Temperature compensation type surface acoustic wave resonator and preparation method thereof

Abstract

The invention relates to the technical field of radio frequency, and provides a temperature compensation type surface acoustic wave resonator and a preparation method thereof, the provided temperature compensation type surface acoustic wave resonator comprises a piezoelectric substrate, an interdigital transducer deposited on the piezoelectric substrate, and a temperature compensation layer covering the piezoelectric substrate and the interdigital transducer; the upper surface of the temperature compensation layer protrudes, and the height of the protruding part is the same as the thickness of an interdigital electrode in the interdigital transducer; the interdigital electrode is made of one metal of Au, Pt and W, the metallization ratio of the interdigital electrode is a / (lambda / 2), a is the width of the interdigital electrode, and lambda is the period of the interdigital transducer; the preparation method comprises the following steps: S1, preparing a piezoelectric substrate; s2, depositing an interdigital transducer; and S3, depositing a temperature compensation layer. According to the invention, clutters between the resonant frequency and the anti-resonant frequency are eliminated, the purity of the passband is improved, the cost is saved, and the yield is improved.

Description

Technical Field

[0001] This application relates to the field of radio frequency technology, and in particular to a temperature-compensated surface acoustic wave resonator and its fabrication method. Background Technology

[0002] Temperature-compensated surface acoustic wave (TC-SAW) resonators are radio frequency devices that significantly improve frequency temperature stability by adding a temperature compensation film to a traditional surface acoustic wave structure.

[0003] Due to the presence of interdigital transducers in TC-SAW, the surface of the temperature compensation layer is uneven, typically requiring chemical mechanical planarization (CMP) for smoothing. Current technology often uses Cu as the interdigital electrode material in TC-SAW. However, because the temperature compensation layer is smoothed after CMP, it resonates perpendicularly to the interdigital electrodes, creating a spur noise on the admittance curve. This spur appears between the resonant and anti-resonant frequencies. Although structural adjustments can reduce the noise, it is difficult to completely eliminate it. Using such a resonator as a filter will produce noticeable ripples in or near the passband.

[0004] How to design a TC-SAW that eliminates the need for CMP on the surface of the temperature compensation layer, removes noise between the resonant and anti-resonant frequencies, and improves the purity of the passband is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by this application is: how to overcome the shortcomings of the prior art and provide a temperature-compensated surface acoustic wave resonator and its preparation method, so that the surface of the temperature compensation layer does not require CMP, eliminating clutter between the resonant frequency and the anti-resonant frequency, and improving the purity of the passband.

[0006] To address the aforementioned technical problems, this application provides a temperature-compensated surface acoustic wave resonator, comprising a piezoelectric substrate, an interdigital transducer deposited on the piezoelectric substrate, and a temperature compensation layer covering the interdigital transducer; the upper surface of the temperature compensation layer protrudes, and the height of the protruding portion is the same as the thickness of the interdigital electrode in the interdigital transducer; the material of the piezoelectric substrate is 128YX LiNbO3; the material of the temperature compensation layer is SiO2; the material of the interdigital electrode is one of gold, platinum, and tungsten, and its metallization ratio is a / (λ / 2), where a is the width of the interdigital electrode and λ is the period of the interdigital transducer.

[0007] Optionally, according to claim 1, the temperature-compensated surface acoustic wave resonator is characterized in that the thickness of the temperature compensation layer is 0.35λ and the thickness of the interdigitated electrodes is 0.065λ.

[0008] Optionally, the interdigitated electrode is made of Au, and its metallization ratio is 0.4 to 0.5.

[0009] Optionally, the interdigitated electrode is made of Pt, and its metallization ratio is 0.5 to 0.75.

[0010] Optionally, the interdigitated electrode is made of W and has a metallization ratio of 0.2 to 0.4.

[0011] Optionally, the sidewalls of the protruding portion on the upper surface of the temperature compensation layer are arc-shaped.

[0012] Optionally, the sidewalls of the protruding portion on the upper surface of the temperature compensation layer are straight.

[0013] Optionally, the protruding portion on the upper surface of the temperature compensation layer is rectangular, and its sidewalls are perpendicular to the upper surface of the temperature compensation layer.

[0014] Optionally, the protruding portion on the upper surface of the temperature compensation layer is trapezoidal, and the angle between its sidewall and the upper surface of the temperature compensation layer is ≥30°.

[0015] This application also provides a fabrication method for a temperature-compensated surface acoustic wave resonator as described above, comprising the following steps: S1, preparing a piezoelectric substrate: cleaning a 128YX LiNbO3 piezoelectric substrate wafer, coating a photoresist on the wafer surface and exposing and developing it to form an interdigitated electrode pattern on the photoresist layer, followed by cleaning and drying the wafer; S2, depositing an interdigitated transducer: using one of Au, Pt, or W as the material for the interdigitated electrodes, first depositing a metal layer on the photoresist layer and the wafer surface exposed by the interdigitated electrode pattern by electron beam evaporation or magnetron sputtering, then removing the photoresist outside the interdigitated electrode pattern and the metal film thereon, leaving a metal interdigitated transducer on the wafer surface; S3, depositing a temperature compensation layer: depositing a temperature compensation layer SiO2 on the wafer surface and the interdigitated transducer by PVD, PECVD, or CVD.

[0016] The technical advantages of adopting the above technical solution compared with the prior art are as follows:

[0017] This application uses one of the metals Au, Pt, and W as the material for the interdigitated electrodes, making the temperature-compensated surface acoustic wave resonator insensitive to the shape of the upper surface of its temperature compensation layer. It does not require planarization by CMP, which eliminates noise between the resonant frequency and the anti-resonant frequency, improves the purity of the passband, saves costs, and increases the yield. Attached Figure Description

[0018] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 This is a cross-sectional structural diagram of a temperature-compensated surface acoustic wave resonator in this application;

[0020] Figure 2 This is the admittance curve of the temperature-compensated surface acoustic wave resonator using Au interdigitated electrodes in this application;

[0021] Figure 3 This is the admittance curve of the temperature-compensated surface acoustic wave resonator using Pt interdigitated electrodes in this application;

[0022] Figure 4 This is the admittance curve of the temperature-compensated surface acoustic wave resonator using W interdigitated electrodes in this application;

[0023] Figure 5 This is the admittance curve of a temperature-compensated surface acoustic wave resonator using Cu interdigitated electrodes and a temperature compensation layer that has been ground smooth by CMP in the existing technology.

[0024] Figure 6 yes Figure 5 Vibration mode diagram at the mid-nanometer burr;

[0025] Figure 7 This is a cross-sectional view of a temperature-compensated surface acoustic wave resonator in the prior art, where the temperature compensation layer is ground smooth by CMP.

[0026] Figure 8 This is another cross-sectional view of the temperature-compensated surface acoustic wave resonator in this application. Detailed Implementation

[0027] The present application will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the present application, and therefore only show the components relevant to the present application.

[0028] Example 1

[0029] like Figure 1As shown, this embodiment provides a temperature-compensated surface acoustic wave resonator, including a piezoelectric substrate, an interdigital transducer deposited on the piezoelectric substrate, and a temperature compensation layer covering the piezoelectric substrate and the interdigital transducer. The upper surface of the temperature compensation layer protrudes with a height of h1, and the thickness of the temperature compensation layer excluding its upper surface protrusion is h2. The thickness of the interdigital electrode in the interdigital transducer is the same as the height h1 of the upper surface protrusion of the temperature compensation layer. Specifically, the material of the piezoelectric substrate is 128YXLiNbO3; the material of the temperature compensation layer is SiO2; the material of the interdigital electrode is one of Au, Pt, and W, and its metallization ratio is a / (λ / 2), where a is the width of the interdigital electrode and λ is the period of the interdigital transducer.

[0030] It should be noted that in this application, the thickness of the temperature compensation layer is 0.35λ, and the thickness of the interdigitated electrode is 0.065λ. Based on this, for the Au interdigitated electrode, the metallization ratio is 0.4–0.5, preferably 0.5; for the Pt interdigitated electrode, the metallization ratio is 0.5–0.75, preferably 0.65; and for the W interdigitated electrode, the metallization ratio is 0.2–0.4, preferably 0.25.

[0031] In some embodiments, the interdigitated electrode material of this application is Au, such as... Figure 2 As shown, the horizontal axis represents frequency (freq), and the vertical axis represents admittance amplitude. There is no noise between the resonant frequency and the anti-resonant frequency.

[0032] In some embodiments, the interdigitated electrode material of this application is Pt, such as... Figure 3 (Meaning of horizontal and vertical axes and...) Figure 2 As shown in the figure, there is no noise between the resonant frequency and the anti-resonant frequency.

[0033] In some embodiments, the interdigitated electrode material of this application is W, such as... Figure 4 (Meaning of horizontal and vertical axes and...) Figure 2 As shown in the figure, there is no noise between the resonant frequency and the anti-resonant frequency.

[0034] In contrast, if the existing structure of Cu interdigitated electrodes and temperature compensation layer smoothed by CMP is used, such as Figure 5 (Meaning of horizontal and vertical axes and...) Figure 2 Consistent) Figure 6 As shown, there is a significant glitch between the resonant frequency and the anti-resonant frequency. The characteristic frequency of this admittance glitch is 853.97 MHz, which disperses and consumes surface acoustic wave energy, resulting in a significant decrease in the quality factor Q of the resonator and disrupting the overall frequency stability of the device.

[0035] Understandably, due to the presence of the interdigital transducer, the surface of the temperature compensation layer is not flat, such as... Figure 7As shown, conventional temperature-compensated surface acoustic wave (SAW) resonators require CMP (chemical mechanical polishing) to remove the protrusions on the upper surface of the temperature compensation layer. For traditional temperature-compensated SAW resonators using Cu interdigitated electrodes, the temperature compensation layer is smoothed out after CMP, forming a resonance perpendicular to the interdigitated electrodes. This results in spur noise appearing on the admittance curve between the resonant frequency and the anti-resonant frequency.

[0036] It is important to emphasize that Au, Pt, and W are all heavy metals with much higher densities than Cu, and their particle motion carries significantly more energy. Therefore, when using heavy metal electrodes, the energy of temperature-compensated surface acoustic wave resonators is more concentrated near the plane where the interdigitated electrodes contact the piezoelectric substrate. On the one hand, this makes the resonator less sensitive to the shape of the upper surface of the compensation layer, eliminating the need for CMP (Continuous Motion Mixing), thereby eliminating clutter between the resonant and anti-resonant frequencies and improving the purity of the passband. On the other hand, it results in lower energy radiated into the piezoelectric substrate, leading to a higher Q value.

[0037] It should be noted that, in this application, the sidewalls of the protruding portion on the upper surface of the temperature compensation layer can be either arc-shaped or straight.

[0038] In some embodiments, the protruding portion on the upper surface of the temperature compensation layer of this application is rectangular, such as... Figure 1 As shown, the sidewalls of the protruding portion on the upper surface of the temperature compensation layer are perpendicular to the upper surface of the temperature compensation layer.

[0039] In some embodiments, the protruding portion on the upper surface of the temperature compensation layer of this application is trapezoidal, such as... Figure 7 As shown, the angle α between the sidewall of the protruding portion on the upper surface of the temperature compensation layer and the upper surface of the temperature compensation layer is ≥30°.

[0040] Example 2

[0041] This embodiment provides a preparation method applied to the temperature-compensated surface acoustic wave resonator provided in Embodiment 1 above, comprising the following steps:

[0042] S1. Prepare the piezoelectric substrate: Clean the 128YX LiNbO3 piezoelectric substrate wafer, apply photoresist to the wafer surface and expose and develop it to form interdigitated electrode patterns on the photoresist layer, and then clean and dry the wafer.

[0043] S2. Depositing interdigital transducers: Using one of the metals Au, Pt, and W as the material for the interdigital electrodes, the metal layer is first deposited on the photoresist layer and the wafer surface exposed by the interdigital electrode pattern through electron beam evaporation or magnetron sputtering. Then, the photoresist outside the interdigital electrode pattern and the metal film on it are removed, leaving a metal interdigital transducer on the wafer surface.

[0044] S3. Deposit temperature compensation layer: Deposit a temperature compensation layer of SiO2 on the wafer surface and interdigital transducers through physical vapor deposition (PVD), plasma enhanced chemical vapor deposition (PECVD), or chemical vapor deposition (CVD).

[0045] 128YX LiNbO3 is a lithium niobate wafer with a crystal plane normal at a 128° angle to the Y-axis and a reference edge perpendicular to the X-axis, also known as 128LN. A temperature compensation layer such as SiO2 is coated on the surface of this wafer, significantly reducing the frequency temperature coefficient and exhibiting a high electromechanical coupling coefficient. Temperature-compensated surface acoustic wave resonators made from this material exhibit minimal changes in center frequency with ambient temperature, low acoustic wave propagation loss, and stable performance.

[0046] In the above steps, this application uses one of the metals Au, Pt, and W as interdigitated electrodes, which is not sensitive to the shape of the upper surface of the temperature compensation layer. Therefore, it is not necessary to use CMP to planarize the temperature compensation layer, resulting in high industrial redundancy, cost savings, and improved yield.

[0047] The above embodiments are only for illustrating the technical concept and features of this application. Their purpose is to enable those skilled in the art to understand the content of this application and implement it. They should not be used to limit the scope of protection of this application. All equivalent changes or modifications made in accordance with the spirit and essence of this application should be covered within the scope of protection of this application.

Claims

1. A temperature-compensated surface acoustic wave resonator, characterized in that, It includes a piezoelectric substrate, an interdigital transducer deposited on the piezoelectric substrate, and a temperature compensation layer covering the piezoelectric substrate and the interdigital transducer; The upper surface of the temperature compensation layer protrudes, and the height of the protrusion is the same as the thickness of the interdigital electrode in the interdigital transducer. The material of the piezoelectric substrate is 128YX LiNbO3; The temperature compensation layer is made of SiO2; The interdigital electrode is made of one of the metals Au, Pt, and W, and its metallization ratio is a / (λ / 2), where a is the width of the interdigital electrode and λ is the period of the interdigital transducer.

2. The temperature-compensated surface acoustic wave resonator according to claim 1, characterized in that, The thickness of the temperature compensation layer is 0.35λ, and the thickness of the interdigitated electrode is 0.065λ.

3. The temperature-compensated surface acoustic wave resonator according to claim 2, characterized in that, The interdigitated electrode is made of Au, and its metallization ratio is 0.4 to 0.

5.

4. The temperature-compensated surface acoustic wave resonator according to claim 2, characterized in that, The interdigitated electrode is made of Pt, and its metallization ratio is 0.5 to 0.

75.

5. The temperature-compensated surface acoustic wave resonator according to claim 2, characterized in that, The interdigitated electrode is made of W and has a metallization ratio of 0.2 to 0.

4.

6. The temperature-compensated surface acoustic wave resonator according to claim 1, characterized in that, The sidewalls of the protruding portion on the upper surface of the temperature compensation layer are arc-shaped.

7. The temperature-compensated surface acoustic wave resonator according to claim 1, characterized in that, The sidewalls of the protruding portion on the upper surface of the temperature compensation layer are straight.

8. The temperature-compensated surface acoustic wave resonator according to claim 7, characterized in that, The protruding portion on the upper surface of the temperature compensation layer is rectangular, and its sidewalls are perpendicular to the upper surface of the temperature compensation layer.

9. The temperature-compensated surface acoustic wave resonator according to claim 7, characterized in that, The protruding portion on the upper surface of the temperature compensation layer is trapezoidal, and the angle between its sidewall and the upper surface of the temperature compensation layer is ≥30°.

10. A method for fabricating a temperature-compensated surface acoustic wave resonator as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Prepare the piezoelectric substrate: Clean the 128YX LiNbO3 piezoelectric substrate wafer, apply photoresist to the wafer surface and expose and develop it to form interdigitated electrode patterns on the photoresist layer, and then clean and dry the wafer. S2. Depositing interdigital transducers: Using one of the metals Au, Pt, and W as the material for the interdigital electrodes, the metal layer is first deposited on the photoresist layer and the wafer surface exposed by the interdigital electrode pattern through electron beam evaporation or magnetron sputtering. Then, the photoresist outside the interdigital electrode pattern and the metal film on it are removed, leaving a metal interdigital transducer on the wafer surface. S3. Deposit temperature compensation layer: Deposit a temperature compensation layer SiO2 on the wafer surface and interdigital transducer by PVD, PECVD or CVD.

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