A SAW resonator structure with high K, high Q, low TCF and small spuriousness

Abstract

The application provides a SAW resonant structure with high K, high Q, low TCF and small stray, which comprises a substrate layer, a high impedance layer arranged above the substrate layer, a first SiO2 temperature compensation layer arranged above the high impedance layer, a piezoelectric layer arranged above the first SiO2 temperature compensation layer, a metal gate arranged above the piezoelectric layer, a second SiO2 temperature compensation layer and a third SiO2 temperature compensation layer arranged above the metal gate. High electromechanical coupling coefficient, high quality factor, low TCF and small stray are design requirements of SAW resonators for the 5G era, and the SAW structure provided by the application realizes the design requirements of high electromechanical coupling coefficient, high quality factor, low TCF and small stray of the SAW resonator, and obtains a resonator with an electromechanical coupling coefficient of greater than or equal to 20%, a quality factor of greater than or equal to 2000, a TCF of less than or equal to 3ppm / ℃ and no stray.

Description

Technical Field

[0001] This invention relates to the field of SAW device technology, and more specifically, to a SAW resonant structure with high K, high Q, low TCF and low spurious emissions. Background Technology

[0002] Surface Acoustic Wave (SAW) resonators are fundamental components of SAW filters. With the continuous development of the RF front-end market, higher standards are being demanded of filters, which in turn places higher design requirements on SAW resonators, such as higher electromechanical coupling coefficient (K), higher quality factor (Q), lower temperature coefficient of frequency (TCF), and lower spurious response. However, some of these design requirements are mutually restrictive. For example, K and Q are contradictory; a lower TCF often accompanies a lower electromechanical coupling coefficient, and different methods of suppressing spurious response can also lead to a decrease in Q. Current designs often only achieve one or two of these requirements. For instance, the electromechanical coupling coefficient can be as high as 30%, but the quality factor is below 1000; or the quality factor can be as high as 3600, but the electromechanical coupling coefficient is far below the design standard. After verifying that the electromechanical coupling coefficient and quality factor meet the requirements, it is also necessary to improve the resonator's temperature stability and suppress spurious response. Both of these processes also involve a decrease in the electromechanical coupling coefficient or quality factor. Summary of the Invention

[0003] This invention aims to solve the aforementioned existing technical problems and proposes a SAW resonant structure with high K, high Q, low TCF, and low spurious emissions. High K refers to an electromechanical coupling coefficient ≥ 20%, high Q refers to a quality factor ≥ 2000, low TCF refers to |TCF| ≤ 3ppm / ℃, and low spurious emissions refers to a smooth admittance frequency response curve of the resonator. Under this structure, a resonator with an electromechanical coupling coefficient of 21.84%, quality factors of 2257.7 and 2201.7 at the resonant frequency and anti-resonant frequency respectively, a TCF of -1.5ppm / ℃, and virtually no spurious emissions is obtained.

[0004] To achieve the above objectives, the specific solution of the present invention is as follows:

[0005] The resonant structure includes: a first substrate layer, a second substrate layer, a high impedance layer, a first SiO2 temperature compensation layer, a piezoelectric layer, a metal gate, a first electrode, a second electrode, a third electrode, a fourth electrode, a fifth electrode, a first busbar, a second busbar, a third busbar, a fourth busbar, a second SiO2 temperature compensation layer, a third SiO2 temperature compensation layer, a first reflective gate, and a second reflective gate; wherein the first substrate layer is placed on the second substrate layer, the high impedance layer is placed on the first substrate layer, the first SiO2 temperature compensation layer is placed on the high impedance layer, the piezoelectric layer is placed on the first SiO2 temperature compensation layer, the metal gate is placed on the piezoelectric layer, and the second and third SiO2 temperature compensation layers are placed on the metal gate. The metal gate is composed of a first electrode, a second electrode, a third electrode, a fourth electrode, a first bus bar, a second bus bar, a first reflective gate, and a second reflective gate; the piezoelectric layer is a piezoelectric material with a negative temperature coefficient; the first electrode and the second electrode are connected to the first bus bar, and the third electrode and the fourth electrode are connected to the second bus bar; the first electrode, the second electrode, the third electrode, the fourth electrode, the first bus bar, and the second bus bar together constitute an interdigital transducer (IDT); the first reflective gate and the second reflective gate together constitute a reflective gate and are symmetrically arranged with respect to the IDT; the fifth electrode, the third bus bar, and the fourth bus bar are connected to form the first reflective gate.

[0006] Furthermore, the common material of the first substrate layer and the second substrate layer is Si, wherein the height of the first substrate layer is 1.25*λ, the height of the second substrate layer is 0.25*λ, and the second substrate layer serves as a perfect matching layer (PML) to absorb anchor loss, where λ is the period length of the resonator.

[0007] Furthermore, the high-impedance layer, which is used to reflect the energy propagating downwards in the secondary mode to reduce stray energy, is made of PolySi and has a height of 0.125*λ.

[0008] Furthermore, the height of the first SiO2 temperature compensation layer is a*λ, where a is a first preset parameter. By adjusting the value of the first preset parameter a, the electromechanical coupling coefficient, quality factor and TCF of the resonator can be adjusted. After obtaining a suitable value of a, a higher electromechanical coupling coefficient, quality factor and temperature stability can be obtained. Optionally, a = 0.095.

[0009] Furthermore, the piezoelectric layer is made of 41°YX-cut LN material and has a height of 0.1*λ.

[0010] Furthermore, the material of the metal gate is Al.

[0011] Furthermore, the width of the first electrode, the second electrode, the third electrode, and the fourth electrode is 0.25*λ, the height is 0.025*λ, and the metallization rate is 0.5. The first electrode and the third electrode are the main electrodes, with the same length and a distribution interval of 0.5*λ. The second electrode and the fourth electrode are pseudo-electrodes, with the same length and a distribution interval of 0.5*λ. The distance between the first and second electrodes is the same as the distance between the third and fourth electrodes, which is b. Optionally, b = 5 μm.

[0012] Furthermore, the first busbar and the second busbar are symmetrically positioned with respect to the centerline of the resonator in the Y direction, with a width of 1.5*λ and a distance d between the two busbars, optionally d = 140um.

[0013] Furthermore, the first busbar is connected to the first electrode and the second electrode to form a terminal, which is set to 1V; the second busbar is connected to the third electrode and the fourth electrode to form a ground terminal.

[0014] Furthermore, the reflective grating is an invariant short-circuit reflective grating, used to form Bragg reflective layers on both sides of the IDT, reflecting the energy escaping from both sides of the IDT back into the IDT, thereby suppressing the spurious response of the SAW resonator and improving the quality factor of the SAW resonator. The invariant reflective grating is composed of a first reflective grating and a second reflective grating, and the first reflective grating and the second reflective grating are symmetrically arranged with respect to the IDT. The first reflective grating is formed by connecting the fifth electrode, the third bus bar, and the fourth bus bar. The fifth electrode is periodically distributed in the first reflective grating, with a period of 1 / 2*λ. The electrode width of the fifth electrode is 0.25*λ, the electrode length is d, and the height is 0.025*λ. The number of its electrodes is n, optionally n=80. The third bus bar and the fourth bus bar are symmetrically arranged with respect to the centerline position of the resonator in the Y direction, with a width of 1.5*λ, and the distance between the two bus bars is d.

[0015] Furthermore, the IDT is an apodization IDT used to suppress the spurious response of the SAW resonator. The length of the first electrode is apodized, and its apodization trajectory is calculated using a cosine window function: L i = (0.54-0.46*cos(2*pi()*(i-1) / (N-1)))*c+debc, where L iThe length of the i-th first electrode along the X-axis direction; i is the i-th first electrode along the X-axis direction; N is the number of first electrodes, optionally N = 89; c is a second preset parameter, adjusting the value of the second preset parameter c can suppress spurious signals of the resonator when a suitable c is selected, optionally c = 45um; e is the shortest length of the pseudo-electrode, adding a pseudo-electrode to the apodization IDT can improve the admittance frequency response of the SAW resonator, optionally e = 2um.

[0016] Furthermore, the length of the second electrode is: P i =dbL i , where P i Let be the length of the i-th second electrode along the X-axis.

[0017] Furthermore, the distance between the apodizing IDT and the non-apodizing short-circuit reflective grating is 0.25*λ.

[0018] Furthermore, the second SiO2 temperature compensation layer is located above the apodization IDT, with a height of 0.025*λ. The second SiO2 temperature compensation layer is an apodization layer, and its apodization trajectory and shape and size are the same as those of the apodization IDT. This is used to suppress stray responses in the SAW resonator and improve the quality factor and temperature stability of the SAW resonator.

[0019] Furthermore, the third SiO2 temperature compensation layer is located above the invariant short-circuit reflector, with a height of 0.025*λ. The third SiO2 temperature compensation layer is an invariant layer, and its trajectory and shape are the same as those of the invariant short-circuit reflector, in order to suppress the spurious response of the SAW resonator and improve the quality factor of the SAW resonator.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] SAW resonators are fundamental components of filters. The electromechanical coupling coefficient of a resonator directly affects the filter's bandwidth, its quality factor is closely related to the filter's insertion loss, its temperature coefficient of flux (TCF) influences the filter's temperature stability, and its spurious emissions affect the filter's in-band ripple and the resonator's Q value. Therefore, high electromechanical coupling coefficient, high quality factor, low TCF, and low spurious emissions are design requirements for SAW resonators in the 5G era. However, some quantities among these design requirements are mutually restrictive. For example, K and Q are contradictory quantities; a smaller temperature coefficient of flux often accompanies a decrease in the electromechanical coupling coefficient, and different methods of suppressing spurious responses can also lead to a decrease in Q. In existing designs, only one or two of these parameters can often be satisfied. Therefore, this invention provides a SAW resonant structure with high K, high Q, low TCF and low spurious emissions. Under this structure, the design requirements of high electromechanical coupling coefficient, high quality factor, low TCF and low spurious emissions of SAW resonators are achieved, resulting in a resonator with electromechanical coupling coefficient ≥20%, quality factor ≥2000, |TCF| ≤3ppm / ℃ and basically no spurious emissions. Attached Figure Description

[0022] Figure 1 It is a three-dimensional equivalent model diagram of a SAW resonator with high K, high Q, low TCF and low spurious emissions.

[0023] Figure 2 This is a top view of the xy plane of the three-dimensional equivalent model of the SAW resonator after removing the second and third SiO2 temperature compensation layers.

[0024] Figure 3 This is a magnified view of region 112 in the top view of the xy plane.

[0025] Figure 4 This is a yz-plane side view of the three-dimensional equivalent model of the SAW resonator.

[0026] Figure 5 This is the xz-plane front view of the three-dimensional equivalent model of the SAW resonator.

[0027] Figure 6 It is a magnified view of region 110 in the front view of the xz plane.

[0028] Figure 7 It is a magnified view of region 111 in the front view of the xz plane.

[0029] Figure 8 This is the apodization trajectory and shape diagram of the IDT in the three-dimensional equivalent model of the SAW resonator.

[0030] Figure 9This is a diagram showing the trajectory and shape of the first reflective grating in the three-dimensional equivalent model of the SAW resonator.

[0031] Figure 10 This is the admittance frequency response diagram of the SAW resonator.

[0032] Figure 11 This is a frequency quality factor diagram of a SAW resonator.

[0033] Figure 12 This is a temperature-frequency drift diagram of a SAW resonator.

[0034] Icon labels:

[0035] 1. Second substrate layer; 2. First substrate layer; 3. High impedance layer; 4. First SiO2 temperature compensation layer; 5. Piezoelectric layer; 6. IDT; 7. Second SiO2 temperature compensation layer; 8. First reflective grid; 9. Third SiO2 temperature compensation layer; 10. Second reflective grid; 50. Fourth electrode; 51. First electrode; 52. Third electrode; 53. Second electrode; 54. Fifth electrode; 60. Second busbar; 61. First busbar; 62. Third busbar; 63. Fourth busbar; 100. Distance between apodized IDT and non-apodized short-circuited reflective grid; 110. Region 1 selected in the xz-plane front view of the three-dimensional equivalent model of the SAW resonator; 111. Region 2 selected in the xz-plane front view of the three-dimensional equivalent model of the SAW resonator; 112. Region selected in the xy-plane top view of the three-dimensional equivalent model of the SAW resonator after removing the second and third SiO2 temperature compensation layers. Detailed Implementation

[0036] The embodiments of the present invention will be described in further detail and clearly below with reference to the accompanying drawings and specific implementations. The described embodiments are merely some of the embodiments included in the present invention.

[0037] The specific implementation scheme of the present invention to solve the above-mentioned technical problems is as follows:

[0038] A SAW resonant structure with high K, high Q, low TCF and low spurious emissions, such as Figures 1-9As shown, it includes: a first substrate layer 2, a second substrate layer 1, a high impedance layer 3, a first SiO2 temperature compensation layer 4, a piezoelectric layer 5, a metal gate, a first electrode 51, a second electrode 53, a third electrode 52, a fourth electrode 50, a fifth electrode 54, a first bus bar 61, a second bus bar 60, a third bus bar 62, a fourth bus bar 63, a second SiO2 temperature compensation layer 7, a third SiO2 temperature compensation layer 9, a first reflective gate 8, and a second reflective gate 10; wherein the first substrate layer 2 is placed on the second substrate layer 1, the high impedance layer 3 is placed on the first substrate layer 2, the first SiO2 temperature compensation layer 4 is placed on the high impedance layer 3, the piezoelectric layer 5 is placed on the first SiO2 temperature compensation layer 4, the metal gate is placed on the piezoelectric layer 5, and the second SiO2 temperature compensation layer 7 and the third SiO2 temperature compensation layer 9 are placed on the metal gate. The metal gate is composed of a first electrode 51, a second electrode 53, a third electrode 52, a fourth electrode 50, a first bus bar 61, a second bus bar 60, a first reflective gate 8, and a second reflective gate 10; the piezoelectric layer 5 is a piezoelectric material with a negative temperature coefficient; the first electrode 51, the second electrode 53 are connected to the first bus bar 61, and the third electrode 52, the fourth electrode 50 are connected to the second bus bar 60; the first electrode 51, the second electrode 53, the third electrode 52, the fourth electrode 50, the first bus bar 61, and the second bus bar 60 together constitute an IDT6; the first reflective gate 8 and the second reflective gate 10 together constitute a reflective gate and are symmetrically arranged with respect to the IDT6; the fifth electrode 54, the third bus bar 62, and the fourth bus bar 63 are connected to form the first reflective gate 8.

[0039] Furthermore, the common material of the first substrate layer 2 and the second substrate layer 1 is Si, wherein the height of the first substrate layer 2 is 1.25*λ, the height of the second substrate layer 1 is 0.25*λ, and the second substrate layer 1 serves as a perfect matching layer PML to absorb anchor loss, where λ is the period length of the resonator, and λ = 4um.

[0040] Furthermore, the high-impedance layer 3 is used to reflect the energy propagating downwards in the secondary mode to reduce stray energy; its material is PolySi and its height is 0.125*λ.

[0041] Furthermore, the height of the first SiO2 temperature compensation layer 4 is a*λ, where a is a first preset parameter. By adjusting the value of the first preset parameter a, the electromechanical coupling coefficient, quality factor and TCF of the resonator can be adjusted. After obtaining a suitable value of a, a higher electromechanical coupling coefficient, quality factor and temperature stability can be obtained. In this embodiment, a = 0.095.

[0042] Furthermore, the piezoelectric layer 5 is made of 41°YX-cut LN material and has a height of 0.1*λ.

[0043] Furthermore, the material of the metal gate is Al.

[0044] Furthermore, the first electrode 51, the second electrode 53, the third electrode 52, and the fourth electrode 50 have an electrode width of 0.25*λ, a height of 0.025*λ, and a metallization rate of 0.5. The first electrode 51 and the third electrode 52 are the main electrodes, with the same length and a distribution interval of 0.5*λ. The second electrode 53 and the fourth electrode 50 are pseudo-electrodes, with the same length and a distribution interval of 0.5*λ. The distance between the first electrode 51 and the second electrode 53 is the same as the distance between the third electrode 52 and the fourth electrode 50, which is b. In this embodiment, b = 5 μm.

[0045] Furthermore, the first busbar 61 and the second busbar 60 are symmetrically arranged with respect to the centerline of the resonator in the Y direction, with a width of 1.5*λ and a distance d between the two busbars. In this embodiment, d = 140um.

[0046] Furthermore, the first busbar 61 is connected to the first electrode 51 and the second electrode 53 to form a terminal, which is set to 1V; the second busbar 60 is connected to the third electrode 52 and the fourth electrode 50 to form a ground terminal.

[0047] Furthermore, the reflective grating is an invariant short-circuit reflective grating, used to form Bragg reflective layers on both sides of the IDT6, reflecting the energy escaping from both sides of the IDT6 back into the IDT6, thereby suppressing the spurious response of the SAW resonator and improving the quality factor of the SAW resonator. The invariant reflective grating is composed of a first reflective grating 8 and a second reflective grating 10, and the first reflective grating 8 and the second reflective grating 10 are symmetrically arranged with respect to the IDT6. The first reflective grating 8 is formed by connecting the fifth electrode 54, the third bus bar 62 and the fourth bus bar 63. The fifth electrode 54 is periodically distributed in the first reflective grating 8, with a period size of 1 / 2*λ. The electrode width of the fifth electrode 54 is 0.25*λ, the electrode length is d, the thickness is 0.025*λ, and the number of its electrodes is n. In this embodiment, n = 80. The third bus bar 62 and the fourth bus bar 63 are symmetrically arranged with respect to the centerline position of the resonator in the Y direction, with a width of 1.5*λ and a distance of d between the two bus bars.

[0048] Furthermore, the IDT6 is an apodization IDT, which apodizes the length of the first electrode 51 to suppress the spurious response of the SAW resonator. Its apodization trajectory is calculated using a cosine window function: L i = (0.54-0.46*cos(2*pi()*(i-1) / (N-1)))*c+debc, where L iHere, is the length of the i-th first electrode 51 along the X-axis; i is the i-th first electrode 51 along the X-axis; N is the number of first electrodes 51, in this embodiment, N = 89; c is a second preset parameter. Adjusting the value of the second preset parameter c can suppress spurious signals of the SAW resonator when a suitable c is selected. In this embodiment, c = 45 μm; e is the shortest length of the pseudoelectrode. Adding a pseudoelectrode to the apodization IDT can improve the admittance frequency response of the SAW resonator. In this embodiment, e = 2 μm.

[0049] Furthermore, the length of the second electrode 53 is: P i =dbL i , where P i Let be the length of the i-th second electrode 53 along the X-axis direction.

[0050] Furthermore, the distance 100 between the apodizing IDT and the non-apodizing short-circuit reflective grating is 0.25*λ.

[0051] Furthermore, the second SiO2 temperature compensation layer 7 is located above the apodization IDT, with a height of 0.025*λ. The second SiO2 temperature compensation layer 7 is an apodization layer, and its apodization trajectory and shape and size are the same as those of the apodization IDT, in order to suppress spurious responses in the SAW resonator and improve the quality factor and temperature stability of the SAW resonator.

[0052] Furthermore, the third SiO2 temperature compensation layer 9 is located above the invariant short-circuit reflector, with a height of 0.025*λ. The third SiO2 temperature compensation layer 9 is an invariant layer, and its trajectory and shape are the same as those of the invariant short-circuit reflector, in order to suppress the spurious response of the SAW resonator and improve the quality factor of the SAW resonator.

[0053] Furthermore, such as Figures 10-12 As shown, the SAW resonator constructed under the above SAW resonant structure has a resonant frequency of 0.907 GHz, an anti-resonant frequency of 0.984 GHz, an electromechanical coupling coefficient of 21.84%, a quality factor of 2257.7 at the resonant frequency, a quality factor of 2201.7 at the anti-resonant frequency, and a TCF of -1.5 ppm / ℃ in the temperature range of -30℃ to 85℃.

[0054] The embodiments described above should be understood only as specific illustrations of this invention and are not intended to limit the specific scope of protection of this invention. After reading the description of this invention, those skilled in the art will understand that this invention can have various changes and modifications. Any changes, modifications, substitutions, combinations, simplifications, improvements, etc., made within the spirit and principles of this application should be considered equivalent substitutions and are included within the scope of protection of this invention.

Claims

1. A SAW resonant structure with high K, high Q, low TCF and low spurious emissions, characterized in that, include: The system comprises: a substrate layer; a high-impedance layer disposed on the substrate layer; a first SiO2 temperature compensation layer disposed on the high-impedance layer; a piezoelectric layer disposed on the first SiO2 temperature compensation layer; a metal gate disposed on the piezoelectric layer, the metal gate being composed of an apodization IDT and a non-apodization short-circuit reflective gate; a second SiO2 temperature compensation layer and a third SiO2 temperature compensation layer disposed on the metal gate; the second SiO2 temperature compensation layer being located only on the apodization IDT, and its apodization trajectory and shape size being the same as those of the apodization IDT; and the third SiO2 temperature compensation layer being located only on the non-apodization short-circuit reflective gate, and its trajectory and shape size being the same as those of the non-apodization short-circuit reflective gate.

2. The SAW resonant structure with high K, high Q, low TCF and low spurious emissions according to claim 1, characterized in that, The piezoelectric layer is a piezoelectric material with a negative temperature coefficient.

3. The SAW resonant structure with high K, high Q, low TCF and low spurious emissions according to claim 2, characterized in that, The piezoelectric material with a negative temperature coefficient includes 41°YX lithium niobate.

4. The SAW resonant structure with high K, high Q, low TCF and low spurious emissions according to claim 1, characterized in that, The materials of the apodizing IDT and the non-apodizing short-circuit reflective grating include Al.

5. A SAW resonant structure with high K, high Q, low TCF and low spurious emissions according to claim 1, characterized in that, The substrate layer is made of Si.

6. A SAW resonant structure with high K, high Q, low TCF and low spurious emissions according to claim 1, characterized in that, The high-resistivity layer is made of PolySi.

7. A SAW resonant structure with high K, high Q, low TCF and low spurious emissions according to claim 1, characterized in that, The apodization trajectory of the apodization IDT is controlled by a cosine window function.

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