Manufacturing method for piezoelectric device

Abstract

The present invention provides a method for manufacturing a piezoelectric device that can perform polarization processing without applying voltage. [Solution] The method for manufacturing a piezoelectric device according to the present disclosure is a method for manufacturing a piezoelectric device that includes a mounting step of mounting a piezoelectric element including a piezoelectric layer on a substrate with an adhesive member, wherein the mounting step includes a heating step of heating the adhesive member and fixing or electrically connecting the piezoelectric element to the mounting substrate with the adhesive member, and the heating step includes a first heating step of heating the adhesive member and the piezoelectric element so that the piezoelectric layer reaches a predetermined temperature or higher, which causes depolarization, and a second heating step after the first heating step of irradiating at least the piezoelectric element with infrared rays to cause polarization in the piezoelectric layer and at the same time heating the adhesive member.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a piezoelectric device.

Background Art

[0002] In piezoelectric materials such as PZT (lead zirconate titanate), it is generally known that when heat is applied, the polarization state of the crystal is disturbed and the piezoelectric performance deteriorates. Specifically, PZT is a solid solution of lead titanate and lead zirconate and can take crystal structures such as tetragonal, rhombohedral, and cubic depending on the mixing ratio and temperature. The polarization direction and magnitude differ depending on the structure and the degree of atomic deviation. When the temperature of PZT is increased, it finally transitions to a cubic crystal (paraelectric state) without polarization. The temperature at which this paraelectric state occurs (Curie temperature) is known to vary depending on the manufacturing method (film quality) and is about 200 to 400°C.

[0003] Also, depolarization is known to occur even below the Curie temperature. The mechanism is not precisely understood, and there are theories such as that the strain due to the thermal expansion difference with the materials constituting the device affects the polarization state of PZT. However, it is presumed that when heated, the atoms in the crystal become more mobile, the crystal is deformed, and as a result, the polarization direction is disturbed for each crystal.

[0004] In order to solve the problem of depolarization occurring during reflow or the like when mounting a piezoelectric element, a method for manufacturing a piezoelectric element described in Patent Document 1 is known. The method for manufacturing a piezoelectric element in Patent Document 1 performs a polarization treatment in which an electric field is applied while heating the piezoelectric thin film to a temperature higher than the heating temperature during the reflow process when mounting the piezoelectric element on a circuit board or the like. The piezoelectric element manufactured by this method can avoid deterioration of piezoelectric characteristics even when heated by the reflow process for mounting on a circuit board or the like. Specific examples include an example of a polarization treatment in which an electric field of 10 V / μm is applied while heating the piezoelectric thin film to 240°C or higher, and an example in which a polarization treatment is performed by applying an electric field of 10 V / μm at room temperature and then an annealing treatment is performed at 240°C or higher.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-340631 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in the method for manufacturing piezoelectric elements described in Patent Document 1, the process is not easy when a polarization treatment is performed by applying an electric field while heating at a high temperature of 240°C or higher. Applying voltage at high temperatures makes it difficult to process a large number of piezoelectric elements. For example, when processing a wafer in which multiple piezoelectric elements are fabricated, the entire surface of the wafer must be heated and an electric field applied simultaneously. If there is a time difference between the heating and electric field application processes, thermal degradation will occur in the wafer while waiting for the electric field to be applied. In addition, in a high-temperature environment, resin tools cannot be used for handling piezoelectric elements, which increases the risk of damage to the individual elements.

[0007] On the other hand, the method described in Patent Document 1, which involves applying an electric field of 10 V / μm at room temperature to perform polarization treatment, followed by annealing treatment at 240°C or higher, is presumed to merely pre-degrade the piezoelectric element through thermal aging and not to maximize the piezoelectric properties of the piezoelectric element. Furthermore, while applying a voltage higher than the operating voltage range when driving the piezoelectric element is effective for electrical polarization treatment, there is a risk that high voltages will destroy crystal defects in the piezoelectric thin film, leading to an electrical short circuit.

[0008] The object of the present invention is to provide a method for manufacturing a piezoelectric device that can perform polarization processing without applying voltage. [Means for solving the problem]

[0009] One aspect of the present invention provides a method for manufacturing a piezoelectric device, which includes a mounting step of mounting a piezoelectric element including a piezoelectric layer onto a mounting substrate using an adhesive member, wherein the mounting step includes a heating step of heating the adhesive member and fixing or electrically connecting the piezoelectric element to the mounting substrate using the adhesive member, and the heating step includes a first heating step of heating the adhesive member and the piezoelectric element so that they reach a predetermined temperature or higher at which the piezoelectric layer depolarizes, and a second heating step after the first heating step of irradiating at least the piezoelectric element with infrared rays to cause polarization in the piezoelectric layer and simultaneously heating the adhesive member.

[0010] Another aspect of the present invention provides a method for manufacturing a piezoelectric device, which includes a mounting step of mounting a piezoelectric element including a piezoelectric layer onto a mounting substrate using an adhesive member, wherein the mounting step includes a heating step of heating the adhesive member and fixing or electrically connecting the piezoelectric element to the mounting substrate using the adhesive member, and the heating step includes a first heating step of heating the adhesive member and the piezoelectric element so that the piezoelectric layer reaches 100°C or higher, and a second heating step after the first heating step of irradiating at least the piezoelectric element with infrared rays and heating the adhesive member and the piezoelectric element so that the piezoelectric layer reaches 200°C or higher.

[0011] A further aspect of the present invention provides a method for manufacturing a piezoelectric device comprising a piezoelectric element including a piezoelectric layer, comprising: a first heating step of heating the piezoelectric element so that the piezoelectric layer reaches a predetermined temperature or higher, thereby causing depolarization; and a second heating step of irradiating the piezoelectric layer with infrared radiation after the first heating step to cause polarization in the piezoelectric layer. [Effects of the Invention]

[0012] According to this disclosure, it is possible to provide a method for manufacturing a piezoelectric device that can perform polarization processing without applying voltage. [Brief explanation of the drawing]

[0013] [Figure 1] A cross-sectional view showing the configuration of a piezoelectric device manufactured by the manufacturing method of Embodiment 1 of the present invention. [Figure 2] (a) A flowchart showing the manufacturing method of the piezoelectric device of Embodiment 1, and (b) A flowchart showing the manufacturing method of the piezoelectric device of the comparative example. [Figure 3] (a) A flowchart showing the mounting process of the manufacturing method of the piezoelectric device 1 of Embodiment 1, and (b) A flowchart of the mounting and evaluation performed to compare the effects of different manufacturing methods. [Figure 4] A cross-sectional view showing the configuration of the piezoelectric device 1 manufactured by the manufacturing method of Example 1. [Figure 5] (a) A graph showing the temperature profile of the heating step in the manufacturing method of Example 1 and Comparative Examples 1 and 2; (b) A graph showing the displacement of the piezoelectric device manufactured by the manufacturing method of Example 1 and Comparative Examples 1 and 2. [Figure 6] A graph showing the temperature profile of the heating step in the manufacturing methods of Example 2 and Comparative Example 3. [Figure 7] A graph showing the displacement of piezoelectric devices manufactured using the manufacturing methods of Example 2 and Comparative Example 3. [Figure 8] A graph showing the displacement of a piezoelectric device manufactured using the manufacturing method of Example 3. [Modes for carrying out the invention]

[0014] An embodiment of the present invention will be described below with reference to the drawings, but the scope of the present invention is not limited to the embodiment described herein, and various modifications can be made without departing from the spirit of the invention. Furthermore, if multiple upper and lower limits are given for a particular parameter, any combination of these upper and lower limits can be used to create a suitable numerical range.

[0015] <<Embodiment 1>> Figure 1 is a cross-sectional view of an example of a piezoelectric device manufactured using the manufacturing method of Embodiment 1. Figures 2(a) and 2(b) are flowcharts showing the manufacturing process of piezoelectric devices in this embodiment and a comparative example (conventional), and Figure 3(a) is a flowchart showing the detailed steps of the mounting process in this embodiment.

[0016] First, an example of a piezoelectric device manufactured by the method for manufacturing a piezoelectric device according to the present embodiment will be described using FIG. 1. The piezoelectric device 1 has a structure in which a piezoelectric element 100 is mounted on a mounting substrate 200, and is, for example, a MEMS (Micro Electro Mechanical Systems) device.

[0017] The piezoelectric element 100 includes a piezoelectric layer 10, a lower surface electrode 20 disposed on the lower surface (the surface on the mounting substrate 200 side) of the piezoelectric layer 10, an upper surface electrode 30 disposed on the upper surface of the piezoelectric layer 10, and a support 40 used as a support substrate when these are formed.

[0018] The piezoelectric layer 10 and the lower surface electrode 20 are provided with through-holes 60 penetrating therethrough. The end surface of the piezoelectric layer 10, the lower surface of the lower surface electrode 20, and the inner wall surface of the through-hole 60 are covered with an insulating film 50. The support 40 is configured such that the central portion of the piezoelectric layer 10 is removed and is disposed only at both ends. Thereby, the piezoelectric layer 10 is configured to be able to bend.

[0019] The mounting substrate 200 has a structure in which a mounting substrate electrode 210 is mounted on the upper surface of a base material 220. In the example of FIG. 1, the mounting substrate 200 is separated into a pair of base materials 220, and the mounting substrate electrodes 210 are respectively disposed on the separated mounting substrates 200. The piezoelectric element 100 is fixed to the mounting substrate electrodes 210 of the separated mounting substrates 200 at both ends thereof by an adhesive member 300 such as solder.

[0020] There are a pair of adhesive members 300. One adhesive member 300 is filled in the through-hole 60 and electrically connects the upper surface electrode 30 and the mounting substrate electrode 210. The other adhesive member 300 electrically connects the lower surface electrode 20 and the mounting substrate electrode 210 through a hole 61 provided in the insulating film 50.

[0021] The piezoelectric layer 10 is made of a ferroelectric material having a piezoelectric effect, such as PZT (lead zirconate titanate). The lower electrode 20 and upper electrode 30 can be made of any electrode material, such as Pt, Au, or Al. In particular, Pt is preferable to Au or Al because it has a higher transmittance of infrared light irradiated onto the piezoelectric layer 10 during the manufacturing process. Therefore, it is preferable to use Pt as the electrode material for the upper electrode 30 (in the case of upper irradiation) or the lower electrode 20 (in the case of lower irradiation) which is placed on the side that is irradiated with infrared light. It is even preferable that the Pt layer has a thickness of 200 nm or less.

[0022] The insulating film 50 can be, for example, SiO2, Si3N4, Al2O3, etc. The support 40 can be, for example, Si. In addition to solder, the adhesive member 300 can be a sintered material, a resin in which conductive particles such as silver paste are dispersed, etc.

[0023] Furthermore, the shape of the support 40 and the mounting substrate 200 are not limited to the shape in which they are arranged at both ends of the piezoelectric layer 10 as shown in Figure 1, but can be arranged and shaped in any way as long as the piezoelectric layer 10 has a deformable structure. For example, it is also possible to arrange the mounting substrate 200 at only one end of the piezoelectric layer 10 to create a cantilever shape that supports the piezoelectric element 100 in a cantilever configuration.

[0024] The adhesive member 300 does not have to serve both to fix the piezoelectric element 100 to the mounting substrate 200 and to provide electrical conductivity; it may perform only one of these functions.

[0025] <Operation of piezoelectric device 1> When operating the piezoelectric device 1 as an actuator, a voltage is applied between the upper electrode 30 and the lower electrode 20 via the adhesive member 300 from the mounting substrate electrode 210 of the mounting substrate 200. As a result, an electric field is applied to the piezoelectric layer 10 in the thickness direction, causing the piezoelectric layer 10 to deform (bend).

[0026] On the other hand, the piezoelectric device 1 can also be used as a force or displacement detection device. When an external force is applied to the piezoelectric layer 10 and deformation (bending) occurs in the piezoelectric layer 10, a voltage is generated between the upper electrode 30 and the lower electrode 20. By detecting the generated voltage via the mounting substrate electrode 210, the deformation can be detected as a voltage.

[0027] <Manufacturing method for piezoelectric device 1> The manufacturing method for the piezoelectric device 1 will be explained using Figures 2(a) and 3(a).

[0028] (Step S301) First, the piezoelectric element 100 is manufactured. The piezoelectric element 100 can be manufactured by known methods.

[0029] A brief explanation of a method for manufacturing the piezoelectric element 100 is provided. A support substrate, which will later become the support 40, is prepared, and the upper electrode 30, the piezoelectric layer 10, and the lower electrode 20 are deposited in order on the surface that will become the lower surface of the support 40.

[0030] Any method may be used for film formation, but it is preferable to form the piezoelectric layer 10 by arc discharge ion plating (ADRIP) because it effectively obtains polarization by infrared irradiation.

[0031] These films are processed into the desired shape shown in Figure 1 using conventional processing methods such as photolithography or etching. Through-holes 60 are also formed simultaneously during this process. Note that film deposition and processing by photolithography, etc., may be performed after all three layers—the upper electrode 30, the piezoelectric layer 10, and the lower electrode 20—have been laminated, or the processing may be performed after each layer has been deposited.

[0032] Next, an insulating film 50 is deposited and covered on the lower surface of the lower electrode 20, the upper electrode 30, the piezoelectric layer 10, the end face of the lower electrode 20, and inside the through hole 60. Subsequently, the deposited insulating film 50 is etched to expose the upper electrode 30 inside the through hole 60 and to form a hole 61 that reaches the lower electrode 20.

[0033] Finally, a portion of the support substrate is removed in the thickness direction from the side that will become the top surface to form the support body 40.

[0034] The piezoelectric element 100 is manufactured as described above.

[0035] (Step S302) In step S302, a mounting process is performed in which the piezoelectric element 100, including the piezoelectric layer 10, is mounted on the mounting substrate 200 using a pair of adhesive members 300. First, a mounting substrate 200 is prepared, on which a pair of mounting substrate electrodes 210 are formed on the upper surface of a base material 220. The pair of mounting substrate electrodes 210 correspond to the positions of the through-hole 60 and hole 61 of the piezoelectric element 100.

[0036] Solder or an adhesive material 300 such as a resin containing dispersed conductive particles is applied to the pair of mounting substrate electrodes 210 on the mounting substrate 200, or to the positions of the through-hole 60 and hole 61 of the piezoelectric element 100, and the lower surface of the piezoelectric element 100 is mounted on the upper surface of the mounting substrate 200.

[0037] Next, a heating process is performed to heat the adhesive member, fixing the piezoelectric element 100 to the mounting substrate 200 with the adhesive member 300 and making it electrically conductive. In this embodiment, the heating process is divided into two stages, a first heating step and a second heating step, as shown in Figure 3(a). In this embodiment, in the second heating step, polarization is generated in the piezoelectric layer 10 by irradiating it with infrared light without applying an electric field.

[0038] ((1st heating step S321)) First, the first heating step involves heating the adhesive member 300 and the piezoelectric element 100 so that the piezoelectric layer 10 reaches a predetermined temperature or higher that causes depolarization (step S321). Preferably, the first heating step involves heating the piezoelectric layer 10 to a temperature of 100°C or higher.

[0039] The heating method for the first heating step involves irradiating the adhesive member 300 and the piezoelectric element 100 with infrared rays or by heat conduction using an oven or hot plate.

[0040] In the first heating step, it is sufficient for the piezoelectric layer 10 to be heated to a temperature above which depolarization occurs. However, if the heating in the first heating step is performed by infrared irradiation, it is necessary to suppress the heater output, i.e., the heating temperature, so that the amount of infrared irradiation to the piezoelectric layer 10 does not become too large. One example is a temperature of 100°C or higher but less than 200°C.

[0041] When the first heating step is performed by heat conduction, the adhesive member 300 and the piezoelectric element 100 are heated so that the piezoelectric layer 10 reaches a temperature higher than the temperature at which depolarization occurs. Therefore, the first heating step causes depolarization in the piezoelectric layer 10.

[0042] ((2nd heating step S322)) The second heating step involves irradiating at least the piezoelectric element 100 with infrared light after the first heating step to heat the piezoelectric layer 10 and generate polarization. Simultaneously with heating the piezoelectric layer 10 with infrared light, the adhesive member 300 is also heated to fix the piezoelectric element 100 to the mounting substrate 200 using the adhesive member 300. It is preferable that the second heating step heats the piezoelectric layer 10 to 200°C or higher.

[0043] For example, the infrared radiation in the second heating step is irradiated by a halogen lamp. The amount of infrared radiation irradiated onto the piezoelectric layer is affected by the specifications of the heating equipment and the configuration of the device being heated, so the achievable temperature and heating time are not limited to those exemplified.

[0044] Thus, in this embodiment, by sequentially performing a first heating step and a second heating step of irradiating with infrared light, and by heating with the adhesive member 300 to fix the piezoelectric element 100 to the mounting substrate 200, the piezoelectric layer 10 can be polarized after the completion of the mounting process without applying an electric field to the piezoelectric layer 10 during the mounting process.

[0045] (Step S303) After the assembly process, the piezoelectric device 1 can be operated without performing any separate polarization treatment.

[0046] As described above, in this embodiment, the polarization of the piezoelectric layer 10, which is disturbed by heating during the mounting process, can be depolarized by the end of the mounting process without performing a polarization treatment process.

[0047] Figure 2(b) shows a conventional process as a comparative example. As shown in Figure 2(b), in the conventional process, when a normal mounting process such as solder reflow (step S311) is performed, the polarization of the piezoelectric layer 10 is disturbed after mounting. Therefore, a polarization treatment process (step S312) is performed thereafter, in which high-temperature heating is performed while applying an electric field, and after the polarization is completed, operation (step S313) is performed.

[0048] Therefore, the manufacturing method of the piezoelectric device 1 in this embodiment eliminates the need for polarization treatment requiring electric field application, resulting in a simpler process. Furthermore, since there is no need for equipment that heats to high temperatures while applying an electric field, the design of mass production equipment becomes easier.

[0049] <<Embodiment 2>> In Embodiment 1, as shown in Figures 2(a) and 3(a), the heating process (S321, S322) in the mounting process (S302) was configured to perform mounting and polarization of the piezoelectric layer 10 simultaneously. However, this embodiment is not limited to this process.

[0050] It is also possible to perform the heating process (S321, S322) at a different time than the mounting process (S302) to generate polarization of the piezoelectric layer 10. In other words, the heating process (S321, S322) can be performed as a polarization process that does not require the application of an electric field. [Examples]

[0051] Examples of the present invention will be described below.

[0052] <Example 1> As Example 1, a piezoelectric device 1 was manufactured using the manufacturing method of Embodiment 1.

[0053] The piezoelectric device 1 manufactured according to Example 1 differs from the piezoelectric device 1 in Figure 1. As shown in Figure 4, the support 40 of the piezoelectric element 100 is provided only at one end of the piezoelectric layer 10, and cantilever-supports the piezoelectric layer 10, the upper electrode 30, and the lower electrode 20. Furthermore, the support 40 is positioned closer to the mounting substrate 200 than the lower electrode 20. The lower surface of the support 40 is fixed to the upper surface of the base material 220 of the mounting substrate 200 by an adhesive member 300. A pair of mounting substrate electrodes 210 are arranged on the upper surface of the base material 220 of the mounting substrate 200. The pair of mounting substrate electrodes 210 are connected to the upper electrode 30 and the lower electrode 20, respectively, by bonding wires 310.

[0054] The piezoelectric layer 10 is a 1.5 μm thick PZT (lead zirconate titanate) film, deposited by arc discharge ion plating (ADRIP). The upper electrode 30 and lower electrode 20 are both 0.1 μm thick platinum (Pt) films, deposited by sputtering. The support 40 is made of an SOI wafer with an active layer thickness of 10 μm and a support layer thickness of 300 μm.

[0055] In the piezoelectric device 1 shown in Figure 4, the adhesive member 300 fixes the piezoelectric element 100 to the mounting substrate 200, and electrical conductivity is provided by the bonding wire 310.

[0056] The manufacturing process will now be explained. The manufacturing process is based on Figure 2(a), but in order to more accurately evaluate the polarization effect, the mounting process S302 was performed using the process shown in Figure 3(b) instead of the process shown in Figure 3(a).

[0057] (Manufacturing process S301 for piezoelectric element 100) In step S301, the piezoelectric element 100 was manufactured. The piezoelectric element 100 in Figure 4 differs from that in Figure 1 in the shape and orientation of the support 40, but it was manufactured by a known manufacturing process as described in the embodiment.

[0058] (Implementation process S302) Next, the implementation process (S302) will be described. In Example 1, steps S331 to S334 in Figure 3(b) were performed as the implementation process (S302).

[0059] (Implementation process S331 for measurement) First, in order to more accurately measure the initial polarization characteristics of the piezoelectric element 100, the piezoelectric element 100 was mounted on the mounting substrate 200 using a conventional method. Specifically, a silicone-based thermosetting adhesive was applied as an adhesive member 300 onto the base material 220 of the mounting substrate 200, and the support 40 of the piezoelectric element 100 was mounted on it. The adhesive was then cured by heating in an oven (Advantech DRM320DA) at 150°C for 2 hours. After that, the upper electrode 30 and lower electrode 20 were connected to the mounting substrate electrode 210 using bonding wires 310. The stage temperature (directly below the mounting substrate 200) during wire bonding was 90°C. (Polarization treatment S332) Because the polarization of the piezoelectric element 100 was disturbed by heating during step S331, a piezoelectric element 100 polarization treatment was performed (heating at 120°C for 5 minutes while applying an electric field of 10 V / μm per unit thickness of the piezoelectric layer 10). This restored the polarization of the piezoelectric layer 10 to its initial state before heating.

[0060] (1st heating step S333) Next, as the first heating step, the mounting substrate 200, adhesive member 300, and piezoelectric element 100 were heated for 60 seconds using a hot plate (manufactured by AS ONE Corporation) at the temperature profile [A] shown in Figure 5(a), reaching a temperature of 260°C, which is assumed to be the temperature for lead-free solder mounting. After heating, they were left at room temperature for about 1 hour.

[0061] (Second heating step S334) Next, as a second heating step, infrared radiation (peak wavelength 1.1 μm) emitted from a high-temperature observation device equipped with a halogen heater (model SK-8000, manufactured by Sanyo Seikou Co., Ltd.) was irradiated onto the piezoelectric element 100, and the temperature was raised to 260°C for 60 seconds according to the temperature profile [B] shown in Figure 5(a).

[0062] Furthermore, the upper electrode 30 and lower electrode 20, which are Pt films, have a lower reflectivity and a thin thickness of 0.1 μm compared to Au and Al, so it is thought that a certain amount of infrared radiation reaches the piezoelectric layer 10, which is a PZT film, during the second heating process. In addition, the edges of the piezoelectric layer 10 are not covered by the upper electrode 30 and lower electrode 20, so infrared radiation reaches the piezoelectric layer 10 directly.

[0063] By performing each of the above steps, the adhesive member 300 was cured and the piezoelectric layer 10 was polarized, thereby manufacturing the piezoelectric device 1 of Example 1.

[0064] <Comparative Example 1> As Comparative Example 1, in the mounting process (S302), only the first heating step (S333), which involves heating with a hot plate, was performed, and the second heating step was omitted. The other steps were carried out in the same manner as in Example 1 to manufacture the piezoelectric device of Comparative Example 1.

[0065] <Comparative Example 2> As Comparative Example 2, in the mounting process (S302), the first heating process was omitted, and only the second heating process (S334), which involves heating by infrared irradiation, was performed. The other processes were carried out in the same manner as in Example 1 to manufacture the piezoelectric device of Comparative Example 1.

[0066] <Rating> A predetermined electric field was applied to the piezoelectric material layer 10 of the piezoelectric material device 1 manufactured according to Example 1 and the piezoelectric material devices of Comparative Examples 1 and 2 by applying a predetermined voltage between the lower electrode 20 and the upper electrode 30 from the mounting substrate electrode 210. The displacement generated in the piezoelectric material layer 10 was measured using a Doppler vibrometer (manufactured by POLYTEC). The measured displacement is shown in Figure 5(b). The measured displacement indicates the polarization state.

[0067] Furthermore, as reference 1, the piezoelectric device 1 immediately after step S332 was subjected to a predetermined voltage, and the displacement of the piezoelectric layer 10 was measured.

[0068] Furthermore, as a reference (2), a piezoelectric device 1 in which the piezoelectric layer 10 was subjected to a predetermined polarization treatment again after the mounting process was similarly subjected to a predetermined voltage and the displacement of the piezoelectric layer 10 was measured.

[0069] The displacement amounts of the piezoelectric devices of References 1 and 2 are also shown in Figure 5(b). As is clear from Figure 5(b), the piezoelectric device of Comparative Example 1, in which only the first heating step was performed using a hot plate, and the piezoelectric device of Comparative Example 2, in which only the second heating step was performed using infrared heating, both showed a displacement amount of approximately 10% lower compared to the displacement amount of the piezoelectric layer 10 immediately after polarization treatment before implementation in Reference 1.

[0070] In contrast, the piezoelectric device 1, which was heated on a hot plate in the first heating step, left at room temperature for about an hour, and then heated to 260°C using infrared radiation in the second heating step, showed a displacement that was almost the same as the displacement of the piezoelectric layer 10 immediately after polarization treatment in Reference 1.

[0071] In other words, it was confirmed that the method for manufacturing the piezoelectric device of this embodiment 1 allows for polarization of the piezoelectric layer 10 solely through a heating step, without applying an electric field during the mounting process.

[0072] Furthermore, as a reference 2, the piezoelectric device 1 of Example 1 and the piezoelectric devices of Comparative Examples 1 and 2, after undergoing a predetermined process again after the mounting process, showed that the displacement amount of the piezoelectric device 1 of Example 1 was further significantly improved, as shown in Figure 5(b).

[0073] From these findings, it can be inferred that irradiating the piezoelectric layer 10 with infrared light causes some kind of modification to the piezoelectric material (PZT) constituting the piezoelectric layer 10. Furthermore, it can be inferred that irradiating the piezoelectric material (PZT), which has been thermally depolarized in the first heating step, with infrared light in the second heating step increases the modification effect and generates polarization.

[0074] <Example 2> The manufacturing method for the piezoelectric device 1 of Example 2 will be described.

[0075] In Example 2, a piezoelectric device 1 with the structure shown in Figure 1 was manufactured.

[0076] The piezoelectric layer 10 is a 1.5 μm thick PZT (lead zirconate titanate) film, deposited by arc discharge ion plating (ADRIP). The upper electrode 30 and lower electrode 20 are both 0.1 μm thick Pt films, deposited by sputtering. The support 40 is made of an SOI wafer with an active layer thickness of 10 μm and a support layer thickness of 300 μm. SnAgCu solder was used for the adhesive member 300.

[0077] The manufacturing process will now be explained. The manufacturing process is the same as the flow charts in Figures 2(a) and 3(b).

[0078] The first and second heating steps (steps S333 and S334) were both performed by infrared irradiation.

[0079] (Manufacturing process S301 for piezoelectric element 100) In step S301, the piezoelectric element 100 shown in Figure 1 was manufactured by a known manufacturing process as described in the embodiment.

[0080] (Implementation process S302) Next, the implementation process (S302) will be described. In Example 2, steps S331 to S334 in Figure 3(b) were performed as the implementation process (S302).

[0081] (Implementation process S331 for measurement) First, in order to more accurately measure the polarization characteristics of the piezoelectric element 100, the piezoelectric element 100 was mounted on the mounting substrate 200 using a conventional method. Specifically, SnAgCu solder paste was applied as an adhesive material 300 onto the mounting substrate electrodes 210 of the mounting substrate 200, and the support 40 of the piezoelectric element 100 was mounted on it. The substrate 200 and the piezoelectric element 100 were then heated on a hot plate to a temperature of 260°C and heated for 60 seconds to bond them together. (Polarization treatment S332) As the polarization of the piezoelectric element is disturbed by the implementation of step S331, a polarization treatment is performed (heating at 120°C for 5 minutes while applying an electric field of 10V / μm per thickness of the piezoelectric layer 10) to return the piezoelectric layer 10 to its initial state before heating.

[0082] (1st heating step S333) Infrared radiation (peak wavelength 1.1 μm) emitted from a high-temperature observation device equipped with a halogen heater (Sanyo Seikou Co., Ltd., model number SK-8000) was irradiated onto the piezoelectric element 100 and heated for 2 minutes at either 120°C, 150°C, or 180°C (see Figure 6).

[0083] (Second heating step S334) Next, as a second heating step, infrared radiation (peak wavelength 1.1 μm) emitted from the same high-temperature observation device as in the first heating step was irradiated onto the piezoelectric element 100, and it was heated at 260°C for 60 seconds (see Figure 6).

[0084] Through the heating process described above, the adhesive member 300 was welded together, and at the same time, the piezoelectric layer 10 was polarized, thereby manufacturing the piezoelectric device 1 of Example 2.

[0085] <Comparative Example 3> As Comparative Example 3, in the mounting process (S302), the first heating process (S333) of Example 2 was omitted, and only the second heating process (S334) was performed. The other processes were carried out in the same manner as in Example 2 to manufacture the piezoelectric device of Comparative Example 3.

[0086] <Rating> The displacements in the piezoelectric layer 10 of Example 2 and Comparative Example 3 were measured in the same manner as in Example 1. The measured displacement amounts are shown in Figure 7. In Figure 7, the displacement amount of the piezoelectric device 1 immediately after a predetermined polarization treatment was applied to the piezoelectric layer 10 to equalize the polarization state of the piezoelectric layer 10 before the mounting process was set to 100%.

[0087] As shown in Figure 7, the piezoelectric device 1 manufactured in Example 2, regardless of the temperature of the first heating step (120°C, 150°C, 180°C), showed a larger displacement than the piezoelectric device of Comparative Example 3, which did not undergo the first heating step.

[0088] <Example 3> The manufacturing method for the piezoelectric device 1 of Example 3 will be described.

[0089] In Example 3, a piezoelectric device 1 with the structure shown in Figure 1 was manufactured, similar to Example 2.

[0090] The difference between Example 3 and Example 2 is that the first heating step was fixed at a temperature of 150°C for 2 minutes, while the second heating step was performed at a temperature of 200°C, 230°C, or 260°C for 1 minute.

[0091] <Rating> The displacement generated in the piezoelectric layer 10 of Example 3 was measured in the same manner as in Example 1. The measured displacement is shown in Figure 8. The displacement of the piezoelectric device 1 of Example 3, manufactured with the second heating step temperature set to 260°C, is shown as 100%. As is clear from Figure 8, even when the second heating step temperature was lowered to 200°C or 230°C, displacement equivalent to or greater than that observed with the second heating step temperature of 260°C was observed.

[0092] Therefore, even if the temperature of the second heating step is lowered to 200°C or 230°C, polarization can be generated in the piezoelectric layer 10 by the mounting process, using low-temperature solder or thermosetting adhesive as the adhesive member 300, in addition to materials that require high-temperature heat treatment such as lead-free solder. [Explanation of Symbols]

[0093] 1. Piezoelectric device 10 Piezoelectric layer 20 Bottom electrode 30 Top electrode 40 Support 50 insulating film 60 Through Hole 61 holes 100 Piezoelectric element 200 mounted circuit boards 210 Electrodes on mounting substrates 220 Base material 300 Adhesive Members 310 Bonding Wire

Claims

1. A method for manufacturing a piezoelectric device, which includes a mounting step of mounting a piezoelectric element including a piezoelectric layer onto a mounting substrate using an adhesive member, The mounting process includes a heating step of heating the adhesive member and fixing or electrically connecting the piezoelectric element to the mounting substrate by the adhesive member, The aforementioned heating step is A first heating step involves heating the adhesive member and the piezoelectric element so that the piezoelectric layer reaches a predetermined temperature or higher that causes depolarization. A method for manufacturing a piezoelectric device, characterized by including a second heating step after the first heating step, in which infrared light is irradiated at least the piezoelectric element to generate polarization in the piezoelectric layer and at the same time the adhesive member is heated.

2. A method for manufacturing a piezoelectric device according to claim 1, characterized in that the first heating step is a step of heating the piezoelectric layer so that it reaches 100°C or higher.

3. A method for manufacturing a piezoelectric device according to claim 1, characterized in that the second heating step is a step of heating the piezoelectric layer to a temperature of 200°C or higher.

4. A method for manufacturing a piezoelectric device according to claim 1, characterized in that the infrared radiation is irradiated from a halogen lamp in the second heating step.

5. A method for manufacturing a piezoelectric device according to claim 1, characterized in that the first heating step involves heating the adhesive member and the piezoelectric element by irradiating them with infrared rays or by heat conduction.

6. A method for manufacturing a piezoelectric device according to claim 5, characterized in that when infrared light is irradiated in the first heating step, the adhesive member and the piezoelectric element are heated at a temperature higher than the temperature at which the piezoelectric layer depolarizes, and lower than the temperature at which the second heating step occurs.

7. A method for manufacturing a piezoelectric device according to claim 6, characterized in that the temperature range is 100°C or more and less than 200°C.

8. A method for manufacturing a piezoelectric device according to claim 5, characterized in that, when the first heating step is performed by heat conduction, the adhesive member and the piezoelectric element are heated so that the piezoelectric layer reaches a temperature higher than the temperature at which depolarization occurs.

9. A method for manufacturing a piezoelectric device according to claim 1, characterized in that the piezoelectric element has a platinum electrode arranged on at least one of the upper and lower sides of the piezoelectric layer.

10. A method for manufacturing a piezoelectric device according to claim 1, wherein the piezoelectric layer is made of PZT.

11. A method for manufacturing a piezoelectric device according to claim 10, characterized in that the PZT of the piezoelectric layer is formed by an arc discharge ion plating method.

12. A method for manufacturing a piezoelectric device, which includes a mounting step of mounting a piezoelectric element including a piezoelectric layer onto a mounting substrate using an adhesive member, The mounting step includes a heating step of heating the adhesive member and fixing or electrically connecting the piezoelectric element to the mounting substrate by the adhesive member, The aforementioned heating step is A first heating step involves heating the adhesive member and the piezoelectric element so that the piezoelectric layer reaches 100°C or higher. A method for manufacturing a piezoelectric device, characterized by including a second heating step after the first heating step, in which infrared light is irradiated to at least the piezoelectric element to heat the adhesive member and the piezoelectric element so that the piezoelectric layer reaches 200°C or higher.

13. A method for manufacturing a piezoelectric device equipped with a piezoelectric element including a piezoelectric layer, A first heating step involves heating the piezoelectric element so that the piezoelectric layer reaches a predetermined temperature or higher that causes depolarization. A method for manufacturing a piezoelectric device, characterized by including a second heating step after the first heating step, in which infrared rays are irradiated onto the piezoelectric layer to generate polarization in the piezoelectric layer.

Images