Temperature-compensated resonator and method of manufacturing the same

Abstract

The present invention provides a temperature-compensated resonator, comprising: a piezoelectric substrate; interdigital electrodes comprising a first electrode and a second electrode forming an interdigital structure, wherein the first electrode and the second electrode are both formed on the piezoelectric substrate; a bus bar comprising a first bus bar and a second bus bar arranged in parallel with each other, wherein the first bus bar and the second bus bar are both formed on the piezoelectric substrate, wherein the first bus bar is connected to one end of the first electrode, and the second bus bar is connected to one end of the second electrode; a thickening layer formed on the interdigital electrodes; and a temperature compensation layer composed of a temperature compensation material and covering the interdigital electrodes, the bus bars and the thickening layer, wherein a groove is excavated in a gap region between the first electrode and the second bus bar of the piezoelectric substrate, and a groove is also excavated in a gap region between the second electrode and the first bus bar of the piezoelectric substrate, wherein the groove is filled with the temperature compensation material.

Description

Technical Field

[0001] The present invention relates to a temperature-compensated resonator and a manufacturing method thereof, and in particular to a temperature-compensated resonator applied to a radio frequency front-end filter and a manufacturing method thereof. Background Art

[0002] Surface acoustic wave (SAW) filters are highly sensitive to temperature, exhibiting frequency drift with operating temperature. Due to the wide operating temperature range (typically -20°C to 85°C) specified for these devices, conventional SAW filters struggle to meet the filter requirements of RF terminals in the increasingly crowded 5G era. To improve the temperature stability of SAW devices and reduce the impact of temperature on operating frequency, demand for TC-SAW (temperature-compensated SAW) filters in mobile phone RF front-ends is increasing.

[0003] For TC-SAW, interdigital electrodes are typically formed on a lithium niobate (LiNbO3) piezoelectric substrate. These electrodes are then covered with a positive temperature coefficient (PTC) temperature compensation material (such as SiO2) to suppress frequency drift due to temperature changes. However, the introduction of a PTC material can also generate strong spurious responses. For high-bandwidth TC-SAW, suppressing in-band ripple and improving device performance is particularly important. Summary of the Invention

[0004] Technical problem to be solved by the invention

[0005] Since low-cut-angle LiNbO3 has a higher electromechanical coupling coefficient, low-cut-angle LiNbO3 piezoelectric substrates are usually used for high-bandwidth TC-SAW.

[0006] In this case, the finger weighting method commonly used in the prior art has little effect, and this method often leads to a decrease in Q value and an increase in device size, which is not conducive to the miniaturization of the device.

[0007] In addition, use piston at the end (in Figure 10 The figure shows a top view of a conventional temperature-compensated resonator. The method of forming thickened and widened layers 11 at the ends of the interdigital electrodes cannot effectively suppress stray emissions and instead faces significant limitations in applications at higher / higher frequencies. This is because high frequencies typically mean significantly reduced interdigital spacing. Due to the limitations of photolithography machine precision, widening the ends (i.e., forming thickened and widened layers 11) can easily cause interdigital short circuits, leading to device failure.

[0008] In addition, existing technologies have proposed the use of trenches between adjacent fingers to suppress spurious signals. However, this approach has only been applied to conventional SAWs using lithium tantalate as the piezoelectric substrate, and its effectiveness in TC-SAWs is unknown. However, this approach is complex to implement, especially at high frequencies, and also reduces the device's stiffness and Q factor, making it difficult to ensure its effectiveness and stability. Therefore, solving these problems is particularly important in TC-SAW design.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a temperature-compensated resonator and a method for manufacturing the same, which can suppress spurious responses and thereby improve device performance.

[0010] Technical solutions used to solve technical problems

[0011] In order to solve the above-mentioned problems, the temperature-compensated resonator of the present invention comprises: a piezoelectric substrate; an interdigital electrode, the interdigital electrode comprising a first electrode and a second electrode formed in an interdigital structure, wherein the first electrode and the second electrode are both formed on the piezoelectric substrate; a bus bar, the bus bar comprising a first bus bar and a second bus bar arranged in parallel with each other, wherein the first bus bar and the second bus bar are both formed on the piezoelectric substrate, the first bus bar being connected to one end of the first electrode, and the second bus bar being connected to the other end of the piezoelectric substrate. one end of the second electrode; a thickening layer formed on the interdigital electrodes; and a temperature compensation layer composed of a temperature compensation material and covering the interdigital electrodes, the bus bar and the thickening layer, wherein a groove is excavated in the gap area between the first electrode and the second bus bar of the piezoelectric substrate, and the groove is also excavated in the gap area between the second electrode and the first bus bar of the piezoelectric substrate, and the groove is filled with the temperature compensation material.

[0012] Effects of the Invention

[0013] The temperature-compensated resonator and the method for manufacturing the same according to the present invention have the following technical effects.

[0014] (1) Compared with the traditional piston method (i.e., forming a widened and thickened layer on the interdigital electrode), the present invention does not need to widen the end of the interdigital electrode (that is, no side piston, i.e., side widening layer is required), so there is no need to worry about the side piston (i.e., side widening layer) causing a short circuit of the interdigital transducer.

[0015] (2) Compared with excavating grooves between adjacent fingers, the present invention excavates grooves in the gap area between the interdigital electrodes and the bus bar, so the engineering workload and operation difficulty are greatly reduced, and the reliability is greatly improved.

[0016] (3) By excavating trenches in the gap region and forming a thickened layer on the interdigital electrodes, spurious responses are eliminated while ensuring a high Q value for the device. This also makes device design more flexible.

[0017] (4) By filling the trench with temperature compensation material, the temperature coefficient of frequency (TCF value) of the device can be further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a detailed structural diagram of a temperature-compensated resonator according to an embodiment of the present invention.

[0019] Figure 2 It is a schematic perspective view of a temperature-compensated resonator according to an embodiment of the present invention.

[0020] Figure 3 yes Figure 2 Cross-sectional view along line AA.

[0021] Figure 4 FIG. 1 is a graph showing the admittance frequency of the temperature-compensated resonator according to the first embodiment.

[0022] Figure 5 FIG. 1 is a graph showing the admittance frequency of the temperature-compensated resonator according to the second embodiment.

[0023] Figure 6 FIG. 1 is a graph showing the admittance frequency of the temperature-compensated resonator according to the third embodiment.

[0024] Figure 7 FIG. 4 is an admittance frequency curve of the temperature-compensated resonator according to the fourth embodiment.

[0025] Figure 8 FIG. 1 is a graph showing the admittance frequency of the temperature-compensated resonator according to the fifth embodiment.

[0026] Figure 9 This is a graph showing the admittance frequency of the temperature-compensated resonator according to the sixth embodiment.

[0027] Figure 10 Schematic top view of a conventional temperature-compensated resonator. DETAILED DESCRIPTION

[0028] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.

[0029] Figure 1 It is a detailed structural diagram of a temperature-compensated resonator according to an embodiment of the present invention. Figure 2 It is a schematic perspective view of a temperature-compensated resonator according to an embodiment of the present invention. Figure 3 yes Figure 2Cross-sectional view along line AA.

[0030] like Figures 1 to 3 As shown, the temperature-compensated resonator of the present invention includes a piezoelectric substrate 1 , interdigital electrodes 2 , a thickened layer 3 , a bus bar 4 , a temperature compensation layer 5 and a frequency modulation layer 6 .

[0031] The piezoelectric substrate 1 is made of lithium niobate (LiNbO3) with a cut angle of 15°±5°YX LiNbO3, and the corresponding Euler angles are (0°, -75°±5°, 0°). Preferably, the cut angle of the piezoelectric substrate 1 is 15°, and the corresponding Euler angles are (0°, -75°, 0°).

[0032] The interdigital electrode 2 is formed on the piezoelectric substrate 1 and is composed of a first electrode 2A and a second electrode 2B. Figure 1 and Figure 2 For convenience of explanation, only one first electrode 2A and one second electrode 2B are shown. However, in reality, a plurality of first electrodes 2A and a plurality of second electrodes 2B are formed on the piezoelectric substrate 1. These electrodes are arranged alternately at intervals to form an interdigital structure, thereby forming the interdigital electrodes 2.

[0033] The interdigital electrodes 2 may be one or more of Al, Cu, and Pt. For ease of processing, the interdigital electrodes 2 are preferably made of Cu.

[0034] Bus bars 4 are also formed on the piezoelectric substrate 1. The bus bars 4 include a first bus bar 4A and a second bus bar 4B arranged in parallel with each other. The bus bar 4A connects the plurality of first electrodes 2A, and the bus bar 4B connects the plurality of second electrodes 2B, thereby forming a complete IDT structure.

[0035] Thickening layers 3 are formed on the interdigital electrodes 2. Two thickening layers 3, namely, thickening layer 3A and thickening layer 3B, are formed on each interdigital electrode (ie, first electrode 2A and second electrode 2B).

[0036] Specifically, thickening layer 3A is formed on the end of first electrode 2A near second bus bar 4B. Similarly, thickening layer 3A is formed on the end of second electrode 2B near first bus bar 4A. Furthermore, thickening layer 3B is formed at a portion of first electrode 2A near first bus bar 4A that is flush with an end of the adjacent second electrode 2B. Similarly, thickening layer 3B is formed at a portion of second electrode 2B near second bus bar 4B that is flush with an end of the adjacent first electrode 2A.

[0037] The thickening layers 3A and 3B are made of the same material as the interdigital electrodes 2, namely one or more of Al, Cu, and Pt. For ease of processing, the thickening layers 3 are preferably made of Cu.

[0038] The thickness of the thickened layer 3 is 40 to 70 nm, preferably 55 nm. The width of the thickened layer 3 may be less than the width of the interdigital electrodes 2 .

[0039] Furthermore, if the wavelength of the acoustic wave excited by the temperature-compensated resonator according to the present invention is λ, the length of the thickened layer 3 is 0.25λ to λ, preferably λ / 2.

[0040] A groove 8 is bored in the gap region between the first electrode 2A and the second bus bar 4B of the piezoelectric substrate 1 , and a groove 8 is also bored in the gap region between the second electrode 2B and the first bus bar 4A of the piezoelectric substrate 1 .

[0041] The width of the gap region is set to L_gap, the width of the trench 8 is set to L, and the depth of the trench 8 is set to H.

[0042] In this case, the width L_gap of the gap region is 0 to 2λ, and preferably, the size of L_gap is 1.6 μm.

[0043] The width L of the trench 8 is less than the width L_gap of the gap region, that is, L≤L_gap. Preferably, L is 1 to 1.6 μm.

[0044] The depth H of the groove 8 satisfies 0<H≤2λ, and preferably, the depth H satisfies λ / 4<H≤λ.

[0045] A temperature compensation layer 5 made of a temperature compensation material covers the interdigitated electrodes 2, the thickened layer 3 and the busbar 4. Furthermore, the temperature compensation material is filled in the groove 8 until it is flush with the surface of the piezoelectric substrate 1. The temperature compensation material is preferably silicon dioxide.

[0046] Furthermore, to account for process errors and facilitate fine-tuning of the operating frequency, a frequency-modulation layer 6 may be provided over the temperature-compensated resonator's temperature-compensated layer 5 to facilitate fine-tuning of the operating frequency. The frequency-modulation layer 6 may be made of one or more of silicon nitride, silicon dioxide, aluminum nitride, and silicon carbide. For example, when the frequency is high, a layer of silicon dioxide may be provided over the temperature-compensated layer 5 to lower the frequency, while when the frequency is low, a layer of silicon nitride may be provided over the temperature-compensated layer 5 to increase the frequency.

[0047] According to the temperature-compensated resonator constructed as described above, compared with the traditional piston method (i.e., forming a widened and thickened layer on the interdigital electrode 2), the present invention does not need to widen the end of the interdigital electrode 2 (that is, no side piston, i.e., a side widening layer is required), so there is no need to worry about the side piston (i.e., the side widening layer) causing a short circuit of the interdigital transducer.

[0048] In addition, compared with excavating grooves between adjacent fingers (ie, interdigital electrodes 2), the present invention excavates grooves 8 in the gap area between the interdigital electrodes 2 and the bus bar 4, so the engineering workload and operation difficulty are greatly reduced, and the reliability is greatly improved.

[0049] By excavating the trench 8 in the gap region and forming the thickened layer 3 on the interdigital electrodes 2, not only the spurious response is eliminated, but also the high Q value of the device is ensured. At the same time, the device design is made more flexible.

[0050] In addition, by filling the trench 8 with a temperature compensation material, the temperature coefficient of frequency (TCF value) of the device can be further improved.

[0051] Hereinafter, embodiments of temperature-compensated resonators having different trench widths L and trench depths H will be described.

[0052] Example 1

[0053] Figure 4 FIG. 1 is a graph showing the admittance frequency of the temperature-compensated resonator according to the first embodiment.

[0054] The piezoelectric substrate 1 is 15°±5°YX LiNbO3, λ=1.7 μm, the interdigital electrodes 2 are made of Cu with a thickness of 0.3125 μm, the temperature compensation layer 5 is made of silicon dioxide with a thickness of 1.5 μm, the depth H of the groove 8 is λ, the width L of the groove 8 is 1 μm, and the thickness of the thickened layer 3 is 55 nm.

[0055] Depend on Figure 4 It can be seen from the admittance frequency curve that the spurious response of the temperature compensated resonator is eliminated and the device performance is better.

[0056] Example 2

[0057] Figure 5 FIG. 1 is a graph showing the admittance frequency of the temperature-compensated resonator according to the second embodiment.

[0058] The piezoelectric substrate 1 is 15°±5°YX LiNbO3, λ=1.7 μm, the interdigital electrodes 2 are made of Cu with a thickness of 0.3125 μm, the temperature compensation layer 5 is made of silicon dioxide with a thickness of 1.5 μm, the depth H of the groove 8 is λ, the width L of the groove 8 is 1.6 μm, and the thickness of the thickened layer 3 is 55 nm.

[0059] Depend on Figure 5 It can be seen from the admittance frequency curve that the spurious response of the temperature compensated resonator is eliminated and the device performance is better.

[0060] Example 3

[0061] Figure 6FIG. 1 is a graph showing the admittance frequency of the temperature-compensated resonator according to the third embodiment.

[0062] Among them, the piezoelectric substrate 1 is 15°±5°YX LiNbO3, λ=1.7μm, the interdigital electrode 2 is composed of Cu and has a thickness of 0.3125μm, the temperature compensation layer 5 is composed of silicon dioxide and has a thickness of 1.5μm, the depth H of the groove 8 is λ / 2, the width L of the groove 8 is 1μm, and the thickness of the thickened layer 3 is 55nm.

[0063] Depend on Figure 6 It can be seen from the admittance frequency curve that the spurious response of the temperature compensated resonator is eliminated and the device performance is better.

[0064] Example 4

[0065] Figure 7 FIG. 4 is an admittance frequency curve of the temperature-compensated resonator according to the fourth embodiment.

[0066] The piezoelectric substrate 1 is 15°±5°YX LiNbO3, λ=1.7μm, the interdigital electrodes 2 are made of Cu with a thickness of 0.3125μm, the temperature compensation layer 5 is made of silicon dioxide with a thickness of 1.5μm, the depth H of the groove 8 is λ / 4, the width L of the groove 8 is 1μm, and the thickness of the thickened layer 3 is 55nm.

[0067] Depend on Figure 7 It can be seen from the admittance frequency curve that the spurious response of the temperature compensated resonator is eliminated and the device performance is better.

[0068] Example 5

[0069] Figure 8 FIG. 1 is a graph showing the admittance frequency of the temperature-compensated resonator according to the fifth embodiment.

[0070] The piezoelectric substrate 1 is 15°±5°YX LiNbO3, λ=1.7μm, the interdigital electrodes 2 are made of Cu with a thickness of 0.3125μm, the temperature compensation layer 5 is made of silicon dioxide with a thickness of 1.5μm, the depth H of the groove 8 is λ / 8, the width L of the groove 8 is 1μm, and the thickness of the thickened layer 3 is 55nm.

[0071] Depend on Figure 8 It can be seen from the admittance frequency curve that the spurious response of the temperature compensated resonator is eliminated and the device performance is better.

[0072] Example 6

[0073] Figure 9 This is a graph showing the admittance frequency of the temperature-compensated resonator according to the sixth embodiment.

[0074] The piezoelectric substrate 1 is 15°±5°YX LiNbO3, λ=1.7μm, the interdigital electrodes 2 are made of Cu with a thickness of 0.3125μm, the temperature compensation layer 5 is made of silicon dioxide with a thickness of 1.5μm, the depth H of the groove 8 is 2λ, the width L of the groove 8 is 1μm, and the thickness of the thickened layer 3 is 55nm.

[0075] Depend on Figure 9 It can be seen from the admittance frequency curve that the spurious response of the temperature compensated resonator is eliminated and the device performance is better.

[0076] As can be seen from the above-described embodiments 1-6, in various cases where the groove 8 has different depths H and widths L, relatively smooth admittance-frequency curves can be obtained, the spurious responses of the temperature-compensated resonator are eliminated, and the device performance is also good. Therefore, the device design becomes more flexible.

[0077] Hereinafter, a method for manufacturing a temperature-compensated resonator according to the present invention will be described.

[0078] (1) A groove 8 is etched (excavated) on the piezoelectric substrate 1 by an etching process.

[0079] (2) A temperature compensation material is grown in the groove 8 until it is flush with the surface of the piezoelectric substrate 1 .

[0080] (3) The interdigital electrodes 2 are grown on the piezoelectric substrate 1 and the bus bars 4 are provided.

[0081] (4) A thickened layer 3 is grown on the interdigital electrodes 2 .

[0082] (5) A temperature compensation material is grown on the interdigital electrodes 2 , the busbars 4 and the thickened layer 3 to form a temperature compensation layer 5 , and the surface of the temperature compensation layer 5 is planarized by a polishing process.

[0083] (6) A frequency modulation layer 6 is grown on the temperature compensation layer 5 .

[0084] Although the present application describes various exemplary embodiments, the various features, forms, and functions described in the embodiments are not limited to being applied to specific embodiments, and can be applied to the embodiments individually or in various combinations.

[0085] Therefore, numerous modifications not shown are conceivable and fall within the technical scope disclosed in this application, including, for example, modifications, additions, or omissions of at least one component.

[0086] Industrial applicability

[0087] The temperature-compensated resonator of the present invention can be used as a high-bandwidth temperature-compensated resonator of a radio frequency front-end filter.

[0088] Description of labels

[0089] 1 Piezoelectric substrate

[0090] 2 interdigitated electrodes

[0091] 2A 1st electrode

[0092] 2B Second electrode

[0093] 3 Thickening layer

[0094] 3A 1st thickening layer

[0095] 3B 2nd thickening layer

[0096] 4 busbars

[0097] 4A Bus 1

[0098] 4B Bus Bar 2

[0099] 5 Temperature compensation layer

[0100] 6 FM layers

[0101] 7 Gap Area

[0102] 8 grooves

[0103] 9 Groove depth

[0104] 10 Groove width

[0105] 11 Widening and thickening layer

[0106] λ is the wavelength of the acoustic wave excited by the temperature-compensated resonator.

Claims

1. A temperature-compensated resonator, characterized in that: include: Piezoelectric substrate; an interdigitated electrode comprising a first electrode and a second electrode formed into an interdigitated structure, and a bus bar including a first bus bar and a second bus bar arranged in parallel with each other, wherein the first electrode and the second electrode, and the first bus bar and the second bus bar are all formed on the piezoelectric substrate, the first bus bar is connected to one end of the first electrode, and the second bus bar is connected to one end of the second electrode; a thickening layer formed on the first electrode and the second electrode of the interdigital electrode; and a temperature compensation layer, which is made of a temperature compensation material and covers the interdigital electrodes and the thickened layer; A groove is excavated in the gap region between the first electrode and the second bus bar of the piezoelectric substrate, and the groove is also excavated in the gap region between the second electrode and the first bus bar of the piezoelectric substrate. The groove is filled with the temperature compensation material.

2. The temperature-compensated resonator according to claim 1, wherein A first thickening layer is formed on one end of the first electrode close to the second bus bar and on one end of the second electrode close to the first bus bar. A second thickening layer is formed at a portion of the first electrode close to the first bus bar and flush with one end of the adjacent second electrode, and at a portion of the second electrode close to the second bus bar and flush with one end of the adjacent first electrode.

3. The temperature-compensated resonator according to claim 1, wherein The piezoelectric substrate is made of lithium niobate, and the cutting angle is 15°±5°YX LiNbO3, and the corresponding Euler angle is (0°, -75°±5°, 0°).

4. The temperature-compensated resonator according to claim 1, wherein The width of the groove is smaller than the width of the gap region between the first electrode and the second bus bar, and the width of the groove is smaller than the width of the gap region between the second electrode and the first bus bar.

5. The temperature-compensated resonator according to claim 4, wherein: The depth of the groove is less than or equal to twice the wavelength of an acoustic wave excited by the temperature compensation resonator.

6. The temperature-compensated resonator according to claim 2, wherein: The thickness of the first thickened layer and the second thickened layer is 40 to 70 nm.

7. The temperature-compensated resonator according to claim 6, wherein: The thickness of the first thickened layer and the second thickened layer is 55 nm.

8. The temperature-compensated resonator according to claim 1, wherein The temperature compensation material is silicon dioxide.

9. The temperature-compensated resonator according to claim 1, wherein: The temperature compensation layer is further covered with a frequency modulation layer, and the frequency modulation layer is one or more of silicon nitride, silicon dioxide, aluminum nitride, and silicon carbide.

10. A method for manufacturing a temperature-compensated resonator, characterized in that: The following steps are involved: etching a groove on the piezoelectric substrate by an etching process; growing a temperature compensation material in the groove until it is flush with the surface of the piezoelectric substrate; growing interdigitated electrodes including electrode fingers and bus bars on the piezoelectric substrate; growing a thickening layer on the electrode fingers of the interdigitated electrode; growing a temperature compensation material on the interdigital electrodes and the thickened layer to form a temperature compensation layer, and planarizing the surface of the temperature compensation layer through a polishing process; as well as A frequency modulation layer is grown on the temperature compensation layer.

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