JP4590871B2 - Method for forming piezoelectric element - Google Patents

Description

The present invention relates to a method of forming a piezoelectric element on a substrate having an opening on one main surface side, such as a piezoelectric element having a diaphragm portion.

  As a conventional film forming method of interest to the present invention, that is, a method of forming a film on a substrate having an opening on one main surface side, such as a piezoelectric element having a diaphragm portion, the method described in Patent Document 1 is described. Although there are some, the conventional film forming method including the one described in Patent Document 1 generally adopts the following film forming method.

That is, when a thin film such as a SiO ₂ thin film, a ZnO piezoelectric thin film, or an electrode film is formed on a substrate having an opening on one main surface side, such as a piezoelectric element having a diaphragm, sputtering, lift-off evaporation And a thin film method such as an electron beam evaporation method is used. Thereby, a piezoelectric element having a diaphragm portion is manufactured (hereinafter referred to as Conventional Technology 1).

  However, the method described in the prior art 1 has the following problems.

  In the method described in the prior art 1, a piezoelectric element having a diaphragm portion manufactured by using this thin film construction method has a very small piezoelectric film, so that a driving force as a piezoelectric body is small and a large driving force is required. Piezoelectric elements such as sounders, buzzers and pumps could not be easily manufactured.

In addition, since the surface of a film such as a piezoelectric thin film or SiO ₂ thin film formed by using the above thin film method is too smooth, the contact area between the above-mentioned film and the electrode film is reduced, and sufficient bonding strength can be obtained. I could not.

  Furthermore, when this thin film construction method is used, the raw materials used and the equipment used for the thin film construction method are very expensive, which is a serious problem in practice.

  Therefore, the present inventors use a thick film method such as an inexpensive screen printing method to form a film on a substrate having an opening on one main surface side, such as a piezoelectric element having a diaphragm portion. However, studies have been made as to whether or not a piezoelectric element that requires a large driving force can be manufactured.

  For example, the present inventors produce a mold having the same shape as the opening of the substrate, fit the mold into the opening of the substrate, on the main surface opposite to the opening of the substrate, A method of forming a film using a screen printing method has been proposed (hereinafter referred to as Conventional Technology 2).

In addition, a thick film is formed on a smooth substrate having no opening by using a screen printing method, and thereafter, a sandblast is formed on the substrate surface opposite to the substrate surface on which the film is formed. A method of forming an opening by performing such fine processing has been proposed. (Hereinafter referred to as Conventional Technology 3).
JP 2001-211053 A

  However, the methods of the prior art 2 and the prior art 3 have the following problems.

  In Prior Art 2, it is necessary to provide a certain degree of tolerance between the size of the mold and the opening of the substrate in order to easily fit the substrate into the mold. In this case, when the film is formed by screen printing, the adhesion between the substrate and the mold is not sufficient, so the mold is removed from the opening of the substrate due to the viscous force of the material paste for film formation, and the substrate itself Often it was damaged. Conversely, if there is almost no tolerance between the size of the mold and the opening of the board, the board itself is damaged by the load applied when the mold is inserted into the board or removed from the board. The probability is very high.

  On the other hand, in the prior art 3, the substrate surface on the side on which the thick film is formed has a level difference due to the formation of the thick film. It was seen. In addition, when fine processing is performed using a chemical etching method using an alkaline solution, the thick film itself is dissolved by the solution, and thus it is very difficult to protect the thick film.

Therefore, in order to solve the above problems, an inexpensive piezoelectric film such as a screen printing method is used without damaging a substrate having an opening on one main surface side, such as a piezoelectric element having a diaphragm portion. It is an object of the present invention to provide a method capable of forming a piezoelectric element using a forming method.

According to a method for forming a piezoelectric element on a substrate according to the present invention, in a substrate having an opening on the second main surface side facing the first main surface, the opening is filled and cured with a liquid material, The height of the surface of the opening filled with the cured liquid material is set to the same position as the substrate surface on the second main surface side, and the piezoelectric film is formed on the first main surface side of the substrate. After the formation, the hardened liquid material is removed from the opening of the substrate.

  The liquid material is preferably an acrylic resin or a silicon resin.

In the method for forming a piezoelectric element according to the present invention, the opening of the substrate is filled and cured with a liquid material, and the height of the surface of the opening filled with the cured liquid material is the second main surface. Since it is located at the same position as the substrate surface on the side, excellent adhesion can be obtained without a gap between the cured liquid material and the substrate.
Accordingly, the cured liquid material is not peeled off from the substrate during screen printing, so that the piezoelectric film can be formed without damaging the substrate.

That is, a piezoelectric film can be formed by using an inexpensive method such as a screen printing method without damaging a substrate having an opening on one main surface side such as a piezoelectric element having a diaphragm portion. There is an advantage that you can.

  In particular, it is an effective method for manufacturing elements that require a large driving force, such as sounders, buzzers, and pumps, and it is possible to sufficiently secure the bonding strength between a film such as a piezoelectric film and an electrode film. Become.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a method for forming a piezoelectric element on a substrate according to the invention will be described in detail with reference to the drawings.

The case where this embodiment can be applied is a particularly effective method when a piezoelectric film is formed on a substrate having an opening on one main surface side, such as a piezoelectric element having a diaphragm. However, the present invention is applicable even when the substrate having the opening on the one main surface side is replaced with a substrate having some unevenness on the surface.

FIG. 1 is a cross-sectional view showing a standard flow of a method for forming a piezoelectric element according to the present invention.
The object to form the piezoelectric film is a substrate having an opening on one main surface side, such as a piezoelectric element having a diaphragm.

First, a substrate 1 having a predetermined thickness, for example, a Si substrate having a SiO ₂ layer formed on the entire surface is prepared. [Refer to (1) in Fig. 1]
Next, the opening 2 is formed in the second main surface 1b (hereinafter referred to as a back surface) of the substrate 1, and a Si substrate having the opening is prepared. For example, it is manufactured as follows. The back surface 1b of the substrate 1 is subjected to resist patterning using a photolithographic technique, and the portion of the SiO ₂ layer used as the opening is etched with a buffered hydrofluoric acid solution (hereinafter referred to as a BHF solution). Then, a mask for substrate etching is formed. Then, the back surface 1b of the substrate 1 is chemically etched using, for example, a tetramethylammonium hydroxide solution (hereinafter abbreviated as TMAH solution) to form an opening 2 having a desired thickness, for example, 50 μm. To do. Incidentally, after this step, by a sputtering method, for example it may be imparted to the intermediate layer and the Pt electrode layer of Al ₂ O _3. In this case, it should be noted that heat treatment conditions that sufficiently secure the bondability between the Si substrate and the Al ₂ O ₃ layer and the bondability between the Al ₂ O ₃ layer and the Pt electrode layer are adopted. [See (2) in Fig. 1]
As described above, a Si substrate having an opening is prepared.

Next, a liquid material, for example, a liquid silicon resin or a liquid acrylic resin, which will be described later, is filled in the opening 2 formed on the back surface 1b of the substrate 1 and cured under a desired condition. So that the height of the surface of the opening 2 filled in is the same position as the substrate surface on the back surface side.
Thereby, the opening part 2 is reinforced.
[Refer to (3) in FIG. 1] Then, on the first main surface (hereinafter referred to as a front surface) 1a side of the substrate 1, a desired film, for example, a piezoelectric body, an electrode, or the like, is used by screen printing. The film is formed.
Note that, as will be described later, there are some differences in the process of firing the printed film depending on the resin used.
[Refer to (4) in FIG. 1] Next, the resin filled and cured in the opening 2 formed on the back surface 1b of the substrate 1 is removed.
As will be described later, there are some differences in the process depending on the resin used.
[Refer to (5) in FIG. 1] As described above, the opening of the substrate is filled and hardened with the liquid material, and the height of the surface of the opening filled with the liquid material is the substrate on the back surface side. Since the position is the same as the surface, excellent adhesion can be obtained without a gap between the liquid substance and the substrate.
Accordingly, the liquid material does not peel from the substrate during screen printing, and thus the piezoelectric film can be formed without damaging the substrate.

1 shows an embodiment relating to a method of forming a piezoelectric element according to the present invention.
In Example 1, a liquid silicone resin is used as the filling resin shown below.

First, for example, a Si substrate having a thickness of 200 μm is prepared with a SiO ₂ layer formed on the entire surface thereof.

Next, the back surface of the Si substrate is subjected to resist patterning using a photolithographic technique, and the SiO ₂ layer at the portion to be the opening is etched with a BHF solution to form a mask for Si etching. .

  Then, the back surface of the Si substrate is chemically etched using a TMAH solution to form an opening having a desired thickness, for example, 50 μm.

Next, for example, an Al ₂ O ₃ intermediate layer is applied to the front surface side of the Si substrate by sputtering, and heat treatment is performed at 950 ° C., for example, to form a fired film of the intermediate layer. Incidentally, the heat treatment conditions, the bonding strength between the Si substrate and the Al ₂ O ₃ layer have adopted sufficient can condition.

Next, for example, a Pt electrode layer is provided on the Al ₂ O ₃ layer by sputtering, and heat treatment is performed at 950 ° C., for example, to form a fired film of the Pt electrode layer. The heat treatment conditions are such that the bonding strength between the Al ₂ O ₃ layer and the Pt electrode layer can be sufficiently secured.

  As described above, a Si substrate having an opening is prepared.

  Next, the opening formed on the back surface side of the Si substrate is filled with a liquid silicon-based resin, for example, heated and cured at 150 ° C. for 10 minutes, and filled with the liquid silicon-based resin. The height of the surface of the opening is set to the same position as the substrate surface on the back surface side. Thereby, an opening part is reinforced.

Thereafter, a piezoelectric paste as shown below is applied to the front surface side of the Si substrate using a screen printing method to give an unfired film of the piezoelectric layer. The piezoelectric paste is a paste containing crystal powder, vehicle, and solvent. Examples of the crystal powder include 97% by weight of a raw material powder containing 85 mol% of Pb (Zr, Ti) O _{3 and} 15 mol% of Pb (Zn _1/3 Nb _2/3 ) O ₃ , A piezoelectric powder containing 2% by weight of Bi ₂ O ₃ powder and 1% by weight of ZnO powder is used. The vehicle uses, for example, an ethyl cellulose binder, and the solvent uses an organic solvent such as diethylene glycol monobutyl ether.

  Next, the liquid silicon resin filled and heat-cured in the opening formed on the back surface side of the Si substrate is removed by manually scraping and peeling. Note that when the resin is filled, if the release agent is applied to the wall surface of the opening, the removal of the liquid silicon-based resin becomes easier.

  After that, the Si substrate is fired to form a fired film of a piezoelectric layer having a thickness of, for example, 10 μm.

As described above, the opening of the substrate is filled and cured with the liquid material, and the height of the surface of the opening filled with the liquid material is set at the same position as the substrate surface on the back surface side. Therefore, excellent adhesion can be obtained without a gap between the liquid substance and the substrate.
Accordingly, since the liquid substance does not peel from the substrate during screen printing, the piezoelectric film can be formed without damaging the substrate.

1 shows an embodiment relating to a method of forming a piezoelectric element according to the present invention.
In Example 2, a liquid acrylic resin is used as the filling resin shown below.

First, for example, a Si substrate having a thickness of 200 μm, for example, is prepared having a SiO ₂ layer formed on the entire surface thereof.

Next, the back surface of the Si substrate is subjected to resist patterning using a photolithographic technique, and the SiO ₂ layer at the portion to be the opening is etched with a BHF solution to form a mask for Si etching. .

  Then, the back surface of the Si substrate is chemically etched using a TMAH solution to form an opening having a desired thickness, for example, 50 μm.

Next, for example, an Al ₂ O ₃ intermediate layer is applied to the front surface side of the Si substrate by sputtering, and heat treatment is performed at 950 ° C., for example, to form a fired film of the intermediate layer. Incidentally, the heat treatment conditions, the bonding strength between the Si substrate and the Al ₂ O ₃ layer have adopted sufficient can condition.

Next, a Pt electrode layer is provided on the Al ₂ O ₃ layer by a sputtering method, and heat treatment is performed at 950 ° C., for example, to form a fired film of the Pt electrode layer. The heat treatment conditions are such that the bonding strength between the Al ₂ O ₃ layer and the Pt electrode layer can be sufficiently secured.

  As described above, a Si substrate having an opening is prepared.

  Next, a liquid acrylic resin is filled in the opening formed on the back side of the Si substrate and cured by UV exposure, and the height of the surface of the opening filled with the liquid silicon resin is filled. Is set to the same position as the substrate surface on the back surface side. Thereby, an opening part is reinforced.

Thereafter, a piezoelectric paste as shown below is applied to the front surface of the Si substrate by screen printing to give an unfired film of the piezoelectric layer. The piezoelectric paste is a paste containing crystal powder, vehicle, and solvent. Examples of the crystal powder include 97% by weight of a raw material powder containing 85 mol% of Pb (Zr, Ti) O _{3 and} 15 mol% of Pb (Zn _1/3 Nb _2/3 ) O ₃ , A piezoelectric powder containing 2% by weight of Bi ₂ O ₃ powder and 1% by weight of ZnO powder is used. The vehicle uses, for example, an ethyl cellulose binder, and the solvent uses an organic solvent such as diethylene glycol monobutyl ether.

  Next, the Si substrate is dried at 100 ° C. for 10 minutes, and then heated at about 450 ° C., for example, to remove the liquid acrylic resin filled and cured in the opening formed on the back surface of the Si substrate. To do. It has been confirmed that heating under conditions of around 450 ° C. does not adversely affect the firing of the thick film, and the thick film characteristics are not deteriorated.

  And after that, the above-mentioned Si substrate is fired to form a fired film of a piezoelectric layer having a thickness of, for example, 10 μm.

As described above, the opening of the substrate is filled and cured with the liquid material, and the height of the surface of the opening filled with the liquid material is set at the same position as the substrate surface on the back surface side. Therefore, excellent adhesion can be obtained without a gap between the liquid substance and the substrate.
Accordingly, since the liquid substance does not peel from the substrate during screen printing, the piezoelectric film can be formed without damaging the substrate.

FIG. 2 is a cross-sectional view showing a standard flow of an embodiment in which a piezoelectric element (here, a piezoelectric pump) having a diaphragm portion is manufactured by using the piezoelectric element forming method according to the present invention.
FIG. 3 is a cross-sectional view of a piezoelectric element (here, a piezoelectric pump) having a manufactured diaphragm portion, and FIG. 4 is a cross-sectional view taken along line AA in FIG.
In Example 3, the filling resin is a liquid acrylic resin.

First, a 200 μm thick Si substrate (hereinafter referred to as Si substrate 11) having an SiO ₂ layer formed on the entire surface is prepared. [Refer to (1) in Fig. 2]
Next, the back surface 11b of the Si substrate 11 is subjected to resist patterning using a photolithographic technique, and a portion to be an opening is etched with a BHF solution to form a mask for Si etching. Then, the back surface 11b of the Si substrate 11 is chemically etched using a TMAH solution to form an opening 12 having a desired thickness, for example, 30 μm. [Refer to (2) in Fig. 2]
As described above, the Si substrate 11 having the opening is prepared.

Next, the opening 12 formed on the side of the back surface 11b of the Si substrate 11 is filled with the liquid acrylic resin 13, cured by UV exposure, and the opening filled with the liquid silicon resin 13. The height of the surface is set to the same position as the substrate surface of the Si substrate 11 on the back surface 11b side. Thereby, the opening part 12 is reinforced. [Refer to (3) in Fig. 2]
Then, using a screen printing method, a barium titanate paste is applied to the entire front surface 11a of the Si substrate 11 and dried at 100 ° C., whereby a dry film of the barium titanate layer 14 is formed. . [Refer to (4) in Fig. 2]
Next, a lead electrode paste is applied onto the barium titanate layer 14 of the Si substrate 11 by the same screen printing method and dried at 100 ° C., so that a dry film of the lead electrode layer 15 is formed. It is formed. [Refer to Fig. 2 (5)]
Next, a dry film of the barium titanate layer 16 is formed by applying a barium titanate paste on the extraction electrode layer 15 of the Si substrate 11 using a screen printing method and drying at 100 ° C. . [Refer to (6) in Fig. 2]
Next, the electrode paste is applied onto the barium titanate layer 16 of the Si substrate 11 in the same manner using a screen printing method, and dried at 100 ° C. to form a dry film of the electrode layer 17. Similarly, a barium titanate paste is applied on the electrode layer 17 to form a dry film of the barium titanate layer 16, and an electrode paste is applied on the dry film of the barium titanate layer 16 to form an electrode. A dry film of layer 17 is formed. [See (7) in Fig. 2]
After that, the Si substrate 11 (see (7) in FIG. 2) is heated and vaporized at, for example, about 450 ° C., thereby opening the opening 12 formed on the side of the back surface 11b of the Si substrate 11. The filled and cured liquid acrylic resin 13 is removed. [Refer to (8) in Fig. 2]
Next, the Si substrate 11 (see (8) in FIG. 2) is subjected to main firing at 1000 ° C., whereby the barium titanate layer and the electrode layer are fired on the Si substrate 11 (see (8) in FIG. 2). A film is formed [not shown].

Next, an end face electrode 18 is formed on the Si substrate 11 (see (8) in FIG. 2) by sputtering. [Refer to (9) in Fig. 2]
Then, after that, for example, under the conditions of 400 ° C. and 75 V, the Si substrate 11 (see (9) in FIG. 2), the groove that becomes the flow path 19a and the groove that becomes the flow path 19a having the taper valve 19b are formed in advance. Glass (not shown) is anodically bonded to produce a piezoelectric element (piezoelectric pump) 20 having a diaphragm portion. [See Figures 3 and 4]
As described above, the opening of the substrate is filled and cured with the liquid material, and the height of the surface of the opening filled with the liquid material is set at the same position as the substrate surface on the back surface side. Therefore, excellent adhesion can be obtained without a gap between the liquid substance and the substrate. Accordingly, since the liquid substance does not peel from the substrate during screen printing, a film can be formed without damaging the substrate. That is, the piezoelectric thick film can be easily formed on the substrate having the opening. Further, an insulating film having high resistance can be formed without peeling off the electrode between the Si substrate and the electrode.

  Therefore, even at an input voltage as high as 50 V, a piezoelectric element having a large driving force can be produced without an electrical short circuit between the Si substrate and the electrode, and the liquid in the pump moves at 50 V. Was confirmed.

It is sectional drawing which shows the standard flow of the formation method of the piezoelectric element which concerns on this invention. It is sectional drawing which shows the standard flow of one Example which produced the piezoelectric element (here piezoelectric pump) which has a diaphragm part using the formation method of the piezoelectric material element concerning this invention. It is sectional drawing of the piezoelectric element (here piezoelectric pump) which has the produced diaphragm part. FIG. 4 is a sectional view taken along line AA in FIG. 3.

Explanation of symbols

1 Substrate 2,12 Opening 3 Liquid material (filling resin)
4 Thick film (film formed by screen printing method)
11 Si substrate on which SiO ₂ layer is formed 13 Liquid acrylic resin 14, 16 BaTiO ₃ layer 15 Lead electrode layer 17 Electrode layer 18 End face electrode 19a Flow path 19b Taper valve 20 Piezoelectric element having a diaphragm portion (piezoelectric pump)

Claims (2)

In the substrate having an opening on the second main surface side facing the first main surface, the surface of the opening filled with the liquid material in the opening and cured, and filled with the hardened liquid material Is set at the same position as the substrate surface on the second main surface side, and after the piezoelectric film is formed on the first main surface side of the substrate, the curing is performed from the opening of the substrate. A method for forming a piezoelectric element , characterized in that the liquid material is removed. The method for forming a piezoelectric element according to claim 1, wherein the liquid material is an acrylic resin or a silicon resin.

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