Acoustic resonator rigidly mounted on a high acoustic velocity substrate

Abstract

The present disclosure relates to a robust acoustic resonator device having a piezoelectric plate supported by a solid substrate. The device includes a substrate, a high acoustic velocity non-piezoelectric substrate layer such as diamond on the substrate, a dielectric layer on the substrate layer, a piezoelectric plate attached to the dielectric layer by a metal layer, and two sets of electrodes connected to first and second bus bars, respectively, and arranged alternately on the piezoelectric plate with a pitch p. The velocity V of a slow shear bulk wave propagating parallel to the surface of the substrate layer (perpendicular to the electrodes) is diam is the phase velocity V in the piezoelectric plate ph =2p*F R Higher than FR. LN / (2d LN ) is the operating frequency of the device. The pitch p is determined by p <V diam / V LN *d LN where V LN is the velocity of the bulk wave resonating in the piezoelectric plate, and d LN is the thickness of the piezoelectric plate.

Description

[Technical Field]

[0001] This disclosure relates to acoustic resonator devices. In particular, this disclosure provides a robust acoustic resonator device having an acoustic resonator comprising a piezoelectric plate rigidly mounted on a substrate (layer). This disclosure also provides a method for operating such an acoustic resonator device. Acoustic resonator devices can typically be used in frequency passband filters that include a "ladder" network of such resonator devices. [Background technology]

[0002] Conventional acoustic resonator devices that utilize a thin piezoelectric layer of submicron thickness as the resonator material—often consisting of lithium niobate—such as bulk acoustic resonators (BARs) like FBARs, XBARs, or YBARs, have known drawbacks.

[0003] For example, a thin-film BAR (FBAR) is a bulk wave resonator. When such a bulk wave resonator is placed on a solid substrate with complete mechanical contact, it does not function efficiently because acoustic energy is radiated into the substrate. Therefore, resonance cannot be obtained in the piezoelectric layer (or only resonance with a very low Q factor can be obtained).

[0004] To prevent this, the piezoelectric layer may be a thin film (plate) suspended across a cavity, where the cavity provides acoustic isolation. However, technically, such a device is difficult to construct. Furthermore, this approach results in a very fragile device because the piezoelectric film is very thin and poorly supported (supported only by its edges). Moreover, this device has poor power handling characteristics due to the low thermal conductivity of the thin film and heat dissipation mainly along the thin, long electrodes.

[0005] Alternatively, the piezoelectric layer may be a system of many λ / 4 layers alternating between high acoustic impedance and low acoustic impedance, and may be firmly attached to a Bragg stack that provides acoustic isolation. The multilayer Bragg stack functions particularly as a strong reflector at the operating frequency, and thus does not allow bulk waves to be radiated into the substrate. However, such a Bragg stack has its own drawbacks. For example, when metal layers are used, the Bragg stack may result in undesirable parasitic coupling between adjacent resonators. The presence of acoustic energy in the Bragg stack reduces the resonance - anti - resonance frequency distance, and thus reduces the pass - band of the filter in which such resonator devices can be used. Further, the Bragg stack increases the complexity of the device manufacturing process.

Summary of the Invention

Problems to be Solved by the Invention

[0006] In view of the above, the present disclosure has the goal of providing an improved acoustic resonator device. One objective is to provide an acoustic resonator device having a piezoelectric layer on a solid substrate. This device should be suitable for operation in the frequency range of 5 GHz. The acoustic resonator device should avoid acoustic energy loss to the substrate, but should not require a reflective structure such as a Bragg stack. The acoustic resonator device should further be manufacturable such that the critical dimension (CD) of the electrodes is CD > 0.3 μm.

[0007] These and other objectives are achieved by the solution of the present disclosure described in the appended independent claims. Advantageous implementations are further defined in the dependent claims.

Means for Solving the Problems

[0008] A first aspect of the present disclosure is an acoustic resonator device, comprising a support substrate; a non - piezoelectric substrate layer disposed on the support substrate; a dielectric layer disposed on the substrate layer; and having a thickness d with a front surface and a back surfaceLN A piezoelectric plate, the back surface of which is covered by a metal layer, and the piezoelectric plate is attached to a dielectric layer by the metal layer; and an interdigital electrode structure (IDES) including a first set of electrodes connected to a first bus bar and a second set of electrodes connected to a second bus bar, wherein the first and second sets of electrodes are sequentially and alternately arranged periodically with a pitch p on the front surface of the piezoelectric plate, and the velocity V of a slow shear bulk wave propagating parallel to the layer surface of the substrate layer in a direction perpendicular to the electrodes diam is, V ph =2p*F R is higher than the phase velocity of the piezoelectric plate determined by, and F R is, V LN / (2d LN ) is the operating frequency of the acoustic resonator device determined by, and the pitch p satisfies p<V diam / V LN *d LN and V LN is the velocity of the bulk wave resonating in the piezoelectric plate, and an acoustic resonator device is provided.

[0009] The support substrate may be a thick substrate or wafer made of silicon, glass, or other dielectric material. The substrate layer may have a high acoustic velocity, particularly, an acoustic velocity higher than that of the piezoelectric plate. When the bulk wave resonates in the piezoelectric plate, it can be reflected between the side surfaces of the piezoelectric plate. The first set of electrodes may have a different polarity from the second set of electrodes, which means that voltages of different polarities are applied to these electrodes during the operation of the acoustic resonator device. Thus, these first and second sets of electrodes may be referred to as "positive" electrodes and "negative" electrodes.

[0010] In the acoustic resonator device of the first side, on the one hand, the pitch p between the first and second sets of electrodes is sufficiently small, and on the other hand, the substrate layer (e.g., made of diamond) has a sufficiently high acoustic wave velocity, thereby suppressing acoustic loss to the substrate. For example, the ram modes SH1, S1 (and even A1) do not radiate acoustic energy into the substrate layer and the bulk of the supporting substrate. The bulk waves or vibrations excited by the electrodes only bounce up and down within the piezoelectric plate, but the acoustic waves are not radiated into and below the substrate layer, and at least they decay exponentially with respect to the depth of the substrate.

[0011] For this reason, the first-sided acoustic resonator device is suitable for operation in the 5 GHz frequency range and is more stable than conventional devices in which a piezoelectric film is suspended across a cavity. Furthermore, the first-sided device avoids the drawback of acoustic energy loss to the substrate without requiring reflective structures such as Bragg stacks. Although the pitch is small, it can still be well manufactured on CDs larger than 0.3 μm using existing techniques.

[0012] In the first aspect of the implementation, the substrate layer includes a diamond layer, or a silicon carbide layer, or a boron nitride layer.

[0013] These materials possess sufficiently high acoustic velocities, specifically high velocities of low-velocity shear bulk waves propagating parallel to the layer surface perpendicular to the electrodes. Therefore, these types of materials are most suitable for the acoustic resonator devices of this disclosure and yield the best results in terms of performance and low acoustic loss.

[0014] In the first aspect of the implementation, the dielectric layer includes at least one of a silicon dioxide layer, an SiOx layer, a SiNO layer, and a SiN layer.

[0015] Such a dielectric layer reduces the acoustic coupling of the piezoelectric plate to the substrate layer. It also reduces the influence of the substrate layer (e.g., vibrations transmitted from the piezoelectric plate to the substrate layer). Furthermore, it allows for the fundamental thickness resonance of the piezoelectric plate, thereby increasing piezoelectric coupling.

[0016] In one of the first aspect configurations, the piezoelectric plate is made of crystalline lithium niobate, lithium tantalate, or aluminum nitride.

[0017] These materials provide the best results for the acoustic resonator devices of this disclosure (e.g., the Q factor, here representing the piezoelectric coupling estimated by the relative resonant-anti-resonant frequency distance). However, other piezoelectric materials are equally suitable.

[0018] In one of the first aspect configurations, the piezoelectric plate made of lithium niobate is a rotated YX-cut LN plate in which the electrodes are arranged perpendicular to the crystal X-axis.

[0019] In the first aspect of the implementation, the metal layer includes a copper layer or an aluminum layer.

[0020] In the first aspect of the implementation, the metal layer covers a limited area on the back of the piezoelectric plate, which corresponds to the area covered by the electrodes on the front of the piezoelectric plate and is at a floating potential.

[0021] Therefore, the defined resonator region is defined between the metal layer and the IDES electrodes.

[0022] In a first aspect of the implementation, the metal layer and the first and second sets of electrodes form a plurality of periodically arranged resonators configured to oscillate in opposite phases.

[0023] As a result, there is little to no acoustic energy leaking onto the circuit board.

[0024] In the first aspect of the implementation, at least the first and last electrodes of the alternately arranged electrodes are floating potential electrodes.

[0025] In one implementation of the first aspect, the first and last electrodes are configured to function as reflectors to reduce the radiation of acoustic energy outside the acoustic resonator device.

[0026] In one implementation of the first aspect, a subset of electrodes at the beginning and end of the IDES structure are at a floating potential.

[0027] Floating electrodes and / or reflector electrodes further improve the performance of the device on the first side because acoustic energy loss is also avoided on the sides (higher Q factor).

[0028] In the first aspect of the implementation, the thickness of the substrate layer is the thickness d of the piezoelectric plate. LN It is within the range of 4 to 20 times.

[0029] In the first aspect of the implementation, the thickness of the dielectric layer is the thickness d of the piezoelectric plate. LN It is about half of the shear wavelength in the dielectric layer, and / or about one-quarter of the shear wavelength in the dielectric layer.

[0030] For example, thickness d LN The particle size may be within the range of 0.25 μm to 0.8 μm, and the pitch p may be within the range of 0.6 μm to 1.2 μm.

[0031] In one implementation of the first aspect, the velocity V of the low-speed shear bulk wave diam It is greater than 8000 m / s, greater than 10000 m / s, or greater than 12000 m / s.

[0032] In one implementation form of the first aspect, V ph =2p*F R The phase velocity determined by is in the range of 2000 m / s to 6000 m / s, and / or the velocity V of the slow shear bulk wave. diam It is lower than that.

[0033] The above parameters for the acoustic resonator device yield the best results (device performance, acoustic loss, etc.).

[0034] In the first aspected implementation, a groove is positioned between each pair of adjacent electrodes of the first and second sets of electrodes, the groove extending into the piezoelectric plate or extending completely through the piezoelectric plate.

[0035] The grooves allow the electrodes to vibrate more freely, increasing piezoelectric coupling. Furthermore, the presence of grooves can reduce the propagation of parasitic waves.

[0036] A second aspect of the present disclosure is an acoustic resonator device comprising: a diamond layer; a silicon dioxide layer disposed on the diamond layer; a lithium niobate plate having a front and a back surface, the back surface being covered by a metal layer, the lithium niobate plate being attached to the silicon dioxide layer by this metal layer; and an IDES including a first set of electrodes connected to a first busbar and a second set of electrodes connected to a second busbar, wherein the first and second sets of electrodes are arranged sequentially and alternately on the front surface of the piezoelectric plate at a pitch p, and the thickness d of the lithium niobate plate. LN The present invention provides an acoustic resonator device in which the diametrical region is in the range of 0.25 μm to 0.8 μm, and the pitch p is in the range of 0.6 μm to 1.2 μm.

[0037] The acoustic resonator device on the second side may have an implementation form corresponding to the implementation form of the acoustic resonator device on the first side. The acoustic resonator device on the second side achieves the same advantages and effects as the device on the first side. In particular, the acoustic resonator device on the second side is a particularly high-performance device.

[0038] A third aspect of this disclosure provides a method for operating an acoustic resonator device according to either the first aspect, the second aspect, or any implementation thereof. This method involves connecting a first and second set of electrodes between first and second busbars, respectively, and V LN / (2d LN This method involves applying a differential AC voltage at a resonant frequency essentially close to ), with the metal layer being grounded. Alternatively, this method may involve V LN / (2dLN The method includes applying an AC voltage at a resonant frequency essentially determined by the first and second busbars to one of the first and second busbars, and maintaining the other of the first and second busbars at ground potential, wherein the metal layer is at a floating potential.

[0039] As described above, the aspects and implementations of this disclosure may include a relatively narrow FBAR periodic structure (for example, having SH1 or S1 ram modes / waves, or also A1 ram modes), which is rigidly mounted on a high-speed substrate and has out-of-phase resonances spaced by a pitch p, where the pitch p can satisfy the non-radiation condition p < λ / 2, where λ is the (minimum) wavelength of any acoustic wave that can propagate through the substrate at the operating frequency.

[0040] In summary, the advantages of the solution of this disclosure include: A particularly robust acoustic resonator device is provided because, instead of having a fragile suspension film structure, it has a piezoelectric plate that is rigidly mounted on the substrate and substrate layers (in particular, not directly on the substrate layers because a dielectric layer is in between). The device can be fabricated using conventional surface acoustic wave (SAW) techniques, and the device can be fabricated using photolithography. The device may be suitable for the 5 GHz frequency range. Furthermore, strong piezoelectric coupling, for example, K 2 A coupling of 20-25% can be achieved. In addition, the high thermal conductivity of the substrate layer and the substrate can enable the device's excellent power handling capabilities. Furthermore, because this device has a small pitch (for comparison, XBARs can have a pitch about 20 times larger), it may exhibit only low levels of parasitic modes. This device also offers the possibility of changing or tuning the resonant frequency, for example, by changing the pitch and / or the geometric shape of the electrodes.

[0041] Furthermore, in all the implementations described, the acoustic resonator device may be covered on top with a thin (e.g., 15 nm to 25 nm) protective (or "passivation") dielectric layer of SiO2, SiOx, or Si3N4 to prevent oxidation of the electrodes and protect them from the effects of moisture, air, etc. [Brief explanation of the drawing]

[0042] The aspects and implementation configurations described above are explained in the following descriptions of specific embodiments in relation to the attached drawings.

[0043] [Figure 1] The acoustic resonator device described herein is shown in a perspective view. The schematic diagram shows the main features of the acoustic resonator device, but geometric ratios, number of electrodes, and other details may not be presented precisely. [Figure 2] A cross-sectional view of one cycle of the acoustic resonator device described in this disclosure is shown. [Figure 3] The acoustic resonator device described herein is shown in a perspective view. [Figure 4] This disclosure presents FEM simulation results for an acoustic resonator device having vibrations close to the shear plate mode (SH1). [Figure 5] This disclosure shows the X-cut simulation results for the acoustic resonator device. [Figure 6] This disclosure shows the simulation results of an acoustic resonator device operating in A1 ram mode. [Figure 7] This disclosure shows a parametric analysis of the pitch and thickness variations of the passivation dielectric coating layer of an acoustic resonator device. [Figure 8] This shows the effect of the thickness of the dielectric layer (SiO2) and the Q factor for bonding. [Figure 9] This disclosure demonstrates the admittance of a finite acoustic resonator device having floating reflector electrodes. [Figure 10] This disclosure describes a method for operating an acoustic resonator device. [Modes for carrying out the invention]

[0044] Figure 1 shows a perspective view of the acoustic resonator device 100 according to this disclosure. Device 100 may be called a bulk acoustic wave (BAW) device or a bulk acoustic resonator (BAR) device. In particular, device 100 may be based on a periodic system of narrow BAR pairs connected in series through a lower electrode metal layer 105. Individual BARs, having a narrow width corresponding to the width of electrodes 106, 108 and interacting with their neighbors, can alternatively be considered a structure supporting a standing SH1 wave. Device 100 may further alternatively be considered based on an SH1 plate mode, or an S1 ram mode / wave (when the compression mode S1 is excited by vertical displacement), or an A1 ram mode / wave. The selection of the operating mode is determined by the cut used of the piezoelectric plate 104, and many useful orientations suitable for excitation of SH1, S1, or A1 modes are described in the literature and are known to those skilled in the art. A common feature here is that the fundamental mode can be selected by the thickness of the piezoelectric plate, which is close to half the thickness of the corresponding acoustic wave that bounces between the sides of the piezoelectric plate.

[0045] The acoustic resonator device 100 shown in Figure 1 comprises a support substrate 101 and a non-piezoelectric substrate layer 102 directly disposed on the support substrate 101. The support substrate 101 may be integrated with the substrate layer 102, or it may be made of the same material as the substrate layer 102. For example, the substrate layer 102 may include a diamond layer, a silicon carbide layer, or a boron nitride layer. That is, the material of the substrate layer 102 and / or the support substrate 101 may be diamond, silicon carbide, or boron nitride. The support substrate 101 may be a silicon substrate or a dielectric substrate such as glass. The acoustic impedance of these layers 101 and 102 may be selected such that only a minimal portion of the vibration energy penetrates into layer 102, and substantially no vibration is observed in the support substrate 101.

[0046] The device 100 further comprises a dielectric layer 103 disposed directly on the substrate layer 102. For example, the dielectric layer 103 may be deposited or grown on the substrate layer 102. The dielectric layer 103 may include a silicon dioxide layer, an SiOx layer, a SiNO layer, and / or a SiN layer.

[0047] The device 100 further comprises a piezoelectric plate 104 disposed on the dielectric layer 103. The piezoelectric plate 104 has a certain thickness d LN It has a front and a back surface (with respect to the direction defining the thickness, i.e., along the stacking direction of the layer stack shown in Figure 1). The back surface may be covered with a metal layer 105, for example, a copper or aluminum layer. The piezoelectric plate 104 is then attached to the dielectric layer 103 by the metal layer 105. That is, the metal layer 105 is placed directly on the dielectric layer 103, and the piezoelectric plate 104 is placed directly on the metal layer 105. The piezoelectric plate 104 itself may be made of crystalline lithium niobate, lithium tantalate, or aluminum nitride, and may be, for example, a rotated YX-cut lithium niobate plate.

[0048] Layers 103, 105 and the piezoelectric plate 104 form a waveguide structure, and virtually all of the acoustic energy of the resonator is concentrated in these layers. The piezoelectric plate 104, which has a strong piezoelectric effect, is a key part of the device 100 and allows for the excitation of acoustic vibrations and the development of resonance.

[0049] Device 100 further comprises an interdigital electrode structure (IDES) including a first set of electrodes 106 and a second set of electrodes 108. At least two of the electrodes 106, 108 may be made of metal, such as aluminum or copper. The first set of electrodes 106 is connected to a first busbar 107, and the second set of electrodes 108 is connected to a second busbar 109. The first set of electrodes 106 and the second set of electrodes 108 are arranged sequentially, alternately, and periodically on the front surface of the piezoelectric plate 104 (opposite the back surface with respect to the thickness of the piezoelectric plate 104). The electrodes 106, 108 are arranged periodically at a pitch p. When the acoustic resonator device is operating, an AC voltage may be applied to the corresponding busbars.

[0050] The acoustic resonator device 100 has the following characteristics: The velocity V of the low-speed shear bulk wave propagating within the substrate layer 102 parallel to the layer surface and perpendicular to the electrodes 106 and 108. diam This is faster than the phase velocity within the piezoelectric plate 104. This phase velocity in the piezoelectric plate 104 is V ph =2p*F R It is determined by this formula, F R This is the operating frequency of the acoustic resonator device 100, and this is V LN / (2d LN Determined by ) in particular by velocity V diam This is the material property of the substrate layer 102. For example, diamond, silicon carbide, or boron nitride have relatively high rates V diam It is a material that possesses these properties.

[0051] Another feature of the acoustic resonator device 100 is that the pitch p is conditional p <V diam / V LN *d LN The condition is that V LN V is the velocity of the bulk wave resonating within the piezoelectric plate 104, and is a material property of the piezoelectric plate 104. diam and thickness d LN As stated above.

[0052] The characteristics of the acoustic resonator device 100 described above, in particular, the velocity Vdiam , V LN , and V ph This is determined by the selection of various materials for the individual layers / plates of device 100. Examples of suitable materials are given above. In particular, the materials of the substrate layer 103 and the piezoelectric plate 104 have the greatest influence on these parameters.

[0053] Figure 2 shows a cross-sectional view of the acoustic resonator device 100 according to this disclosure. The acoustic resonator device 100 in Figure 2 is built upon, or may be identical to, the one shown in Figure 1. The same elements in Figure 2 and Figure 1 are labeled with the same reference numerals and may be implemented as described above with reference to Figure 1.

[0054] The structure of device 100 is multilayered and periodic. Figure 2 shows a single period of the structure of device 100, and there may be many such periods in device 100. For example, device 100 may have two, three or more, or even hundreds of such periods.

[0055] Each period includes at least two electrodes 106, 108 of opposite polarity (for example, at least one "positive" electrode 106 in the first set and at least one "negative" electrode 108 in the second set), which are arranged at a periodic pitch p. The pitch p is determined by the distance between the centers of adjacent electrodes 106, 108, as shown in the figure. For the lithium niobate plate 104 and the diamond layer 102, the pitch p is approximately p < 2.4d. LN This may also be the case, and here, d LN This is the thickness of the piezoelectric plate 104.

[0056] As already shown in Figure 1, the acoustic resonator device 100 comprises a piezoelectric plate 104 and a non-piezoelectric dielectric layer 103 (for example, an SiO2 layer). The thickness of the piezoelectric plate 104 is half the wavelength d of the resonant wave. LN =λ LN This corresponds to / 2, which is the resonant frequency F R =V LN / (2d LNThe thickness of the dielectric layer 103 is determined by the thickness of the piezoelectric plate 104 d. LN It may be about half of (assuming the wave velocities in both are equivalent, as are the case for LN and SiO2). For example, the thickness of the dielectric layer 103 may be about one-quarter of the shear wavelength in the dielectric layer 103. Thus, in the case of the SiO2 layer 103, the thickness is about λ SiO2 / 4 is also acceptable.

[0057] The dielectric layer 103 is placed between the piezoelectric plate 104 and the substrate layer 102 (for example, the diamond layer). The dielectric layer 103 reduces the acoustic coupling of the piezoelectric plate 104 to the substrate layer 102. Furthermore, the dielectric layer 103 reduces the influence of the substrate layer 102 (for example, in the case of a hard diamond material, i.e., vibrations transmitted from the piezoelectric plate 104 to the substrate layer 102 are greatly reduced, and therefore the influence of layer 102 is also reduced). For example, the acoustic damping in this layer 102 does not significantly degrade the Q factor of the resonator device 100. In addition, the dielectric layer 103 allows for fundamental thickness resonance in the piezoelectric plate 104, ultimately increasing piezoelectric coupling.

[0058] The substrate layer 102 may be mounted or deposited on the support substrate 101, for example, it may be provided by a standard support wafer made from silicon or glass. However, it is beneficially dielectric, and conductive support substrates are not ideal for use. The substrate layer 102 can be a relatively thin layer (e.g., 4 to 20 times thicker than the piezoelectric plate 104). However, the substrate layer 102 can be made sufficiently thicker than the piezoelectric plate 104 so that the bulk waves cancel each other out due to the canceling interference of out-of-phase waves generated under the individual electrodes of the IDES. The thickness of the substrate layer 103 is, for example, the thickness d of the piezoelectric plate 104. LN It may be at least four times that amount.

[0059] When diamond is used as the material for the substrate layer 102, the diamond does not need to be perfect; that is, it may contain crystal grains larger than 1 nm in size in order to still benefit from its thermal conductivity and high acoustic velocity (which can be about 12,000 m / s). This is because only a small fraction of the acoustic energy is concentrated within the diamond. The substrate layer 102 may also be made of other materials that are mechanically close to diamond and have a high velocity of (all) bulk acoustic waves. Such materials may be, for example, silicon carbide or boron nitride. The acoustic velocity of the substrate layer 102 may be, for example, twice the acoustic velocity of the piezoelectric plate 104.

[0060] Pitch p is p <V diam / V LN *d LN The following conditions are met. Speed ​​V diam The velocity V may be greater than 8000 m / s, greater than 10000 m / s, and greater than 12000 m / s. LN The frequency in the piezoelectric plate 104 may be approximately 4000 m / s. Therefore, for example, if diamond is used as the material for the substrate layer 102, the pitch p may be approximately 1 / 2.4 of the thickness of the piezoelectric plate 104. This allows for reaching 5 GHz with a pitch p < 1.2 μm, which is suitable for fabrication by photolithography.

[0061] Grooves can be formed in the piezoelectric plate 104 between electrodes 106 and 108 (partially or completely formed through the piezoelectric plate 104, e.g., by etching). The grooves allow electrodes 106 and 108 to vibrate more freely, thus increasing piezoelectric coupling. The presence of grooves can also reduce the propagation of parasitic waves. The positive effects of grooves have been experimentally demonstrated for YBAR devices.

[0062] Figure 3 shows a perspective view of the acoustic resonator device 100 according to this disclosure, the acoustic resonator device 100 of Figure 3 is built upon, or may be identical to, those shown in Figure 1 and / or Figure 2. The same elements in Figure 3 and Figure 1 are labeled with the same reference numerals and may be implemented as described above with reference to Figure 1.

[0063] Figure 3 shows that device 100 may also include at least two reflector electrodes 301 and 302 positioned at each end of the IDT structure. For example, at least the first electrode 301 and the last electrode 302 of all electrodes periodically arranged on the piezoelectric plate 104 may be configured to function as reflectors to reduce the radiation of acoustic energy outside the IDES generated by the first and second sets of electrodes 106 and 108. The reflector electrodes 301 and 302 may be stray electrodes, i.e., they may be at a stray potential, and these electrodes 301 and 302 are not connected to any signal source and are not grounded.

[0064] Figure 4 shows the simulation results of the periodic structure of an exemplary acoustic resonator device 100 according to the present disclosure. In this example, the piezoelectric plate 104 is made of lithium niobate (specifically, Y-cut lithium niobate with a 90° sidewall angle of the Cu electrode), the dielectric layer 103 is made of silicon dioxide (SiO2), and the substrate layer 102 is made of diamond. The metal layer 105 and electrodes 106 and 108 are made of copper, respectively. The pitch p is 0.7 μm (20 periods are used). The thickness of the piezoelectric plate 104 is 300 nm, the thickness of electrodes 106 and 108 is 50 nm, the thickness of the metal layer 105 is 10 nm, and the thickness of the dielectric layer 103 is 150 nm.

[0065] The resonant frequency is 6049.3 MHz, the resonant Q factor is 4130, the anti-resonant frequency is 6632.6 MHz, the anti-resonant Q factor is 3620, and the relative resonant-anti-resonant frequency is 9.20%. Admittance is calculated for a pair of electrodes with an aperture W = 20 * (2p). In the 2D FEM simulation, resistive losses in electrodes 106 and 108, and many other loss mechanisms were ignored. The shown Q factor can be considered an ideal limit that cannot be achieved in a realistic device, and the expected Q factor is in the range of 300 to 600.

[0066] In Figure 4(a), the amplitude inside the resonator is shown on a grayscale (dark gray represents "zero"), with the interface position between the diamond substrate layer 102 and the SiO2 dielectric layer 103 at 0 on the vertical axis. In practice, no waves are radiated from the diamond substrate layer 102 and the substrate (below the interface marked "0"), but the waves bounce up and down within the piezoelectric plate 104. Essentially, it can be seen that only the shear component SH1 of the displacement, uy, is present in the simulated Y-cut LN piezoelectric plate (electrodes perpendicular to the crystal X-axis).

[0067] The curve in Figure 4(b) shows the admittance per pair of electrodes 106, 108 (one period including the first pair of electrodes 106 and the second pair of electrodes 108, as shown in Figure 2). A Y-cut lithium niobate was used as the piezoelectric plate 104. However, other possible cuts exist, which may include, for example, Z, Y+64, Y+36 degree cuts for S1 mode propagation and a Y+163 degree cut for SH1 mode.

[0068] The proposed cut can provide even stronger coupling. As an additional example, Figure 5 shows similar results for another cut (X cut, 30° propagation) of lithium niobate used in the acoustic resonator device 100 according to this disclosure. Even higher coupling can be obtained with a RaR relative frequency gap of 12.7% (K 2(>25%). However, parasitic modes appear around 7000MHz with horizontal displacement. The location and intensity of these modes depend on the device's geometry, which can be further optimized.

[0069] The same approach is also valid for the S1 mode (classical FBAR with longitudinal waves propagating in the z direction). In the case of piezoelectric plate 104 made of lithium niobate and / or lithium tantalate, the coupling for the S1 mode may be weaker than that for the SH1 mode.

[0070] This approach can also be used for the A1 mode, as shown in Figure 6. In this case, the metal layer 105 between the piezoelectric plate 104 and the dielectric layer 103 is not necessary. The electrodes 106 and 108 may become narrower as the distance between them increases (the metallization ratio may be a / p < 0.5). The main displacement component is ux (horizontal in Figure 6), and there is no y vibration uy. This corresponds to a "rigidly mounted XBAR".

[0071] Figure 6 shows, in particular, the simulation results for a device with an A1 ram mode on diamond. Coupled K 2 In this case, it is approximately 5% (compared to the typical 20% for the SH1 mode). The field distribution is typical of XBAR, and the waves attenuate rapidly at the depth of the diamond substrate layer 102. Therefore, there is no bulk wave radiation.

[0072] Figure 7 shows a parametric analysis of the solution of this disclosure for the main SH1 case. The left column shows that the resonant frequency (top left) and Q factor (bottom left) depend slightly on the pitch p. The piezoelectric plate 104 (lithium niobate as an example here) defines the resonant frequency, where f=V LN / (2d LN ) and V LNis the speed of sound within the piezoelectric plate 104. The frequency can be adjusted by changing the pitch p, or by changing the geometric shape of electrodes 106, 108, for example by changing the width of electrodes 106, 108, or by constructing electrodes 106, 108 having a trapezoidal cross-sectional shape.

[0073] In practice, the entire device is often covered by a “passivation layer,” such as a thin layer of SiOx or silicon nitride, to protect electrodes 106 and 108 from oxidation, moisture, etc. The right column of Figure 7 shows how such an upper cover dielectric layer (SiO2 here as an example), not shown in Figures 1-3, can be used for small variations in resonant and anti-resonant frequencies. The Q factor and the resonant / anti-resonant frequency gap (coupling) decrease with increasing thickness of the “passivation” dielectric layer covering the entire resonator device.

[0074] Figure 8 shows the effect of the thickness of the dielectric layer 103. For the device geometry shown in Figure 2, the optimal thickness of the dielectric layer (for example, made of SiO2) is approximately 180 nm (for example, approximately λ) at a given frequency. SiO2 / 4) However, the maximum piezoelectric bond K 2 This is not always necessary, and the thickness of the dielectric layer 103 may be, for example, in the range of 150 to 200 nm, or about ±10% from the optimal value.

[0075] The temperature coefficient of frequency (TCF) characterizes the thermal frequency stability of a resonator. In contrast to a negative TCF for the LN, the presence of a dielectric layer 103 having a positive temperature coefficient of frequency (TCF), which adds to the temperature stability of the structure, and a low coefficient of thermal expansion of the substrate layer 102 (e.g., diamond or SiC), can improve the TCF for the device 100 of this disclosure.

[0076] Figure 9 shows the FEM simulation results of the finite acoustic resonator device 100 according to this disclosure, having 121 periods of the proposed periodic structure and the floating reflectors 301 and 302 shown in Figure 3, respectively. Improved results may be obtained using the floating reflectors 301 and 302. The results for device 100 in Figure 9 confirm that the simulation of a periodic device structure (when only one period is simulated) also works for devices with multiple periods of the same structure.

[0077] Figure 10 shows possible methods 1001 and 1002 for operating the acoustic resonator device 100 according to this disclosure, for example, one of the acoustic resonator devices 100 shown in Figure 1, Figure 2, or Figure 3.

[0078] Method 1001 involves essentially V between the first busbar 107 and the second busbar 109 to which the electrodes 106 and 108 of the first and second sets are connected, respectively. LN / (2d LN This involves applying a differential AC voltage at a resonant frequency close to ), and the metal layer 105 is grounded. This method 1001 can be used in grid filters with balanced input / output. These filters are now used relatively rarely because they require complex networks in duplexers and multiplexers.

[0079] Alternatively, method 1002 is V LN / (2d LN This involves applying an AC voltage at a resonant frequency essentially determined by the first busbar 107 and the second busbar 109 to one of them, and keeping the other of the first busbar 107 and the second busbar 109 at ground potential (or another potential), with the metal layer 105 at a floating potential. This is a method of using this resonator device in a "ladder" type filter with a single-ended signal.

[0080] This disclosure describes various exemplary embodiments and their application in relation to implementation. However, other variations can be understood and implemented by those skilled in the art to perform the claimed matters from a study of the drawings, this disclosure, and the independent claims. In the claims and specification, the term “has” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude plurals. A single element or other unit may satisfy the function of multiple entities or items described in the claims. The mere fact that certain measures are described in different dependent claims does not imply that combinations of these measures cannot be used in a favorable implementation.

Claims

1. It is an acoustic resonator device: Support substrate and; A non-piezoelectric substrate layer disposed on the support substrate; A dielectric layer disposed on the non-piezoelectric substrate layer, wherein the dielectric layer includes at least one of a SiNO layer and a SiN layer; Thickness d with front and back LN A piezoelectric plate wherein the back surface is covered with a metal layer, and the piezoelectric plate is attached to the dielectric layer by the metal layer; The device comprises an interdigital electrode structure (IDES) including a first set of electrodes connected to a first busbar and a second set of electrodes connected to a second busbar, wherein the first and second sets of electrodes are arranged sequentially and alternately on the front surface of the piezoelectric plate at a pitch p. The velocity V of the low-speed shear bulk wave propagating parallel to the layer surface of the non-piezoelectric substrate layer in a direction perpendicular to the first and second sets of electrodes. diam V ph = 2p*F R The phase velocity of the piezoelectric plate determined by F is higher than F R V LN / (2d LN The operating frequency of the acoustic resonator device is determined by ) The pitch p satisfies p < V diam / V LN *d LN and satisfies the condition of LN where V is the velocity of the bulk wave resonating within the piezoelectric plate Acoustic resonator device.

2. The non-piezoelectric substrate layer includes a diamond layer, a silicon carbide layer, or a boron nitride layer. The acoustic resonator device according to claim 1.

3. The piezoelectric plate is made of crystalline lithium niobate, lithium tantalate, or aluminum nitride. The acoustic resonator device according to claim 1 or 2.

4. The piezoelectric plate made of lithium niobate is a rotated YX-cut lithium niobate plate in which the electrodes are arranged perpendicular to the crystal X-axis. The acoustic resonator device according to claim 3.

5. The aforementioned metal layer includes a copper layer or an aluminum layer. The acoustic resonator device according to claim 1 or 2.

6. The metal layer covers a limited area on the back of the piezoelectric plate, and the limited area corresponds to the area on the front of the piezoelectric plate that is covered by the electrode and is at a floating potential. The acoustic resonator device according to claim 5.

7. The metal layer and the first and second sets of electrodes form a plurality of periodically arranged resonators, and the resonators formed by the first set of electrodes and the resonators formed by the second set of electrodes are configured to vibrate in opposite phases to each other. The acoustic resonator device according to claim 1 or 2.

8. The interdigital electrode structure, which includes the first set of electrodes and the second set of electrodes, is provided with at least one floating potential electrode on each side along the direction perpendicular to the electrodes, The acoustic resonator device according to claim 1 or 2.

9. The floating potential electrodes provided on both sides are configured to function as reflectors to reduce the radiation of acoustic energy outside the acoustic resonator device. The acoustic resonator device according to claim 8.

10. The acoustic resonator device according to claim 8, wherein the first set of electrodes, the second set of electrodes, and the floating potential electrode are arranged sequentially at a pitch p.

11. The thickness of the non-piezoelectric substrate layer is the thickness d of the piezoelectric plate. LN It is within the range of 4 to 20 times. The acoustic resonator device according to claim 1 or 2.

12. The thickness of the dielectric layer is the thickness d of the piezoelectric plate. LN It is about half of and / or about one-quarter of the shear wavelength in the dielectric layer. The acoustic resonator device according to claim 1 or 2.

13. The velocity V of the low-speed shear bulk wave diam This is greater than 8000 m / s, or greater than 10000 m / s, or greater than 12000 m / s. The acoustic resonator device according to claim 1 or 2.

14. V ph = 2p*F R The phase velocity determined by is in the range of 2000 m / s to 6000 m / s, and / or the velocity V of the low-speed shear bulk wave. diam Lower than The acoustic resonator device according to claim 1 or 2.

15. A groove is positioned between each of two adjacent electrodes of the first and second sets of electrodes, the groove extending into the piezoelectric plate or extending completely through the piezoelectric plate. The acoustic resonator device according to claim 1 or 2.

16. A method for operating an acoustic resonator device according to any one of claims 1 to 15: Between the first and second busbars to which the first and second sets of electrodes are respectively connected, V LN / (2d LN Applying a differential AC voltage at a resonant frequency essentially close to ), wherein the metal layer is grounded; or, V LN / (2d LN The method involves applying an AC voltage to one of the first and second busbars at a resonant frequency essentially determined by the first and second busbars, and maintaining the other of the first and second busbars at ground potential, wherein the metal layer is at a floating potential. method.

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