A surface acoustic wave device with high electromechanical coupling coefficient based on etched piezoelectric film

Abstract

The present invention discloses a surface acoustic wave device with a high electromechanical coupling coefficient based on an etched piezoelectric film, and belongs to the field of electronic information materials. The surface acoustic wave device includes, from bottom to top, a high acoustic velocity substrate, a partially etched piezoelectric film, and a top electrode. The top electrode is an interdigitated electrode, and the piezoelectric film between the interdigitated electrodes is partially etched. The surface acoustic wave device of the present invention has two modes, namely, a quasi-Rayleigh wave mode and a quasi-Sishawar wave mode, wherein the quasi-Rayleigh wave mode has the characteristics of low frequency and high electromechanical coupling coefficient, and can meet the needs of low-frequency miniaturization of surface acoustic wave devices; the quasi-Sishawar wave mode has the characteristics of high frequency and high electromechanical coupling coefficient, and is suitable for preparing high-frequency and large-bandwidth surface acoustic wave devices. The surface acoustic wave device of the present invention is a multi-layer composite structure, which is easy to prepare and mass-produce, and is of great significance for practical applications.

Description

Technical Field

[0001] The invention relates to the field of electronic information materials, and in particular to a high electromechanical coupling coefficient surface acoustic wave device based on an etched piezoelectric film. Background Art

[0002] Mobile communications play a huge role in today's human production and life, and have become an indispensable part of people's lives. The wireless communication module of the terminal equipment includes three parts: RF front-end module, RF transceiver module and baseband signal processor. As the most important device in the RF front-end module, the demand for filters has been increasing year by year. The advent of the 5G era has put forward higher requirements on the performance of filters, including high frequency, large bandwidth, high power tolerance and temperature compensation capability. The frequency and bandwidth of surface acoustic wave devices mainly depend on the sound velocity and electromechanical coupling coefficient of piezoelectric materials. Therefore, in order to pursue trends such as high frequency and large bandwidth, scholars at home and abroad have devoted themselves to the research and development of piezoelectric materials with better comprehensive performance and the design of new piezoelectric layer structures.

[0003] The composite substrate structure of piezoelectric film and high acoustic velocity substrate is a common solution for preparing high-frequency and large-bandwidth devices. Zinc oxide, as a commonly used piezoelectric film material, has the advantages of high acoustic velocity and large electromechanical coupling coefficient. Diamond is the material with the highest hardness, largest elastic modulus, best thermal conductivity and highest acoustic velocity in nature. It has always been widely concerned by people, but its high price and unsatisfactory large-size wafer quality limit its application. Silicon carbide also has high acoustic velocity, high elastic modulus and high thermal conductivity. Zinc oxide / silicon carbide composite structure surface acoustic wave filters have been reported, and a narrowband filter with an operating frequency of 6.8GHz has been successfully prepared, which is a useful exploration of high-frequency surface acoustic wave filters. Although the piezoelectric film / high acoustic velocity substrate composite substrate structure has a high frequency, the electromechanical coupling coefficient is relatively small. How to further improve the electromechanical coupling coefficient of the piezoelectric film / high acoustic velocity substrate structure has become an urgent problem to be solved. Summary of the invention

[0004] The present invention provides a surface acoustic wave device with a high electromechanical coupling coefficient based on an etched piezoelectric film. The device has two modes, namely a quasi-Rayleigh wave mode and a quasi-Sishawar wave mode. The quasi-Rayleigh wave mode has the characteristics of low frequency and high electromechanical coupling coefficient, and can meet the needs of low-frequency miniaturization of surface acoustic wave devices; the quasi-Sishawar wave mode has the characteristics of high frequency and high electromechanical coupling coefficient, and is suitable for preparing high-frequency and large-bandwidth surface acoustic wave devices.

[0005] The present invention firstly provides a surface acoustic wave device, which comprises, from bottom to top, a high acoustic velocity substrate, a partially etched piezoelectric film and a top electrode.

[0006] In the above-mentioned surface acoustic wave device, the total thickness of the partially etched piezoelectric film is h, the depth of the etched part is d, and the etching ratio d / h is 0<d / h≤1; specifically, it can be 0.1≤d / h≤1; more specifically, d / h can be 0.1, 0.3, 0.5, 0.7, 0.9 or 1.

[0007] In the above-mentioned surface acoustic wave device, the top electrode is an interdigitated electrode, and the piezoelectric film between the interdigitated electrodes is partially etched;

[0008] The thickness of the top electrode is t1;

[0009] The width of the top electrode and the width of the unetched piezoelectric film are kept consistent as w;

[0010] The metallization ratio is 2w / λ, 0.1≤2w / λ≤0.9; specifically, it may be 0.3≤2w / λ≤0.7; more specifically, 2w / λ is 0.5 or 0.65.

[0011] The normalized thickness of the top electrode is t1 / λ, 0<t1 / λ≤0.3; specifically, it may be 0.01≤t1 / λ≤0.13; more specifically, it may be 0.13, 0.03 or 0.05.

[0012] The normalized thickness of the piezoelectric film is h / λ, 0<h / λ≤3; specifically, it can be 0.5≤h / λ≤1; more specifically, it can be 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0013] The λ is the wavelength of the surface acoustic wave;

[0014] The wavelength λ of the surface acoustic wave is 1 μm≤λ≤5 μm, and may be specifically 2 μm.

[0015] In the above-mentioned surface acoustic wave device, the etching shape of the piezoelectric film between the interdigitated fingers is a column, specifically a rectangular column;

[0016] The etched portion of the piezoelectric film is adjacent to one side of the top electrode.

[0017] The above-mentioned surface acoustic wave device, a bottom electrode is added between the high acoustic velocity substrate and the partially etched piezoelectric film;

[0018] Specifically, the material of the bottom electrode is one of the following metals or a binary alloy of two metals: Al, Cu, Pt, Mo, W, Ni; specifically, it may be Al, Cu, or Ni.

[0019] In the above-mentioned surface acoustic wave device, the thickness of the bottom electrode is t2, and the normalized thickness of the bottom electrode is t2 / λ, 0<t2 / λ≤0.3, specifically 0.01≤t2 / λ≤0.1.

[0020] In the above-mentioned surface acoustic wave device, the high acoustic velocity substrate is a silicon carbide substrate, a sapphire substrate or a diamond substrate; specifically, it can be a silicon carbide single crystal substrate.

[0021] The material of the top electrode is one of the following metals or a binary alloy of two metals: Al, Cu, Pt, Mo, W, Ni.

[0022] In the above-mentioned surface acoustic wave device, the partially etched piezoelectric film is a zinc oxide film or a doped zinc oxide film;

[0023] The doping element of the doped zinc oxide film is Cr, Fe or V.

[0024] The application of the above-mentioned surface acoustic wave device in the preparation of filters also falls within the protection scope of the present invention.

[0025] The present invention has the following advantages:

[0026] (1) The surface acoustic wave device of the present invention has a simple structure. It only needs to etch the piezoelectric film between the interdigital electrodes on the basis of the conventional surface acoustic wave device, and has strong operability.

[0027] (2) The surface acoustic wave device of the present invention has two acoustic wave modes, and the electromechanical coupling coefficients of both are increased compared with the traditional high acoustic velocity substrate / piezoelectric film structure. By controlling the etching portion ratio and the thickness of the piezoelectric layer, quasi-Sishawar waves with high acoustic velocity and high electromechanical coupling coefficient and quasi-Rayleigh waves with low acoustic velocity and high electromechanical coupling coefficient can be obtained respectively, which have two functions.

[0028] (3) The surface acoustic wave device of the present invention is a multi-layer composite structure, which is easy to prepare and mass-produce, and has important significance for practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic structural diagram of a surface acoustic wave device according to Embodiment 1 of the present invention;

[0030] The marks in the figure are as follows:

[0031] 1. Top electrode; 2. Partially etched piezoelectric film; 3. High acoustic velocity substrate.

[0032] Figure 2 The wave velocity and electromechanical coupling coefficient curves of quasi-Rayleigh wave and quasi-Xishawar wave under different normalized thicknesses (h / λ) of ZnO piezoelectric films at different etching ratios d / h in Example 1, when the top electrode is Al, the normalized thickness t1 / λ=0.05, the metallization ratio is 0.5; wherein, (a) is the sound velocity curve of quasi-Rayleigh wave, (b) is the electromechanical coupling coefficient curve of quasi-Rayleigh wave, (c) is the sound velocity curve of quasi-Xishawar wave, and (d) is the electromechanical coupling coefficient curve of quasi-Xishawar wave.

[0033] Figure 3 When the etching ratio d / h=1 in Example 1, the normalized thickness of the ZnO piezoelectric film h / λ=0.5, the metallization ratio is 0.5, and the top electrodes are Al, Cu, Pt, Mo, and W, respectively, the wave velocity and electromechanical coupling coefficient curves of the quasi-Rayleigh wave under different normalized top electrode thicknesses (t1 / λ); wherein (a) is the wave velocity curve, and (b) is the electromechanical coupling coefficient curve.

[0034] Figure 4 The wave velocity and electromechanical coupling coefficient curves of quasi-Rayleigh waves at different metallization ratios when the etching ratio d / h=1 in Example 1, the normalized thickness of the ZnO piezoelectric film h / λ=0.5, the top electrode is Cu and the normalized thickness t1 / λ is 0.07; wherein (a) is the wave velocity curve and (b) is the electromechanical coupling coefficient curve.

[0035] Figure 5 When the etching ratio d / h=0.7 in Example 1, the normalized thickness of the ZnO piezoelectric film h / λ=0.6, the metallization ratio is 0.5, and the top electrodes are Al, Cu, Pt, Mo, and W, respectively, the wave velocity and electromechanical coupling coefficient curves of the quasi-Sishawar wave under different normalized top electrode thicknesses (t1 / λ); wherein (a) is the wave velocity curve, and (b) is the electromechanical coupling coefficient curve.

[0036] Figure 6 The wave velocity and electromechanical coupling coefficient curves of quasi-Sishawar waves at different metallization ratios when the etching ratio d / h=0.7 in Example 1, the normalized thickness of the ZnO piezoelectric film h / λ=0.6, the top electrode is Al and the thickness is 0.13λ; (a) is the wave velocity curve, and (b) is the electromechanical coupling coefficient curve.

[0037] Figure 7 Schematic diagram of the structure of a surface acoustic wave device according to Embodiment 2 of the present invention;

[0038] The marks in the figure are as follows:

[0039] 1. Top electrode; 2. Partially etched piezoelectric film; 3. High acoustic velocity substrate; 4. Bottom electrode.

[0040] Figure 8 The wave velocity and electromechanical coupling coefficient curves of the quasi-Rayleigh wave under different normalized bottom electrode thicknesses (t2 / λ) in case (1) of Example 2; wherein (a) is the wave velocity curve, and (b) is the electromechanical coupling coefficient curve.

[0041] Fig. 9 The wave velocity and electromechanical coupling coefficient curves of the quasi-Sishawar wave under different normalized bottom electrode thicknesses (t2 / λ) in case (2) of Example 2; wherein (a) is the wave velocity curve, and (b) is the electromechanical coupling coefficient curve. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with specific embodiments. The given examples are only for illustrating the present invention, but not for limiting the scope of the present invention.

[0043] The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0044] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0045] Example 1

[0046] like Figure 1 As shown, it is a cross-sectional view of the structure without the bottom electrode. The surface acoustic wave device of this embodiment comprises, from bottom to top, a high acoustic velocity substrate 3, a partially etched piezoelectric film 2 and a top electrode 1; the high acoustic velocity substrate is a silicon carbide single crystal substrate, and the piezoelectric film is a zinc oxide film;

[0047] The total thickness of the piezoelectric film layer is h, the depth of the etched part is d, and d / h is defined as the etching ratio; the thickness of the top electrode is t1, the width of the top electrode is consistent with the width of the unetched zinc oxide column, which is w, the wavelength of the surface acoustic wave λ=2μm, the metallization ratio duty factor=2w / λ, the normalized thickness of the top electrode is t1 / λ, and the normalized thickness of the ZnO piezoelectric film is h / λ.

[0048] The units of h, d, w, t1 and λ above are all micrometers.

[0049] (1) When the top electrode material is Al, the top electrode normalized thickness t1 / λ=0.05, and the metallization ratio is 0.5, Figure 2 The wave velocity and electromechanical coupling coefficient curves of quasi-Rayleigh wave and quasi-Sishawar wave under different etching ratios d / h and different normalized thicknesses (h / λ) of ZnO piezoelectric films.

[0050] Figure 2 Figure a shows that under different etching ratios, the sound velocity of the quasi-Rayleigh wave decreases monotonically with the increase of the film thickness of the zinc oxide film. As the etching ratio increases, the sound velocity decreases faster. For the same zinc oxide film thickness, the larger the etching ratio, the lower the sound velocity. Figure 2 Figure b shows that under different etching ratios, except for the case where d / h=0.1, the electromechanical coupling coefficient of the quasi-Rayleigh wave increases with the increase of the film thickness of the zinc oxide film. When the etching ratio is 1, the electromechanical coupling coefficient increases most significantly; when h / λ=1, the electromechanical coupling coefficient is 11.09%. Figure 2 As shown in Figure c, under different etching ratios, the sound velocity of the quasi-Xishawar wave decreases monotonically with the increase of the film thickness of the zinc oxide film. Figure 2As shown in Figure d, under different etching ratios, the electromechanical coupling coefficient of the quasi-Xishawar wave first increases and then decreases with the increase of the film thickness of the zinc oxide film. Among them, when the etching ratio is 0.5 and h / λ=0.9, the electromechanical coupling coefficient is 8.6%.

[0051] (2) When the etching ratio d / h = 1, the normalized thickness of the ZnO piezoelectric film h / λ = 0.5, and the metallization ratio is 0.5, Figure 3 The wave velocity and electromechanical coupling coefficient curves of quasi-Rayleigh waves under different normalized top electrode thicknesses (t1 / λ) when the top electrode is Al, Cu, Pt, W, and Mo, respectively. Figure 3 It is shown in the figure that the sound velocity decreases with the increase of the thickness of the top electrode, and the electromechanical coupling coefficient increases with the increase of the thickness of the top electrode. In the range of 0.01≤t1 / λ≤0.10, the sound velocity range is 1500m / s-2400m / s, and the electromechanical coupling coefficient range is 7.79%-10.50%.

[0052] Figure 4 The wave velocity and electromechanical coupling coefficient curves of quasi-Rayleigh waves under different metallization ratios are shown when the etching ratio d / h=1, the normalized thickness of the ZnO piezoelectric film h / λ=0.5, the top electrode is Cu and the normalized thickness of the top electrode is t1 / λ=0.07. The sound velocity first decreases and then increases with the increase of the metallization ratio. When the duty factor=0.65, the sound velocity reaches the minimum value of 2011.1m / s. The electromechanical coupling coefficient decreases with the increase of the metallization ratio. In the range of 0.3≤duty factor≤0.7, the electromechanical coupling coefficient ranges from 8.90% to 10.51%.

[0053] (3) When the etching ratio d / h = 0.7, the normalized thickness of the ZnO piezoelectric film h / λ = 0.6, and the metallization ratio is 0.5, Figure 5 The wave velocity and electromechanical coupling coefficient curves of the quasi-Xishawar wave under different normalized top electrode thicknesses (t1 / λ) when the top electrode is Al, Cu, Pt, W, and Mo, respectively. Figure 5 It is shown in the figure that the sound velocity decreases with the increase of the top electrode thickness. In the range of 0.01≤t1 / λ≤0.15, the sound velocity range is 4400m / s-5600m / s. The electromechanical coupling coefficient first increases and then decreases with the increase of the top electrode thickness. Al, Cu, Pt, Mo and W achieve the maximum electromechanical coupling coefficient when their normalized thicknesses are 0.13, 0.05, 0.03, 0.05 and 0.03, respectively, and the maximum values ​​are 6.94%, 7.06%, 7.06%, 7.04% and 7.04%, respectively.

[0054] Figure 6The wave velocity and electromechanical coupling coefficient curves of quasi-Sishawar waves under different metallization ratios are shown when the etching ratio d / h=0.7, the normalized thickness of the ZnO piezoelectric film h / λ=0.6, the top electrode is Al and the normalized thickness of the top electrode t1 / λ=0.13. The sound velocity first increases and then decreases with the increase of the metallization ratio. When the duty factor=0.5, the sound velocity reaches a maximum value of 5349.5m / s. The electromechanical coupling coefficient increases with the increase of the metallization ratio. In the range of 0.3≤duty factor≤0.7, the electromechanical coupling coefficient ranges from 5.25% to 7.94%.

[0055] Embodiment 2,

[0056] like Figure 7 As shown, it is a cross-sectional view of the structure containing the bottom electrode layer. The surface acoustic wave device of this embodiment comprises, from bottom to top, a high acoustic velocity substrate 3, a bottom electrode layer 4, a partially etched piezoelectric film 2 and a top electrode 1; the high acoustic velocity substrate is a silicon carbide single crystal substrate, and the piezoelectric film is a zinc oxide film;

[0057] The total thickness of the piezoelectric film layer is h, the depth of the etched part is d, and d / h is defined as the etching ratio; the thickness of the top electrode is t1, the thickness of the bottom electrode is t2, the width of the top electrode is consistent with the width of the unetched zinc oxide column, which is w, the wavelength of the surface acoustic wave λ=2μm, the metallization ratio duty factor=2w / λ, the normalized thickness of the top electrode is t1 / λ, the normalized thickness of the bottom electrode is t2 / λ, and the normalized thickness of the ZnO piezoelectric film is h / λ.

[0058] The units of h, d, w, t1, t2 and λ above are all micrometers.

[0059] (1) When the top electrode is Cu, the normalized thickness of the top electrode is t1 / λ=0.07, and the etching ratio is d / h=1, the normalized thickness of the ZnO piezoelectric film is h / λ=0.5, and the metallization ratio is 0.5.

[0060] Figure 8 The wave velocity and electromechanical coupling coefficient curves of quasi-Rayleigh waves under different normalized bottom electrode thicknesses (t2 / λ) when the bottom electrode is Al, Cu or Ni respectively. The figure shows that the wave velocity decreases with increasing bottom electrode thickness, and the electromechanical coupling coefficient decreases with increasing bottom electrode thickness. At the same normalized bottom electrode thickness, the sound velocity is Ni>Cu>Al, while the electromechanical coupling coefficient is Ni>Cu>Al.

[0061] (2) When the top electrode is Al and the normalized thickness of the top electrode is t1 / λ=0.13, the etching ratio d / h=0.7, the normalized thickness of the ZnO piezoelectric film is h / λ=0.6, and the metallization ratio is 0.5.

[0062] Fig. 9 The wave velocity and electromechanical coupling coefficient curves of the quasi-Sishawar wave under different normalized bottom electrode thicknesses (t2 / λ) when the bottom electrode is Al, Cu or Ni respectively. The figure shows that the wave velocity decreases with the increase of the bottom electrode thickness, and the electromechanical coupling coefficient increases with the increase of the bottom electrode thickness. At the same normalized bottom electrode thickness, the sound velocity is Ni>Al>Cu, while the electromechanical coupling coefficient is Al>Cu>Ni.

[0063] It should be noted that the above are only two embodiments of the present invention and are not intended to limit the present invention. Within the limitations and principles of the present invention, any modifications, equivalent substitutions, improvements, etc. of the present invention should be included in the protection scope of the present invention.

Claims

1. A surface acoustic wave device, comprising, from bottom to top, a high acoustic velocity substrate, a partially etched piezoelectric film and a top electrode; The total thickness of the partially etched piezoelectric film is h, the depth of the etched portion is d, and the etching ratio d / h is 0<d / h≤1; The top electrode is an interdigitated electrode, and the piezoelectric film between the interdigitated electrodes is partially etched; The thickness of the top electrode is t1; The width of the top electrode and the width of the unetched piezoelectric film are kept consistent as w; The metallization ratio is 2w / λ, 0.1≤2w / λ≤0.9; The normalized thickness of the top electrode is t1 / λ, 0<t1 / λ≤0.3; The normalized thickness of the piezoelectric film is h / λ, 0<h / λ≤3; The λ is the wavelength of the surface acoustic wave; The wavelength λ of the surface acoustic wave is 1 μm≤λ≤5 μm.

2. The surface acoustic wave device according to claim 1, characterized in that: The normalized thickness of the top electrode is 0.01≤t1 / λ≤0.13; The normalized thickness of the piezoelectric film is 0.5≤h / λ≤1; The wavelength λ of the surface acoustic wave is 2 μm.

3. The surface acoustic wave device according to claim 1, characterized in that: The etching shape of the piezoelectric film between the interdigitated fingers is columnar; The etched portion of the piezoelectric film is adjacent to one side of the top electrode.

4. The surface acoustic wave device according to claim 3, characterized in that: The etching shape of the piezoelectric film between the interdigitated fingers is a rectangular column.

5. The surface acoustic wave device according to any one of claims 1 to 4, characterized in that: A bottom electrode is added between the high acoustic velocity substrate and the partially etched piezoelectric film.

6. The surface acoustic wave device according to claim 5, characterized in that: The material of the bottom electrode is one of the following metals or a binary alloy of two metals: Al, Cu, Pt, Mo, W, Ni.

7. The surface acoustic wave device according to claim 5, characterized in that: The thickness of the bottom electrode is t2, and the normalized thickness of the bottom electrode is t2 / λ, where 0<t2 / λ≤0.

3.

8. The surface acoustic wave device according to claim 7, characterized in that: The normalized thickness of the bottom electrode is 0.01≤t2 / λ≤0.

1.

9. The surface acoustic wave device according to any one of claims 1 to 4, characterized in that: The high acoustic velocity substrate is a silicon carbide substrate, a sapphire substrate or a diamond substrate; The material of the top electrode is one of the following metals or a binary alloy of two metals: Al, Cu, Pt, Mo, W, Ni.

10. The surface acoustic wave device according to any one of claims 1 to 4, characterized in that: The partially etched piezoelectric film is a zinc oxide film or a doped zinc oxide film; The doping element of the doped zinc oxide film is Cr, Fe or V.

11. A filter comprising the surface acoustic wave device according to any one of claims 1 to 10.

Images