An active matrix liquid crystal display device 10 of the present invention includes: a plurality of signal lines Y1, . . . Ym and scanning lines X1, . . . Xn, Xn+1, Xn+2 which are arranged in a matrix state on a substrate; switching transistors 14 arranged near the intersection of each of the signal lines and the scanning lines; and pixel electrodes that are severally arranged in positions surrounded by the signal lines and the scanning lines and connected to the switching transistors, in which the pixel electrode is made up of a pixel electrode for display 12(25) that contributes to display, which is provided in an effective display region, and a dummy pixel electrode 27 that does not contribute to display, which is provided in a non-effective display region, and the dummy pixel electrode has a smaller area than the area of the pixel electrode for display and a plurality of the dummy pixel electrodes are parallelly provided for each signal line. Consequently, it is possible to provide an active matrix liquid crystal display device in which a large number of dummy pixel electrodes are provided without increasing the area of the non-effective display region and which is capable of dealing with multiple entries of static electricity from terminals.

1. Field of the Invention
The present invention relates to an active matrix liquid crystal display device, more particularly to an active matrix liquid crystal display device provided with preventing means for thin film transistor (hereinafter, referred to as "TFT") destruction caused by static electricity, which uses TFTs as a semiconductor switching element.
2. Description of the Related Art
Liquid crystal display devices generally have characteristics of slim, lightweight and low power consumption, and active matrix liquid crystal display devices of thin film transistor method are widely used in areas from mobile terminals to large-sized television sets.
First, description will be made for a general constitution of a conventional active matrix liquid crystal display device by referring to FIG. 4 that is a plan view of an area for several pixels, FIG. 5 that is a schematic equivalent circuit diagram for the several pixels, and FIG. 6 that is a cross-sectional view taken along VI-VI line of FIG. 4. In a conventional liquid crystal display device 10A, pixel electrodes 12 are provided for each region surrounded by scanning lines X1, X2, . . . Xn and signal lines Y1, Y2, . . . Ym, which are provided in a matrix state on a first translucent substrate 11, and the pixel electrode 12 is shown by a liquid crystal capacitance CLC in an equivalent manner in FIG. 5. Generally, an auxiliary capacitance Cs formed by an auxiliary capacitance electrode 13 is parallelly connected to the liquid crystal capacitance CLC. One end of the liquid crystal capacitance CLC is connected to a switching transistor 14 for driving, and the other end is connected to a common electrode 16, which is provided on a second translucent substrate 15 via a color filter layer CF, and predetermined common potential Vc is applied to the other end.
The switching transistor 14 consists of an insulated-gate field-effect thin film transistor (TFT), its source electrode S is connected to the signal lines Y1, Y2, . . . Ym and supplied with image signal Vs, and a drain electrode D is connected to one end of the liquid crystal capacitance CLC, that is, the pixel electrode 12. Further, the gate electrode G of the switching transistor 14 is connected to the scanning lines X1, X2, . . . Xn and gate pulse Vg having predetermined voltage is applied to the gate electrode.
Further, orientation films (not shown) are severally provided on the surface of the pixel electrode 12 and the common electrode 16, and liquid crystal 17 is filled between the first translucent substrate 11 and the second translucent substrate 15. Note that reference numerals 18 and 19 denote insulating films that are made of SiO2 or SiN respectively, and reference numeral 20 denotes an a-Si layer. Then, a plurality of the scanning lines X1, X2, . . . Xn and the signal lines Y1, Y2, . . . Ym are extracted in two directions or one direction of the frame portion of substrate (peripheral portion of substrate), and scanning line input terminals 21 and signal line input terminals 22 are provided at their terminal portions respectively.
The active matrix liquid crystal display device of such constitution has been recently manufactured in various sizes from a small size for cell phones to a large size having diagonal 40 inches (about 102 cm) to 50 inches (about 127 cm). However, if static electricity enters the display region of the liquid crystal display device in a manufacturing process, display defect occurs at the point where the liquid crystal display device is completed. Particularly, electrostatic defect occurs more easily than before with the advance for higher definition in middle and small display device models. Static electricity occurs only by allowing the device to contact other objects both in the manufacturing process and in transporting panels. Further, static electricity occurs most easily by friction during the rubbing of the orientation films. Therefore, it is imperative that the display defect caused by static electricity be eliminated in the manufacturing technology field of liquid crystal display devices.
Several technologies for preventing the occurrence of pixel defect caused by static electricity are known. For example, the invention of an active matrix liquid crystal display device 30, which is disclosed in Japanese Patent Laid-Open No. 10-213816 publication (claims, paragraphs [0029] to [0034], [0039], [0048], FIG. 2), has: stripe-shaped gate signal lines 31; stripe-shaped source signal lines 32 that are orthogonal to the gate signal lines; switching elements TFT provided near the crossing portions of the lines; and a plurality of pixel electrodes that are connected to the switching elements TFT and formed in a matrix state, on a substrate, and the pixel electrode is made up of a pixel electrode for display 33A that is provided in an effective display region and contributes to display and a dummy pixel electrode 33B that is provided in a non-effective display region and does not contribute to display, and a gate signal line 34 for driving the dummy pixel electrode 33B is formed by branching from the gate signal line 31 of the effective display region, as shown in FIG. 7. Furthermore, the above Japanese Patent Laid-Open No. 10-213816 also suggests that the dummy pixel electrodes 33B be provided in plural rows in order to protect the effective display regions without fail.
Specifically, the liquid crystal display device 30 is capable of protecting the switching elements connected to the pixel electrodes for display in the effective display region because switching elements that are connected to the dummy pixel electrodes 33B provided in the non-effective display region are preferentially destroyed when static electricity enters the liquid crystal display device via the first or the second signal lines 31, 32 during the manufacturing process of the device.
On the other hand, in a liquid crystal display device 40 disclosed in Japanese Patent Laid-Open No. 11-052427 publication (claims, FIG. 1), as shown in FIG. 8, scanning lines 41 and signal lines 42 which are formed so as to be orthogonal to each other, switching elements TFT formed on the crossing portions of the scanning lines 41 and the signal lines 42, and pixel electrodes for display 43A, which are connected to the switching elements TFT and driven controlled by signals supplied from the scanning lines 41 and the signal lines 42, are formed in plural numbers in the effective display region, while dummy pixel electrodes 43B separated from the scanning lines 41 and the signal lines 42 are formed in plural numbers on the peripheral portion of the effective display region, and additional auxiliary capacitance electrodes 44 are formed so as to face the dummy pixel electrodes 43B.
Specifically, in the liquid crystal display device 40, the static electricity is charged in the dummy pixel electrodes 43B provided in the non-effective display region when it enters the liquid crystal display device via the first or the second signal lines 41, 42 during the manufacturing process of the device, the charged static electricity is discharged via the additional auxiliary capacitance electrodes 44 or other auxiliary capacitance electrodes 45, and thus it is possible to protect switching elements TFT connected to the pixel electrodes for display 43A in the effective display region.
However, only one dummy pixel electrode 33B is provided for the gate signal line 31 or the source signal line 32 in the liquid crystal display device 30 disclosed in the above-described Japanese Patent Laid-Open No. 10-213816, so that once the switching element TFT of the dummy pixel electrode 33B is destroyed by static electricity, the dummy pixel electrode 33B loses its capability. Consequently, there is a danger that the switching elements TFT of the pixel electrodes 33A in the display region will be destroyed when static electricity enters the device again. In other words, since static electricity occurs only by contacting other objects not only during the rubbing of orientation films but also during the transportation of panels when manufacturing the liquid crystal display device, static electricity could enter the device many times until a finished product is obtained, and there is a possibility that the liquid crystal display device 30 disclosed in the above-described Japanese Patent Laid-Open No. 10-213816 cannot deal with such multiple entries of static electricity.
Note that the above-described Japanese Patent Laid-Open No. 10-213816 also suggests providing the dummy pixel electrodes 33B in plural rows in order to protect the effective display region without fail (refer to paragraph [0039]). In this case, since the dummy pixel electrodes 33B are formed in the same size as or larger than the pixel electrodes 33A of the effective display region (refer to claim 3, paragraph [0048]), there exists a problem that the non-effective display region becomes large.
Furthermore, in the liquid crystal display device 40 disclosed in the above-described Japanese Patent Laid-Open No. 11-052427, static electricity is charged in the dummy pixel electrodes 43B provided in the non-effective display region when it enters the liquid crystal display device via the scanning lines 41 or the signal lines 42 during the manufacturing process of the device. Since the dummy pixel electrodes 43B are separated from the scanning lines 41 and the signal lines 42 to function as a capacitor, there is a possibility that the static electricity will enter the pixel electrodes 43A of the effective display region before it is discharged via the additional auxiliary capacitance electrodes 44 or the other auxiliary capacitance electrodes 45, and the switching elements TFT connected to the pixel electrodes 43A in the effective display region will suffer from electrostatic destruction.
The present inventors, as a result of various kinds of study to solve the problems in the technology of preventing electrostatic destruction of the switching elements that are connected to the pixel electrodes of the effective display region as shown in the above-described conventional example, have found out the following and completed the present invention. To effectively discharge static electricity entered from outside, when only a constitution same as the switching elements TFT connected to the pixel electrodes of the effective display region is provided as the dummy pixels to be provided in the non-effective display region, electrostatic destruction occurs preferentially in the switching elements of the dummy pixels even if the area of the dummy pixel electrode is very small and there is no danger that static electricity will enter the effective display region, and the switching elements connected to the pixel electrodes can be effectively protected. Additionally, since the number of dummy pixels about ten times the conventional pixel electrodes of the effective display region can be provided in the same area, they can deal with multiple entries of static electricity without increasing the area of the non-effective display region.

Active matrix liquid crystal display device


A conductive paste is provided, which has good conductivity and good adhesiveness to substrates and has good long-lasting stability of these properties, and which, when applied to a through-hole of a multi-layered substrate, ensures improved reliability of bonding to the end faces of conductive layers in the through-hole. Therefore, the paste does not require through-hole plating. The conductive paste comprises (A) 100 parts by weight of a resin component that contains an acrylate resin and an epoxy resin, (B) from 200 to 1800 parts by weight of a metal powder of at least two metals that contain at least one low-melting-point metal having a melting point of not higher than 180° C. and at least one high-melting-point metal having a melting point of not lower than 800° C., (C) from 0.5 to 40 parts by weight of a curing agent that contains from 0.3 to 35 parts by weight of a phenol-type curing agent, and (D) from 0.3 to 80 parts by weight of a flux.

A conductive paste that may be used for substrate hole filling generally comprises a thermosetting resin and a conductive filler added to it, and in such a paste, the conductive filler is kept in contact with each other to ensure the conductivity of the paste.
Recently, a multi-layered substrate has become used for high-density mounting thereon, which is prepared by alternately laminating multiple conductive layers and multiple insulating layers. FIG. 3 is an enlarged, schematic cross-sectional view showing one example of such a multi-layered substrate, in which the reference numeral 31 indicates a conductive layer of copper foil or the like, the reference numeral 31m indicates an inner conductive layer of the type, and the reference numeral 32 indicates an insulating layer of resin or the like.
For inner layer conduction in the multi-layered substrate of the type, a through-hole that runs through the multi-layered substrate is formed in the substrate, a through-hole plate 33 is applied to it, then this is filled with a hole-filling paste 34, and after cured, the excess hole-filling paste 34 is removed by polishing, and thereafter this is covered with a cover plate 35 (for example, see JP-A 4-91489, FIG. 3; Material Technology and Production Process in Built-up Wiring Board (published by the Association of Technology Information, page 60). However, the process is problematic in that the accuracy in pattern formation therein could not be increased since the copper foil on the substrate surface will be thick owing to the twice-plating step of through-hole plating and cover plating therein. Accordingly, it is desired to attain the intended inner layer conduction with a conductive paste alone, without effecting through-hole plating and cover plating. However, the above-mentioned, conventional powder contact-type paste is unsatisfactory in point of the reliability of bonding to the end faces of inner layers, and it could not ensure stable inner layer conduction.
Contrary to this, a multi-layered substrate that may be formed according to the process shown in FIG. 4 is now employed in the art. In FIG. 4, the reference numeral 41 indicates a conductive layer, the reference numeral 42 indicates an insulating layer, and the reference numeral 43 indicates a conductive paste. The multi-layered substrate of the type is produced as follows: A hole is formed in every layer, and filled with a conductive paste 43, and then the layers are laminated in such a controlled manner that the filled holes could be in a line, and thereafter stacked by pressing. However, the multi-layered substrate is also problematic in that it requires a number of production steps and its production costs therefore increase, since the layers are separately holed and the respective holes are also separately filled with paste. In addition, since the production process includes the pressing step, it is still problematic in that the conductivity of the products may fluctuate owing to the fluctuation in the pressing pressure, and the process could not apply to multi-layered substrates with parts buried therein, and therefore its application area is limited.
The present invention has been made in consideration of the above-mentioned matters, and its object is to provide a conductive paste which has good conductivity and good adhesiveness to substrates and which, when applied to a through-hole of a multi-layered substrate, ensures improved reliability of bonding to the end faces of conductive layers in the through-hole. Another object of the invention is to provide a multi-layered substrate using the paste, which enables high-accuracy patterning thereon, not requiring through-hole plating and cover plating as in the related art. Still another object is to provide a method of producing such a multi-layered substrate, in which the production steps are significantly simplified as compared with those in the related art and which therefore enables cost reduction.

Conductive paste multilayered board including the conductive paste and process for producing the same


A resin composition for powder coatings that comprises a composition (A) and a blocked polyisocyanate compound (B), the composition (A) being based on both a carboxyl group containing polyester resin having a hydroxyl value of 10 to 100 and a softening point of 50.degree. to 150.degree. C. and a glycidyl group containing acrylic resin having a hydroxyl value of 30 to 150 and a softening point of 50.degree. to 150.degree. C., and further containing a copolymer prepared by reaction between said polyester and acrylic resins. This resin composition is capable of providing an ideal paint film that possesses the features of a paint film prepared from polyester resins (high degrees of smoothness, gloss and strength) and those of a paint film prepared from acrylic resins (high levels of hardness, stain resistance and weatherability).

In order to ensure that paints coated on metal surfaces will exhibit their two principal functions, i.e., protection and decoration, for a prolonged period of time, it is often required to provide paint films in at least two layers. Heretofore, to meet this need, resins having improved adhesion and corrosion resistance have been used in primers, and resins having improved weatherability, stain resistance and hardness have been used in topcoats.
As for application techniques, there has been a shift to the two-coat, one-bake process from the two-coat, two-bake process. From the viewpoint of energy saving, the one-coat, one-bake process should ultimately be an ideal method.
Because of their high performance and low cost, demands for powder coatings have constantly been growing. On the other hand, powder coatings are applied in single layers which perform single functions, so there inevitably is a limit to the future growth of demands for powder coatings although their use is growing in applications that suit the specific performance of individual types of coatings.
Under these circumstances, active efforts are being made to study a resin composition of the polyesteracrylic hybrid type for powder coatings that possess both the features of a powder coating resin composition made of a polyester resin and the features of a powder coating resin composition made of an acrylic resin (JP-B-55-1945) (the term "JP-B" as used herein refers to an "examined Japanese patent publication"). With a view to improving the stain resistance and solvent resistance of blocked isocyanate cured polyester powder coatings, a composition characterized by a blend with an acrylic resin having at least one of a hydroxyl group and a glycidyl group has been proposed (JP-A-59-6267) (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application").
Most of the conventional resin compositions of the polyester-acrylic hybrid type for powder coatings are characterized by merely blending polyester and acrylic resins. When polyester and acrylic resins that are not highly miscible with each other are blended, smooth coating surfaces are not attainable. On the other hand, polyester and acrylic resins that are highly miscible with each other are only capable of forming paint films that display a performance intermediate between those of the respective resins even in the most favorable case.


A brushroll having a pulley driven spindle with an end assembly at each end rotatably mounting the spindle in a vacuum cleaner nozzle. On the pulley end of the spindle, a projecting pin is knurled at one end and inserted into the end of the spindle. An outboard portion of the pin is threaded. The knurling on the pin forms an abutment shoulder outboard of the end of the spindle. The drive pulley is threaded onto the threaded end of the pin until it contacts a bearing and presses it against the abutment shoulder, so as to prevent the pin from being jacked out of the spindle when the pulley is threaded onto the pin.

A conventional form of brushroll comprises a wood spindle which carries a plurality of tufts of bristles or beater bar elements. The brushroll is rotatably supported at both ends by end assemblies mounted in the vacuum cleaner nozzle. Each end assembly includes a disk carried on the end of the spindle, a pin fixed to the spindle and projecting from its end through the disk, a bearing having its inner race fixed on the projecting end of the pin, and an end cap having a pocket that receives the outer race of the bearing. The end caps mount the spindle for rotation in the nozzle of the vacuum cleaner. In a belt driven spindle arrangement, one of the pins extends through an end cap and a pulley is threaded onto the pin so that the spindle can be rotated by a belt connected to the vacuum cleaner motor.
In a known construction over which the present invention is an improvement, one end of the pin that carries the pulley is knurled and is frictionally engaged in a hole in the spindle. The knurling on the pin stops short of the outer face of the end cap. During assembly, the pulley would be threaded onto the end of the pin until the bearing was captured between the pulley and the disk at the end of the spindle. With the prior art design, it was possible to continue to thread the pulley on the pin. Since the bearing was already engaged with the plastic disk, this continued threading of the pulley would withdraw the pin endwise from the hole in the spindle.
The movement of the pin caused by overthreading the pulley onto the pin would unbalance the brushroll which typically rotates at speeds of 5500-6000 rpm. The unbalanced condition results in eccentric rotation. The pin would wobble in the hole of the spindle and enlarge it, which results in brushroll rattle and general unsatisfactory operation.
The problem is accentuated when large die cast pulleys are used. The larger die cast pulleys are themselves unbalanced. As the pin supporting the pulley is withdrawn from the hole, the unbalanced large pulleys accentuate wobbling of the pin.


An image blur prevention apparatus for use with an image blur prevention device which prevents image blur and a restricting device which restricts movement of the image blur prevention device. The apparatus includes a releasing device which releases the image blur prevention device from a restricted state in which movement of the image blur prevention device is prevented by the restricting device and a holding device which holds a released state in which the image blur prevention device is released from the restricted state. The holding device holds the released state in a holding operation when electric current is supplied thereto. Operation of the holding device switches from the holding operation to a state in which the holding operation is not effected, when the supply of electric current is substantially discontinued.

1. Field of the Invention
The present invention relates to an image blur prevention apparatus for preventing image blur which may occur due to camera shake or the like in a camera, an optical apparatus or the like.
2. Description of the Related Art
The prior art targeted by the present invention will be described below by using a camera as an example.
Cameras at the present time have become increasingly automated, and the possibility that persons unskilled in the handling of cameras will fail in photo-taking is very small. However, it has been difficult to automatically prevent a failure in photo-taking due to camera shake.
Therefore, in recent years, research and development of cameras for the purpose of preventing a failure in photo-taking due to camera shake of a photographer has been vigorously under way.
As a method of suppressing camera shake caused by a photographer, there is a method in which vibrations due to camera shake are detected, and a correction lens is displaced in correspondence with the detected value in order to correct the optical displacement of the image. To describe in more detail, shake vibrations are detected by vibration sensors, such as accelerometers or angular speedometers, angular velocity is detected electrically or mechanically on the basis of sensor signals, the correction optical system (which is a part of or the whole of the photographic optical system) is parallelly off-set in a direction at right angles to the optical axis on the basis of the detected information, or a correction lens is displaced in a direction different from the optical axis, for example, the optical axis is inclined.
As a method of driving a correction optical system, when the correction optical system is parallelly off-set in a direction at right angles to the optical axis, a connection member is secured to a fixation section of a photographic apparatus in such a manner as to be movable in a direction (e.g., up and down) at right angles to the optical axis, and a correction lens frame is secured to the connection member, to which correction lens frame a correction lens is secured so as to be movable in a different direction (e.g., from side to side) at right angles to the optical axis. Thus, the correction optical system can be moved in any direction at right angles to the optical axis with respect to the fixation section.
As an actuator for driving a correction lens, two electromagnetic coils corresponding to the above-described two directions at right angles to the optical axis are mounted in the correction lens frame, and a yoke and a permanent magnet in a pair are mounted in correspondence with the two coils in the fixation section. In this way, a moving coil type actuator is formed which is capable of controlling two direction components independently of each other.
Further, the position of the correction lens is detected, and the positional information is fed back, thereby realizing drive control of the correction lens with a high degree of accuracy.
In the above, shake correction employing a correction optical system has been described. After photographing is terminated, it is necessary to hold the correction optical system at a predetermined position. In a case where, in particular, the correction optical system moves in any direction because of the weight of the system itself as a result of the shut-off of the power supply, as in a moving coil type, a lock mechanism is especially required. When the fact that photographing is performed without correction of shake is taken into consideration, it is preferable that the correction optical system is held at the position where the optical axis of the correction optical system is made to coincide with the optical axis of the whole photographic optical system in terms of the position with the greatest optical performance.
Conventional examples of a lock mechanism formed to achieve such an object:
(1) A lock member is provided for holding the correction optical system at a neutral position, and the lock member is urged in a direction on which it is locked by a spring. When shake is to be corrected, the lock member is retracted from the lock position in opposition to the urging force of the spring by means of a solenoid so that the state in which the correction lens can be moved is maintained. When the correction of shake is terminated, by shutting off the supply of electric current to the solenoid, the lock member is driven to the lock position by the urging force of the spring, and the correction optical system is held at the neutral position again.
(2) By making the lock member for holding the correction optical system at the neutral position retract from the lock position by a motor, a shake correctable state is formed. By making the motor rotate reversely (or, further rotating), the lock member is driven to the lock position.
(3) A similar lock member is previously urged by a spring in a direction in which it is locked. When the shake is to be corrected, while the lock member is kept retracted from the lock position by a motor, the lock member is locked by a hook, and the state in which the correction optical system can be moved is maintained. When the correction of shake is terminated, the motor is slightly moved reversely, and the locking of the hook is released. In this way, the lock member is driven to the lock position by the spring. In this case, even if the power supply is discontinued suddenly while the correction of shake is being performed, the lock member can be locked by merely making the motor slightly rotate reversely by a back-up power supply.
(4) A bistable plunger is provided. When no correction of shake is to be performed, the correction lens is driven to the neutral position by a conventional actuator for correcting shake. In that state, a projection provided in the fixation section is inserted by the plunger into a hole provided in the correction lens frame, and the correction lens is locked.
However, the conventional examples have the following problems.
In the conventional example (1) described above, the solenoid requires a huge amount of electric power in order to drive the lock member by the solenoid to the state in which shake can be corrected. If less electric power is to be used, the shake correction range (correction angle) must be made narrower.
In the conventional examples (2) and (4) described above, if the power supply is discontinued suddenly while the correction of shake is being performed, the correction optical system cannot be locked. Not only can the subsequent photographing not be performed, but also the correction optical system which is not locked becomes unsteady because of the movement of the apparatus. There is even the risk that the apparatus might be damaged.
In the conventional example (3) described above, it is possible to lock the correction optical system even when the power supply is suddenly turned off. However, a capacitor serving as a back-up power supply is physically too large to be disposed in, in particular, a camera or a lens barrel, impeding the compactness of the apparatus.

Image blur prevention apparatus with locking device


A switch device used for a laser device, includes series-parallel connected switch elements or modules. The switch elements or modules are simultaneously turned on by trigger signals from trigger circuits. The transmission lines for connecting the trigger circuits to respective switch elements are equal to one another in length. A protecting circuit is provided for the switch elements, and indicators are provided for indicating the shortcircuit of the switch elements. In the switch device, the number of wires for the switch elements is made small and heat generated from the switch elements is effectively radiated. The modules are easily stacked, and firmly connected to a control unit for controlling the switch elements. A discharge excited laser device using the switch device has a high efficiency and a long lifetime and is reliable.

The present invention relates to a switch device used for a laser device, in which a number of high speed solid-state switch elements, such as field effect transistors (FETs), are simultaneously turned on and off, and more particularly to a switch device used as a high voltage switch for a discharge excited laser device and the like.
FIG. 1 is a circuit diagram showing a discharge circuit used for an excimer (excited dimer) laser device as a conventional discharge excited laser device. In the figure, reference numeral 10 designates a high voltage power source; 11 a charge reactor connected to one end of the high voltage power source 10; 2 a charge capacitor connected in series to the reactor 11; 9 a pair of discharge electrodes connected between the charge capacitor 2 and the other end of the high voltage power source 10; 13 a laser beam resulting from the discharge between the paired electrodes 9; 12 a charge reactor connected in parallel to the paired electrodes 9; 8 a capacitor connected in parallel to the paired electrodes 9 and receiving electric charges from the capacitor 2; and 1 a thyratron, serving as a high voltage switch, connected between the other end of the high voltage power source 10 and a node between the reactor 11 and the capacitor 2. The pair of electrodes 9 are disposed in discharge gas, such as rare gas and halogen gas.
FIG. 2 is a perspective view showing an excimer laser device using the discharge circuit of FIG. 1. In the figure, like reference symbols are used for designating like or equivalent portions in FIG. 1. In the illustration of FIG. 2, the high voltage power source 10, and the reactors 11 and 12, which are shown in FIG. 1, are omitted, for simplicity.
In FIG. 2, the thyratron 1 as a high voltage switch is contained in a tubular container 6 made of conductive material. One end of the container 6 is closed by a cover 7 made of insulating material.
A plurality of charge capacitors 2 are arrayed in a line. One end of the line of the capacitors 2 is connected to one end of the thyratron 1 by means of an L-shaped conductive plate 4. The other end of the line of the capacitors 2 is connected to an elongated conductive plate 3. A parallelepiped case 5 made of conductive material is provided. The case 5 is filled with discharge gas. A pair of electrodes 9 are disposed in the case 5. One of the paired electrodes 9 is mounted on the conductive plate 3, while the other is mounted on the bottom of the case 5. One end of the case 5 is connected to the other end of the thyratron 1 through the container 6. The plurality of capacitors 8 are provided between one of the inner side walls of the case 5 and the side wall of the conductive plate 3, both the side walls facing each other. Similarly, the plurality of capacitors 8 are provided between the other of the inner side walls of the case 5 and the side wall of the conductive plate 3, both the side walls facing each other.
The assembly thus constructed may be electrically expressed by an equivalent circuit, which is substantially the same as that of FIG. 1.
The operation of the discharge circuit thus constructed will be described.
In FIG. 1, when the high voltage power source 10 is turned on while the thyratron 1 is in an off state, a charge loop of the high voltage power source 10 - reactor 11 - capacitor 2 - reactor 12 - high voltage power source 10 is formed to charge the capacitor 2. Then, when the thyratron 1 is fired, a charge transfer loop of capacitor 2 - thyratron 1 - capacitor 8 is formed. Through the charge transfer loop, the capacitor 2 is discharged and the charge discharged is transferred to the capacitor 8. Accordingly, the voltage across the capacitor 8, i.e., the voltage between the paired electrodes 9, rises. When it reaches the discharge voltage, discharge occurs between the paired electrodes 9. The discharge excites the gas in the case 5 to emit a pulsative laser beam 13.
The conventional discharge circuit employs the thyratron 1 as the high voltage switch. However, the thyratron 1 has a large inductance, and therefore the voltage between the electrodes 9 slowly rises. As a result, the discharge is instable. Further, since the thyratron requires a preheating time and is sensitive to temperature, a temperature controller must be provided.
To cope with this, a switch consisting of a number of high speed switch elements such as FETs, IGBTs or thyristors, as a switch to be used in place of the thyratron, was proposed by the applicants of the present application. FIG. 3 is a schematic illustration of a switch device 15 for a laser device consisting of a number of high speed switch elements 14 in which series-connected elements are further connected in parallel. By simultaneously turning on all the high speed switch elements 14 making up the switch device 15 which is used in place of the thyratron 1 in FIG. 1, the discharge current is allowed to flow from the capacitor 2.
Since the switch device 15 using the high speed switch elements 14 is thus constructed, when it is applied to the discharge exciting pulse laser device such as the excimer laser device, a switching speed of the discharge circuit influences an exciting efficiency of the laser medium. In order to obtain a higher exciting efficiency, a high speed switch must be used for the discharge circuit. However, in general, high speed switches have small rated voltage and current. Thus, such switches, if used, must be connected in a series-parallel fashion.
In a switch consisting of series-parallel connected high speed switches, if the number of series-parallel elements is large, the switch suffers from the following problems:
a) The inductance associated with the wires is increased.
b) Reliability of the wires deteriorates.
c) Intricate work is required for wiring and maintenance.
In a case where MOSFETs (900 V and 15 A, as rated values), suitable for high speed operation, are used as the switch elements 14 in the discharge circuit of the excimer laser device, and the switch consisting of the MOSFETs must withstand 30 kV and 4000 A, (solid-state switch) elements 14 totaling 9078 (=34.times.267) must be series-parallel connected. Accordingly, the above problems become actualized.
Particularly when the inductance in the circuit increases, the switching speed is made slow, and the efficiency of the charge transfer from the capacitor 2 to the capacitor 8 is reduced. This results in reduction of the laser oscillation efficiency. For this reason, the circuit inductance must be minimized.
Further, in the laser switch device as shown in FIG. 3, if some of the high speed switches connected in series, parallel or series-parallel connected break down to be shortcircuited, the voltage applied to the normal switches is increased. Thus, even if the number of the series and/or parallel connections is selected so that each high speed switch has the rated voltage larger than the required voltage, when some switches break down, a problem arises that a voltage larger than the rated voltage is applied to the normal switches, and a steep pulse voltage destroys the high speed switch if the laser device is continued to run leaving the switch trouble unrepaired. Also, in a situation where some of the series and/or parallel connected high speed switches are shortcircuited, but the remaining ones are normally operating, an operator may fail to find the switch trouble. This is a very dangerous situation.
To realize the switch device 15, a plurality of FETs 14 (in the following description, the high speed switch element 14 will be referred to as FETs 14) are interconnected into a single module. A plurality of such modules are connected into the switch device 15.
FIG. 4 is a perspective view showing an excimer laser device using the switch device 15 consisting of the modules, which is to be used in place of the thyratron 1. In the figure, like reference symbols are used for designating like or equivalent portions in FIG. 2.
In FIG. 4, reference numeral 20 designates the module with a terminal plate 20a. A set of modules 20 are mounted on each of conductive plates 617. The conductive plates 617 are interconnected through the terminal plates 20a of the modules 20. The conductive plates 617 are placed on insulating members 619, which are layered on both sides of conductive plate 618 with a T-shaped top. The terminal plates 20a of the set of the modules 20 mounted on the uppermost conductive plates 617 are connected to the T-shaped top of the conductive plate 618. In this instance, although the lowermost conductive plates 617 are integral with a case 5, those conductive plates 617 may be formed separately from the case 5. The bottom end of the conductive plate 618 is connected to one end of a plurality of capacitors 2.
The operation of the laser device thus constructed will be described.
Voltage is first applied from the high voltage power source 10 to the top of the conductive plate 618. The capacitors 2 are charged through the conductive plate 618. Then, all of the FETs 14 contained in all of the modules 20 are simultaneously turned on, to form a charge transfer loop of the capacitor 2 - switch device 15 - case 5 - capacitor 8. Thus, the charge is transferred from the capacitors 2 to the capacitors 8. Consequently, the voltage between the paired electrodes 9 rises and a discharge starts.
In the laser device under discussion, all of the FETs 14 are turned on at a high speed. The voltage between the paired electrodes 9 sharply rises, providing a stable discharge.
However, since the switch device consisting of the FET modules, used for the laser device of FIG. 4, is thus constructed, the heat due to the operation of a number of FETs 14 fabricated into modules, may damage the FETs 14 per se.
FIG. 5 is a cross sectional view showing the module 20. The module 20 contains a circuit in which a plurality of FETs 14 are simultaneously turned on. A drain electrode 190, common to those FETs 14, is provided on the upper surface of the module 20. A source electrode 200 common to the FETs and a gate electrode 210 are provided on the lower surface of the module 20. The drain electrode 190 is shaped in a thin plate, and the source electrode 200 and the gate electrode 210 are shaped in line pin terminals and protruded from the side edge of the module 20 outwardly.
The module 20 constituting the switch device 15, which consists of a number of solid-state switch elements such as FETs, is constructed as shown in FIG. 5. As shown, the source electrode 200 and the gate electrode 210 are protruded from the lower surface of the module 20. One approach to construct the switch device 15 using a number of modules 20, is to arrange the modules 20 two dimensionally as shown in FIG. 4. Another approach is to arrange the modules 20 into a stack. Particularly in the approach to stacking the modules, the protrusion of the pin-terminal like electrodes from the lower surface of the module 20 makes it difficult to stack the modules and to save the space. Accordingly, it is difficult to make the switch device miniatured and compact. Additionally, the inductance of the circuit is increased.
FIG. 6 is a perspective view showing the combination of the module 1116 and a controlling unit for control the module. The module 1116 contains a plurality of FETs. The control unit 1117 for driving and controlling the module is provided on a substrate board 1117a. The control unit 1117 applies control signals to the module 1116 through lead wires 1118.
FIG. 7 is a perspective view showing an excimer laser device using the switch device 15 consisting of the modules 20, in place of the thyratron 1. In the figure, like reference symbols are used for designating like or equivalent portions in FIG. 6.
In FIG. 7, a number of modules 1116 are grouped into sets of modules each consisting a predetermined number of modules. Each set of modules is provided on each conductive plate 1119 which is disposed on a side of a conductive plate 1120. The lower end of the conductive plates 1120 is connected to one end of each capacitor 2. A container 1121, accommodating the case 5 and the like, has a hole 21a through which a laser beam 13 passes to exterior.
The operation of the laser device thus constructed is the same as that of the device shown in FIG. 4.
In the switch device 15 consisting of the modules each containing a plurality of solid-state switch elements constructed as shown in FIG. 6, the control unit 1117 and the module 1116 are connected by means of the lead wires 1118. With such a connection, the control unit 1117 is suspended from the module 1116 by the lead wires 1118, and a number of connection points are required. Therefore, failure frequently occurs. Further, if the lengths of the lead wires 1118 are unequal, the drive times are not uniform, deteriorating the switching performance. If the nonuniformity of the drive times is great, overvoltage is applied on a number of solid-state switch elements, possibly destroying the elements.
FIG. 8 is a block diagram showing a conventional control circuit 211 for controlling the high speed solid-state switch elements 14. The control circuit 211 is constructed such that a trigger circuit 213 is provided on a substrate 212, and the trigger circuit applies a trigger signal to the switch elements 14 through signal lines 214 to 217 formed on the substrate 212, and through trigger terminals 218 of the switch elements 14.
The thus constructed switch device 15 consisting of the plurality of switch elements 14 has the problems on the switching operation as follows.
Those problems will be described using a case where the switch device 15 is applied to the excimer laser device. In the following description, a "switch time" is defined as the time which is required for the voltage across the capacitor 2 in FIG. 1 to fall from 90 to 10% of a predetermined voltage. The rise time of a high voltage applied to the pair of electrodes 9 in FIG. 1 is within 100 to 300 ns. The switch time of the switch device 15 that is required at that time, must be 50 ns or less. In a case where the switch device 15 consists of a number of high speed switch elements 14, if those switch elements 14 are asynchronously switched, many problems arise. For example, the switch time of the whole switch device 15 is elongated, an overcurrent flows into the switch element 14 switched earlier than the other switch elements, and an overvoltage is applied to the switch element 14 switched later than the others. In the latter two cases, the switch elements are damaged or reduced in lifetime. Preferably, it is necessary to synchronize the switching operations of the switch elements 14, so that before the voltage assigned to one switch element falls to 20% of its initial value after the switch elements 14 are turned on, the remaining switch elements 14 are turned on. That is, it is necessary that the synchronization is achieved in terms of time within 10 ns or less.
The control circuit 211 of FIG. 8 is designed such that one trigger circuit 213 applies a trigger signal to the respective switch elements 14. Therefore, the signal lines 214-217 are not equal in length to each other. As a result, the switch elements 14 are driven at different time points. That is, the switching operations of those elements cannot be synchronized within a predetermined time. Thus, a jitter occurs in the fall of the voltage as shown in FIG. 9, and the switch time exceeds a predetermined switch time (for example, 50 ns).
In the series-parallel circuit of the switch device 15 shown in FIG. 3, when coincidence among the conduction timings of the parallel circuits is lost, overvoltage is applied to those parallel circuits later conductive, possibly destroying the high speed solid-state switch elements 14 such as FETs. To cope with this, protecting circuits 316 shown in FIGS. 10 and 11 were proposed by the applicants of the present Patent Application.
The protecting circuit 316 shown in FIG. 10 is constructed such that a reverse-current blocking diode 317 and a parallel circuit consisting of a capacitor 318 and a resistor 319 are connected in series. The protecting circuit 316 is connected in parallel to each parallel circuit 320 consisting of the switch elements (FETs) 14.
In the protecting circuit 316 thus constructed, when an overvoltage is applied to the parallel circuit 320 and the current flows through the parallel circuit, the capacitor 318 is gradually charged through the diode 317 according to a time constant determined by the capacitor 318 and the resistor 319. Accordingly, the overvoltage is not directly applied to the switch elements 14, thereby protecting the switch elements.
In the protecting circuit 316' shown in FIG. 11, a reverse current blocking diode 321 and an FET 322 are connected in series. A series circuit consisting of a Zener diode 323, a reverse current block diode 324, and a resistor 325, is branched from the cathode of the reverse current blocking diode 321. A node between the reverse current block diode 324 and the resistor 325 is connected to the gate terminal of an FET 322.
In the protecting circuit, when an overvoltage is applied to the parallel circuit 320', the Zener diode 323 becomes conductive through the reverse current blocking diode 321 and voltage appears across the resistor 325. This voltage is applied to the gate terminal of the FET 322, which in turn is conductive. As a result, the current caused by the overvoltage flows through the diode 321 and the FET 322, thereby protecting the switch elements (FETs) 14.
As seen from the foregoing description, the protecting circuits 316 of FIGS. 10 and 11 are both by-paths for the current caused by the overvoltage.
Since the switch device 15 with the conventional protecting circuit 316, 316' is thus constructed, if the switch device 15 is applied to the discharge circuit as shown in FIG. 1, the following problems arise.
When, in each of the parallel circuits 320, 320' shown in FIGS. 10 and 11, a power source (not shown) is provided on the left side on the drawings of those figures, inductance L of the conductor constituting a current loop for the current I at a location close to the power source is smaller than that at a location distant from the power source. FIG. 12 is a diagram useful in explaining the reason for this. In the figure, an area of the current loop of the current I is A and its depth is "l". In an actual circuit, the parallel circuits 320, 320' are arrayed in parallel while extending in the direction "l". Accordingly, "l" indicates the length of the array, and is a fixed length in the description to follow.
In FIG. 12, inductance L of the conductor forming the current loop I is given EQU L=.mu..sub.o .times.(A/l) (1)
where .mu..sub.o : dielectric constant.
The equation (1) indicates that in FIG. 12, the inductance L becomes larger toward the right side of the current loop I. The cross sectional area enclosed by the current loop I is referred to as the "inner side of the current loop". Then, inductance L of a subcurrent-loop within a main current loop is smaller than that outside the main current loop. To be more specific, in each of the circuits of FIGS. 10 and 11, with regard to the switch elements (FETs) 14 making up the parallel circuit 320, 320', the inductance L of the current loop for the switch elements (FET) 14 on the left side is small, and that for the switch elements (FET) 14 on the right side is large. The current I depends on the inductance L as follows: ##EQU1## where
Vo: Voltage
C: Synthesized capacitance of capacitors 2 and 8
t: Time.
FIG. 13 is a graph showing waveforms of the current I for two different inductances L and L' (L'<L As seen from the graph, in the case of the small inductance L', the current waveform is sharp within a short time.
As seen from the foregoing description, in the circuits of FIGS. 10 and 11, even if the protecting circuit 316 is used, an overvoltage is earlier applied to the switch elements (FETs) 14 on the left side, viz., in the inner side of the current loop than the protecting circuit 316, 316'. As a result, the switch elements (FETs) will be destroyed.
FIGS. 14(A) and 14(B) are circuit diagrams showing a conventional pulse generating circuit for a discharge excited pulse laser as disclosed in Japanese Patent Application No. Heisei 2-34251. In the figures, reference numeral 42 designates a charge reactor; 43 a charge diode; 44 a main capacitor for charge and discharge; 45 a charge resistor; 46 a peaking capacitor; and 47 a discharge tube (laser tube) for generating a laser output by heating and evaporating metal (e.g., copper) contained therein through the gas discharge. A switch 415 for pulse generation consists of a number of FETs (field effect transistors) 49 as solid-state switch elements. Those FETs are connected in parallel to one another, and those parallel connections are connected in series. One specific FET 49A (also called an overvoltage protecting FET) of those FETs 49 of each parallel connection is connected such that the gate of the FET 49A is not connected to the gates of the other FETs 49.
A series connection of a Zener diode 411 and a diode 412 is connected between the gate and drain of the overvoltage protecting FET 49A. A resistor 413 is connected between the gate and source of the FET 49A. The Zener diode 411, the diode 412, and the resistor 413 make up a dynamic clamper. A diode 420, coupled with the drain of the FET 49A, is a reverse-current blocking diode.
When a gate signal is applied to the series-parallel connected FETs 49, the FETs 49 are turned on. A large charge voltage across the main capacitor 44 is applied through those FETs 49 to the discharge tube 47, feeding the discharge current thereto. If the coincidence among the switch timings of the FETs 49 is lost in an FET series connection, for example, a switch time t.sub.1 of one of the FETs 49 in the first series-connection stage S.sub.1 among those stages S.sub.1 to Sn is behind the switch time t.sub.0 of each of the FETs 49 of the remaining series-connection stages (FIG. 15(a)), a large voltage is concentrically applied across the source-drain paths of the FETs in the first series-connection stage (FIG. 15(b)). Under this condition, the FETs 49 in the first series-connection stage will possibly be damaged. When the overvoltage in excess of the Zener voltage Vb shown in FIG. 16 is applied to the Zener diode 411 connected between the drain and gate of the FET 49A, which is connected across the FET 49 in the first series-connection stage, since the diode cannot withstand the voltage exceeding the voltage Vb, current flows through the diode 412 to the resistor 413. The current i.sub.b flowing into the resistor 413 is as shown in FIG. 15(d). Accordingly, the voltage across the resistor 413 rises and the gate voltage also rises (FIG. 15(c)). When the gate voltage exceeds the threshold voltage, the drain-source path of the FET 49A immediately becomes conductive. Under this condition, the current, which otherwise is to be shunted into the respective FETs of the first series-connection stage, concentrically flows through the drain-source path of the FET 49A. Meanwhile, stray inductance 421 is parasitic on the source of the FET 49, and parallel stray inductance 422 is parasitic on the source of the FET 49A, as shown in FIG. 14(b). In the FIG. 14 circuit, the arrangement of circuit components are usually laid out so that the stray inductance 422 has a small value. If not so laid out, the rise of the current i.sub.b flowing through the resistor 413 becomes dull, and the rise of the gate voltage of the FET 49 becomes gentle. The conduction of the FET 49A retards, making its protecting function ineffectual. It is for this reason that the stray inductance 422 is selected to be smaller than the stray inductance 421. Accordingly, immediately after the FET is switched, the reverse current will flow into the FET 49A of the lower inductance by the electric energy stored in the stray inductances 421 and 422. The reverse-current blocking diode 420 blocks the rush of the reverse current into the FET 49A, thereby to protecting the FET 49A from being destroyed by the reverse current.
In the pulse generating circuit thus constructed, if the conduction timings of the series-parallel connected FETs are staggered, the FET (e.g., FET 49A) in the bank in which the conduction timing is behind may be destroyed by an overvoltage applied thereto. To cope with this, a dynamic clamper is connected in series to each FET, thereby to prevent the overvoltage being applied to the FET. However, since the overvoltage destruction of the FET is due to instantaneous electric energy, even the response delay of the Zener diode cannot be neglected. A slight response delay of the Zener diode, when combined with bad conditions, possibly leads to the overvoltage destruction.
FIGS. 17 and 18 are a side view and a perspective view showing a conventional discharge excited laser device as disclosed in Japanese Patent Application No. Heisei 2-163228. In the figure, reference numerals 1A and 1B indicate solid-state switch elements of 500 ns or less in switching time. Radiating plates 2A and 2B are provided for cooling the solid-state switching elements 1A and 1B. Conductive plates 3A, 3B, 60, 7A and 7B allow large current to pass therethrough. Numeral 2 designates a charge capacitor; 5 a case; 8 a peaking capacitor; and 9 discharge electrodes. FIG. 19 is an electric circuit showing the discharge portion in FIGS. 17 and 18. In the figure, reference numeral 10 designates a high voltage power source; and 11 and 12 charge reactors.
The operation of the discharge circuit shown in FIG. 19 is the same as that of the discharge circuit shown in FIG. 1 in which the thyratron 1 is used for the solid-state switch elements 1A and 1B. In the circuit shown in FIG. 19, the solid-state switching elements 1A and 1B are stacked in a multiple of stages, in order to obtain a high breakdown voltage. A number of banks of the switching elements are arrayed in parallel in the optical axis, in order to obtain a large current capacity. As viewed in the direction orthogonal to the optical axis, the switch groups are disposed on both sides of a phantom line passing through the paired discharge electrodes. Two discharge energy transfer loops are formed. One is a counterclockwise loop of charge capacitor 2 - conductive plate 60 - conductive plate 7A - solid-state switching element 1A - conductive plate 3A - conductive plate 60 - charge capacitor 2. The other is a clockwise loop of charge capacitor 2 - conductive plate 60 - conductive plate 7B - solid-state switching element 1B - conductive plate 3B - conductive plate 60 - charge capacitor 2. The direction of current flow of one loop is opposite to that of the other loop, so that the inductances caused by the currents are canceled out. Further, the switching elements 1A and 1B are disposed separately from each other in the optical axis direction. Such a layout of the switching elements successfully eliminates the phenomenon of the temporary current concentration, which may occur when the thyratron as a switch device is used. The result is a considerable reduction of the inductance of the charge transfer loop, and the consequent increase of dv/dt. Hence, a uniform and stable discharge can be obtained. For example, when the switch elements 1A and 1B of 40 ns in switching time is used, 100 nH or less of an overall inductance is attained.
In the solid-state switch device thus constructed, the portions of the switch device near the radiator plates is satisfactorily cooled, but the inner portion and some specific portions are unsatisfactorily cooled. As a result, a nonuniform temperature distribution appears in each of the solid-state switch elements (switches, such as FETs, IGBTs, and SITs, or other types of switches having a switching time comparable with that of the former switches) or in modules containing a plurality of switch elements. Accordingly, their switching characteristics are also not uniform, so that an overvoltage is applied to the switches turned on later. Extremely, those switches are destroyed.
FIG. 20 is a circuit diagram showing a conventional discharge excitated pulse laser device. FIG. 21 is a diagram showing waveforms for explaining the operation of the pulse laser device. In FIG. 20, reference numeral 141 designates a capacitor for storing energy for the main discharge; 142 a peaking capacitor; 143 a charge inductance; 144 a high voltage switch such as a thyratron for starting the discharge; 145 a first main electrode disposed within a laser medium 1410, the longitudinal direction of which coincides with the laser optical axis direction; 146 a second main electrode with a plurality of holes, which is disposed in opposition to and spaced by a predetermined distance from the first main electrode 145; 147 a dielectric material interposed between the second main electrode 146 and an auxiliary electrode 148 in a sandwich fashion; and 149 a high voltage generator. Letter A indicates a circuit used exclusively for a preparatory ionization. The circuit, provided for oscillation period adjustment, is made up of inductances 1411A, 1411B and a capacitor 1412 directly coupled with each other, for setting a time constant. Numeral 1413 represents a mid point between the time constant setting capacitor 1412 and the auxiliary electrode 148.
The operation of the discharge excited pulse laser device thus constructed will be described. The capacitor 141 is charged, with a high voltage, through the charge inductance 143, and the capacitor 1412 is charged, with a high voltage, through the charge inductances 1411A and 1411B. The charge current path for the capacitor 141 is denoted as 141X, and that for the capacitor 1412, as 141Y. Thereafter, the high voltage switch 144 is turned on. Voltage across the peaking capacitor 142, viz., voltage between the second main electrode 146 and the auxiliary electrode 148, rises like voltage V in FIG. 21. Current having a waveform denoted as I.sub.A in FIG. 21, which is for charging the peaking capacitor 142 and a capacitance formed of the second main electrode 146 and the auxiliary electrode 148, flows from the capacitor 141. A rate of the flow of the current 142X is determined by a combined capacitance of the capacitors 141 and 142, and the capacitor formed of the second main electrode 146 and the auxiliary electrode 148, and a stray inductance in the circuit, and rises within 50 to 100 ns, as current I.sub.B in FIG. 21. At the same time, the circuit, or the preparatory ionization dedicated circuit A, which is made up of the inductances 1411A and 1411B, and the capacitor 1412, which set a time constant, the auxiliary electrode 148, the dielectric material 147, the second main electrode 146, and the high voltage switch 144. The charge, which has been stored in the time constant setting capacitor 1412 and the capacitor constructed with the second main electrode 146, the dielectric material 147, and the auxiliary electrode 148, is discharged therefrom through a path 142Y. Through the discharge, a creeping discharge occurs at the plurality of holes of the second main electrode 146, so that a preparatory discharge is performed.
Assuming that the capacitance of the preparatory ionization dedicated circuit A is C, and the sum of the inductances of the same circuit is L, then the oscillation period is 2.pi..sqroot.LC.
Generally, a quantity of charge necessary for the preparatory ionization is approximately 1% of the quantity of charge for the main discharge. Therefore, by setting the C to be small, the oscillation period of the preparatory ionization dedicated circuit A may be 1/10 or less of the oscillation period of the main discharge circuit. Waveforms of the operation as stated above is shown in FIG. 21. As shown, until the main discharge occurs, current I.sub.B of the preparatory ionization oscillates two to three times, improving the uniformity of the preparatory ionization. Thus, the transfer of the main discharge to the arc is suppressed and hence uniform main discharge condition is set up.
Since the conventional discharge excited pulse laser device is thus constructed, if the thyratron is used for the high voltage switch for discharge start, the current of the discharge circuit concentrates at the electrodes to cause great inductance. The great inductance makes it difficult to switch at high speed. To cope with this, a measure has been taken in which the current of the main discharge circuit is temporarily restricted by a saturable reactor, for example, and the preparatory discharge is performed during the current restriction period. The measure makes the circuit construction complicated.
FIG. 22 is a circuit diagram showing a basic pulse generating circuit used for a conventional laser oscillator that is disclosed in IEEE Journal of Quantum Electronics, Vol. QE-15, No. 5, May, 1979, PP311-313. The pulse generating circuit includes a pulse circuit called an LC inverting circuit. In the figure, reference numeral 161 designates a thyratron used as a high voltage switch; 162 a first capacitor C.sub.1 ; 163 a second capacitor C.sub.2 ; 164 a high voltage power source; 165 a charge resistor; and 166 a discharge section.
In operation, the high voltage power source 164 feeds charge current into the following two charge loops; a first loop containing inductive element L, a diode D, the second capacitor 163, and the charge resistor 165; and a second loop including the inductive element L, the diode D, and the first capacitor 162. As the result of the current flow, charge is stored in both the capacitors. At this time, the voltage at point A is zero. Then, the thyratron 161 as a high voltage switch is closed, and the discharge is performed through a loop including the first capacitor 162 and the thyratron 161. As a result, the voltage at point A rises to be doubled. With progress of the above operation, the voltage between the main electrodes in the discharge section 166 rapidly rises and eventually a discharge space is broken down. The energy stored in the capacitor is fed into the discharge section 166. The gas in the discharge space is excited to emit a laser beam by the stimulated emission. In the LC inverting circuit, the charge voltage may be lower than the voltage necessary for the discharge section 166. Therefore, the switch of a low withstanding voltage may be used for the high voltage switch. Additionally, the size of the high voltage power source 164 and the like may be reduced.
FIG. 23 is a circuit diagram showing a discharge section of a conventional discharge excited laser device. This circuit additionally includes a magnetic saturation switch 167 and a peaking capacitor 168. In this circuit, the current flowing into the discharge section 166 is temporarily shut off by utilizing the characteristic of the magnetic saturation switch 167. As far as the magnetic member of the magnetic saturation switch 167 is not saturated, its impedance .omega.L is extremely high. When the magnetic member is saturated, the impedance is abruptly decreased. For example, when the thyratron 161 is turned on, the impedance .omega.L of the magnetic saturation switch 167 is large, so that the rise of the discharge current is delayed. When the magnetic saturation switch 167 is saturated, charge is transferred to the peaking capacitor 168, and its charge applies a high voltage to the discharge section 166 to cause it to start a discharge.
The conventional discharge excited pulse laser device is thus arranged. Accordingly, a pulse (high frequency) circuit including the inductive element is formed in the charge transfer loop including the thyratron, so that a response time of the loop is long. Thus, a charging time for voltage inversion in the loop including the first capacitor 162 and the thyratron 161 is long. As a result, the discharge is impelled to start before the voltage at point A is doubled. Accordingly, the charge fed into the discharge section is insufficient in amount, and the resultant oscillation efficiency of the laser device is unsatisfactory.
The magnetic saturation switch, when used, is advantageous in that the voltage at point A is doubled and the load for the thyratron is small. However, since the magnetic saturation switch is an active element, when the charge voltage is varied or ambient temperature is varied, the switching time also varies. In this respect, difficulty exists in using this type of the switch.
FIG. 24 is a circuit diagram showing a conventional exciting circuit for an excimer laser as discussed in "Electrical Society Technical Report (Part II), No. 217 (Present State of Shortwave Laser), page 5, issued April, 1986 (Showa 61). In the figure, reference numerals 171 and 172 designate a pair of main discharge electrodes; 173 a peaking capacitor connected in parallel to the main discharge electrodes 171 and 172; and 174 a pulse generating capacitor connected at one end to the main discharge electrode 171. A switch 175, for which a thyratron was used, is connected between the other end of the pulse generating capacitor 174 and the main discharge electrode 172. Numeral 176 represents a charge reactor connected in parallel to the peaking capacitor 173, and numeral 177 indicates a charge terminal.
The operation of the excimer laser exciting circuit thus arranged will be described. When a high positive voltage is applied to the charge terminal 177, a charge current i.sub.1 flows through the charge reactor 176 to charge the pulse generating capacitor 174 with the polarities as shown. Under this condition, when the switch 175 is turned on at time point t.sub.0, the voltages across the pulse generating capacitor 174 and the peaking capacitor 173 vary as shown in FIGS. 25(a) and 25(b). The pulse generating capacitor 174 at charge voltage V.sub.1 starts to discharge, and current i.sub.2 flows through the peaking capacitor 173, to perform the charge transfer.
During a period between t.sub.0 .ltoreq.t.ltoreq.t.sub.1, the charge stored in the pulse generating capacitor 174 is transferred to the peaking capacitor 173. At time point t=t.sub.1, the discharge starts between the main discharge electrodes 171 and 172, and current i.sub.3 flows in the direction of arrow. In the excimer laser, actually, a preparatory ionizing discharge is performed prior to the main discharge. The electrodes and circuit for the preparatory ionizing discharge are omitted in FIG. 24 for simplicity. During a period between t.sub.1 .ltoreq.t.ltoreq.t.sub.2, when energy is injected into the discharge section from the peaking capacitor 173, the main discharge is performed between the main discharge electrodes 171 and 172, to cause a laser oscillation. In the laser of a small discharge resistance (e.g., 0.2 .OMEGA.), such as an excimer laser, the voltage V.sub.2 across the peaking capacitor 173 takes an oscillation voltage waveform as shown in FIG. 25(b), and hence a voltage of the reversed polarity is caused (t=t.sub.2 in FIG. 25(b)). At a time point where the oscillation almost terminates, a voltage having the polarity reverse to that of the voltage at the time of the charging, appears across the pulse generating capacitor 174 (Vr in FIG. 25(a)). The voltage Vr causes the reverse current i.sub.4 to flow.
FIG. 26 is a circuit diagram showing another conventional exciting circuit for a pulse laser. In this circuit, the charge in the pulse generating capacitor 174 flows in the form of a charge current i.sub.20 through a saturable reactor 178, which acts like a switch, and transfers to the peaking capacitor 173. This circuit, generally called an MPC (magnetic pulse compression) circuit, includes additionally another pulse generating capacitor 179 and a current restricting reactor 1710, in order to reduce a switching loss at the switch 175. Operating waveforms of the signals in the MPC circuit are as shown in FIGS. 11(a), 11(b) and 11(c). As in the conventional circuit of FIG. 24, at time point t=t.sub.1, the discharge starts between the main discharge electrodes 171 and 172. Subsequently, the reverse current i.sub.4 oscillates. Finally, the voltage Vr having the polarity reverse to that of the voltage at the initial stage, appears across the pulse generating capacitor 174.
In the conventional pulse laser device thus constructed, the reverse voltage Vr of the reversed polarity appears across the pulse generating capacitor, after the main discharge current flows. The reverse voltage energy (=1/2CVr.sup.2) is consumed in the form of arc or streamer between the main discharge electrodes after a relatively long time (e.g., approximately 1 .mu.s) from the main discharge occurrence. This is called an after-current, and does not contribute to the laser oscillation, but damages the main discharge electrodes to reduce the lifetime of the electrodes. Further, when the after-current flows, the laser device cannot oscillate at a high repetitive frequency.
FIG. 28 is a circuit diagram showing an electrical circuit of another conventional discharge excited pulse laser as disclosed in Electrical Society Technical Report (part II), No. 217 (Present State of Short Wave Laser), P5, issued April, 1986 (Showa 61). In the figure, reference numerals 181 and 182 designate paired main discharge electrodes disposed confronting each other; numeral 183 a peaking capacitor C.sub.2 made of SrTiO.sub.3 (titanic acid strontium) and disposed in parallel to the main discharge electrodes 181 and 182; numeral 184 a pulse generating capacitor C.sub.1, one terminal of which is connected to the main discharge electrode 181. A switch 185 of a thyratron is connected between the other terminal of the capacitor 184 and the main discharge electrode 182. A charge reactor 186 is disposed in parallel to the peaking capacitor 183. Reference numeral 187 designates a high voltage power source. Numerals 188 and 189 indicate inductance components contained in the circuit.
In operation, when a positive high voltage is applied from the high voltage power source 187 to the pulse generating capacitor 184, charge current i.sub.1 flows through the charge reactor 186 to charge the capacitor 184 with the polarity as shown. When the switch 185 is turned on, the charge of the capacitor (C.sub.1) 184 flows, in the form of pulse current i.sub.2, into the peaking capacitor (C.sub.2) 183. In this way, the charge transfer is performed. Succeedingly, a discharge starts between the main discharge electrodes 181 and 182, and discharge current i.sub.3 flows in the direction of an arrow. In the excimer laser device, a preparatory discharge is performed prior to the main discharge. The electrodes and electric circuit for the preparatory discharge are not illustrated here. When the energy is injected from the peaking capacitor (C.sub.2) 183 into the discharge section, the main discharge occurs between the paired main discharge electrodes 181 and 182, causing a laser oscillation. In the laser device of a low discharge resistance (e.g., 0.2 .OMEGA.), such as an excimer laser device, the voltage across peaking capacitor (C.sub.2 ) 183 varies as indicated by an oscillation voltage waveform shown in FIG. 30(a). As seen, the voltage component of the inverted polarity is observed. The voltage component Vr of the inverted polarity causes an inverted current (after-current) as shown in FIG. 30(b), which in turn causes an arcing. As a result, the lifetime of the main discharge electrodes 181 and 182, and the laser gas are remarkably reduced.
FIG. 29 is a graph showing a characteristic curve representing a variation of the capacitance of the peaking capacitor (C.sub.2) 183 vs. DC voltage, when the capacitor 183 is made of SrTiO.sub.3. The graph shows that the capacitance hardly changes even if the voltage is decreased up to a value near to the rated voltage. This shows that after the discharge starts, energy is left in the peaking capacitor (C.sub.2) 183, and the residual energy causes the arc discharge owing to the aftercurrent.
In the conventional discharge excited pulse laser device thus constructed, when the peaking capacitor (C.sub.2) 183 is made of SrTiO.sub.3, its capacitance hardly varies even if the voltage is increased up to approximately the rated voltage. Accordingly, after the discharge starts, energy is left in the peaking capacitor (C.sub.2) 183, and the residual energy causes the arc discharge owing to the after-current.
In the charge transfer type circuit, when a voltage higher than the voltage Vo applied from the high voltage power source, is applied to the discharge section, if a ratio of C.sub.1 /C.sub.2 is set large, the voltage applied to the discharge section can be increased up to a value two times the applied voltage Vo. However, also in this case, after the discharge starts, the amount of charge left in the peaking capacitor is large, so that arc discharge owing to the after-current tends to occur.


A vehicle seat includes a seat-cushion frame supported on a vehicle body, a fastener fixed to the seat-cushion frame in a lateral direction, an absorption member supported by the fastener inserted in the absorption member, a seat-back frame supported via the absorption member, and a seat back fixed to the seat-back frame.

As a related vehicle seat, Patent Literature 1 discloses a seat including: side panels arranged on the left and right sides of a seating part of the seat; a front member laid between and fixed to front end portions of the side panels; and a rear member laid between rear end portions of the side panels and fixed to only one of the side panels. Without increasing in weight, this vehicle seat is configured to prevent vibrations of the vehicle body caused by travel from being transmitted to the seat and thereby avoid sympathetic vibrations of the seat (this phenomenon will be referred to as resonance. The same applies hereinafter).


An authentication technique with a teaching phase and authentication phase. In the teaching phase, authentication information is collected for a user in at least two categories, wherein one category relates to measurable physical characteristics of the user, another category relates to communication resources available to the user; and a third category relates to knowledge possessed by the user. In the authentication phase, some of the collected authentication information is used to formulate challenge(s) for presentation to the user. Response(s) to the formulated challenge(s) is/are received from the user and correctness of the received response is determined based at least partially on comparison with at least a portion of the collected authentication information. A correctness metric is calculated for the response(s). The user is authenticated if the correctness metric meets or exceeds a first threshold value.

A number of authentication schemes have been developed to authenticate users of data processing devices or communications terminals. A well-known authentication scheme involves a teaching phase in which setting up a new user account comprises teaching a username (login name) and password to an authentication element. A subsequent authentication phase comprises requesting the user to enter the username-password combination. If the entered username-password combination matches a pre-stored (taught) combination, the user is positively authenticated.
Such simple systems are vulnerable to intrusion and fraudulent behavior. Intruders can tap into the authentication system in several ways. They can cause installation of malware software in the users' computers. The malware software records keyboard entries by the user during login and relays the keyboard entries to the intruders. Another technique is to eavesdrop communication channels between an authentication server and the users' terminals. A third technique is to hack into the authentication server.
Attempts have been made to alleviate the security problems relating to current authentication schemes. Many improved authentication schemes are based on a paradigm known as "what you know and what you have". The username-password combination is an example of "what you know", while a mobile network identity is an example of "what you have". For instance, the teaching phase of authentication may involve teaching a mobile identity, such as an MSISDN number, to the authentication system. In the authentication phase the authentication server may generate a pseudo-random code and send it to the user's mobile terminal and request the user to return the pseudo-random code from another terminal, such as a computer, within a relatively short period of time. Because modern mobile communication systems use a PIN-code-based authentication, possession of a mobile terminal coupled with the mobile identity taught to the authentication system is an additional measure of security relating to the user being authenticated. Reference documents #1 and #2, which are a commonly-owned PCT application and US patent application, respectively, disclose various techniques for authentication. In particular, Reference document #1 discloses a technique called Dynamic Dialog Matrix (DDM), in which a mediator (proxy server) varies a sender number assigned to Short Message Service (SMS) messages and assigns a different sender number to each SMS message of a sequence. When clients (mobile users) respond to the SMS messages of the sequence, each reply message has a unique combination of sender address (the mobile terminal numbers) and recipient address (the address the mediator as sender address assigned to the query message). The unique combination of sender address and recipient address act as row and column addresses to data structure (called the DDM), and the cell identified by the two addresses contains the reply. With the DDM, the mediator knows not only which reply belongs to which query, but the mediator also knows, with a reasonable certainty, that the mobile user sending a reply message is the person to whom the query message was sent. Nobody else knows which sender address has been assigned to a query of interest. Accordingly, nobody else knows which recipient address a reply message should be sent.
In Reference document #2, FIGS. 9A, 9B and 9B of and their associated descriptions disclose techniques in which a combination of a general-purpose computer and a mobile terminal is used for authentication (and for additional functions, some of which may not be relevant for the present invention). FIG. 10 of Reference document #2 and its associated description disclose a system architecture which can be used to implement the present invention. The contents of said reference documents are incorporated herein by reference.
In spite of improvements of known authentication schemes, some residual problems remain. For instance, most authentication schemes are unnecessarily rigid, which means that the same level of security is required regardless of the value of a transaction or the user's prior history or other related factors. Another problem is that the combination of username, password and mobile identity can all be stolen from a legitimate user.
Accordingly, there is still need for improvements to authentication techniques, with respect to flexibility, security or both.


The present invention provides a nano-scaled graphene platelet-based composite material composition for use as an electrode, particularly as an anode of a lithium ion battery. The composition comprises: (a) micron- or nanometer-scaled particles or coating which are capable of absorbing and desorbing lithium ions; and (b) a plurality of nano-scaled graphene platelets (NGPs), wherein a platelet comprises a graphene sheet or a stack of graphene sheets having a platelet thickness less than 100 nm; wherein at least one of the particles or coating is physically attached or chemically bonded to at least one of the graphene platelets and the amount of platelets is in the range of 2% to 90% by weight and the amount of particles or coating in the range of 98% to 10% by weight. Also provided is a lithium secondary battery comprising such a negative electrode (anode). The battery exhibits an exceptional specific capacity, an excellent reversible capacity, and a long cycle life.

The description of prior art will be primarily based on the list of references presented at the end of this section.
Concerns over the safety of earlier lithium secondary batteries led to the development of lithium ion secondary batteries, in which pure lithium metal sheet or film was replaced by carbonaceous materials as the anode. The carbonaceous material may comprise primarily graphite that can be intercalated with lithium and the resulting graphite intercalation compound may be expressed as LixC6, where x is typically less than 1. In order to minimize the loss in energy density due to this replacement, x in LixC6 must be maximized and the irreversible capacity loss Qir in the first charge of the battery must be minimized. Carbon anodes can have a long cycle life due to the presence of a protective surface-electrolyte interface layer (SEI), which results from the reaction between lithium and the electrolyte during the first several cycles of charge-discharge. The lithium in this reaction comes from some of the lithium ions originally intended for the charge transfer purpose. As the SEI is formed, the lithium ions become part of the inert SEI layer and become irreversible, i.e, they can no longer be the active element for charge transfer. Therefore, it is desirable to use a minimum amount of lithium for the formation of an effective SEI layer. In addition to SEI formation, Qir has been attributed to graphite exfoliation caused by electrolyte solvent co-intercalation and other side reactions [Refs. 1-4].
The maximum amount of lithium that can be reversibly intercalated into the interstices between graphene planes of a perfect graphite crystal is generally believed to occur in a graphite intercalation compound represented by LixC6 (x=1), corresponding to a theoretical specific capacity of 372 mAh/g. In other graphitized carbon materials than pure graphite crystals, there exists a certain amount of graphite crystallites dispersed in or bonded by an amorphous or disordered carbon matrix phase. The amorphous phase typically can store lithium to a specific capacity level higher than 372 mAh/g, up to 700 mAh/g in some cases, although a specific capacity higher than 1,000 mAh/g has been sporadically reported. Hence, the magnitude of x in a carbonaceous material LixC6 varies with the proportion of graphite crystallites and can be manipulated by using different processing conditions, as exemplified in [Refs. 1-4]. An amorphous carbon phase alone tends to exhibit a low electrical conductivity (high charge transfer resistance) and, hence, a high polarization or internal power loss. Conventional amorphous carbon-based anode materials also tend to give rise to a high irreversible capacity.
The so-called "amorphous carbons" commonly used as anode active materials are typically not purely amorphous, but contain some micro- or nano-crystallites with each crystallite being composed of a small number of graphene sheets (basal planes) that are stacked and bonded together by weak van der Waals forces. The number of graphene sheets varies between one and several hundreds, giving rise to a c-directional dimension (thickness Lc) of typically 0.34 nm to 100 nm. The length or width (La) of these crystallites is typically between tens of nanometers to microns. Among this class of carbon materials, soft and hard carbons made by low-temperature pyrolysis (550-1,000° C.) exhibit a reversible capacity of 400-800 mAh/g in the 0-2.5 V range [Refs. 1-3]. Dahn et al. have made the so-called house-of-cards carbonaceous material with enhanced capacities approaching 700 mAh/g [Refs. 1,2]. Tarascon's research group obtained enhanced capacities of up to 700 mAh/g by milling graphite, coke, or carbon fibers [Ref. 3]. Dahn et al. explained the origin of the extra capacity with the assumption that in disordered carbon containing some dispersed graphene sheets (referred to as house-of-cards materials), lithium ions are adsorbed on two sides of a single graphene sheet [Refs. 1,2]. It was also proposed that Li readily bonded to a proton-passivated carbon, resulting in a series of edge-oriented Li—C—H bonds. This provides an additional source of Li+ in some disordered carbons [Ref. 5]. Other researchers suggested the formation of Li metal mono-layers on the outer graphene sheets [Ref. 6] of graphite nano-crystallites. The amorphous carbons of Dahn et al. were prepared by pyrolyzing epoxy resins and may be more correctly referred to as polymeric carbons. Polymeric carbon-based anode materials were also studied by Zhang, et al. [Ref. 8] and Liu, et al. [Ref. 9].
Peled and co-workers improved the reversible capacity of a graphite electrode to ˜400 mAh/g by mild air oxidation [Ref. 4]. They showed that mild oxidation (burning) of graphite produces well-defined voids or nano-channels, having an opening of a few nanometers and up to tens of nanometers, on the surface of the graphite. They believed that these nano-channels were small enough to prevent co-intercalation of the solvent molecule but large enough to allow Li-ion penetration [Ref. 4]. These nano-channels were formed at the La-Lc interface, called "zigzag and armchair faces" between two adjacent crystallites, and in the vicinity of defects and impurities. Both natural and synthetic graphite materials typically have a wide variety of functional groups (e.g., carbonate, hydrogen, carboxyl, lactone, phenol, carbonyl, ether, pyrone, and chromene) at the edges of crystallites defined by La and Lc [Ref. 7]. These groups can react with lithium and/or electrolyte species to form a so-called in situ CB-SEI (chemically bonded solid electrolyte interface) [Ref. 4] on which, for example, carboxylic acid surface films are converted into Li-carboxylic salts.
In summary, in addition to the above-cited three mechanisms, the following mechanisms for the extra capacity over the theoretical value of 372 mAh/g have been proposed [Ref. 4]: (i) lithium can occupy nearest neighbor sites; (ii) insertion of lithium species into nano-scaled cavities; (iii) in very disordered carbons containing large fractions of single graphene sheets (like the structure of a house of cards) lithium may be adsorbed on both sides of single layer sheets [Refs. 1,2]; (iv) correlation of H/C ratio with excess capacity led to a proposal that lithium may be bound somehow in the vicinity of the hydrogen atoms (possible formation of multi-layers of lithium on the external graphene planes of each crystallite in disordered carbons) [Ref. 6]; and (vi) accommodation of lithium in the zigzag and armchair sites [Ref. 4].
In addition to carbon- or graphite-based anode materials, other inorganic materials that have been evaluated for potential anode applications include metal oxides, metal nitrides, metal sulfides, and the like, and a range of metals, metal alloys, and intermetallic compounds that can accommodate lithium atoms/ions. In particular, lithium alloys having a composition formula of LiaA (A is a metal such as Al, and "a" satisfies 0<a≦5) has been investigated as potential anode materials. This class of anode material has a higher theoretical capacity, e.g., Li4Si (3,829 mAh/g), Li4.4Si (4,200 mAh/g), Li4.4Ge (1,623 mAh/g), Li4.4Sn (993 mAh/g), Li3Cd (715 mAh/g), Li3Sb (660 mAh/g), Li4.4Pb (569 mAh/g), LiZn (410 mAh/g), and Li3Bi (385 mAh/g). However, for the anodes composed of these materials, pulverization (fragmentation of the alloy particles) proceeds with the progress of the charging and discharging cycles due to expansion and contraction of the anode during the absorption and desorption of the lithium ions. The expansion and contraction also tend to result in reduction in or loss of particle-to-particle contacts or contacts between the anode and its current collector. These adverse effects result in a significantly shortened charge-discharge cycle life.
To overcome the problems associated with such mechanical degradation, composites composed of small electrochemically active particles supported with less active or non-active matrices have been proposed for use as an anode material. Examples of these active particles are Si, Sn, and SnO2. However, most of prior art composite electrodes have deficiencies in some ways, e.g., in most cases, less than satisfactory reversible capacity, poor cycling stability, high irreversible capacity, ineffectiveness in reducing the internal stress or strain during the lithium ion insertion and extraction steps, and/or undesirable side effects.
For instance, as disclosed in U.S. Pat. No. 6,007,945 (Dec. 28, 1999) by Jacobs, et al., a solid solution of titanium dioxide and tin dioxide was utilized as the anode active substance in the negative electrode of a rechargeable lithium battery. The density of the negative electrode made as described above was 3.65 g/cm3, and the reversible capacity of the negative electrode containing TiO2—SnO2 in a ratio of 39:61 by weight, was found to be 1130 mAh/cm3. This was equivalent to 309.6 mAh/g, although the obtained rechargeable lithium battery was calculated to have energy density of 207 watt.hour per liter. Furthermore, the nanoparticles of the anode material react with the electrolyte during the charge-discharge cycles, resulting in reduced long-term utility.
As described in U.S. Pat. No. 6,143,448 (Nov. 7, 2000), by Fauteux et al., a composite was formed by mixing carbon with a metal salt in water, followed by evaporation, heating and further treatment. The process produces a composite with many pores, which are not always preferred. The best achievable capacity was reported to be in the range of 750-2,000 mAh/cm3. With a density of 4 g/cm3, this implies a maximum capacity of 500 mAh/g
In U.S. Pat. No. 6,103,393 (Aug. 15, 2000), Kodas et al. provided carbon-metal particles by mixing the reactant, making the mixture into an aerosol, and then heating. Every particle contains a carbon phase and a metal phase. This study was primarily on carbon-supported platinum, silver, palladium, ruthenium, osmium and alloys thereof, which are for electro-catalysis purpose (e.g., for fuel cell applications).
In U.S. Pat. No. 7,094,499 (Aug. 22, 2006), Hung disclosed a method of forming a composite anode material. The steps include selecting a carbon material as a constituent part of the composite, chemically treating the selected carbon material to receive nanoparticles, incorporating nanoparticles into the chemically treated carbon material, and removing surface nanoparticles from an outside surface of the carbon material with incorporated nanoparticles. A material making up the nanoparticles alloys with lithium. The resulting carbon/nanoparticle composite anodes did not exhibit any significant increase in capacity, mostly lower than 400 mAh/g.
In summary, the prior art has not demonstrated a composite material that has all or most of the properties desired for use in an anode for the lithium-ion battery. Thus, there is a need for a new anode for lithium-ion batteries that has a high cycle life, high reversible capacity, and low irreversible capacity. There is also a need for a method of readily or easily producing such a material.

Nano graphene platelet-base composite anode compositions for lithium ion batteries