This invention aims to provide a protecting method for a semiconductor wafer which can prevent breakage of a semiconductor wafer even when a semiconductor wafer is thinned to a thickness of 200 xcexcm or less, and a surface protecting adhesive film for a semiconductor wafer used in the protecting method. According to this invention, there is provided a protecting method for a semiconductor wafer comprising a first step of adhering a surface protecting adhesive film for a semiconductor wafer to a circuit-formed surface of the semiconductor wafer, a second step of processing a non-circuit-formed surface of the semiconductor wafer and a third step of adhering a bonding film for die bonding to the non-circuit-formed surface of the semiconductor wafer, characterized in that the third step is performed without peeling the surface protecting adhesive film for the semiconductor wafer, and an adhesive film in which an adhesive layer is formed on one surface of a substrate film at least one layer of which is made of a resin having a melting point of 200xc2x0 C. or more is used, and a surface protecting adhesive film for a semiconductor wafer used in the protecting method.

This invention relates to a protecting method for a semiconductor wafer and a surface protecting adhesive film for a semiconductor waver used in said method. More specifically, it relates to a protecting method for a semiconductor wafer which is useful to prevent breakage of a semiconductor wafer in a step of thinning a semiconductor wafer and which can improve productivity, and a surface protecting adhesive film for a semiconductor wafer used in said method.
A step of processing a semiconductor wafer comprises a step of adhering a surface protecting adhesive film for a semiconductor wafer to a circuit-formed surface of the semiconductor wafer, a step of processing a non-circuit-formed surface of the semiconductor wafer, a step of peeling the surface protecting adhesive film for the semiconductor wafer, a dicing step of dividing and cutting the semiconductor wafer, a die bonding step of bonding the divided semiconductor chip to a lead frame, then a molding step of sealing the semiconductor chip with a resin for protecting the outer portion, and the like.
In the die bonding step, a method in which a resin paste as a die bonding material is supplied to a lead frame and a semiconductor chip is put thereon for bonding has been so far mostly used. However, when the resin paste is used, it is hard to uniformly coat the same on the lead frame. Accordingly, there are problems that voids are generated in curing the bonding layer, chip crack is generated, and so forth.
For improving a non-uniform coating property which is a defect of the resin paste as the die bonding material and rationalizing the overall step, Japanese Patent Laid-Open No. 302,629/1994 discloses a method in which a bonding film for die bonding is used in a die bonding step. This method is a method in which after a step of adhering a bonding film for die bonding to a non-circuit-formed surface of a semiconductor wafer, a die bonding step of adhering the semiconductor wafer to which the bonding film for die bonding is fixed on a dicing tape and dividing and cutting the same and a step of peeling the dicing tape, a step of die-bonding the semiconductor chip to a lead frame is performed.
This method is a method in which prior to conducing the dicing step, the bonding film for die bonding is heat-adhered to the non-circuit-formed surface of the semiconductor wafer having a thickness of approximately 300 xcexcm at 150 to 180xc2x0 C. using a roll, the semiconductor wafer with the bonding agent adhered is stuck to a dicing tape and divided and cut into the semiconductor chip with the bonding agent, and the semiconductor chip with the bonding agent adhered is then peeled from the dicing tape and hot-pressed on the lead frame. This method, however, involves serious problems that when the non-circuit-formed surface of the semiconductor wafer is processed to further thin the semiconductor wafer, especially to less than 200 xcexcm, the semiconductor wafer is broken with a pressure of a roll in adhering the bonding film for die bonding unless a surface protecting adhesive film for a semiconductor wafer is adhered, and so forth.
In recent years, thinning of a semiconductor chip has been in high demand, and a chip having a thickness of 30 to 100 xcexcm has been required. Consequently, a protecting method for a semiconductor wafer by which a bonding film for die bonding can be adhered without breaking even the thus-thinned semiconductor wafer has been in demand.
This invention aims to provide, in view of the foregoing problems, a protecting method for a semiconductor wafer which can prevent breakage of a semiconductor wafer even when a semiconductor wafer is thinned to a thickness of 200 xcexcm or less, and a surface protecting adhesive film for a semiconductor wafer used in the protecting method.
The present inventors have assiduously conducted investigations, and have consequently found that the foregoing problems can be solved such that in performing a series of steps of adhering a surface protecting adhesive film for a semiconductor wafer to a circuit-formed surface of the semiconductor wafer, processing a non-circuit-formed surface of the semiconductor wafer and then adhering a bonding film for die bonding to the non-circuit-formed surface of the semiconductor wafer, the bonding film for die bonding is adhered to the non-circuit-formed surface of the semiconductor wafer in a state where the surface protecting adhesive film for the semiconductor wafer is adhered to the circuit-formed surface of the semiconductor wafer and a surface protecting adhesive film for a semiconductor wafer in which an adhesive layer is formed on one surface of a substrate film at least one layer of which is made of a resin having a melting point of 200xc2x0 C. or more is used. This finding has led to the completion of the invention.
That is, the first aspect of this invention is a protecting method for a semiconductor wafer comprising a first step of adhering a surface protecting adhesive film for a semiconductor wafer to a circuit-formed surface of the semiconductor wafer, a second step of processing a non-circuit-formed surface of the semiconductor wafer and a third step of adhering a bonding film for die bonding to the non-circuit-formed surface of the semiconductor wafer, characterized in that the third step is performed without peeling the surface protecting adhesive film for the semiconductor wafer and a surface protecting adhesive film for a semiconductor wafer in which an adhesive layer having a storage elastic modulus at 150xc2x0 C. of at least 1xc3x97105 Pa and a thickness of 3 to 100 xcexcm is formed on one surface of a substrate film at least one layer of which is made of a resin having a melting point of 200xc2x0 C. or more is used.
The characteristic features of the first aspect of this invention are that in a series of the steps from the adhesion of the surface protecting adhesive film for the semiconductor wafer to the circuit-formed surface of the semiconductor wafer to the peeling thereof, the step of adhering the bonding film for die bonding to the non-circuit-formed surface of the semiconductor wafer is performed subsequently to the step of processing the non-circuit-formed surface of the semiconductor wafer in a state where the surface protecting adhesive film for the semiconductor wafer is adhered to the circuit-formed surface of the semiconductor wafer, and that the adhesive film in which the adhesive layer is formed on one surface of the substrate film at least one layer of which is made of the resin having the melting point of 200xc2x0 C. or more is used as the surface protecting adhesive film for the semiconductor wafer used in these steps.
Further, the second aspect of this invention is a surface protecting adhesive film for a semiconductor wafer used in the protecting method for the semiconductor wafer according to the first aspect, and it is a surface protecting adhesive film for a semiconductor wafer suitably used to produce a thin semiconductor wafer, in which an adhesive layer having a storage elastic modulus at 150xc2x0 C. of at least 1xc3x97105 Pa and a thickness of 3 to 100 xcexcm is formed on one surface of a substrate film at least one layer of which is made of a resin having a melting point of 200xc2x0 C. or more and which has a thickness of 50 to 350 xcexcm.
According to this invention, breakage, contamination and the like of the semiconductor wafer in the foregoing series of the steps can be prevented even in a thin semiconductor wafer having a thickness of 200 xcexcm or less.
This invention is described in detail below. In a method of producing a semiconductor wafer to which the protecting method for the semiconductor wafer according to this invention is applied, as described above, the first step of adhering the surface protecting adhesive film for the semiconductor wafer to the circuit-formed surface (hereinafter referred to as a surface) of the semiconductor wafer and the second step of processing the non-circuit-formed surface (hereinafter referred to as a back surface) of the semiconductor wafer are first performed in sequence, and the third step of adhering the bonding film for die bonding to the back surface of the semiconductor wafer without peeling the surface protecting adhesive film is then performed. The subsequent steps are not particularly limited. For example, a method of producing a semiconductor wafer is mentioned in which a step of peeling a surface protecting adhesive film for a semiconductor wafer, a dicing step of dividing and cutting the semiconductor wafer, a molding step of sealing the semiconductor chip with a resin for protecting the outer portion, and the like are performed in sequence.
To begin with, the protecting method for the semiconductor wafer in this invention is described in detail below. In the protecting method for the semiconductor wafer in this invention, the step of adhering the surface protecting adhesive film for the semiconductor wafer to the surface of the semiconductor wafer and the second step of processing the back surface of the semiconductor wafer are performed in sequence, and the third step of adhering the bonding film for die bonding to the back surface of the semiconductor wafer without peeling the surface protecting adhesive film for the semiconductor wafer is then performed. At this time, an adhesive layer having a storage elastic modulus at 150xc2x0 C. of at least 1xc3x97105 Pa and a thickness of 3 to 100 xcexcm is formed on one surface of a substrate film at least one layer of which is made of a resin having a melting point of 200xc2x0 C. or more.
With respect to the details of the protecting method for the semiconductor wafer according to this invention, first, the peeling film is peeled from the side of the adhesive layer of the surface protecting adhesive film for the semiconductor wafer (hereinafter abbreviated as a surface protecting adhesive film) to expose the surface of the adhesive layer, and the surface protecting adhesive film is adhered to the surface of the semiconductor wafer through the adhesive layer (first step). Then, the semiconductor wafer is fixed on a chuck table of a back surface processing machine or the like through the substrate film layer of the surface protecting adhesive film to process the back surface of the semiconductor wafer (second step). In the second step, all of a step of grinding the back surface of the semiconductor wafer, a wet etching step and a polishing step may be performed or any one of these steps may be performed. Subsequently, the semiconductor wafer is transported to the step of adhering the bonding film for die bonding without peeling the surface protecting adhesive film to adhere the bonding film for die bonding (third step). Thereafter, the surface protecting adhesive film is peeled. Further, after peeling the surface protecting adhesive film, treatment such as water washing, plasma washing or the like is applied to the surface of the semiconductor wafer as required.
In general method, in the back surface processing step, a semiconductor wafer having a thickness of 500 to 1,000 xcexcm before grinding back surface has been thinned to 200 to 600 xcexcm depending on a type of a semiconductor chip or the like. On the other hand, by applying the protecting method of this invention, it can be thinned to a thickness of 200 xcexcm or less. In this case, the minimum thickness of the semiconductor wafer is approximately 20 xcexcm. When the semiconductor wafer is thinned to 200 xcexcm or less, it is preferable that a wet etching step or a polishing step is performed subsequently to the back grinding. The thickness of the semiconductor wafer before grinding the back surface is properly determined depending on the diameter, the type or the like of the semiconductor wafer, and the thickness of the semiconductor wafer after grinding the back surface is properly determined depending on the size of the resulting chip, the type of the circuit or the like.
The procedure of adhering the surface protecting adhesive film to the surface of the semiconductor wafer is sometimes manually conducted. However, it is generally conducted with a device, called an automatic laminator, fitted with a rolled surface protecting adhesive film. Examples of such a laminator include models: ATM-1000B, ATM-1100 and TEAM-100 manufactured by Takatori Corporation and model: STL Series manufactured by Teikoku Seiki K. K.
As a back surface grinding method, known grinding methods such as a through-feed method, an in-feed method and the like are employed. In any of these methods, the back surface grinding is usually conducted while cooling a semiconductor wafer and a grindstone by feeding water thereto. After the completion of the back surface grinding, the wet etching and the polishing are conducted as required. The wet etching step and the polishing step are conducted for removing warpage generated on the back surface of the semiconductor wafer, further thinning the semiconductor wafer, removing an oxide layer or the like, conducting pretreatment in forming an electrode on the back, and the like. The etching solution is properly selected according to the foregoing purposes.
As a device used in the step of adhering the bonding film for die bonding, for example, model: ATM-8200, DM-800 manufactured by Takatori Corporation are illustrated. As the bonding film for die bonding, a bonding film obtained by coating a varnish made of a mixture of a polyimide resin and a thermosetting resin on a surface of a polyester or polypropylene film to form a bonding layer is mentioned. At this time, the mixture of the polyimide resin and the thermosetting resin may sometimes contain additives as required. The bonding film for die bonding is heat-adhered to the back surface of the semiconductor wafer with a roll to form the semiconductor film with the bonding agent adhered.
After the back surface grinding step, the etching step and the step of adhering the bonding film for die bonding are completed respectively, the surface protecting adhesive film is peeled from the surface of the semiconductor wafer. The series of these steps are sometimes conducted manually, but generally with a device called an automatic peeler. As this automatic peeler, models: ATRM-2000B and ATRM-2100 manufactured by Takatori Corporation, and model: STP series manufactured by Teikoku Seiki K. K. are illustrated. Further, for improving a peeling property, it is preferable to conduct heat-peeling as required.
The surface of the semiconductor wafer after peeling the surface protecting adhesive film is washed as required. Examples of the washing method include wet washing such as water washing, solvent washing or the like, dry washing such as plasma washing or the like, and so forth. In the wet washing, ultrasonic washing may be used in combination. These washing methods are properly selected depending on the contamination condition on the surface of the semiconductor wafer.
Next, the surface protecting adhesive film used in this invention is described below. The surface protecting adhesive film according to this invention is produced by forming an adhesive layer on one surface of the substrate film. For protecting the adhesive layer, a peeling film is usually adhered to the surface of the adhesive layer. In consideration of the adhesion to the surface of the semiconductor wafer through the surface of the adhesive layer exposed when peeling the peeling film, a method in which the adhesive agent coating solution is coated on one surface of the peeling film and dried to form the adhesive layer and the resulting adhesive layer is transferred on one surface of the substrate film is preferable for preventing contamination on the surface of the semiconductor wafer by the adhesive layer.
At least one layer of the substrate film is preferably a heat-resistant film which is made of a resin having a melting point of 200xc2x0 C. or more. It is more preferably a film made of a resin having a melting point of 250xc2x0 C. or more. The resin film includes those made of polyesters such as polyethylene terephthalate, polyethylene naphthalate and the like, polyimides, polyether ether ketones, polyether sulfones and mixed resins thereof. Typical commercial products thereof include trade name: Teonex manufactured by Teijin Ltd., trade name: Torlon 4203L manufactured by Mitsubishi Chemical Corporation, and trade names: 45G and 200P manufactured by ICI, and so forth.
When the substrate film of the surface protecting adhesive film has at least one layer of a heat resistant layer which is made of a resin having a melting point of 200xc2x0 C. or more, it may be laminated with an other film. When the melting point of all layers is less than 200xc2x0 C., deformation with heat is generated on the surface protecting adhesive film in the step of adhering the bonding film for die bonding, which might break the thinned semiconductor wafer.
For increasing the protecting property in grinding the back surface of the semiconductor wafer, a film made of a resin having a low elastic modulus may be laminated in addition to the heat-resistant film. Examples of the film having the low elastic modulus include resin films made of an ethylene-vinyl acetate copolymer, an ethylene-alkyl acrylate copolymer (alkyl group having 1 to 4 carbon atoms), a low-density polyethylene, an ethylene-xcex1-olefin copolymer (xcex1-olefin having 3 to 8 carbon atoms) and the like. Of these, an ethylene-vinyl acetate copolymer film having the content of the vinyl acetate unit of 5 to 50% by weight is preferable.
A typical method of producing the substrate film is a method in which while extrusion-molding a film having a low elastic modulus with an extruder, it is laminated with a heat-resistant film prepared in advance. For enhancing an adhesion between the film having the low elastic modulus and the heat-resistant film, a bonding layer may newly be formed therebetween. For enhancing the adhesion between the substrate film and the adhesive layer, it is preferable to apply corona discharge treatment, chemical treatment or the like to the surface of the substrate film on which the adhesive layer is formed. The thickness of the overall substrate film is preferably 50 to 350 xcexcm. When the heat-resistant film and the film having the low elastic modulus are laminated, it is preferable that the thickness of the former layer is 10 to 300 xcexcm and the thickness of the latter layer is 20 to 300 xcexcm. More preferably, the thickness of the former layer is 15 to 200 xcexcm. The film layer having the low elastic modulus is effective for absorbing raised and depressed portions formed by the circuit on the surface of the semiconductor wafer and preventing breakage generated in the step of grinding the back surface of the semiconductor wafer. The substrate film layer on which to form the adhesive agent layer is either on the side of the heat-resistant film or on the side of the film having the low elastic modulus. However, in consideration of the heat-adhering step in the die bonding step or the like, the side of the film having the low elastic modulus is preferable.
In consideration of preventing warpage of the semiconductor wafer thinned to 200 xcexcm or less, the storage elastic modulus of the substrate film layer made of the resin having the melting point of 200xc2x0 C. or more is 103 to 105 MPa, preferably 103 to 104 MPa at 0 to 100xc2x0 C., and 10 to 104MPa, preferably 102 to 103 MPa at 100 to 300xc2x0 C.
It is preferable that the adhesive agent forming the adhesive layer of the surface protecting adhesive film according to this invention fully functions as an adhesive agent even under temperature conditions in adhering the bonding film for die bonding. Specific examples thereof include an acrylic adhesive agent, a silicon adhesive agent and the like. The thickness of the adhesive layer is preferably 3 to 100 xcexcm. In the adhesive agent layer, it is preferable that after peeling the surface protecting adhesive film, contamination due to adhesive transfer or the like does not occur on the circuit-formed surface of the semiconductor wafer.
It is preferable that the adhesive layer is crosslinked with a crosslinking agent having a reactive functional group, a peroxide, radioactive rays or the like at a high density lest the adhesion is increased too much in exposing to high temperatures in the die bonding step of heat adhering the bonding film for die bonding and the contamination on the surface of the semiconductor wafer is increased. Further, in adhering the bonding film for die bonding, it is preferable that even when the heat treatment is conducted under a condition of a temperature of 150xc2x0 C. or more, insufficient peeling due to the increase in adhesion does not occur and that adhesive transfer does not occur. Accordingly, it is preferable that the adhesive layer has storage elastic modulus at 150xc2x0 C. of at least 1xc3x97105 Pa. It is more preferable that the adhesive layer has storage elastic modulus at 200xc2x0 C. of at least 1xc3x97105 Pa. The higher the storage elastic modulus, the better. However, the upper limit is usually 1xc3x97108 Pa.
Moreover, in consideration of preventing warpage of the semiconductor wafer thinned to 200 xcexcm or less, it is advisable that the ratio of the storage elastic modulus [(G) MPa] and the thickness [(D) xcexcm] of the substrate film layer made of the resin having the melting point of 200xc2x0 C. or more meets the relations represented by the following equation (1) at 0 to 100xc2x0 C. and the following equation (2) at 100 to 300xc2x0 C.
3xe2x89xa6G/Dxe2x89xa610,000xe2x80x83xe2x80x83(1)
0.03xe2x89xa6G/Dxe2x89xa61,000xe2x80x83xe2x80x83(2)
More preferably, aforementioned ratio meets the relations represented by the following equation (3) at 0 to 100xc2x0 C. and the following equation (4) at 100 to 300xc2x0 C.
5xe2x89xa6G/Dxe2x89xa6700xe2x80x83xe2x80x83(3)
0.5xe2x89xa6G/Dxe2x89xa670xe2x80x83xe2x80x83(4)
As a method of forming the adhesive layer having the foregoing characteristics, a method using an acrylic adhesive agent is mentioned. The adhesive layer is formed by using an acrylic adhesive agent which is an emulsion polymerization copolymer containing a (meth)acrylic acid alkyl ester monomer unit (A), a monomer unit (B) having a functional group capable of reacting with a crosslinking agent and a difunctional monomer unit (C) in specific amounts respectively, and a solution or an emulsion containing a crosslinking agent having two or more functional groups in a molecule for increasing a cohesive force or adjusting an adhesion. In case of using the acrylic adhesive agent in the form of a solution, the acrylic adhesive agent is separated from an emulsion obtained by emulsion polymerization through desalting or the like, re-dissolved in a solvent or the like, and used. The acrylic adhesive agent has quite a high molecular weight, and is, in many cases, less dissolved or not dissolved in a solvent. Therefore, in view of the cost as well, it is preferable to use the acrylic adhesive agent in the form of an emulsion as such.
As the acrylic adhesive agent used in this invention, an acrylic adhesive agent obtained by using an acrylic acid alkyl ester, a methacrylic acid alkyl ester or a mixture thereof as a main monomer [hereinafter referred to as a monomer (A)] and copolymerizing the same with a monomer mixture containing a comonomer having a functional group capable of reacting with a crosslinking agent is mentioned.
Examples of the monomer (A) include an acrylic acid alkyl ester or a methacrylic acid alkyl ester containing an alkyl group having 1 to 12 carbon atoms [these are generally referred to as a (meth)acrylic acid alkyl ester]. Preferable is a (meth)acrylic acid alkyl ester containing an alkyl group having 1 to 8 carbon atoms. Specific examples thereof include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate and the like. These may be used either singly or in admixture of two or more. Usually, the amount used of the monomer (A) is preferably in the range of 10 to 98.9% by weight based on the total amount of all the monomers as starting materials of the adhesive agent. More preferably, it is 85 to 95% by weight. By specifying the amount used of the monomer (A) in such a range, a polymer containing 10 to 98.9% by weight, preferably 85 to 95% by weight of the (meth)acrylic acid alkyl ester monomer unit (A) is obtained.
Examples of the monomer (B) forming the monomer unit (B) having the functional group capable of reacting with the crosslinking agent include acrylic acid, methacrylic acid, itaconic acid, mesaconic acid, citraconic acid, fumaric acid, maleic acid, itaconic acid monoalkyl ester, mesaconic acid monoalkyl ester, citraconic acid monoalkyl ester, fumaric acid monoalkyl ester, maleic acidmonoalkyl ester, glycidyl acrylate, glycidyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, acrylamide, methacrylamide, tertiary-butylaminoethyl acrylate, tertiary-butylaminoethyl acrylate and the like. Preferable are acrylic acid, methacrylic acid, 2-hydroxylethyl acrylate, 2-hydroxylethyl methacrylate, acrylamide, methacrylamide and the like. One of these may be copolymerized with the main monomer, or two or more thereof may be copolymerized therewith. Generally, it is preferable that the amount used of the monomer (B) having the functional group capable of reacting with the crosslinking agent is in the range of 1 to 40% by weight based on the total amount of all the monomers as starting materials of the adhesive agent. More preferable amount is 1 to 10% by weight. Thus, the polymer having the structural unit (B) with approximately the same composition as the monomer composition is obtained.
Moreover, in order that the adhesive layer fully functions as an adhesive agent even under temperature conditions in processing the back surface of the semiconductor wafer, adhering the bonding film for die bonding and the like, it is advisable to adjust the adhesion or the peeling property. As its approach, it is advisable to consider a crosslinking method of a particulate bulk for maintaining a cohesive force of emulsion particles.
Since the emulsion particles have 1xc3x97105 Pa or more even under temperature conditions of 150 to 200xc2x0 C., it is advisable to improve a crosslinking method to maintain a cohesive force by copolymerizing the difunctional monomer (C). Examples of the monomer to be copolymerized well include allyl methacrylate, allyl acrylate, divinylbenzene, vinyl methacrylate, vinyl acrylate, a material in which, for example, both ends are a diacrylate or a dimethacrylate and a structure of a main chain is propylene glycol [trade names: PDP-200, PDP-400, ADP-200 and ADP-400, manufactured by Nippon Oils and Fats Co., Ltd.], tetramethylene glycol [trade names: ADT-250 and ADT-850, manufactured by Nippon Oils and Fats Co., Ltd.] or a mixture thereof [trade names: ADET-1800 and ADPT-4000, manufactured by Nippon Oils and fats Co., Ltd.], and the like.
When the difunctional monomer (C) is emulsion-copolymerized, the amount used thereof is preferably 0.1 to 30% by weight, more preferably 0.1 to 5% by weight based on all the monomers. Thus, a polymer having the structural unit (C) with the composition which is approximately equal to the monomer composition is obtained.
In addition to the main monomer constituting the adhesive agent and the comonomer having the functional group capable of reacting with the crosslinking agent, a specific comonomer having a property as a surfactant (hereinafter referred to as a polymerizable surfactant) may be copolymerized. The polymerizable surfactant has a property of being copolymerized with a main monomer and a comonomer and also serves as an emulsifying agent in emulsion polymerization. In case of using an acrylic adhesive agent obtained by emulsion polymerization using a polymerizable surfactant, contamination on a surface of a semiconductor wafer due to a surfactant does not usually occur. Further, even when slight contamination occurs due to an adhesive agent layer, it can easily be eliminated by washing the surface of the semiconductor wafer with water.
Examples of such a polymerizable surfactant include polyoxyethylene nonylphenyl ether with a polymerizable 1-propenyl group introduced in a benzene ring [trade names: Aquaron RN-10, Aquaron RN-20, Aquaron RN-30, Aquaron RN-50 and the like, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.], ammonium salt of sulfuric acid ester of polyoxyethylene nonylphenyl ether with a polymerizable 1-propenyl group introduced inabenzene ring [trade names: Aquaron HS-10, Aquaron HS-20 and the like, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.], and sulfosuccinic acid diester series having a polymerizable double bond in a molecule [trade names: Latemul S-120A, Latemul S-180A and the like, manufactured by Kao Corporation]. Further, a monomer having a polymerizable double bond, such as vinyl acetate, acrylonitrile, styrene or the like may be copolymerized as required.
Examples of the polymerization reaction mechanism of the acrylic adhesive agent include radical polymerization, anionic polymerization, cationic polymerization and the like. Considering the production cost of the adhesive agent, the influence of the functional groups of the monomers, the influence of ions on the surface of the semiconductor wafer and the like, the polymerization by radical polymerization is preferable. Examples of the radical polymerization initiator in the polymerization by the radical polymerization reaction include organic peroxides such as benzoyl peroxide, acetyl peroxide, isobutyl peroxide, octanoyl peroxide, di-tert-butyl peroxide, di-tert-amyl peroxide and the like, inorganic peroxides such as ammonium persulfate, potassium persulfate, sodium persulfate and the like, and azo compounds such as
2,2xe2x80x2-azobisisobutyronitrile,
2,2xe2x80x2-azobis-2-methylbutyronitrile,
4,4xe2x80x2-azobis-4-cyanovaleric acid and the like.
In the polymerization by the emulsion polymerization method, among these radical polymerization initiators, water-soluble inorganic peroxides such as ammonium persulfate, potassium persulfate, sodium persulfate and the like, and also water soluble azo compounds having a carboxyl group in a molecule, such as 4,4xe2x80x2-azobis-4-cyanovaleric acid and the like are preferable. In consideration of the influence of ions on the surface of the semiconductor wafer, ammonium persulfate and azo compounds having a carboxyl group in a molecule, such as 4,4xe2x80x2-azobis-4-cyanovaleric acid and the like are more preferable. Azo compounds having acarboxyl group inamolecule, such as 4,4xe2x80x2-azobis-4-cyanovaleric acid and the like are most preferable.
The crosslinking agent having two or more crosslinkable functional groups in a molecule, which is used in this invention, is used to be reacted with the functional group of the acrylic adhesive agent for adjusting an adhesion and a cohesive force. Examples of the crosslinking agent include epoxy compounds such as sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, neopentylglycol diglycidyl ether, resorcin diglycidyl ether and the like, isocyanate compounds such as tetramethylene diisocyanate, hexamethylene diisocyanate, trimethyloipropane toluene diisocyanate 3-addition product, polyisocyanate and the like, aziridine compounds such as trimethylolpropane-tri-xcex2-aziridinyl propionate, tetramethylolmethane-tri-xcex2-aziridinyl propionate, N,Nxe2x80x2-diphenylmethane-4,4xe2x80x2-bis(1-aziridinecarboxyamide), N,Nxe2x80x2-hexamethylene-1,6-bis(1-aziridinecarboxyamide), N,Nxe2x80x2-toluene-2,4-bis( 1-aziridinecarboxyamide), trimethylolpropane-tri-xcex2-(2-methylaziridine) propionate and the like, tetrafunctional epoxy compounds such as N,N,Nxe2x80x2,Nxe2x80x2-tetraglycidyl-m-xylenediamine, 1,3-bis(N,Nxe2x80x2-diglycidylaminomethyl)cyclohexane, and melamine compounds such as hexamethoxymethylolmelamine and the like. These may be used either singly or in admixture of two or more.
Usually, the content of the crosslinking agent is preferably in such a range that the number of functional groups in the crosslinking agent is not larger than the number of functional groups in the acrylic adhesive agent. However, when a functional group is newly generated in the crosslinking reaction or when the crosslinking reaction proceeds slowly, the crosslinking agent may be contained in a larger amount as required. The preferable content of the crosslinking agent is 0.1 to 15 parts by weight per 100 parts by weight of the acrylic adhesive agent. When the content is too low, sometimes, the cohesive force of the adhesive agent layer is insufficient, and the elastic modulus is less than 1xc3x97105 Pa at 150 to 200xc2x0 C., reducing a heat resistance. Accordingly, sometimes, adhesive transfer due to the adhesive agent layer tends to occur, the adhesion is increased, the peeling trouble happens in an automatic peeler when peeling the surface protecting adhesive film from the surface of the semiconductor wafer, and the semiconductor wafer is completely broken. When the content is too much, sometimes, the adhesion between the adhesive layer and the surface of the semiconductor wafer is decreased, with the result that water or dust is entered between the surface of the semiconductor wafer and the adhesive layer in the step of grinding the back surface of the semiconductor wafer, and breakage of the semiconductor wafer or contamination of the surface of the semiconductor wafer occurs.
The adhesive agent coating solution used in this invention may properly contain, in addition to the acrylic adhesive agent and the crosslinking agent obtained by copolymerizing the specific difunctional monomer, tackifiers for adjusting a tackiness, such as rosin resins, terpene resins and the like, various surfactants and the like to such an extent that the aim of this invention is not influenced. Moreover, when the coating solution is an emulsion, film-forming agents such as ethylene glycol monoalkyl ethers and the like may properly be added to such an extent that the aim of this invention is not influenced. Diethylene glycol monoalkyl ethers and their derivatives used as film-forming agents, when present in large amounts in the adhesive layer, might contaminate the surface of the semiconductor wafer to such an extent that washing is impossible. For this reason, it is advisable that materials which are volatilized at a drying temperature of the adhesive agent coating solution are used to minimize the residual amounts of these in the adhesive agent layer.
The adhesion of the surface protecting adhesive film in this invention can properly be adjusted in consideration of the processing conditions of the semiconductor wafer, the diameter of the semiconductor wafer, the thickness of the semiconductor wafer after grinding the back surface, the adhesion temperature of the bonding film for die bonding and the like. When the adhesion is too low, it is, sometimes, difficult to adhere the surface protecting adhesive film to the surface of the semiconductor wafer, and a protecting property of the surface protecting adhesive film becomes insufficient, whereby the semiconductor wafer is broken or the surface of the semiconductor wafer is contaminated with grinding dusts or the like. Further, when the adhesion is too high, a peeling workability might be decreased such that a peeling trouble occurs in an automatic peeler in peeling the surface protecting adhesive film from the surface of the semiconductor wafer after performing the back processing of the semiconductor wafer, or the semiconductor wafer might be broken. Usually, the adhesion is 5 to 500 g/25 mm, preferably 10 to 300 g/25 mm in terms of an adhesion to an SUS304-BA plate.
As a method of coating the adhesive agent coating solution on one surface of the substrate film or the peeling film, known coating methods such as a roll coater method, a reverse roll coater method, a gravure roll method, a bar coating method, a comma coater method, a die coater method or the like can be applied. The conditions for drying the coated adhesive agent are not particularly limited. Generally, it is preferable to dry the same in a temperature range of 80 to 200xc2x0 C. for 10 seconds to 10 minutes. It is more preferable to dry the same at 80 to 170xc2x0 C. for 15 seconds to 5 minutes. For satisfactorily expediting the crosslinking reaction of the crosslinking agent and the adhesive agent, the surface protecting adhesive film may be heated at 40 to 80xc2x0 C. for 5 to 300 hours after the drying of the adhesive agent coating solution is completed.
The method of producing the surface protecting adhesive film for the semiconductor wafer in this invention is as described above. In view of preventing the contamination on the surface of the semiconductor wafer, it is preferable that the atmosphere of producing all the starting materials such as the substrate film, the peeling film, the adhesive agent and the like and the atmosphere of preparing, storing, coating and drying the adhesive agent coating solution are maintained at a cleanliness of class 1,000 or less regulated in U.S. Federal Standard 209b.
The semiconductor wafer to which the protecting method for the semiconductor wafer in this invention can be applied includes a silicon wafer as well as wafers of germanium, gallium-arsenic, gallium-phosphorus, gallium-arsenic-aluminum and the like.

Protecting method for semiconductor wafer and surface protecting adhesive film for semiconductor wafer used in said method


Safety apparatus is disclosed for providing ballistic train interruption in a perforating system. The safety apparatus comprises a generally tubular shaped housing having first and second ends which are fabricated to permit the housing to be positioned at any location in the perforating system. The apparatus comprises first and second ballistic sections in the housing and a third ballistic section which is rotatably mounted in the housing to move between a disarmed position and an armed position based on downhole pressure. Upon retrieval of the perforating system from the wellbore, the safety apparatus functions to return a third ballistic section to its disarmed position. Additionally, apparatus is provided to permanently disable the third ballistic section to insure that no inadvertent detonation of the guns occurs when retrieving the system from a wellbore.

1. Field of the Invention
The present invention relates to a safety apparatus for a perforating system.
2. Description of the Prior Art
Safety is a substantial issue in connection with the providing of perforating services and procedures and is of the utmost concern on a tubing conveyed perforating ("TCP") job when the firing head is first attached to the gun string or when a firing head is removed from a non-detonated gun string which has been retrieved from its downhole position. The attachment or removal of the firing head has typically been done on the rig floor when personnel are near the equipment, and if detonation occurs at this time, severe property damage and bodily harm, including death, may result.
One safety technique which has been employed is to install a predetermined length of pipe with no shape charges, e.g., 10 feet, on top of a gun string prior to installing the firing head. By following this procedure, the gun string is below the rig floor when the firing head is being installed. If the guns were to detonate when the firing head is installed, the harm to human life would be somewhat protected inasmuch as personnel are not directly in the line of fire of the guns. Another safety technique has been to require that two parameters, e.g., mechanical action and pressure, be satisfied in order to detonate the firing head. At the surface where the firing head is installed, there is typically insufficient pressure to satisfy the pressure requirements, and the firing heads can be considered safe while at the surface.
Other safety systems employ techniques where the firing head is mechanically blocked until the system is downhole near the zone to be perforated. These systems are known as "downhole arming" systems and can include eutectic material which is solid at low temperatures and melts at slightly higher temperatures. These eutectic materials function to block a firing pin from impacting a detonator at the surface. When the system is run downhole, however, the eutectic material melts and the firing pin has a clear path to strike the detonator. A drawback to this type of system is that, once the eutectic material melts, it flows away from its original blocking cavity. Thus, when a non-detonated gun string is retrieved from the well, the path of the firing pin to the detonator would no longer be blocked.
Other safety methods may include a utilization of techniques to interrupt the ballistic train from the firing head to the gun string. One such device called a "hammer stop" also utilizes eutectic material as described above. The eutectic material is physically positioned to block the path of the firing pin from impacting a percussion detonator. As the system is run into the well, the downhole temperature increases and the eutectic material melts. The physical barrier between the firing pin and the detonator is thus removed.
Another ballistic interruption-type safety method involves the use of a radial blocking pin. The pin is positioned between a firing pin and a percussion detonator, and the pin is held in the blocked position by a spring. The pin has O-ring seals and seals against an atmospheric chamber. As the system is run into the hole, well pressure causes the pin to move against the atmospheric chamber. When the pin is moved to its final position, a hole in the pin allows the firing pin to have a clear path to the detonator.


This application relates to an abstract description generating method, an abstract description generation model training method, a computer device, and a storage medium. The abstract description generating method includes: inputting a labeled training sample into an abstract description generation model; performing first-phase training on an encoding network and a decoding network of the abstract description generation model based on supervision of a first loss function; obtaining a backward-derived hidden state of a previous moment through backward derivation according to a hidden state of each moment outputted by the decoding network; obtaining a value of a second loss function according to the backward-derived hidden state of the previous moment and an actual hidden state of the previous moment outputted by the decoding network; and obtaining final model parameters of the abstract description generation model determined based on supervision of the second loss function to reach a preset threshold value.

Abstract description means describing information with a statement representing an abstract (alternatively referred as "summary" in this disclosure) of the information. The information may be an image, a video, or a text. An abstract description model may include a neural network model configured to obtain an abstract of information according to the inputted information.
Generally, the abstract description model includes an encoding network and a decoding network. The encoding network is configured to extract features from inputted data (an image or a text) to obtain an eigenvector of the inputted data. The eigenvector is inputted to a decoding network to obtain a hidden state at each time moment, and words of a current time moment are predicted according to the hidden state, thus outputting a descriptive statement.
In a conventional abstract description model training process, the decoding network independently predicts the words of the current time moment according to the hidden state of the current time moment. However, context of a descriptive statement is generally correlated, and the correlation between two neighboring hidden states is not considered in a conventional abstract decoding network, resulting in low prediction accuracy of the abstract description model.

Summary generation method, summary generation model training method, and computer device

Tencent Technology (Shenzhen) Company Limited


The habitat or castle for maintaining a minicrab within an underwater environment, such as within an aquarium, comprises a top shell which can encase an air bubble therein, and a platform which engages within the top shell to provide a perch for the minicrab within the air bubble. A base is provided which rests within, for example, gravel in the bottom of the aquarium, and a plurality of positionable legs are provided to elevate the habitat above the base plate at one of a plurality of preselected positions available.

1. Field of the Invention
The present invention relates to a crab castle for housing a so-called mini or Fiddler crab in an air filled environment within an aquarium. More specifically, the castle is designed to trap a bubble of air therein, the castle having a platform or perch therein upon which the crab can rest, while in the oxygen rich air bubble.
2. Description of the Prior Art
Heretofore various crab ensnaring structures, commonly referred to as crab pots, have been proposed for use in the crabbing industry,
However, it has recently become fashionable to incorporate small crabs, such as the species commonly referred to as the Fiddler crab, within a fresh water aquarium environment.
Such crabs, and most particularly the species Uca Minax, are well adapted to such an environment. They are useful within this environment as well, scavenging off the gravel bed of the aquarium, thereby breaking down particulate matter and increasing efficiency of the filtration system.
Such crabs, however, prefer and inherently do better in, an amphibious environment. If given the opportunity, they will spend the majority of time above the surface of the water.
Also, during periods of growth, the crabs shed their exoskeleton, making them vulnerable to cannibalistic activity, especially when housed in large numbers.
Thus, in order to provide an optimization of healthful conditions for Fiddler crab species to be maintained in an aquarium, the crab castle or habitat of the present invention is proposed.

Crab castle for an aquarium and combination therewith


An electrical receptacle has multiple thermal sensors, each of which can trigger automatic shut off when the temperature rises above a predetermined threshold. After automatically turning off, the receptacle remains permanently non-conducting.

The present invention relates to an electrical plug receptacle having multiple sensors for sensing the temperature at multiple points within an enclosure of the receptacle, and that automatically shuts off when any of these temperatures reach a pre-determined temperature.
Many fires are believed to be caused by overloaded electrical outlets, that is, outlets operated with more power transfer than the outlet was designed for. Fires are sometimes caused by a loose connection, a glowing connection and/or a high resistance path. A glowing connection occurs when copper oxide is formed between a copper wire and a screw in a small air gap creating carbon which glows.
The condition of too much power usage is always accompanied by increased temperature in at least one of the ambient temperature, the receptacle temperature and the temperature of a prong of an electrical plug inserted into the receptacle, collectively referred to herein as "operating temperature". To avoid fires, it is desirable for the outlet to sense when the operating temperature is too hot, and to cease operation.
Bimetallic switches are electromechanical thermal sensors. The bimetallic or bi-metal portion consists of two different metals bonded together such as brass and Invar. Some bimetallic portions consist of three layers sandwiched together. The metals expand at different rates as they warm, causing the element to twist or curve. The changing geometry is used to make or break an electrical contact. Once temperature has returned to normal levels, they revert back to their original geometry.
For a bimetal comprising brass and invar, the bending occurs at a metal temperature of about 200° F.; the actual temperature threshold is determined by the design of the bimetal and its materials. The metal can be heated by a loose connection or by ambient air temperature. Typical plastic household wiring insulation and outlet housing melts at a temperature of about 300° F. but operation above 200° F. is not recommended due to its high probability of material distortion.
It has been proposed to use a bimetal to sense the temperature of an electrical receptacle, and to interrupt operation of the receptacle when the temperature increases beyond a threshold. In practice, proposed designs do not trigger properly because of the time it takes for heat to propagate from the fault area to the bimetal.
Accordingly, there is a need for an electrical receptacle with improved thermal sensitivity.

Electrical receptacle with multiple heat sensors


Methods and structures for improving alignment contrast for patterning a metal layer generally includes depositing a metal layer having a plurality of grains, wherein grain boundaries between the grains forms grooves at a surface of the metal layer. The metal layer is subjected to surface treatment to form an oxide or a nitride layer and fill the surface grooves. The metal layer can be patterned using alignment marks in the metal layer and/or underlying layers. Filling the grooves with the oxide or nitride increases alignment contrast relative to patterning the metal layer without the surface treating.

The present invention generally relates to the manufacture of semiconductor integrated circuits, and more particularly, surface treatment of a metal layer including alignment marks to increase alignment contrast associated with the alignment marks.
Semiconductor integrated circuit (IC) fabrication involves forming multiple material layers with designed patterns on a semiconductor wafer. Each layer has to be aligned with previous layers such that the formed circuit can function properly. Various marks are used for this purpose. For example, alignment marks are used for alignment between a mask (a photo mask) and a semiconductor wafer. In another example, overlay marks are used to monitor overlay deviation between multiple layers on a wafer. In order to provide proper alignment of mask layers, photolithography tools are equipped to locate certain alignment marks on preceding layers, which can be optically detected by techniques well known in the art, such as bright field or dark field alignment. As semiconductor technology continues progressing to circuits having smaller feature sizes, alignment requirements become more stringent.

Metal surface preparation for increased alignment contrast

INTERNATIONAL BUSINESS MACHINES CORPORATION


Disclosed is a keyword extraction apparatus and method capable of overcoming a problem in the conventional automatic keyword extraction wherein character strings in a sentence to be processed are employed, as they are, to assign a document with an index in terms of keywords; hence words having the similar meaning but different expressions in written language cannot be retrieved. The keyword extraction apparatus comprises technical term storage means for storing technical terms with proper expressions and different expressions thereof, and basic word storage means for storing general basic words of high frequency. Technical-term segmentation point setting means cuts out a range of any of the technical terms stored in technical term storage means from an input sentence. When the cut-out technical term is written in a different expression, the different expression is replaced by a corresponding proper expression in proper expression replacing means. Character-type segmentation point setting means detects a difference in character type in the input sentence. Basic-word segmentation point setting means cuts out, from the input sentence, a range of any of the basic words stored in the basic word storage means. Partial character string cutting means cuts out, as keywords, all relevant partial character strings based on segmentation points set by the technical-term segmentation point setting means, the character-type segmentation point setting means and the basic-word segmentation point setting means.

1. Field of the Invention
The present invention relates to a keyword extraction apparatus, a keyword extraction method and a computer readable recording medium storing a keyword extraction program, which are used in a system for retrieving a document written in natural language to automatically extract keywords from the document beforehand for creating an index of the document in terms of keywords and, at the time of retrieval, to extract a keyword from an input sentence for retrieving the document through collation of the keyword.
2. Description of the Related Art
As a method of retrieving documents in electronic form, it has been hitherto known to previously assign keywords to a document in the form of an index and, at the time of retrieval, to search the document by collating a designated keyword with the keywords assigned to the document. This method has problems in that manually assigning keywords to a document requires a lot of time and labor, and the retrieval cannot work if the keywords assigned by a person who has engaged in creating the index differ from keywords designated by persons who are going to perform retrieval.
For lessening time and labor required to assign keywords, methods of automatically extracting keywords from documents in electronic form have been proposed.
FIG. 64 is a block diagram showing a conventional keyword extraction system disclosed in, for example, Japanese Unexamined Patent Publication No. 8-30627. In FIG. 64, denoted by 6401 is a character type discriminating portion for discriminating types of individual characters in an input text and then transferring the discriminated types to character type storage means 6402. The character type storage means 6402 stores the types and corresponding positions of the individual characters in the input text which have been discriminated by the character type discriminating portion 6401. Denoted by 6403 is an effective-character-type character string cutting portion for cutting out all effective-character-type character strings, each of which is as long as any of four effective character types, i.e., katakana (the square form of Japanese letters hiragana), kanji (Chinese characters), alphabets and numerals, continue, based on the information stored in the character type storage means 6402.
Denoted by 6406 is a character-type boundary discriminating portion for discriminating all boundary positions between different character types of all the effective-character-type character strings based on the information stored in the character type storage means 6402, and then transferring the discriminated positions to character-type segmentation point storage means 6407. The character-type segmentation point storage means 6407 stores every boundary position, at which the character type changes from one to another, discriminated by the character-type boundary discriminating portion 6406.
Denoted by 6409 is affix storage means for storing affixes of high frequency. 6410 is an affix discriminating portion for discriminating all affixes in a character string and then transferring the discriminated affixes to affix segmentation point storage means 6411. The affix segmentation point storage means 6411 stores, as affix segmentation points, positions before and behind all the affixes discriminated by the affix discriminating portion 6410.
Denoted by 6413 is basic word storage means for storing, as basic words, nouns of high frequency. 6414 is a basic-word discriminating portion for discriminating all basic words in a character string and then transferring the discriminated basic words to basic-word segmentation point storage means 6415. The basic-word segmentation point storage means 6415 stores, as basic-word segmentation points, positions before and behind all the basic words discriminated by the basic-word discriminating portion 6414.
Denoted by 6412 is a partial-character-string cutting portion for cutting out partial character strings based on the character-type segmentation points stored in the character-type segmentation point storage means 6407, the affix segmentation points stored in the affix segmentation point storage means 6411, or the basic-word segmentation points stored in the basic-word segmentation point storage means 6415.
Denoted by 6404 is a noun discriminating portion which, when a character succeeding each of the effective-character-type character string cut out by the effective-character-type character string cutting portion 6403 is hiragana, compares the hiragana with hiragana character strings stored in noun-succeeding-hiragana storage means 6405, and then deletes the effective-character-type character string when a head portion of the hiragana succeeding to that effective-character-type character string does not match with any of the hiragana character strings stored in the noun-succeeding-hiragana storage means 6405.
Denoted by 6416 is a basic-word deleting portion for deleting the partial character string which matches with any of the basic words stored in the basic word storage means 6413.
Denoted by 6417 is a necessary keyword storage means for storing keyword character strings designated beforehand. 6418 is a necessary keyword cutting portion which, when character strings matching with the character strings stored in the necessary keyword storage means 6417 appear in a text, cuts out all those character strings and adds them to keywords.
The operation of the conventional keyword extraction system will be described below. The description will be made on the case of entering a text "{character pullout} (oekaki mohdo=painting mode)", for example.
First, the character type discriminating portion 6401 discriminates types of individual characters in an input text, and the character type storage means 6402 stores the types and corresponding positions of the individual characters in such a way that the first character is hiragana, the second character is kanji, the third character is kanji, the fourth character is hiragana, and so on.
Next, the effective-character-type character string cutting portion 6403 cuts out "{character pullout}" and "{character pullout}". Since there are no differences in character type within the partial character strings of "{character pullout}" and "{character pullout}", character-type segmentation points are not stored in the character-type segmentation point storage means 6407. Also, since no affixes are included in the partial character strings of "{character pullout}" and "{character pullout}", affix segmentation points are not stored in the affix segmentation point storage means 6411. Further, since no basic words are included in the partial character strings of "{character pullout}" and "{character pullout}", basic-word segmentation points are not stored in the basic-word segmentation point storage means 6415.
Then, since "{character pullout}" and "{character pullout}" do not include any of the character-type segmentation point, the affix segmentation point and the basic-word segmentation point, the partial-character-string cutting portion 6412 eventually cut outs two partial character strings of "{character pullout}" and "{character pullout}".
Subsequently, since hiragana "{character pullout}" succeeding to "{character pullout}" is not registered in the noun-succeeding-hiragana storage means 6405, the noun discriminating portion 6404 deletes "{character pullout}". On the other hand, since there is no hiragana succeeding to "{character pullout}", "{character pullout}" is not deleted in the noun discriminating portion 6404. The basic-word deleting portion 6416 then deletes the basic word which matches with any of those stored in the basic word storage means 6413. If "{character pullout}" is assumed here not to be a basic word, "{character pullout}" would not be deleted.
Next, the necessary keyword cutting portion 618 cuts out "{character pullout}" from the text "{character pullout}" stored in the necessary keyword storage means 6417 and adds it to keywords. Finally, "{character pullout}" and "{character pullout}" are output.
When "{character pullout}" or "{character pullout}" is designated as a retrieval key at the time of retrieval, the document including the original text "{character pullout}" is retrieved.
In retrieval with the thus-constructed keyword extraction system disclosed in Japanese Unexamined Patent Publication No. 8-30627, the retrieval is hit only when the character string designated as a keyword completely matches with any of the keywords assigned to a document. In retrieval, however, words having the similar meaning and pronunciation but different expressions (in written language) must be often taken into account. For example, "{character pullout} (oekaki=painting)" may be entered as a retrieval key rather than "{character pullout}" at the time of retrieval. Thus the keyword extraction system disclosed in Japanese Unexamined Patent Publication No. 8-30627 has a problem that retrieval cannot be effected unless there is a complete match between character strings.
To cope with the problem caused by words having the similar meaning and pronunciation but different expressions, a document retrieval method and apparatus are proposed in Japanese Unexamined Patent Publication No. 8-137892. In the document retrieval method and apparatus proposed in Japanese Unexamined Patent Publication No. 8-137892, when a character string designated upon retrieval is a compound word, the compound word is divided into individual words composing it and synonym expressions for the compound word are created in combinations of synonyms for each of the divided words by using a synonym dictionary.
FIG. 65 is a block diagram of the conventional document retrieval method and apparatus disclosed in Japanese Unexamined Patent Publication No. 8-137892. In FIG. 65, denoted by 6501 is a control unit comprised of a CPU and memory, 6502 is an input unit such as a keyboard or mouse through which the user enters a retrieval keyword and performs retrieval operation, 6503 is a display unit for displaying the retrieval keyword entered through the input unit 6502, the retrieval operation instructed by the user, and retrieved results, 6504 is an external storage unit for storing data to be retrieved, 6505 is a synonym dictionary in which synonym information for retrieved keywords is stored, and 6506 is a segmentation dictionary in which the retrieved keywords are stored. A character string designated for retrieval is segmented based on words registered in the segmentation dictionary 6506.
The operation of the conventional document retrieval method will be described below. FIG. 66 is a flowchart illustrating a flow of processing disclosed in Japanese Unexamined Patent Publication No. 8-137892. The following description will be made on the case of designating, for example, "{character pullout} (bunsbo kensaku=document retrieval)*{character pullout} (wahku sutehshon=work station)" (where "*" indicates logical product) as a retrieval formula. It is assumed that "{character pullout}" and "{character pullout}" are registered in the segmentation dictionary. Also, the synonym dictionary is assumed to store such information that "{character pullout}" and "{character pullout} (tekisuto=text)" are synonyms, "{character pullout}" and "{character pullout} (sahchi=search)" are synonyms, and "{character pullout}" and "WS" are synonyms.
In step 6612, a value in a synonym-dictionary usage flag buffer to set whether to use the synonym dictionary or not is checked. Assuming here that the buffer value is set to "1" indicating the use of the synonym dictionary, the processing follows the path indicated by at Y.
Next, in step 6613, the retrieval formula is segmented into a character string to be retrieved and a logical formula. Then, in step 6614, the character string to be retrieved is compared with words in the segmentation dictionary for segmentation of a keyword. Subsequently, in step 6615, synonyms which correspond to each of the segmented keywords are extracted from the synonym dictionary.
It is determined in step 6616 whether or not the processing for all keywords has been completed, and the processing of steps 6614 and 6615 is repeated until all keywords are processed.
Next, in step 6617, the synonyms corresponding to the segmented keywords are combined with each other to create retrieval keywords.
Subsequently, in step 6618, the created retrieval keywords are joined by putting logical sum ("+") between adjacent two. As a result, for "{character pullout}", a retrieval formula "({character pullout}+{character pullout}+{character pullout}+{character pullout}") is created in step 6619.
It is then checked in step 6620 whether or not a logical formula storage buffer is empty. The processing now returns to step 6614 to repeat the similar processing as explained above for the next character string to be retrieved, i.e., "{character pullout}".
For "{character pullout}", a retrieval formula "({character pullout}+WS)" is created in step 6619.
Although it is checked in step 6620 whether or not the logical formula storage buffer is empty, the processing now follows the path indicated by Y because there is no more retrieved character string to be processed. As a result, for the designated retrieval formula "{character pullout}* {character pullout}", "{character pullout}+{character pullout} {character pullout}+{character pullout}+{character pullout}" * ({character pullout}+WS)" is created as a retrieval formula for use in actual retrieval.
However, the document retrieval method and apparatus disclosed in Japanese Unexamined Patent Publication No. 8-137892 are designed to perform retrieval for character strings created by all possible combinations of different expressions, and hence have a problem that a longer time is required for retrieval as the number of combinations increases.
As another related art for creation of different expressions, Japanese Unexamined Patent Publication No. 3-15980 discloses a different expression and synonym developing method.
FIG. 67 is a block diagram of the different expression and synonym developing method for retrieval of character strings which is disclosed in Japanese Unexamined Patent Publication No. 3-15980. In FIG. 67, denoted by 6711 and 6713 are conversion rule tables for storing conversion rules which instruct a relevant character string in an input character string to be replaced by another character string, and 6712 is a synonym dictionary in which words having the similar meaning but different expressions are collected. Denoted by 6700 is a keyboard, 6701 and 6703 are different expression developing processes for developing a character string into character strings having the similar pronunciation and meaning but different expressions, and 6702 is a synonym developing process for developing a character string into character strings having the similar meaning by using a synonym dictionary 6712.
FIG. 68 shows an outline of the different expression and synonym developing process. A character string 6801 designated by the user is once subjected to different expression development, and a synonym development is then performed on a group of developed character strings 6802 by using the synonym dictionary 6712. After that, another different expression development is performed on a group of character strings 6803 resulted from the synonym development, whereby a group of character strings 6804 is obtained as a final development result. An example of FIG. 68 represents the case where the user designates a character string "{character pullout} (takujougata intafohn=desktop interphone)" on condition that each of the conversion tables stores rules for converting "{character pullout}(foh)" into "{character pullout} (ho)" and "{character pullout} (gata)" into "{character pullout} (gata)", and the synonym dictionary stores information that "{character pullout}" and "{character pullout}" are synonyms.
Thus, the method disclosed in Japanese Unexamined Patent Publication No. 3-15980 is designed to avoid a retrieval omission by developing various representations of different expressions and synonyms. However, because the disclosed method creates all possible different expressions, it is required to collate an input character string with all the different expressions created by the above-mentioned processing in order to determine whether or not there occurs a match for each word.
The conventional keyword extraction methods for use in retrieval of documents have had problems below because of their constructions described above.
First, in such a conventional automatic keyword extraction process as disclosed in Japanese Unexamined Patent Publication No. 8-30627, character strings appearing in a sentence to be processed are cut out, as they are, to be used as keywords which are assigned in the form of an index to a document. The conventional automatic keyword extraction process cannot therefore perform retrieval for words having the similar meaning and pronunciation but different expressions.
Although techniques to permit retrieval for words having similar meaning and pronunciations but different expressions are disclosed in Japanese Unexamined Patent Publication No. 8-137892 and No. 3-15980, those techniques require a word designated for retrieval to be collated with all possible combinations of individual words composing the designated word which have the similar pronunciation and meaning but different expressions. Thus, there has been a problem that a long time is required for retrieval processing.
Assuming, for example, that words having the similar meaning and pronunciation but different expressions are "{character pullout} (sahbah=server)" for "{character pullout} (sahba=server)" and "{character pullout}", "{character pullout}", "{character pullout}" for "{character pullout}" (each kirikae=switching), a total of eight keywords, i.e., "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", and "{character pullout}" have been created and collated for a keyword "{character pullout}".
Secondly, where a keyword contains a word which succeeds to a prefix and has different expressions, it has been required to create all combinations of the presence/absence of the prefix and the different expressions of the word succeeding to the prefix, and then collate an input keyword with all those combinations.
Assuming, for example, that there are three words having the similar meaning and pronunciation but different expressions, i.e., "{character pullout}", "{character pullout}" and "{character pullout}", for "{character pullout}" (each kirikae=switching), a total of eight keywords, i.e., "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", and "{character pullout}" "{character pullout}" have been created and collated for a keyword "{character pullout} (zenkirikae=full switching". Thus, the necessity of collating an input keyword with all of the created keywords has raised a problem that a long time is required for retrieval processing.
Thirdly, where a keyword contains a word which precedes a suffix and has different expressions, it has been required to create all combinations of the presence/absence of the suffix and the different expressions of the word preceding the suffix, and then collate an input keyword with all those combinations.
Assuming, for example, that there are three words having the similar meaning and pronunciation but different expressions, i.e., "{character pullout}", "{character pullout}" and "{character pullout}", for "{character pullout}" (each kirikae=switching), a total of eight keywords, i.e., "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", "{character pullout}", and "{character pullout}" have been created and collated for a keyword "{character pullout} (kirikaego=after switching". Thus, the necessity of collating an input keyword with all of the created keywords has raised a problem that a long time is required for retrieval processing.
Fourthly, the conventional automatic keyword extraction process as disclosed in Japanese Unexamined Patent Publication No. 8-30627 is designed to set a limit in length of keywords and deleted the keywords which have a length beyond the limit. However, such a design employed in the process disclosed in Japanese Unexamined Patent Publication No. 8-30627 may cause a problem of uneven keyword extraction that, for keywords which have the similar meaning but different expressions and which are different in length, some keywords are extracted, but other keywords are deleted.
Assuming, for example, that "{character pullout} (konpyubta=computer)" and "{character pullout} (konpyuhtah=computer)" are registered as words having the similar meaning and pronunciation but different expressions, and a limit of the keyword length is set to be less than 15 characters, "{character pullout}{character pullout} (konpyubta ahkitekuchah=computer architecture)" is extracted, but "{character pullout}{character pullout} (konpyuhtah ahkitekuchah=computer architecture)" is deleted.
Stated otherwise, when combinations of a compound word are created in accordance with the method disclosed in Japanese Unexamined Patent Publication No. 8-137892 to cope with retrieval for words having the similar meaning and pronunciation but different expressions, there has been a problem of uneven keyword extraction that, even upon the same retrieval key being designated, documents containing "{character pullout}{character pullout}" are retrieved, but documents containing "{character pullout}" {character pullout} are not retrieved.
Fifthly, with the conventional keyword extraction process disclosed in Japanese Unexamined Patent Publication No. 8-30627, because character strings appearing in a sentence to be processed are cut out, as they are, to be used as keywords, words having the similar meaning and pronunciation but different expressions are extracted as separate words. Accordingly, there has been a problem that precise frequency totalization which is necessary for, e.g., a keyword weighting process, cannot be achieved for the words having the similar meaning and pronunciation but different expressions.
Sixthly, in compound words such as "{character pullout}. {character pullout} (yuza intafehsu=user interface), for example, symbolic characters such as ".cndot." and "/" may be put between individual words composing the compound word; e.g., "{character pullout}. {character pullout}" and "{character pullout}. {character pullout}", in addition to different expressions for each of the individual words composing the compound word; i.e., "{character pullout}" and "{character pullout}". It is therefore required to unify the expression format for compound words.
The conventional keyword extraction process disclosed in Japanese Unexamined Patent Publication No. 8-30627 includes a method of deleting ".cndot." and "/" to unify the expression format for compound words, but it cannot deal with different expressions for each word which have the similar meaning and pronunciation, as described above. Also, Japanese Unexamined Patent Publication No. 8-137892 and No. 3-15980 disclose methods of creating combinations of different expressions for each word which have the similar meaning and pronunciation, but cannot deal with a process needed to unify the expression format for compound words. Accordingly, even if the above conventional techniques are combined with each other, an input keyword must be collated with all possible combinations of different expressions of individual words composing a compound word; hence a problem of requiring a long time for retrieval processing still remains.
Assuming, for example, that "{character pullout} (yuhza=user)" has a different expression "{character pullout} (yuhzah=user)" which has the similar meaning and pronunciation, and "{character pullout} (intafehsu=interface)" has a different expression of "{character pullout} (intafeisu=interface)", four expressions "{character pullout}", "{character pullout}","{character pullout}{character pullout}", "{character pullout}{character pullout}", and "{character pullout}{character pullout}" would be produced for "{character pullout}. {character pullout}" even if the above conventional techniques are combined with each other. Accordingly, a problem of requiring collation with all those different expressions is encountered.
Seventhly, in the methods disclosed in Japanese Unexamined Patent Publication No. 3-15980 and No. 8-137892, different expressions of a retrieval key, which have the similar meaning and pronunciation, are created at the time of retrieval in combinations of different expressions for each word and character string. As a result, a large number of retrieval keys to be collated are produced and a retrieval speed is reduced.
Furthermore, the methods disclosed in Japanese Unexamined Patent Publication No. 3-15980 and No. 8-137892 have a risk that an improper retrieval key may be produced when replacing a short word, in particular. For example, because the method disclosed in Japanese Unexamined Patent Publication No. 3-15980 holds a rule that "{character pullout} (tah)" is a different expression of "{character pullout} (ta)", "{character pullout} (intahfohn=interphone)" is created as a different expression of "{character pullout} (intafohn=interphone)" in the step of creating a different expression of "{character pullout} (intafohn=interphone)". However, the rule that "{character pullout} (tah)" is a different expression of "{character pullout} (ta)" can be applied to "{character pullout}", but not to "{character pullout} (takushih=taxi)", for example. It is therefore demanded to avoid a short word and store a relatively long word, such as a compound word, as information in a different expression dictionary used for replacement of one to another of different expressions. Hitherto, there have been no techniques to assist construction of a different expression dictionary responding to such a demand. As a result, a number of retrieval keys are produced and a problem that a keyword extraction method for realizing a high-speed document retrieval cannot be achieved has been encountered.

Keyword extraction apparatus, keyword extraction method, and computer readable recording medium storing keyword extraction program


A deodorizing composition containing: (a) from about 10 to 30% by weight of a dialkyl carbonate corresponding to formula I:

In the field of personal care, deodorants are used to eliminate unpleasant body odors. Examples of such substances are aluminium compounds, such as aluminium sulfate or aluminium chlorhydrate, zinc salts and citric acid compounds. Since the problem of odor inhibition has by no means been completely solved, there is still a need for new preparations in which the deodorants can readily be emulsified and incorporated. This is intended to ensure more uniform distribution of the deodorants and, hence, an improvement in their effect, i.e. minimization of perspiration and a reduction in odor formation. In addition, the feeling of the skin after the application of deodorants should be improved and greater stability of the final formulations achieved in relation to the prior art.
Accordingly, the problem addressed by the invention was to provide such products.

Abstract: wherein R1 is a linear alkyl and/or alkenyl group containing from about 6 to 22 carbon atoms, a 2-ethylhexyl, an isotridecyl, an isostearyl group or a group derived from a polyol containing 2 to 15 carbon atoms and at least two hydroxyl groups; R2 has the same meaning as R1 or is an alkyl group containing from about 1 to 5 carbon atoms; and n and m, independently of one another, represent a number up to 100, and (b) an antiperspirant.


A programmable memory cell including a thick oxide spacer transistor, a programmable thin oxide anti-fuse disposed adjacent to the thick oxide spacer transistor, and first and second thick oxide access transistors. The thick oxide spacer transistor and first and second thick oxide access transistors can include an oxide layer that is thicker than an oxide layer of the programmable thin oxide anti-fuse. The programmable thin oxide anti-fuse and the thick oxide spacer transistor can be natively doped. The first and second thick oxide access transistors can be doped so as to have standard threshold voltage characteristics.

The field of data storage includes both volatile memory and non-volatile memory. Volatile memory loses stored information when power is removed from the volatile memory circuit. Non-volatile memory retains stored information even after power is removed. Some non-volatile memory designs permit reprogramming while other designs only permit one-time programming.
One time programmable (OTP) memory represents a type of non-volatile memory that may be programmed only once, typically, by opening a fuse to create a high impedance connection or by permanently closing an anti-fuse to create a low-impedance connection. An anti-fuse can be programmed by applying a high voltage to rupture the anti-fuse and create the low impedance connection.
OTP memory cells utilizing an anti-fuse may exhibit an unpredictable and wide range of IV (current-voltage) characteristics following programing because the anti-fuse rupture site location may vary from device to device. Consequently, there is a need for an OTP memory cell that exhibits improved predictability and improved IV characteristics.
The embodiments of the present disclosure will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.


A hand-held electronic device with a hidden keyboard, especially for small size electronic devices with a display screen (such as PDAs, mobile phones, etc), provides a keyboard coupling design to allow a retractable keyboard retreated and hidden inside a device body of the electronic device when not in use, and pulled out for data entry when in use.

The invention relates to a hand-held electronic device with a hidden keyboard and particularly a small information device (such as PDA, mobile phone) coupled with a keyboard for users to selectively enter data therewith.
Rapid innovations and developments in communication technology now enable people using hand-held personal computers, personal digital assistants (PDA), mobile phones or other devices to access and enjoy a wide variety of added value services and multimedia information and contents from the Internet anytime anywhere.
Although the related technologies are well developed at present, there are still bottlenecks to be overcome in terms of accessing networks in mobile fashion. For instance, difficulty of data entry on small size information products (such as PDAs, mobile phones, etc.) is one of the problems not yet fully resolved. In order to facilitate carrying and offer desired portability, the small information products often are being made about the size of a human palm. They usually have a display screen for displaying messages, especially the PDAs. For a general PDA, the display screen almost occupies the entire casing with only a small space left for a few function keys. Data entry usually is done manually through a T P (Touch Panel). Mobile phones generally do not have display screens as large as the PDAs, and have numeric keys and some function keys on the casings. Nevertheless, when there is a need to enter a large amount of data, T P or numeric key data entry simply is too slow and cumbersome to meet users"" requirements.
To address the inconvenience of data entry on small size information products, there are designs equipped with attached keyboards now available on the market. FIG. 1 shows one of the examples that has a keyboard and a display screen facing each other. The keyboard and display screen are respectively mounted to two independent bodies and are engaged together through a hinge. When in use, open the product from the middle to extend and lay the display screen and keyboard. Then the keyboard may be used for data entry. When not in use, the bodies may be folded and the display screen will be encased in the bodies and not visible. As the product should be opened when in use, it is not user-friendly. The keyboard also is exposed to exterior when not in use and occupies an extra space.
In view of aforesaid disadvantages, the primary object of the invention is to provide a handheld electronic device with a keyboard for data entry that has a novel keyboard structure to allow the display screen visible from outside all the times and conceal the keyboard when not in use to save space.
To achieve the foregoing objects, the electronic device according to the invention is coupled with a retractable keyboard which may be hidden inside the device body when not in use and may be pulled out when in use to allow users entering data.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

Hand-held electronic device with hidden keyboard


The flow of gas between two vessels, each of which undergoes cyclic changes in gas pressure, is controlled by two check valves installed in parallel between the vessels. The first check valve allows gas to flow from the first vessel to the second vessel when the differential pressure between the vessels exceeds a first value, and the second check valve allows gas to flow from the second vessel to the first vessel when the differential pressure between the vessels exceeds a second value. The gas flow control method is particularly useful in pressure swing adsorption processes.

Pressure swing adsorption is a well-known method for the separation of bulk gas mixtures and for the purification of gas streams containing low concentrations of undesirable components. The method has been developed and adapted for a wide range of operating conditions, product purity, and product recovery. Many pressure swing adsorption systems utilize two or more adsorber beds operated in a cyclic sequence in order to maintain a constant product flow rate while selected beds undergo various steps including adsorption, depressurization, desorption, purge, pressure equalization, repressurization, and other related steps. Multiple adsorber beds using numerous process steps are required to achieve high purity and/or recovery of valuable gaseous products such as hydrogen, carbon oxides, synthesis gas, light hydrocarbons, and the like. The high cost of generating the feed gas mixtures containing these valuable components and the high purity requirements for certain products usually justify the complexity and capital expense of multiple-bed pressure swing adsorption systems.
A number of single-bed pressure swing adsorption (PSA) processes have been developed and are known in the art. Many of these processes operate partially at pressures below atmospheric and are described as vacuum swing adsorption (VSA) or vacuum-pressure swing adsorption (VPSA) processes. In the present specification, pressure swing adsorption (PSA) is used as a generic term to describe all types of cyclic adsorption systems regardless of operating pressure levels.
Other gaseous products amenable to recovery by PSA do not require the high purity and/or recovery of the above-named products. In the recovery of oxygen and nitrogen from air by PSA, for example, a lower purity product containing 90 to 95 vol % oxygen is acceptable for many end uses, and simpler PSA systems can be used to provide such a product. These simpler PSA systems have significantly lower capital and operating costs than the multiple-bed systems earlier described. The simplest of these PSA systems for air separation utilize a single adsorber bed in conjunction with one or more gas storage vessels to allow constant product flow and provide gas for adsorber purge and pressurization during the regeneration portion of the PSA cycle.
U.S. Pat. No. 4,561,865 discloses a single-bed PSA system comprising an adsorber and a surge tank operated with a feed compressor in a three-step cycle. First, compressed feed air is introduced into the adsorber, which increases the pressure in the adsorber, and simultaneously adsorber effluent is withdrawn into the surge tank. A portion of the gas is withdrawn from the surge tank as an oxygen-enriched product. The adsorber feed is then discontinued and the adsorber is vented countercurrently (i.e. through the adsorber feed end) to the atmosphere. During this venting step, purge gas from the surge tank is introduced into the product end of the adsorber. Upon completion of the vent/purge step, the adsorber and the surge tank are pressure equalized through the adsorber product end (i.e. countercurrently). The steps are repeated in a cyclic manner. U.S. Pat. No. 4,511,377 describes a modular apparatus using this PSA process.
A single-bed PSA system is described in U.S. Pat. No. 4,892,566 which utilizes an adsorber in conjunction with a surge tank, feed compressor, and switch valves to carry out a series of steps. First, compressed feed air is introduced into the adsorber, which increases the pressure in the adsorber while at the same time adsorber effluent is withdrawn into the surge tank. A portion of the gas is withdrawn from the surge tank as an oxygen-enriched product. The adsorber feed is discontinued and the adsorber outlet closed, and the adsorber is vented countercurrently (i.e. through the adsorber feed end) to the atmosphere. Gas from the surge tank is introduced into the adsorber countercurrently (i.e. through the adsorber product end) and the pressures in the adsorber and surge tank are equalized. The adsorber is then pressurized with feed air through the feed end and pressure equalized with the surge tank. The adsorber is further pressurized to a pressure above that of the surge tank, and finally the adsorber and surge tank are pressure equalized. The steps are then repeated in cyclic fashion.
U.S. Pat. No. 5,032,150 discloses a single-bed PSA process which utilizes multiple gas storage tanks in a PSA cycle to separate air. Compressed air is fed from an air feed tank into an adsorber presaturated with oxygen-rich gas from a previous cycle and the adsorber effluent is directed into a product collector tank, from which a portion of the gas is withdrawn as an oxygen-rich product. The adsorber outlet is then closed and the adsorber is pressure equalized with the air feed tank. Next, the adsorber is rinsed with nitrogen-rich gas from a nitrogen product tank, and the displaced gas is stored in the air feed tank. The nitrogen-saturated adsorber then is depressurized countercurrently (i.e. through the adsorber feed end) into the nitrogen product tank. Nitrogen may be withdrawn as a product if required. Finally the adsorber is purged countercurrently with oxygen-rich gas from the product collector tank to displace the nitrogen therein and then is pressurized countercurrently with the oxygen-rich gas to the adsorption pressure. The steps are repeated in a cyclic manner.
A single-vessel rapid PSA system is described in U.S. Pat. No. 5,071,449 in which the vessel contains dual adsorption layers and operates in alternating fashion with a continuous feed gas and two continuous product streams. A product surge tank is not used. Another rapid PSA system utilizing a single adsorbent bed operating in a cycle of 30 seconds or less is described in U.S. Pat. No. 4,194,892. The adsorber effluent optionally flows through a product surge tank to dampen flow fluctuations during adsorber cycling.
A single-bed PSA system with a product surge tank and an equalization tank is disclosed in U.S. Pat. No. 5,370,728. In the operation of this system, compressed air feed is introduced into the adsorbent bed, pressurizing the bed from an intermediate pressure up to a maximum adsorption pressure, and the effluent product is withdrawn from the bed into the product surge tank. The adsorbent bed then is isolated and depressurized cocurrently (i.e. through the product end) into an equalization tank at the intermediate pressure. Next, the bed is further depressurized countercurrently (i.e. through the feed end) to a lower desorption pressure, and the bed is purged countercurrently with gas from the product surge tank. The bed is then pressurized countercurrently to the intermediate pressure with gas from the equalization tank. Finally the bed is pressurized with feed air and the steps are repeated in a cyclic manner.
Other single-bed PSA processes are described in U.S. Pat. Nos. 4,065,272; 4,477,264; 5,228,888; 5,415,683; 5,658,371; 5,679,134; and 5,772,737; and in Japan Patent Application Kokai Nos. H9-77502 and H10-1947080; and in European Patent Application EP 0 771 583 A1.
Several of the above-cited documents disclose multiple gas storage tanks to provide purge and repressurization gas. U.S. Pat. No. 5,370,728, U.S. Pat. No. 5,658,371, and European Patent Application EP 0 771 583 A1 describe the use of dual gas storage tanks in single-bed air separation systems for oxygen recovery. One tank stores void space gas or partial depressurization gas having lower oxygen purity and the other tank stores higher purity oxygen product gas. Stored gas having lower oxygen purity is used for partial repressurization of the adsorber while a portion of stored higher purity product gas is used for adsorber purging. U.S. Pat. No. 5,032,150 describes the recovery of nitrogen from air in a PSA system which use multiple gas storage tanks, wherein one tank stores oxygen-rich gas for purging the adsorber and another tank stores nitrogen-rich product for displacing oxygen from the adsorber after purging is completed.
The PSA processes and systems described above provide for the efficient production of an enriched gaseous product from a feed gas mixture. These processes require multiple valves and appropriate control systems to control gas flow rate and flow direction during the cyclic adsorption, depressurization, evacuation, and repressurization steps. Future improvements will encourage the wider use of these PSA processes and systems, and such improvements should include the simplification of equipment, particularly blowers, valves, and associated gas flow control systems, which are required in PSA processes. The invention described below and defined in the appended claims offers a simplified gas flow control method and system which is particularly useful in PSA processes.

Pressure swing adsorption gas flow control method and system