Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/01—Manufacture or treatment
  • H10N30/06—Forming electrodes or interconnections, e.g. leads or terminals
  • H10N30/063—Forming interconnections, e.g. connection electrodes of multilayered piezoelectric or electrostrictive parts
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
  • H10N30/87—Electrodes or interconnections, e.g. leads or terminals
  • H10N30/872—Interconnections, e.g. connection electrodes of multilayer piezoelectric or electrostrictive devices
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/42—Piezoelectric device making

Definitions

• a thin plate made of an electromechanical conversion material such as an electrostrictive material or a piezoelectric material used for an ultrasonic motor or the like is used for an industrial robot.
• the present invention relates to a method for manufacturing a multilayer displacement element (hereinafter, sometimes referred to as an electrostrictive effect element) in which the displacement amount is increased by laminating a plurality of layers via internal electrodes. It selectively and highly reliably insulates the internal electrodes exposed on the side surfaces.
• the laminated displacement element used for the displacement element used for the positioning mechanism of the XY stage, the braking brake, etc. is polarized by providing electrodes on a thin plate made of piezoelectric ceramic material processed into a predetermined shape. Later, a method of joining with an organic adhesive directly or via a thin metal is used.
• the adhesive layer absorbs the displacement caused by the braking of the piezoelectric element depending on the use conditions, or the adhesive may be used in a high-temperature environment or when used for a long period of time. There are disadvantages such as deterioration.
• a conventional laminated displacement element has, for example, a configuration shown in FIG.
• reference numeral 41 denotes a thin plate formed of a piezoelectric ceramic material, and positive and negative internal electrodes 42 a and 42 b are alternately sandwiched and laminated to form a laminated body 4.
• the inner electrodes 4 2a and 4 2b are formed such that one edge is exposed to the outside, and are connected to the outer electrodes 4 3a and 4 3b extending in the laminating direction, respectively. Connect lead wire 4 through 7.
• FIG. 19 is a so-called full-electrode type in which the piezoelectric displacement efficiency is improved (for example, Japanese Patent Application Laid-Open No. 58-58).
• Japanese Patent Application Publication No. 196068 Japanese Patent Application Publication No. 196068.
• FIG. 19 the same parts are indicated by the same reference numerals as in FIG. 18, but the internal electrodes 42a and 42b are formed so as to cover the entire surface of the thin plate 1 to reduce the required number of sheets. Lamination is performed in the same manner as described above.
• an insulating material is formed at every other edge of the internal electrodes 42 a and 42 b (for example, only for the internal electrode 42 b).
• a coating 44a is provided, and an external electrode 43a made of a conductive material is applied on the coating 44a.
• the coating 44b is provided on the edge of the internal electrode (eg, 42a) where the coating 44a is not provided, and the external electrode 4 3b is deposited.
• the operation of the above configuration is the same as that in FIG. 18 described above. In this case, since there is substantially no non-displacement portion, more uniform deformation can be obtained than in the configuration shown in FIG. 18, and stress concentration does not occur. Therefore, there is an advantage that a large amount of strain peculiar to the electromechanical conversion material can be obtained, and no destruction occurs upon deformation.
• a so-called full-surface electrode structure having internal electrodes with the same cross-sectional area as that of the electrostrictive effect element Is effective.
• special measures are required to electrically connect the internal electrodes of the same area as the element cross section every other layer in parallel.
• the distance between adjacent electrodes is several 10 ⁇ to several 100 ⁇ , and the thickness of the exposed electrode is very small. Since it is about several mm, it is extremely difficult to take out electrodes (lead wires) every other layer.
• Japanese Patent Application Laid-Open No. 60-196681 discloses a method in which the end faces of the internal electrodes exposed on the side faces of such an electrostrictive material laminate are provided one by one by a plating.
• An electrical connection method characterized by depositing a metal in a strip shape has been proposed.
• FIG. 20 is a longitudinal sectional view of the electrostrictive effect element connected by the method. First, a method of manufacturing the electrostrictive element shown in FIG. 20 will be described. No.
• a laminated body in which the electrostrictive materials 1 and 2 and the internal electrodes 3 and 4 are alternately laminated as shown in Fig. 1 is created by applying the multilayer ceramic capacitor manufacturing technology. Many internal electrodes 3 and 4 are exposed on the opposing side surfaces of the front and back surfaces, and two temporary external electrodes 1 3 formed on the other side surface (the other two opposing surfaces). , 14 alternately connected every other layer.
• this laminate and the metal plate for the counter electrode are placed in a plating bath, and a DC voltage is applied from the metal plate for the counter electrode to the temporary external electrodes 13 and 14, a positive charge in the plating bath is obtained.
• the metal ions thus deposited are deposited on the internal electrodes 3 and 4 to obtain deposited metals 5 and 6 as shown in FIG.
• FIG. 22 is a partial cross-sectional view showing a laminate in which an insulating film 7 is applied on a deposited metal 5.
• the insulators 7, 8 on the deposited metals 5, 6 are scraped off until the deposited metals 5, 6 are exposed.
• FIG. 23 when external electrodes 9 are formed on the surface on which the deposited metal 5 and the insulating film 7 are applied, a large number of internal electrodes inside the element are connected to each other.
• the portions excluding the small pieces with the temporary external electrodes at both ends become electrostrictive elements.
• the element can be driven by applying a DC voltage between these temporary external electrodes.
• a base metal is used as a plating material for connecting to an external electrode because the metal to be deposited must be ionized. Therefore, in the device having the above structure, when the device is exposed to a high temperature to form an insulating layer or an external electrode, the deposited metal is oxidized and cannot be electrically connected, or the wire is mechanically disconnected. In the worst case, there was a problem that cracks occurred in the insulating layer around the deposited metal due to volume expansion due to oxidation and the insulation resistance was reduced.
• the present inventors have performed an external electrode forming process in a reducing atmosphere, but the electrostrictive material is also reduced at the same time. A new problem has arisen.
• a method of depositing a noble metal that does not oxidize by plating can be considered.For example, silver has a problem of lowering the insulated resistance due to migration. A problem occurred.
• an organic resin-based insulating layer and external electrodes that can be formed at a relatively low temperature, but there are concerns about problems such as long-term use or deterioration due to moisture, and a drop in mechanical strength at high temperatures. Is difficult to apply.
• a sufficient insulating layer thickness cannot be obtained because the thickness of the insulating layer depends on the height of the metal projections due to the plating. That is, as shown in FIG. 24, assuming that the thickness of the insulating layer 7 is t and the distance between the internal electrode 3 having a polarity that is electrically different from that of the deposited metal 5 is W, the larger the distance W is, from the viewpoint of continuity. desirable. However, if the width of the deposited metal 5 is reduced for the purpose of increasing the distance W between the deposited metal 5 and the internal electrode 3, the height of the deposited metal 5 is also reduced, and a sufficient insulating layer thickness t cannot be obtained. On the other hand, as shown in FIG. 25, when the thickness of the deposited metal 5 is increased to increase the thickness t of the insulating layer 7, the width of the deposited metal 5 is increased, and the There is a problem that the distance W of 3 becomes small, and a sufficient absolute distance cannot be obtained.
• the present invention solves the above problems and proposes a method for selectively and highly reliably insulating internal electrodes.
• the electrostriction effect layer and the internal electrode are alternately laminated, and two surfaces where the ends of the internal electrode are exposed (normally, these two surfaces are opposed to each other). Then, a laminate having the other two surfaces where the internal electrodes are exposed is formed every other layer, and the laminate is formed every other layer of the laminate. Temporary external electrodes are formed on the two surfaces where the internal electrodes are exposed.
• metal is deposited every other layer on the exposed internal electrode on one surface of the laminate by plating, and then, similarly, using the other temporary external electrode as a cathode.
• the metal is further deposited on the internal electrode exposed portion on the internal electrode exposed surface different from the surface on which the metal is deposited by plating.
• an insulating film is formed on the surface subjected to the plating. Thereafter, part of the insulating film and part or all of the deposited metal are removed by appropriate means such as machining to expose the deposited metal or the end of the internal electrode. Finally, the external electrode is formed. Thereby, the internal electrodes are connected every other layer.
• well-known mechanical processing for example, processing using a dicer
• processing using a dicer can be applied as a means for removing the exposed portion of the inner electrode and the peripheral portion where no metal is deposited by plating. It has been found that more preferable shot blasting can be applied.
• the electrostrictive material on the surface on which the temporary external electrodes are not provided is removed.
• Means for projecting the internal electrode by partially removing it by etching can be employed. In this case Since the end of the internal electrode protrudes and the metal due to plating is deposited there, there is an advantage that the adhesion strength of the deposited metal is increased, and a more reliable element can be realized.
• a method of removing metal projections deposited by plating may be employed.
• an insulating film is formed.
• polishing or the like is performed.
• the metal protrusions are removed until the internal electrodes are eliminated, and the internal electrodes are exposed every other layer.
• the external electrodes are formed, whereby the internal electrodes can be connected every other layer.
• a part of the insulating film and a part of the deposited metal are removed by appropriate means such as machining to expose the deposited metal, and then the exposed deposited metal is removed.
• the internal electrodes can be exposed every other layer, and finally, by forming the external electrodes, the internal electrodes can be connected every other layer.
• the deposited metal that is a base metal is completely removed, an oxide film is not substantially formed even when the element is at a high temperature at the time of forming the external electrode, and the electrical contact failure due to the oxide and the mechanical Problems such as disconnection can be eliminated.
• the plating height can be increased by performing plating on the internal electrode protruded by etching, so that a sufficient insulating layer thickness can be obtained, and at the same time, the internal electrode and the deposited metal can be formed. Since the bonding area is large, the bonding strength of the deposited metal can be improved. Furthermore, by performing the process of removing the non-metal deposited portion, the interface distance between the electrostrictive effect layer and the insulating layer, which leads to the internal electrode having a different electrical polarity from the deposited metal, can be substantially lengthened. improves. [Brief description of drawings]
• FIG. 1 is a view showing an internal electrode pattern of an alternate electrode laminate block according to the present invention.
• FIG. 2 is a diagram in which the alternate electrode laminate block is plated every other layer.
• FIG. 3 is a schematic view showing a processing step in the present invention.
• FIG. 4 is a schematic view showing a processing step in the present invention.
• FIG. 5 is a schematic view showing a processing step in the present invention.
• FIG. 6 is a schematic view showing a processing step in the present invention.
• FIG. 7 is a sectional view of a laminate according to the present invention.
• FIG. 8 is a perspective view of the alternate electrode laminate block after the surface to be plated is etched.
• FIG. 9 is a diagram in which alternate layered laminates are plated every other layer.
• FIG. 10 is a schematic view showing a processing step in the present invention.
• FIG. 11 is a schematic view showing a processing step in the present invention.
• FIG. 12 is a schematic view showing a processing step in the present invention.
• FIG. 13 is a schematic view showing a processing step in the present invention.
• FIG. 14 is a sectional view of a laminate according to the present invention.
• FIG. 15 is a sectional view of a laminate according to the present invention.
• FIG. 16 is a perspective view and a schematic cross-sectional view showing the processing steps (a) to (i) of the first embodiment.
• FIG. 17 is an enlarged cross-sectional view showing the state near the external electrodes of the stacked displacement element formed according to the first embodiment.
• FIG. 18 and FIG. 19 are schematic views of different conventional laminated displacement elements.
• FIG. 20 is a sectional view of a laminate having a conventional structure.
• FIG. 21 is a perspective view showing an alternate electrode laminate block having temporary external electrodes.
• FIG. 22 is a schematic view showing a processing step of a laminate having a conventional structure.
• FIG. 23 is a schematic view showing a processing step of a laminated body having a conventional structure.
• FIG. 24 is a view for explaining a defect of the conventional structural element.
• FIG. 25 is a view for explaining a defect of the conventional structural element.
• FIG. 16 (a) to (i) are a perspective view and a schematic cross-sectional view, respectively, showing the processing steps in this embodiment.
• a sheet made of an electromechanical conversion material for example, having a thickness of 100 / xm is cut to form a thin plate 21 having a side of, for example, 47 mm square as shown in FIG. 16 (a).
• a platinum conductive paste or a silver-palladium paste on which the internal electrodes 22a (22b) are to be formed is printed, leaving 2 to 3 mm.
• 100 thin plates 21 are alternately stacked to form a laminate 25.
• it is sintered at a predetermined temperature to form a laminated body 25 having, for example, a side of 40 mm square as shown in FIG. 16 (c).
• the alternating electrode portions 25a and 25b of the laminate 25 are cut at intervals of, for example, 5 mm so that the force of the alternate electrode portions 25a and 25b remains, and a block-like laminate 51 shown in FIG. Formed.
• the edges of the internal electrodes 22a and 22b are exposed on the side surfaces other than the alternating electrode portions 25a and 25b of the block-shaped laminate 51.
• 26 is a protective film. It is made of, for example, glass or silica, and is formed at the edge of the internal electrode 22a and in the vicinity thereof. Note that on the other opposing side surface, a similar protective film is formed on the end of the internal electrode 22b and in the vicinity thereof.
• the protective film 26 can be formed by, for example, an electrophoresis method. That is, first, an adhesive tape or the like is attached to the side surface on the back side of the laminate 51 shown in FIG. 16 (e) to cover the exposed edges of the internal electrodes 22a and 22b. Next, a temporary external electrode (not shown) is provided on the alternating electrode portion 25a, and the laminate 51 is immersed in a suspension containing glass powder. A counter electrode plate (not shown) is placed in front of the side surface on the front side, and a DC voltage of, for example, 10 to 200 V is applied between the counter electrode plate and the temporary external electrode.
• an adhesive tape or the like is attached to the side surface on the back side of the laminate 51 shown in FIG. 16 (e) to cover the exposed edges of the internal electrodes 22a and 22b.
• a temporary external electrode (not shown) is provided on the alternating electrode portion 25a, and the laminate 51 is immersed in a suspension containing glass powder.
• a counter electrode plate (not shown) is placed in front of
• the positively charged glass powder receives a force due to the electric field generated from the counter electrode plate toward the edge of the internal electrode 22a, moves in the suspension, and moves along the edge of the internal electrode 22a. And adhere to its vicinity.
• the glass powder since no voltage is applied to the internal electrode 22 b, the glass powder does not adhere, and the protective film 26 can be formed only at the end of the internal electrode 22 a and in the vicinity thereof.
• the laminate 51 is pulled up from the suspension, and the protective film 26 is fixed.
• the fixing means of the protective film 26 may be fired after drying, but may be, for example, a temporary fixing method of glass using an instant adhesive or the like.
• a protective film is formed on the back side surface by the same means as described above. That is, in FIG. 16 (e), after covering the side surface on the front side with an adhesive tape or the like, and installing a temporary external electrode (not shown) on the alternate electrode portion 25b shown in FIG. 16 (d), The laminate 51 is immersed in the suspension, a counter electrode plate (not shown) is placed in front of the back side, and a DC voltage is applied between the counter electrode plate and the temporary external electrode. Then, a protective film similar to the above is formed on the edge of the internal electrode 22b and in the vicinity thereof.
• Protective film 26 is formed on the edges of internal electrodes 22a and 22b as above
• the laminated body 51 thus obtained is subjected to a shot blast process. That is, a plurality of volume bodies 51 and crow beads or abrasive grains such as A123, SiC, Si02 are used, and a groove or a concave portion is formed by the impact of the abrasive grains.
• the surface other than the protective film 26 is selectively polished by collision of abrasive grains and rubbing to form a curved concave portion 29.
• an insulating material such as glass is applied or printed in the concave portion 29 to form an insulating layer 30.
• FIG. 17 is an enlarged sectional view showing a state near the external electrode 23a of the stacked displacement element formed as described above.
• the distance 10 between the outer electrode 23 a and the edge of the inner electrode 22 b existing through the insulating layer 30 is equal to the curved surface of the concave portion 29.
• the lengths are along the length, and can be formed to be larger than the distance between the internal electrodes 22a and 22b, so that the insulation withstand voltage can be improved.
• the concave portion 29 is formed substantially uniformly along the edges of the internal electrodes 22a and 22b, the creepage distance 10 can be formed substantially constant, and the laminated type having excellent reliability is provided. It can be a displacement element.
• the material for forming the protective film covering the exposed portion of the internal electrode was glass or silica powder.
• the material may be formed of other materials. What is necessary is just to have a function that remains without being removed in the step of selectively polishing the side surfaces other than the protective film.
• the means for forming the concave portion for forming the insulating layer may be any means other than the shot blast processing, and may be any means capable of selectively polishing the side surface of the laminate other than the protective film.
• the insulating layer can be deposited and the external electrodes can be installed in the block-shaped laminate before being made into a single element, the handling is easy and the processing efficiency can be improved. . Further, since the creeping distance between the electrodes is along the curved surface, it can be formed larger than the conventional one, and the insulation withstand voltage can be improved.
• This slurry was formed into a sheet having a thickness of 100 ⁇ m on a Mylar film by a doctor blade method. This was peeled off from the film, and a platinum base was printed on one side in the pattern shown in FIG. 1 to obtain internal electrodes 3 and 4. Dozens of these are sequentially laminated and heated and pressed.
• binder removal is performed, and firing is performed at 110 to 1250 ° for 1 to 5 hours to form a laminate in which internal electrodes are exposed alternately on both left and right sides as shown in FIG.
• temporary external electrodes 13 and 14 were formed on both side surfaces.
• the opposing surface is plated.
• the composition of the plating solution is 300 g of nickel sulfate, 45 g of nickel chloride, and 45 g of boric acid per liter of pure water.
• the laminated body and the nickel counter electrode were immersed in this plating solution, the temporary external electrode was connected to the negative side, the counter electrode was connected to the positive side, and DC current was applied at a current density of 40 A / dm2 for 20 minutes.
• strips 5 of nickel plating having a height of 30 jum and a width of 40 ⁇ m are formed on the internal electrodes alternately.
• nickel plating is also formed on the masked rear side surface by the same means as described above.
• FIG. 2 is an external view of a laminate subjected to nickel plating. Number 5 in the figure indicates a nickel-like band-like precipitate.
• an insulating material was applied to the surface subjected to the shot blasting and baked to form an insulating layer 7.
• both sides are subjected to lapping to remove a part of the insulating layer 7 and the entire nickel plating 5. Due to this lapping, the terminals of the internal electrodes 3 and 4 are again exposed on the side surfaces of the laminated body every other layer.
• the laminated block obtained in this manner is cut along a dotted line parallel to the temporary external electrode as shown in FIG. 6, and as a single element, the external electrodes 9, 10 are formed as shown in FIG. If provided, they can be connected to the corresponding internal electrodes 3 and 4. According to the present embodiment, it is possible to remove all the metal projections deposited by plating, and it is possible to eliminate problems such as poor electrical connection and mechanical disconnection due to oxidation of the metal projections. In addition, since a sufficient insulating layer thickness can be obtained, the absolute reliability of the device is greatly improved.
• the upper and lower surfaces of the laminated body where the temporary external electrodes and the internal electrodes are not exposed are masked, and as shown in FIG. 8, the internal electrodes are protruded by etching the ceramics on the surface of the laminated body to be plated.
• the ceramics were etched 10 ⁇ m by immersion in a 10% hydrochloric acid solution at 50 ° C for 60 minutes.
• FIG. 9 is an external view of a laminate subjected to nickel plating
• FIG. 10 is a partial cross-sectional view. Number 5 in the figure indicates a nickel band-like precipitate.
• shot blasting was performed in the same manner as in Example 2 to form a concave removal portion 15 as shown in FIG. 11, and then, prior shot blasting was performed as shown in FIG. Apply insulating material 7 to the surface and bake. Further, as shown in FIG. 13, both sides are subjected to lapping to remove a part of the insulating layer 7 to expose the nickel plating 5.
• the laminate block thus obtained was cut in the same manner as in Example 2 to form a single element, and then external electrodes 9 and 10 were provided as shown in FIG. , 4 can be connected.
• the adhesion strength between the internal electrode and the deposited metal is large, and a sufficient insulating layer thickness can be obtained without growing the deposited metal at a high level, the absolute reliability of the element is greatly improved. I do.
• a laminate is formed in which the external electrodes are exposed every other layer, and the temporary external electrodes 13 and 14 are formed on both side surfaces, and then the upper and lower surfaces of the laminate where the temporary external electrodes and the internal electrodes are not exposed are masked. Then, the internal electrodes are made to protrude by etching the ceramics on the surface of the laminate to be plated. The etching was performed by immersing in a 10% hydrochloric acid solution at 50 ° C. for 60 minutes. As a result, the ceramic was etched by 10 ⁇ m.
• Example 2 Next, one of the etched side surfaces of the laminate was masked with a masking material, and the opposite surface was plated under the same conditions as in Example 2 to obtain a height of 50 wm and a width of 40 wm. Band deposits 5 of nickel plating of wm are formed every other layer on the internal electrode.
• the surface on which the insulating layers 7 and 8 are formed is subjected to lapping to remove a part of the insulating layer 7 and expose the nickel plating 5.
• the laminate was immersed in a 10% nickel chloride solution, the temporary external electrodes 13 and 14 were connected to the anode, the nickel counter electrode plate was connected to the cathode, and a current density of 30 AZ dm was used. A direct current voltage was applied for one minute, and the exposed deposited metals 5 and 6 of the laminate were removed by electrolytic etching.
• the laminate block thus obtained was cut in the same manner as in Example 2. Then, after forming a single element, if the external electrodes 9 and 10 are provided as shown in FIG. 15, it can be connected to the corresponding internal electrodes 3 and 4.
• Table 1 shows the characteristics of the devices according to the conventional method and the present invention.
• the remaining nickel plating is oxidized and there are internal electrodes that are not connected to the external electrodes. It is smaller than the element used.
• all the metal projections deposited by plating can be removed, so that problems such as poor electrical connection and mechanical disconnection due to oxidation of the deposited metal can be eliminated. Furthermore, by plating the internal electrodes protruding by etching, the plating height can be increased.Thus, a sufficient insulating layer thickness can be obtained, and at the same time, the adhesion area between the internal electrodes and the deposited metal is large. Therefore, the adhesive strength of the deposited metal can be improved. Further, by performing groove processing using a shot blast or the like, the electrostrictive effect layer 1 and the insulating layer reaching the internal electrode 3 electrically different from the deposited metal 5 shown in FIGS. 24 and 25 are obtained. Since the interface distance W of No. 7 can be substantially lengthened, absolute reliability is improved.
• a platinum paste was used as the internal electrode material, but a silver-palladium paste may be used.
• band-like gold deposited on the laminate Nickel was used as the metal material, but any plating liquid other than nickel can be used as long as it is a plating liquid that does not damage the electrostrictive effect layer.Even if copper, iron, chromium, tin, etc. are used The effect was obtained. Further, an acid solution was used to project the internal electrodes. However, if an electrostrictive material can be selectively etched, for example, ion etching may be used. Further, although the electric field etching was used as a means for removing the deposited metal, a method other than the above embodiment may be used. For example, a chemical etching using an acid solution or the like, an ion etching or the like may be used.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)
• Fixed Capacitors And Capacitor Manufacturing Machines (AREA)
• Transducers For Ultrasonic Waves (AREA)

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• 1991
  • 1991-09-09 US US07/855,048 patent/US5254212A/en not_active Expired - Fee Related
  • 1991-09-09 WO PCT/JP1991/001196 patent/WO1992005593A1/ja active Application Filing
  • 1991-09-09 DE DE19914192278 patent/DE4192278T/de not_active Ceased
• 1992
  • 1992-03-23 GB GB9206294A patent/GB2252869A/en not_active Withdrawn

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