Surface acoustic wave device with heavy metal electrode stack

Abstract

A surface acoustic wave (SAW) device includes a piezoelectric substrate (12) in which at least one electrode (20A, 20b) is located on a top surface of the piezoelectric substrate. The electrode is formed from an electrode stack (40) comprising a first heavy metal layer (42) formed from a heavy electrode metal and a first conductive layer (44) formed from a conductive material stacked on each other.

Description

Technical Field

[0001] The present disclosure relates to acoustic wave devices, and in particular to surface acoustic wave (SAW) devices. Background Art

[0002] Acoustic wave devices are widely used in modern electronics. For the most part, an acoustic wave device includes a piezoelectric material in contact with one or more electrodes. Piezoelectric materials acquire an electrical charge when they are compressed, twisted, or distorted, and similarly, they compress, twist, or distort when an electrical charge is applied to the piezoelectric material. Thus, when an alternating electrical signal is applied to one or more electrodes in contact with the piezoelectric material, a corresponding mechanical signal (i.e., an oscillation or vibration) is transduced therein. Based on the characteristics of the one or more electrodes on the piezoelectric material, the properties of the piezoelectric material, and other factors such as the shape of the acoustic wave device and other structures provided on the device, the mechanical signal transduced in the piezoelectric material exhibits a frequency dependence on the alternating electrical signal. Acoustic wave devices exploit this frequency dependence to provide one or more functions.

[0003] Surface acoustic wave (SAW) devices, such as SAW resonators and SAW filters, are used in many applications such as radio frequency (RF) filters. For example, SAW filters are commonly used in wireless receiver front ends, duplexers, and receive filters. The widespread use of SAW filters is due, at least in part, to the fact that SAW filters exhibit low insertion loss and good rejection, can achieve wide bandwidths, and are a fraction of the size of conventional cavity and ceramic filters. With the continued use of SAW filters in modern RF communication systems, there is a need for SAW filters with sharp transitions between desired passband frequencies and frequencies outside the desired passband, as well as a need to reduce the size of SAW devices while maintaining and / or improving performance. Summary of the invention

[0004] A surface acoustic wave (SAW) device includes a piezoelectric substrate, wherein at least one electrode is located on the top surface of the piezoelectric substrate. The electrode is formed by an electrode stack, and the electrode stack includes a first heavy metal layer formed of a heavy electrode metal and a first conductive layer formed of a conductive material stacked on each other.

[0005] In certain embodiments, the resistivity of the conductive material is less than the resistivity of the heavy electrode metal.

[0006] In certain embodiments, the thickness of the heavy metal layer is greater than 20% of the thickness of the electrode stack.

[0007] In some embodiments, the mass density of the conductive material is greater than 3.0 g / cm 3 .

[0008] In certain embodiments, the heavy electrode material is selected from at least one of the following: platinum (Pt), tungsten (W), gold (Au), iridium (Ir), rhodium (Rh), rhenium (Re), silver (Ag), osmium (Os), ruthenium (Ru), and alloys comprising Pt, W, Au, Ir, Rh, Re, Os, Ru, and Ag.

[0009] In certain embodiments, the conductive material is selected from at least one of the following: copper (Cu), Ag, Au, and an alloy including Cu, Ag, and Au.

[0010] In certain embodiments, the conductive material is selected from at least one of aluminum (Al) and an alloy containing Al.

[0011] In certain embodiments, the SAW device is configured such that:

[0012] ● the resistivity of the conductive material is less than the resistivity of the heavy electrode metal;

[0013] The thickness of the heavy metal layer is greater than 20% of the thickness of the electrode stack; and

[0014] ●The mass density of the conductive material is greater than 3.0 g / cm 3 .

[0015] In some embodiments, the cutting angle of the piezoelectric substrate is in a range of 118 degrees YX to 122 degrees YX.

[0016] In some embodiments, the cutting angle of the piezoelectric substrate is 120 degrees YX.

[0017] In certain embodiments, the piezoelectric substrate is formed of lithium niobate having a cut angle in a range of 118 degrees YX to 122 degrees YX or lithium tantalate having a cut angle in a range of 0-50 degrees.

[0018] In certain embodiments, the SAW device comprises a first piston mode rail and a second piston mode rail, wherein:

[0019] • the at least one electrode comprises a first electrode having a first plurality of fingers and a second electrode having a second plurality of fingers, the first electrode and the second electrode being arranged to provide an interdigital transducer;

[0020] The first piston mode rail extends over lateral ends of the first plurality of fingers; and

[0021] - The second piston mode rail extends over lateral ends of the second plurality of fingers.

[0022] In certain embodiments, the first piston modal rail and the second piston modal rail may each be formed from a heavy piston modal rail material.

[0023] In certain embodiments, a duty cycle associated with the first electrode and the second electrode is at least 55%.

[0024] In certain embodiments, an overcoat may be disposed over the first electrode, the second electrode, and the top surface portion of the piezoelectric substrate, wherein the first piston mode rail and the second piston mode rail reside in the overcoat.

[0025] In some embodiments, the first heavy metal layer is located above the first conductive layer in the electrode stack. The electrode stack may further include a second conductive layer located above the first heavy metal layer. The electrode stack further includes:

[0026] A first adhesion layer between the first conductive layer and the piezoelectric substrate;

[0027] a barrier layer between the first conductive layer and the first heavy metal layer; and

[0028] • A second adhesion layer located on top of the first heavy metal layer.

[0029] In one embodiment, in the electrode stack, the first conductive layer is located above the first heavy metal layer. The electrode stack may include a second heavy metal layer located above the first conductive layer and formed of a heavy electrode material. The electrode stack may include:

[0030] ● a first adhesion layer between the first heavy metal layer and the piezoelectric substrate;

[0031] a barrier layer between the first conductive layer and the first heavy metal layer; and

[0032] • A second adhesion layer located on top of the first conductive layer.

[0033] A method for manufacturing a surface acoustic wave (SAW) device is also provided. The method may include:

[0034] ● providing a piezoelectric substrate; and

[0035] ● Providing at least one electrode, the at least one electrode being located on the top surface of the piezoelectric substrate and being formed by an electrode stack, the electrode stack comprising a first heavy metal layer formed of a heavy electrode metal and a first conductive layer formed of a conductive material stacked on each other.

[0036] On the other hand, any of the aforementioned aspects and / or various individual aspects and features as described herein can be combined to obtain additional advantages. Unless otherwise indicated herein, any of the various features and elements disclosed herein can be combined with one or more other disclosed features and elements.

[0037] In one embodiment, a resonator is provided having a heavy electrode on a piezoelectric substrate and a silicon oxide cap on the heavy electrode, wherein the silicon oxide cap has a thickness exceeding 1.5 periods.

[0038] The resonator may further include a substrate formed of lithium niobate oriented between 118 degrees XY and 122 degrees XY, wherein the heavy electrode is located on the substrate.

[0039] The resonator may further include a substrate formed of lithium niobate oriented between 0 degrees XY and 50 degrees XY, wherein the heavy electrode is located on the substrate.

[0040] The resonator may further include a slow region, wherein a heavy metal is used on the slow region.

[0041] In one embodiment, a resonator is provided having a heavy electrode on top of a piezoelectric substrate and a silicon oxide cover on top of the heavy electrode, wherein the silicon oxide cover is thick enough to keep the acoustic energy on top of the cover small. This avoids the need to leave the top surface free and allows the device to operate in a package without a cavity. Covers with a thickness of more than two periods are suitable. In some cases, a thickness of more than three or four periods is suitable.

[0042] Those skilled in the art will appreciate the scope of the present disclosure and become aware of additional aspects thereof after reading the following detailed description of the preferred embodiments and the associated drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0044] FIG. 1 is a perspective view illustration of a representative surface acoustic wave (SAW) device.

[0045] 2 is a top view of the SAW device of FIG. 1 without the piston mode rail.

[0046] FIG. 3 is a cross-sectional view of a SAW device having a related art electrode stack.

[0047] 4 is a top view of the SAW device of FIG. 1 having a piston mode rail.

[0048] Figure 5 is a cross-sectional view of a SAW device according to a first embodiment of the present disclosure.

[0049] Figure 6 is a cross-sectional view of a SAW device according to a second embodiment of the present disclosure.

[0050] Figure 7 is a top view of a SAW device according to one embodiment of the present disclosure.

[0051] Figure 8 is the speed (v) of the conventional SAW device and the SAW device using the improvement described in this article. s ) versus frequency.

[0052] Fig. 9 is a plot of electrode spacing (P) versus frequency for a conventional SAW device and a SAW device employing the improvements described herein.

[0053] Fig.10 is the total electrostatic capacitance per unit area (C tot / A) Plotted against frequency.

[0054] Fig.11 The conductance (real part of the admittance Re(Y)), admittance (absolute value of the admittance |Y|), and return loss (|S|) of a larger conventional SAW resonator with a 2.47 micron pitch (P) and an approximately 18% shorter resonator with a 2.05 micron pitch (P) and employing the improvements described herein are plotted. 11 |) relative to frequency.

[0055] Fig.12 and Fig.13 Further embodiments are shown in which the electrode stack of the SAW device has more than two main layers, and the conductive metal layers alternate with heavy metal layers.

[0056] Figures 14A-14C 15A-15C are simulations of infinite silicon oxide overlays on different platinum thicknesses. Using different substrate orientations results in different coupling coefficients.

[0057] Fig.16 is a block diagram of user elements in which the concepts of the present disclosure may be employed. DETAILED DESCRIPTION

[0058] The embodiments set forth below represent information necessary to enable those skilled in the art to practice the embodiments and to illustrate the best mode for practicing the embodiments. After reading the following description with reference to the accompanying drawings, those skilled in the art will understand the concepts of the present disclosure and will appreciate the applications of these concepts not specifically set forth herein. It should be understood that these concepts and applications are within the scope of the present disclosure and the appended claims.

[0059] It will be appreciated that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish different elements. For example, without departing from the scope of the present disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the term "and / or" includes any and all combinations of one or more items in the associated listed items.

[0060] It should be understood that when an element such as a layer, a region or a substrate is referred to as being "on another element" or "extending onto another element", it may be directly located on another element or directly extended onto another element, or there may also be an intermediate element. In contrast, when an element is referred to as being "directly located on another element" or "directly extended onto another element", there are no intermediate elements. Similarly, it should be understood that when an element such as a layer, a region or a substrate is referred to as being "located on another element" or "extending on another element", it may be directly located on another element or directly extended on another element, or there may also be an intermediate element. In contrast, when an element is referred to as being "directly located on another element" or "extending directly on another element", there are no intermediate elements. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it may be directly connected or coupled to another element, or there may be an intermediate element. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intermediate elements.

[0061] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe one element, layer or region's relationship to another element, layer or region as illustrated in the figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0062] The terms used herein are only used for the purpose of describing specific embodiments and are not intended to limit the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are also intended to include the plural forms. It should also be understood that when used herein, the terms "comprises", "comprising", "includes", and / or "including" specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0063] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. It will be further understood that, unless expressly defined herein, the terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art, and will not be interpreted in an idealized or overly formal sense.

[0064] The present disclosure relates to a surface acoustic wave (SAW) device, which includes a piezoelectric substrate, wherein at least one electrode is located on the top surface of the piezoelectric substrate. The electrode is formed by an electrode stack, and the electrode stack includes a first heavy metal layer formed of a heavy electrode metal and a first conductive layer formed of a conductive material stacked on each other.

[0065] Before further describing the novel concepts of the present disclosure, a general discussion of SAW devices is provided. FIGS. 1 and 2 are isometric and top views of a representative SAW device 10 of the related art. The SAW device 10 includes a piezoelectric substrate 12, an IDT 16 on the top surface of the piezoelectric substrate 12, a first reflector structure 18A located on the top surface of the piezoelectric substrate 12 adjacent to the IDT 16, and a second reflector structure 18B located on the top surface of the piezoelectric substrate 12 adjacent to the IDT 16 opposite to the first reflector structure 18A. As is well known, the resonator 10 can be connected to other resonators on the die to form a more complex device, such as a filter. In addition, it should be understood that FIGS. 1 and 2 are only simplified representations of SAW resonators. A real resonator may be more complex. For example, the period between the electrodes or their polarity may vary along the transducer. In addition, only a single-port resonator, i.e., a transducer between two reflectors, is shown. It is well known that coupled resonator filters (CRFs) can be designed by inserting several transducers between reflectors, which are connected to separate electrical ports (usually input and output ports). It is well known that several of these CRFs can be connected together or to a single-port resonator to form a device (usually a filter or a duplexer). Even if these devices are not specifically described, it should be understood that they are within the scope of the present disclosure.

[0066] The IDT 16 includes a first electrode 20A and a second electrode 20B, each of which includes a plurality of electrode fingers 22 interlaced with each other as shown. The lateral distance between adjacent electrode fingers 22 of the first electrode 20A and the second electrode 20B defines the electrode pitch P of the IDT 16. The electrode pitch P may at least partially define the center frequency wavelength λ of the SAW device 10, wherein the center frequency is the main frequency of the mechanical waves generated by the IDT 16 in the piezoelectric substrate 12. The finger width W of the adjacent electrode fingers 22 above the electrode pitch P may define the metallization rate or the fill factor (DF) of the IDT 16, which will determine certain operating characteristics of the SAW device 10, as understood by those skilled in the art.

[0067] In operation, the alternating electrical input signal provided at the first electrode 20A is transduced into a mechanical signal in the piezoelectric substrate 12, thereby obtaining one or more acoustic waves therein. In the case of the SAW device 10, the obtained acoustic waves are mostly surface acoustic waves. As discussed above, due to the electrode spacing P, the metallization rate of the IDT 16, the characteristics of the material of the piezoelectric substrate 12, and other factors, the amplitude and frequency of the acoustic waves transduced in the piezoelectric substrate 12 depend on the frequency of the alternating electrical input signal. This frequency dependence is usually described by the change in impedance and / or the phase shift between the first electrode 20A and the second electrode 20B relative to the frequency of the alternating electrical input signal.

[0068] The alternating potential between the first electrode 20A and the second electrode 20B generates an electric field in the piezoelectric material that generates the acoustic wave. The acoustic wave travels at the surface and is eventually transferred back into the electrical signal between the first electrode 20A and the second electrode 20B. The first reflector structure 18A and the second reflector structure 18B reflect the acoustic wave in the piezoelectric substrate 12 back toward the IDT 16 to confine the acoustic wave to the area around the IDT 16. FIG. 2 is a top view of the SAW device 10.

[0069] 3 is a cross-sectional view of a SAW device 10 in which a first electrode 20A and a second electrode 20B are formed by a more conventional electrode stack 24. The conventional electrode stack 24 is shown as having a first adhesion layer 26 on the piezoelectric substrate 12, a conductive metal layer 28 on the first adhesion layer 26, and a second adhesion layer 30 on the conductive metal layer 28. In an exemplary configuration, the first adhesion layer 26 is titanium (Ti), the conductive metal layer 28 is Cu, and the second adhesion layer 30 is Al. The first adhesion layer 26 and the second adhesion layer 30 promote adhesion of adjacent layers. If the piezoelectric substrate is lithium niobate LiNbO3 (LN), the piezoelectric cut angle is typically close to 127 degrees YX. This means that the substrate orientation is defined by starting from a plane whose normal is the Y axis of the crystal and rotating this axis 127 degrees around the X axis of the crystal.

[0070] One or more dielectric overcoats 32 are disposed over the first and second electrodes 20A, 20B and the remainder of the piezoelectric substrate 12. The dielectric overcoat 32 provides a temperature compensation layer to improve temperature stability through its positive temperature coefficient of frequency (TCF), which compensates for the negative TCF of the piezoelectric substrate 12 and other materials in the SAW device 10. The dielectric overcoat 32 may be formed of silicon dioxide (SiO2), doped SiO2, or the like.

[0071] The elongated piston mode rail (PMR) 34 may be buried in the dielectric outer coating 32 or disposed between the dielectric outer coatings 32 in the region extending above the lateral ends of the fingers 22 of the first electrode 20A and the second electrode 20B. The region above which the PMR 34 is disposed is more clearly shown in FIG. 4 , which is a top view of the SAW device 10, wherein the dielectric outer coating 32 is not shown. The function of the PMR 34 is to enable piston mode operation with better lateral mode suppression. A slow region (SR) having a relatively slow acoustic wave velocity is disposed below the PMR 34. A fast region (FR) having a relatively fast acoustic wave velocity is disposed outside the slow region (SR). A main region (MR) is disposed between the slow region (SR) and the fast region (FR). The main region (MR) has a desired acoustic wave velocity, which is generally between the slower and faster acoustic wave velocities of the slow region (SR) and the fast region (FR). The presence of a sufficiently large fast region results in the acoustic wave being guided in the resonator and thus avoiding energy leakage, but also results in the presence of a lateral mode. The presence of the slow region essentially results in one of the guided modes being rectangular in shape and being the only (or almost the only) mode excited. As known to those skilled in the art, there are other implementations that may also achieve the same result. For example, the slow region may be achieved by adding additional metal to the electrodes in region 34 and / or increasing the duty cycle in this region. Several of these implementations may be combined to achieve the desired result.

[0072] A passivation layer 36 may be formed on the dielectric overcoat layer 32 for passivation and / or trimming. The passivation layer 36 may be formed of SiO2, Si3N4, or the like.

[0073] The concepts provided herein provide novel improvements to conventional electrode stacks 24 and the PMR 34 described above. These improvements are first referred to as Figure 5 Described, the figure depicts an exemplary embodiment of an improved SAW device 38. Notably, the conventional electrode stack 24 of the first electrode 20A and the second electrode 20B is replaced by an electrode stack 40 including a heavy metal layer (HML) 42 and a conductive metal layer (CML) 44.

[0074] The heavy metal layer 42 is a layer formed of a heavy electrode material. A heavy electrode material is defined as having a mass density higher than 10.28 g / cm 3 , a metal or alloy that exhibits metallic properties and / or has a certain degree of conductivity. For reference, the mass density of molybdenum (Mo) is 10.28 g / cm 3In one embodiment, the thickness of heavy metal layer 42 is at least 20%, at least 30%, or at least 40% of the total thickness of electrode stack 40. Exemplary but non-limiting heavy electrode materials of heavy metal layer 42 include Pt, W, Au, Ir, Rh, Re, Os, Ru, Ag, or any alloy including Pt, W, Au, Ir, Rh, Re, Os, Ru, and / or Ag. In certain embodiments, the duty factor (DF) of electrodes 20A and 20B is at least 55%, at least 65%, or at least 75%.

[0075] The conductive metal layer 44 is a layer formed of a conductive material, and the conductive material is defined by a metal having a resistivity lower than 1e-7 Ohm*m. In one embodiment, the conductive metal layer 44 is formed of a conductive material having a resistivity lower than that of the heavy electrode material of the heavy metal layer 42. In some embodiments, the mass density of the conductive material of the conductive metal layer 44 is greater than 3.0 g / cm 3 , greater than 5.0g / cm 3 , less than the mass density of the heavy electrode material of the heavy metal layer 42, or a combination thereof. Exemplary but non-limiting conductive materials for the conductive metal layer 44 may include Cu, Ag, Au, Al, or any alloy including Cu, Ag, Au, and / or Al. In some embodiments, the conductive material of the conductive metal layer 44 is more conductive than the heavy electrode material of the heavy metal layer 42. Other options include alloying high mass density metals in the electrode or piston mode rail stack to achieve material hardening to improve robustness and power handling (i.e., alloying Pt by adding Ag, Au, Cu, Co, Cr, Fe, Ga, Ge, In, Mg, Mn, Mo, Ni, Si, Sn, Ta, Ti, V, W, or Zr, etc.).

[0076] As shown, the electrode stack 40 resides on or directly on the piezoelectric substrate 12 with a first adhesion layer 46. The heavy metal layer 42 resides on or directly on the first adhesion layer 46. The barrier layer 48 resides on or directly on the heavy metal layer 42. The conductive metal layer 44 resides on or directly on the barrier layer 48, and the second adhesion layer 50 resides on the conductive metal layer 44.

[0077] The first adhesion layer 46 and the second adhesion layer 50 may be formed of Ti, chromium (Cr), nickel (Ni), etc. or / any alloys thereof, and function to provide good adhesion to adjacent layers. The barrier layer 48 may be formed of Ti, Cr, Ni, etc. or / any alloys thereof, and function to reduce or avoid material diffusion between the heavy metal layer 42 and the conductive metal layer 44 of the electrode stack 40.

[0078] In one exemplary embodiment, the following configuration of the SAW device 38 is provided. It is noted that for the thickness ranges, alternative ranges are provided in parentheses; however, these ranges are exemplary only and are not intended to limit the scope of the present disclosure or the subsequent claims unless otherwise specified. The piezoelectric substrate 12 can be lithium niobate with a cut angle in the range of 118°YX to 122°YX. In one embodiment, the cut angle is 120°YX. The piezoelectric substrate 12 can also be lithium niobate with a cut angle in the range of 0°YX to 50°YX.

[0079] The adhesive layer 46 is in direct contact with the piezoelectric substrate 12 and has a thickness between The heavy metal layer 42 is formed by a thickness of The barrier layer 48 is also formed with a thickness of The conductive metal layer 44 has a thickness of In some embodiments, Cu may be preferred over Al due to its better conductivity and higher mass density; however, other embodiments may use Al. The top adhesion layer 50 is a Cu with a thickness of Ti within the range.

[0080] The dielectric outer coating 32 is a layer having a thickness (as measured from the top of the electrode stack 40 to the bottom of the piston mode rail 52) of The piston mode rail 52 has a thickness of The bottom layer 54 and the top layer 56 are formed by Ti with a thickness of The thickness of the dielectric outer coating 32 on the piston mode rail is in the range of The thickness of the passivation layer 38 is within the range of In addition, it is worth mentioning that the high fill factor (DF) of electrodes 22A and 22B (for example, greater than 50%) is conducive to reducing the size and reducing the resistance of the electrodes in some embodiments. These materials and ranges are also applicable to the embodiments described below.

[0081] The conductive metal layer 44 and the heavy metal layer 42 may be Figure 6 . For this embodiment, the electrode stack 40 is located on the piezoelectric substrate 12 or directly on the piezoelectric substrate with a first adhesion layer 46. The conductive metal layer 44 is lower in the electrode stack 40 and resides on the first adhesion layer 46 or directly on the first adhesion layer. The barrier layer 48 resides on the conductive metal layer 44 or directly on the conductive metal layer. The heavy metal layer 42 resides on the barrier layer 48 or directly on the barrier layer, and the second adhesion layer 50 resides on the conductive metal layer 44.

[0082] As described above, if the piezoelectric substrate 12 is lithium niobate LiNbO3 (LN), the piezoelectric cut angle of the piezoelectric substrate 12 can be changed to 120°YX+ / -2°. A change in the cut angle from 127 degrees YX to about 120 degrees YX is provided to reduce coupling with stray shear horizontal modes. This coupling depends on the substrate orientation and on the electrode and oxide stack. For the previous stack, the stray excitation is reduced for an orientation close to 127 degrees. When heavy electrodes are used, the stray excitation is minimized when the orientation is around 120 degrees.

[0083] In some embodiments, a novel PMR 52 having an enhanced material stack may also be used. The enhanced material stack of the PMR 52 may have one or more layers, wherein one of the layers includes a heavy metal or alloy. In the illustrated embodiment, the PMR 52 has a lower layer 54, an intermediate layer 56 located on or directly on the lower layer 54, and an upper layer 58 located on or directly on the intermediate layer 56. The location of the PMR 52 is generally the same as that of the PMR 34 described above, as shown in FIG. Figure 6 and 7 As shown in .

[0084] In one embodiment, one of the lower layer 54, the middle layer 56, and the upper layer 58 may be formed of a heavy PMR material, which is defined as a metallic material having a mass density greater than the mass density of Ti. In other embodiments, the mass density may be greater than 4.51 g / cm 3 , greater than 5.5 g / cm 3 , greater than 6.5 g / cm 3 or greater than 7.5 g / cm 3 For example, the middle layer 56 may be formed of a heavy PMR material, while the adjacent lower layer 54 and upper layer 58 are adhesion layers. The mass density of the heavy PMR material may be greater than the mass density of the conductive material of the conductive metal layer 44, and less than the mass density of the heavy metal material of the heavy metal layer 42. Exemplary but non-limiting materials of the heavy PMR material include Os, Ir, Pt, Re, W, Au, Ru, Ag, Mo, Cu, Ni, Cr, and Zr, and alloys of these materials.

[0085] Figure 8 is the velocity (v) of the conventional SAW device 10 and the SAW device using the improvements described above for the SAW device 38 at the resonant frequency. s) versus frequency. The vertical lines define the band 12 (B12) frequency range of the Long Term Evolution (LTE) communication standard for mobile communications for transmit uplink (Tx) and receive downlink (Rx) paths. Through the improvements provided herein, the speed of sound waves in the B12 frequency range is reduced by approximately 18%. The reduction in speed means that the size of the SAW device 38 can be reduced.

[0086] Fig. 9 1 is a plot of the electrode spacing (P) of a conventional SAW device 10 and a SAW device employing the improvements described above for SAW device 38 versus frequency. The vertical line defines the band 12 (B12) frequency range. With the improvements provided herein, the spacing of the electrode fingers is reduced by approximately 18%, which directly translates into a reduction in the size of the SAW device 38.

[0087] Fig.10 is the total electrostatic capacitance per unit area (C tot / A) plotted against frequency. Increasing the total capacitance per unit area can achieve the desired capacitance in a smaller area. Through the improvements provided herein, the total capacitance per unit area is increased by 28% in the frequency range of Band 12 (B12).

[0088] Fig.11 The conductance (real part of the admittance Re(Y)), admittance (absolute value of the admittance |Y|), and return loss (|S|) of a larger conventional SAW resonator 10 having a 2.47 micron pitch (P) and an approximately 18% shorter resonator having a 2.05 micron pitch (P) and employing the improvements described above are plotted. 11 |) vs. frequency. The 18% reduction in pitch affects both the longitudinal and lateral directions since everything scales with pitch. The total area of ​​the resonator will be reduced by about 33% (1-0.82*0.82). For completeness and accuracy, the required area for a specific capacitor is determined by the capacitance per unit area of ​​each resonator and may differ from a rough estimate based on speed / pitch.

[0089] The reflectivity of the electrode defines a stopband where the wave is reflected. For a synchronous resonator, the lower edge of this stopband is very close to the resonant frequency. The upper edge of the stopband can cause spurious, which can be seen on the conductance. With the improved but smaller SAW device 38, the reflectivity is significantly improved, while the coupling and return losses are similar. Higher reflectivity (Re) is beneficial because the upper stopband edge moves higher in the frequency range and is further away from the series and parallel resonant frequencies. In fact, using a smaller SAW device 38 including the enhancements described herein, the out-of-band (OOB) losses are significantly better (i.e., lower).

[0090] Fig.12 and Fig.13 Additional embodiments are shown in which the electrode stack 40 of the SAW device 38 has more than two main layers, with conductive metal layers 44 alternating with heavy metal layers 42 . Fig.12 An electrode stack 40 is provided in which one conductive metal layer 44 is disposed between two heavy metal layers 42. One barrier layer 48 is disposed between the upper heavy metal layer 42 and the conductive layer 44, and another barrier layer 48 is disposed between the lower heavy metal layer 42 and the conductive metal layer 44. Adding the upper heavy metal layer 42 can promote better small signal performance and manufacturability (e.g., for frequency fine tuning), and provide better large signal performance, greater power handling capability, longer service life, and less nonlinearity.

[0091] Fig.13 An electrode stack 40 is provided in which one heavy metal layer 42 is disposed between two conductive metal layers 42. One barrier layer 48 is disposed between the upper conductive metal layer 44 and the heavy metal layer 42, and another barrier layer 48 is disposed between the lower conductive metal layer 44 and the heavy metal layer 42.

[0092] The need for cavity packaging can be suppressed by using a sufficiently thick dielectric cover. If this is the case, the acoustic energy is located at the interface between the piezoelectric substrate and the cover. Typical cover thickness is greater than 1λ or two electrode periods. In some embodiments, the cover thickness is greater than 1.5λ. In this case, electrodes heavy enough can be selected to reduce the resonant frequency to below the overall cutoff frequency and the cover cutoff frequency. In this case, the solution described for the temperature compensated SAW (TC-SAW) device is effective. For example, electrodes containing heavy material films and conductive material films (such as platinum-aluminum or platinum-copper) or other options using tungsten or molybdenum are exemplary solutions. In order to suppress lateral modes, piston mode resonators are also possible, but heavy materials for slow regions may be required. Materials such as copper, platinum, tungsten or gold are good materials. When using lithium niobate (LN), an orientation close to 120° is a beneficial orientation. Alternating orientations between Y and Y+50 provide greater coupling coefficients, but are more sensitive to stray modes.

[0093] Figures 14A-14C 15A-15C provide periodic simulations of infinite silicon oxide coverage and various platinum thicknesses. The electrodes are made of platinum film and 1550A thick aluminum film. A thin titanium layer is used as an adhesion layer between the substrate and the electrode and between the platinum and the aluminum. The electrode period is 1.6um and the duty cycle is 50%. As in Figures 14A-14CThe solid curves shown in 15A-15C represent the admittance, and the dashed curves represent the conductance. The frequencies with non-zero conductance (above about 1.1 GHz) are above the silicon dioxide cutoff frequency, meaning that most of the energy is lost in the oxide. The use of thick electrodes allows the resonant frequency to be lowered below the cutoff frequency. For Figures 14A-14C , the lithium niobate orientation is about Y+120 degrees (e.g., between 118 and 122 degrees), and the coupling coefficient is about 8% for platinum thicknesses of 3500 angstroms, 4000 angstroms, and 4500 angstroms. This orientation provides a spurious-free response. Figures 15A-15C , the lithium niobate orientation is about Y+8, and the coupling coefficient is about 16% for platinum thicknesses of 3500 angstroms, 4000 angstroms, and 4500 angstroms. This orientation also provides a spurious-free response for these metal stacks. Solutions when the lithium niobate orientation is Y 0 degrees to 50 degrees are also beneficial. Depending on the metal stack, duty cycle, and cover material, the spurious-free orientation varies within this 0 degree to 50 degree range.

[0094] In certain embodiments, a resonator is provided with a heavy electrode having a silicon oxide capping with a thickness exceeding 1.5, 2, 3, or 4 periods. The lithium niobate orientation may be about 120 degrees, between 0 and 50 degrees, etc. Further, the heavy metal may be disposed in the slow region (e.g., piston mode resonator).

[0095] refer to Fig.16 , the concepts described above can be implemented in various types of user elements 100 such as mobile terminals, smart watches, tablet computers, computers, navigation devices, access points, and similar wireless communication devices that support wireless communications such as cellular, wireless local area network (WLAN), Bluetooth, and near field communication. The user element 100 will generally include a control system 102, a baseband processor 104, a transmission circuit system 106, a reception circuit system 108, an antenna switching circuit system 110, a plurality of antennas 112, and a user interface circuit system 112. In a non-limiting example, the control system 102 can be a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). In this regard, the control system 102 can include at least a microprocessor, an embedded memory circuit, and a communication bus interface. The reception circuit system 108 receives radio frequency signals from one or more base stations via the antenna 112 and through the antenna switching circuit system 110. The low noise amplifier and filter of the reception circuit system 108 cooperate to amplify and eliminate broadband interference from the received signal for processing. Downconversion and digitization circuitry (not shown) then downconverts the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams using an analog-to-digital converter (ADC).

[0096] The baseband processor 104 processes the digitized received signal to extract the information or data bits transmitted in the received signal. This processing typically includes demodulation, decoding, and error correction operations, which will be discussed in more detail below. The baseband processor 104 is typically implemented in one or more digital signal processors (DSPs) and application specific integrated circuits (ASICs).

[0097] For transmission, the baseband processor 104 receives digitized data that may represent voice, data, or control information from the control system 102, and the baseband processor encodes the digitized data for transmission. The encoded data is output to the transmit circuit system 106, where a digital / analog converter (DAC) converts the digitally encoded data into an analog signal, and a modulator modulates the analog signal onto a carrier signal at a desired transmit frequency or frequencies. The power amplifier amplifies the modulated carrier signal to a level suitable for transmission, and delivers the modulated carrier signal to the antenna 112 through the antenna switching circuit system 110. Multiple antennas 112 and duplicate transmit circuit systems 106 and receive circuit systems 108 can provide spatial diversity. Those skilled in the art will understand the modulation and processing details. The SAW device 10, 38 is particularly useful in filters, duplexers, and N-in-1 multiplexers, which can be provided in the antenna switching circuit system 110, the receive circuit system 108, and / or the transmit circuit system 106.

[0098] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered to be within the scope of the concepts disclosed herein and the claims below.

Claims

1. A surface acoustic wave (SAW) device comprising: Piezoelectric substrate; At least one electrode is located on the top surface of the piezoelectric substrate and is formed of an electrode stack including a first heavy metal layer formed of a heavy electrode metal and a first conductive layer formed of a conductive material stacked on each other. 2 . The SAW device according to claim 1 , wherein the resistivity of the conductive material is lower than the resistivity of the heavy electrode metal. 3 . The SAW device of claim 1 , wherein a thickness of the heavy metal layer is greater than 20% of a thickness of the electrode stack.

4. The SAW device of claim 1, wherein the mass density of the conductive material is greater than 3.0 g / cm 3 .

5. The SAW device of claim 1, wherein the heavy electrode material is selected from at least one of the following: Pt, W, Au, Ir, Rh, Re, Os, Ru, Ag, and an alloy comprising Pt, W, Au, Ir, Rh, Re, Os, Ru, and Ag. 6 . The SAW device of claim 1 , wherein the conductive material is selected from at least one of the following: Cu, Ag, Au, and an alloy including Cu, Ag, and Au. The SAW device according to claim 1 , wherein the conductive material is selected from at least one of Al and an alloy including Al.

8. The SAW device of claim 1, wherein: The resistivity of the conductive material is less than the resistivity of the heavy electrode metal; The thickness of the heavy metal layer is greater than 20% of the thickness of the electrode stack; and The mass density of the conductive material is greater than 3.0 g / cm 3 .

9. The SAW device of claim 8, wherein: The heavy electrode material is selected from at least one of the following: Pt, W, Au, Ir, Rh, Re, Os, Ru, Ag, and an alloy comprising Pt, W, Au, Ir, Rh, Re, Os, Ru, and Ag; and The conductive material is selected from at least one of the following: Cu, Ag, Au, and an alloy containing Cu, Ag, and Au. 10 . The SAW device according to claim 9 , wherein a cut angle of the piezoelectric substrate is in a range of 118 degrees YX to 122 degrees YX.

11. The SAW device according to claim 10, wherein the cut angle of the piezoelectric substrate is 120 degrees YX.

12. The SAW device of claim 1, further comprising a first piston mode rail and a second piston mode rail, wherein: The at least one electrode comprises a first electrode having a first plurality of fingers and a second electrode having a second plurality of fingers, the first electrode and the second electrode being arranged to provide an interdigital transducer; the first piston mode rail extending over lateral ends of the first plurality of fingers; and The second piston mode rail extends over lateral ends of the second plurality of fingers.

13. The SAW device of claim 12, wherein the first piston mode rail and the second piston mode rail are each formed of a heavy piston mode rail material.

14. The SAW device of claim 13, wherein a duty cycle associated with the first electrode and the second electrode is at least 55%.

15. The SAW device of claim 13, further comprising an overcoat layer over the first electrode, the second electrode, and a portion of the top surface of the piezoelectric substrate, wherein the first and second piston mode rails reside in the overcoat layer. 16 . The SAW device according to claim 1 , wherein a cut angle of the piezoelectric substrate is in a range of 118 degrees YX to 122 degrees YX.

17. The SAW device of claim 16, wherein the piezoelectric substrate is formed of lithium niobate.

18. The SAW device according to claim 1, wherein a cutting angle of the piezoelectric substrate is 120 degrees YX.

19. The SAW device of claim 1, wherein in the electrode stack, the first heavy metal layer is located above the first conductive layer.

20. The SAW device of claim 19, the electrode stack further comprising a second conductive layer located above the first heavy metal layer.

21. The SAW device of claim 19, wherein the electrode stack further comprises: a first adhesion layer between the first conductive layer and the piezoelectric substrate; a barrier layer between the first conductive layer and the first heavy metal layer; and A second adhesion layer is located on the first heavy metal layer.

22. The SAW device of claim 1, wherein in the electrode stack, the first conductive layer is located above the first heavy metal layer.

23. The SAW device of claim 22, wherein the electrode stack further comprises a second heavy metal layer located on the first conductive layer and formed of a heavy electrode material.

24. The SAW device of claim 22, wherein the electrode stack further comprises: a first adhesion layer between the first heavy metal layer and the piezoelectric substrate; a barrier layer between the first conductive layer and the first heavy metal layer; and A second adhesion layer is located on the first conductive layer.

25. The SAW device of claim 1, wherein in the electrode stack, the first heavy metal layer is located above the first conductive layer, and the electrode stack further comprises: a second conductive layer located on the first heavy metal layer; a first adhesion layer between the first conductive layer and the piezoelectric substrate; a first barrier layer between the first conductive layer and the first heavy metal layer; a second barrier layer between the first heavy metal layer and the second conductive layer; as well as A second adhesion layer is located on the second conductive layer.

26. The SAW device of claim 1, wherein in the electrode stack, the first conductive layer is located above the first heavy metal layer, and the electrode stack further comprises: a second heavy metal layer located on the first conductive layer and formed of a heavy electrode material; a first adhesion layer between the first heavy metal layer and the piezoelectric substrate; a first barrier layer between the first conductive layer and the first heavy metal layer; a second barrier layer between the second heavy metal layer and the first conductive layer; as well as A second adhesion layer is located on the second heavy metal layer.

27. The SAW device of claim 1, wherein a cut angle of the piezoelectric substrate is in a range of 0 degrees YX to 50 degrees YX.

28. The SAW device of claim 27, wherein the piezoelectric substrate is formed of lithium tantalate.

29. A method for manufacturing a surface acoustic wave (SAW) device, the method comprising: providing a piezoelectric substrate; and At least one electrode is provided, the at least one electrode being located on a top surface of the piezoelectric substrate and being formed of an electrode stack including a first heavy metal layer formed of a heavy electrode metal and a first conductive layer formed of a conductive material stacked on each other.

30. A resonator comprising a heavy electrode on a piezoelectric substrate and a silicon oxide cap on the heavy electrode, wherein the silicon oxide cap has a thickness exceeding 1.5 periods.

31. The resonator of claim 30, further comprising a substrate formed of lithium niobate oriented between 118 degrees XY and 122 degrees XY, wherein the heavy electrode is located above the substrate.

32. The resonator of claim 30, further comprising a substrate formed of lithium niobate oriented between 0 degrees XY and 50 degrees XY, wherein the heavy electrode is located above the substrate.

33. The resonator of claim 30, further comprising a slow region, wherein a heavy metal is used on the slow region.

34. A resonator comprising a heavy electrode on a piezoelectric substrate and a silicon oxide cap on the heavy electrode, wherein the silicon oxide cap has a thickness exceeding 2 periods.

35. A resonator comprising a heavy electrode on a piezoelectric substrate and a silicon oxide cap on the heavy electrode, wherein the silicon oxide cap has a thickness exceeding 3 periods.

36. A resonator comprising a heavy electrode on a piezoelectric substrate and a silicon oxide cap on the heavy electrode, wherein the silicon oxide cap has a thickness exceeding 4 periods.

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