POI substrate, SAW resonator and SAW filter
By embedding a high acoustic impedance layer in the TR-POI substrate, the problem of out-of-band spurs in the SAW filter based on the TR-POI substrate is solved, and the effect of improving acoustic insulation performance and suppressing spurs is achieved.
Patent Information
- Application Number
- CN202310956846.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-07-28
- Publication Date
- 2025-02-14
AI Technical Summary
The SAW filter based on the TR-POI substrate has severe out-of-band spurs, which reduces the insulation performance of the filter in the high frequency band range.
A high-acoustic impedance layer is embedded in a traditional TR-POI substrate. The acoustic impedance of the high-acoustic impedance layer is greater than the acoustic impedance of the insulating layer and the piezoelectric layer, forming a large acoustic impedance difference to improve acoustic insulation performance and suppress out-of-band Strange.
It effectively suppresses out-of-band spurs, improves the acoustic insulation performance of the SAW filter, and maintains the comprehensive performance of the SAW resonator and filter.
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Figure CN119448965A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of filters, and in particular to a POI substrate, a SAW resonator and a SAW filter. Background Art
[0002] Radio Frequency (RF) devices play a very important role in mobile communication systems. The 5G era has higher and higher requirements for data transmission speed, and has put forward higher requirements for various performances of the RF front end of mobile devices, especially the design of filters is becoming more and more challenging. Among them, the piezoelectric on insulator (POI) substrate has a high electromechanical coupling coefficient (k 2 ), controllable temperature coefficient of frequency (TCF), flexible frequency scalability, high power resistance, integration with silicon and suitability for large-scale production and manufacturing, it has now become the focus of surface acoustic wave (SAW) filter research.
[0003] The traditional POI substrate includes a substrate, an insulating layer, and a piezoelectric layer stacked in sequence. A TR-POI substrate has been proposed, which embeds a trap rich (TR) layer between the substrate and the insulating layer to increase the quality factor (Q value) and reduce dielectric loss. However, the filter based on the TR-POI substrate has a serious out-of-band spurious phenomenon, which reduces the insulation performance of the filter in the high-frequency band. Summary of the invention
[0004] Based on this, it is necessary to provide a POI substrate, a SAW resonator and a SAW filter to suppress out-of-band spurious of the TR-POI substrate.
[0005] The above object of the present invention is achieved through the following technical solutions:
[0006] In a first aspect, the present invention provides a POI substrate, comprising a substrate, a trap-rich layer, a functional layer and a piezoelectric layer stacked in sequence;
[0007] The functional layer includes an insulating layer and a high acoustic impedance layer which are stacked, and the acoustic impedance of the high acoustic impedance layer is greater than the acoustic impedance of the insulating layer and the acoustic impedance of the piezoelectric layer.
[0008] In one embodiment, the high acoustic impedance layer is located between the insulating layer and the piezoelectric layer.
[0009] In one embodiment, the high acoustic impedance layer is located between the trap-rich layer and the insulating layer.
[0010] In one embodiment, there are multiple insulating layers and / or multiple high acoustic impedance layers, and the insulating layers and the high acoustic impedance layers are alternately stacked.
[0011] In one embodiment, the material of the high acoustic impedance layer is selected from one or more of iron, tin, platinum, tungsten, molybdenum, ruthenium, iridium, tantalum pentoxide, aluminum oxide, titanium dioxide, hafnium oxide, silicon carbide, silicon nitride and aluminum nitride.
[0012] In one embodiment, the thickness of the high acoustic impedance layer is 10 nm to 300 nm.
[0013] In one embodiment, the material of the insulating layer is silicon dioxide and / or silicon oxynitride; and / or
[0014] The thickness of the insulating layer is 20nm-550nm.
[0015] In one embodiment, the material of the trap-rich layer is polysilicon and / or polycrystalline germanium; and / or
[0016] The thickness of the trap-rich layer is 500nm-1000nm.
[0017] In one embodiment, the material of the piezoelectric layer is lithium tantalate crystal and / or lithium niobate crystal; and / or
[0018] The thickness of the piezoelectric layer is 400nm-1000nm.
[0019] In one embodiment, the material of the substrate is selected from one or more of single crystal silicon, silicon on insulator, gallium nitride, silicon nitride, silicon carbide, sapphire, diamond and gallium arsenide; and / or
[0020] The thickness of the substrate is 600 μm to 700 μm.
[0021] According to a second aspect of the present invention, a SAW resonator is provided, which comprises the POI substrate described above.
[0022] According to a second aspect of the present invention, a SAW filter is provided, which comprises the SAW resonator described above.
[0023] The present invention has the following beneficial effects:
[0024] The present invention embeds a high acoustic impedance layer in a traditional TR-POI substrate. Since the acoustic impedance of the high acoustic impedance layer is greater than the acoustic impedance of the insulating layer and the acoustic impedance of the piezoelectric layer, there is a large difference in the acoustic impedances of different layers in the POI substrate, thereby achieving a good acoustic impedance conversion effect, improving the acoustic insulation performance of the TR-POI substrate, and preventing the leakage of acoustic wave energy to the substrate, thereby effectively suppressing out-of-band spurious phenomena, while also maintaining the comprehensive performance of the SAW resonator and the SAW filter. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 Schematic diagram of the structure of the POI substrate and the TR-POI substrate in the traditional technology;
[0026] Figure 2 is the admittance diagram of the filter based on the TR-POI substrate in the high frequency band;
[0027] Figure 3 for Figure 2 Displacement simulation diagram of the four out-of-band spurious modes in;
[0028] Figure 4 is a schematic structural diagram of a POI substrate in an embodiment;
[0029] Figure 5 is a schematic structural diagram of the POI substrate in Example 1;
[0030] Figure 6 To adopt Figure 5 Admittance diagram of the resonator of the POI substrate shown;
[0031] Figure 7 To adopt Figure 5 The performance test result diagram of the resonator of the POI substrate shown;
[0032] Figure 8 is a schematic structural diagram of a POI substrate in Example 2;
[0033] Fig. 9 To adopt Figure 8 Admittance diagram of the resonator of the POI substrate shown;
[0034] Fig.10 To adopt Figure 8 The performance test results of the resonator of the POI substrate are shown in the figure.
[0035] Reference numerals: substrate 11 , insulating layer 12 , piezoelectric layer 13 ; substrate 21 , trap-rich layer 22 , insulating layer 23 , piezoelectric layer 24 ; substrate 31 , trap-rich layer 32 , piezoelectric layer 33 , insulating layer 34 , high acoustic impedance layer 35 . DETAILED DESCRIPTION
[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.
[0037] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.
[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.
[0039] See also Figure 1 , which is a schematic diagram of the structure of the POI substrate and the TR-POI substrate in the traditional technology. Figure 1 Figure (a) is a schematic diagram of the structure of a traditional POI substrate, and the line graph on the left represents the curve of the acoustic impedance (AcousticImpedance, symbolized by Z) of the POI substrate versus thickness (Thickness, THK); Figure 1 Figure (b) is a schematic diagram of the structure of a traditional TR-POI substrate, and the line graph on the left is a curve showing the change of acoustic impedance of the TR-POI substrate with thickness.
[0040] The traditional POI substrate includes a substrate 11, an insulating layer 12 and a piezoelectric layer 13 which are stacked in sequence. Among them, the material of the substrate 11 is single crystal silicon (Si), and the material of the piezoelectric layer 13 is lithium niobate (LiNbO3, LN) crystal or lithium tantalate (LiTaO3, LT) crystal. The acoustic impedance of both is relatively high and it is difficult to bond directly. Generally, the piezoelectric layer 13 and the substrate 11 are bonded through the insulating layer 12. The material of the insulating layer 12 is SiO2, and its acoustic impedance is lower than the acoustic impedance of the piezoelectric layer 13 and the acoustic impedance of the substrate 11. It has good acoustic insulation effect, can greatly suppress the leakage of acoustic wave energy to the substrate 11, and reduce the transmission loss of the device. However, in this POI substrate, carriers are easily concentrated near the interface between the substrate 11 and the insulating layer 12 to form a conductive film layer, which will interact with the electromagnetic waves penetrating down, generate dielectric loss, and reduce the quality factor of the SAW device.
[0041] There are reports that Figure 1 The TR-POI substrate shown in Figure (b) includes a substrate 21, a trap-rich layer (TR-layer, TR layer) 22, an insulating layer 23 and a piezoelectric layer 24 stacked in sequence. The TR-POI substrate has a trap-rich layer 22 between the substrate 21 and the insulating layer 23. The trap-rich layer 22 has a large number of defects that can capture carriers, which can reduce the conductivity between the substrate 21 and the insulating layer 23, effectively improve the quality factor and reduce the dielectric loss. However, further research has found that the SAW device based on the TR-POI substrate has serious out-of-band spurious phenomena.
[0042] See also Figures 2-3 ,in, Figure 2 Figure 2 is the admittance diagram of the filter based on the TR-POI substrate in the high frequency band. The upper and lower curves represent the imaginary part of the admittance curve and the real part of the admittance curve, respectively. The signal peak at 2000MHz is the main mode of the filter, and the signal peaks in the elliptical dashed boxes 1 to 4 represent the out-of-band spurious modes appearing at 2660MHz, 2923MHz, 3762MHz and 4671MHz, respectively. Figure 3 for Figure 2 Displacement simulation diagram of the four out-of-band spurious modes in Figure 3 Figures (1) to (4) represent Figure 2 The displacement simulation diagram of the out-of-band spurious modes in the elliptical dashed boxes 1 to 4 in FIG. Figure 3It can be seen that the out-of-band spurious mode between the trap-rich layer 22 and the piezoelectric layer 24 originates from the mismatch between the acoustic impedance of the trap-rich layer 22 and the acoustic impedance of the substrate 21; the reflection of the scattered wave occurring in the thickness direction of the layer structure with different acoustic impedances is the out-of-band spurious mode; out-of-band spurious modes of different frequencies will be generated according to the differences in the reflection center (layer) and energy constraints within the region; and the attenuation caused by the out-of-band spurious mode has a negative impact on the high-band emission spectrum and the inter-band insulation of the filter, thereby reducing the achievable data transmission rate.
[0043] Based on this, the first aspect of the present invention provides a POI substrate to effectively suppress out-of-band spurious signals caused by the TR-POI substrate. Figure 4 , which is a schematic diagram of the structure of a POI substrate in an embodiment, and the line graph on the left represents a curve of the change of the acoustic impedance of the POI substrate with thickness.
[0044] The POI substrate comprises a substrate 31, a trap-rich layer 32, a functional layer and a piezoelectric layer 33 which are stacked in sequence;
[0045] The functional layer includes an insulating layer 34 and a high acoustic impedance layer 35 which are stacked, and the acoustic impedance of the high acoustic impedance layer 35 is greater than the acoustic impedance of the insulating layer 34 and the acoustic impedance of the piezoelectric layer 33 .
[0046] It can be understood that the high acoustic impedance layer 35 can be located between the insulating layer 34 and the piezoelectric layer 33 , or between the insulating layer 34 and the trap-rich layer 32 .
[0047] The present invention embeds a high acoustic impedance layer 35 in a traditional TR-POI substrate. Since the acoustic impedance of the high acoustic impedance layer 35 is greater than the acoustic impedance of the insulating layer 34 and the acoustic impedance of the piezoelectric layer 33, there is a large difference in the acoustic impedances between different layers in the POI substrate, thereby achieving a good acoustic impedance conversion effect, improving the acoustic insulation performance of the TR-POI substrate, and preventing the leakage of acoustic wave energy to the substrate 31, thereby effectively suppressing out-of-band spurious phenomena, while also maintaining the comprehensive performance of the SAW resonator and the SAW filter.
[0048] In some embodiments, the high acoustic impedance layer 35 is located between the insulating layer 34 and the piezoelectric layer 33 .
[0049] The high acoustic impedance layer 35 embedded between the insulating layer 34 and the piezoelectric layer 33 provides good acoustic insulation between the piezoelectric layer 33 and the substrate 31. Due to the influence of the acoustic impedance gradient formed between different layers in the POI substrate, the out-of-band spurious will migrate to the low-frequency band range, and the amplitude and Q value of the above-mentioned spurious mode can also be effectively suppressed.
[0050] In some embodiments, the high acoustic impedance layer 35 is located between the trap-rich layer 32 and the insulating layer 34 .
[0051] The high acoustic impedance layer 35 embedded between the trap-rich layer 32 and the insulating layer 34 can acoustically insulate the out-of-band spurious between the piezoelectric layer 33 - insulating layer 34 - trap-rich layer 32 - substrate 31 , and has a strong out-of-band spurious suppression effect.
[0052] In some embodiments, there are multiple insulating layers 34 and / or multiple high acoustic impedance layers 35 , and the insulating layers 34 and the high acoustic impedance layers 35 are alternately stacked.
[0053] Optionally, the number of the high acoustic impedance layers 35 is two, and the POI substrate includes a substrate 31, a trap-rich layer 32, a high acoustic impedance layer 35, an insulating layer 34, a high acoustic impedance layer 35 and a piezoelectric layer 33 which are stacked in sequence.
[0054] Optionally, the number of the insulating layer 34 and the number of the high acoustic impedance layer 35 are at least two, and the insulating layer 34 and the high acoustic impedance layer 35 are alternately stacked to form a distributed Bragg reflector (DRB) structure.
[0055] In some embodiments, the material of the high acoustic impedance layer 35 is selected from one or more of iron (Fe), tin (Sn), platinum (Pt), tungsten (W), molybdenum (Mo), ruthenium (Ru), iridium (Ir), tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), aluminum oxide (Al2O3), titanium dioxide (TiO2), hafnium oxide (HfO2), silicon carbide (SiC), silicon nitride (Si3N4) and aluminum nitride (AIN).
[0056] Preferably, the material of the high acoustic impedance layer 35 is selected from one or more of tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), aluminum oxide (Al2O3), titanium dioxide (TiO2), hafnium oxide (HfO2), silicon carbide (SiC), silicon nitride (Si3N4) and aluminum nitride (AIN).
[0057] The above materials all have high acoustic impedance characteristics and large relative dielectric constants, which can suppress the out-of-band spurious signals of the TR-POI substrate without affecting the overall performance of the resonator.
[0058] Further preferably, the material of the high acoustic impedance layer 35 is tantalum pentoxide (Ta2O5).
[0059] Optionally, the high acoustic impedance layer 35 is a patterned structure, which includes a high acoustic impedance region and a low acoustic impedance region; the high acoustic impedance region is a region with sound waves, and the material of the high acoustic impedance region is selected from one or more of iron (Fe), tin (Sn), platinum (Pt), tungsten (W), molybdenum (Mo), ruthenium (Ru), iridium (Ir), tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), aluminum oxide (Al2O3), titanium dioxide (TiO2), hafnium oxide (HfO2), silicon carbide (SiC), silicon nitride (Si3N4) and aluminum nitride (AIN); the low acoustic impedance region is a region without sound waves, and the material of the low acoustic impedance region is one or more of low acoustic impedance materials such as air, silicon (Si) and silicon dioxide (SiO2).
[0060] The high acoustic impedance layer 35 is designed as a patterned structure, and the high acoustic impedance material can be deposited in a targeted manner in the area with sound waves, which can not only achieve a good out-of-band stray suppression function, but also reduce the amount of high acoustic impedance material used, which is conducive to reducing costs.
[0061] Further optionally, the high acoustic impedance layer 35 includes a high acoustic impedance region and a low acoustic impedance region; the material of the high acoustic impedance region is tantalum pentoxide (Ta2O5), and the material of the low acoustic impedance region is air.
[0062] In some embodiments, the high acoustic impedance layer 35 has a thickness of 10 nm to 300 nm.
[0063] When the thickness is within the range of 10 nm to 300 nm, the high acoustic impedance layer 35 can not only suppress out-of-band spurious signals, but also perform well in terms of the phase velocity, electromechanical coupling coefficient, frequency temperature coefficient and power durability of the resonator.
[0064] Optionally, the high acoustic impedance layer 35 has a thickness of 80 nm to 160 nm.
[0065] Optionally, the high acoustic impedance layer 35 has a thickness of 40 nm to 60 nm.
[0066] In some embodiments, the material of the insulating layer 34 is silicon dioxide (SiO2) and / or silicon oxynitride (SiO x N y ); and / or
[0067] The thickness of the insulating layer 34 is 20 nm to 550 nm.
[0068] The insulating layer 34 is also called a buried oxide layer or a temperature compensation layer. Its acoustic impedance is lower than the acoustic impedance of the piezoelectric layer 33 and the acoustic impedance of the insulating layer 34. Together with the high acoustic impedance layer 35, it plays the role of acoustic impedance conversion to improve the acoustic insulation performance of the POI substrate. In addition, the insulating layer 34 can also play a role in temperature compensation for the device, which can prevent the piezoelectric material from causing the resonant frequency of the resonator to shift due to changes in temperature.
[0069] Preferably, the insulating layer 34 is made of silicon dioxide (SiO2).
[0070] SiO 2 has a low acoustic impedance and can form a relatively large acoustic impedance gradient with the high acoustic impedance layer 35 , thereby ensuring the acoustic insulation effect of the POI substrate.
[0071] Optionally, the thickness of the insulating layer 34 is 40 nm to 100 nm.
[0072] Optionally, the thickness of the insulating layer 34 is 300 nm to 500 nm.
[0073] In some embodiments, the material of the trap-rich layer 32 is polycrystalline silicon (Poly-Si) and / or polycrystalline germanium (Poly-Ge); and / or
[0074] The thickness of the trap-rich layer 32 is 500 nm to 1000 nm.
[0075] By utilizing a large number of defects inside polycrystalline silicon or polycrystalline germanium, the movement of carriers between grains can be limited, and the interface conductivity between the insulating layer 34 and the substrate 31 can be reduced, thereby reducing dielectric loss and improving the quality factor.
[0076] Preferably, the material of the trap-rich layer 32 is polysilicon (Poly-Si).
[0077] In some embodiments, the material of the piezoelectric layer 33 is selected from one or more of lithium tantalate (LiTaO3, LT) crystals, lithium niobate crystals (LiNbO3, LN), quartz (SiO2) crystals, gallium arsenide (GaAs) crystals, potassium titanyl phosphate (KTiOPO4, KTP) crystals, rubidium titanyl phosphate crystals (RbTiOPO4, RTP) and lithium tetraborate (Li2B4O7) crystals; and / or
[0078] The thickness of the piezoelectric layer 33 is 400 nm to 1000 nm.
[0079] Preferably, the material of the piezoelectric layer 33 is selected from lithium tantalate (LiTaO 3 , LT) crystals and / or lithium niobate (LiNbO 3 , LN) crystals.
[0080] LT crystal and lithium niobate LN crystal have similar structures. Both have excellent piezoelectric, ferroelectric, acousto-optic and electro-optical properties. They are artificially synthesized multifunctional crystal materials. Compared with other piezoelectric crystals, LT crystal and LN crystal have more advantages in realizing high-frequency and large-bandwidth SAW devices.
[0081] Further preferably, the material of the piezoelectric layer 33 is lithium tantalate (LiTaO 3 , LT) crystal.
[0082] In some embodiments, the material of the substrate 31 is selected from one or more of single crystal silicon, silicon-on-insulator (SOI), gallium nitride (GaN), silicon nitride (Si3N4), silicon carbide (SiC), sapphire, diamond and gallium arsenide (GaAs); and / or
[0083] The thickness of the substrate 31 is 600 μm to 700 μm.
[0084] Preferably, the material of the substrate 31 is single crystal silicon and / or silicon on insulator.
[0085] Further preferably, the material of the substrate 31 is single crystal silicon.
[0086] According to a second aspect of the present invention, a SAW resonator is provided, which comprises the POI substrate described above.
[0087] Two interdigital transducers (IDT) are formed on the piezoelectric layer 33 of the POI substrate, which are used as a transmitting transducer and a receiving transducer respectively. The transmitting transducer converts the RF signal into a surface acoustic wave (SAW), which propagates on the surface of the piezoelectric layer 33. After a certain delay, the receiving transducer converts the acoustic signal into an electrical signal for output. Since a high acoustic impedance layer 35 is embedded in the POI substrate, the out-of-band spurious of the resonator is effectively suppressed, thereby improving the insulation performance of the resonator in the high frequency band.
[0088] According to a third aspect of the present invention, a SAW filter is provided, which comprises the SAW resonator described above.
[0089] The present invention is further described in detail below in conjunction with specific examples. The raw materials used in the following examples, unless otherwise specified, are commercially available products.
[0090] Example 1
[0091] The high acoustic impedance layer 35 of this embodiment is located between the insulating layer 34 and the piezoelectric layer 33 .
[0092] See also Figures 5-6 ,in, Figure 5 is a schematic diagram of the structure of the POI substrate in this embodiment, and the line graph on the left represents the curve of the change of the acoustic impedance of the POI substrate with the thickness; Figure 6 To adopt Figure 5 In the admittance diagram of the resonator of the POI substrate shown, the upper and lower curves represent the imaginary part curve of the admittance and the real part curve of the admittance respectively. The material of the high acoustic impedance layer 35 of the POI substrate is Ta2O5, and the thicknesses are 10nm (corresponding to 0.005 surface acoustic wave wavelength, 0.005L) and 130nm (corresponding to 0.065 surface acoustic wave wavelength, 0.065L) respectively. The material of the insulating layer 34 is SiO2, and the thickness is 500nm.
[0093] The POI substrate includes a substrate 31, a trap-rich layer 32, an insulating layer 34, a high acoustic impedance layer 35 and a piezoelectric layer 33 which are stacked in sequence. The material of the substrate 31 is single crystal silicon, the trap-rich layer 32 is polycrystalline silicon, the material of the insulating layer 34 is SiO2, the material of the high acoustic impedance layer 35 is Ta2O5, and the material of the piezoelectric layer 33 is LT crystal. The physical parameters of the materials in the POI substrate are shown in Table 1. The physical parameters of the LT crystal are highly anisotropic, so they are not listed in Table 1.
[0094] Table 1. Physical parameters of the materials in the POI substrate of Examples 1 to 2
[0095] Physical quantity Si <![CDATA[SiO2]]> <![CDATA[Ta2O5]]> <![CDATA[Density, g / cm 3 > 2330 2170 8200 Young's modulus, GPa 80～170 66 168 <![CDATA[Acoustic impedance, ×10 6 kg / (m 2 ·s)]]> 20 13 39 Thermal conductivity, W / (m·K) 142 1.3 3* <![CDATA[Coefficient of thermal expansion, 10 -6 / K]]> 2.6 0.55 4 Relative dielectric constant 11.7 3.6 50～100*
[0096] As can be seen from Table 1, Ta2O5 has the characteristics of a high acoustic impedance material, and its acoustic impedance is three times that of SiO2 and twice that of single crystal silicon, and it also has a relative dielectric constant much larger than that of SiO2 and single crystal Si. After the high acoustic impedance Ta2O5 layer is embedded between the SiO2 layer and the LT crystal layer, there is a large difference in acoustic impedance between adjacent stacked layers, so that good acoustic insulation can be formed between the piezoelectric layer 33 and the substrate 31.
[0097] Due to the influence of the acoustic impedance gradient formed in the POI substrate, the out-of-band spurious will migrate to the low-frequency band range. At the same time, the amplitude and Q value of the above spurious mode can also be effectively suppressed. The result of out-of-band spurious suppression is as shown in Figure 6 When the thickness of the high acoustic impedance layer 35 exceeds 100 nm (corresponding to 0.05 surface acoustic wave wavelength, 0.05L), it can be observed that Figure 5 The resonator of the POI substrate shown has a good spurious suppression effect.
[0098] After the high acoustic impedance layer 35 is embedded, it will affect the performance of the resonator. Therefore, this embodiment further tests the use of Figure 5 The performance of the POI-based resonator is shown in Figure 2. Figure 7As shown. Among them, Figure 7 Figure (a) shows the SAW phase velocity and electromechanical coupling coefficient (k) of the resonator when the SiO2 layer thickness is 500nm and the relative thickness of the Ta2O5 layer is different. 2 ) curve; Figure 7 Figure (b) shows the SAW phase velocity and k of the resonator when the Ta2O5 layer thickness is 130nm and the relative thickness of the SiO2 layer is different. 2 The relative thickness of the Ta2O5 layer and the relative thickness of the SiO2 layer are expressed as the thickness normalized to the wavelength of the surface acoustic wave, for example, Figure 7 The 0.08 on the horizontal axis in Figure (a) indicates that the thickness of the Ta2O5 layer = 0.08×the wavelength of the surface acoustic wave = 0.08L.
[0099] Depend on Figure 7 As shown in Figure (a), the relative thickness of the Ta2O5 layer is preferably 0.04-0.08 (as shown by the shaded area in the horizontal axis), that is, the thickness of the Ta2O5 layer is preferably 80nm-160nm. As the thickness of the Ta2O5 layer increases, the SAW phase velocity of the resonator gradually decreases, which is conducive to the miniaturization of low-frequency band resonators and filter applications; at the same time, k 2 It also decreases with the increase of the thickness of the Ta2O5 layer; when the thickness of the Ta2O5 layer is less than 100nm (the horizontal axis is 0.05), k 2 The function of the thickness of the Ta2O5 layer is approximately linear. When other parameters remain unchanged, the function can be used to calculate k 2 Effective control. Figure 7 As shown in Figure (b), for high k 2 For devices, the relative thickness of the SiO2 layer is preferably 0.02-0.05 (as shown by the shaded area in the horizontal axis), that is, the thickness of the SiO2 layer should be 40nm-100nm. Within this range, the SAW phase velocity and k 2 It also decreases with the increase of the thickness of the SiO2 layer.
[0100] Example 2
[0101] The high acoustic impedance layer 35 of this embodiment is located between the trap-rich layer 32 and the insulating layer 34 .
[0102] See also Figures 8-9 ,in, Figure 8 is a schematic diagram of the structure of the POI substrate in this embodiment, and the line graph on the left represents the curve of the change of the acoustic impedance of the POI substrate with the thickness; Fig. 9 To adopt Figure 8In the admittance diagram of the resonator of the POI substrate shown, the upper and lower curves represent the imaginary part curve of the admittance and the real part curve of the admittance respectively. The material of the high acoustic impedance layer 35 of the POI substrate is Ta2O5, and the thicknesses are 10nm (corresponding to 0.005 surface acoustic wave wavelength, 0.005L) and 60nm (corresponding to 0.03 surface acoustic wave wavelength, 0.03L) respectively. The material of the insulating layer 34 is SiO2, and the thickness is 500nm.
[0103] The POI substrate comprises a substrate 31, a trap-rich layer 32, a high acoustic impedance layer 35, an insulating layer 34 and a piezoelectric layer 33 which are stacked in sequence. The substrate 31 is made of single crystal silicon, the trap-rich layer 32 is made of polycrystalline silicon, the high acoustic impedance layer 35 is made of Ta2O5, the insulating layer 34 is made of SiO2, and the piezoelectric layer 33 is made of LT crystal.
[0104] Depend on Figure 8 It can be seen that the high acoustic impedance Ta2O5 layer is embedded between the trap-rich layer 32 and the insulating layer 34, which effectively acoustically insulates the out-of-band spurious generated between the piezoelectric layer 33-insulating layer 34-trap-rich layer 32. Fig. 9 It can be seen that the high acoustic impedance layer 35 has a strong stray suppression effect. When the thickness of the Ta2O5 layer is greater than 50nm, the out-of-band stray is almost decoupled, that is, the out-of-band stray is completely suppressed.
[0105] When the high acoustic impedance Ta2O5 layer is located between the insulating layer 34 and the trap-rich layer 32, the out-of-band spurious suppression of the high overall performance (Figure of Merit, FOM) resonator can be achieved. Figure 8 The performance of the POI-based resonator is shown in Figure 2. Fig.10 As shown. Among them, Fig.10 Figure (a) shows the SAW phase velocity and k of the resonator with a SiO2 layer thickness of 500nm and different relative thicknesses of the Ta2O5 layer. 2 The curve of Fig.10 Figure (b) shows the SAW phase velocity and k of the resonator when the Ta2O5 layer thickness is 50nm and the relative thickness of the SiO2 layer is different. 2 curve.
[0106] Depend on Fig.10 As shown in Figure (a), the relative thickness of the Ta2O5 layer is preferably 0.02-0.03 (as shown by the shaded area in the horizontal axis), that is, the thickness of the Ta2O5 layer is preferably 40nm-60nm. The increase in the thickness of the Ta2O5 layer has a significant effect on the SAW phase velocity and k of the resonator. 2The effect is small because the high acoustic impedance layer 35 is not in direct contact with the piezoelectric layer 33, and the stray suppression effect is mainly applied to the out-of-band stray mode generation region at the interface between the insulating layer 34 and the trap-rich layer 32. Figure 8 The POI substrate shown here can avoid the k 2 The degradation of the resonator can be reduced by reasonable optimization. 2 Slightly higher than the k of the resonator using the traditional POI substrate 2 .
[0107] The optimal thickness of the low acoustic impedance SiO2 layer depends on the thickness of the high acoustic impedance Ta2O5 layer. Both should be optimized simultaneously, taking into account other properties of the POI resonator, such as the frequency temperature coefficient and power durability. Fig.10 As shown in Figure (b), for Figure 8 For the POI substrate shown, the relative thickness of the SiO2 layer is preferably 0.15-0.25 (as shown by the shaded area in the abscissa), and the optimal thickness range of the SiO2 layer is 300nm-500nm.
[0108] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0109] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description and drawings can be used to interpret the content of the claims.
Claims
1. A POI substrate, characterized in that: It includes a substrate, a trap-rich layer, a functional layer and a piezoelectric layer which are stacked in sequence; The functional layer includes an insulating layer and a high acoustic impedance layer which are stacked, and the acoustic impedance of the high acoustic impedance layer is greater than the acoustic impedance of the insulating layer and the acoustic impedance of the piezoelectric layer.
2. The POI substrate according to claim 1, characterized in that: The high acoustic impedance layer is located between the insulating layer and the piezoelectric layer.
3. The POI substrate according to claim 1, characterized in that: The high acoustic impedance layer is located between the trap-rich layer and the insulating layer.
4. The POI substrate according to claim 1, characterized in that: The number of the insulating layer and / or the high acoustic impedance layer is plural, and the insulating layers and the high acoustic impedance layers are alternately stacked.
5. The POI substrate according to any one of claims 1 to 4, characterized in that: The material of the high acoustic impedance layer is selected from one or more of iron, tin, platinum, tungsten, molybdenum, ruthenium, iridium, tantalum pentoxide, aluminum oxide, titanium dioxide, hafnium oxide, silicon carbide, silicon nitride and aluminum nitride.
6. The POI substrate according to claim 5, characterized in that: The thickness of the high acoustic impedance layer is 10nm-300nm.
7. The POI substrate according to claim 6, characterized in that: The material of the insulating layer is silicon dioxide and / or silicon oxynitride; and / or The thickness of the insulating layer is 20nm-550nm.
8. The POI substrate according to any one of claims 1 to 4, characterized in that: The material of the trap-rich layer is polycrystalline silicon and / or polycrystalline germanium; and / or The thickness of the trap-rich layer is 500nm-1000nm.
9. The POI substrate according to any one of claims 1 to 4, characterized in that: The material of the piezoelectric layer is selected from one or more of lithium tantalate crystals, lithium niobate crystals, quartz crystals, gallium arsenide crystals, potassium titanyl phosphate crystals, rubidium titanyl phosphate crystals and lithium tetraborate crystals; and / or The thickness of the piezoelectric layer is 400nm-1000nm.
10. The POI substrate according to any one of claims 1 to 4, characterized in that: The material of the substrate is selected from one or more of single crystal silicon, silicon on insulator, gallium nitride, silicon nitride, silicon carbide, sapphire, diamond and gallium arsenide; and / or The thickness of the substrate is 600 μm to 700 μm.
11. A SAW resonator, characterized in that: It comprises the POI substrate as described in any one of claims 1 to 10.
12. A SAW filter, characterized in that: Comprising the SAW resonator as claimed in claim 11.