Radio frequency front-end surface acoustic wave resonator

Abstract

A radio frequency front-end surface acoustic wave resonator provided by the present invention comprises a substrate and an electrode arranged on the substrate, the electrode comprises a bus and an interdigital transducer, the interdigital transducer comprises a first bus bar, a second bus bar, a first modulation region, a second modulation region and a plurality of electrode fingers, the interdigital transducer comprises two electrode fingers in a single period, and the first bus bar is connected with the second bus bar. Wherein one electrode finger extends to the first modulation area, then is connected with the first bus bar and is arranged at an interval with the second bus bar, the electrode finger is partially overlapped with the first modulation area, the first modulation area is connected with the first bus bar, and the other electrode finger extends to the second modulation area, then is connected with the second bus bar and is arranged at an interval with the first bus bar. The second modulation region is connected to the second bus bar, and the electrode fingers connected to the first bus bar and the electrode fingers connected to the second bus bar are alternately arranged at intervals. Through the scheme of the invention, the Q value is improved, and high-order impure modes and energy loss are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of radio frequency filtering, and in particular to a radio frequency front-end surface acoustic wave resonator. Background Art

[0002] POI SAW is an advanced technology for surface acoustic wave (SAW) filters. It utilizes a POI (Piezo Oxidized Insulator) substrate, which has a single crystal piezoelectric layer on the top layer, an oxide buried layer in the middle, and a high resistivity silicon material on the bottom. The main advantages of the POI substrate SAW filter are its excellent temperature characteristics and high power tolerance. By bonding the piezoelectric body and the supporting substrate together, temperature changes are suppressed and heat dissipation is improved, thereby achieving high power tolerance.

[0003] POI substrate SAW filters are particularly important in 5G RF front-end modules because they can provide higher energy efficiency and lower energy loss than traditional TC-SAW (temperature compensated SAW) and BAW (bulk acoustic wave) filters. In addition, the process flow of POI substrate SAW filters is relatively simple, the cost is lower, and they can achieve a smaller area and wider bandwidth.

[0004] In terms of performance, the quality factor (Q value) of the POI SAW filter is greater than 4000, the coupling coefficient (k2) is greater than 8%, and the temperature coefficient of frequency (TCF) is less than 10ppm / ℃. These parameters are better than traditional TC-SAW and BAW filters. With the development of 5G technology, POI SAW filters are expected to become the standard of the filter industry in the next few years.

[0005] However, the finger tip structure used in POI SAW often has a shorter gap area in order to improve the Q value. However, the shorter gap area makes the traditional pison / hammer structure no longer applicable because it changes the reflection coefficient of the finger tip structure, making the transverse mode suppression effect worse. At the same time, a large amount of transverse acoustic wave energy is transmitted to the gap area and the bus bar, which will cause unnecessary stray resonance, thereby greatly deteriorating the loss and standing wave in the filter passband. Summary of the invention

[0006] In view of the above problems, the present invention proposes a radio frequency front-end surface acoustic wave resonator, aiming to solve the problem of heterogeneous modes in the passband of POI SAW.

[0007] A radio frequency front-end surface acoustic wave resonator proposed in the present invention comprises a substrate and an electrode arranged on the substrate, wherein the electrode comprises a busbar and an interdigital transducer;

[0008] The interdigital transducer includes a first bus bar, a second bus bar, a first modulation region, a second modulation region, and a plurality of electrode fingers. The modulation region and the plurality of electrode fingers are both located between the first bus bar and the second bus bar;

[0009] In a single period of the interdigital transducer, there are two electrode fingers. One electrode finger extends to the first modulation region and then connects to the first bus bar, and is spaced from the second bus bar. This electrode finger partially overlaps with the first modulation region, and the first modulation region is connected to the first bus bar. The other electrode finger extends to the second modulation region and then connects to the second bus bar, and is spaced from the first bus bar. The second modulation region is connected to the second bus bar. The electrode finger connected to the first bus bar and the electrode finger connected to the second bus bar are alternately and spaced apart;

[0010] Each electrode finger includes a modulation region, a gap region, and a central region connected in sequence.

[0011] Further, each electrode finger further includes an edge region, and the edge region is located between the gap region and the central region.

[0012] Further, the substrate includes a bottom substrate, a charge trapping layer, a temperature compensation and acoustic reflection layer, and a piezoelectric layer from bottom to top. The interdigital transducer is disposed on the surface of the piezoelectric layer facing away from the substrate; the bottom substrate serves as a support, the charge trapping layer is used to absorb electrons accumulated at the interface of the bottom substrate, the temperature compensation and acoustic reflection layer is used to compensate the negative temperature coefficient of the piezoelectric layer and reflect the energy leaked from the piezoelectric layer. The acoustic reflection includes low acoustic impedance and / or high acoustic impedance. The acoustic impedance of the low acoustic impedance is less than the acoustic impedance of the piezoelectric layer, and the acoustic impedance of the high acoustic impedance is greater than the acoustic impedance of the piezoelectric layer.

[0013] Further, the modulation region is located between the bus bar and the gap region. The modulation region is cosine-shaped or arc-shaped. Let the length of the wave peak of the modulation region in the aperture direction be L F , and the width of the electrode finger bar, that is, the length in the propagation direction, is W. Then W / 8 < L F < W / 2, and the length of the wave peak in the propagation direction = W; let the length of the wave valley of the modulation region in the aperture direction be L G , then there is L F / 4 < L G ≤ L F , and the length of the wave valley in the propagation direction = the spacing between two finger bars. The etching depth of the wave valley is D G , and the thickness of the piezoelectric layer is D. Then 0 ≤ D G < 0.3*D.

[0014] Further, in the arrangement direction of the first bus bar and the second bus bar, if the length of the gap region is L2 and the length of the edge region is L3, then 0.1λ < L2 < 1λ and 0.3λ < L3 < 1λ, where λ is the period of the sound wave.

[0015] Further, the material of the bottom substrate is single-crystalline silicon or polycrystalline silicon, the material of the temperature compensation and sound reflection layer is aluminum nitride or silicon oxide with a positive temperature coefficient characteristic, and the material of the piezoelectric layer is one of quartz, aluminum nitride, sapphire, lithium niobate, and lithium tantalate.

[0016] Further, the bus bar and the electrode are selected from one of aluminum, molybdenum, copper, gold, platinum, silver, nickel, chromium, and tungsten.

[0017] Further, in the arrangement direction of the first bus bar and the second bus bar, the sound velocity in the central region is V1, the sound velocity in the edge region is V2, and the sound velocity in the gap region is V3, and the sound velocity relationship is V3 > V1 > V2.

[0018] Further, the electrode fingers in the edge region are widened in the form of Hammer, thickened in the form of Piston, and widened and thickened to achieve the above sound velocity relationship.

[0019] A surface acoustic wave resonator for a radio frequency front end proposed by the present invention is provided with a modulation region in the resonator, so that the first and second bus bars form a wave crest and two wave troughs. The pattern of the modulation region is an arc or a cosine curve. In this way, the wave crest can play a role in smoothing the electric field lines, improving the Q value, and reducing the high-order spurious modes. The etched wave troughs can increase the wave velocity at that place, thereby increasing the average sound velocity of the entire modulation region, reducing the energy loss, and increasing the Q value. At the same time, the wave troughs of the present invention are etched under the piezoelectric layer, which can further increase the sound velocity of the modulation region, thereby further reducing the energy loss, and the overall unevenness of the resonator further reduces the conditions for generating spurious mode resonances in the gap region. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 is a cross-sectional view of the resonator provided by the embodiment of the present invention;

[0022] Figure 2 is a structural schematic diagram of a single period of the interdigital transducer provided by the embodiment of the present invention Figure 1 ;

[0023] Figure 3 The structure of a single cycle of an IDT provided by an embodiment of the present invention is shown in FIG. Figure 2 ;

[0024] Figure 4 It is a schematic diagram of the structure of a multi-period interdigital transducer with piston thickening in the edge region provided by an embodiment of the present invention;

[0025] Figure 5 It is a schematic diagram of the structure of a multi-period interdigital transducer with hammer widening in the edge region provided by an embodiment of the present invention.

[0026] Explanation of reference numerals: 10 - bottom substrate, 20 - charge trapping layer, 30 - temperature compensation and acoustic reflection layer, 40 - piezoelectric layer, 50 - electrode. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The sound field propagation direction in the present invention refers to the direction parallel to the bus bar, and the aperture direction refers to the direction perpendicular to the bus bar.

[0029] The present invention proposes a radio frequency front-end surface acoustic wave resonator, such as Figure 1 As shown, the resonator includes a substrate and an electrode 50 disposed on the substrate, and the electrode includes a busbar and an interdigital transducer;

[0030] The substrate comprises, from bottom to top, a bottom substrate 10, a charge trapping layer 20, a temperature compensation and acoustic reflection layer 30, and a piezoelectric layer 40, and the interdigital transducer is arranged on the surface of the piezoelectric layer away from the substrate; the substrate adopts a multi-layer substrate, and the bottom substrate 10 comprises a single crystal material or a polycrystalline material such as silicon and silicon carbide, which mainly plays a supporting role; the charge trapping layer 20 is used to absorb electrons deposited on the interface of the bottom substrate; the material of the temperature compensation and acoustic reflection layer 30 is a material with a positive temperature coefficient characteristic such as aluminum nitride and silicon oxide, which can compensate for the negative temperature coefficient of the piezoelectric layer, so that the overall temperature coefficient of the surface acoustic wave device is close to zero, and can reflect the energy leaked from the piezoelectric layer to improve the Q value, and the acoustic reflection comprises low acoustic impedance and / or high acoustic impedance, the acoustic impedance of the low acoustic impedance is less than the acoustic impedance of the piezoelectric layer, and the acoustic impedance of the high acoustic impedance is greater than the acoustic impedance of the piezoelectric layer, and when both low acoustic impedance and high acoustic impedance are included, the low acoustic impedance and the high acoustic impedance are arranged alternately in the direction from bottom to top of the substrate;

[0031] The piezoelectric layer 40 is generally a substrate made of a piezoelectric material. The material of the piezoelectric layer 40 is one of quartz, aluminum nitride, sapphire, LN (lithium niobate, LiNbO3), and LT (lithium tantalate, LiTaO3). Preferably, 30°-50° YX-LiTaO3 or 120°-170° YX-LiNbO3 can be adopted, so that there are fewer spurious modes near the main mode energy concentration region (i.e., the overlapping region A), and the transverse modes can be reduced. The thickness of the piezoelectric layer 40 is 0.1λ-0.5λ, where λ is the period of the acoustic wave, which is beneficial to confine most of the energy of the surface acoustic wave in the piezoelectric layer 40.

[0032] As Figure 2 shown, the interdigital transducer includes a first bus bar, a second bus bar, a first modulation region, a second modulation region, and a plurality of electrode fingers. The modulation region and the plurality of electrode fingers are both located between the first bus bar and the second bus bar;

[0033] In a single period of the interdigital transducer, there are two electrode fingers. One electrode finger extends to the first modulation region and then connects to the first bus bar, and is spaced from the second bus bar. This electrode finger partially overlaps with the first modulation region. The first modulation region is connected to the first bus bar. The other electrode finger extends to the second modulation region and then connects to the second bus bar, and is spaced from the first bus bar. The second modulation region is connected to the second bus bar. The electrode fingers connected to the first bus bar and the electrode fingers connected to the second bus bar are arranged alternately and spaced apart;

[0034] Each electrode finger includes a modulation region, a gap region, and a central region connected in sequence.

[0035] As Figure 3 shown, each electrode finger further includes an edge region, and the edge region is located between the gap region and the central region.

[0036] In the arrangement direction of the first bus bar and the second bus bar, let the length of the gap region be L2 and the length of the edge region be L3. Then 0.1λ < L2 < 1λ and 0.3λ < L3 < 1λ, where λ is the period of the interdigital transducer of the surface acoustic wave device. The mass load of the gap region is smaller, so the sound speed is higher than that of the central region. When the acoustic wave propagates to the interface of the gap region, it will be reflected due to a large sound speed difference. Therefore, the energy can be confined in the active region (the edge region and the central region). In POISAW, the length of the gap region is generally shorter than that of the gap region in TCSAW or Normal SAW. This is to increase the Q value. However, the shorter gap region structure will cause energy to leak to the passive region outside the gap region and form resonance in the gap region, resulting in an increase in the spurious modes of the device.

[0037] Therefore, in the present invention, the modulation region is provided to supplement the short gap region. The modulation region is located between the bus bar and the gap region, and the modulation region is cosine-shaped or arc-shaped. Its arc-shaped or cosine-shaped outer surface makes it difficult to generate stray resonance in the gap region. At the same time, the appearance of two wave valleys results in a relatively low overall sound speed in the modulation region, effectively lengthening the gap region, increasing the reflection efficiency of energy. The existence of the wave peak makes the electric field lines at the other finger bar smoother, reducing the electric field gradient, minimizing the generation of spurious modes, and improving the Q value of the device.

[0038] For the modulation region, let the length of the wave peak in the aperture direction be L F , and the width of the electrode finger bar, that is, the length along the propagation direction, be W. Then there is W / 8 < L F < W / 2. An excessive length will cause the wave peak to be too long, resulting in too large a local electric field, a relatively low maximum power of the device, and a relatively short high sound speed region. An excessively short length leads to no obvious effect. Let the length of the wave peak in the propagation direction = W, and the length of the wave valley in the propagation direction = the distance between two finger bars. Such a setting makes the electric field more uniform, and the thickness is consistent with the electrode. The length of the wave valley in the aperture direction is L G , then there is L F / 4 < L G ≤ L F , the etching depth of the wave valley is D G , and the thickness of the piezoelectric layer is D. Then there is 0 ≤ D G < 0.3*D. An overly deep etching depth not only increases the process difficulty but also increases the local distribution of the electric field, posing a breakdown risk.

[0039] The electrode is usually rectangular. Usually, the extension direction of the long side of the electrode is perpendicular to the extension direction of the bus bar, and multiple electrodes are parallel to each other. At the same time, there is a certain gap between adjacent electrodes. In the embodiment of the present invention, the electrode needs to be in contact with a bus bar to achieve electrical connection. The ratio of a single finger bar occupying half of a finger bar period is called the metallization rate, and here the metallization rate can be selected from 0.25 - 0.5.

[0040] The above-mentioned bus bar and electrode can be made of metal materials such as aluminum, molybdenum, copper, gold, platinum, silver, nickel, chromium, tungsten, etc. in the embodiment of the present invention. Of course, the specific materials of the bus bar and electrode are not specifically limited in the embodiment of the present invention and depend on the specific situation. However, usually, the material needs to have good electrical conductivity.

[0041] The resonator also includes a piston structure, which is arranged in the edge area. The setting of the piston structure can increase the mass load of the electrode fingers on the opposite sides of the aperture direction to enhance the resonator's suppression of transverse modes. Specifically, the piston structure can increase the mass load of the corresponding area, reduce the sound speed on the opposite sides of the active area in the aperture direction, so that the edge area forms a low sound speed area with a lower sound speed than the central area, thereby forming a piston mode and changing the phase of the sound wave in the area to further reduce the lateral loss of the sound wave, which helps to further suppress the noise mode.

[0042] In the arrangement direction of the first bus bar and the second bus bar, the sound speed of the central area is V1, the sound speed of the edge area is V2, and the sound speed of the gap area is V3, and the sound speed relationship is V3>V1>V2

[0043] The piston structures used in the edge area include Hammer widening, Piston thickening, and widening and thickening, such as Figure 4 and Figure 5 As shown, Figure 4 This is a schematic diagram of the structure of a multi-period interdigital transducer with piston thickening in the edge area. Figure 5 It is a schematic diagram of the structure of a multi-period interdigital transducer with hammer widening in the edge region.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A radio frequency front-end surface acoustic wave resonator, characterized in that: The resonator includes a substrate and an electrode disposed on the substrate. The electrode includes a bus bar and an interdigital transducer; The interdigital transducer includes a first bus bar, a second bus bar, a first modulation region, a second modulation region, and a plurality of electrode fingers. The modulation regions and the plurality of electrode fingers are both located between the first bus bar and the second bus bar; In a single period of the interdigital transducer, there are two electrode fingers. One electrode finger extends to the first modulation region and then connects to the first bus bar, and is spaced from the second bus bar. This electrode finger partially overlaps with the first modulation region, and the first modulation region is connected to the first bus bar. The other electrode finger extends to the second modulation region and then connects to the second bus bar, and is spaced from the first bus bar. The second modulation region is connected to the second bus bar. The electrode finger connected to the first bus bar and the electrode finger connected to the second bus bar are alternately and spacedly arranged; Each electrode finger includes a modulation region, a gap region, and a central region connected in sequence.

2. The resonator according to claim 1, characterized in that Each electrode finger further includes an edge region, and the edge region is located between the gap region and the central region.

3. The resonator according to claim 1, characterized in that The substrate includes a bottom substrate, a charge trapping layer, a temperature compensation and acoustic reflection layer, and a piezoelectric layer from bottom to top. The interdigital transducer is disposed on the surface of the piezoelectric layer facing away from the substrate; the bottom substrate serves as a support, the charge trapping layer is used to absorb electrons accumulated at the interface of the bottom substrate, the temperature compensation and acoustic reflection layer is used to compensate the negative temperature coefficient of the piezoelectric layer and reflect the energy leaked from the piezoelectric layer. The acoustic reflection includes a low acoustic impedance and / or a high acoustic impedance. The acoustic impedance of the low acoustic impedance is less than the acoustic impedance of the piezoelectric layer, and the acoustic impedance of the high acoustic impedance is greater than the acoustic impedance of the piezoelectric layer.

4. The resonator according to claim 3, characterized in that The modulation region is located between the bus bar and the gap region. The modulation region is cosine-shaped or arc-shaped. Let the length of the modulation region peak in the aperture direction be L F , the width of the electrode finger strip, that is, the length in the propagation direction, is W, then W / 8 < L F < W / 2, the length of the peak in the propagation direction = W; Let The length of the modulation zone trough in the aperture direction is L G , then L F / 4 <L G ≤L F , the length of the trough in the propagation direction = the distance between two fingers, and the etching depth of the trough is D G , the thickness of the piezoelectric layer is D, then 0≤D G <0.3*D.

5. The resonator according to claim 2, characterized in that In the arrangement direction of the first bus bar and the second bus bar, if the length of the gap region is L2 and the length of the edge region is L3, then 0.1λ < L2 < 1λ, 0.3λ < L3 < 1λ, where λ is the period of the acoustic wave.

6. The resonator according to claim 3, characterized in that The material of the bottom substrate is single crystal silicon or polycrystalline silicon. The material of the temperature compensation and acoustic reflection layer is aluminum nitride or silicon oxide with a positive temperature coefficient characteristic. The material of the piezoelectric layer is one of quartz, aluminum nitride, sapphire, lithium niobate, and lithium tantalate.

7. The resonator according to claim 1, characterized in that The bus bar and the electrode are selected from one of aluminum, molybdenum, copper, gold, platinum, silver, nickel, chromium, and tungsten.

8. The resonator according to claim 2, characterized in that In the arrangement direction of the first bus bar and the second bus bar, the sound velocity in the central region is V1, the sound velocity in the edge region is V2, and the sound velocity in the gap region is V3. The sound velocity relationship is V3 > V1 > V2.

9. The resonator according to claim 8, characterized in that The electrode fingers in the edge region achieve the above sound velocity relationship in the form of Hammer widening, Piston thickening, and widening and thickening.

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