Temperature Compensated Resonator

Abstract

The present invention relates to a temperature-compensated resonator, comprising a piezoelectric substrate (1), a plurality of interdigital electrodes (2), and a temperature compensation layer (3), wherein a portion of the interdigital electrodes (2) is embedded in the piezoelectric substrate (1), and the other portions of the interdigital electrodes (2) except the portion embedded in the piezoelectric substrate (1) are covered by the temperature compensation layer (3). Thus, by adopting the structure of the present invention, the temperature-compensated resonator can obtain a good temperature coefficient of frequency (TCF) value while suppressing stress concentration at the interface between the piezoelectric substrate (1) and the temperature compensation layer (3).

Description

Technical Field

[0001] The present invention relates to a temperature-compensated resonator, in particular to a temperature-compensated resonator based on buried electrodes and applied to a radio frequency front-end filter. Background Art

[0002] For surface acoustic wave filters (SAW), their operating frequency is very sensitive to temperature and has the characteristic of frequency drifting with the operating temperature. In engineering, the magnitude of the frequency drift with temperature is usually measured by the temperature coefficient of frequency (TCF). The TCF value represents the change in the natural frequency when the temperature changes by 1°C, and can be used to measure the temperature stability of the SAW. That is, the smaller the TCF value, the smaller the temperature dependence of the SAW and the more stable the device performance. Due to the large specified operating temperature range of the equipment (usually -20°C to 85°C), and the increasing congestion of filter frequency bands for radio frequency terminals in the 5G era, ordinary SAW is difficult to meet the requirements. Therefore, it is crucial to improve the temperature stability of surface acoustic wave devices and reduce the impact of temperature on the operating frequency.

[0003] In the prior art, there are two common ways to improve the temperature stability of SAW filters. One way is to bond the piezoelectric substrate to a substrate with a low thermal expansion coefficient (TEC) (such as sapphire, Si, or spinel) to improve the TEC of the device and thus improve the TCF value, such as Figure 1 (a) However, this method is usually applied to the bottom of the lithium tantalate (LiTaO3) substrate. In most cases, the temperature rise of the device is mainly due to the heat generated by the interdigitated diode (IDT) fingers. Therefore, this method cannot effectively suppress the thermal strain on the upper surface of the piezoelectric substrate (i.e., the surface in contact with the interdigitated diodes), and thus has limited effect on improving the TCF value. At the same time, under this condition, the electromechanical coupling coefficient is low, which makes it difficult to meet the requirements of high bandwidth.

[0004] Another way is to deposit a layer of temperature compensation material with a positive temperature coefficient (such as SiO2) on the piezoelectric substrate to suppress the frequency drift caused by temperature changes and improve the temperature coefficient of frequency (TCF) of the device, such as Figure 1 In this case, due to the difference in thermal expansion coefficient, strong stress concentration is easily generated at the interface between the piezoelectric substrate and the temperature compensation layer, thus affecting the device performance. Summary of the Invention

[0005] In summary, how to obtain a good temperature coefficient of frequency (TCF) value while controlling the stress concentration at the interface between the piezoelectric substrate and the temperature compensation layer has great practical significance.

[0006] In response to the problems existing in the above-mentioned prior art, the present invention proposes a temperature-compensated resonator based on buried electrodes, comprising a piezoelectric substrate, a plurality of interdigitated electrodes, and a temperature compensation layer, wherein a portion of the interdigitated electrodes is buried in the piezoelectric substrate, and the other portions of the interdigitated electrodes except the portion buried in the piezoelectric substrate are covered by the temperature compensation layer, thereby enabling the temperature-compensated resonator to obtain a good temperature coefficient of frequency (TCF) value while suppressing stress concentration at the interface between the piezoelectric substrate and the temperature compensation layer.

[0007] A first embodiment of a temperature-compensated resonator according to the present invention includes a piezoelectric substrate, a plurality of interdigital electrodes, and a temperature compensation layer. Parts of the interdigital electrodes are embedded in the piezoelectric substrate, and the interdigital electrodes, excluding the portions embedded in the piezoelectric substrate, are covered by the temperature compensation layer.

[0008] In the second aspect of the temperature-compensated resonator of the present invention, in the first aspect, preferably, the height of the portion of the interdigital electrode embedded in the piezoelectric substrate is set to h1, the thermal expansion coefficient of the piezoelectric substrate is set to α1, the thermal expansion coefficient of the temperature compensation layer is set to α2, and the thickness of the interdigital electrode is set to H, so that the following relationship is satisfied:

[0009]

[0010] In a third aspect of the temperature-compensated resonator of the present invention, in the first aspect, preferably, the height of the portion of the interdigital electrode embedded in the piezoelectric substrate is set to h1, the temperature coefficient of the acoustic velocity of the piezoelectric substrate is set to β1, the temperature coefficient of the acoustic velocity of the temperature compensation layer is set to β2, and the thickness of the interdigital electrode is set to H, so that the following relationship is satisfied:

[0011]

[0012] In a fourth aspect of the temperature-compensated resonator of the present invention, in the first aspect, preferably, the height of the portion of the interdigital electrode embedded in the piezoelectric substrate is set to h1, the thermal expansion coefficient of the piezoelectric substrate is set to α1, the thermal expansion coefficient of the temperature compensation layer is set to α2, the temperature coefficient of the sound velocity of the piezoelectric substrate is set to β1, the temperature coefficient of the sound velocity of the temperature compensation layer is set to β2, and the thickness of the interdigital electrode is set to H, so that the following relationship is satisfied:

[0013]

[0014] The fifth mode of the temperature-compensated resonator of the present invention, in the first to fourth modes, preferably further includes a thickening layer, which is stacked above the interdigital electrode and located in the temperature compensation layer, and the thickening layer is arranged at the end of the interdigital electrode and the position of the adjacent interdigital electrode corresponding to the end.

[0015] The sixth mode of the temperature-compensated resonator of the present invention, in the first to fourth modes, preferably further includes a frequency modulation layer, which covers the temperature compensation layer, and the material of the frequency modulation layer includes at least one of silicon dioxide, silicon nitride, aluminum nitride, and silicon carbide.

[0016] A seventh aspect of the temperature-compensated resonator of the present invention, in the first to fourth aspects, is preferably such that a material of the temperature compensation layer includes silicon dioxide.

[0017] An eighth aspect of the temperature-compensated resonator of the present invention, in the first to fourth aspects, is preferably such that the material of the piezoelectric substrate is one of lithium niobate and lithium tantalate.

[0018] A ninth aspect of the temperature-compensated resonator of the present invention, in the first to fourth aspects, is preferably such that the material of the interdigital electrodes includes at least one of aluminum, copper, platinum, and gold.

[0019] A tenth aspect of the temperature-compensated resonator of the present invention, in the fifth aspect, is preferably such that the material of the thickened layer is the same as the material of the interdigital electrodes.

[0020] The eleventh aspect of the filter of the present invention preferably includes the temperature-compensated resonator according to any of the first to tenth aspects.

[0021] Effects of the Invention

[0022] By adopting the above-described structure of the present invention, it is possible to obtain a good temperature coefficient of frequency (TCF) value for the temperature-compensated resonator while suppressing stress concentration at the interface between the piezoelectric substrate and the temperature compensation layer.

[0023] In addition, in the present invention, the heat generated by the interdigital electrodes is proportionally distributed between the piezoelectric substrate and the temperature compensation layer, thereby weakening the stress concentration at the interface between the piezoelectric substrate and the temperature compensation layer, and effectively alleviating the thermal stress level at the interface.

[0024] Furthermore, in the present invention, the ratio of the height h1 of the portion of the interdigital electrode embedded in the piezoelectric substrate to the height h2 of the remaining portion of the interdigital electrode covered by the temperature compensation layer is set to be complementary to the ratio of the acoustic velocity temperature coefficient β1 of the piezoelectric substrate and the acoustic velocity temperature coefficient β2 of the temperature compensation layer. , so that the temperature coefficient of sound velocity TCV of the resonator can be made as small as possible, which can effectively improve the temperature coefficient of frequency TCF value of the resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 (a) is a schematic cross-sectional view showing a structure in which a piezoelectric substrate with high TEC is bonded to a substrate with low TEC in the prior art; Figure 1 (b) is a schematic cross-sectional view showing a structure in the prior art in which a temperature compensation layer of a positive TCV is deposited on a piezoelectric substrate of a negative TCV.

[0026] Figure 2 Schematic diagram showing a cross-sectional structure of a temperature-compensated resonator according to an embodiment of the present invention.

[0027] Figure 3 Schematic diagram showing a cross-sectional structure of a modified example of the temperature-compensated resonator according to the embodiment of the present invention.

[0028] Figure 4 It is a schematic diagram showing a cross-sectional structure of another modified example of the temperature-compensated resonator according to the embodiment of the present invention.

[0029] Figure 5 It is a schematic diagram showing a planar structure of another modified example of the temperature-compensated resonator according to the embodiment of the present invention. DETAILED DESCRIPTION

[0030] Hereinafter, preferred embodiments of the temperature-compensated resonator according to the present invention will be described with reference to the accompanying drawings. In each of the drawings, identical or corresponding parts are denoted by the same reference numerals for description.

[0031] <Structure of Temperature Compensated Resonator According to Embodiment of the Present Invention>

[0032] Figure 2 Schematic diagram showing a cross-sectional structure of a temperature-compensated resonator according to an embodiment of the present invention.

[0033] like Figure 2 As shown, the temperature-compensated resonator of the present invention includes a piezoelectric substrate 1, a plurality of interdigital electrodes 2, and a temperature compensation layer 3. A portion of the interdigital electrodes 2 ( Figure 2 h1) is embedded in the piezoelectric substrate 1, and the other parts of the interdigital electrode 2 except the part embedded in the piezoelectric substrate 1 ( Figure 2 h2) in the figure is covered by the temperature compensation layer 3.

[0034] In addition, as an example, the material of the temperature compensation layer includes silicon dioxide; the material of the piezoelectric substrate is one of lithium niobate and lithium tantalate; and the material of the interdigital electrodes includes at least one of aluminum, copper, platinum, and gold.

[0035] Therefore, by adopting the above structure, the present invention can suppress the stress concentration at the interface between the piezoelectric substrate and the temperature compensation layer while enabling the temperature-compensated resonator to obtain a good temperature coefficient of frequency TCF value; and the thickness of the temperature compensation layer (such as silicon dioxide) required to be covered by this structure is smaller, which is conducive to the miniaturization design of the resonator.

[0036] In addition, the depth of the interdigital electrodes 2 embedded in the piezoelectric substrate 1 is determined by the thermal expansion coefficient (TEC) and / or the temperature coefficient of sound velocity (TCV) of the piezoelectric substrate 1 and the temperature compensation layer 3 .

[0037] In the present invention, the thermal expansion coefficient of the piezoelectric substrate 1 is set to α1, the sound velocity temperature coefficient of the piezoelectric substrate 1 is set to β1, the thermal expansion coefficient of the temperature compensation layer 3 is α2, the sound velocity temperature coefficient of the temperature compensation layer 3 is set to β2, the height of the interdigital electrode 2 is set to H, the height of the part of the interdigital electrode 2 buried in the piezoelectric substrate 1 is set to h1, and the height of the part of the interdigital electrode 2 not buried in the piezoelectric substrate 1 is set to h2, where H=h1+h2.

[0038] (Design based on thermal expansion coefficient TEC)

[0039] When considering the strong stress concentration at the interface between the piezoelectric substrate 1 and the temperature compensation layer 3, the relative thermal strain at the interface between the piezoelectric substrate 1 and the temperature compensation layer 3 can be considered. The heat generated by the interdigital electrodes 2 can be proportionally distributed between the piezoelectric substrate 1 and the temperature compensation layer 3, thereby reducing the stress concentration at the interface. In this case, the embedment depth h1 of the interdigital electrodes 2 can be designed based on the proportional relationship between the thermal expansion coefficients. This embedment depth h1 can be calculated using the following equation 1.

[0040]

[0041] Therefore, in the present invention, by distributing the heat generated by the interdigital electrodes proportionally between the piezoelectric substrate and the temperature compensation layer, stress concentration at the interface between the piezoelectric substrate and the temperature compensation layer can be weakened, and the thermal stress level at the interface can be effectively alleviated.

[0042] (Design based on the temperature coefficient of sound velocity TCV)

[0043] When improving the TCF value is the primary consideration, since the resonator excitation frequency is primarily determined by the acoustic velocity when the interdigital electrodes 2 are arranged in a fixed pattern (i.e., at a fixed wavelength), the effect of temperature on the acoustic velocity must be minimized by minimizing the resonator's temperature coefficient of acoustic velocity (TCV). To this end, in the present invention, the ratio of the height h1 of the portion of the interdigital electrodes 2 embedded in the piezoelectric substrate 1 to the height h2 of the remaining portion of the interdigital electrodes 2 covered by the temperature compensation layer 3 is set to be complementary to the ratio of the acoustic temperature coefficient β1 of the piezoelectric substrate 1 to the acoustic temperature coefficient β2 of the temperature compensation layer 3, namely:

[0044]

[0045] By transforming the above formula (4), the embedding depth h1 can be calculated (that is, the following formula 2 can be obtained).

[0046]

[0047] Therefore, in the present invention, by setting the ratio of the height h1 of the portion of the interdigital electrode 2 buried in the piezoelectric substrate 1 to the height h2 of the remaining portion of the interdigital electrode 2 covered by the temperature compensation layer 3 to be complementary to the ratio of the temperature coefficient of the acoustic velocity β1 of the piezoelectric substrate 1 and the temperature coefficient of the acoustic velocity β2 of the temperature compensation layer 3 (i.e., Formula 2), the temperature coefficient of the acoustic velocity TCV of the resonator can be made as small as possible, and the temperature coefficient of frequency TCF value of the resonator can be effectively improved.

[0048] (Design based on both thermal expansion coefficient TEC and temperature coefficient of sound velocity TCV)

[0049] When considering the TCF value and the stress concentration at the interface between the piezoelectric substrate and the temperature compensation layer, in order to obtain a good TCF value while effectively controlling the stress level at the interface, the embedding depth h1 of the interdigital electrode 2 is set to meet the following conditions:

[0050]

[0051] That is, the embedding depth h1 of the interdigital electrode 2 is set to be equal to or greater than the smaller value of Expression 1 and Expression 2 and equal to or less than the larger value of Expression 1 and Expression 2.

[0052] Therefore, in the present invention, the thermal stress level at the interface between the piezoelectric substrate and the temperature compensation layer can be controlled to a low level while effectively improving the TCF value of the resonator.

[0053]

[0054] Figure 3 Schematic diagram showing a cross-sectional structure of a modified example of the temperature-compensated resonator according to the embodiment of the present invention.

[0055] like Figure 3 As shown, the temperature-compensated resonator of the present invention may further include a frequency-modulation layer 4, which covers the temperature-compensating layer 3 and is used to adjust the operating frequency of the resonator. The material of the frequency-modulation layer 4 includes at least one of silicon dioxide, silicon nitride, aluminum nitride, and silicon carbide.

[0056] Furthermore, after depositing the temperature compensation layer 3, the frequency can be measured using a probe. If the frequency is too high, a silicon dioxide layer can be added over the temperature compensation layer 3 as a frequency modulation layer 4 to lower the frequency. If the frequency is too low, a layer made of silicon nitride, aluminum nitride, or silicon carbide can be added over the temperature compensation layer 3 as a frequency modulation layer 4 to increase the frequency.

[0057] <Another Modification of the Temperature Compensated Resonator According to the Embodiment of the Present Invention>

[0058] Figure 4 It is a schematic diagram showing a cross-sectional structure of another modified example of the temperature-compensated resonator according to the embodiment of the present invention. Figure 5 It is a schematic diagram showing a planar structure of another modified example of the temperature-compensated resonator according to the embodiment of the present invention.

[0059] like Figure 4 As shown, the temperature-compensated resonator of the present invention may further be provided with a thickening layer 5, which is stacked above the interdigital electrodes 2 and located in the temperature compensation layer 3. In addition, in the present invention, it is preferred that the thickening layer 5 is provided at the ends of the interdigital electrodes 2 and at the portions of the adjacent interdigital electrodes corresponding to the ends. As an example, Figure 5 In the embodiment, 7 interdigital electrodes 2 are provided, and 14 thickening layers 5 are provided in two rows and seven columns, with gaps 7 between the interdigital electrodes 2 and the busbars 6. In the present invention, by further providing the thickening layers 5, stray responses can be suppressed.

[0060] In the present invention, the material of the thickened layer 5 is preferably the same as that of the interdigital electrodes 2. By making the material of the thickened layer 5 the same as that of the interdigital electrodes 2, the manufacture of the thickened layer 5 and the interdigital electrodes 2 becomes easier.

[0061] <Filter According to Embodiment of the Present Invention>

[0062] A filter according to an embodiment of the present invention includes the temperature-compensated resonator described in the above embodiment.

[0063] The descriptions in the above specific embodiments are only some embodiments of the present invention. For those skilled in the art, further modifications and improvements can be made without departing from the inventive concept of the present invention, and these modifications and improvements are all included in the protection scope of the present invention.

[0064] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution. In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0065] Industrial applicability

[0066] The buried electrode-based temperature-compensated resonator of the present invention can be applied to, for example, resonators of radio frequency front-end filters.

[0067] Description of labels

[0068] 201 High TEC Piezoelectric Substrate

[0069] 202 Low TEC substrate

[0070] 301 Piezoelectric Substrate for Negative TCV

[0071] 302 Temperature compensation layer of positive TCV

[0072] 1 Piezoelectric substrate

[0073] 2 interdigitated electrodes

[0074] 3 Temperature compensation layer

[0075] 4 FM layers

[0076] 5 Thickening layer

[0077] 6 Busbars

[0078] 7 gaps.

Claims

1. A temperature-compensated resonator comprising a piezoelectric substrate, a plurality of interdigital electrodes, and a temperature compensation layer, characterized in that: A portion of the interdigital electrodes is embedded in the piezoelectric substrate, The portions of the interdigital electrodes other than the portions embedded in the piezoelectric substrate are covered by the temperature compensation layer. The height of the portions of the interdigital electrodes embedded in the piezoelectric substrate is set to h1, the thermal expansion coefficient of the piezoelectric substrate is set to α1, the thermal expansion coefficient of the temperature compensation layer is set to α2, and the thickness of the interdigital electrodes is set to H. The following relationship is satisfied:

2. A temperature-compensated resonator comprising a piezoelectric substrate, a plurality of interdigital electrodes, and a temperature compensation layer, characterized in that: A portion of the interdigital electrodes is embedded in the piezoelectric substrate, The other parts of the interdigital electrodes except the parts buried in the piezoelectric substrate are covered by the temperature compensation layer. The height of the portion of the interdigital electrode buried in the piezoelectric substrate is set to h1, the acoustic velocity temperature coefficient of the piezoelectric substrate is set to β1, the acoustic velocity temperature coefficient of the temperature compensation layer is set to β2, and the thickness of the interdigital electrode is set to H, then the following relationship is satisfied:

3. A temperature-compensated resonator comprising a piezoelectric substrate, a plurality of interdigital electrodes, and a temperature compensation layer, characterized in that: A portion of the interdigital electrodes is embedded in the piezoelectric substrate, The other parts of the interdigital electrodes except the parts buried in the piezoelectric substrate are covered by the temperature compensation layer. The height of the portion of the interdigital electrode buried in the piezoelectric substrate is set to h1, the thermal expansion coefficient of the piezoelectric substrate is set to α1, the thermal expansion coefficient of the temperature compensation layer is set to α2, the sound velocity temperature coefficient of the piezoelectric substrate is set to β1, the sound velocity temperature coefficient of the temperature compensation layer is set to β2, and the thickness of the interdigital electrode is set to H, then the following relationship is satisfied:

4. The temperature-compensated resonator according to any one of claims 1 to 3, wherein: It also includes a thickening layer, which is stacked above the interdigital electrodes and located in the temperature compensation layer. The thickening layer is arranged at the end of the interdigital electrode and at a portion of the adjacent interdigital electrode corresponding to the end.

5. The temperature-compensated resonator according to any one of claims 1 to 3, wherein: It also includes a frequency modulation layer, which covers the temperature compensation layer. The material of the frequency modulation layer includes at least one of silicon dioxide, silicon nitride, aluminum nitride, and silicon carbide.

6. The temperature-compensated resonator according to any one of claims 1 to 3, wherein: The material of the temperature compensation layer includes silicon dioxide.

7. The temperature-compensated resonator according to any one of claims 1 to 3, characterized in that: The material of the piezoelectric substrate is one of lithium niobate and lithium tantalate.

8. The temperature-compensated resonator according to any one of claims 1 to 3, wherein: The material of the interdigital electrodes includes at least one of aluminum, copper, platinum, and gold.

9. The temperature-compensated resonator according to claim 4, wherein: The material of the thickened layer is the same as that of the interdigital electrodes.

10. A radio frequency front-end filter, characterized in that: The invention comprises the temperature-compensated resonator according to any one of claims 1 to 9.

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