CN112953454B - High-frequency low-loss surface acoustic wave resonator and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of design and preparation of single crystal thin film devices, and particularly relates to a high-frequency low-loss surface acoustic wave resonator and a preparation method thereof. According to the invention, a special tangential film piezoelectric material is adopted to excite a high-sound-speed surface acoustic wave with a specific mode, so that the high electromechanical coupling coefficient is realized, and the resonant frequency is improved; and the double-deck acoustic reflection structure of cooperation just effectually suppresses the leakage of high acoustic surface acoustic wave to the volume direction, restricts the energy of surface acoustic wave at piezoelectric film, has promoted device Q value. Compared with the mode of inhibiting energy leakage of the multilayer Bragg reflection layer, the invention reduces the number of the reflection layer, not only ensures the reflection layer to have better quality, but also avoids the adverse effect on the resonator caused by the quality difference of the layer-by-layer grown film, and simultaneously reduces the preparation material and/or process cost.

Description

A high frequency, low loss surface acoustic wave resonator and preparation method thereof

technical field

The invention belongs to the field of design and preparation of single crystal thin film devices, in particular to a high-frequency, low-loss surface acoustic wave resonator and a preparation method thereof.

Background technique

SAW resonators are widely used in the field of wireless communication with the advantages of reliable performance, good consistency, large design flexibility, and small input and output impedance errors. The traditional surface acoustic wave resonator uses the piezoelectric effect of piezoelectric material to excite the surface acoustic wave by preparing interdigitated electrodes on the piezoelectric material, which is a simple bulk structure. Its resonant frequency is proportional to the velocity of the excited surface acoustic wave and inversely proportional to the width of the interdigital electrode. Due to the limitation of the structure, the acoustic energy of the traditional SAW device is very easy to leak to the bulk direction, so the device quality factor (Q value) is low. lower. To obtain high-frequency and high-Q resonators, it is necessary to limit the leakage of resonant energy while increasing the surface acoustic wave velocity.

Some existing high-frequency SAW resonators mainly include the following: 1. SAW devices prepared with piezoelectric thin films on high-sonic-speed substrates such as diamond, which can achieve high-speed and high-frequency, but the electromechanical coupling coefficient is usually only about 3% , and the preparation of piezoelectric thin films is more complicated; 2. The cavity-type SAW device prepared by using the Lamb wave of the A1 mode also achieves high frequency through high sound velocity, but the thin film is prepared by sputtering, which is expensive and expensive. The stability of the structure is low, and the A1 modal sound velocity is unstable, which fluctuates greatly with the thickness of the piezoelectric layer; 3. The Bragg reflector is used to prepare the SAW device by imitating the preparation method of the reflector layer of the bulk acoustic wave resonator, but the multilayer structure makes The cost of fabrication of SAW devices increases and the film flatness has a huge impact on device performance, which puts forward higher requirements for mass production.

SUMMARY OF THE INVENTION

In view of the above problems or deficiencies, in order to solve the technical problems such as high preparation cost and low electromechanical coupling coefficient when preparing high-frequency surface acoustic wave resonators in the prior art, the present invention provides a high-frequency, low-loss surface acoustic wave resonator The preparation method thereof has the advantages of high frequency, high Q, large electromechanical coupling coefficient, low preparation cost and stable structure.

A high-frequency, low-loss surface acoustic wave resonator, comprising interdigital electrodes, a piezoelectric film, a reflective layer, a bonding layer and a substrate in order from top to bottom; or, from top to bottom, interdigitated electrodes, Piezoelectric films, bonding layers, reflective layers and substrates.

The piezoelectric thin film is a single crystal lithium niobate X cut from 0° to 40°, 150° to 180°, Y to excite the S ₀ mode Lamb wave; single crystal lithium niobate Y is cut from 0° to 30°, 40° ° to 50°, 130° to 140°, 150° to 180° X to excite S ₀ mode Lamb wave, SH ₀ wave or LLSAW; single crystal lithium niobate Z cut 0° to 10°, 50° to 70°, 110° to 130°, 170° to 180° X to excite S ₀ mode, A ₁ mode Lamb wave; or single crystal lithium tantalate X cut 20° to 40° Y to excite S ₀ mode State Lamb waves.

Further, the thickness of the piezoelectric film is 50-5000 nm.

Further, the material of the interdigital electrode is AI, Au, Mo, Pt or W, the thickness of the interdigital electrode is 5%-10%λ, and λ is the interdigital period.

Further, the thicknesses of the low acoustic impedance reflective layer and the high acoustic impedance reflective layer are related to the designed interdigital period, and the thickness ranges from 0.1 to 0.5λ, where λ is the interdigital period.

Further, the substrate is Si, silicon-on-insulator SOI, glass, lithium niobate LN or lithium tantalate LT.

Further, the material of the low acoustic impedance reflective layer is one of Al, Ti, SiO ₂ or BCB (Benzobutene); the material of the high acoustic impedance reflective layer is Mo, Au, Nb, Ni , Pt, Ta, W, Ir, ZnO, HfO ₂ , TiO ₂ , Ta ₂ 0 ₅ or WO ₃ .

The preparation method of the above-mentioned high-frequency, low-loss surface acoustic wave resonator, comprising the following steps:

Step 1. Take the piezoelectric material that has undergone ion implantation, grow high and low acoustic impedance reflective layers in sequence under the implanted surface of the piezoelectric material, and then bond the substrate to the side of the piezoelectric material with the reflective layer;

Or, take the piezoelectric material that has undergone ion implantation and the substrate with high and low acoustic impedance reflective layers grown in turn, and bond one side of the substrate growth reflective layer to the side of the ion implanted surface of the piezoelectric material;

Alternatively, take the ion-implanted piezoelectric material and grow a low-acoustic-impedance reflective layer under the implanted surface, take the substrate to grow a high-acoustic-impedance reflective layer above it, and then connect the side of the piezoelectric material with the reflective layer to the substrate with a reflective layer. One side of the reflective layer is bonded;

Step 2: Heat treatment of the bonded product obtained in Step 1 to peel off the thin film of the piezoelectric material, and then grow an interdigital electrode on the peeled side of the piezoelectric material.

Further, the bonding in the step 1 is selected from polymer bonding or hydrophilic bonding.

Further, the polymer bonding is performed by coating an organic insulating material on the bonding side of the substrate and/or the piezoelectric material; the organic insulating material is benzocyclobutene and/or polyimide; The total thickness of the bonding layer is 50nm-4000nm.

Further, the hydrophilic bonding is a bond growing on the bonding side of the substrate and/or the piezoelectric material; wherein, the bonding is silicon oxide, silicon nitride, aluminum oxide and/or Or aluminum nitride; the total thickness of the bonding layer is 50nm-4000nm.

Further, the step 2 is specifically heating the bonded product obtained in the step 1 to 150-350° C., and annealing for 20-120 min to obtain a peeling film.

Compared with the prior art, the advantages and beneficial effects of the present invention are:

1. The high-frequency, low-loss SAW resonator of the present invention uses a special tangential thin-film piezoelectric material to excite a high-speed SAW in a specific mode. Raised resonance frequency. By adopting the acoustic reflection structure, the leakage of the high-speed surface acoustic wave to the bulk direction is suppressed, and the energy of the surface acoustic wave is confined to the piezoelectric film, thereby improving the Q value of the device.

2. The high-frequency, low-loss surface acoustic wave resonator preparation method of the present invention uses wafer bonding and transfer technology to prepare high-quality piezoelectric thin films, and combined with the solid reflective layer structure, a resonator with high structural strength and excellent performance can be prepared. The bonding layer can be arranged between the piezoelectric layer and the reflective layer, or between the reflective layer and the substrate, so that the bonding method has great flexibility to meet the needs of different preparation situations and improve the bonding power. . In addition, the prepared high-frequency and low-loss surface acoustic wave resonator meets the requirements of broadband filtering on the premise of meeting high frequency and high electromechanical coupling coefficient, and is not easy to generate harmonics, which solves the problem of electron beam deposition. It is difficult to ensure the quality orientation of the film, and the quality of the film is not high, which causes the device to generate multiple harmonics and has a large impact on the resonant frequency, and it is difficult to realize the technical problem of broadband filtering.

3. The high-frequency, low-loss surface acoustic wave resonator of the present invention only needs to grow two layers of a low-acoustic impedance reflective layer and a high-acoustic impedance reflective layer. Compared with the SAW resonator with multilayer Bragg reflection layers, when the multilayer material is grown, the roughness of the uppermost film will gradually increase with the increase of the number of layers, and the quality of the film will become worse and worse, and the film closest to the piezoelectric The quality of one reflective layer of the material has the greatest influence on the sound wave reflection effect of the solid reflective layer. On the premise of effectively restricting the leakage of resonance energy in the bulk direction, the invention reduces the number of reflective layers, which not only ensures good quality of the reflective layers, but also avoids the adverse effects on the resonator caused by the poor quality of the layer-by-layer growth film. Reduced manufacturing material and/or process costs.

Description of drawings

FIG. 1 is a schematic structural diagram of the present invention.

FIG. 2 is a schematic diagram of the preparation process of Example 1. FIG.

FIG. 3 is a schematic structural diagram of Comparative Example 1. FIG.

FIG. 4 is a deformation and displacement diagram of Example 1 at the center frequency point.

FIG. 5 is a deformation and displacement diagram of Comparative Example 1 at the center frequency point.

Reference numerals: 1-interdigital electrode, 2-piezoelectric film, 3-low acoustic impedance reflection layer, 4-high acoustic impedance reflection layer, 5-bonding layer, 6-substrate.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and the accompanying drawings; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that, if specific conditions are not indicated in the embodiments of the present invention, conventional conditions or conditions suggested by manufacturers are used. The reagents or instruments used without the manufacturer's indication are conventional products that can be obtained from the market. The raw materials of different manufacturers and models do not affect the implementation of the technical solution of the present invention and the realization of the technical effect.

Preferably, the piezoelectric material after ion implantation is obtained by the following method: taking the piezoelectric material, and performing ion implantation on the piezoelectric material, and the implanted ions are one or more of H ions, He ions, B ions, and As ions The energy of implanted ions is 100KeV-1000KeV; the implantation dose is 2-8×10 ¹⁶ /cm ² ; the ion beam current is 0.1-10um/cm ^-2 ; the implantation depth is 0.3-8um.

Example 1

The preparation method of the high-frequency, low-loss surface acoustic wave resonator of the present embodiment, as shown in Figure 2, comprises the following steps:

Step 1. Take the piezoelectric material that has undergone ion implantation, and grow a reflective layer under the implanted surface of the piezoelectric material, then take the substrate, and bond the substrate to the side of the piezoelectric material with the reflective layer.

The piezoelectric material is the single crystal lithium niobate of Y-cut and Z-transmission. The piezoelectric material is implanted with H ions. The energy of the implanted ions is 100KeV, the implantation dose is 2×10 ¹⁶ /cm ² , and the ion beam current is 8um/cm ^-2 , the implantation depth is 4um, and the piezoelectric material after ion implantation is obtained.

A low-acoustic impedance reflective layer is grown under the implanted surface of the ion-implanted piezoelectric material, and then a high-acoustic impedance reflective layer is grown on the low-acoustic impedance reflective layer. The total thickness of the grown reflective layer is 800 nm, and the material of the low-acoustic impedance reflective layer is is Al, and the material of the high-acoustic impedance reflective layer is Mo.

Then, take the substrate Si, bond the substrate to the side with the reflective layer of the piezoelectric material, the bonding in this embodiment is polymer bonding, and coat the bond on the bonding side of the substrate and the piezoelectric material The compound is bonded, and the bond is benzocyclobutene BCB.

The pre-bonding pressure for bonding is 4×10 ⁵ Pa, and the pressure holding time is 30min; then, the temperature is slowly raised to 200°C, and the temperature is kept at 200°C for 2h, so that the benzocyclobutene is completely cured, The bonding is completed and the bonded product is obtained.

Step 2: Heat treatment of the bonded product obtained in Step 1 to peel off the thin film of the piezoelectric material, and then grow an interdigital electrode on the peeled side of the piezoelectric material.

Heat treatment: at a temperature of 350 °C, annealing for 2 hours, so that the piezoelectric material is split along the damaged layer generated by the implanted ions to obtain a single crystal piezoelectric thin film material, that is, a piezoelectric thin film layer, as shown in (4) in Figure 1 .

Finally, an interdigital electrode is grown on the peeling side of the piezoelectric material. In this embodiment, the electrode material of the grown interdigital electrode is A1 and the thickness is 160 nm, that is, as shown in (5) in FIG. 1 .

Comparative Example 1

The preparation method of the surface acoustic wave resonator of this comparative example, as shown in Figure 3, includes the following steps:

Step 1. Take the Y-cut and Z-transmitted single crystal lithium niobate after surface polishing as a piezoelectric material, and grow interdigital electrodes on the polished surface.

Effect test example

In order to verify the technical effect of the high-frequency, low-loss surface acoustic wave resonator of the present invention, the high-frequency, low-loss surface acoustic wave resonator prepared by the method in Example 1 and Comparative Example 1, according to The following steps are carried out to carry out the comparative detection test:

1. Take the resonator prepared by the method in Example 1 and Comparative Example 1, use a probe station and a vector network analyzer to test the S parameter of the resonator, and obtain S11.

2. Import the S11 of each spectral resonator into the ADS simulation software, use the ADS software to simulate the input impedance Zin of the three devices, and read the series resonant frequency fs and parallel resonant frequency fp of each resonator from the impedance curve.

3. Calculate the Q value of the resonator according to the following formula:

4. Calculate the electrical coupling coefficient k _t ² according to the following formula:

After the above experiments, the experimental data obtained are as follows

group fs fp Q K_t² Example 1 2335 2434 2176 10.24% Comparative Example 1 1487 1552 647 4.3%

4 and 5 are displacement diagrams of Example 1 and Comparative Example. The thickness of the device represented by the abscissa is shown in Figure 4. At points other than the thickness of the piezoelectric layer, the displacement is lower and the vibration is smaller, indicating that the energy is confined to the piezoelectric layer. Figure 5 shows that the points outside the thickness of the piezoelectric layer still have a large displacement, there is a large vibration, and there is a large leakage of energy.

To sum up, it can be seen that the present invention uses a special tangential thin-film piezoelectric material to excite a high-sonic surface acoustic wave of a specific mode, which not only achieves a high electromechanical coupling coefficient, but also increases the resonant frequency; The reflection structure can effectively suppress the leakage of the high-speed surface acoustic wave to the bulk direction, confine the energy of the surface acoustic wave to the piezoelectric film, and improve the Q value of the device. Compared with the method of suppressing energy leakage of the multilayer Bragg reflection layer, the present invention reduces the number of reflection layers, which not only ensures the better quality of the reflection layer, but also avoids the adverse effects on the resonator caused by the poor quality of the layer-by-layer growth film. At the same time, the cost of preparation materials and/or process is reduced.

It can be seen from the above results that the surface acoustic wave resonator designed and prepared by the present invention has higher frequency, Q value and electromechanical coupling coefficient, and has excellent performance. It is known from the technical common sense that the present invention can be realized by other embodiments without departing from its spirit or essential characteristics. Accordingly, the above-disclosed embodiments are, in all respects, illustrative and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims (10)

1. a high-frequency, low-loss surface acoustic wave resonator, characterized in that: from top to bottom, comprise interdigital electrodes, piezoelectric thin film, reflection layer, bonding layer and substrate in turn; or, from top to bottom The order is the interdigital electrode, the piezoelectric film, the bonding layer, the reflective layer and the substrate; The piezoelectric thin film is a single crystal lithium niobate X cut from 0° to 40°, 150° to 180°, Y to excite the S ₀ mode Lamb wave; single crystal lithium niobate Y is cut from 0° to 30°, 40° ° to 50°, 130° to 140°, 150° to 180° X to excite S ₀ mode Lamb wave, SH ₀ wave or LLSAW; single crystal lithium niobate Z cut 0° to 10°, 50° to 70°, 110° to 130°, 170° to 180° X to excite S ₀ mode, A ₁ mode Lamb wave; or single crystal lithium tantalate X cut 20° to 40° Y to excite S ₀ mode state Lamb wave; The reflection layer includes a low acoustic impedance reflection layer and a high acoustic impedance reflection layer, the thickness of the low acoustic impedance reflection layer and the high acoustic impedance reflection layer is 0.1-0.5λ, and λ is an interdigital period. 2 . The high-frequency, low-loss surface acoustic wave resonator according to claim 1 , wherein the piezoelectric film has a thickness of 50-5000 nm. 3 . 3. The high-frequency, low-loss surface acoustic wave resonator of claim 1, wherein the material of the interdigital electrode is AI, Au, Mo, Pt or W, and the interdigital electrode thickness is 5%- 10%λ, where λ is the interdigital period. 4. The high-frequency, low-loss surface acoustic wave resonator of claim 1, wherein the substrate is Si, silicon-on-insulator SOI, glass, lithium niobate LN or lithium tantalate LT. 5. The high-frequency, low-loss surface acoustic wave resonator of claim 1, wherein: the material of the low-acoustic impedance reflective layer is Al, Ti, SiO or BCB styrene _; the The material of the high acoustic impedance reflection layer is Mo, Au, Nb, Ni, Pt, Ta, W, Ir, ZnO, HfO ₂ , TiO ₂ , Ta ₂ 0 ₅ or WO ₃ . 6. the preparation method of the high-frequency, low-loss surface acoustic wave resonator of claim 1, is characterized in that, comprises the steps: Step 1. Take the piezoelectric material that has undergone ion implantation, grow high and low acoustic impedance reflective layers in sequence under the implanted surface of the piezoelectric material, and then bond the substrate to the side of the piezoelectric material with the reflective layer; Or, take the piezoelectric material that has undergone ion implantation and the substrate with high and low acoustic impedance reflective layers grown in turn, and bond one side of the substrate growth reflective layer to the side of the ion implanted surface of the piezoelectric material; Alternatively, take the ion-implanted piezoelectric material and grow a low-acoustic-impedance reflective layer under the implanted surface, take the substrate to grow a high-acoustic-impedance reflective layer above it, and then connect the side of the piezoelectric material with the reflective layer to the substrate with a reflective layer. One side of the reflective layer is bonded; Step 2: Heat treatment of the bonded product obtained in Step 1 to peel off the thin film of the piezoelectric material, and then grow an interdigital electrode on the peeled side of the piezoelectric material. 7 . The method for preparing a high-frequency, low-loss surface acoustic wave resonator according to claim 6 , wherein the bonding in the step 1 is polymer bonding or hydrophilic bonding. 8 . 8. the preparation method of the high frequency, low loss surface acoustic wave resonator as claimed in claim 7, is characterized in that: described polymer bonding is to coat organic insulating material on substrate and/or piezoelectric material The bonding side is carried out; the organic insulating material is benzocyclobutene and/or polyimide; the total thickness of the bonding layer is 50nm-4000nm. 9. The preparation method of the high-frequency, low-loss surface acoustic wave resonator according to claim 7, wherein the hydrophilic bonding is grown on the bonding side of the substrate and/or the piezoelectric material The bonding compound is bonded; wherein, the bonding compound is silicon oxide, silicon nitride, aluminum oxide and/or aluminum nitride; the total thickness of the bonding layer is 50nm-4000nm. 10. The method for preparing a high-frequency, low-loss surface acoustic wave resonator according to claim 6, wherein the step 2 is to heat the bonded product obtained in the step 1 to 150-350°C, Annealed for 20-120 min to obtain a peeled film.

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