Piezoelectric element, piezoelectric actuator, and mass flow controller

Abstract

This piezoelectric element is provided with a stack, a conductor layer, a wiring member, and a bonding material. For the stack, a plurality of piezoelectric bodies and a plurality of internal electrodes are stacked. The conductor layer is connected to the internal electrodes and is positioned along a stacking direction of the stack. The wiring member is electrically connected to the conductor layer. The bonding material, which is conductive, bonds the conductor layer and the wiring member together. A first region in which bismuth is segregated is positioned in the vicinity of the interface between the conductor layer and the bonding material.

Description

Piezoelectric element, piezoelectric actuator and mass flow controller

[0001] The present disclosure relates to a piezoelectric element, a piezoelectric actuator, and a mass flow controller.

[0002] Conventionally, a piezoelectric actuator has been known that includes piezoelectric elements stacked in a columnar shape and a metal case that houses the piezoelectric elements so that both ends of the piezoelectric elements abut against an inner wall (see, for example, Patent Document 1).

[0003] In this piezoelectric actuator, for example, a conductor layer that is electrically connected to an internal electrode is provided on the side surface of a pillar-shaped piezoelectric element, and a drive voltage is applied to the piezoelectric element via this conductor layer.

[0004] Japanese Patent Application Laid-Open No. 2009-043516

[0005] The piezoelectric element of the present disclosure includes a laminate, a conductor layer, a wiring member, and a bonding material. The laminate is formed by stacking a plurality of piezoelectric bodies and internal electrodes. The conductor layers are connected to the internal electrodes and are positioned along the stacking direction of the laminate. The wiring members are electrically connected to the conductor layers. A conductive bonding material bonds the conductor layers to the wiring member. A first region in which bismuth segregates is located near the interface between the conductor layer and the bonding material.

[0006] FIG. 1 is a perspective view showing the overall configuration of a piezoelectric actuator according to an embodiment. FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1. FIG. 3 is a perspective view showing the internal structure of a piezoelectric actuator according to an embodiment. FIG. 4 is an enlarged cross-sectional view showing the configuration of a piezoelectric element according to an embodiment. FIG. 5 is an enlarged cross-sectional view showing the configuration of a piezoelectric element according to another embodiment 1. FIG. 6 is an enlarged cross-sectional view showing the configuration of a piezoelectric element according to another embodiment 2. FIG. 7 is an enlarged cross-sectional view showing the configuration of a piezoelectric element according to another embodiment 2. FIG. 8 is an enlarged cross-sectional view showing the configuration of a piezoelectric element according to another embodiment 3. FIG. 9 is a block diagram showing the configuration of a mass flow controller according to an embodiment.

[0007] Hereinafter, embodiments for carrying out a piezoelectric element, a piezoelectric actuator, and a mass flow controller according to the present disclosure (hereinafter referred to as "embodiments") will be described in detail with reference to the drawings. Note that the present disclosure is not limited to these embodiments.

[0008] Furthermore, the embodiments can be combined as appropriate within the scope of not causing any contradiction in the processing content. Furthermore, the same components in the following embodiments are denoted by the same reference numerals, and redundant explanations will be omitted.

[0009] It should also be noted that the drawings are schematic and that the dimensional relationships and ratios of elements may differ from reality. Furthermore, the drawings may contain parts whose dimensional relationships and ratios differ from one another.

[0010] A conventional piezoelectric actuator includes piezoelectric elements stacked in a columnar shape and a metal case that houses the piezoelectric elements so that both ends of the piezoelectric elements abut against an inner wall. In this piezoelectric actuator, for example, a conductor layer that is electrically connected to an internal electrode is provided on the side surface of the columnar piezoelectric element, and a drive voltage is applied to the piezoelectric element via the conductor layer.

[0011] However, in the prior art, when a piezoelectric actuator is driven in a high temperature environment, the bonding strength between the conductor layer and the bonding material that bonds the wiring member to the conductor layer may decrease.

[0012] Therefore, it is desired to realize a technology that can solve the above problems and improve the bonding strength between the conductor layer and the bonding material.

[0013] <Overall Configuration of Piezoelectric Actuator> First, the overall configuration of a piezoelectric actuator 1 according to an embodiment will be described with reference to Figures 1 to 3. Figure 1 is a perspective view showing the overall configuration of the piezoelectric actuator 1 according to an embodiment, and Figure 2 is a cross-sectional view taken along line A-A in Figure 1. Also, Figure 3 is a perspective view showing the internal structure of the piezoelectric actuator 1 according to an embodiment.

[0014] 1 to 3, a piezoelectric actuator 1 according to an embodiment includes a piezoelectric element 10, a pair of electrode plates 20, a pair of lead terminals 30, and a case 40. The electrode plates 20 are an example of a wiring member. The pair of electrode plates 20 include electrode plate 20A and electrode plate 20B, and the pair of lead terminals 30 include lead terminal 30A and lead terminal 30B.

[0015] 3, the piezoelectric element 10 has a columnar shape. The piezoelectric element 10 is, for example, a square pillar (rectangular parallelepiped) with a length of 0.5 mm to 10 mm, a width of 0.5 mm to 10 mm, and a height of 1 mm to 100 mm. Note that the shape of the piezoelectric element 10 is not limited to a square pillar, and may be a hexagonal pillar, an octagonal pillar, a cylindrical pillar, or the like.

[0016] 2, the piezoelectric element 10 includes a piezoelectric body 11, an internal electrode 12, a planned fracture layer 13, and a pair of conductor layers 14. The pair of conductor layers 14 includes a conductor layer 14A and a conductor layer 14B.

[0017] The piezoelectric element 10 is configured by laminating a plurality of piezoelectric bodies 11, internal electrodes 12, and planned fracture layers 13 in a predetermined order along a lamination direction D. In the present disclosure, the lamination direction D of the piezoelectric element 10 coincides with the longitudinal direction of the piezoelectric element 10.

[0018] The piezoelectric body 11 is made of a piezoelectric material having piezoelectric properties, such as piezoelectric ceramics. Examples of the material of such piezoelectric ceramics include lead zirconate titanate (PbZrO ３ -PbTiO ３ , hereinafter also referred to as PZT) or potassium sodium niobate ((K,Na)NbO ３ , hereinafter also referred to as KNN), a perovskite oxide made of lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO ３ ) etc.

[0019] The average particle size of such piezoelectric ceramics is, for example, 1.6 μm to 2.8 μm, and the thickness of one layer of piezoelectric body 11 is, for example, 3 μm to 250 μm.

[0020] The internal electrode 12 is made of a conductive material and includes a plurality of first electrodes 12a and a plurality of second electrodes 12b. The first electrodes 12a are electrically connected to a conductor layer 14A. The conductor layer 14A is located on one side surface 10a of the piezoelectric element 10 along the stacking direction D. A predetermined positive voltage is applied to the first electrodes 12a, for example, via the conductor layer 14A.

[0021] The second electrode 12b is electrically connected to the conductor layer 14B. The conductor layer 14B is located along the stacking direction D on the side surface 10b of the piezoelectric element 10 opposite to the side surface 10a. A predetermined negative voltage (or ground voltage), for example, is applied to the second electrode 12b via the conductor layer 14B.

[0022] 2, inside the piezoelectric element 10, the first electrode 12a, the second electrode 12b, and the piezoelectric body 11 are laminated so that the piezoelectric body 11 is located between the first electrode 12a and the second electrode 12b. This allows the piezoelectric element 10 to apply a drive voltage to the piezoelectric body 11 by the first electrode 12a and the second electrode 12b.

[0023] The piezoelectric element 10 according to the embodiment is composed of an active portion formed by alternately stacking piezoelectric bodies 11 and internal electrodes 12, and an inactive portion located on both ends of the active portion in the stacking direction D and having the piezoelectric bodies 11.

[0024] The active portion is a portion that expands or contracts (hereinafter also referred to as expansion and contraction) in the stacking direction D when a drive voltage is applied to the piezoelectric element 10 from the outside. On the other hand, the inactive portion is a portion that does not expand or contract even when a drive voltage is applied to the piezoelectric element 10 from the outside.

[0025] In addition, in the present disclosure, the end of the case 40 on the base 41 side is the base end 10 e of the piezoelectric element 10 , and the end of the case 40 on the lid 43 side is the tip end 10 f of the piezoelectric element 10 .

[0026] In the piezoelectric actuator 1 according to the embodiment, the base end 10e of the piezoelectric element 10 (i.e., the base body 41) is fixed, and the tip end 10f of the piezoelectric element 10 (i.e., the lid body 43) is displaced along the stacking direction D.

[0027] The material of the internal electrodes 12 is, for example, a metal whose main component is silver, silver-palladium, silver-platinum, or copper. The internal electrodes 12 can be formed, for example, by co-firing with the piezoelectric body 11. The thickness of the internal electrodes 12 is, for example, 0.1 μm to 5 μm.

[0028] The planned rupture layer 13 is a layer for alleviating stress caused by driving the piezoelectric element 10. Examples of the planned rupture layer 13 include an extremely porous metal layer that does not function as the internal electrode 12, or an extremely porous piezoelectric layer. Note that the planned rupture layer 13 may be omitted in the piezoelectric element 10 according to the embodiment.

[0029] As described above, the pair of conductor layers 14 includes the conductor layer 14A located on the side surface 10a of the piezoelectric element 10 and the conductor layer 14B located on the side surface 10b of the piezoelectric element 10. The conductor layer 14 is located so as to extend over the entire active portion of the piezoelectric element 10.

[0030] The material of the conductor layer 14 is, for example, a metal containing silver or copper as a main component. For example, a metallized layer made of a sintered body of the above metal and glass can be used for the conductor layer 14. The thickness of the conductor layer 14 is, for example, 5 μm to 500 μm.

[0031] Although not shown in the present disclosure, a coating layer made of an insulating material may be disposed on side surface 10c (see FIG. 3) and side surface 10d (see FIG. 3) located between side surface 10a and side surface 10b of piezoelectric element 10. By disposing such a coating layer on side surfaces 10c and 10d, it is possible to reduce creeping discharge that occurs between the electrodes when a high voltage is applied during operation.

[0032] The insulating material for the coating layer may be, for example, a ceramic material, which can follow the expansion and contraction of the piezoelectric element 10 when the piezoelectric actuator 1 is driven and is deformable by stress so that the coating layer itself does not peel off and cause creeping discharge.

[0033] Specifically, the coating layer is made of partially stabilized zirconia, Ln １－Ｘ Si Ｘ AlO ３＋０．５Ｘ Examples of ceramic materials include: Ln represents at least one selected from Sn, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, and x is 0.01 to 0.3.

[0034] Alternatively, the coating layer may be a piezoelectric material such as barium titanate, lead zirconate titanate, or potassium sodium niobate, which changes the inter-ionic distance within the crystal lattice to relieve the induced stress.

[0035] The pair of electrode plates 20 includes electrode plate 20A and electrode plate 20B, which are electrically connected to the pair of conductor layers 14. Specifically, electrode plate 20A is electrically connected to conductor layer 14A, and electrode plate 20B is electrically connected to conductor layer 14B.

[0036] 3, the electrode plate 20 is positioned along the stacking direction D of the laminate as a whole, and locally meanders so as to intersect with the stacking direction D. At least a portion of the portion of the electrode plate 20 that intersects with the stacking direction D is joined to the conductor layer 14 via a conductive bonding material 21.

[0037] The bonding material 21 may be, for example, an epoxy resin or polyimide resin containing metal powder having high conductivity, such as Ag powder or Cu powder.

[0038] The material of the electrode plate 20 is, for example, a metal such as copper, iron, stainless steel, or phosphor bronze. The width of the electrode plate 20 is, for example, 0.5 (mm) to 10 (mm), and the thickness of the electrode plate 20 is, for example, 0.01 (mm) to 1.0 (mm). The surface of the electrode plate 20 may be plated with a plating film such as tin plating or silver plating to improve electrical conductivity and thermal conductivity.

[0039] 1 and 2, the pair of lead terminals 30 includes lead terminal 30A and lead terminal 30B. The pair of lead terminals 30 are electrically connected to the pair of electrode plates 20, respectively. For example, as shown in FIG. 2, lead terminal 30A is electrically connected to electrode plate 20A via conductive member 31A and conductive adhesive 32A, and lead terminal 30B is electrically connected to electrode plate 20B via conductive member 31B and conductive adhesive 32B.

[0040] As shown in Fig. 2, the case 40 accommodates the piezoelectric element 10 and the electrode plate 20. The case 40 has a base 41, a cylindrical body 42, and a lid 43. The base 41 is columnar (for example, cylindrical) and may have a cylindrical portion 41a that protrudes cylindrically from one end (the upper side in Fig. 2).

[0041] Furthermore, an inner bottom surface 41b located at the bottom of the cylindrical portion 41a contacts the base end 10e of the piezoelectric element 10. The inner bottom surface 41b of the base 41 and the base end 10e of the piezoelectric element 10 may be bonded together with a bonding material (not shown).

[0042] In addition, the base 41 has a pair of through holes 41d that penetrate between the inner bottom surface 41b and the end surface 41c opposite the inner bottom surface 41b, and a pair of lead terminals 30 are inserted into the pair of through holes 41d, respectively.

[0043] An insulating material (such as soft glass) is filled in the gap between the through hole 41d of the base 41 and the lead terminal 30, thereby fixing the lead terminal 30 to the base 41. Furthermore, as shown in FIG. 2 , the lead terminal 30 is inserted through the base 41 from inside the case 40 and protrudes outward from an end surface 41c of the base 41.

[0044] The cylinder 42 has a cylindrical shape (for example, a cylindrical shape). The cylinder 42 also has a bellows shape, and the axial direction of the cylinder coincides with the stacking direction D of the piezoelectric element 10. This allows the cylinder 42 to expand and contract in the axial direction in response to the expansion and contraction of the piezoelectric element 10 in the stacking direction D.

[0045] Furthermore, the cylindrical body 42 has a predetermined spring constant so that it can follow the expansion and contraction of the piezoelectric element 10. The spring constant of the cylindrical body 42 can be adjusted by the thickness of the cylindrical body 42, the shape of the grooves in the cylindrical body 42, the number of grooves in the cylindrical body 42, etc. The thickness of the cylindrical body 42 is, for example, 0.1 (mm) to 0.5 (mm), and the diameter of the cylindrical body 42 is, for example, 5 (mm) to 50 (mm).

[0046] Furthermore, the end 42 a of the cylindrical body 42 on the base body 41 side is welded, for example, in a state where a compressive load is applied to the piezoelectric element 10. Furthermore, the cylindrical body 42 may be welded after being provided with a flange that expands radially outward in a trumpet shape at the end 42 a on the base body 41 side.

[0047] The cylindrical body 42 is formed, for example, by preparing a seamless pipe of a predetermined shape and then processing the seamless pipe into a bellows shape by rolling, isostatic pressing, or the like.

[0048] The lid 43 has a cylindrical shape (for example, a cylindrical shape) with one end closed. The lid 43 is fitted into the end 42 b of the cylindrical body 42, and the inner wall of the end 42 b and the side wall of the lid 43 are fixed together by, for example, welding.

[0049] The inner bottom surface 43a of the lid 43 contacts the tip 10f of the piezoelectric element 10. The inner bottom surface 43a of the lid 43 and the tip 10f of the piezoelectric element 10 may be bonded together with a bonding material (not shown).

[0050] <Embodiment> Next, the detailed configuration of the piezoelectric element 10 according to the embodiment will be described with reference to Fig. 4. Fig. 4 is an enlarged cross-sectional view showing the configuration of the piezoelectric element 10 according to the embodiment.

[0051] 4 , in the piezoelectric element 10 according to the embodiment, a first region 22 is located near the interface between the conductor layer 14 and the bonding material 21. Bismuth (Bi) segregates in the first region 22. In this case, the first region 22 being located near the interface between the conductor layer 14 and the bonding material 21 means, for example, that the first region 22 is located between the conductor layer 14 and the bonding material 21.

[0052] When the bismuth segregated in this first region 22 comes into contact with the resin 21c (see FIG. 7) contained in the bonding material 21 in a high-temperature environment isolated from the outside air, the bismuth reacts with the resin 21c to form an organic synthetic compound of bismuth.

[0053] That is, in the embodiment, the first region 22 where bismuth segregates is located near the interface between the conductor layer 14 and the bonding material 21, and thus a reaction layer containing an organic synthetic compound of bismuth is formed near the interface. Therefore, according to the embodiment, the bonding strength between the conductor layer 14 and the bonding material 21 can be improved.

[0054] Furthermore, in the embodiment, the first region 22 where bismuth segregates is located near the interface between the conductor layer 14 and the bonding material 21, so that even if a crack occurs in the bonding material 21 when the piezoelectric actuator 1 is driven, the heat generated during driving can be used to cause a reaction between the bismuth and the resin 21c. This makes it possible to reduce the extension of the crack that occurs in the bonding material 21.

[0055] 4 illustrates an example in which the first region 22 is located near one conductor layer 14A of the pair of conductor layers 14, but the present disclosure is not limited to this example. For example, the first region 22 may be located near the other conductor layer 14B. This can improve the bonding strength between the other conductor layer 14B and the bonding material 21.

[0056] In the present disclosure, a pair of first regions 22 may be located near each of the conductor layers 14A and 14B, thereby improving the bonding strength between the conductor layers 14A and 14B and the pair of bonding materials 21.

[0057] In one method for forming the first region 22 according to the embodiment, for example, a bismuth oxide paste (bismuth oxide powder and binder) that will become the first region 22 is first printed on the side surface of a laminate that is composed of the piezoelectric body 11, the internal electrode 12, the planned fracture layer 13, and the conductor layer 14. Then, the laminate on which the bismuth oxide paste has been printed is fired.

[0058] Next, a bonding material paste that will become the bonding material 21 is printed on the side surface of the fired laminate, and the electrode plate 20 is placed on the bonding material paste. Then, the laminate on which the bonding material paste has been printed and the electrode plate 20 has been placed is heat-treated, thereby forming the first region 22 according to the embodiment.

[0059] Another method for forming the first region 22 according to the embodiment is, for example, to first print bismuth oxide paste on the side of a laminate composed of the piezoelectric body 11, the internal electrode 12, the planned fracture layer 13, and the conductor layer 14.

[0060] Next, a bonding material paste that will become the bonding material 21 is printed on the side surface of the laminate on which the bismuth oxide paste has been printed, and the electrode plate 20 is placed on the bonding material paste. Then, the laminate on which the bismuth oxide paste and the bonding material paste have been printed and the electrode plate 20 has been placed is fired to form the first region 22 according to the embodiment.

[0061] 4, the first region 22 may be located in a layer near the interface between the conductor layer 14 and the bonding material 21. As a result, even if a tensile stress is generated between the bonding material 21 and the conductor layer 14 due to expansion and contraction of the piezoelectric body 11 when the piezoelectric actuator 1 is driven, causing cracks in the bonding material 21 at the interface between the bonding material 21 and the conductor layer 14 and the risk of peeling, the heat generated during driving can be used to cause a reaction between the bismuth and the resin 21c, thereby making it possible to self-repair the cracks generated at the interface over the entire first region 22, thereby preventing peeling at the interface.

[0062] <Another embodiment 1> Next, various other embodiments will be described with reference to Fig. 5 to Fig. 8. Fig. 5 is an enlarged cross-sectional view showing the configuration of a piezoelectric element 10 according to another embodiment 1, and is an enlarged cross-sectional view showing another example of the configuration of the H1 portion shown in Fig. 4.

[0063] 5 , in another embodiment 1, the configuration of the first region 22 is different from that of the above-described embodiment. Specifically, in another embodiment 1, the first region 22 may be scattered near the interface between the conductor layer 14 and the bonding material 21.

[0064] This also positions the first region 22 where bismuth segregates near the interface between the conductor layer 14 and the bonding material 21, thereby forming a reaction layer containing an organic synthetic compound of bismuth near the interface. Therefore, according to another embodiment 1, the bonding strength between the conductor layer 14 and the bonding material 21 can be improved.

[0065] Furthermore, in another embodiment 1, the first region 22 where bismuth segregates is located near the interface between the conductor layer 14 and the bonding material 21, so that even if a crack occurs in the bonding material 21 when the piezoelectric actuator 1 is driven, the heat generated during driving can be used to cause a reaction between the bismuth and the resin 21c (see FIG. 7 ), thereby making it possible to reduce the extension of the crack that occurs in the bonding material 21.

[0066] In another embodiment 1, the first regions 22 are scattered near the interface between the conductor layer 14 and the bonding material 21, and therefore stress is applied to the peripheral portions of the scattered first regions 22 when the piezoelectric actuator 1 is driven, and this stress is dispersed throughout the entire interface between the conductor layer 14 and the bonding material 21.

[0067] 6 and 7 are enlarged cross-sectional views showing the configuration of a piezoelectric element 10 according to another embodiment 2. Fig. 6 is an enlarged cross-sectional view showing another example of the configuration of the H1 portion shown in Fig. 4, and Fig. 7 is a cross-sectional view further enlarged from Fig. 6. As shown in Fig. 6, in another embodiment 2, the configuration of the bonding material 21 differs from that of the above-described another embodiment 1.

[0068] Specifically, in another embodiment 2, a second region 21 a where bismuth is diffused may be located inside the bonding material 21. The second region 21 a may be located near the interface between the conductor layer 14 and the bonding material 21, for example.

[0069] 7, the bonding material 21 includes a plurality of metal particles 21b and a resin 21c. In another embodiment 2, bismuth may be diffused into the metal particles 21b in the second region 21a.

[0070] This can increase the bonding strength between adjacent metal particles 21 b inside the bonding material 21. Therefore, according to the embodiment, the adjacent metal particles 21 b can be in good contact with each other, and therefore the conductivity of the bonding material 21 can be increased.

[0071] In another embodiment 2, the plurality of metal particles 21b may include particulate and scale-like particles, as shown in Fig. 7. The scale-like metal particles 21b deform when stress is applied by driving the piezoelectric actuator 1, thereby dispersing the stress.

[0072] In other words, by containing scale-like metal particles 21b in addition to particulate metal particles 21b, the bonding material 21 can alleviate stress applied to the particulate metal particles 21b by deformation of the scale-like metal particles 21b adjacent to such particulate metal particles 21b.

[0073] Therefore, according to the second alternative embodiment, the bond durability between the adjacent particulate metal particles 21b and the adjacent flake metal particles 21b is excellent.

[0074] In another embodiment 2, bismuth may be segregated at the interface between the metal particles 21 b and the resin 21 c. Inside the bonding material 21, the resin 21 c does not easily transmit electricity and heat, but by segregating bismuth at the interface between the metal particles 21 b and the resin 21 c, i.e., on the surface of the resin 21 c, electricity and heat are more likely to propagate along the surface of the resin 21 c.

[0075] This reduces heat generation when the piezoelectric actuator 1 is driven, thereby improving the durability of the bonding material 21. Furthermore, since the bonding material 21 is less susceptible to thermal expansion, cracks are less likely to occur between adjacent metal particles 21b.

[0076] In another embodiment 2, bismuth may be segregated at the crystal grain boundaries 14b formed between adjacent metal particles 14a inside the conductor layer 14. This improves the adhesion strength between adjacent metal particles 14a inside the conductor layer 14. Therefore, according to another embodiment 2, the durability of the conductor layer 14 is improved.

[0077] In another embodiment 2, bismuth may be segregated near the interface between the conductor layer 14 and the bonding material 21 between adjacent metal particles 14a, between adjacent metal particles 21b, or between adjacent metal particles 14a and 21b.

[0078] This improves the adhesion strength between adjacent metal particles 14a, between adjacent metal particles 21b, or between adjacent metal particles 14a and 21b near the interface between the conductor layer 14 and the bonding material 21. Therefore, according to another embodiment 2, the bonding strength between the conductor layer 14 and the bonding material 21 is improved.

[0079] 6 shows an example in which the first regions 22 are scattered near the interface between the conductor layer 14 and the bonding material 21 having the second regions 21 a, but the present disclosure is not limited to such an example. For example, the first regions 22 may be located in a layered form near the interface between the conductor layer 14 and the bonding material 21 having the second regions 21 a, as shown in FIG.

[0080] <Alternative Embodiment 3> Fig. 8 is an enlarged cross-sectional view showing the configuration of a piezoelectric element 10 according to alternative embodiment 3. As shown in Fig. 8, in alternative embodiment 3, the wiring member bonded to the conductor layer 14 by the bonding material 21 may be a wire 50 instead of the electrode plate 20 (see Fig. 4). In other words, the wire 50 is another example of a wiring member.

[0081] This also positions the first region 22 where bismuth segregates near the interface between the conductor layer 14 and the bonding material 21, thereby forming a reaction layer containing an organic synthetic compound of bismuth near the interface. Therefore, according to another embodiment 3, the bonding strength between the conductor layer 14 and the bonding material 21 can be improved.

[0082] In another embodiment 3, the first region 22 where bismuth segregates is located near the interface between the conductor layer 14 and the bonding material 21, so that even if a crack occurs in the bonding material 21 when the piezoelectric actuator 1 is driven, the heat generated during driving can be used to cause a reaction between the bismuth and the resin 21c (see FIG. 7 ), thereby reducing the propagation of the crack that occurs in the bonding material 21.

[0083] <Configuration of Mass Flow Controller> Next, an example of a mass flow controller 100 equipped with the piezoelectric actuator 1 according to the embodiment will be described with reference to Fig. 9. Fig. 9 is a block diagram showing the configuration of the mass flow controller 100 according to the embodiment.

[0084] 9, the mass flow controller 100 includes a flow path 101, a flow sensor unit 102, a flow control valve 103, and a control circuit unit 104. A fluid such as a gas flows through the flow path 101. The fluid flows in through an inlet 101a and flows out through an outlet 101b.

[0085] A flow rate sensor unit 102 is connected, for example, in a bypass manner, to a portion of the flow path 101. This flow rate sensor unit 102 is configured to be able to detect the flow rate (mass flow rate) of the fluid flowing through the flow path 101. A flow rate signal detected by the flow rate sensor unit 102 is amplified by an amplifier circuit or the like and transmitted to the control circuit unit 104.

[0086] The flow control valve 103 includes the piezoelectric actuator 1 according to the embodiment, and is configured to be able to control the flow rate of the fluid flowing through the flow path 101. The flow control valve 103 can control the flow rate by, for example, expanding and contracting the piezoelectric actuator 1.

[0087] The control circuit section 104 controls each section. For example, the control circuit section 104 compares the flow rate signal transmitted from the flow rate sensor section 102 with a flow rate signal set in advance by the user or the like.

[0088] Then, a drive signal (drive voltage) that eliminates the difference between the transmitted flow rate signal and a preset flow rate signal is input to the piezoelectric actuator 1 provided in the flow rate control valve 103 .

[0089] The piezoelectric actuator 1 expands and contracts in response to the input drive voltage, and this expansion and contraction controls the opening and closing amount of the flow control valve 103 , thereby controlling the flow rate of the fluid flowing through the flow path 101 .

[0090] As described above, the embodiment includes the piezoelectric element 10 that is highly durable even in high temperature environments, and therefore the mass flow controller 100 can be stable for a long period of time even when used in harsh environments.

[0091] The present disclosure has been described in detail above, but the present disclosure is not limited to the above-described embodiments, and various modifications, improvements, etc. are possible within the scope that does not deviate from the gist of the present disclosure.

[0092] The disclosed embodiments should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0093] The present technology can be configured as follows. (1) A piezoelectric element including: a laminate including a plurality of piezoelectric bodies and internal electrodes stacked one on the other; conductor layers connected to the internal electrodes and positioned along the stacking direction of the laminate; wiring members electrically connected to the conductor layers; and a conductive bonding material bonding the conductor layers to the wiring members, wherein a first region in which bismuth segregates is located near the interface between the conductor layers and the bonding material. (2) The piezoelectric element according to (1), wherein the first region is scattered near the interface between the conductor layers and the bonding material. (3) The piezoelectric element according to (1) or (2), wherein the bonding material includes a plurality of metal particles, and bismuth is diffused inside the plurality of metal particles. (4) The piezoelectric element according to (3), wherein the plurality of metal particles include particulate and flake-shaped particles. (5) The piezoelectric element according to any one of (1) to (4), wherein the bonding material includes a plurality of metal particles and a resin, and bismuth is segregated at the interface between the metal particles and the resin. (6) A piezoelectric actuator comprising: the piezoelectric element according to any one of (1) to (5); and a case accommodating the piezoelectric element therein. (7) A mass flow controller comprising: a flow path; a flow sensor unit that detects a flow rate of a fluid flowing through the flow path; a flow control valve that has the piezoelectric element according to any one of (1) to (5) and controls the flow rate of the fluid flowing through the flow path by expanding and contracting the piezoelectric element; and a control circuit unit that controls each unit.

[0094] REFERENCE SIGNS LIST 1 Piezoelectric actuator 10 Piezoelectric element 11 Piezoelectric body 12 Internal electrode 14, 14A, 14B Conductor layer 20, 20A, 20B Electrode plate (an example of a wiring member) 21 Bonding material 21a Second region 21b Metal particles 21c Resin 22 First region 40 Case 50 Wire (an example of a wiring member) 100 Mass flow controller 101 Flow path 102 Flow rate sensor section 103 Flow rate control valve 104 Control circuit section D Stacking direction

Claims

1. A piezoelectric element comprising: a laminate comprising a plurality of piezoelectric bodies and internal electrodes stacked together; conductor layers connected to the internal electrodes and positioned along the stacking direction of the laminate; wiring members electrically connected to the conductor layers; and a conductive bonding material bonding the conductor layers to the wiring material, wherein a first region in which bismuth segregates is located near the interface between the conductor layers and the bonding material.

2. The piezoelectric element according to claim 1, wherein the first regions are interspersed in the vicinity of the interface between the conductor layer and the bonding material.

3. The piezoelectric element according to claim 1 or 2, wherein the bonding material contains a plurality of metal particles, and bismuth is diffused into the interior of the plurality of metal particles.

4. The piezoelectric element according to claim 3, wherein the plurality of metal particles include granular and flake-shaped particles.

5. A piezoelectric element according to any one of claims 1 to 4, wherein the bonding material contains a plurality of metal particles and a resin, and bismuth is segregated at the interface between the metal particles and the resin.

6. A piezoelectric actuator comprising: a piezoelectric element according to any one of claims 1 to 5; and a case for accommodating the piezoelectric element therein.

7. A mass flow controller comprising: a flow path; a flow sensor unit for detecting a flow rate of a fluid flowing within said flow path; a flow control valve having a piezoelectric element as defined in any one of claims 1 to 5, the flow control valve controlling the flow rate of the fluid flowing within said flow path by the expansion and contraction of the piezoelectric element; and a control circuit unit for controlling each of the components.

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