ba is relatively small. In other words, because Ba has the higher NOx absorption ability than the other elements, the presence of the other elements makes the S poisoning of Ba relatively small, the deterioration of the NOx absorption ability is lessened.
According to an analysis, it appears that Ba and Sr (at least a part of each) form one compound (a mixed oxide or double salt) with both the elements being constituent elements. It is assumed that such a Baxe2x80x94Sr compound (hereinafter, referred to as a double compound as needed) is less susceptible to the S poisoning compared with the case of Ba alone, and for this reason, deterioration of the NOx absorption ability can be suppressed.
Also, according to an analysis, it appears that Ba and Mg (at least a part of each) do not form a crystal, but are in an almost amorphous state by coming in close proximity to each other or bonding to each other. It is assumed that such a Baxe2x80x94Mg coexisting substance suppresses the S poisoning of Ba (formation of barium sulfate) compared with the case of Ba alone, and for this reason, deterioration of the NOx absorption ability can be suppressed.
Also, it is affirmed from analysis that K neither forms a complex nor undergoes affinity with Ba, Sr, and Mg, and resides dispersedly in the periphery of the Baxe2x80x94Sr compound or Baxe2x80x94Mg coexisting substance. K with the foregoing nature is relatively highly reactive with sulfur, and therefore, is assumed to prevent the S poisoning of Baxe2x80x94Sr compound or the Baxe2x80x94Mg coexisting substance. In addition, K promotes crystallization of Baxe2x80x94Sr double carbonate and activates the NOx absorber, thereby contributing to the improvement of the heat resistance of the catalyst.
It is also assumed that interaction of the elements forming a quaternary material of Baxe2x80x94Kxe2x80x94Srxe2x80x94Mg serving as the NOx absorber weakens the bond to SOx, so that even if SOx is bonded, it is readily detached.
Further, when the NOx absorber 25 is made of a single element of Ba, if an amount of Ba is increased, a particle size becomes larger but a specific surface area hardly increases. However, in a case where Ba and other elements (K, Sr, and Mg) are combined, when the amount of the elements are increased, it is assumed that a particle size hardly increases, but a specific surface area, or an active site, increases, which makes an absorption capacity of NOx and SOx larger. Hence, even when the S poisoning occurs to some degree, the NOx absorption ability is not deteriorate significantly.
Also, combining Ba and the other elements (K, Sr, and Mg) as discussed above is effective in making the NOx absorber into fine particles. In particular, Sr is notably excellent in making Ba and Mg into fine particles. Hence, the NOx absorber is dispersed on the substrate at a high degree, which makes the occurrence of heat sintering difficult. In short, the heat resistance of the catalyst becomes high.
Also, the reason why alumina is used as a support material of the above-discussed NOx absorber and precious metal is because alumina hardly undergoes sintering nor decomposes when it is heated high, and therefore, is advantageous in preventing heat deterioration of the catalyst. In the case of alumina, Ba and the substrate react with each other when the catalyst is heated high, which readily causes deterioration, but Mg suppresses the reaction between the substrate and Ba, and as a result, heat deterioration of the catalyst is prevented.
The support material can be made of both alumina and a ceria material. The ceria material serves as an oxygen storage material, and releases oxygen when oxygen concentration in the exhaust gas drops, thereby promoting a ternary reaction (oxidation-reduction reaction) among HC (hydrocarbon), CO, and NOx in the exhaust gas. In addition, it is advantageous to increase an amount of the ceria material in improving resistance to the S poisoning of the catalyst. In particular, a ceria material containing Zr increases the resistance to the S poisoning.
In the case of a ternary catalyst, an addition alumina added with Ba, Zr, La, etc. is used occasionally as alumina to suppress reduction of a specific surface area when exposed to a high temperature. However, using non-addition alumina that does not contain these additional elements is advantageous to NOx purification at a lean ratio. In other words, the precious metal at a lean ratio serves as a catalyst to oxidize NO in the exhaust gas to NO2, and assists the NOx absorber to absorb NOx. The alumina serves to assist this catalytic reaction of precious metal, but when an additive is present as discussed above, a heat resistance is improved but the function of alumina as a co-catalyst is deteriorated. For this reason, a non-addition alumina is advantageous to NOx purification at a lean ratio.
The ceria material may be composed of CeO2 alone, but it may be a mixed oxide of Ce and Zr discussed above. Further, it may be a ternary mixed oxide of Cexe2x80x94Zrxe2x80x94Sr. Adopting the ternary complex oxide of Cexe2x80x94Zrxe2x80x94Sr is advantageous in improving the heat resistance, resistance to the S poisoning, regeneration properties from the S poisoning of the catalyst, which will be discussed below.
It is preferable to combine alumina with the ceria material at a mass ratio of 1:1 or in the vicinity thereof, which provides an advantage in improving both heat resistance and resistance to the S poisoning of the catalyst.
It is preferable to use Pt as the precious metal, because it shows an excellent catalytic function for the oxidation of NO to NO2 at a lean ratio, and the reduction of NO2 to N2 at stoichimetric or rich ratio. Also, it is more preferable to use both Pt and Rh. Rh serves to assist the catalytic reaction by Pt, in other words, it promotes the above-discussed ternary reaction at a stoichimetric or rich ratio while promoting a reduction-decomposition reaction of NOx released from the NOx absorber. When the support amount of Rh per 1 L of the substrate is in a range from 0.1 to 1.0 g, variance of the amount does not make a significant difference in the NOx purification ratio, and therefore, a small amount is sufficient.
A preferable support amount of Pt per 1 L of the substrate is 1 to 15 g. This is because when the amount is less than 1 g, NOx is not sufficiently purified by means of reduction, whereas when the amount exceeds 15 g, no further improvement of the NOx purification ratio is expected and the costs is increased. It is sufficient to set the Rh support amount to approximately {fraction (1/10)} to {fraction (1/100)} of the Pt support amount.
In the above catalyst for purifying an exhaust gas, the support amount of Sr per 1 L of the substrate is preferably 8 to 20 g, and the support amount of Mg per 1 L of the substrate is preferably 5 to 15 g, and more preferably 8 to 12 g.
The above arrangement makes it possible to achieve an effect in improving resistance to the S poisoning by Mg and Sr while achieving an effect in improving the heat resistance by Mg as discussed above. The support amount of Ba per 1 L of the substrate is preferably 25 to 60 g.
In the above catalyst for purifying an exhaust gas, the mass ratio of Ba, Sr, and Mg in the catalyst layer is preferably Ba:Sr:Mg=30:(8 to 20):(8 to 12).
This provides an advantage in improving the heat resistance of the NOx absorber while suppressing the S poisoning of the NOx absorber.
In the above catalyst for purifying an exhaust gas, the mass ratio of Ba, K, Sr, and Mg in the catalyst layer is preferably Ba:K:Sr:Mg=30:(2 to 12):(8 to 20):(8 to 12).
This provides a further advantage in improving the heat resistance of the NOx absorber while suppressing the S poisoning of the NOx absorber.
In the above catalyst for purifying an exhaust gas, the support amount of K per 1 L of the substrate is preferably 2 to 12 g.
In other words, the above-discussed promotion of crystallization of Baxe2x80x94Sr double carbonate by K, and the effect of improving the heat resistance of the catalyst resulted therefrom are exerted when the support amount of K is 2 g/L or more. It should be noted, however, that when the support amount of K exceeds 12 g/L, the exertion of the effect becomes weak. In this case, a more preferable support amount of K is 4 to 10 g/L.
Also, in the above catalyst for purifying an exhaust gas, the support amount of K per 1 L of the substrate is preferably 2 to 6 g.
In other words, because the support amount of K per 1 L of the substrate is set to 6 g/L or less, when the oxygen concentration in the exhaust gas drops after being exposed to a high temperature atmosphere (when an atmosphere with reductants (xcexxe2x89xa61) is reached), it is possible to suppress deterioration of HC oxidation-purifying performance due to the precious metal.
Also, because the support amount of K per 1 L of the substrate is set to 2 g/L or more, it is possible to achieve the above-discussed effects in preventing the S poisoning of Ba, Mg and Sr by K. Hence, it is possible to purify NOx released from the NOx absorber when the lean combustion operation is switched to the theoretical air-fuel ratio combustion operation or rich combustion operation by reacting NOx with HC in a satisfactory manner.
In case that the support amount of K per 1 L of the substrate is 2 to 6 g, a mass ratio of Ba and K in the catalyst layer is preferably Ba:K=(5 to 15):1.
In other words, because the mass ratio of the support amount of Ba to the support amount of K is set to 5 or higher, the NOx absorption ability will not be deteriorated because the support amount of Ba is too small. Also, because the mass ratio is set to 15 or less, neither the NOx absorbing site of Ba will be decreased by sintering caused when the catalyst is calcined, nor Ba will be crystallized on the substrate and separated therefrom because the support amount of Ba is too large.
Hence, it is possible to properly perform the function to allow NOx released from Ba to react with HC in a satisfactory manner when the oxygen concentration becomes high (at the theoretical air-fuel ratio combustion operation or rich combustion operation) without deteriorating the NOx absorption ability of Ba when the oxygen concentration in the exhaust gas is high (at lean combustion operation of the engine).
In the above catalyst for purifying an exhaust gas, when the oxygen concentration in the exhaust gas is high means when the oxygen concentration is, for example, 5% or higher.
In the above catalyst for purifying an exhaust gas, the engine may be a lean burn gasoline engine or a diesel engine.
Also, the present invention provides a method of manufacturing a catalyst for purifying an exhaust gas, disposed in an exhaust passage of an engine, for lowering the NOx concentration in an exhaust gas containing NOx, sulfur, and oxygen, characterized by including the steps of:
forming an alumina layer by coating a substrate with alumina; and
impregnating the alumina layer with a Ba solution, a K solution, a Sr solution, a Mg solution, and a precious metal solution.
This makes it possible to obtain an exhaust gas purifying catalyst in which the catalyst layer is formed on the substrate by supporting Ba, K, Sr, and Mg as NOx absorber and the precious metal for reducing NOx on alumina. Consequently, it is possible to improve the heat resistance of the NOx absorber while suppressing the S poisoning of the NOx absorber.
In the above method of manufacturing a catalyst for purifying an exhaust gas, each of the Ba solution, the K solution, the Sr solution, and the Mg solution may be a solution of acetic acid.
In the above method of manufacturing a catalyst for purifying an exhaust gas, it is preferable to form the alumina layer into a lamination by coating the substrate with the alumina twice, after which the Ba solution, the K solution, the Sr solution, the Mg solution, and the solution of the precious metal are impregnated into the two alumina layers.
In other words, in a case where a thick catalyst layer is formed on the substrate, if the substrate is coated with alumina at one time, an amount of alumina is so large that the thickness of the alumina layer readily becomes irregular. Also, it takes a time to dry and calcine the alumina layer. On the contrary, coating alumina twice separately as discussed above is advantageous in attaining the alumina layer with an even thickness, and it also shortens a drying and calcining time. Also, by providing a double-layer alumina layer, when the NOx absorber is impregnated, the concentration of the NOx absorber in the outer alumina layer is higher than that in the inner alumina layer, and therefore, SOx is chiefly trapped by the NOx absorber on the outer alumina layer, and the NOx absorber less damaged by the S poisoning can be secured on the inner alumina layer, which provides an advantage in maintaining the NOx purifying performance.
In the above method of manufacturing a catalyst for purifying an exhaust gas, it is preferable that the Ba solution, the K solution, the Sr solution, the Mg solution, and the solution of the precious metal are mixed and impregnated into the alumina layer simultaneously.
In other words, if the solution of the precious metal and the solutions of the NOx absorber are separated from each other, and the solution of the precious metal is impregnated first, then the precious metal is covered with the NOx absorber impregnated later and is readily buried in the alumina layer. On the other hand, if the solution of the precious metal is impregnated later, the NOx absorber impregnated and supporting first, especially Ba, dissolves into the solution of the precious metal, which causes unsatisfactory dispersion.
On the contrary, if the solutions are impregnated simultaneously like in the present invention, it is possible to place the precious metal in close proximity to the NOx absorber without burying the precious metal, and unsatisfactory Ba dispersion does not occur, which is advantageous to reduction-purification of NOx. Also, by the simultaneous impregnation of the solutions of four kinds of the NOx absorber, it is possible to efficiently form the above-described Baxe2x80x94Sr compound or Baxe2x80x94Mg coexisting substance and to disperse K in the periphery of these compounds. This is advantageous not only in suppressing the S poisoning of the NOx absorber, but also in making the NOx absorber into fine particles, in particular, in making Ba and Mg into fine particles by Sr, thereby making it possible to increase the heat resistance of the catalyst.
In the above method of manufacturing a catalyst for purifying an exhaust gas, in a case where the Ba solution, the K solution, the Sr solution, and the Mg solution are divided into two groups including a group which is impregnated into the alumina layer first, and a group which is impregnated later, it is preferable to impregnate the K solution later.
In other words, in a case where the Ba solution, the K solution, the Sr solution, and the Mg solution are impregnated into the alumina layer simultaneously, if too large amounts of Ba, K, Sr, and Mg are to be supported, the concentrations of these kinds of metals in their respective impregnation solutions becomes high, and for example, Ba with low solubility may not be dissolved and remain in the impregnation solution. In this case, impregnation of these metal components becomes uneven, which causes deterioration of the catalytic performance.
On the contrary, heating the impregnation solutions can raise the solubility of metal components, so that the entire metal components are dissolved without increasing a total amount of the impregnation solutions, but this requires a heating process. In order to solve this problem, the Ba solution, the K solution, the Sr solution, and the Mg solution are divided into two groups including a group which is impregnated into the alumina layer first, and a group which is impregnated later, and the K solution is impregnated later.
In this case, because K neither forms a complex nor undergoes affinity with the other NOx absorber, it is not essentially necessary to impregnate the K solution simultaneously with the other NOx absorber. On the contrary, impregnating the K solution later is advantageous in placing K in the periphery of the other NOx absorber and hence in improving the heat resistance of the catalyst.
In the above method of manufacturing a catalyst for purifying an exhaust gas, in a case where the Ba solution, the K solution, the Sr solution, and the Mg solution are divided into two groups including a group which is impregnated into the alumina layer first, and a group which is impregnated later, it is preferable to impregnate the Sr solution first.
In other words, because it is assumed that Sr makes Ba and Mg into fine particles as discussed above, making Ba and Mg into fine particles by having Sr be supported first is advantageous in increasing the heat resistance of the catalyst.
Also, the present invention provides a device for purifying an exhaust gas as shown in FIG. 1, comprising:
a NOx absorber 25, disposed in an exhaust passage 22 of an engine 1 or the like, for absorbing NOx and a sulfur component in an exhaust gas in an excess oxygen atmosphere where an oxygen concentration in the exhaust gas is high, and releasing NOx absorbed therein as the oxygen concentration drops;
sulfur excessive absorption determining means a for determining an excessive absorption state of the sulfur component in the NOx absorber 25; and
sulfur detaching means b for, when the sulfur excessive absorption determining means a determines the excessive absorption state of the sulfur component, causing the NOx absorber 25 to detach the sulfur component by raising a temperature of the NOx absorber 25 while lowering the oxygen concentration,
characterized in that at least one of K, Sr, Mg, and La, and Ba are included as elements forming the NOx absorber 25.
According to the above arrangement, by activating the sulfur detaching means b after the sulfur component (SOx) in the exhaust gas is absorbed excessively into the NOx absorber 25, the NOx absorption ability is readily regenerated to nearly the ability before the sulfur component were absorbed. In other words, the NOx absorber 25 has higher NOx absorption ability after the regeneration (regeneration from the S poisoning, and the same applies to the description below) or causes less deterioration of the NOx absorption ability when exposed to high temperatures, that is, the heat resistance becomes high, compared with a case where the NOx absorber is composed of Ba alone. This improvement of the heat resistance plays advantageously for the regeneration of the NOx absorber 25. The relation between the improvement of the heat resistance and the regeneration of the NOx absorber 25 is as follows.
In other words, the sulfur detaching means b causes the NOx absorber 25 to detach sulfur component not only by lowering the oxygen concentration in the exhaust gas, but also by raising the temperature of the NOx absorber 25. Hence, if the NOx absorber has a poor heat resistance, it becomes difficult to raise the temperature of the NOx absorber 25 for detaching the sulfur component, which makes it impossible to achieve the originally intended object. On the contrary, if the heat resistance of the NOx absorber 25 becomes high like in the present invention, it is possible to regenerate the NOx absorption ability by effectively using the sulfur detaching means b. In short, it is possible to avoid deterioration of the NOx absorber 25 by heat generated at the sulfur detaching treatment.
The reason why the present invention can make the NOx absorption ability after the regeneration higher or why it can improve the heat resistance compared with a case where the NOx absorber is composed of Ba alone is not obvious, but it is assumed as follows.
That is, it is assumed that any of the elements (K, Sr, Mg, or La) other than Ba is more susceptible to the S poisoning than Ba, and for this reason, the S poisoning of Ba is comparatively small, which lessens deterioration of the NOx absorption ability after the S poisoning. In other words, because Ba has higher NOx absorption ability than the other elements, the presence of the other elements makes the S poisoning of Ba relatively small, and thereby the deterioration of the NOx absorption ability is lessened.
It is also assumed that any of the other elements (K, Sr, Mg, or La) regenerates from the S poisoning more readily than Ba, and for this reason, the NOx absorption ability after the regeneration becomes high. In other words, although a sulfate of a produced compound of Ba and SOx is stable, but a sulfate of the other elements is less stable than sulfate of Ba. Hence, it is assumed that when a temperature rises high in a low oxygen concentration atmosphere, SOx is readily detached.
It is also assumed that formation of a complex by Ba with any of the other elements (Sr, Mg or La) except K (formation of a mixed oxide or double salt or turning into an almost amorphous state by coming in close proximity to each other or bonding with each other) makes the occurrence of the S poisoning difficult.
Further, when an amount of Ba is increased as a single element forming the NOx absorber 25, neither the NOx absorption ability before the S poisoning nor the NOx absorption ability after the regeneration is improved significantly. The reason for this is assumed that when an amount of Ba exceeds a certain amount, only a particle size is increased and a specific surface area remains the same. On the contrary, in a case where Ba and the other elements (at least one of K, Sr, Mg and La) are combined, it is assumed that each element resides separately because of a difference in their natures, which not only increases a specific surface area or a reaction site, but also makes the occurrence of heat sintering difficult. Further, it is assumed that the interaction of different elements forming the NOx absorber makes detachment of the sulfur component readily.
Also, combining Ba and the other elements (at least one of K, Sr, Mg and La) as discussed above is effective in making the NOx absorber into fine particles, and Sr is particularly effective in making Ba and Mg into fine particles. Consequently, the NOx absorber disperses on the substrate at a high degree, which makes the occurrence of heat sintering difficult. In short, the heat resistance of the catalyst becomes high.
Also, in case that the substrate is alumina, Ba and the substrate reacts with each other when the catalyst is heated high, which readily causes deterioration. However, because Mg suppresses the reaction between the substrate and Ba, the heat resistance of the catalyst is improved.
In a case where Ba and the foregoing other elements (at least one of K, Sr, Mg and La) are supported on a substrate of a honeycomb shape or the like, the support amount of Ba per 1 L of the substrate is approximately 10 to 50 g, and preferably 20 to 40 g, and the support amounts of the other elements are preferably as large as or less than the support amount of Ba.
The excess oxygen exhaust gas with high oxygen concentration is, for example, an exhaust gas (oxygen concentration is approximately 4 to 20%) when an engine is run on a lean mixture (particularly, A/F=18 to 50) with an air-fuel ratio A/F greater than 16.
As the elements forming the NOx absorber 25, it is preferable to include K in addition to Ba. According to this arrangement, the NOx absorption ability before the S poisoning becomes high. Also, because K does not form a complex with Ba, but is highly reactive with sulfur, K resides in the periphery of Ba and prevents the S poisoning of Ba, thereby suppressing deterioration of the NOx absorption ability caused by the S poisoning of Ba. Also, because it is assumed that K detaches the sulfur component more readily than Ba, the NOx absorption ability after the regeneration becomes high. A preferable mass ratio of Ba and K is, for example, Ba:K=30:(1 to 30).
As the elements forming the NOx absorber 25, it is preferable to include at least one of Sr, Mg, and La in addition to Ba and K. This makes the NOx absorber 25 have a high heat resistance, which is advantageous in avoiding heat deterioration at the sulfur detaching treatment.
Also, according to an analysis, it appears that Ba and Sr (at least a part of each) form one compound (mixed oxide or double salt) with both the elements being constituent elements. It is assumed that such a Baxe2x80x94Sr compound (hereinafter, referred to as a double compound as needed) is less susceptible to the S poisoning compared with the case of Ba alone, and for this reason, deterioration of the NOx absorption ability is suppressed.
Also, according to an analysis, it appears that Ba and Mg (at least a part of each) do not form a crystal, but are in an almost amorphous state by coming in close proximity to each other or bonding to each other. It is assumed that such a Baxe2x80x94Mg coexisting substance suppresses the S poisoning of Ba compared with the case of Ba alone, and for this reason, deterioration of the NOx absorption ability is suppressed.
Also, it is affirmed from analysis that K neither forms a complex nor undergoes affinity with Ba, Sr, and Mg, and resides dispersedly in the periphery of the Baxe2x80x94Sr compound or Baxe2x80x94Mg coexisting substance. K with the foregoing nature is relatively highly reactive with sulfur, and therefore, is assumed to prevent the S poisoning of Baxe2x80x94Sr compound or the Baxe2x80x94Mg coexisting substance.
In a case where Ba, K, and Mg are used as the elements forming the NOx absorber 25 and are supported on a substrate of a honeycomb shape or the like, it is preferable to set the support amount of Ba to 10 to 50 g, the support amount of K to 1 g or more (the upper limit is, for example, 15 g), and the support amount of Mg to 3 to 17 g per 1 L of the substrate. It is more preferable to set the support amount of Mg to 5 to 15 g and further 8 to 12 g. Consequently, the heat resistance can be obtained, and also regeneration properties from the S poisoning becomes satisfactory. A preferable mass ratio of Ba, K, and Mg is, for example, Ba:K:Mg=30:(1 to 30):(1 to 30).
In a case where Ba, K, and Sr are used as the elements forming the NOx absorber 25 and are supported on a substrate of a honeycomb shape or the like, the support amount of Ba and the support amount of K per 1 L of the substrate may preferably be equal to those in the above Baxe2x80x94Kxe2x80x94Mg-based absorber, and the support amount of Sr may be 10 to 20 g. The support amount of Sr may preferably be 13 to 17 g. Consequently, the heat resistance can be obtained, and also regeneration properties from the S poisoning becomes satisfactory. A preferable mass ratio of Ba, K, and Sr is, for example, Ba:K:Sr=30:(1 to 30):(1 to 30).
As the elements forming the NOx absorber 25, it is preferable to include Sr in addition to Ba. Thus, the NOx absorber 25 has a high heat resistance, which provides an advantage in avoiding heat deterioration during the sulfur detaching treatment.
As the elements forming the NOx absorber 25, it is preferable to include at least one of Mg and La in addition to Ba and Sr. Thus, the NOx absorber 25 has a high heat resistance, which provides a further advantage in avoiding heat deterioration during the sulfur detaching treatment.
As the elements forming the NOx absorber 25, it is preferable to include Mg in addition to Ba. Thus, the NOx absorber 25 has a high heat resistance, which provides an advantage in avoiding heat deterioration during the sulfur detaching treatment.
As the elements forming the NOx absorber 25, it is preferable to include La in addition to Ba and Mg. Thereby, the NOx absorber 25 has a high heat resistance, which provides a further advantage in avoiding heat deterioration during the sulfur detaching treatment.
Raising the temperature of the NOx absorber 25 by the sulfur detaching means b can be achieved by raising a temperature of an exhaust gas, and for example, increasing a temperature of the exhaust gas to 500 to 1100xc2x0 C. (preferably 600 to 1100xc2x0 C.) is advantageous to detachment of sulfur from the NOx absorber 25. Alternatively, a heater may be provided to the NOx absorber 25 so that the heater is heated. Also, lowering of oxygen concentration in the exhaust gas by the sulfur detaching means b can be achieved by controlling an air-fuel ratio in the engine, and for example, by setting xcex (oxygen-excessive ratio) to around 1 or to 1 or less, oxygen concentration in the exhaust gas becomes 0.5% or less, and further, an amount of reduction components, such as HC, CO, and H2, in the exhaust gas is increased, which is advantageous to detachment of the sulfur component from the NOx absorber 25.
In case that a spark ignition direct injection engine is used as the engine, the sulfur detaching means b is preferably fuel injection control means that operates a fuel injection valve to divide injection, so that fuel is injected into a combustion chamber in the cylinder at least twice from a start of an air-intake stroke and an end of a compression stroke. Consequently, it is possible to raise the temperature of the NOx absorber 25 by increasing the temperature of the exhaust gas while lowering the oxygen concentration in the exhaust gas. In particular, the divided injection as discussed above can raise CO concentration in the exhaust gas, which is further advantageous to detachment of the sulfur component from the NOx absorber 25.
More specifically, in a case where the NOx absorber 25 is Ba, it is assumed that SOx is adsorbed on the surface of barium particles in the form of sulfate, and barium sulfate undergoes the following reaction with a supply of CO, so that barium carbonate and sulfur dioxide are generated.
BaSO4+COxe2x86x92BaCO3+SO2↑ (coefficients omitted)
Meanwhile, a so-called water gas shift reaction between CO and water in the exhaust gas proceeds with increasing CO concentration, and as a result, hydrogen is generated at the reaction site on the catalyst.
CO+H2Oxe2x86x92H2+CO2
Then, hydrogen causes the sulfur component adsorbed in the NOx absorber 25 to be detached, which is advantageous to detachment of the sulfur component. Moreover, because the water gas shift reaction can proceed at a relatively low temperature, the temperature of the NOx absorber 25 does not have to be raised significantly.
Also, as the sulfur excessive absorption determining means a for determining a sulfur component excessive absorption condition of the NOx absorber 25, it is possible to, for example, adopt means arranged so that an amount of absorbed SOx in the NOx absorber 25 is estimated based on a travel distance of an automobile and a total amount of fuel consumed on that distant with a consideration given to the temperature conditions of the NOx absorber 25 during a corresponding period, and the sulfur component excessive absorption condition is determined when the estimated amount exceeds a predetermined value.
Also, the present invention provides an exhaust gas purifying method of purifying an exhaust gas containing NOx and sulfur component, characterized in that:
when the exhaust gas is in an excess oxygen absorption condition where an oxygen concentration is high, the exhaust gas is brought into contact with an NOx absorber 25 including at least one of K, Sr, Mg, and La, and Ba, so that NOx and the sulfur component are absorbed into the NOx absorber 25; and
when a sulfur component absorption condition of the NOx absorber 25 becomes a predetermined excessive absorption condition, the sulfur component are detached from the NOx absorber 25 by raising a temperature of the NOx absorber 25 and lowering the oxygen concentration in the exhaust gas.
In other words, according to the above method, as can be obvious from the foregoing description, when the NOx absorption ability of the NOx absorber 25 is deteriorated by the S poisoning, the NOx absorption ability can be readily regenerated to a high level by causing the NOx absorber 25 to detach the sulfur component, which is advantageous to NOx purification.
Also, the present invention provides an exhaust gas purifying catalyst for decreasing NOx in an exhaust gas from an engine that is run in such a manner that an exhaust gas therefrom contains sulfur and oxygen and oxygen concentration therein drops intermittently, comprising:
a substrate; and
a catalyst layer formed on the substrate by supporting, on alumina, a NOx absorber that absorbs NOx when an oxygen concentration in the exhaust gas is high and releases NOx when the oxygen concentration drops, and a precious metal for reducing NOx,
characterized in that the NOx absorber includes Ba, K, Sr, and Mg.
Hence, when an engine is run to increase the oxygen concentration in the exhaust gas, the NOx absorber absorbs NOx in the exhaust gas, and when the engine is run to lower the oxygen concentration in the exhaust gas, NOx is released from the NOx absorber, so that NOx is purified by means of reduction with the precious metal. The exhaust gas purifying catalyst as discussed above can obtain a heat resistance, and also is advantageous in improving the regeneration properties from the S poisoning.

Device for purifying exhaust gas, method for purifying exhaust gas, catalyst for purifying exhaust gas, and method for manufacturing exhaust gas purifying catalyst


A process for the preparation of a polymer which is electrically conductive and which is based on polythiophene, the process including polymerizing thiophene in a reaction medium including thiophene, from 2.5 to 20 moles of an anhydrous ferric salt per mole of thiophene, from 0.04 to 1 liter of an alkyl halide per gram of thiophene, and from 0.1 to 5% by weight of water introduced into the reaction medium based on the amount of alkyl halide.

1. Field of the Invention
The present invention relates to a process for the preparation of electrically conductive polymers based on polythiophenes (also called doped polythiophenes) by chemical polymerization of thiophene.
2. Description of the Related Art
A process for preparing aromatic polymers by chemical polymerization in the presence of a Friedel-Crafts catalyst, such as ferric chloride, at a temperature of between 100.degree. and 800.degree. C., was proposed in Patent DE 1,178,529. The polymers obtained by this process have conductivities of between 10.sup.-10 and 10.sup.-0.5 siemens per cm.
The polymerization of thiophene is usually carried out by an electrochemical route in order to obtain products which are reasonably reproducible.
However, these electrochemical polymerization processes result in polymers which are poorly conductive, thermally unstable and difficult to process. Furthermore, in most cases the degree of conversion of monomer to polymer is low.

Process for the preparation of polythiophenes by use of ferric salts and alkyl halides


A lift spring assembly has a compression spring rod with a housing having a longitudinal axis and axially opposite ends, and having a rod member coaxial with the axis and having an inner end in the housing and an outer end axially outwardly of one of the opposite ends. A guide member is provided on the inner end of the rod member for supporting the rod member during movement of the rod member. A first stage spring assembly extends between one of the opposite ends of the housing and the guide member. A second stage spring assembly extends between the other of the opposite ends of the housing and the guide member. A mounting member extending from one of the opposite ends of the housing for mounting the spring rod assembly to a hood assembly. A locking member is pivotally connected to the mounting member and pivots into locking engagement with one of the ends of the housing.

The invention relates to a spring mechanism typically used for biasing hoods, tops, doors, hinged covers, and other elements from a closed to an open position. The invention involves the use of springs in conjunction with a rod member to exert a driving force on the elements to be displaced. The following patents are incorporated herein by reference as background information with regard to spring mechanisms: U.S. Pat. No. 6,199,843 to DeGrace; U.S. Pat. No. 5,810,339 to Küspert, et al.; and U.S. Pat. No. 4,962,916 to Palinkas.
Compression spring rods are used in various applications; for example, to assist in lifting, opening, and damping. Typical applications include lifting a lid hinged to a stationary base. Other applications include lifting and/or balancing elements for a trunk or hood of an automobile. The present invention uses the compression spring rod assembly to assist a hood of a bus during opening of the hood and securing the hood in place in a fully opened position. A two stage spring assembly is used in which the first stage spring assists during the opening process and the second stage spring assembly is used to prevent the hood from falling after passing a center of gravity point of the hood.
Existing mechanical lifts for bus hoods, such as for school busses, use a combination of extension springs and cable for assisting opening and closing of the bus hoods. The force needed to open a school bus hood is typically required to be less than 25 lbs. The existing systems have difficulty meeting this requirement. In contrast, the two stage spring assembly of the present invention only requires approximately 15 lbs. of handle load to open the hood. The system assists the hood in opening, and slows the hood as it approaches the end of the stroke and limits the travel of the hood. Accordingly, it is considered desirable to provide a new and improved two stage spring assembly which overcomes the foregoing difficulties and others while providing better and more advantageous results.
Typically, bus hoods are oriented such that the top of the hood is essentially parallel to the ground thus providing the driver with a limited line of vision with respect to objects or persons in front of the bus. An improved bus hood design provides a downward angle or slope to the top of the hood from the windshield thus providing increased visibility to the area in front of the bus. Thus, the driver has a better view of either objects or children or persons walking in front of or positioned in front of the bus. Thus, the slant or slope design of the hood increases the safety to people around the bus while the bus is either stationary or in transit.
The hood is lifted away from the windshield towards the front of the bus. Once the hood passes a vertical position balanced with respect to its center of gravity, it tends to drop or fall due to gravity and may injure the person opening the hood. Thus, a two stage spring assembly is desired for controlling movement of the hood before and after it reaches a vertical position balanced at its center of gravity.


A Silicon-On-Insulator (SOI) CMOS circuit comprises a plurality of PMOS transistors connected in series to each other, each of the plurality of PMOS transistors having its body and gate connected to each other, and at least an NMOS transistor connected to one of the plurality of PMOS transistors, the NMOS transistor having its body connected to a low reference potential having a value of ground. The SOI CMOS circuit can further comprise a plurality of potential limiting circuits each connected between the body and gate of each of the plurality of PMOS transistors, for setting a lower limit of the potential of the body of each of the plurality of PMOS transistors to a voltage between a high reference potential and a potential obtained by subtracting a built-in potential from the high reference potential.

1. Field of the Invention
The present invention relates to a Silicon-On-Insulator (SOI) CMOS circuit provided with a plurality of PMOS transistors connected in series to each other.
2. Description of the Prior Art
Large-scale integration or LSI circuits have grown continually more powerful. Researches into integrating a more huge number of components on a single chip and speeding up LSI circuits have been ongoing. These researches have resulted in increases in power dissipation in LSI circuits. Some of the latest microprocessors consume tens of watts of power. Such increases in power dissipation in LSI circuits cause the following problems. The first problem is that heat internally generated in a chip has a deleterious effect on the reliability of the chip. The second problem is that a measure directed toward the dissipation of the internally generated heat, such as a cooling fan, causes an increase in the cost of manufacturing the chip. The third problem is that mobile information terminal equipment employing such high power LSI circuits is not easy-to-use because battery life is short. Thus the urgent challenge for manufactures, as well as users' desire, is to reduce the power dissipation in LSI circuits while maintaining their performance.
The most effective measure of reducing the power dissipation in an LSI circuit is to reduce the power supply voltage. However, a reduction in the power supply voltage causes a reduction in the response performance of MOS transistors included in the LSI circuit and hence a reduction in the operating speed of the LSI circuit. Various measures directed toward the prevention of reduction in the operation speed of LSI circuits caused by reduction in the power supply voltage have been taken. Recently Silicon-On-Insulator (SOI) CMOS circuits have captured much of the spotlight as such the measures.
SOI CMOS circuits provide three advantages as follows. The first advantage is that SOI CMOS circuits have low parasitic capacitance because they have a buried oxide film, resulting in reduction in the time required for charging and discharging a load and hence increases in the circuit speed, as disclosed in lines 2 through 8 on the right column of pp. 1106 of "Research and development trends of SOI technology", Journal of Applied Physics Society of Japan, Vol. 64, No. 11, pp.1104-1110, 1995. In other words, the first advantage is that even though a measure is taken to reduce the power supply voltage applied to an SOI CMOS circuit, the circuit speed can be maintained as it is high.
The second advantage is that even though a measure is taken to reduce the power supply voltage applied to an SOI CMOS circuit, the switching speed of MOS transistors is not reduced because the threshold voltages of the MOS transistors do not increase by virtue of the bias potential of their substrates, as disclosed in lines 23 through 33 on the right column of pp. 1106 of the above reference. Accordingly, even though a measure is taken to reduce the power supply voltage applied to an SOI CMOS circuit, the circuit speed can be maintained as it is high.
The third advantage is that the current drive capability of MOS transistors can be maintained at low power supply voltages by controlling the potential of the bodies of the MOS transistors, as disclosed in "A Dynamic Threshold Voltage MOSFET (DTMOS) for Ultra-Low Voltage Operation", IEDM94, pp.809-812, 1994. Accordingly, even though a measure is taken to reduce the power supply voltage applied to an SOI CMOS circuit, the circuit speed can be maintained as it is high.
Referring next to FIG. 14, there is illustrated a schematic circuit diagram of a prior art SOI CMOS circuit. The prior art SOI CMOS circuit serves as a NOR gate. In FIG. 14, reference numerals 101 and 102 denote first and second PMOS transistors, respectively, 103 and 104 denote first and second NMOS transistors, respectively, 105 denotes a high reference potential line with a power supply potential connected to a power supply, 106 denotes a low reference potential line with a ground potential connected to ground, A and B denote first and second input terminals to which signals are applied to, respectively, and C denotes an output terminal through which an output signal is furnished.
The prior art SOI CMOS circuit shown in FIG. 14 can maintain a high operating speed even at low power supply voltages by tying the bodies and gates of the first and second PMOS transistors 1 and 2 together, respectively, and by tying the bodies and gates of the first and second NMOS transistors 3 and 4 together, respectively.
While such the prior art SOI CMOS circuit can maintain a high operating speed even at low power supply voltages, it suffers from the following problems. The first problem with the prior art SOI CMOS circuit is that when NMOS transistors have the same size as PMOS transistors, the amount of current flowing in each NMOS transistor is two times as large as that flowing in each PMOS transistor, and an increase in a difference between the carrier mobility of each NMOS transistor and that of each PMOS transistor and hence an increase in a difference between the amount of current flowing in each NMOS transistor and the amount of current flowing in each PMOS transistor result from higher integration of components into the chip and lower power supply voltages, resulting in no margin for the operation of the prior art SOI CMOS circuit, such as a NOR gate, including the PMOS transistors connected in series to each other and hence low noise immunity because of a displacement of the logical threshold voltage of the SOI CMOS circuit, which determines the logic levels of signals, from a voltage intermediate between a power supply potential and a ground potential, as disclosed in FIG. 11 of pp.153 of Journal of NIKKEI Micro Device issued in September, 1994. Another problem is that since the length of the rising time of output signals furnished by such the prior art SOI CMOS circuit differs considerably from that of their falling time, it is difficult to design and manufacture a high performance LSI circuit which operates with a high degree of reliability.
Although changing the sizes of NMOS and PMOS transistors included in SOI CMOS circuits can be a measure to solve the above problems, this measure causes another problem that the circuit layout increases in complexity because it is difficult to efficiently arrange and wire NMOS and PMOS transistors.

Silicon-on-insulator circuit having series connected PMOS transistors each having connected body and gate


A solid-state image pickup device includes a plurality of pixels on a light-receiving surface, photodiodes disposed on the light-receiving surface of a semiconductor substrate while being partitioned on the pixel basis, signal transferring portions which are disposed on the semiconductor substrate and which read signal charges generated and stored in the photodiodes or voltages corresponding to the signal charges, insulating films disposed on the semiconductor substrate while covering the photodiodes, concave portions disposed in the insulating films, pad electrodes disposed on the insulating films, a passivation film which covers inner walls of the concave portions, which is disposed on the pad electrodes, and which has a refractive index higher than that of silicon oxide, and a core layer which is disposed on the passivation film while being filled in the concave portions and which has a refractive index higher than that of silicon oxide.

The present invention relates to a solid-state image pickup device, a method for manufacturing the solid-state image pickup device, and a camera. In particular, the present invention relates to a solid-state image pickup device, in which pixels having diodes are arranged in a matrix on a light-receiving surface, the method for manufacturing the solid-state image pickup device, and a camera provided with the solid-state image pickup device.
For example, in the configuration of a solid-state image pickup device, e.g., a CMOS sensor or a CCD element, light is allowed to enter photodiodes (photoelectric conversion portion) disposed on a surface of a semiconductor substrate, and an image signal is obtained on the basis of signal charges generated in the photodiodes.
In the CMOS sensor, for example, pixels are arranged in a two-dimensional matrix on a light-receiving surface, and a photodiode is disposed on the pixel basis. Signal charges generated and stored in each photodiode during reception of light are transferred to a floating diffusion by driving a CMOS circuit, and the signal charges are converted to signal voltages so as to be read.
In the CCD element, for example, pixels are arranged in a two-dimensional matrix on a light-receiving surface, and a photodiode is disposed on the pixel basis, as in the CMOS sensor. Signal charges generated and stored in each photodiode during reception of light are transferred through a CCD vertical transfer line and a horizontal transfer line so as to be read.
In the above-described solid-state image pickup device, e.g., a CMOS sensor, for example, the above-described photodiodes are disposed on a surface of a semiconductor substrate. An insulating film of, for example, silicon oxide, is disposed as a layer covering the photodiodes. Wiring layers are disposed in the insulating film except photodiode regions so as to avoid hindering the entrance of light into the photodiodes.
However, regarding the above-described solid-state image pickup device, the area of the light-receiving surface has been reduced as elements have been made finer. Accompanying this, a problem occurs in that the rate of incident light decreases and the sensitivity characteristics deteriorate.
A structure, in which light is condensed by using an on-chip lens, an interlayer lens, or the like, has been developed as a countermeasure against this. In particular, a solid-state image pickup device has been developed, in which an optical waveguide for guiding the light incident from the outside to a photodiode has been disposed in the insulating film above the photodiode.
Japanese Unexamined Patent Application Publication Nos. 2003-224249 and 2003-324189 disclose solid-state image pickup devices in which concave portions are disposed in insulating films above photodiodes, the concave portions are filled with silicon nitride that is a substance having a refractive index higher than the refractive index of silicon oxide (hereafter referred to as high-refractive index substance) and, thereby, optical waveguides for guiding the incident light to the photodiodes are disposed.
Japanese Unexamined Patent Application Publication No. 2004-207433 discloses a solid-state image pickup device in which a concave portion of an insulating film above a photodiode is filled with a silicon nitride film and a polyimide film and, thereby, an optical waveguide is disposed.
Japanese Unexamined Patent Application Publication No. 2006-190891 discloses a solid-state image pickup device in which an insulating film including a diffusion-preventing layer in the layer, a concave portion is disposed in a portion of the insulating film, the portion being above a photodiode, in such a way that the diffusion-preventing layer is removed, and the concave portion is filled with a silicon oxide film.
On the other hand, Japanese Unexamined Patent Application Publication No. 2006-222270 discloses a solid-state image pickup device, in which a concave portion of an insulating film above a photodiode is filled with a TiO-dispersion type polyimide resin and, thereby, an optical waveguide is disposed.

Solid-state image pickup device with an optical waveguide, method for manufacturing solid-state image pickup device, and camera