A surface acoustic wave device

Abstract

A surface acoustic wave (SAW) device includes a piezoelectric layer, a high acoustic velocity layer coupled with the piezoelectric layer, and at least one transducer. The SAW device can include a multi-layer graphene layer in an electrode of the at least one transducer and a multi-layer graphene layer in a conductive layer coupled with the piezoelectric layer.

Description

Technical Field

[0001] This application relates to a surface acoustic wave (SAW) device. In various examples, this application relates to any or all of SAW filters, resonators, and duplexers with improved electromechanical coupling and higher power endurance. Background Technology

[0002] Surface acoustic wave (SAW) filters and resonators are widely used in communication systems (terminals and base station infrastructure). For next-generation 5G new radio (NR) wireless communication, the demand for at least one of the following is constantly increasing: higher operating frequency, lower insertion loss, higher transmit power, and greater channel bandwidth. New piezoelectric materials or structures are needed to support the growing demand for higher frequencies and greater channel bandwidth. SAW filters typically require high electromechanical coupling coefficients. As transmit power increases, the durability of SAW devices decreases. Therefore, improving durability can help increase operating frequency and transmit power.

[0003] Scandium-doped aluminum nitride (ScAlN) films have attracted much attention due to their good piezoelectricity, high thermal conductivity, and relatively high acoustic velocity. Hashimoto et al. described this structure in their paper "High-Q surface acoustic resonators in the 2-3 GHz range using ScAlN-single-crystal diamond structure" (Conference: 2012 IEEE International Ultrasonics Symposium (IUS)).

[0004] Similarly, Zhang Qiaozhen et al. also described another such structure in their paper "Surface Acoustic Wave Propagation Characteristics of ScAlN / Diamond Structures with Embedded Electrodes" (2014 Symposium on Piezoelectricity, Acoustics and Device Applications, pp. 271-274, 2014).

[0005] These structures have been explored, but they are insufficient to address the specific problems described in this paper. Summary of the Invention

[0006] In the various examples described in this paper, multiple layers of graphene are added to SAW devices to achieve high electromechanical coupling coefficients, high operating frequencies, and high power endurance.

[0007] In some aspects, this application describes a surface acoustic wave (SAW) device. The SAW device includes a piezoelectric layer, a high-velocity acoustic layer coupled to the piezoelectric layer on a first surface of the piezoelectric layer, and at least one transducer between the piezoelectric layer and the high-velocity acoustic layer. The at least one transducer includes a first multilayer graphene layer. The at least one transducer is used to propagate a surface acoustic wave having an operating wavelength (λ) along the piezoelectric layer.

[0008] In any of the above aspects / embodiments, the first multilayer graphene layer may include 2-10 atomic layers of graphene.

[0009] In any of the above aspects / embodiments, the first multilayer graphene layer may include 3-5 atomic layers of graphene.

[0010] In any of the above aspects / embodies, the SAW device may include a conductive layer coupled to a second surface of the piezoelectric layer, the second surface of the piezoelectric layer being opposite to the first surface of the piezoelectric layer.

[0011] In any of the above aspects / embodiments, the conductive layer may be a second multilayer graphene layer coupled to the metal layer.

[0012] In any of the above aspects / embodiments, the second multilayer graphene layer may include 3-10 atomic layers of graphene.

[0013] In any of the above aspects / embodiments, the conductive layer may be a second multilayer graphene layer.

[0014] In any of the above aspects / embodiments, the second multilayer graphene layer may include 3-10 atomic layers of graphene.

[0015] In any of the above aspects / embodiments, the transducer may include the first multilayer graphene layer coupled to the metal layer.

[0016] In any of the above aspects / embodiments, the first multilayer graphene layer may include 3-10 atomic layers of graphene.

[0017] In any of the above aspects / embodies, the at least one transducer may be embedded in the piezoelectric layer.

[0018] In any of the above aspects / embodiments, the at least one transducer may be embedded in the hypersonic layer.

[0019] In some aspects, this application describes a surface acoustic wave (SAW) device. The SAW device includes a piezoelectric layer and a high-velocity acoustic layer coupled to the piezoelectric layer on a first surface of the piezoelectric layer. The piezoelectric layer and the high-velocity acoustic layer are coupled to each other through a conductive layer. The SAW device also includes at least one transducer coupled to a second surface of the piezoelectric layer, the second surface of the piezoelectric layer being opposite to the first surface of the piezoelectric layer. The at least one transducer includes a first multilayer graphene layer coupled to a metal layer. The at least one transducer is used to propagate a surface acoustic wave having an operating wavelength (λ) along the piezoelectric layer.

[0020] In any of the above aspects / embodiments, the conductive layer may be a second multilayer graphene layer.

[0021] In any of the above aspects / embodiments, the second multilayer graphene layer may include 3-10 atomic layers of graphene.

[0022] In any of the above aspects / embodiments, the first multilayer graphene layer may include 3-10 atomic layers of graphene. Attached Figure Description

[0023] The accompanying drawings, by way of example, illustrate exemplary embodiments of this application, wherein:

[0024] Figure 1 This is a top cross-sectional view of an exemplary SAW device with interdigital transducer (IDT) electrodes.

[0025] Figure 2 This is a side cross-sectional view of an exemplary configuration of a SAW device;

[0026] Figure 3A and Figure 3B This is a graph showing the simulation results of von Mises stress in conductive layers and electrodes with different layer configurations when the number of atomic layers in the graphene layers in both the conductive layer and the electrode varies.

[0027] Figure 4 This is a side cross-sectional view of another exemplary configuration of the SAW device;

[0028] Figure 5A This is a graph showing the simulation results of the electromechanical coupling coefficient for the change in the thickness of the metal layer in the electrode;

[0029] Figure 5B This is a graph showing the simulation results of von Mises stress under different electrode configurations when the number of atomic layers in both the conductive layer and the graphene layer in the electrode varies.

[0030] Figure 6 This is a side cross-sectional view of another exemplary configuration of the SAW device;

[0031] Figure 7A The graph shows the simulation results of von Mises stress in electrodes with different numbers of atomic layers in the graphene layer.

[0032] Figure 7B The graph shows the simulation results of von Mises stress in electrodes at different positions and with different electrode configurations;

[0033] Figure 8 This is a side cross-sectional view of another exemplary configuration of the SAW device;

[0034] Figure 9 and Figure 10 This is a flowchart of exemplary manufacturing methods for various SAW devices disclosed herein.

[0035] Similar figure numbers can be used to represent similar parts in different accompanying drawings. Detailed Implementation

[0036] In the 5G New Radio spectrum, the 1-6GHz band offers a good mix of coverage and capacity for 5G services, while the 3.3-3.8GHz band provides a solid foundation for the initial commercialization of 5G. In particular, the 3.4-3.6GHz band drives the economies of scale required for low-cost equipment. To achieve this in the 3.4-3.6GHz range (f0 = 3.5GHz, BW...), 3db =200MHz, with a relative bandwidth of 5.7%) to obtain a broadband SAW filter for 5G service deployment, which requires a high electromechanical coupling coefficient k 2 (For example, k) 2 >17%) of piezoelectric structures. Although some ScAlN / diamond multilayer structures can exhibit sufficient electromechanical coupling (e.g., k 2 The coupling coefficient of this structure is generally lower with increasing metal electrode thickness (>17%), resulting in a lower electromechanical coupling in practical applications. Although the ScAlN / diamond structure outperforms traditional SAW filters in terms of power handling capability due to the excellent thermal conductivity of the diamond layer, SAW filters used in 5G NR base station RF front-end applications still need further improvement in device power handling capability.

[0037] In various examples, this application describes SAW devices that maintain a high electromechanical coupling coefficient and provide power endurance. Examples of the disclosed SAW devices utilize multilayer graphene layers to reduce stress in the electrodes and keep the electrodes thin and lightweight.

[0038] Figure 1An example of a physical implementation of a surface acoustic wave (SAW) device 100 is shown, for example, a broadband transverse filter. The SAW device can be used in the front end of a radio-frequency (RF) transmitter / receiver capable of handling high power, for example, greater than 32 dBm. Although the description below refers to the specific SAW device 100, the techniques described herein are equally applicable to other types of SAW filters, SAW resonators, or combinations thereof. For example, any SAW transducer, interdigital transducer (IDT), inter-digitated interdigital transducer (IIDT), trapezoidal filter, or other such device can be incorporated into the multilayer structure described herein.

[0039] In this exemplary embodiment, for clarity, only a basic filter is shown for the SAW device 100, which may include a multilayer body 102 (discussed further below) having an input transducer 104 and an output transducer 106, indicated by dashed boxes, respectively. In this example, the upper conductive layer 202 and piezoelectric layer 204 of the body 102 have been partially cut to show the transducers 104 and 106. The input transducer 104 and the output transducer 106 may be coupled to the body 102. The input transducer 104 and the output transducer 106 each include a plurality of conductive interdigitated transducer (IDT) electrodes 108. The IDT electrodes 108 are typically parallel to each other within their respective transducers 104 / 106, and each finger of each IDT electrode 108 may be spaced half the operating wavelength (λ / 2). IDT electrode 108 can be electrically coupled to lead-out pad 110 for supplying power to IDT electrode 108 via input terminal 112 (in the case of input transducer 104), or receiving power from IDT electrode 108 via output terminal 114 (in the case of output transducer 106). The IDT thickness of IDT electrode 108 can be between about 0λ and about 0.10λ, for example, between about 0.01λ and about 0.10λ, for example, about 0.02λ or about 0.08λ. In this application, a layer or material can be described as having a thickness of about 0λ to indicate that the layer or material is conductive but has no mechanical mass loading effect (e.g., for simulation purposes); a thickness of about 0λ does not indicate that the layer or material is omitted. For example, in various cases, a thickness of about 0λ can be achieved using materials with a thickness of tens of atoms, such as multilayer graphene materials.

[0040] When power is supplied to input 112, input transducer 104 converts the electrical signal energy into a SAW (e.g., a transducer) propagating along body 102. The SAW can be carried within body 102 and can be converted back into an electrical signal by output transducer 106. An electrical signal, such as one received by a processor (not shown) via an analog-to-digital converter (not shown), can then be provided at output 114. The center frequency of the SAW filter can be obtained by dividing the speed of the SAW by the operating wavelength.

[0041] Figure 2 An exemplary configuration of the SAW device 100 is shown along the edge. Figure 1 A side cross-sectional view of line AA in the diagram. For clarity, the dimensions of some features have been enlarged. The body 102 of the SAW device 100 includes a hypersonic layer 206 (e.g., a diamond layer), a piezoelectric layer 204 (e.g., a ScAlN film), and a conductive layer 202 (also referred to as a short layer or short surface). Both the input transducer 104 and the output transducer 106 include electrodes 108. The transducers 104 and 106 are located between the piezoelectric layer 204 and the hypersonic layer 206 for propagating surface acoustic waves along the piezoelectric layer 204 at an operating frequency f0.

[0042] In the various examples described herein, the layers of body 102 may be arranged in different orders. Electrodes 108 may be located between pairs of layers of body 102 and may be embedded in different layers of body 102. In this example, the electrode 108 may be embedded in the piezoelectric layer 204; in other examples, the electrode 108 may be embedded in the hypersonic layer 206.

[0043] The electrode 108 in this example can be made of multiple layers of graphene, for example, multilayer graphene with 2-10 atomic layers, or for example, 3-5 atomic layers. Simulations show that in Figure 2 In this configuration, using this multilayer graphene layer for electrode 108 achieves the highest electromechanical coupling coefficient. Typically, for metals with a thickness of less than 50 nm, the thinner the material, the greater the ohmic loss, especially at high operating frequencies; this is not the case with graphene.

[0044] In this example, the conductive layer 202 can be a metal layer 202a coupled to another multilayer graphene layer 202b. The metal layer 202a can be copper (Cu), and the multilayer graphene layer 202b can have 2-10 atomic layers, for example, 3-5 atomic layers. In this example, the transducers 104 and 106 are considered to be coupled to a first surface of the piezoelectric layer 204, and the conductive layer 202 is considered to be coupled to a second surface of the piezoelectric layer 204, with the second surface of the piezoelectric layer 204 opposite to the first surface.

[0045] In one exemplary implementation, Figure 2 The configuration shown can have an operating frequency of 2.1 GHz and an operating wavelength λ = 3.85 μm. The thickness of the piezoelectric layer 204 (e.g., a ScAlN layer) can be about 0.2λ (0.77 μm), and the thickness of the hypersonic layer 206 (e.g., a diamond layer) can be about 10 μm. In the conductive layer 202, the thickness of the metal layer 202a (e.g., a copper layer) can be about 0.01λ (38.5 nm). The thickness of the electrode 108 made of the multilayer graphene layer can be substantially 0λ. The thickness of the multilayer graphene layer 202b of the conductive layer 202 can also be substantially 0λ.

[0046] Even at very high operating frequencies (e.g., up to 10 GHz), multilayer graphene layers used for electrode 108 can provide a high effective electromechanical coupling coefficient because the multilayer graphene layers are highly conductive and very thin.

[0047] Using a combination of metal and multilayer graphene in the conductive layer 202 can provide higher power endurance and, in some embodiments, can help achieve the desired high electromechanical coupling coefficient. It has been found that using 2-10 atomic layers for the multilayer graphene layer 202b can provide high power endurance for the SAW device 100, with better performance than when using fewer atomic layers of graphene. Figure 3A This is a graph showing the von Mises stress in conductive layer 202a when different numbers of atomic layers are used for the multilayer graphene layer 202b in conductive layer 202 and for the electrode 108. Figure 3B This is a graph showing the von Mises stress in electrode 108 when different numbers of atomic layers are used for the multilayer graphene layer 202b in conductive layer 202 and for electrode 108. Figure 3A and Figure 3B In the process, the thicknesses of the multilayer graphene layer 202b and the electrode 108 both vary (i.e., the x-axis value reflects that the number of atomic layers of graphene in the graphene layer 202b is the same as the number of atomic layers of graphene in the electrode 108). Figure 3A and Figure 3B Showing the target Figure 2 The simulation results shown are based on the example dimensions provided above, with variations in the thickness of the multilayer graphene layer 202b and the electrode 108. Further, Figure 3A Simulation results are shown for different configurations of the conductive layer 202, specifically by coupling the graphene layer 202b on top of the metal layer 202a (graphene / Cu); by coupling the metal layer 202a on top of the graphene layer 202b (Cu / graphene); and by sandwiching the metal layer 202a between two graphene layers 202b (graphene / Cu / graphene).

[0048] like Figure 3A As shown, compared to the case without a graphene layer (i.e., the number of graphene layers is 0), a reduction in von Mises stress occurs only in the conductive layer configuration where the graphene layer 202b is coupled to the top of the metal layer 202a (graphene / Cu), as... Figure 2 As shown in the figure. Interestingly, simulations revealed that among the three conductive layer configurations, the graphene / Cu / graphene conductive layer configuration exhibited the largest decrease in electromechanical coupling coefficient with increasing graphene thickness, and the graphene / Cu / graphene conductive layer configuration also showed the highest von Mises stress among the three conductive layer structures.

[0049] Therefore, the following text discusses... Figure 3A and Figure 3B The discussion will focus solely on the graphene / Cu configuration of the conductive layer 202.

[0050] like Figure 3A and Figure 3B As shown, using monolayer graphene for the graphene layer 202b and the electrode 108 resulted in higher von Mises stress in the conductive layer 202 and the electrode 108. Using 2-10 atomic layers for the graphene layer 202b and the electrode 108 resulted in lower von Mises stress in the conductive layer 202 and the electrode 108. Furthermore, using 3-5 atomic layers for the graphene layer 202b and the electrode 108 resulted in even lower von Mises stress in the conductive layer 202 and the electrode 108. Therefore, simply using the thinnest possible graphene (e.g., monolayer graphene) may not be ideal. Figure 3A and Figure 3B It was also shown that, compared to the case where no graphene layer 202b was used (i.e., when the number of graphene atomic layers was 0), using a graphene layer 202b with 2-10 atomic layers on the metal layer 202a reduced the von Mises stress in the conductive layer 202 and the electrode 108. When the number of atomic layers is greater than 10, the multilayer graphene begins to exhibit graphite properties and loses the characteristics of graphene.

[0051] The simulation also found that when Figure 2 When the exemplary SAW device 100 operates in the second mode (i.e., Sezawa mode), and the electromechanical coupling coefficient is expected to reach its maximum value (k) when the thickness of the metal layer 202a (e.g., copper layer) is approximately 0.01λ. 2 >17.5%.

[0052] The simulation also found that, Figure 2In the configuration shown, the sound velocity increases when the thickness of electrode 108 decreases, the thickness of metal layer 202a of conductive layer 202 decreases, and the number of atomic layers of graphene layer 202b in conductive layer 202 increases (thus resulting in a higher operating frequency of SAW device).

[0053] Taking into account the above factors, such as the trade-off between higher sound speed and higher electromechanical coupling coefficient, it has been found that using an electrode 108 with a thickness of essentially 0λ (e.g., the electrode 108 uses 2-10 atomic layers or 3-5 atomic layers of graphene), a metal layer 202a with a thickness of 0.01λ (e.g., a copper layer with a thickness of 0.01λ), and a graphene layer 202b with 2-10 atomic layers or 3-5 atomic layers on the metal layer 202a, a SAW device 100 with ideal performance can be obtained.

[0054] Figure 4 A side cross-sectional view of another exemplary configuration of the SAW device 100 is shown. For ease of illustration, the dimensions of certain features have been enlarged. The body 102 of the SAW device 100 includes a hypersonic layer 206 (e.g., a diamond layer), a piezoelectric layer 204 (e.g., a ScAlN film), and a conductive layer 202. Figure 2 The exemplary configurations are different. Figure 4 In the example configuration, the conductive layer 202 is positioned between the hypersonic layer 206 and the piezoelectric layer 204, and the transducers 104 and 106 are placed on top of the piezoelectric layer 204. In this example, the conductive layer 202 is considered to be coupled to a first surface of the piezoelectric layer 204, and the transducers 104 and 106 are considered to be coupled to a second surface of the piezoelectric layer 204, with the second surface of the piezoelectric layer 204 opposite to the first surface.

[0055] In this example, the conductive layer 202 may be multilayer graphene, for example, having 3-10 atomic layers. In this example, the electrodes 108 of transducers 104 and 106 may include a metal layer 108a coupled to another multilayer graphene layer 108b. The metal layer 108a may be copper (Cu), and the multilayer graphene layer 108b may have 3-10 atomic layers.

[0056] In one exemplary implementation, Figure 4The configuration shown can have an operating frequency of 2.1 GHz and an operating wavelength λ = 2.63 μm. The thickness of the piezoelectric layer 204 (e.g., ScAlN layer) can be 0.8λ (2.11 μm), and the thickness of the hypersonic layer 206 (e.g., diamond layer) can be about 10 μm. The thickness of the conductive layer 202 (e.g., multilayer graphene) can be 3-10 atomic layers (thickness essentially 0λ). In the electrode 108, the thickness of the metal layer 108a (e.g., copper layer) can be about 0.08λ (0.21 μm), and the multilayer graphene layer 108b can have a thickness of 3-10 atomic layers (thickness essentially 0λ).

[0057] Figure 4 The example configuration is applicable to wave propagation in the Sezawa mode. Figure 5A Simulation results are shown based on the exemplary dimensions provided above and the variation in thickness of the metal layer 108a of the electrode 108. For example... Figure 5A As shown, simulations revealed that the maximum electromechanical coupling coefficient can be achieved when the thickness of electrode 108 is approximately 0.08λ, rather than the principle that thinner is always better. Therefore, unlike... Figure 2 The exemplary configuration shows that using graphene alone as electrode 108 may not be ideal. Figure 5B Simulation results are shown, based on the exemplary dimensions provided above, and varying the number of atomic layers in the multilayer graphene layer 108b and conductive layer 202 of electrode 108 for different layer arrangements. Specifically, Figure 5B The performance of an electrode 108 formed by coupling the graphene layer 108b to the top of the metal layer 108a (graphene / Cu) was compared; the performance of an electrode 108 formed by coupling the metal layer 108a to the top of the graphene layer 108b (Cu / graphene); and the performance of an electrode 108 formed by sandwiching the metal layer 108a between two graphene layers 108b (graphene / Cu / graphene). Figure 5B In the process, the thicknesses of the multilayer graphene layer 108b and the conductive layer 202 both vary.

[0058] like Figure 5B As shown, compared to the case without a graphene layer (i.e., the number of graphene layers is 0), a reduction in von Mises stress occurred only in the electrode configuration where the graphene layer 108b is coupled to the top of the metal layer 108a (graphene / Cu). This is Figure 4 The configuration shown is interesting. Interestingly, the electrode configuration with metal layer 108a sandwiched between two graphene layers 108b (graphene / Cu / graphene) exhibits the largest von Mises stress among the three electrode configurations.

[0059] like Figure 5BAs shown, regardless of the configuration of electrode 108, the highest von Mises stress was observed in electrode 108 when there was only one atomic layer of graphene. Therefore, using the thinnest possible graphene in both electrode 108 and conductive layer 202 may not be ideal. Compared to not using graphene layer 108b (i.e., when the number of graphene atomic layers is 0), it was found that using 3-10 atomic layers in both graphene layer 108b and conductive layer 202 resulted in lower von Mises stress in electrode 108, thereby enhancing the high-power durability of electrode 108.

[0060] These simulation results show that in the design Figure 4 When designing the exemplary SAW device 100, important considerations include selecting an appropriate number of atomic layers for the graphene layer 108b and how to couple the graphene layer 108b to the metal layer 108a to form the electrode 108.

[0061] Simulations also revealed that using 3-10 atomic layers of graphene in the conductive layer 202 between the multilayer graphene layer 108b and the piezoelectric layer 204 and the hypersonic layer 206 can achieve the maximum electromechanical coupling coefficient.

[0062] Figure 6 A side cross-sectional view of another exemplary configuration of the SAW device 100 is shown. For clarity, the dimensions of certain features have been enlarged. The body 102 of the SAW device 100 includes a hypersonic layer 206 (e.g., a diamond layer), a piezoelectric layer 204 (e.g., a ScAlN film), and a conductive layer 202. In this example, an electrode 108 is located between the piezoelectric layer 204 and the hypersonic layer 206, and the conductive layer 202 is coupled to the piezoelectric layer 204, similar to... Figure 2 The configuration. With Figure 2 The examples in the text are different. Figure 6 In the example, transducers 104 and 106 are embedded in a hypersonic layer 206, and the electrodes 108 of transducers 104 and 106 include multiple layers of graphene 108b (e.g., having 3-10 atomic layers, similar to...). Figure 4 In the example, the electrode 108) is coupled to a metal layer 108a (e.g., copper), and the conductive layer 202 consists only of multiple layers of graphene, for example, having 3-10 atomic layers.

[0063] In this example, the transducers 104 and 106 are considered to be coupled to the first surface of the piezoelectric layer 204, and the conductive layer 202 is considered to be coupled to the second surface of the piezoelectric layer 204, with the second surface of the piezoelectric layer 204 opposite to the first surface.

[0064] In one exemplary implementation, Figure 6The configuration shown can have an operating frequency of 2.1 GHz and an operating wavelength λ = 3.76 μm. The thickness of the piezoelectric layer 204 (e.g., ScAlN layer) can be about 0.2λ (0.77 μm), and the thickness of the hypersonic layer 206 (e.g., diamond layer) can be about 10 μm. The thickness of the conductive layer 202 (e.g., multilayer graphene) can be 3-10 atomic layers (thickness substantially 0λ). In the electrode 108, the thickness of the metal layer 108a (e.g., copper layer) can be about 0.01λ (38.5 μm), and the multilayer graphene layer 108b can have a thickness of 3-10 atomic layers (thickness substantially 0λ).

[0065] Figure 7A Simulation results are shown based on the exemplary dimensions provided above, with variations in the number of atomic layers in the multilayer graphene layer 108b and the conductive layer 202 of the electrode 108. Figure 7A In this process, the thicknesses of both the multilayer graphene layer 108b and the conductive layer 202 vary. For example... Figure 7A As shown, it was found that using single or double layers of graphene in the graphene layer 108b and the conductive layer 202 resulted in higher von Mises stress in the electrode 108. Therefore, simply using the thinnest possible graphene layer 108b (e.g., a single layer of graphene) may not be ideal. Compared to not using the graphene layer 108b (i.e., when the number of graphene atomic layers is 0), it was found that using 3-10 atomic layers in the graphene layer 108b and the conductive layer 202 resulted in lower von Mises stress in the electrode 108, thereby enhancing the high-power durability of the electrode 108.

[0066] Figure 7B The simulation results of von Mises stress in electrode 108 at different positions are shown. Figure 7B As shown, compared to when the pure metal electrode 108 is embedded in the hypersonic layer 206, the von Mises stress in the electrode 108 is higher when the electrode 108 only has a metal layer 108a and is embedded in the piezoelectric layer 204. Furthermore, Figure 7BThis demonstrates how coupling a multilayer graphene layer 108b to the metal layer 108a to form an electrode 108 can reduce von Mises stress in the electrode 108. These results illustrate some possible benefits of coupling the multilayer graphene layer 108b to the metal layer 108a of the electrode 108, namely, reduced von Mises stress in the electrode 108 (and therefore longer failure time). This may be because the multilayer graphene layer 108b acts as a metal diffusion barrier layer, thereby reducing acoustic migration (e.g., due to voids and hillocks in the metal layer 108a) and reducing stress in the electrode 108, thus enhancing the power endurance of the SAW device 100. Embedding the electrode 108 in the hypersonic layer 206 with high thermal conductivity can also help provide a good thermal path for heat dissipation of the electrode 108, thus also enhancing the power endurance of the SAW device 100. Although Figure 7B Not shown, when the electrode 108 includes a multilayer graphene layer 108b coupled to the metal layer 108a and the electrode 108a is embedded in the piezoelectric layer 204, the von Mises stress in the electrode 108 can also be appropriately low.

[0067] Simulations also revealed that the phase velocity of the SAW device 100 increases with the number of atomic layers in the multilayer graphene layer 108b of the electrode 108, and the fewer the number of atomic layers in the multilayer graphene layer 108b of the electrode 108, the larger the electromechanical coupling coefficient. Therefore, selecting an appropriate number of atomic layers for the multilayer graphene layer 108b and the placement of the electrode 108 involves various trade-offs and is neither trivial nor easy.

[0068] Figure 8 A side cross-sectional view of another exemplary configuration of the SAW device 100 is shown. For ease of illustration, the dimensions of certain features have been enlarged. The body 102 of the SAW device 100 includes a hypersonic layer 206 (e.g., a diamond layer) and a piezoelectric layer 204 (e.g., a ScAlN film). Electrodes 108 of transducers 104, 106 are located between the piezoelectric layer 204 and the hypersonic layer 206. Figure 8 The configuration is similar to Figure 2 An exemplary configuration is shown, but the conductive layer 202 is omitted. This configuration is applicable to wave propagation in Rayleigh mode. In this example, transducers 104, 106 can be embedded in the piezoelectric layer 204. The electrode 108 in this example can be made of multiple layers of graphene, for example, multilayer graphene with 3-10 atomic layers.

[0069] In one exemplary implementation, Figure 8The configuration shown can have an operating frequency of 10 GHz and an operating wavelength λ = 0.46 μm. The thickness of the piezoelectric layer 204 (e.g., a ScAlN layer) can be about 0.45λ (0.21 μm), and the thickness of the hypersonic layer 206 (e.g., a diamond layer) can be about 5 μm. The electrode 108 can have 3-10 atomic layers of graphene (with a thickness of essentially 0λ).

[0070] Simulations revealed that using highly conductive multilayer graphene as electrode 108 resulted in a high electromechanical coupling coefficient and high sound velocity in SAW device 100. This is significant compared to other SAW devices with similar layer arrangements but using metal instead of graphene for electrode 108. Figure 8 The example configuration allows for higher operating frequencies (e.g., 10 GHz) while maintaining low ohmic losses (and thus a high electromechanical coupling coefficient) by keeping the electrode 108 low in thickness.

[0071] As mentioned above, Figure 8 The example configuration is suitable for wave propagation in the Rayleigh mode, while Figure 2 , Figure 4 and Figure 6 The example configuration is suitable for wave propagation in the Sezawa mode. Therefore, different configurations of the SAW device 100 can be selected according to the required application.

[0072] The exemplary SAW device 100 disclosed herein can be manufactured using any suitable manufacturing technique. Figure 9 and Figure 10 These are flowcharts of exemplary manufacturing methods 900 and 1000 that can be used.

[0073] Figure 9 The exemplary method 900 shown can be used to manufacture Figure 2 , Figure 6 , Figure 8 An exemplary SAW device 100, for example, depends on which steps are performed and which steps are not performed.

[0074] In 902, a high-velocity layer 206 is provided. For example, chemical vapor deposition (or other suitable techniques) can be used to provide an appropriate thickness for the diamond layer (typically several times thicker than λ). The diamond layer can also be polished and cleaned.

[0075] If electrode 108 is embedded in hypersonic layer 206 (for example, in...) Figure 6 In the example ( ), then in 904, the hypersonic layer 206 is etched using a mask used for patterning electrode 108. Otherwise, 904 is not performed.

[0076] If the electrode 108 includes multiple graphene layers 108b (e.g., in...), Figure 6In the example, the coupled metal layer 108a is then formed to the desired thickness in 906, for example, using a metal deposition technique. If 904 is not performed, the metal layer 108a can be patterned using a mask.

[0077] In 908, multilayer graphene is formed and coupled to the metal layer 108a (e.g., in...). Figure 6 (in the example) or formed directly on the hypersonic layer 206 (e.g., in Figure 2 and Figure 8 (as in the example). This can be achieved by adding epitaxial graphene to the desired number of atomic layers on the hypersonic layer 206 and then patterning (e.g., by electron beam nano-etching) the hypersonic layer 206.

[0078] In 910, a piezoelectric layer 204 is formed. For example, this can be achieved by sputtering or chemical vapor deposition of ScAlN to the desired thickness.

[0079] If conductive layer 202 is required (for example, in...) Figure 2 and Figure 6 In the example), then in 912, by adding multiple layers of graphene (e.g., in...). Figure 6 In the example, a conductive layer 202 is formed, or by first depositing a metal layer 202a and then adding multiple layers of graphene 202b (e.g., in...). Figure 2 In the example, conductive layer 202 is formed.

[0080] therefore, Figure 2 Examples can be obtained through manufacturing steps 902, 908, 910, and 912; Figure 6 Examples can be obtained through manufacturing steps 902, 904, 906, 908, 910, and 912; Figure 8 Examples can be obtained through manufacturing steps 902, 908, and 910.

[0081] Figure 4 Examples can be found through Figure 10 The exemplary method 1000 shown is used to obtain this.

[0082] In 1002, a high-velocity layer 206 is set. For example, chemical vapor deposition (or other suitable techniques) can be used to provide an appropriate thickness for the diamond layer (typically several times thicker than λ). The diamond layer can also be polished and cleaned.

[0083] If conductive layer 202 is required (for example, in...) Figure 4 In the example), then in 1004, by adding multiple layers of graphene (e.g., in...). Figure 4 In the example, a conductive layer 202 is formed. The conductive layer 202 can also be formed by depositing a metal layer, with or without adding multiple layers of graphene on top.

[0084] In 1006, a piezoelectric layer 204 is formed. For example, this can be achieved by sputtering or chemical vapor deposition of ScAlN to the desired thickness.

[0085] If the electrode 108 includes multiple graphene layers 108b (e.g., in...), Figure 4 In the example, the coupled metal layer 108a is formed to the desired thickness in 1008, for example, using a metal deposition technique. In some examples, the electrode 108 is embedded in the piezoelectric layer 204, which may be etched before the electrode 108 is formed.

[0086] In 1010, a multilayer graphene layer 108b is formed over the electrode 108. This can be achieved by adding epitaxial graphene to the desired number of atomic layers on the metal layer 108a formed in 1008, and then patterning (e.g., by electron beam nano-etching) the metal layer 108a.

[0087] therefore, Figure 4 Examples can be obtained through manufacturing steps 1002, 1004, 1006, 1008, and 1010.

[0088] In various examples, the metal layer used in the graphene / metal electrode or graphene / metal conductive layer is described as copper (Cu). Other metals may also be applicable, such as aluminum (Al), platinum (Pt), aluminum-copper alloys (Al / Cu / Al), molybdenum (Mo), tungsten (W), titanium (Ti), gold (Au), nickel (Ni), titanium nitride (TiN), silver (Ag), cobalt (Co), chromium (Cr), copper-iron alloys (Cu-Fe), niobium (Nb), nickel (Ni), zinc (Zn), zirconium (Zr), and alloys comprising any number of these metals.

[0089] In various examples, the piezoelectric layer has been described as a ScAlN layer. Other materials can also be used for the piezoelectric layer, such as aluminum nitride (AlN), zinc oxide (ZnO), and other piezoelectric materials.

[0090] In various examples, hypersonic layers have been described as diamond layers. Other materials can also be used for hypersonic layers, such as silicon carbide (SiC) or other substrate materials.

[0091] This article discloses different configurations of SAW devices. Specific configurations can be selected based on the specific application. For example, for lower operating frequencies, the electrodes can be designed as metal layers coupled to multilayer graphene, while for higher operating frequencies, the electrodes can be designed as graphene only. However, if the SAW device is only used to generate waves without reflecting sound waves, the electrodes can be designed as graphene only, even at lower operating frequencies.

[0092] Among the various examples disclosed herein, one SAW device is provided that can achieve a high electromechanical coupling coefficient (k 2 High power endurance (>17.5%) and high operating frequencies (2.1 GHz or higher) are achieved by using multilayer graphene as at least one of the electrodes and conductive layers. The performance degradation of existing SAW devices can be addressed by using multilayer graphene layers with a selected number of atomic layers (e.g., 3-10 atomic layers), while achieving the desired high electromechanical coupling coefficient and high operating frequency.

[0093] Achieving a high electromechanical coupling coefficient enables the creation of broadband SAW filters, such as filters with a relative bandwidth of 5.7% for E-UTRA band 42. Furthermore, SAW filters with high electromechanical coupling coefficients can be used instead of bulk acoustic resonator (FBAR) filters at the termination, resulting in cost savings, as SAW filters are generally less expensive than FBAR filters.

[0094] Achieving high phase velocity in SAW devices can also enable high-frequency (e.g., 10 GHz) SAW filters.

[0095] The disclosed SAW devices can be used to implement SAW filters in mobile terminals, base stations and other infrastructure equipment.

[0096] This application may be embodied in other specific forms without departing from the subject matter of the claims. The exemplary embodiments described are merely illustrative in all respects and not restrictive. Features selected from one or more of the foregoing embodiments may be combined to create alternative embodiments not explicitly described. Features suitable for such combinations are to be understood within the scope of this application. For example, although a specific size and shape of the IDT electrode 108 is disclosed herein, other sizes and shapes may be used. In another example, although a particular SAW device 100 (e.g., a filter) may be described herein, the structure may be adapted to other SAW device configurations.

[0097] The thicknesses of each layer described herein are illustrative and not restrictive. For ease of illustration and reference, the heights of these layers may be enlarged or minimized in the accompanying drawings.

[0098] Although exemplary embodiments may be described in conjunction with specific orientations (e.g., top and bottom), this is merely for convenience and ease of reference when describing the accompanying drawings.

[0099] All values ​​and sub-ranges within the scope of the disclosure are also disclosed. Furthermore, although the systems, devices, and processes disclosed and illustrated herein may include a specific number of elements / components, systems, devices, and components may be modified to include more or fewer such elements / components. For example, although any element / component disclosed may be referenced as a single element, embodiments disclosed herein may be modified to include multiple such elements / components. The subject matter described herein is intended to cover and include all suitable variations of the art.

Claims

1. A surface acoustic wave (SAW) device, characterized in that, include: piezoelectric layer; A high-velocity acoustic layer coupled to the piezoelectric layer on the first surface of the piezoelectric layer; as well as At least one transducer between the piezoelectric layer and the hypersonic layer, wherein the at least one transducer includes an electrode, the electrode using a first multilayer graphene layer, the electrode having a thickness of substantially 0λ, the substantially 0λ thickness comprising graphene of 3-5 atomic layers of the first multilayer graphene layer, the at least one transducer being used to propagate surface acoustic waves having an operating wavelength (λ) along the piezoelectric layer. The SAW device further includes a conductive layer coupled to a second surface of the piezoelectric layer, the second surface of the piezoelectric layer being opposite to the first surface of the piezoelectric layer. The conductive layer is a metal layer coupled to a second multilayer graphene layer, the second multilayer graphene layer being coupled to the top of the metal layer. The thickness of the metal layer is 0.01λ, and the second multilayer graphene layer comprises 3-5 atomic layers of graphene.

2. The SAW device according to claim 1, characterized in that, The at least one transducer is embedded in the piezoelectric layer.

3. The SAW device according to claim 1, characterized in that, The at least one transducer is embedded in the hypersonic layer.

4. A surface acoustic wave (SAW) device, characterized in that, include: piezoelectric layer; A high-velocity acoustic layer coupled to the piezoelectric layer on the first surface of the piezoelectric layer; The piezoelectric layer and the hypersonic layer are coupled to each other through a conductive layer; as well as At least one transducer coupled to a second surface of the piezoelectric layer, the second surface of the piezoelectric layer being opposite to a first surface of the piezoelectric layer, wherein the at least one transducer includes an electrode comprising a first multilayer graphene layer coupled to a first metal layer, the first multilayer graphene layer being coupled on top of the first metal layer, the thickness of the first multilayer graphene layer being substantially 0λ, the substantially 0λ thickness comprising graphene of 3-5 atomic layers, the thickness of the first metal layer being 0.08λ, the at least one transducer being used to propagate surface acoustic waves having an operating wavelength (λ) along the piezoelectric layer; The conductive layer is a second multilayer graphene layer, which comprises 3-5 atomic layers of graphene.

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