KR101303924B1 - High-density piezoelectric thick film having alumina buffer layer and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a high-density piezoelectric thick film and a method of manufacturing the same. The present invention is a silicon substrate; An alumina buffer layer formed on the silicon substrate; And a piezoelectric thick film layer formed on the alumina buffer layer. In addition, the present invention comprises a first step of forming an alumina buffer layer on a silicon substrate; And a second step of screen printing a piezoelectric paste on the alumina buffer layer and then sintering to form a piezoelectric thick film layer. According to the present invention, diffusion of Si of the silicon substrate into the piezoelectric thick film layer is blocked by the alumina buffer layer formed between the silicon substrate and the piezoelectric thick film layer. In addition, the buffer layer is formed of alumina having a coefficient of thermal expansion similar to that of the piezoelectric thick film layer, thereby improving mechanical and electrical properties while preventing crystalline sintering during sintering. Accordingly, it has excellent piezoelectric properties due to the dense and fine microstructure.

Description

High-density piezoelectric thick film including alumina buffer layer and its manufacturing method {HIGH-DENSITY PIEZOELECTRIC THICK FILM HAVING ALUMINUM BUFFER LAYER AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a high-density piezoelectric thick film and a method for manufacturing the same, and more particularly, to an alumina buffer layer formed between a silicon substrate and a piezoelectric thick film layer, and having a high density of dense microstructure, It relates to a piezoelectric thick film and a method of manufacturing the same.

Piezoelectric films, such as piezoelectric films using piezoelectric ceramics such as PZT [Pb (Zr, Ti) O ₃ ], have not only high energy density and fast response speed but also high sensitivity to small displacements. Accordingly, piezoelectric films are frequently used in actuators, sensors, and the like.

Piezoelectric films are classified into thin films and thick films based on a thickness of about 1 μm. Recently, there is a growing demand for thick films for piezoelectric microelectromechanical system (MEMS) actuators requiring greater displacement and driving force, piezoelectric MEMS energy harvesters requiring high electrical energy generation, and the like. However, piezoelectric thick films having a thickness of 3 to 100 μm are difficult to be processed from bulk ceramics or manufactured through a deposition process.

In general, a piezoelectric thick film includes a substrate and a piezoelectric thick film layer formed on the substrate. In this case, the piezoelectric thick film layer is generally formed by screen printing a piezoelectric paste mixed with a piezoelectric ceramic, a binder, and a solvent on a substrate. Screen printing has the advantages of simple process, low cost and high productivity. In addition, screen printing has the advantage that a patterning process is not required separately, and a thick film having a desired pattern size (width and thickness) can be directly formed. However, the piezoelectric thick film layer formed by screen printing has a big disadvantage that its microstructure is not dense. Accordingly, for the purpose of compact microstructure, after screen printing, the substrate is sintered at a high temperature of 1000 ° C or higher and a high temperature of approximately 1200 ° C to 1250 ° C.

However, a piezoelectric thick film applied as a MEMS (Micro Electro Mechanical System) device is used as a substrate, and a silicon substrate is used as the substrate. In this case, when the screen is printed on the silicon substrate and sintered at high temperature, Si diffuses into the piezoelectric thick film layer to generate a secondary phase. As the binder is degreased, the density decreases. Specifically, Si of the silicon substrate penetrates and reacts with the piezoelectric thick film layer to generate a secondary phase, and the piezoelectric property is deteriorated due to poor crystallinity of the piezoelectric thick film layer. , Density decreases. Such secondary phase formation and density reduction adversely affect piezoelectric properties.

In recent years, in order to solve this problem, the technique of changing the composition component and process conditions of a piezoelectric thick film layer is tried. For example, Korean Patent Laid-Open Publication No. 10-2002-0090275 [Patent Document 1] describes a piezoelectric thick film layer having a composition of Pb (Zr, Ti) O ₃ + xPb (Cd, W) O ₃ (x is 0.01 to 0.20). A technology composed of the present invention is proposed, and in Korean Patent Laid-Open Publication No. 10-2011-0017592 [Patent Document 2], the piezoelectric thick film layer is made of a solid solution of Pb (Zr, Ti) O ₃ and Pb (Mn, Nb) O ₃ , The technique of forming this by the room temperature vacuum powder injection method is proposed. In addition, Korean Patent Laid-Open Publication No. 10-2008-0048760 [Patent Document 3] discloses a technology in which a seeding layer is formed between a substrate and a piezoelectric thick film layer, and the seeding layer is made of the same or similar piezoelectric material as the piezoelectric thick film layer. It is.

However, the piezoelectric thick film according to the prior art, including the prior patent documents, has a high density through the improvement of the composition or the process conditions of the piezoelectric thick film layer as described above, but the phenomenon that Si of the silicon substrate diffuses into the piezoelectric thick film layer. It does not prevent.

Republic of Korea Patent Publication No. 10-2002-0090275 Republic of Korea Patent Publication No. 10-2011-0017592 Republic of Korea Patent Publication No. 10-2008-0048760

Accordingly, the present invention forms a buffer layer between the silicon substrate and the piezoelectric thick film layer in order to prevent the Si of the silicon substrate from diffusing into the piezoelectric thick film layer, wherein the buffer layer has a thermal expansion coefficient similar to that of the piezoelectric thick film layer. Branches are composed of alumina (Al ₂ O ₃ ) to block the diffusion of Si, as well as to reduce the pores generated due to binder degreasing during sintering by a similar coefficient of thermal expansion, piezoelectric properties due to having a dense and fine microstructure Its purpose is to provide this excellent high-density piezoelectric thick film and its manufacturing method.

The present invention to achieve the above object,

A silicon substrate;

An alumina buffer layer formed on the silicon substrate; And

It provides a piezoelectric thick film comprising a piezoelectric thick film layer formed on the alumina buffer layer.

In this case, the alumina buffer layer is preferably deposited on a silicon substrate, and then heat treated.

Further, according to the present invention,

Forming a alumina buffer layer on the silicon substrate; And

And a second step of screen printing a piezoelectric paste on the alumina buffer layer and sintering to form a piezoelectric thick film layer.

In this case, the first step may include a deposition process of depositing an alumina buffer layer on a silicon substrate; And a heat treatment step of heat treating the deposited alumina buffer layer.

According to the present invention, diffusion of Si of the silicon substrate into the piezoelectric thick film layer is blocked by the alumina buffer layer formed between the silicon substrate and the piezoelectric thick film layer. In addition, the buffer layer is formed of alumina (Al ₂ O ₃ ) having a coefficient of thermal expansion similar to that of the piezoelectric thick film layer, thereby reducing the pores generated due to binder degreasing during sintering. Accordingly, the mechanical and electrical properties are improved while having a high density and dense microstructure, and thus have excellent piezoelectric properties.

1 is a cross-sectional configuration diagram of a piezoelectric thick film according to the present invention.
2 is a PE curve of the piezoelectric thick film according to the embodiment of the present invention.

Figure 1 shows a cross-sectional configuration of the piezoelectric thick film according to the present invention.

Referring to FIG. 1, the piezoelectric thick film according to the present invention includes a silicon substrate 10, an alumina buffer layer 20 formed on the silicon substrate, and a piezoelectric thick film layer 30 formed on the alumina buffer layer 20. . Specifically, the piezoelectric thick film according to the present invention has a structure in which an alumina buffer layer 20 is formed between the silicon substrate 10 and the piezoelectric thick film layer 30.

In addition, in the method of manufacturing a piezoelectric thick film according to the present invention, the first step of forming the alumina buffer layer 20 on the silicon substrate 10 and the piezoelectric thick film layer 30 on the alumina buffer layer 20 are formed. It includes a second step. Hereinafter, the present invention will be described in detail through the manufacturing method.

First, the silicon substrate 10 is prepared. The silicon substrate 10 may be one that is commonly used. Next, a buffer layer 20 is formed on the prepared silicon substrate 10. According to the present invention, the buffer layer 20 is composed of alumina (Al ₂ O ₃ ). In this case, the lower electrode may be selectively formed on one surface of the alumina buffer layer 20 after the buffer layer 20 is formed according to the use and purpose of the piezoelectric thick film. As such, when the lower electrode is formed, the lower electrode may be formed on the buffer layer 20.

According to the present invention, the diffusion of Si in the silicon substrate 10 into the piezoelectric thick film layer 30 is blocked by the buffer layer 20. In addition, the buffer layer 20 is composed of alumina according to the present invention. The alumina has a higher barrier property of Si than other oxides (for example, SiO _2, etc.), and the coefficient of thermal expansion is particularly similar to that of the piezoelectric thick film layer 30. To have a high density.

Specifically, the alumina has a similar thermal expansion coefficient to piezoelectric ceramics such as PZT system, which are widely used as the piezoelectric thick film layer 30 in the art, thereby forming a dense microstructure after sintering. More specifically, as described below, the piezoelectric thick film layer 30 is formed by screen-printing a piezoelectric paste including piezoelectric ceramic (PZT-based) on the buffer layer 20 and then sintering the alumina. The thermal expansion coefficient is similar to that of piezoelectric ceramics (PZT type), so that the pores generated due to binder degreasing after sintering shrink the piezoelectric ceramics (PZT type). In addition, the interlayer crystallinity of the buffer layer 20 and the piezoelectric thick film layer 30 is improved while the diffusion of Si is blocked, thereby producing a high-density piezoelectric thick film. In addition, alumina improves the mechanical properties (tensile strength, flexural strength, etc.) and electrical properties (electric conductivity, etc.) of the piezoelectric thick film.

The buffer layer 20 is included in the present invention as long as it is composed of alumina, but is not particularly limited, but preferably has a thickness of 0.01 μm to 20 μm. At this time, when the thickness of the buffer layer 20 is less than 0.01 μm, Si barrier properties and pore shrinkage effects may be insignificant, and it may be difficult to show excellent piezoelectric properties. When the thickness of the buffer layer 20 exceeds 20 μm, the total thickness of the piezoelectric thick film is too thick to be unsuitable for the MEMS process. can do. In consideration of this point, it is more preferable that the buffer layer 20 has a thickness of 0.3 μm to 10 μm.

In addition, the buffer layer 20 may be formed through deposition. The deposition method is not limited. Deposition may be performed using alumina as a target, for example sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), pulsed laser deposition; PLD), electron beam evaporation, atomic layer deposition (ALD), molecular beam epitaxy (MBE), and the like. Preferably, sputtering, specifically, an RF sputtering method may be usefully used.

In addition, according to a preferred embodiment of the present invention, after forming the buffer layer 20 through the deposition as described above, it is preferable to heat-treat the deposited buffer layer 20. When the heat treatment in this way, the crystallinity of the alumina is improved to improve the Si barrier properties, mechanical properties more than before the heat treatment. At this time, the heat treatment step is preferably carried out at a temperature of 800 ℃ or more. The heat treatment is more preferably carried out at a temperature of 800 ℃ to 1000 ℃. When the heat treatment temperature is less than 800 ℃, the effect of the heat treatment, that is, the Si barrier properties and the density improvement effect of the piezoelectric thick film due to the improved crystallinity of the alumina may be insignificant. And when the heat treatment temperature exceeds 1000 ℃, the synergistic effect of the excessive temperature is not very large and the crystallinity of the alumina due to oversintering may be inferior. In addition, the heat treatment is preferably carried out for 3 minutes or more, specifically 3 minutes to 1 hour at a temperature in the above range. In this case, if the heat treatment time is less than 3 minutes, the effect of the heat treatment may be insignificant, and if more than 1 hour, the synergistic effect according to the heat treatment time is not very large, it is not preferable in terms of energy loss and rather the crystallinity due to oversintering Can be. For this reason, it is good to heat-process for 3 minutes-1 hour at the temperature of 800 degreeC-1000 degreeC.

After the alumina buffer layer 20 is formed as described above, the piezoelectric thick film layer 30 is formed on the alumina buffer layer 20. The piezoelectric thick film layer 30 is formed in the same manner as usual. Specifically, the piezoelectric thick film layer 30 is formed by screen printing a piezoelectric paste on the alumina buffer layer 20 and then sintering it.

In the present invention, the piezoelectric material constituting the piezoelectric thick film layer 30, that is, the piezoelectric ceramic constituting the piezoelectric paste is not limited as long as it has piezoelectric properties, and it can be used that is commonly used. The piezoelectric ceramics may be preferably selected from PZT system and the like including Pb, Zr and Ti as basic elements.

The piezoelectric ceramic is specifically one using PZT [Pb (Zr, Ti) O ₃ ] or based on the PZT, but selected from Zn, Mg, Ni, Nb, Y, W, Mn, Cr, etc. in the PZT. The above elemental compound may be selected from the complexed PZT-complex. The PZT-composite may be, for example, PZT-PMN [Pb (Zr, Ti) O ₃ -Pb (Mn, Nb) O ₃ ], PZT-PCW [Pb (Zr, Ti) O ₃ -Pb (Cd, W) O ₃ ], and PZT-PMN-PNN [Pb (Zr, Ti) O ₃ -Pb (Mg, Nb) O ₃ -Pb (Ni, Nb) O ₃ ] and the like.

The piezoelectric paste includes a piezoelectric ceramic, but may be enough to screen printing. The piezoelectric paste may specifically include a piezoelectric ceramic, a binder, and a solvent, and the binder and the solvent may be ones commonly used. In addition, the piezoelectric paste may further include other additives such as a dispersant. More specifically, the piezoelectric paste may be prepared by first obtaining a vehicle in which a binder, a solvent, a dispersant, and the like are mixed, and then adding and mixing the piezoelectric ceramics, followed by roll milling.

After screen printing the piezoelectric paste as described above on the alumina buffer layer 20, sintering is performed, and sintering may be performed at a temperature of 700 ° C. or higher. At this time, the sintering temperature in the present invention is not limited, high temperature sintering is possible. That is, according to the present invention, since the Si of the silicon substrate 10 is prevented from diffusing into the piezoelectric thick film layer 30 by the alumina buffer layer 20, high temperature sintering of 1000 ° C. or more is possible. Sintering of the piezoelectric thick film layer 30 may be specifically carried out at a temperature of 700 ℃ to 1300 ℃. At this time, if the sintering temperature is less than 700 ℃ sintering (crystallization) of the piezoelectric thick film layer 30 is difficult, if it exceeds 1300 ℃, the piezoelectric thick film may be bent or broken due to overheating. Preferably, the piezoelectric thick film layer 30 may be sintered at a high temperature of 800 ° C. to 1200 ° C., rather than a low temperature, so as to have a high density of a dense fine structure. At this temperature, rapid sintering for several seconds or more, but not particularly limited, for 30 seconds to 30 minutes is preferable.

The piezoelectric thick film layer 30 may be 1 µm or more in thickness. The piezoelectric thick film layer 30 may specifically have a thickness of 1 μm to 500 μm, and preferably may have a thickness of 20 μm to 100 μm. In addition, the piezoelectric thick film according to the present invention may include a lower electrode and an upper electrode as usual. In this case, the lower electrode may be formed between the alumina buffer layer 20 and the piezoelectric thick film layer 30, and the upper electrode may be formed on the piezoelectric thick film layer 30. Specifically, the method of manufacturing a piezoelectric thick film according to the present invention comprises the steps of forming a lower electrode between the alumina buffer layer 20 and the piezoelectric thick film layer 30, and the upper electrode on the piezoelectric thick film layer 30 It may comprise the step of forming.

At this time, the lower electrode and the upper electrode is not particularly limited as long as it has conductivity, which is, for example, silver (Ag), platinum (Pt), gold (Au), aluminum (Al), copper (Cu) and ruthenium oxide ( RuO) and the like may include one or more conductive materials. In addition, the lower electrode and the upper electrode may be formed by vapor deposition, or by screen printing an electrode paste including the conductive material, followed by heat treatment.

According to the present invention described above, as described above, the buffer layer 20 is formed between the silicon substrate 10 and the piezoelectric thick film layer 30, so that the sintering of the piezoelectric thick film layer 30 is performed. The diffusion of Si into the piezoelectric thick film layer 30 is blocked. In addition, the buffer layer 20 is made of alumina having a high Si barrier property, particularly similar to the piezoelectric thick film layer 30 and the thermal expansion coefficient, thereby improving the sinterability and crystallinity of the piezoelectric thick film layer 30 during sintering. As a result, the decrease in density due to the generation of the secondary phase and the generation of pores due to the diffusion of Si and the difference in thermal expansion coefficient is prevented, and it has a high density and dense microstructure and has excellent piezoelectric properties. In addition, alumina greatly improves the mechanical and electrical properties of the piezoelectric thick film.

The piezoelectric thick film according to the present invention can be applied to piezoelectric elements of various products, and can be applied to various piezoelectric elements such as piezoelectric MEMS, piezoelectric actuators, piezoelectric sensors, and piezoelectric energy harvesters that require high piezoelectric properties as a high density. .

Hereinafter, examples and comparative examples of the present invention will be exemplified. The following examples are provided for illustrative purposes only and should not be construed as limiting the technical scope of the present invention.

Example 1

First, a solvent was prepared by completely adding butoxy ethoxy ethyl acetate and polyvinyl butyral as a binder to α-terpineol as a solvent. In addition, PZT powders commonly used in vehicles were roll milled to prepare piezoelectric pastes mixed and dispersed.

In addition, an alumina (Al ₂ O ₃ ) target was mounted on the RF sputter, and argon gas (Ar gas) was injected at 30 sccm at a deposition vacuum of 2.0 x 10 ^-6 , and the deposition conditions of the RF power 300W at a pressure of 0.02 torr were obtained. By sputtering with alumina (Al ₂ O ₃ ) was deposited on the silicon substrate to a thickness of 1100nm. Then, the deposited specimen (Al ₂ O ₃ / Si) was put in an electric furnace and heat-treated for 5 minutes at a temperature of 900 ℃.

Next, after screen printing a silver (Ag) lower electrode on the alumina (Al ₂ O ₃ ) layer of the heat-treated specimen (Al ₂ O ₃ / Si) into the electric furnace and heat-treated at 600 ℃ temperature for 10 minutes. The prepared piezoelectric paste was screen printed on the heat treated specimen (Ag / Al ₂ O ₃ / Si) in the same manner as usual. The screen printed specimen (PZT / Ag / Al ₂ O ₃ / Si) was put into an electric furnace and sintered at a temperature of 860 ° C. for 300 seconds.

Thereafter, a platinum (Pt) upper electrode is deposited (DC sputtering) on the PZT layer of the sintered specimen (PZT / Ag / Al ₂ O ₃ / Si) to form a structure of Pt / PZT / Ag / Al ₂ O ₃ / Si. A piezoelectric thick film having was prepared.

[Examples 2 to 5]

Compared with Example 1, it was prepared by performing the same, except that a different layer thickness of the alumina (Al ₂ O ₃₎ in the formation of the layer of alumina (Al ₂ O _3). Deposition thickness of the alumina (Al ₂ O ₃ ) layer according to each embodiment is shown in Table 1 below.

Comparative Example 1

Compared with Example 1, except that the alumina (Al ₂ O ₃ ) layer is not formed, it was carried out in the same manner. Specifically, the piezoelectric thick film according to Comparative Example 1 had a structure of Pt / PZT / Ag / Si as usual.

Comparative Example 2

Compared to Example 1, it was carried out in the same manner except that silica (SiO ₂ ) was used instead of alumina (Al ₂ O ₃ ). Specifically, the piezoelectric thick film according to Comparative Example 2 had a structure of Pt / PZT / SiO ₂ / Ag / Si.

For the piezoelectric thick film specimens according to the examples and the comparative examples prepared as described above, the maximum P _r value (remanent polarization, residual polarization value) was measured, and the results are shown in the following [Table 1]. In addition, Figure 2 attached shows a PE curve of the piezoelectric thick film specimen according to Example 1.

  <Pr value measurement result> Remarks Buffer layer Thickness of buffer layer (nm) P _r value (μC / cm 2) Example 1 Al ₂ O ₃ 1100 42 Example 2 Al ₂ O ₃ 900 35 Example 3 Al ₂ O ₃ 700 31 Example 4 Al ₂ O ₃ 500 27 Example 5 Al ₂ O ₃ 300 23 Comparative Example 1 - 0 20 Comparative Example 2 SiO ₂ 1100 22

As shown in Table 1, in Examples (1 to 5) according to the present invention, it can be seen that the P _r value representing the piezoelectric properties is significantly higher than that of the conventional Comparative Example 1 due to the high density. In addition, in the case of Comparative Example 2 using silica (SiO ₂ ) as a buffer layer instead of alumina (Al ₂ O ₃ ), it is improved than Comparative Example 1, but this is due to the difference in thermal expansion coefficient with the piezoelectric ceramic (PZT) It was found to be significantly lower than the examples (1 to 5).

In addition, as shown in [Table 1], it was found that the piezoelectric properties were varied depending on the thickness of the alumina (Al ₂ O ₃ ) layer, and in particular, as compared with Examples 1 and 5, alumina (Al _As the thickness of the ₂ O ₃ ) layer was increased, the piezoelectric properties were further increased. In addition, when the thickness of the alumina (Al ₂ O ₃ ) layer was 1100 nm as in Example 1, it was found to have excellent piezoelectric properties of about 42 μC / cm 2. In addition, when the thickness of the alumina (Al ₂ O ₃ ) layer is 1100nm or more showed a characteristic value similar to 1100nm thickness.

10 silicon substrate 20 buffer layer
30: piezoelectric thick film layer

Claims (9)

A silicon substrate;
An alumina buffer layer formed on the silicon substrate; And
It includes a piezoelectric thick film layer formed on the alumina buffer layer,
And the alumina buffer layer is deposited on the silicon substrate and then heat treated.
The method of claim 1,
The piezoelectric thick film, characterized in that the heat treatment is performed for 3 minutes to 1 hour at a temperature of 800 ℃ ~ 1000 ℃.
3. The method according to claim 1 or 2,
The alumina buffer layer is a piezoelectric thick film, characterized in that having a thickness of 0.01㎛ ~ 20㎛.
Forming a alumina buffer layer on the silicon substrate; And
And a second step of screen printing a piezoelectric paste on the alumina buffer layer and then sintering to form a piezoelectric thick film layer.
The first step may include a deposition process of depositing an alumina buffer layer on the silicon substrate; And
And a heat treatment step of heat treating the deposited alumina buffer layer.
delete 5. The method of claim 4,
Forming a lower electrode comprising at least one selected from Ag, Pt, Au, Al, Cu, and RuO between the alumina buffer layer and the piezoelectric thick film layer; And
And forming an upper electrode including one or more selected from Ag, Pt, Au, Al, Cu, and RuO on top of the piezoelectric thick film layer.
5. The method of claim 4,
The heat treatment process is a piezoelectric thick film manufacturing method characterized in that the heat treatment at a temperature of 800 ℃ ~ 1000 ℃.
5. The method of claim 4,
The sintering is a method for producing a piezoelectric thick film, characterized in that carried out at a temperature of 800 ℃ ~ 1200 ℃. The method of claim 7, wherein
The heat treatment process is a piezoelectric thick film manufacturing method characterized in that the heat treatment for 3 minutes to 1 hour at a temperature of 800 ℃ ~ 1000 ℃.

Images