Composite layer structure for supporting micro-acoustic frequency tuning and resonator

Abstract

The invention provides a composite layer structure for supporting micro-acoustic frequency tuning and a resonator. The composite layer structure comprises a piezoelectric layer, a semiconductor layer and an insulating substrate, the piezoelectric layer and the semiconductor layer are stacked to form a piezoelectric semiconductor composite structure; the piezoelectric semiconductor composite structure is arranged on the insulating substrate to form a composite layer structure capable of adjusting the frequency of the resonator; the composite layer structure is further provided with an interdigital transducer and an electrode, a frequency-adjustable surface acoustic wave resonator can be formed, direct-current unbalance loading voltage or current is applied to the semiconductor layer through the electrode, a micro-acoustic electric field and a carrier generate a giant acoustoelectric effect, remarkable change of the micro-acoustic wave velocity is caused, and the acoustic wave velocity is changed. The resonant frequency of the resonator is changed in a wide frequency range. Based on a composite layer structure formed by piezoelectricity, a semiconductor and an insulating substrate, the composite layer structure is applied to the resonator, resonant frequency tuning within the range of 5% or above can be achieved through volt-level voltage, and meanwhile the gain characteristic of the acoustoelectric effect can compensate the Q value of the resonator.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency front-end filters, and specifically to a composite layer structure and resonator supporting micro-acoustic frequency tuning, especially a novel piezoelectric-semiconductor-insulating substrate layered structure material system for supporting the realization of a frequency-tunable SAW resonator. Background Art

[0002] Low-loss SAW filters in the RF front end are composed of several SAW resonators connected in series and parallel. Due to their high cost-effectiveness and small size, they have become an indispensable and irreplaceable component in RF and microwave frequency band (100MHz to 4GHz) receiving / transmitting systems for mobile communication smart terminals, radars, and other applications. However, to meet the requirements of multiple frequency bands and multiple standards, the dramatic increase in the number of filters equipped has led to unprecedented system complexity, significantly increased losses, and increased system size, which does not conform to the mainstream trend of miniaturization, integration, and low energy consumption of receiving / transmitting systems. For example, in mobile communication terminals, in order to comply with different communication standards and multiple technical standards such as carrier aggregation, Wi-Fi, Bluetooth, and Global Positioning System, the number of micro-acoustic filters in mobile phones that support 5G communication will increase from 30 in the 4G era to nearly 100, occupying 60% to 80% of the area of ​​the RF circuit board.

[0003] Without changing the hardware, it is a recognized mainstream solution to configure the resonant frequency of the SAW resonator by applying an external electrical signal and finally achieve filter frequency reconstruction. Figure 1 As shown in the figure, frequency tunable resonator technology can significantly reduce the number of filters, which will attract great attention from the industry and have a significant impact on simplifying the RF system architecture.

[0004] Existing SAW tuning technologies mainly include: 1. Connecting a SAW resonator in series or parallel with a variable capacitor, and adjusting the capacitance value by applying an external electrical signal to ultimately change the resonant frequency, as described in References 1 and 2 below; 2. Integrating a SAW resonator with a ferroelectric material, and adjusting the dielectric properties of the ferroelectric layer by applying an external electrical signal to ultimately change the resonant frequency, as described in Reference 3 below; 3. Transferring semiconductor materials onto a piezoelectric substrate to prepare a SAW delay line, and generating an acoustic-electric effect by applying an external electrical signal to ultimately change the SAW frequency, as described in References 4 and 5 below. The disadvantages of existing technologies are:

[0005] a. Current reconfigurable solutions use series / parallel electrically tunable capacitors. However, due to the low quality factor (Q value) of tunable capacitors in the GHz band, the effective electromechanical coupling coefficient of each microacoustic resonator branch is reduced, resulting in deterioration of filter performance such as insertion loss and hysteresis suppression.

[0006] b. The tuning voltage required to control the dielectric properties of ferroelectric materials is as high as tens of volts, and is accompanied by significant inherent losses, which is not accepted by the industry;

[0007] c. Acoustoelectric effect SAW frequency modulation solutions all use a hybrid material system of semiconductors transferred onto piezoelectric substrates. In this material system, the semiconductor material and SAW transducer cannot overlap spatially. The basic unit of the frequency modulation device can only be made into a delay line or introduce a dielectric isolation layer, making it impossible to use it to create a low-loss RF front-end filter. Furthermore, the coupling efficiency between the microacoustic and the semiconductor is very low, resulting in a weak acoustoelectric effect and a narrow frequency modulation range.

[0008] Reference 1, Aigner R. Tunable filters? Reality check foreseeable trends in system architecture for tunable RF filters [J]. IEEE Microwave Magazine, 2015, 16(7): 82-8. This document discusses the practical needs of tunable RF filters covering multiple frequency bands and proposes multiple technical paths to achieve high-performance tunable filters, such as connecting SAW resonators in series and parallel with variable capacitors, and adjusting the capacitance value by applying an external electrical signal to ultimately change the resonant frequency.

[0009] Reference 2, Reinhardt A, Soulat E, Perreau P, et al. Composite tunable bulk acoustic wave resonator based on Lithium Niobate thin films[C]. 2023 IEEE International Ultrasonics Symposium. This document studies a composite tunable bulk acoustic wave (BAW) tunable resonator based on thin film lithium niobate (LiNbO3), and connects the above-mentioned BAW resonator in series and parallel with a variable capacitor. The capacitance value is controlled by an external electrical signal, and the resonant frequency is finally changed, aiming to realize a tunable high-frequency acoustic device.

[0010] Document 3, Berge J.Switchable and tunable bulk acoustic wave resonators based on Ba x Sr 1-x TiO3 thin films[D]. Chalmers University of Technology, 2012. This paper mainly studies a new type of microwave device based on ferroelectric material Ba x Sr 1-xThe tunable thin film bulk acoustic resonator (TFBAR) of TiO3 (BST) thin film is different from the traditional fixed-frequency TFBAR used in filtering applications of wireless communication systems. This tunable TFBAR utilizes the DC field-induced piezoelectric effect in ferroelectric films to achieve DC field tuning of the resonant frequency and switching between resonator and capacitive responses.

[0011] Reference 4, Bahamonde J, Kymissis IA reconfigurable surface acoustic wavefilter on ZnO / AlGaN / GaN heterostructure[J].IEEE Transactions on ElectronDevices,2020,67(10):4507-14, uses a hybrid material system of semiconductor transferred on a piezoelectric body to stimulate the acoustoelectric effect to tune the frequency of the microacoustic device. This document uses a whole lithium niobate single crystal as the substrate material, and transfers a GaN / AlGaN semiconductor heterojunction and a zinc oxide piezoelectric semiconductor layer on the lithium niobate. Electrodes are prepared at both ends of the GaN / AlGaN semiconductor heterojunction to apply a DC voltage, and two sets of interdigitated electrodes are prepared on the upper surface of the zinc oxide layer to connect the RF signal, forming a frequency-adjustable microacoustic delay line transducer structure based on the acoustoelectric effect.

[0012] Document 5, patent document with publication number CN116760382A, discloses a reconfigurable SAW resonator structure, including a substrate and an ε-phase gallium oxide piezoelectric film arranged on the substrate; a conductive layer is obtained by injecting negative ions into the upper end of the ε-phase gallium oxide piezoelectric film away from the substrate; a dielectric layer is arranged on the conductive layer; a pair of interdigital electrodes are arranged on the dielectric layer; one interdigital electrode is connected to a DC bias voltage and an RF signal, respectively, and the other interdigital electrode is grounded.

[0013] In the frequency modulation schemes of References 1 and 2 that use external variable capacitors, the low Q value of the external capacitors limits the frequency adjustment range, with the actual frequency modulation range exceeding 2%. The present invention proposes tuning the resonant frequency of a SAW resonator based on the acoustoelectric effect. In this process, the acoustic gain characteristics of the acoustoelectric effect can compensate for the Q value of the resonator, thus avoiding the disadvantage of the low Q value of the external capacitor and achieving an adjustable range of more than 5%.

[0014] Regarding Document 3, the voltage required to adjust the capacitance of the external capacitor is as high as 25V. Using a tuning control signal above 10V in a mobile terminal would significantly increase system cost, size, and complexity, and is unacceptable in the industry. The present invention utilizes an external voltage of less than 10V to achieve wide frequency range adjustment of a microacoustic resonator while maintaining high performance, meeting the practical needs of mobile terminals.

[0015] Reference 4 utilizes the acoustoelectric effect for SAW frequency modulation, but employs a hybrid material system of semiconductors transferred onto piezoelectric elements. This material system has the following drawbacks: First, the semiconductor material and SAW transducer cannot overlap, and the basic unit of the frequency modulation device can only be made into a delay line, making it unsuitable for making a low-loss RF front-end filter (the basic unit is a SAW resonator). Second, the coupling efficiency between the microacoustic and semiconductor in this material system is very low, resulting in a very weak acoustoelectric effect. Only a 0.78% frequency shift was achieved with an external voltage of 80V.

[0016] Reference 5 also uses the acoustoelectric effect for SAW frequency modulation, employing a similar hybrid material system of semiconductors transferred on a piezoelectric substrate. Because the semiconductor material and the SAW transducer cannot overlap, this reference introduces a dielectric isolation layer between the interdigital transducer and the semiconductor layer. This dielectric isolation layer shields the interaction between the RF electric field and the semiconductor, resulting in a weak acoustoelectric effect and a narrow frequency modulation range.

[0017] Compared with references 4 and 5, the present invention is based on a piezoelectric-semiconductor-insulating substrate layered structure material system, supporting a resonator-type transducer structure. The distribution of the piezoelectric microacoustic electric field excited by the interdigital transducer directly overlaps and interacts with the distribution of semiconductor carriers in the spatial domain, and the acoustic characteristic impedance of the microacoustic matches the electrical impedance of the semiconductor, resulting in a giant acoustic-electric effect. Therefore, the frequency modulation range and sensitivity are improved by an order of magnitude compared to the piezoelectric substrate-transferred semiconductor material system. Summary of the Invention

[0018] In view of the defects in the prior art, the object of the present invention is to provide a composite layer structure and a resonator that support micro-acoustic frequency tuning.

[0019] According to the present invention, a composite layer structure supporting micro-acoustic frequency tuning includes: a piezoelectric layer, a semiconductor layer and an insulating substrate;

[0020] The piezoelectric layer and the semiconductor layer are stacked to form a piezoelectric semiconductor composite structure; the piezoelectric semiconductor composite structure is provided on the insulating substrate;

[0021] When adjusting the resonator frequency, the piezoelectric effect of the piezoelectric layer excites the microacoustic resonance mode to generate piezoelectric microacoustics. The accompanying electric field of the piezoelectric microacoustics overlaps with the distribution of the directionally drifting carriers in the semiconductor layer in the spatial domain, and the acoustic characteristic impedance of the piezoelectric microacoustics matches the electrical impedance of the semiconductor layer, generating an acoustoelectric effect, causing the wave velocity of the piezoelectric microacoustics to change, changing the resonant frequency of the piezoelectric microacoustics, and thus changing the frequency of the resonator.

[0022] The present invention also provides a resonator, comprising the composite layer structure supporting micro-acoustic frequency tuning described above;

[0023] The resonator further comprises: an interdigital transducer and an electrode;

[0024] The IDT and the electrode are arranged on a composite layer structure, the IDT can apply a radio frequency signal to the piezoelectric layer, and the electrode can apply a DC bias voltage to the semiconductor layer;

[0025] When adjusting the resonator frequency, the radio frequency signal on the interdigital transducer acts on the piezoelectric layer, and the microacoustic resonance mode is excited by the piezoelectric effect of the piezoelectric layer to generate piezoelectric microacoustics. The accompanying electric field of the piezoelectric microacoustics overlaps with the distribution of the directionally drifting carriers in the semiconductor layer in the spatial domain, generating an acoustoelectric effect, and the acoustic characteristic impedance of the piezoelectric microacoustics matches the electrical impedance of the semiconductor layer, causing the wave velocity of the piezoelectric microacoustics to change, changing the resonant frequency of the piezoelectric microacoustics, and thus changing the resonant frequency of the resonator.

[0026] Preferably, the interdigital transducer is connected to the piezoelectric layer and is located on the upper surface of the piezoelectric layer or inside the piezoelectric layer;

[0027] The electrode is connected to the semiconductor layer and is located on the upper surface of the semiconductor layer or inside the semiconductor layer.

[0028] Preferably, the electrodes are arranged around the periphery of the IDT.

[0029] Preferably, the piezoelectric layer, the semiconductor layer and the insulating substrate are stacked in sequence;

[0030] The interdigital transducer is arranged on the upper surface of the piezoelectric layer; a through hole is provided on the piezoelectric semiconductor composite structure, and the electrode is arranged in the through hole;

[0031] The through hole is provided through the piezoelectric layer, and the electrode is located on the upper surface of the semiconductor layer; or, the through hole is provided through the piezoelectric layer and the semiconductor layer, and the electrode is located inside the semiconductor layer.

[0032] Preferably, the semiconductor layer, the piezoelectric layer and the insulating substrate are stacked in sequence;

[0033] The interdigital transducer is arranged on the upper surface of the insulating substrate and is wrapped by the piezoelectric layer; a through hole is provided on the piezoelectric semiconductor composite structure, and the electrode is arranged in the through hole;

[0034] The through hole is provided through the semiconductor layer, and the electrode is located inside the semiconductor layer; or, the electrode is provided on the upper surface of the semiconductor layer.

[0035] Preferably, the material of the interdigital transducer is metal material;

[0036] And / or, the thickness of the IDT is 50 nm to 600 nm;

[0037] And / or, the period of the IDT is 0.5 um to 5 um.

[0038] Preferably, the material of the piezoelectric layer is a piezoelectric single crystal or a piezoelectric thin film material;

[0039] And / or, the piezoelectric layer has a thickness of 100 nm to 1000 nm.

[0040] Preferably, the material of the piezoelectric layer is any one of the following: lithium niobate, lithium tantalate, potassium niobate, aluminum nitride, gallium nitride, zinc oxide, gallium arsenide, potassium sodium niobate, and barium titanate;

[0041] When the material of the piezoelectric layer is a lithium niobate single crystal thin film, the Euler angle of the piezoelectric layer is any one of the following: (0~20°, -20~-80°, 0~90°), (100~140°, -20~-80°, 0~90°), (40~80°, 20~80°, 0~90°), (160~180°, 20~80°, 0~90°), (0~20°, 30~70°, 0~90°), (160~180°, -20~-80°, 0~90°).

[0042] Preferably, the material of the semiconductor layer is any one of the following: a single-element semiconductor, a III-V semiconductor compound, a heterojunction of a single-element semiconductor and a III-V semiconductor compound, a heterojunction of a single-element semiconductor and a single-element semiconductor, and a heterojunction of a III-V semiconductor compound and a III-V semiconductor compound;

[0043] And / or, the thickness of the semiconductor layer is 100 nm to 4000 nm;

[0044] And / or, the carrier concentration of the semiconductor layer is 10 13 cm -3 ~10 20 cm -3 ;

[0045] And / or, the material of the insulating substrate is any one of the following: silicon carbide, sapphire, high-resistance silicon, diamond, glass;

[0046] And / or, the thickness of the insulating substrate is 200um to 1000um.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] 1. The piezoelectric-semiconductor-insulating substrate layered structure material system of the present application, through the piezoelectric effect of the piezoelectric layer, stimulates micro-acoustic resonance mode, the accompanying electric field of the piezoelectric micro-acoustic is in the matching excitation state with the directional drift carrier in the semiconductor layer, produces giant acoustic electric effect, causes the significant change of micro-acoustic velocity and wave velocity, finally changes the resonance frequency of micro-acoustic in wide frequency range.

[0049] 2. Based on the piezoelectric-semiconductor-insulating substrate layered structure material system of the present application, the acoustic electric effect adjustable micro-acoustic resonator is arranged, the radio frequency signal on the interdigital transducer acts on the piezoelectric layer, the direct current voltage on the electrode acts on the semiconductor layer, the distribution of the piezoelectric micro-acoustic electric field excited by the interdigital transducer directly overlaps and interacts with the distribution of the semiconductor carrier under the action of the bias voltage or current in the spatial domain, and the acoustic characteristic impedance of the micro-acoustic is matched with the semiconductor impedance, the giant acoustic electric effect is produced, the frequency modulation sensitivity is significantly improved, the resonance frequency tuning can be realized through the voltage level voltage, and the gain characteristics of the acoustic electric effect can compensate the Q value of the resonator; the present application is a technology for realizing the wide frequency range adjustment of the micro-acoustic resonator by using low external voltage under the condition of maintaining high performance.

[0050] 3. The present application adopts the structure form of high acoustic velocity substrate, semiconductor frequency modulation layer, piezoelectric film and interdigital electrode superposition, has the ability of actively adjusting the resonance frequency of the micro-acoustic resonator in wide frequency range through external electric signal, and will produce revolutionary significance for simplifying the radio frequency system architecture. BRIEF DESCRIPTION OF DRAWINGS

[0051] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments made with reference to the following drawings:

[0052] Figure 1 (a) is a schematic diagram of a low frequency radio frequency front end of an existing communication system, and (b) is a schematic diagram of a simplified radio frequency front end based on a reconfigurable filter;

[0053] Figure 2 is a structural schematic diagram of the frequency adjustable micro-acoustic resonator in embodiment one;

[0054] Figure 3 is a structural schematic diagram of the frequency adjustable micro-acoustic resonator in embodiment two;

[0055] Figure 4 is a structural schematic diagram of the frequency adjustable micro-acoustic resonator in embodiment three;

[0056] Figure 5 is a structural schematic diagram of the frequency adjustable micro-acoustic resonator in embodiment four;

[0057] Figure 6 is a schematic diagram of the effect of a piezoelectric single crystal film in different cut types;

[0058] Figure 7 Schematic diagram of the frequency modulation performance of the acoustoelectric effect tunable resonator.

[0059] The figure shows:

[0060] Interdigital transducer 1 Semiconductor layer 4

[0061] Electrode 2 Insulating substrate 5

[0062] Piezoelectric layer 3 Through hole 6 DETAILED DESCRIPTION

[0063] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0064] Example 1

[0065] like Figure 2 As shown, this embodiment provides a piezoelectric-semiconductor-insulating substrate layered structure material system, including a piezoelectric layer 3, a semiconductor layer 4, and an insulating substrate 5. Layer 3 and semiconductor layer 4 are stacked to form a piezoelectric semiconductor composite structure; the piezoelectric semiconductor composite structure is provided on the insulating substrate 5.

[0066] This embodiment also provides a frequency-tunable SAW resonator, including the above-mentioned piezoelectric-semiconductor-insulating substrate layered structure material system, and also including an interdigital transducer 1 and an electrode 2. The interdigital transducer 1 and the electrode 2 are arranged on the piezoelectric-semiconductor-insulating substrate layered structure material system to form a frequency-tunable SAW resonator.

[0067] The interdigital transducer 1 and the electrode 2 are arranged on a piezoelectric semiconductor composite structure. The interdigital transducer 1 can apply a radio frequency signal to the piezoelectric layer 3, and the electrode 2 can apply a DC bias voltage to the semiconductor layer 4. The radio frequency signal on the interdigital transducer 1 acts on the piezoelectric layer 3, and the microacoustic resonance mode is excited through the piezoelectric effect of the piezoelectric layer 3. The accompanying electric field of the piezoelectric microacoustic directly overlaps and interacts with the distribution of the directionally drifting carriers in the semiconductor layer 4 in the spatial domain, and the acoustic characteristic impedance of the microacoustic matches the electrical impedance of the semiconductor, resulting in a giant acoustic-electric effect, causing a significant change in the microacoustic wave velocity, and changing the resonant frequency of the resonator within a wide frequency range.

[0068] The electrical impedance of the semiconductor layer 4 matches the acoustic characteristic impedance of the acoustic mode of vibration in the piezoelectric layer 3. The electrodes 2 are arranged around the circumference of the interdigital transducer 1.

[0069] The IDT 1 is connected to the piezoelectric layer 3 and is located on the upper surface of the piezoelectric layer 3 or inside the piezoelectric layer 3 ; the electrode 2 is connected to the semiconductor layer 4 and is located on the upper surface of the semiconductor layer 4 or inside the semiconductor layer 4 .

[0070] like Figure 2 As shown, in this embodiment, the piezoelectric layer 3, the semiconductor layer 4 and the insulating substrate 5 are stacked in sequence; the interdigital transducer 1 is arranged on the upper surface of the piezoelectric layer 3; a through hole 6 is provided on the piezoelectric semiconductor composite structure, and the electrode 2 is provided in the through hole 6; the through hole 6 is provided through the piezoelectric layer 3, and the electrode 2 is located on the upper surface of the semiconductor layer 4.

[0071] First, in a typical SAW resonator structure, electrodes 2 and through-holes 6 do not exist. This embodiment proposes adding a semiconductor layer to the SAW resonator and, based on the principle of the acoustic-electric effect between the piezoelectric layer and the semiconductor layer, frequency modulation by applying a bias voltage. In order to apply a bias voltage to the semiconductor layer 4, through-holes 6 must be etched and electrodes 2 must be grown for applying the bias voltage. Therefore, electrodes 2 and through-holes 6 are newly added structures to accommodate the addition of semiconductor layer 4, which are not present in conventional structures.

[0072] Secondly, to maximize the frequency modulation effect of the acoustoelectric effect, the electrical impedance of the semiconductor layer 4 must match the acoustic characteristic impedance of the acoustic mode of vibration in the piezoelectric layer 3. The electrical impedance of the semiconductor layer 4 depends on the semiconductor material type and carrier concentration. The acoustic characteristic impedance of the piezoelectric layer 3 depends on the thickness of the piezoelectric layer 3, the thickness of the interdigital transducer 1, and the period length. The parameter ranges proposed below are calculated according to the principle of impedance matching and are designed to adapt the electrical impedance of the semiconductor layer 4 to maximize the acoustoelectric effect.

[0073] The IDT 1 is made of any of the following metal materials: aluminum, copper, platinum, gold, molybdenum, silver, chromium, indium, titanium, iron, nickel, lead, palladium, tungsten, or antimony. These are commonly used metal materials for the interdigital electrodes of SAW resonators. The MEMS process for these metal materials is relatively mature, making them convenient for fabricating IDTs. The material itself has a relatively low resistivity, which helps reduce resonator losses.

[0074] The thickness of the interdigital transducer 1 is 200nm to 300nm. The electrode has a "mass loading" effect on the resonance of the resonator, which will affect the frequency of the main resonant mode. Inappropriate "mass loading" may even introduce spurious interference modes. Within the above thickness range, it can ensure that the excitation effect of the main mode is good and the suppression effect of the spurious mode is obvious. In addition, the thinner the electrode, the more serious the loss of the resonator, but the existing process cannot prepare an electrode layer that is too thick, and excessive "mass loading" may also interfere with the main resonant mode. Therefore, the above electrode thickness range is determined by comprehensively considering multiple factors such as the excitation of the main resonant mode of the resonator, the suppression of the spurious resonant mode, and the control of the resonator loss.

[0075] The period of the interdigital transducer 1 is 4.4um. Under the condition that other parameters are fixed, the period of the interdigital transducer mainly determines the resonant frequency value of the resonator. The shorter the period, the higher the resonant frequency; conversely, the lower the resonant frequency. As mentioned in the background, the application scenario of this embodiment is mobile terminal communication, and the dense frequency band of mobile terminal communication mainly exists around 700MHz to 800MHz. The resonant frequency of the resonator corresponding to the above period range is exactly 700MHz to 800MHz, which meets the mainstream requirements of mobile communications.

[0076] The material of the piezoelectric layer 3 is a piezoelectric single crystal material or a piezoelectric thin film material. The material of the piezoelectric layer 3 is any one of the following: lithium niobate, lithium tantalate, potassium niobate, aluminum nitride, gallium nitride, zinc oxide, gallium arsenide, potassium sodium niobate, and barium titanate. These materials are common piezoelectric single crystal materials or piezoelectric thin film materials with strong piezoelectricity in the industry. Their strong piezoelectricity can ensure that the resonant response of the resonator has a large electromechanical coupling coefficient. The larger the electromechanical coupling coefficient, the stronger the acoustoelectric effect will be, and the more significant the frequency modulation effect will be. In addition, the electromechanical coupling coefficient of the resonator ultimately determines the bandwidth of the formed filter. Only a sufficient electromechanical coupling coefficient can meet the bandwidth requirements of the mobile communication frequency band.

[0077] When the material of the piezoelectric layer 3 is a lithium niobate single crystal thin film, the Euler angle of the piezoelectric layer 3 is any one of the following: (0-20°, -20--80°, 0-90°), (100-140°, -20--80°, 0-90°), (40-80°, 20-80°, 0-90°), (160-180°, 20-80°, 0-90°), (0-20°, 30-70°, 0-90°), (160-180°, -20--80°, 0-90°)

[0078] In this embodiment, the Euler angle of the piezoelectric layer 3 is: Euler angle is: (0°, -20 to -50°, 0°). In the above cutting range, it has the most significant frequency modulation effect, such as Figure 6 shown.

[0079] The thickness of the piezoelectric layer 3 is 700nm-800nm. On one hand, the thickness of the piezoelectric layer has a significant impact on the resonant frequency value, and the above thickness range can ensure that the resonant frequency of the resonator is in the range of 700MHz-800MHz, which is consistent with the actual situation of the communication system. On the other hand, the above thickness range of the piezoelectric layer can ensure that the energy of the acoustic wave is concentrated on the surface of the resonator, and does not spread downward to the base layer, thereby ensuring that the resonator has a high quality factor (low loss).

[0080] The material of the semiconductor layer 4 is any one of the following: elemental semiconductor, ternary semiconductor compound, heterojunction composed of elemental semiconductor and ternary semiconductor compound, heterojunction composed of elemental semiconductor and elemental semiconductor, heterojunction composed of ternary semiconductor compound and ternary semiconductor compound, such as silicon, germanium, gallium arsenide, gallium nitride, zinc oxide, indium phosphide, gallium aluminum arsenide, gallium indium arsenide, gallium aluminum nitride, cadmium sulfide, aluminum arsenide, gallium arsenide\ gallium aluminum arsenide heterojunction, gallium arsenide\ gallium indium arsenide heterojunction, gallium nitride\ gallium aluminum nitride heterojunction, graphene, molybdenum disulfide. These semiconductor materials have piezoelectricity and high carrier mobility characteristics, and their piezoelectricity can enhance the acoustoelectric effect and make the frequency modulation effect more significant; high carrier mobility can improve the sensitivity of frequency modulation and ensure that a wide range of frequency modulation can be achieved with low voltage.

[0081] The thickness of the semiconductor layer 4 is 100nm-300nm. This thickness range can ensure that the piezoelectric micro-acoustic electric field in the piezoelectric layer 3 during resonance can effectively penetrate the semiconductor layer, realizing sufficient acoustoelectric interaction. At the same time, this thickness range does not introduce too many spurious modes to the response of the resonator.

[0082] The carrier concentration of the semiconductor layer 4 is 10 16 cm -3 -10 17 cm -3 . In order to maximize the frequency modulation effect of the acoustoelectric effect, the electrical impedance of the semiconductor layer 4 and the acoustic characteristic impedance of the acoustic mode vibrating in the piezoelectric layer 3 must be matched. The carrier concentration is a decisive parameter of the electrical impedance of the semiconductor, and this carrier concentration range can ensure that the electrical impedance of the semiconductor is matched with the acoustic characteristic impedance of the piezoelectric layer 3 determined by the other parameters, maximizing the frequency modulation effect of the acoustoelectric effect.

[0083] The material of the insulating substrate 5 is any one of the following: silicon carbide, sapphire, high-resistance silicon, diamond, glass. These substrates have high resistivity on the one hand, which can ensure that the electric field distribution in the piezoelectric layer and the semiconductor layer on the surface of the resonator is not disturbed, and the electrical quality factor of the resonator is guaranteed. In addition, these substrate materials have high acoustic velocity characteristics, and form an acoustic waveguide structure with the surface piezoelectric layer as a whole, which can suppress the leakage of acoustic waves downward to the substrate, ensure that the resonant energy is concentrated on the surface of the resonator, and improve the quality factor of the resonator.

[0084] The thickness of the insulating substrate 5 is 300-500 um. This thickness range can firstly ensure the rigidity of the overall structure of the resonator, and at the same time, it is consistent with the volume capacity in the actual radio frequency front-end chip.

[0085] The embodiment provides a surface acoustic wave (SAW) device design with adjustable resonant frequency, which adopts a structure form of high sound speed substrate, semiconductor frequency modulation layer, piezoelectric film and interdigital electrode superposition, has the ability of actively regulating the resonant frequency of the micro sound resonator through an external electric signal, and has revolutionary significance for simplifying the radio frequency system architecture.

[0086] The embodiment provides a frequency-adjustable SAW resonator based on a novel piezoelectric-semiconductor-insulating substrate layered structure material system, which comprises a piezoelectric layer, a semiconductor layer and an insulating substrate, the piezoelectric layer and the semiconductor layer are superposed to form a piezoelectric semiconductor composite structure, and the piezoelectric semiconductor composite structure is arranged on the insulating substrate; an interdigital transducer and an electrode are arranged on the layered structure material system to form a frequency-adjustable surface acoustic wave (SAW) resonator; a direct current bias voltage or current is applied to the semiconductor layer through the electrode arranged on the semiconductor layer, the distribution of the piezoelectric micro sound electric field excited by the interdigital transducer directly overlaps the distribution of the semiconductor carrier under the action of the bias voltage or current, the acoustic characteristic impedance of the piezoelectric micro sound is matched with the semiconductor impedance, the micro sound electric field and the carrier produce a giant acoustoelectric effect, a significant change in the micro sound velocity is caused, and the resonant frequency of the resonator is changed in a wide frequency range.

[0087] The embodiment is based on the SAW resonator on the piezoelectric-semiconductor-insulating substrate layered structure material system, and can realize the resonant frequency tuning in a range of more than 5% through a voltage level, and meanwhile, the gain characteristics of the acoustoelectric effect can compensate the Q value of the resonator.

[0088] Example 2

[0089] As shown in FIG. 1, the embodiment is different from the embodiment 1 in that the through hole 6 is arranged through the piezoelectric layer 3 and the semiconductor layer 4, and the electrode 2 is arranged in the semiconductor layer 4. Figure 3

[0090] Example 3 As shown in FIG. 1, the embodiment is different from the embodiment 1 in that the through hole 6 is arranged through the piezoelectric layer 3 and the semiconductor layer 4, and the electrode 2 is arranged in the semiconductor layer 4.

[0091] As shown in FIG. 1, the embodiment is different from the embodiment 1 in that the through hole 6 is arranged through the piezoelectric layer 3 and the semiconductor layer 4, and the electrode 2 is arranged in the semiconductor layer 4. Figure 4 As shown in FIG. 1, the embodiment is different from the embodiment 1 in that the through hole 6 is arranged through the piezoelectric layer 3 and the semiconductor layer 4, and the electrode 2 is arranged in the semiconductor layer 4.

[0092] The piezoelectric layer 3 is directly connected to the substrate layer 5. The IDT 1 exists at the interface between the piezoelectric layer 3 and the substrate layer 5, and is covered by the piezoelectric layer 3. The semiconductor layer 4 covers the piezoelectric layer 3, and has through-holes 6 etched at both ends above the area where the IDT 1 is located, and the electrodes 2 are grown within the through-holes 6.

[0093] Example 4

[0094] like Figure 5 As shown, the difference between this embodiment and embodiment 3 is that the electrode 2 is arranged on the upper surface of the semiconductor layer 4.

[0095] Example 5

[0096] Those skilled in the art may understand this embodiment as a more specific description of Embodiment 1, Embodiment 2, Embodiment 3, and Embodiment 4.

[0097] like Figure 2 As shown, this embodiment provides a microacoustic resonator based on a piezoelectric-semiconductor-insulating substrate layered structure material system. The microacoustic resonator comprises an interdigital transducer 1, an electrode 2, a piezoelectric layer 3, a semiconductor layer 4, and an insulating substrate 5. The insulating substrate 5 is a high-acoustic-velocity insulating substrate.

[0098] IDT 1, located on the upper surface of the piezoelectric layer, applies an RF signal to excite the acoustic resonance mode of the resonator. Through holes are etched between the piezoelectric layer and the semiconductor layer at both ends of the IDT, and electrodes 2 are provided. Electrodes 2 apply a DC bias voltage to the semiconductor layer, regulating the resonant frequency of the resonator.

[0099] The material of the interdigital transducer 1 and the electrode 2 can be any one of the following: aluminum, copper, platinum, gold, molybdenum, silver, chromium, indium, titanium, iron, nickel, lead, palladium, tungsten, antimony. The thickness of the interdigital transducer 1 is 200nm~300nm, and the period of the interdigital transducer 1 (that is, the wavelength of the resonator microacoustic mode) is 4.4um. The material of the piezoelectric layer 3 can be any one of the following: lithium niobate, lithium tantalate, potassium niobate, aluminum nitride, gallium nitride, zinc oxide, gallium arsenide, potassium sodium niobate, barium titanate, with a thickness of 700nm~800nm. The material of the semiconductor layer 4 is any one of the following: gallium arsenide, gallium nitride, zinc oxide, indium phosphide, gallium aluminum arsenide, gallium indium arsenide, gallium aluminum nitride, cadmium sulfide, aluminum arsenide, silicon, germanium, with a thickness of 100nm~300nm and a carrier concentration of 10 16 cm -3 ~10 17 cm -3 The insulating substrate 5 is made of silicon carbide, sapphire, high-resistance silicon, diamond, or glass, and has a thickness of 300um to 500um.

[0100] In this frequency-tunable resonator, the radio frequency signal from the interdigital transducer 1 acts on the piezoelectric layer 3, exciting the microacoustic resonance mode through the piezoelectric effect of the piezoelectric layer 3. The accompanying electric field of the piezoelectric microacoustic resonance and the directionally drifting carriers in the semiconductor layer 4 produce an acoustoelectric effect, causing changes in the microacoustic velocity and wave speed, ultimately changing the resonant frequency of the resonator.

[0101] The admittance curve simulation results of an example design of the above device structure are as follows: Figure 7 shown.

[0102] In this design, the material of the interdigital transducer 1 is copper, with a thickness of 300nm to 350nm and a period of 4um to 4.5um. The material of the piezoelectric layer 3 is lithium niobate, with a thickness of 700nm to 800nm. The material of the semiconductor layer 4 is gallium nitride, N-type doped, with a carrier concentration of 10 16 cm -3 ~10 17 cm -3 , with a thickness of 100nm to 200nm. The insulating substrate layer 5 is made of sapphire and has a thickness of 500um to 600um. A bias voltage of 10V applied to the semiconductor layer 4 via the electrode 2 can cause the resonant frequency fr to change by 1.94% and the antiresonant frequency fa to change by 5.12%. During the frequency modulation process, the acoustic gain characteristic of the acoustoelectric effect compensates for the Q value of the resonator.

[0103] This embodiment provides a frequency-adjustable surface acoustic wave resonator, which controls the wave velocity of the surface acoustic wave based on the acoustoelectric effect of a piezoelectric-semiconductor composite structure to achieve tuning of the resonant frequency of the resonator.

[0104] The frequency-tunable surface acoustic wave resonator of this embodiment has a layered structure, including interdigital electrodes 1 , bias voltage electrodes 2 , a piezoelectric layer 3 , a semiconductor layer 4 and an insulating substrate 5 .

[0105] The material of the insulating substrate layer 5 used in this embodiment is any one of the following: silicon carbide, sapphire, high-resistance silicon, diamond, and glass, and the thickness is 300um to 500um.

[0106] The material of the semiconductor layer 4 used in this embodiment is any one of the following: gallium arsenide, gallium nitride, zinc oxide, indium phosphide, gallium aluminum arsenide, gallium indium arsenide, gallium aluminum nitride, cadmium sulfide, aluminum arsenide, silicon, germanium, with a thickness of 100nm to 300nm and a carrier concentration of 10 16 cm -3 ~10 17 cm -3 .

[0107] The material of the piezoelectric layer 3 used in this embodiment is any one of the following: lithium niobate, lithium tantalate, potassium niobate, aluminum nitride, gallium nitride, zinc oxide, gallium arsenide, potassium sodium niobate, barium titanate, and has a thickness of 100 nm to 300 nm.

[0108] The materials used in the IDT 1 and electrodes 2 of this embodiment can be any of the following: aluminum, copper, platinum, gold, molybdenum, silver, chromium, indium, titanium, iron, nickel, lead, palladium, tungsten, and antimony. The IDT 1 has a thickness of 200 nm to 300 nm and a period of 4.4 μm.

[0109] The present invention is based on a piezoelectric-semiconductor-insulating substrate structure to prepare a SAW resonator, which produces a giant acoustoelectric effect and can tune the resonant frequency through a volt-level voltage. At the same time, the gain characteristics of the acoustoelectric effect can compensate for the resonator Q value.

[0110] In the description of this application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0111] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A composite layer structure supporting micro-acoustic frequency tuning, characterized in that: include: A piezoelectric layer (3), a semiconductor layer (4) and an insulating substrate (5); The piezoelectric layer (3) and the semiconductor layer (4) are stacked to form a piezoelectric semiconductor composite structure; the piezoelectric semiconductor composite structure is arranged on the insulating substrate (5); When adjusting the resonator frequency, the piezoelectric effect of the piezoelectric layer (3) excites the micro-acoustic resonance mode to generate piezoelectric micro-acoustics. The accompanying electric field of the piezoelectric micro-acoustics overlaps with the distribution of the directionally drifting carriers in the semiconductor layer (4) in the spatial domain, and the acoustic characteristic impedance of the piezoelectric micro-acoustics matches the electrical impedance of the semiconductor layer (4), generating an acoustoelectric effect, causing a change in the wave velocity of the piezoelectric micro-acoustics, changing the resonant frequency of the piezoelectric micro-acoustics, and thus changing the frequency of the resonator.

2. A resonator, characterized in that The composite layer structure comprising the micro-acoustic frequency tuning support according to claim 1; The resonator further comprises: an interdigital transducer (1) and an electrode (2); The interdigital transducer (1) and the electrode (2) are arranged on a composite layer structure, the interdigital transducer (1) is capable of applying a radio frequency signal to the piezoelectric layer (3), and the electrode (2) is capable of applying a DC bias voltage to the semiconductor layer (4); When adjusting the resonator frequency, the radio frequency signal on the interdigital transducer (1) acts on the piezoelectric layer (3), and the microacoustic resonance mode is excited by the piezoelectric effect of the piezoelectric layer (3), thereby generating piezoelectric microacoustics. The accompanying electric field of the piezoelectric microacoustics overlaps with the distribution of the directionally drifting carriers in the semiconductor layer (4) in the spatial domain, thereby generating an acoustoelectric effect. The acoustic characteristic impedance of the piezoelectric microacoustics matches the electrical impedance of the semiconductor layer (4), thereby causing a change in the wave velocity of the piezoelectric microacoustics, changing the resonant frequency of the piezoelectric microacoustics, and further changing the resonant frequency of the resonator.

3. The frequency-tunable SAW resonator according to claim 2, characterized in that: The interdigital transducer (1) is connected to the piezoelectric layer (3) and is located on the upper surface of the piezoelectric layer (3) or inside the piezoelectric layer (3); The electrode (2) is connected to the semiconductor layer (4) and is located on the upper surface of the semiconductor layer (4) or inside the semiconductor layer (4).

4. The frequency-tunable SAW resonator according to claim 2, wherein: The electrodes (2) are arranged around the circumference of the interdigital transducer (1).

5. The frequency-tunable SAW resonator according to claim 3, characterized in that: The piezoelectric layer (3), the semiconductor layer (4) and the insulating substrate (5) are stacked in sequence; The interdigital transducer (1) is arranged on the upper surface of the piezoelectric layer (3); a through hole (6) is provided on the piezoelectric semiconductor composite structure, and the electrode (2) is arranged in the through hole (6); The through hole (6) is arranged through the piezoelectric layer (3), and the electrode (2) is located on the upper surface of the semiconductor layer (4); or, the through hole (6) is arranged through the piezoelectric layer (3) and the semiconductor layer (4), and the electrode (2) is located inside the semiconductor layer (4).

6. The frequency-tunable SAW resonator according to claim 3, characterized in that: The semiconductor layer (4), the piezoelectric layer (3) and the insulating substrate (5) are stacked in sequence; The interdigital transducer (1) is arranged on the upper surface of the insulating substrate (5) and is wrapped by the piezoelectric layer (3); a through hole (6) is provided on the piezoelectric semiconductor composite structure, and the electrode (2) is arranged in the through hole (6); The through hole (6) is provided through the semiconductor layer (4), and the electrode (2) is located inside the semiconductor layer (4); or, the electrode (2) is provided on the upper surface of the semiconductor layer (4).

7. The frequency-tunable SAW resonator according to claim 2, characterized in that: The material of the interdigital transducer (1) is a metal material; And / or, the thickness of the interdigital transducer (1) is 50 nm to 600 nm; And / or, the period of the interdigital transducer (1) is 0.5um to 5um.

8. The frequency-tunable SAW resonator according to claim 2, wherein: The material of the piezoelectric layer (3) is a piezoelectric single crystal or a piezoelectric thin film material; And / or, the thickness of the piezoelectric layer (3) is 100 nm to 1000 nm.

9. The frequency-tunable SAW resonator according to claim 8, characterized in that: The material of the piezoelectric layer (3) is any one of the following: lithium niobate, lithium tantalate, potassium niobate, aluminum nitride, gallium nitride, zinc oxide, gallium arsenide, potassium sodium niobate, and barium titanate; When the material of the piezoelectric layer (3) is a lithium niobate single crystal thin film, the Euler angle of the piezoelectric layer (3) is any one of the following: (0-20°, -20--80°, 0-90°), (100-140°, -20--80°, 0-90°), (40-80°, 20-80°, 0-90°), (160-180°, 20-80°, 0-90°), (0-20°, 30-70°, 0-90°), (160-180°, -20--80°, 0-90°).

10. The frequency-tunable SAW resonator according to claim 2, characterized in that: The material of the semiconductor layer (4) is any one of the following: a simple semiconductor, a III-V semiconductor compound, a heterojunction of a simple semiconductor and a III-V semiconductor compound, a heterojunction of a simple semiconductor and a simple semiconductor, and a heterojunction of a III-V semiconductor compound and a III-V semiconductor compound; and / or, the thickness of the semiconductor layer (4) is 100 nm to 4000 nm; And / or, the carrier concentration of the semiconductor layer (4) is 10 13 cm -3 ~10 20 cm -3 ; And / or, the material of the insulating substrate (5) is any one of the following: silicon carbide, sapphire, high-resistance silicon, diamond, glass; And / or, the thickness of the insulating substrate (5) is 200um to 1000um.

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