JP2005235878A - Laminate structure and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a detailed laminate structure object equivalent to a green sheet method even in the case that a piezoelectric material of bulk is used. <P>SOLUTION: This laminate structure includes a piezoelectric element in which a plurality of electrode layers 2, 3 are formed among a plurality of piezoelectric material layers 1 which disconnect the piezoelectric material to be obtained, a first insulating film 4 which covers electrode layers 2 of a first group in the plurality of the electrode layers in the first field of the piezoelectric element, a second insulating film 5 which covers the electrode layers 3 of a second group in the plurality of the electrode layers, first wiring 8 electrically connected to the electrode layers of the second group and insulated from the electrode layers of the first group by the first insulating film in the first field of the piezoelectric element, and second wiring 7 electrically connected to the electrode layers of the first group and insulated from the electrode layers of the second group by the second insulating film in the second field of the piezoelectric element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laminated structure in which insulators and electrodes are alternately formed and a method for manufacturing the same.

  A laminated structure in which insulators (dielectrics) and electrodes are alternately formed is used for various applications such as a piezoelectric pump, a piezoelectric actuator, and an ultrasonic transducer in addition to a laminated capacitor. In recent years, along with the development of MEMS (micro electro mechanical system) related devices, miniaturization and integration of elements having such a laminated structure have been advanced.

  In miniaturization of an element having a counter electrode, if the area of the element is reduced, the capacitance between the electrodes is reduced, which causes a problem that the electrical impedance of the element increases. For example, when the electrical impedance rises in the piezoelectric actuator, impedance matching with the signal circuit for driving the piezoelectric actuator cannot be achieved, and it becomes difficult to supply power, and the performance as a piezoelectric actuator is reduced. Or in the ultrasonic transducer using a piezoelectric element, the detection sensitivity of an ultrasonic wave will fall. Therefore, in order to increase the interelectrode capacitance while miniaturizing the element, a plurality of piezoelectric material layers and a plurality of electrode layers are alternately stacked. That is, the inter-electrode capacitance of the entire device can be increased by connecting a plurality of stacked layers in parallel.

  As a manufacturing method of a laminated structure including a piezoelectric material layer, a bulk method using a bulk piezoelectric material is conventionally known. In the bulk method, a method is used in which a bulk piezoelectric material cut to a desired thickness is alternately stacked with electrode layers and bonded using an adhesive or fixed by tightening a bolt.

  However, this method is generally used for manufacturing a relatively large laminated structure, and when used for the manufacture of a minute laminated structure, handling is difficult because a thinly cut piezoelectric material is fragile and easily cracked. In addition, since the fine processing is difficult, the manufacturing process becomes complicated. In particular, a piezoelectric material having a thickness of 100 μm or less is easily cracked. In addition, the finished product has a problem in mounting properties by the adhesive and a problem that stress is generated in the bonded portion. Therefore, according to this method, the manufacturing yield decreases and the manufacturing cost increases, which is not appropriate from the viewpoint of productivity. Therefore, a green sheet method or a screen printing method for manufacturing a laminated structure by film formation has been studied.

  In the green sheet method or the screen printing method, a green sheet (piezoelectric sheet) formed by mixing an unplasticized piezoelectric material powder with a binder such as an organic substance is used. In this method, a plurality of sheets coated with electrode material paste by screen printing are stacked on a piezoelectric sheet, and the binder is scattered from the piezoelectric sheet by firing at a high temperature of about 1000 ° C. Is a strong film.

  In a laminated structure manufactured using such a method, wiring is performed on the side surface of the laminated structure in order to connect a plurality of electrode layers to each other. FIG. 10 is a cross-sectional view for explaining a general wiring method of the laminated structure. The laminated structure 100 includes a plurality of piezoelectric material layers 101, a plurality of electrode layers 102 and 103, and side wirings 104 and 105.

  The electrode 102 is formed so that one end thereof extends to one wall surface of the multilayer structure, and the electrode 103 is formed so that one end thereof extends to the other wall surface of the multilayer structure. As a result, the electrode 102 is connected to one side wiring 104 and insulated from the other side wiring 105 by the insulating region 106. On the contrary, the electrode 103 is connected to the side wiring 105 and insulated from the side wiring 104 by the insulating region 106. By applying a potential difference between the side wiring 104 and the side wiring 105, a voltage is applied to each of the piezoelectric material layers 101 disposed between the electrode 102 and the electrode 103, and the piezoelectric material layer 101 is caused to have a piezoelectric effect. It expands and contracts.

  However, the electrodes 102 and 103 are provided with an insulating region 106 in which no electrode is formed in order to insulate from one of the side wirings. The insulating region 106 does not expand or contract even when a voltage is applied to the laminated structure 100. For this reason, the piezoelectric material layer 101 has a first region that expands and contracts and a second region that does not expand and contract, and there is a problem that stress is easily concentrated between these regions and is easily damaged.

  As a related technique, Patent Document 1 below discloses a method for manufacturing a long-life multilayer piezoelectric actuator. According to Patent Document 1, an internal electrode is formed on the entire surface of a green sheet mainly composed of a piezoelectric ceramic material, the green sheet is laminated in layers and sintered, and machined on both sides of the object to be sintered. Processing is performed, and end portions on both sides are insulated with resin every other layer, and a conductive layer is formed on each surface from the top of the workpiece. As a result, the durability can be improved compared to the conventional case where the full-surface electrode cannot be formed, and there is no need for alignment for partially forming the internal electrode, and miniaturization is possible. It becomes.

However, since the laminate formed by the green sheet (piezoelectric sheet) and the internal electrode sheet is generally fired at a high temperature of about 1000 ° C., a conductive material (for example, silver) used for the internal electrode is used. By diffusing into the piezoelectric body, the characteristics of the piezoelectric body deteriorate. Furthermore, in the piezoelectric body manufactured by the green sheet method, the number of holes formed after the binder such as organic matter contained therein is removed is larger than that of the bulk piezoelectric body. It is about 60% to 70% of the characteristics. Therefore, there is a problem that the piezoelectric performance of the multilayer structure manufactured by the green sheet method is inferior to the piezoelectric performance of the multilayer structure manufactured by the bulk method. The screen printing method has the same problem.
JP-A-60-128683 (2nd page, FIG. 2)

  Therefore, in view of the above points, an object of the present invention is to realize a fine laminated structure equivalent to the green sheet method even when a bulk piezoelectric material is used.

  In order to solve the above problems, a multilayer structure according to the present invention includes a piezoelectric element in which a plurality of electrode layers are formed between a plurality of piezoelectric material layers obtained by cutting a piezoelectric material, and a piezoelectric element A first insulating film covering a first group of electrode layers of the plurality of electrode layers on the first surface; and a second group of electrodes of the plurality of electrode layers on the second surface of the piezoelectric element. The second insulating film covering the layer and the first surface of the piezoelectric element are electrically connected to the second group of electrode layers and insulated from the first group of electrode layers by the first insulating film. A first wiring and a second wiring electrically connected to the first group of electrode layers and insulated from the second group of electrode layers by a second insulating film on the second surface of the piezoelectric element; It comprises.

  Also, in the method for manufacturing a laminated structure according to the present invention, a piezoelectric material is cut and separated into a plurality of piezoelectric material layers, and a conductive paste is injected between the plurality of piezoelectric material layers and fired. A step (a) of obtaining a piezoelectric element in which a plurality of electrode layers are respectively formed between the piezoelectric material layers; and covering a first group of the plurality of electrode layers on the first surface of the piezoelectric element. A step (b) of forming a first insulating film, and a step of forming a second insulating film covering the second group of electrode layers of the plurality of electrode layers on the second surface of the piezoelectric element ( and c) forming a first wiring electrically connected to the second group of electrode layers on the first surface of the piezoelectric element and insulated from the first group of electrode layers by the first insulating film. (D) and the second surface of the piezoelectric element is electrically connected to the first group of electrode layers, Comprising a step (e) forming a second wiring which is insulated from the second group of electrode layers by Enmaku.

  According to the present invention, the piezoelectric material is cut and separated into a plurality of piezoelectric material layers, and the conductive paste is injected and then fired, so that even when a bulk piezoelectric material is used, it is equivalent to the green sheet method. A fine laminated structure can be realized.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a diagram showing a structure of a laminated structure according to an embodiment of the present invention. As shown in FIG. 1, the laminated structure 10 is a minute columnar structure having, for example, a side of the bottom surface of about 0.3 to 1.0 mm and a height of about 2.1 mm. The laminated structure 10 includes a plurality of PZT (Pb (lead) zirconate titanate) layers 1, a plurality of first electrode layers 2, a plurality of second electrode layers 3, and a plurality of first insulations. The film 4 includes a plurality of second insulating films 5, a plurality of third insulating films 6, and wirings 7 and 8. In the present embodiment, bulk PZT is used as the PZT layer 1.

  Between the PZT layers 1, the first electrode layers 2 and the second electrode layers 3 are alternately arranged, and the first electrode layer 2 or the second electrode layer 3 is directly bonded to each PZT layer 1. Has been. The wiring 7 covers one side surface and the bottom surface of the multilayer structure 10, the wiring 8 covers the other side surface and top surface of the multilayer structure 10, and the wiring 7 and the wiring 8 are insulated by the third insulating film 6. ing.

  The first electrode layer 2 is electrically connected to the wiring 7 on one side and is insulated from the wiring 8 by the first insulating film 4 disposed on the other side. The second electrode layer 3 is insulated from the wiring 7 by the second insulating film 5 disposed on one side surface, and is electrically connected to the wiring 8 on the other side surface.

  By applying a voltage to the PZT layer 1 via the wirings 7 and 8, the first electrode layer 2, and the second electrode layer 3, the PZT layer 1 expands and contracts due to the piezoelectric effect. Such a laminated structure using a piezoelectric material such as PZT as an insulating layer (dielectric layer) is used for a piezoelectric pump, a piezoelectric actuator, an ultrasonic transducer that transmits and receives ultrasonic waves in an ultrasonic probe, and the like. . Since the structure having a stacked structure increases the area of the opposing electrode as compared with a single-layer structure, the electrical impedance can be lowered. Therefore, it operates efficiently with respect to the applied voltage as compared with a single-layer structure.

  In this embodiment, bulk PZT is used as the piezoelectric material, but in addition to the bulk material obtained by firing the powder, a piezoelectric material formed by an aerosol deposition (AD) method or a pulling method. A single crystal piezoelectric material formed by the above method may be used.

  Next, the manufacturing method of the laminated structure according to the present embodiment will be described with reference to FIGS. FIG. 2 is a flowchart showing a method for manufacturing a laminated structure according to this embodiment. Moreover, FIGS. 3-6 is a figure for demonstrating the manufacturing method of the laminated structure which concerns on this embodiment.

  First, the PZT layer 1 is formed in steps S1 to S3 shown in FIG. In step S1, bulk PZT is prepared as shown in FIG. In this embodiment, PZT having a 25 mm square and a thickness of 0.3 mm is used. Next, in step S2, as shown in FIG. 3B, an adhesive sheet is attached to the back surface of the bulk PZT.

  In step S <b> 3, as shown in FIG. 3C, bulk PZT is cut using a dicer cutting machine to form a PZT layer 1. Here, in order to fix each PZT layer 1, the pressure-sensitive adhesive sheet is prevented from being cut by a dicer type cutting machine. Thus, since the PZT can be easily finely processed by using the dicer type cutting machine, the PZT layer 1 having a desired dimension can be formed with high accuracy.

  According to the present embodiment, since a dicer type cutting machine capable of microfabrication is used, polishing for adjusting the thickness of the PZT layer 1 is not required, the packing density is 90% or more, and A minute laminated structure can be manufactured. In addition, since it is not necessary to handle the PZT layers 1 one by one, it is possible to prevent damage due to the handling of one PZT layer one by one and improve the yield.

  Next, in steps S4 to S6, the first electrode layer 2 and the second electrode layer 3 are formed. In step S4, as shown in FIG. 4A, a conductor paste such as silver paste or silver palladium paste is injected into the groove formed by the dicer type cutting machine. In step S5, as shown in FIG. 4B, the pressure-sensitive adhesive sheet on which the PZT layer 1 is fixed is peeled off.

  In step S <b> 6, as shown in FIG. 4C, the conductor paste is dried and fired to form the first electrode layer 2 and the second electrode layer 3. In this embodiment, drying is performed at about 100 ° C. for 10 minutes, and baking is performed at about 600 ° C. Here, at the time of firing, organic components and moisture are removed from the conductor paste, so that the volume of the conductor paste is reduced. Therefore, in this embodiment, a constant force is applied in the stacking direction so as to gradually narrow the interval between the PZT layers 1 during firing.

  Next, in steps S7 to S10, the first insulating film 4, the second insulating film 5, and the third insulating film 6 are formed. In step S7, as shown in FIG. 5A, a resist mask having a desired pattern is formed on the first surface of the multilayer structure 10 using a photolithography process. Note that a metal mask may be formed instead of the resist mask. In step S8, as shown in FIG. 5B, the first insulating film 4 and the third insulating film 6 are formed on the first surface using a resist mask, and then the resist mask is removed.

  In step S9, the stacked structure 10 is turned upside down, and as shown in FIG. 5C, using a photolithography process, a second surface opposite to the first surface of the stacked structure 10 is used. A resist mask having a desired pattern is formed. In step S10, as shown in FIG. 5D, the resist mask is used to form the second insulating film 5 and the third insulating film 6 on the second surface, and then the resist mask is removed.

In the above, the insulating films 4 to 6 are formed by a film forming method by an AD method which will be described later. As a material of the insulating films 4 to 6, for example, PZT, alumina, Zr-based oxides such as ZrO ₂ , TiO ₂ , and the like can be used. In other words, any material can be used as long as it can form an insulating film using a film formation method by the AD method.

  Next, wirings 7 and 8 are formed in steps S11 to S13. In step S11, as shown in FIG. 6A, unnecessary peripheral portions of PZT are cut. In step S <b> 12, as shown in FIG. 6B, a conductor paste is applied to portions other than the front surface, the rear surface, and the third insulating film 6 of the laminated structure 10. In step S13, as shown in FIG. 6C, the conductor paste is dried and fired to form the wirings 7 and 8.

  Here, the AD method used for forming the insulating film in the present embodiment will be described. FIG. 7 shows an apparatus used for film formation by the AD method. This apparatus has an aerosol generation container 20 and a film forming chamber 30. Aerosol refers to solid or liquid fine particles floating in a gas. In this embodiment, PZT fine particles having an average particle diameter of 0.2 μm to 1 μm are used to form an insulating film.

  The aerosol generation container 20 is a container in which the film forming raw material powder is placed, and generation of the aerosol is performed here. The aerosol generation container 20 is provided with a carrier gas introduction part 21, an aerosol lead-out part 22, and a pressure adjustment nozzle 23. The carrier gas introduction unit 21 introduces a carrier gas, which is a gas used to carry the raw material powder, into the aerosol generation container 20. That is, the aerosol is generated by spraying the raw material powder disposed in the aerosol generation container 20 with the carrier gas.

  As this carrier gas, dry air, nitrogen gas, argon gas, oxygen gas, helium gas or the like is used. Further, the aerosol deriving unit 22 sucks the aerosol generated in the aerosol generation container 20 and guides it to the film forming chamber 30. The pressure adjustment nozzle 33 is used when adjusting the pressure difference between the aerosol generation container 20 and the film forming chamber 30.

  Such an aerosol generation container 20 is placed on the vibration table 24. The vibration table 24 agitates the raw material powder disposed in the aerosol generation container 20 by applying vibration to the aerosol generation container 20 so that the aerosol is efficiently generated.

  The film forming chamber 30 is provided with an exhaust pipe 31, an aerosol introduction part 32, a nozzle 33, and a movable stage 34. The exhaust pipe 31 is connected to a vacuum pump and exhausts the film forming chamber 30. The aerosol introducing unit 32 is connected to the aerosol deriving unit 22 of the aerosol generating unit 20, and introduces the aerosol generated in the aerosol generating unit 20 into the film forming chamber 30. The nozzle 33 injects the aerosol introduced through the aerosol introduction part 32 toward the laminated structure 10 disposed on the movable stage 34.

  According to this embodiment, since bulk PZT is used as the PZT layer 1, the piezoelectric performance is better than PZT formed by using a green sheet method or a screen printing method. Further, unlike the green sheet method, baking at about 1000 ° C. is not required, so that silver as an electrode material hardly diffuses. Furthermore, since the electrode layer 2 or 3 is directly bonded to the PZT layer 1 without using an adhesive, stress due to the adhesive does not occur and good piezoelectric actuator performance can be obtained. Further, since the electrode layers 2 and 3 are disposed on the entire surface of the PZT layer 1, stress is not concentrated on a part of the PZT layer 1. As a result, the laminated structure 10 has better durability than the conventional laminated structure.

  In this embodiment, the insulating film is formed using the AD method. However, the insulating film may be formed using a sputtering method, a vapor deposition method, an electrophoresis method, a plating method, or the like. In the present embodiment, the wirings 7 and 8 are formed using a conductor paste. However, the wirings 7 and 8 may be formed by sputtering platinum using platinum titanium as an adhesion layer. Furthermore, in this embodiment, bulk PZT is cut using a dicer type cutting machine, but bulk PZT may be cut using a laser cutter. In that case, a substrate is used instead of the adhesive sheet.

  By arranging a plurality of the laminated structures described above, an arrayed laminated structure can be manufactured. For example, as shown in FIG. 8, a laminated structure in which a plurality of laminated structures 10 are arranged in a two-dimensional array on a substrate can be produced.

  FIG. 9 is a partial cross-sectional perspective view showing an example in which the two-dimensional array laminated structure as shown in FIG. 8 is applied to an ultrasonic probe. The ultrasonic probe includes an ultrasonic transducer array 40 including a plurality of ultrasonic transducers that transmit and receive ultrasonic waves, an acoustic matching layer 41, an acoustic lens 42, and a backing layer 43. These units 40 to 43 are housed in a housing 44. Further, the wirings of the plurality of ultrasonic transducers included in the ultrasonic transducer array 40 are connected to the ultrasonic imaging apparatus main body via the cable 45.

  A filler such as an epoxy resin is disposed between these ultrasonic transducers. The acoustic matching layer 41 is formed of glass, ceramic, metal powder-containing epoxy resin, or the like that can easily transmit ultrasonic waves. The acoustic matching layer 41 eliminates the mismatch of acoustic impedance between the subject that is a living body and the ultrasonic transducer. Thereby, the ultrasonic wave transmitted from the ultrasonic transducer can be efficiently propagated into the subject.

  The acoustic lens 42 is made of, for example, silicon rubber. The acoustic lens 42 focuses the ultrasonic beam transmitted from the ultrasonic transducer array 40 and having the acoustic impedance matched in the acoustic matching layer 41 at a predetermined depth. The backing layer 43 is formed of a material having a large acoustic attenuation, such as a material in which a metal powder such as ferrite or a PZT powder is mixed in an epoxy resin or rubber. The backing layer 43 quickly attenuates unnecessary ultrasonic waves generated from the ultrasonic transducer array 40.

  When producing such an ultrasonic probe, a plurality of laminated structures are arranged in an array on a substrate made of glass or Macor (registered trademark), and between the laminated structures. By arranging the filler, the ultrasonic transducer 40 and the acoustic matching layer 41 are produced. In this case, a plurality of acoustic matching layers may be provided by attaching another acoustic matching layer to the substrate.

  In this embodiment, when a PZT layer is produced using bulk PZT, the PZT layer is less thermally contracted during firing of the conductive paste, and compared with the green sheet method or screen printing method in which the PZT layer is thermally contracted. Thus, a thick laminated structure can be manufactured stably. As a result, an ultrasonic transducer that transmits and receives low-frequency ultrasonic waves can be manufactured.

  The present invention can be used in a laminated structure in which insulators and electrodes are alternately formed and a method for manufacturing the same.

It is a figure which shows the structure of the laminated structure which concerns on one Embodiment of this invention. It is a flowchart which shows the manufacturing method of the laminated structure which concerns on this embodiment. It is a figure for demonstrating formation of the PZT layer of the laminated structure which concerns on this embodiment. It is a figure for demonstrating formation of the electrode layer of the laminated structure which concerns on this embodiment. It is a figure for demonstrating formation of the insulating film of the laminated structure which concerns on this embodiment. It is a figure for demonstrating formation of the wiring of the laminated structure which concerns on this embodiment. It is a figure which shows the apparatus used in order to form into a film by AD method. It is a figure which shows the some laminated structure arrange | positioned on the board | substrate at the two-dimensional array form. It is a partial cross section perspective view which shows the example which applied the laminated structure of a two-dimensional array shape to the probe for ultrasonic waves. It is sectional drawing for demonstrating the general wiring method of a laminated structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 PZT layer 2, 3 Electrode layers 4-6 Insulating film 7, 8 Wiring 10 Laminated structure 20 Aerosol production | generation container 21 Carrier gas introduction part 22 Aerosol derivation part 23 Pressure adjustment nozzle 24 Shaking table 30 Deposition chamber 31 Exhaust pipe 32 Aerosol Introduction unit 33 Pressure adjusting nozzle 34 Stage 40 Ultrasonic transducer array 41 Acoustic matching layer 42 Acoustic lens 43 Backing layer 44 Housing 45 Cable

Claims (9)

A laminated structure,
A piezoelectric element in which a plurality of electrode layers are respectively formed between a plurality of piezoelectric material layers obtained by cutting a piezoelectric material;
A first insulating film covering a first group of electrode layers of the plurality of electrode layers on the first surface of the piezoelectric element;
A second insulating film covering a second group of electrode layers of the plurality of electrode layers on the second surface of the piezoelectric element;
A first wiring electrically connected to the second group of electrode layers on the first surface of the piezoelectric element and insulated from the first group of electrode layers by the first insulating film;
A second wiring electrically connected to the first group of electrode layers on the second surface of the piezoelectric element and insulated from the second group of electrode layers by the second insulating film;
A laminated structure comprising:   The laminated structure according to claim 1, wherein the first group of electrode layers and the second group of electrode layers are alternately arranged.   The laminated structure according to claim 1, wherein the first group and the second group of electrode layers are formed by firing a conductive paste injected between the plurality of piezoelectric material layers.   The laminated structure according to claim 1, wherein the first and second insulating films are formed using one of an aerosol deposition method, a sputtering method, a vapor deposition method, an electrophoresis method, and a plating method. A method of manufacturing a laminated structure,
The piezoelectric material is cut and separated into a plurality of piezoelectric material layers, and a conductive paste is injected between the plurality of piezoelectric material layers and baked, whereby a plurality of electrode layers are formed between the plurality of piezoelectric material layers. Obtaining each formed piezoelectric element (a);
Forming a first insulating film covering a first group of electrode layers of the plurality of electrode layers on the first surface of the piezoelectric element;
Forming a second insulating film covering the second group of electrode layers of the plurality of electrode layers on the second surface of the piezoelectric element;
Forming a first wiring electrically connected to the second group of electrode layers on the first surface of the piezoelectric element and insulated from the first group of electrode layers by the first insulating film; (D) and
Forming a second wiring electrically connected to the first group of electrode layers on the second surface of the piezoelectric element and insulated from the second group of electrode layers by the second insulating film; (E) and
A manufacturing method comprising:   The manufacturing method according to claim 5, wherein the first group of electrode layers and the second group of electrode layers are alternately arranged. Step (b) includes forming a mask for forming the first insulating film;
Step (c) includes forming a mask for forming the second insulating film.
The manufacturing method of Claim 5.   The manufacturing method according to claim 7, wherein the mask formed in step (b) or (c) includes a resist mask or a metal mask.   In step (b) or (c), the first or second insulating film is formed using one of an aerosol deposition method, a sputtering method, a vapor deposition method, an electrophoresis method, and a plating method. The manufacturing method of Claim 5 containing.

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