Acoustic wave filter and preparation method thereof
By adopting a superlattice structure of periodically alternating ε-Ga2O3 and ε-AlGaO layers in the acoustic wave filter, the crack problem caused by lattice mismatch during the growth of ε-Ga2O3 is solved, and the piezoelectric performance of the high-frequency filter is improved to meet the working requirements at frequencies of 1GHz to 5GHz.
Patent Information
- Application Number
- CN202510720456.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-30
- Publication Date
- 2025-09-30
AI Technical Summary
In existing acoustic wave filters, the lattice mismatch and thermal expansion coefficient mismatch between ε-Ga2O3 and the substrate during growth leads to residual strain and cracks, which affects the piezoelectric performance and makes it difficult to meet the needs of ultra-high-efficiency, broadband filters.
The piezoelectric layer of the superlattice structure is formed by periodically alternating stacked ε-Ga2O3 layers and ε-AlGaO layers, which are grown by MOCVD at 550℃~700℃ and combined with doping elements Sc, Hf, and Mg to reduce residual strain and improve crystal quality.
Significantly reduce residual stress, improve piezoelectric constant and electromechanical coupling coefficient, meet the requirements of high-frequency filters at frequencies of 1GHz to 5GHz, with piezoelectric constant >10pm/V and electromechanical coupling coefficient >10%.
Smart Images
Figure CN120729231A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of semiconductor technology, and in particular to an acoustic wave filter and a preparation method thereof. Background Art
[0002] Acoustic wave filters are core components of the RF front-end, and include surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters. SAW filters are mainly made of piezoelectric materials lithium niobate (LiNbO3, LN) or lithium tantalate (LiTaO3, LT) single crystal thin films, have large insertion loss, and are commonly used in RF components with frequencies below 3 GHz. Compared with SAW filters, BAW filters can provide lower insertion loss, with an operating frequency of approximately 0.7 GHz to 10 GHz, which is more in line with the development trend of miniaturization, broadbandization, and high frequency of RF components. BAW filters are mainly made of piezoelectric material aluminum nitride (AlN) thin films. Aluminum nitride has excellent piezoelectric properties, but the electromechanical coupling coefficient is low, which limits the improvement of device performance. Metastable ε-Ga2O3 has begun to be used in BAW filters due to its good piezoelectric constant and electromechanical coupling coefficient. However, the lattice mismatch and thermal expansion coefficient mismatch between ε-Ga2O3 and the substrate during the growth process will lead to severe residual strain, which in turn causes the formation of cracks. Traditional strain relief methods (such as gradient buffer layers) will reduce piezoelectric performance and increase manufacturing complexity. Summary of the Invention
[0003] The technical problem to be solved by the present invention is to provide an acoustic wave filter and a preparation method thereof, so as to improve the crystallization quality of the piezoelectric layer and meet the requirements of ultra-high efficiency and broadband filters.
[0004] In order to solve the above problems, the present invention discloses an acoustic wave filter, comprising a wafer substrate, a piezoelectric layer and an electrode layer arranged in sequence; wherein the piezoelectric layer comprises periodically alternately stacked ε-Ga2O3 layers and ε-AlGaO layers.
[0005] As an improvement of the above technical solution, the piezoelectric layer is grown by MOCVD at 550°C to 700°C.
[0006] As an improvement of the above technical solution, the alternating stacking period of the piezoelectric layers is 10 to 100.
[0007] As an improvement of the above technical solution, in each period, the thickness of the ε-Ga2O3 layer is 5nm to 50nm, and the thickness of the ε-AlGaO layer is 5nm to 50nm.
[0008] As an improvement of the above technical solution, in each period, the thickness ratio of the ε-AlGaO layer to the ε-Ga2O3 layer is 1:(1 to 10).
[0009] As an improvement of the above technical solution, the ε-AlGaO layer is ε-Al 2-x Ga x O3 layer, 0.2<x<0.7.
[0010] As an improvement of the above technical solution, the ε-AlGaO layer is a doped ε-AlGaO layer, the doping element is one or more of Sc, Hf, and Mg, and the doping concentration is 0.1% to 10%.
[0011] As an improvement of the above technical solution, the material of the wafer substrate is one or more of Si, sapphire, SiC, and GaN;
[0012] A cavity is provided on the wafer substrate, the piezoelectric layer contacts a side of the wafer substrate where the cavity is provided, and the depth of the cavity is greater than the thickness of the electrode layer;
[0013] The electrode layer includes an upper electrode layer and a lower electrode layer respectively arranged on the upper and lower surfaces of the piezoelectric layer.
[0014] Accordingly, the present invention also discloses a method for preparing an acoustic wave filter, which is used to prepare the above-mentioned acoustic wave filter, comprising the following steps:
[0015] providing a temporary substrate;
[0016] Growing a piezoelectric layer on the temporary substrate, the piezoelectric layer comprising periodically alternating stacked ε-Ga2O3 layers and ε-AlGaO layers; the piezoelectric layer is grown by MOCVD at a growth temperature of 550° C. to 700° C.;
[0017] removing the temporary substrate and growing an electrode layer on at least one side of the piezoelectric layer;
[0018] A wafer substrate is provided, and the piezoelectric layer formed after the electrode layer is grown is combined with the wafer substrate to obtain the acoustic wave filter.
[0019] As an improvement to the above technical solution, the residual strain of the piezoelectric layer is less than 0.1%; when the acoustic wave filter is configured to operate at a frequency of 1 GHz to 5 GHz, the piezoelectric constant is greater than 10 pm / V, and the electromechanical coupling coefficient is greater than 10%.
[0020] The implementation of the present invention has the following beneficial effects:
[0021] The piezoelectric layer of the present invention is a periodically alternating stack of ε-Ga2O3 layers and ε-AlGaO layers. The superlattice redistributes strain accumulation at the heterogeneous interface. Compared with the ε-Ga2O3 film as the piezoelectric layer, the residual stress is reduced by more than 70%. Even in the piezoelectric layer with a thickness greater than 600nm, no cracks are generated, and the crystal quality is significantly improved. In addition, the ε-AlGaO material has a high piezoelectric constant. The acoustic wave resonator obtained based on the piezoelectric layer of the alternating stack of ε-Ga2O3 layers and ε-AlGaO layers can meet the use requirements of high-frequency filters and is configured to operate at an operating frequency of 1GHz to 5GHz. The piezoelectric constant is greater than 10pm / V and the electromechanical coupling coefficient is greater than 10%. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 1 is a schematic structural diagram of an acoustic wave filter provided by an embodiment of the present invention;
[0023] Figure 2 Schematic diagram of the structure of the piezoelectric layer provided by an embodiment of the present invention;
[0024] Figure 3 1 is a schematic structural diagram after step S2 in the method for preparing an acoustic wave filter provided by one embodiment of the present invention;
[0025] Figure 4 1 is a schematic structural diagram after step S2 in a method for preparing an acoustic wave filter provided by another embodiment of the present invention. DETAILED DESCRIPTION
[0026] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in further detail below.
[0027] like Figure 1 As shown, the present invention provides an acoustic wave filter, comprising a wafer substrate 10, a piezoelectric layer 20 and an electrode layer 30 arranged in sequence; wherein the piezoelectric layer 20 comprises an ε-Ga2O3 layer 21 and an ε-AlGaO layer 22 that are periodically alternately stacked.
[0028] Compared with the conventional ε-Ga2O3 layer as the piezoelectric layer, the ε-Ga2O3 layer 21 and the ε-AlGaO layer 22 are periodically and alternately stacked to form a piezoelectric layer 20 with a superlattice structure. The superlattice redistributes the strain accumulation at the heterogeneous interface. Compared with the ε-Ga2O3 film as the piezoelectric layer 20, the residual stress is reduced by more than 70%, and the residual strain is less than 0.1%. Even in the piezoelectric layer 20 with a thickness greater than 600nm, no cracks are generated, and the crystal quality of the piezoelectric layer 20 is significantly improved. In addition, the ε-AlGaO material has a high piezoelectric constant. The acoustic wave resonator obtained by the piezoelectric layer based on the alternating stacking of ε-Ga2O3 layers and ε-AlGaO layers can meet the use requirements of high-frequency filters, and is configured to operate at an operating frequency of 1GHz to 5GHz. The piezoelectric constant is greater than 10pm / V, and the electromechanical coupling coefficient is greater than 10%, which is particularly suitable for 5G / 6G systems.
[0029] The superlattice generates a strain field with enhanced piezoelectric polarization, which effectively improves the overall electromechanical coupling coefficient. In one embodiment, the alternating stacking period of the piezoelectric layer 20 is 10 to 100, exemplarily 20, 40, 50, 60 or 80, but not limited thereto. If the alternating stacking period is too small, the interface polarization enhancement effect is weak, which is not conducive to the improvement of the piezoelectric performance of the piezoelectric layer 20; if the alternating stacking period is too large, interface defects will accumulate with the increase of the alternating stacking period, resulting in enhanced acoustic wave scattering and increased insertion loss. Preferably, the alternating stacking period of the piezoelectric layer 20 is 10 to 30.
[0030] Specifically, in each period, the thickness of the ε-Ga2O3 layer 21 is 5nm to 50nm, exemplarily 10nm, 20nm, 25nm, 30nm, or 40nm, but not limited thereto; the thickness of the ε-AlGaO layer 22 is 5nm to 50nm, exemplarily 10nm, 20nm, 25nm, 30nm, or 40nm, but not limited thereto. If the thickness of the ε-Ga2O3 layer 21 and / or the thickness of the ε-AlGaO layer 22 in each period is too small, it will be difficult to achieve precise epitaxial control of each film layer, and phenomena such as component diffusion will easily occur, destroying the periodicity. If the thickness of the ε-Ga2O3 layer 21 and / or the thickness of the ε-AlGaO layer 22 in each period is too large, the material quality will be reduced.
[0031] In a preferred embodiment, in each period, the thickness ratio of the ε-AlGaO layer 22 to the ε-Ga2O3 layer 21 is 1:(1 to 10). More preferably, the ε-AlGaO layer 22 is thinner than the ε-Ga2O3 layer 21, exemplarily 1:2, 1:4, 1:5, 1:6 or 1:8, but not limited thereto.
[0032] The ε-AlGaO layer 22 is ε-Al 2-x Ga xThe O3 layer, where 0.1 < x < 1, and exemplarily 0.2, 0.4, 0.5, 0.6 or 0.8, but not limited thereto. Compared with Ga2O3, AlGaO has a smaller lattice constant, which decreases as the Al component increases. Therefore, by adjusting the thickness of the ε-AlGaO layer and the Al component, the required stress can be obtained in the piezoelectric layer 20 formed by periodically laminating the ε-Ga2O3 layer 21 and the ε-AlGaO layer 22 in a superlattice structure, thereby suppressing the cracks caused by the mismatch of the thermal expansion coefficients between the epitaxial crystal and the substrate. Preferably, 0.2 < x < 0.7. When x < 0.7, the piezoelectric constant of the ε-AlGaO layer 22 > 11 pm / V. When periodically laminated with the ε-Ga2O3 layer 21 to form a superlattice piezoelectric layer, the overall piezoelectric constant is high, which can meet the piezoelectric performance required for broadband. In addition, adjusting the proportion of the Al component can also balance the lattice and thermal expansion coefficient matching between the ε-AlGaO layer 22, the wafer substrate 10 and the ε-Ga2O3 layer 21.
[0033] In a preferred embodiment, the ε-AlGaO layer 22 is a doped ε-AlGaO layer, and the doping element is one or more of Sc, Hf, Mg, and the doping concentration is 0.1% - 10%, and exemplarily 0.5%, 1%, 3%, 5% or 7%, but not limited thereto. Doping can further improve the electromechanical coupling coefficient.
[0034] In one embodiment, the material of the wafer substrate 10 is one or more of Si, sapphire, SiC, GaN.
[0035] As Figure 1 described, in one embodiment, a cavity 11 is provided on the wafer substrate 10, the piezoelectric layer 20 is in contact with the side of the wafer substrate 10 where the cavity 11 is provided, and the depth of the cavity 11 is greater than the thickness of the electrode layer 30.
[0036] Specifically, the electrode layer 30 includes an upper electrode layer 31 and a lower electrode layer 32 respectively provided on the upper and lower surfaces of the piezoelectric layer 20. The materials of the upper electrode layer 31 and the lower electrode layer 32 are one or more of Pt, Ag, W, Mo, Al, and the thickness is 100 nm - 500 nm.
[0037] Correspondingly, the present invention also provides a preparation method of an acoustic wave filter for preparing the above acoustic wave filter, including the following steps:
[0038] S1. Provide a temporary substrate 40;
[0039] The material of the temporary substrate 40 is one or more of Si, sapphire, SiC, GaN.
[0040] S2. As Figure 2 [[ID=**28**]]and Figure 3 As shown, a piezoelectric layer 20 is grown on the temporary substrate 40 , and the piezoelectric layer 20 includes ε-Ga 2 O 3 layers 21 and ε-AlGaO layers 22 that are periodically and alternately stacked.
[0041] The piezoelectric layer 20 can be made by MOCVD, MBE, PLD, etc. In one embodiment, the piezoelectric layer 20 is grown by MOCVD. Specifically, the growth temperature of the ε-Ga2O3 layer 21 is 550℃~700℃, the growth pressure is 20Torr~200Torr, the Ga source is TMGa or TEGa, and the O source is one of O2, H2O or N2O. The growth temperature of the ε-AlGaO layer 22 is 550℃~700℃, the growth pressure is 20Torr~200Torr, the Ga source is TMGa or TEGa, the Al source is TMAl, and the O source is one of O2, H2O or N2O. The low temperature and low pressure MOCVD environment is conducive to the efficient and high-quality growth of the metastable ε-Ga2O3 layer 21 and the ε-AlGaO layer 22, and the purity of the ε-Ga2O3 layer 21 and the ε-AlGaO layer 22 is high. In addition, the metastable ε-Ga2O3 layer 21 and the ε-AlGaO layer 22 are stably grown at low temperatures, which can reduce the thermal budget and enable integration with temperature-sensitive substrates or processes.
[0042] In a preferred embodiment, Figure 4 As shown, an AlN buffer layer 50 is first grown on the temporary substrate 40, and then the piezoelectric layer 20 is grown on the AlN buffer layer 50. By growing the piezoelectric layer 20 on the buffer layer, the growth quality of the piezoelectric layer 20 can be further improved.
[0043] S3 , removing the temporary substrate 40 , and growing an electrode layer 30 on at least one side of the piezoelectric layer 20 .
[0044] In one embodiment, an upper electrode layer 31 and a lower electrode layer 32 are grown on the upper and lower sides of the piezoelectric layer 20 respectively.
[0045] The electrode layer 30 is made of one or more materials selected from the group consisting of Pt, Ag, W, Mo, and Al, and has a thickness of 100 nm to 500 nm.
[0046] S4. Provide a wafer substrate 10, and combine the piezoelectric layer 20 after the electrode layer 30 is grown with the wafer substrate 10 to obtain the acoustic wave filter.
[0047] The wafer substrate 10 is made of one or more materials selected from Si, sapphire, SiC, and GaN.
[0048] In one embodiment, one side of the wafer substrate 10 is etched to form a cavity 11, the depth of which is greater than the thickness of the electrode layer 30, and then the lower surface of the piezoelectric layer 20 is combined with the upper surface of the wafer substrate 10 so that the lower electrode 32 is disposed in the cavity 11.
[0049] The present invention will be further described below with specific embodiments:
[0050] Example 1
[0051] This embodiment provides an acoustic wave filter, comprising a wafer substrate, a piezoelectric layer and an electrode layer arranged in sequence. The piezoelectric layer comprises periodically alternating layers of ε-Ga2O3 and ε-Al 0.5 Ga 1.5 O3 layer, the alternating stacking period is 30, in each period, the thickness of the ε-Ga2O3 layer is 20nm, the ε-Al 0.5 Ga 1.5 The thickness of the O3 layer is 20 nm.
[0052] The method for preparing the acoustic wave filter comprises the following steps:
[0053] S1. providing a temporary substrate;
[0054] The material of the temporary substrate is Si.
[0055] S2. Growing a piezoelectric layer on a temporary substrate, wherein the piezoelectric layer includes periodically alternately stacked ε-Ga2O3 layers and ε-AlGaO layers.
[0056] The piezoelectric layer was grown by MOCVD. The ε-Ga2O3 layer was grown at 750°C and a pressure of 100 Torr, using TMGa as the Ga source and H2O as the O source. The ε-AlGaO layer was grown at 750°C and a pressure of 90 Torr, using TMGa as the Ga source, TMAl as the Al source, and H2O as the O source.
[0057] S3. Remove the temporary substrate and grow an upper electrode layer and a lower electrode layer on the upper and lower sides of the piezoelectric layer respectively.
[0058] S4. Provide a wafer substrate, and combine the piezoelectric layer after the electrode layer is grown with the wafer substrate to obtain an acoustic wave filter.
[0059] The material of the wafer substrate is Si.
[0060] Example 2
[0061] This embodiment provides an acoustic wave filter, which differs from the embodiment 1 in that the ε-Al 0.5 Ga 1.5 The O3 layer is Sc-doped ε-Al0.5 Ga 1.5 O3 layer, doping concentration is 5%.
[0062] The rest are the same as in Example 6.
[0063] The rest are the same as in Example 1.
[0064] The piezoelectric constant of Example 1 and Example 2 was measured by PFM, and the electromechanical coupling coefficient was measured by the resonance-antiresonance frequency method. The specific results are as follows:
[0065]
[0066] The above is a preferred embodiment of the invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.
Claims
1. An acoustic wave filter, characterized in that It comprises a wafer substrate, a piezoelectric layer and an electrode layer arranged in sequence; wherein the piezoelectric layer comprises periodically alternately stacked ε-Ga2O3 layers and ε-AlGaO layers.
2. The acoustic wave filter according to claim 1, wherein The piezoelectric layer is grown at 550° C. to 700° C. by MOCVD.
3. The acoustic wave filter according to claim 1, wherein The alternating stacking period of the piezoelectric layers is 10 to 100.
4. The acoustic wave filter according to claim 1, wherein In each period, the thickness of the ε-Ga2O3 layer is 5nm-50nm, and the thickness of the ε-AlGaO layer is 5nm-50nm.
5. The acoustic wave filter according to claim 1, wherein In each period, the thickness ratio of the ε-AlGaO layer to the ε-Ga2O3 layer is 1:(1-10).
6. The acoustic wave filter according to claim 1, wherein The ε-AlGaO layer is ε-Al 2-x Ga x O3 layer, 0.2<x<0.
7.
7. The acoustic wave filter according to claim 1, wherein The ε-AlGaO layer is a doped ε-AlGaO layer, the doping element is one or more of Sc, Hf, and Mg, and the doping concentration is 0.1% to 10%.
8. The acoustic wave filter according to claim 1, wherein The material of the wafer substrate is one or more of Si, sapphire, SiC, and GaN; A cavity is provided on the wafer substrate, the piezoelectric layer contacts a side of the wafer substrate where the cavity is provided, and the depth of the cavity is greater than the thickness of the electrode layer; The electrode layer includes an upper electrode layer and a lower electrode layer respectively arranged on the upper and lower surfaces of the piezoelectric layer.
9. A method for preparing an acoustic wave filter, for preparing the acoustic wave filter according to any one of claims 1 to 8, characterized in that: The following steps are involved: providing a temporary substrate; Growing a piezoelectric layer on the temporary substrate, the piezoelectric layer comprising periodically alternating stacked ε-Ga2O3 layers and ε-AlGaO layers; the piezoelectric layer is grown by MOCVD at a growth temperature of 550° C. to 700° C.; removing the temporary substrate and growing an electrode layer on at least one side of the piezoelectric layer; A wafer substrate is provided, and the piezoelectric layer formed after the electrode layer is grown is combined with the wafer substrate to obtain the acoustic wave filter.
10. The acoustic wave filter according to any one of claims 1 to 8 or the acoustic wave filter obtained by the preparation method according to claim 9, characterized in that: The residual strain of the piezoelectric layer is less than 0.1%. When the acoustic wave filter is configured to operate at a frequency of 1 GHz to 5 GHz, the piezoelectric constant is greater than 10 pm / V and the electromechanical coupling coefficient is greater than 10%.