Surface acoustic wave resonator with LN-POI multilayer structure

Abstract

The invention belongs to the field of piezoelectric acoustic wave devices, and particularly relates to an acoustic surface wave resonator of an LN-POI multilayer structure. The resonator comprises an interdigital electrode layer, a piezoelectric layer, an oxide buried layer, a polycrystalline silicon layer and a substrate which are stacked from top to bottom, the interdigital electrode layer is composed of a first bus bar, a second bus bar and electrode finger bars connected to the inner sides of the two bus bars. The electrode finger strips connected with the same bus bar are parallel, and all the electrode finger strips and the bus bar form an inclination angle of 20-25 degrees; the large electromechanical coupling coefficient and the working frequency of the resonator are improved, the transverse mode can be suppressed, and the performance of the resonator is improved.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric acoustic wave devices, specifically relating to a surface acoustic wave resonator with an LN-POI multilayer structure. Background Technology

[0002] With the development of microwave communication technology, increasingly higher requirements are being placed on the operating frequency and bandwidth of SAW filters. Taking the B41 filter used in 5G base stations as an example, its center frequency is 2593MHz, and its relative bandwidth reaches 6.1%. Fabricating high-frequency, high-bandwidth SAW filters requires SAW resonators with high acoustic velocity and a large electromechanical coupling coefficient. Although traditional IHP substrates based on 42Y-X LT piezoelectric thin films exhibit excellent performance at operating frequencies of 1-2GHz, their performance degrades above 2GHz. The electromechanical coupling coefficient of these resonators is 10%, making it difficult to design filters with a relative bandwidth of 6.1%. The interdigitated electrode linewidth of the resonator is 380nm. While this does not reach the photolithographic linewidth limit, the smaller electrode linewidth affects the device's power handling capability, making it difficult to meet the high-power application requirements of base stations.

[0003] In summary, there is an urgent need for a high-frequency resonator with a large electromechanical coupling coefficient to meet the requirements of 5G radio frequency filters. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes an LN-POI multilayer surface acoustic wave resonator, which includes: an interdigitated electrode layer, a piezoelectric layer, a buried oxide layer, a polysilicon layer, and a substrate stacked from top to bottom; the interdigitated electrode layer is composed of a first bus bar, a second bus bar, and electrode fingers connected to the inner sides of the two bus bars; the electrode fingers connected to the same bus bar are parallel, and all electrode fingers are tilted at an angle of 20-25° to the bus bar.

[0005] Preferably, in the interdigitated electrode layer, the electrode strips include dummy fingers and aperture fingers; the dummy fingers and aperture fingers are periodically connected inside two busbars with the same period, and the dummy fingers and aperture fingers are interleaved; the aperture fingers connected to one busbar correspond one-to-one with the dummy fingers connected to the other busbar and are located on the same straight line.

[0006] Furthermore, there is a gap between the spurs and the aperture strips located on the same straight line, and the gaps between all spurs and the aperture strips are equal.

[0007] Furthermore, a small hammer is provided at the end of all the aperture fingers.

[0008] Furthermore, the length of the pseudo-finger is 2.16 times the half-cycle, and the total length of the overlapping portion of the aperture finger strips connected by the two busbars, plus the two small hammers, is 40 times the half-cycle.

[0009] Furthermore, the width of the small hammer is greater than that of the aperture finger.

[0010] Preferably, the interdigitated electrode layer material is aluminum, the buried oxide layer material is silicon dioxide, and the substrate material is silicon.

[0011] Preferably, the piezoelectric layer material is single-crystal lithium niobate, and the cut is X-160°Y, with the Euler angles of the cut set to (-20°, -90°, 90°).

[0012] The beneficial effects of this invention are as follows: By using lithium niobate as the piezoelectric layer, compared with lithium tantalate, lithium niobate increases the electromechanical coupling coefficient and sound velocity, thereby improving the bandwidth and operating frequency of the resonator; in addition, this invention adopts methods such as tilted interdigital transducers, adding small hammers to the ends of the interdigital transducers, and optimizing the aperture finger length to suppress transverse modes, thereby improving the performance of the resonator. Attached Figure Description

[0013] Figure 1 This is a cross-sectional view of the surface acoustic wave resonator in this invention;

[0014] Figure 2 This is a top view of the interdigitated structure of the standard resonator in this invention;

[0015] Figure 3 This is the impedance curve of the standard resonator in this invention;

[0016] Figure 4 This is a stress-displacement diagram of the transverse modes of the standard resonator in this invention;

[0017] Figure 5 This is a schematic diagram of the tilted surface acoustic wave resonator in this invention;

[0018] Figure 6 The impedance curves of the tilted surface acoustic wave resonator in this invention under different aperture lengths are shown.

[0019] Figure 7 This is a comparison diagram of the impedance of the tilted surface acoustic wave resonator in this invention at different tilt angles;

[0020] Figure 8 This is a comparison diagram of the impedance of the surface acoustic wave resonator in this invention under different electrode finger structures;

[0021] Figure 9 This is a comparison diagram of the real part of the impedance of the surface acoustic wave resonator in this invention under different electrode finger structures. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention proposes a surface acoustic wave resonator with an LN-POI (insulating substrate-lithium niobate) multilayer structure, such as... Figure 1 As shown, the resonator includes: an interdigitated electrode layer, a piezoelectric layer, a buried oxide layer, a polysilicon layer, and a substrate stacked from top to bottom; the interdigitated electrode layer is composed of a first bus bar, a second bus bar, and electrode fingers connected to the inner sides of the two bus bars.

[0024] In some preferred embodiments of the present invention, the interdigitated electrode layer is made of Al (aluminum); the piezoelectric layer material is selected as single-crystal lithium niobate with an X-160°Y cut, the Euler angles of which are set to (-20°, -90°, 90°); the buried oxide layer is made of SiO2 (silicon dioxide), which can reduce the temperature frequency coefficient (TCF) of the device; then comes the polycrystalline silicon layer, which can eliminate the surface parasitic conduction effect (PSC effect) between SiO2 and the substrate Si, thereby reducing dielectric loss and improving Q value; the substrate is made of Si, which can prevent downward energy leakage. Preferably, the present invention uses X160°-LiNbO3 (0.3 μm) / SiO2 (0.5 μm) / Poly-Si (1 μm) / Si (350 μm) as the substrate, and the interdigitated electrodes are made of Al material with a thickness of 0.115 μm.

[0025] A top view of the interdigital structure of a standard resonator is shown below. Figure 2 As shown in the figure, in the interdigitated electrode layer, the electrode strips include dummy fingers and aperture fingers. The dummy fingers and aperture fingers are periodically connected inside two busbars with the same period, and the dummy fingers and aperture fingers intersect each other. The aperture fingers connected to one busbar correspond one-to-one with the dummy fingers connected to the other busbar and are located on the same straight line. There is a gap between the dummy fingers and aperture fingers located on the same straight line, and the gaps between all dummy fingers and aperture fingers are equal. The overlapping part of the two fingers is called the aperture length. Specifically, in this invention, the total length of the overlapping part of the aperture fingers connected to the two busbars plus the two small hammers is called the aperture length.

[0026] The impedance curve of a standard resonator is as follows: Figure 3 As shown in the figure, the standard resonator has too many transverse spurious modes between the resonant frequency and the anti-resonant frequency. Resonators fabricated in this way will severely damage the performance of filters when used as components. The stress-displacement diagram of the transverse modes is shown below. Figure 4As shown, it is clear that the standard resonator has many transverse modes, and some transverse mode energy has already leaked into the bus region. Therefore, measures need to be taken to suppress transverse modes.

[0027] In some preferred embodiments of the present invention, such as Figure 5 As shown, all electrode fingers are tilted at a 20-25° angle to the busbar; this structure is consistent with... Figure 2 The structural parameters are the same; the only difference is the tilt angle between the interdigitated electrodes and the busbar.

[0028] When the electrode fingers are all tilted at a 25° angle to the busbar, the impedance curves for different aperture lengths are as follows: Figure 6 As shown in the figure, increasing the aperture length will cause the transverse mode of the resonator to become smaller and smaller until it disappears; however, an excessively large aperture length will introduce new boundary scattering interference, leading to increased acoustic energy loss and affecting the performance of the resonator. Preferably, all aperture fingers are provided with a small hammer at the end, and the pseudo-finger length is smaller than the aperture fingers. The pseudo-finger length of the resonator of this invention is 2.16P, the total length of the aperture fingers and the small hammer is selected to be 40P, and the width of the small hammer is larger than the aperture fingers, with a width of 0.65P, where P is the half-cycle length.

[0029] The tilt angle between the electrode fingers and the busbar affects the transverse mode suppression effect of the resonator, as shown in the figure. Figure 7 As shown in the figure, with the increase of the tilt angle, the transverse mode between the resonant and anti-resonant points begins to decrease. However, when the tilt angle increases to a certain extent, such as 30°, the transverse mode begins to increase again. The figure also shows that a tilt angle of around 20-25° provides good transverse mode suppression; increasing the tilt angle beyond 25° leads to a further increase in the transverse mode. Figure 4 It can also be seen that as the tilt angle increases, the frequency at the anti-resonance point gradually shifts to the left, while the resonance point frequency remains almost unchanged. Therefore, the larger the tilt angle, the smaller the electromechanical coupling coefficient. In some preferred embodiments of the present invention, the electrode fingers connected to the same busbar are parallel, and all electrode fingers are tilted at a 20-25° angle to the busbar.

[0030] Evaluation of the present invention:

[0031] When the electrode fingers are all tilted at a 25° angle to the busbar, the impedance comparison of different structures is as follows: Figure 8 As shown, it can be clearly seen that the anti-resonance frequency of the tilted resonator is lower than that of the non-tilted one, which leads to a decrease in the electromechanical coupling coefficient. Moreover, the transverse mode suppression capability of the tilted resonator is much better than that of the non-tilted one.

[0032] When the electrode fingers are all tilted at a 25° angle to the busbar, the real part of the impedance of different structures is compared, for example... Figure 9As shown, it can be seen that the resonator with the added single hammer structure has slightly better suppression capability than the resonator without the single hammer structure.

[0033] In summary, this invention designs a surface acoustic wave resonator with an LN-POI multilayer structure that meets the requirements of the 5G NR band. By using lithium niobate as a piezoelectric layer, the electromechanical coupling coefficient and sound velocity are increased, thereby improving the bandwidth and operating frequency of the resonator. In addition, this invention adopts methods such as tilting the resonator, adding small hammers to the ends of the interdigitated fingers, and optimizing the aperture finger length to suppress transverse modes, thereby improving the performance of the resonator.

[0034] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A surface acoustic wave resonator with an LN-POI multilayer structure, characterized in that, include: The interdigitated electrode layer, piezoelectric layer, buried oxide layer, polysilicon layer and substrate are stacked from top to bottom; the interdigitated electrode layer is composed of a first bus bar, a second bus bar and electrode fingers connected to the inner side of the two bus bars; the electrode fingers connected to the same bus bar are parallel, and all electrode fingers are tilted at an angle of 20-25° to the bus bar.

2. The LN-POI multilayer surface acoustic wave resonator according to claim 1, characterized in that, In the interdigitated electrode layer, the electrode strips include dummy fingers and aperture fingers; the dummy fingers and aperture fingers are periodically connected inside two busbars with the same period, and the dummy fingers and aperture fingers are interleaved; the aperture fingers connected to one busbar correspond one-to-one with the dummy fingers connected to the other busbar and are located on the same straight line.

3. The LN-POI multilayer surface acoustic wave resonator according to claim 2, characterized in that, There is a gap between the spurs and the aperture bar located on the same straight line, and the gap between all spurs and the aperture bar is equal.

4. The LN-POI multilayer surface acoustic wave resonator according to claim 2, characterized in that, All the finger bars with apertures are equipped with small hammers at their ends.

5. The LN-POI multilayer surface acoustic wave resonator according to claim 4, characterized in that, The length of the pseudofinger is 2.16 times the half-cycle, and the total length of the overlapping part of the aperture finger connected by the two busbars plus the two small hammers is 40 times the half-cycle.

6. The LN-POI multilayer surface acoustic wave resonator according to claim 4, characterized in that, The width of the hammer is greater than the diameter of the finger bar.

7. The LN-POI multilayer surface acoustic wave resonator according to claim 1, characterized in that, The interdigitated electrode layer is made of aluminum, the buried oxide layer is made of silicon dioxide, and the substrate is made of silicon.

8. The LN-POI multilayer surface acoustic wave resonator according to claim 1, characterized in that, The piezoelectric layer material is single-crystal lithium niobate, and the cut is X-160°Y, with Euler angles set to (-20°, -90°, 90°).

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