Patent ID: 12255600

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following description of certain embodiments presents various descriptions of specific embodiments. However, the innovations described herein can be embodied in a multitude of different ways, for example, as defined and covered by the claims. In this description, reference is made to the drawings where like reference numerals can indicate identical or functionally similar elements. It will be understood that elements illustrated in the figures are not necessarily drawn to scale. Moreover, it will be understood that certain embodiments can include more elements than illustrated in a drawing and/or a subset of the elements illustrated in a drawing. Further, some embodiments can incorporate any suitable combination of features from two or more drawings.

Acoustic wave filters can filter radio frequency (RF) signals in a variety of applications, such as in an RF front end of a mobile phone. An acoustic wave filter can be implemented with surface acoustic wave (SAW) devices. The SAW devices include SAW resonators, SAW delay lines, and multi-mode SAW (MMS) filters (e.g., double mode SAW (DMS) filters).

A manufacturing process for a SAW device can include a photolithography process. In certain photolithography processes, some undesirable effects can occur. For example, light used in the photolithography process can reflect back, which can cause standing waves and/or swing curves. For SAW resonators that include an interdigital transducer (IDT) electrode with a relatively high reflectivity material, such as an aluminum IDT electrode, reflection from the IDT electrode is relatively high. Reflection from aluminum IDT electrode layers has presented technical challenges in manufacturing IDT electrode patterns with certain line widths in a photolithography process.

One approach to eliminate and/or mitigate such undesirable effects is to include an anti-reflection material over the aluminum IDT electrode layer. An anti-reflection epoxy resin film can suppress the reflectivity of an aluminum layer. Fixing properties of an epoxy resin anti-reflection film can involve a heating process. However, in such a heating process, the aluminum IDT electrode layer can react with the anti-reflection film to form a compound layer with carbon and aluminum. The thickness of the compound layer can be about 10 nanometers (nm) to 20 nm. This thickness can be about 10% to 15% of the thickness of the aluminum IDT electrode. The compound layer can be sparse and a wiring resistance value measured using a resistance wire test (also referred to as a wiring resistance measurement) with this structure can increase about 10% compared to a similar structure without an anti-reflection resin film. The surface of an aluminum IDT electrode with the compound film can be rough. The compound film can contribute to filter loss and/or larger frequency distribution due to the variable thickness of the compound layer with aluminum and resin throughout a wafer.

Aspects of this disclosure relate to an anti-reflection film over an IDT electrode layer of an acoustic wave device. For example, a SAW resonator can include a piezoelectric layer, an IDT electrode over the piezoelectric layer, and an anti-reflection layer over the IDT electrode. The anti-reflection layer can include silicon. For example, the anti-reflection layer can be a silicon oxynitride layer or an amorphous silicon layer. Anti-reflection layers disclosed herein can be free from material of an IDT electrode layer in contact with the anti-reflection layer. With such an anti-reflection layer, the wiring resistance value can be substantially the same as a similar structure without an anti-reflection layer. The anti-reflection layer can have a thickness that causes the reflectivity to satisfy a threshold. With anti-reflection layers disclosed herein, IDT electrodes of acoustic wave resonators can be patterned with line widths in a range from 0.25 micrometers (μm) to 0.4 μm in a photolithography process without significant electrical degradation in filters that include such acoustic wave resonators.

Although embodiments may be discussed with reference to SAW resonators, any suitable principles and advantages discussed herein can be applied to any suitable SAW device and/or any other suitable acoustic wave device. Embodiments will now be discussed with reference to drawings. Any suitable combination of features of the embodiments disclosed herein can be implemented together with each other.

FIG.1Aillustrates a cross section of a surface acoustic wave resonator structure at a stage of a manufacturing process. The manufacturing process may include a photolithography process. The illustrated SAW resonator structure inFIG.1Aincludes a piezoelectric layer10, an interdigital transducer (IDT) electrode12over the piezoelectric layer10, an anti-reflection epoxy resin film14over the IDT electrode12, and a resist film16over the epoxy resin film14. The IDT electrode12has an upper surface12ain contact with the epoxy resin film14. The epoxy resin film14is subjected to a heat processing to fix its properties in another stage in the manufacturing process. The epoxy resin film14is heated prior to removing the resist film16. The resist film16gets removed later at a later stage in the manufacturing process. For example, the manufacturing process can include: (1) depositing an IDT electrode material layer on the piezoelectric layer10; (2) coating the anti-reflection epoxy resin film14on the IDT electrode material layer; (3) coating the resist film16on the anti-reflection epoxy resin film14; (4) patterning the resist film16; (5) etching the IDT electrode material layer to form the IDT electrode12; and (6) removing the resist film16. The anti-reflection epoxy resin film14can mitigate and/or eliminate back reflection of light from the IDT electrode12during the photolithography process. As discussed below, this reduction of a reflectivity of the IDT electrode12can make a line width range smaller.

FIG.1Billustrates a cross section of a surface acoustic wave resonator1formed using the surface acoustic wave resonator structure illustrated inFIG.1A. The illustrated SAW resonator1includes the piezoelectric layer10, the IDT electrode12over the piezoelectric layer10, a compound layer14′ over the IDT electrode12, and a temperature compensation layer18over the compound layer14′.

The piezoelectric layer10may include any suitable piezoelectric material, such as a lithium niobate (LN) layer or a lithium tantalate (LT) layer. A thickness t1of the piezoelectric layer10can be selected based on a wavelength λ or L of a surface acoustic wave generated by the surface acoustic wave resonator1in certain applications. The IDT electrode12has a pitch that sets the wavelength λ or L of the surface acoustic wave resonator1.

The IDT electrode12can be an aluminum (Al) IDT electrode. The IDT electrode12has a thickness t2. In some embodiments, the thickness t2of the IDT electrode12can be about 0.05 L. For example, when the wavelength L is 4 μm, the thickness t2can be 200 nm.

The compound layer14′ is formed when the epoxy resin film14is heated and/or the resist film16is heated. Carbon included in the resist film16can react with a material (e.g., aluminum) of the IDT electrode12when heated, forming a compound that includes the material (e.g., aluminum) and carbon. Due to this reaction, relative heights of an upper surface14a′ of the compound layer14′ inFIG.1Band an upper surface12aof the IDT electrode inFIG.1Acan be approximately the same. The compound layer14′ has a thickness t3. The thickness t3may vary along its width. The thickness t3of the compound layer14′ may depend at least on a thickness of the epoxy resin layer14and/or a duration of the heat processing. The thickness t3of the compound layer14′ can be, for example, in a range from 10 nm to 20 nm. The thickness t3of the compound layer14′ can be, for example, in a range from 10% to 15% of thickness t2of the IDT electrode12.

A final thickness t2′ of the IDT electrode12may be different from the original IDT electrode thickness t2. For example, the final thickness t2′ of the IDT electrode12can be approximately the thickness t2of the original thickness minus the thickness t3of the compound layer14′. In certain embodiments, the final thickness t2′ can be about 180 nm. However, the IDT electrode12may be designed to have a thicker original thickness t2such that the final thickness t2′ after the formation of the compound layer14′ can be about 200 nm or about 0.05 L.

The temperature compensation layer18can include any suitable material. For example, the temperature compensation layer18can be a silicon dioxide (SiO2) layer. The temperature compensation layer18can bring the temperature coefficient of frequency (TCF) of the SAW resonator1closer to zero relative to a similar SAW resonator without the temperature compensation layer18. The temperature compensation layer18has a thickness t4.

FIG.2Aillustrates a cross section of a surface acoustic wave resonator structure at a stage of a manufacturing process according to an embodiment. The manufacturing process can include a photolithography process. The illustrated SAW resonator structure ofFIG.2Aincludes a piezoelectric layer10, an interdigital transducer (IDT) electrode12over the piezoelectric layer10, an anti-reflection layer20over the IDT electrode12, and a resist film16over the anti-reflection layer20. The resist film16can be removed at a later stage in the manufacturing process. For example, the manufacturing process can include: (1) depositing an IDT electrode material layer on the piezoelectric layer10; (2) forming the anti-reflection layer20on the IDT electrode material layer; (3) coating the resist film16on the anti-reflection layer20; (4) patterning the resist film16; (5) etching the IDT electrode material layer to form the IDT electrode12; and (6) removing the resist film16.

The anti-reflection layer20can include silicon. For example, the anti-reflection layer20can be silicon (Si), silicon oxynitride (SiON), amorphous silicon (a-Si), silicon dioxide (SiO2), or another suitable silicon compound. The anti-reflection layer20can be a material that is similar to silicon dioxide. In certain instances, the anti-reflection layer20can include a non-silicon material that sufficiently mitigates back reflection in a photolithography process and does not react (e.g., does not form a compound) with the IDT electrode12. In certain applications, the anti-reflection material can be any suitable material having a reflectivity of 0.3 or less for light having a wavelength of 365 nm. According to some such applications, the anti-reflection material can be any suitable material having a reflectivity of 0.2 or less for light having a wavelength of 365 nm. For example, the reflectivity can be in between 0.01 to 0.2, in some embodiments. In some embodiments, the anti-reflection layer20does not include carbon.

FIG.2Billustrates a cross section of a surface acoustic wave resonator2formed using the surface acoustic wave resonator structure illustrated inFIG.2Aaccording to an embodiment. The SAW resonator2and other SAW resonators with a similar temperature compensation layer can be referred to as a temperature compensated SAW (TC-SAW) resonator.

The illustrated SAW resonator2includes the piezoelectric layer10, the IDT electrode12over the piezoelectric layer10, the anti-reflection layer20over the IDT electrode12, and a temperature compensation layer18over the anti-reflection layer20. The SAW resonator2illustrated inFIG.2Bincludes some generally similar features to the SAW resonator1illustrated inFIG.1B. However, unlike the SAW resonator1, the SAW resonator2does not include the compound layer14′ and includes the anti-reflection layer20. Unlike the anti-reflection epoxy resin film14ofFIG.1A, the anti-reflection layer20does not react with the IDT electrode12. Accordingly, the anti-reflection layer20is distinct from the material of the IDT electrode12. The anti-reflection layer20is free from material of the IDT electrode12. In some embodiments, the chemical properties of the anti-reflection layer20can be the same inFIGS.2A and2B.

An upper surface20aof the anti-reflection layer20opposite the IDT electrode12can be relatively flat in the surface acoustic wave device2. A surface roughness of the upper surface20aof the anti-reflection layer20can be about 3.5 nm. In some embodiments, the roughness of the upper surface20acan be in a range from, for example, 3 nm to 4 nm. In some embodiments, the roughness of the upper surface20acan be less than, for example, 4.5 nm. The smoother and/or flatter surface of upper surface20aof the anti-reflection layer20opposite the IDT electrode12relative to the upper surface14a′ of the anti-reflection layer14′ ofFIG.1Bcan result in less variation in resistance and less electrical degradation in a filter.

The piezoelectric layer10may include any suitable piezoelectric material, such as a lithium niobate (LN) layer or a lithium tantalate (LT) layer. A thickness t1of the piezoelectric layer10can be selected based on a wavelength λ or L of a surface acoustic wave generated by the surface acoustic wave resonator2in certain applications. The IDT electrode12has a pitch that sets the wavelength λ or L of a surface acoustic wave generated by the surface acoustic wave device2. The piezoelectric layer10can be sufficiently thick to avoid significant frequency variation.

The IDT electrode12can be an aluminum (Al) IDT electrode. The IDT electrode12may include any other suitable IDT material. For example, the IDT electrode12may include copper (Cu), magnesium (Mg), titanium (Ti), etc. The IDT electrode12may include alloys, such as AlMgCu, AlCu, etc. The IDT electrode12can include a conductive layer that has a reflectivity of at least 0.3 for light having a wavelength of 365 nanometers. The IDT electrode12can include a conductive layer that has a reflectivity of at least 0.5 for light having a wavelength of 365 nanometers. The IDT electrode12can include a conductive layer that has a reflectivity of at least 0.75 for light having a wavelength of 365 nanometers. As shown inFIG.7, the IDT electrode can be a multi-layer IDT in certain embodiments.

The IDT electrode12has a thickness t2. In some embodiments, the thickness t2of the IDT electrode12can be about 0.05 L. For example, when the wavelength L is 4 μm, the thickness t2can be 200 nm. Unlike the embodiment illustrated inFIG.1B, the original thickness and the final thickness of the IDT electrode12can be the same or very similar in the embodiment inFIGS.2A and2B. The thickness t5of the anti-reflection layer20can be in a range from, for example, 0.004 L to 0.06 L or 8 nm to 240 nm. The thickness t2of the IDT electrode12can be about 0.05 L. For example, when the wavelength L is 4 μm, the thickness t2can be 200 nm.

The anti-reflection layer20can have a thickness t5. The thickness t5can vary for different materials used for the anti-reflection layer20. Also, the determination of the thickness t5can be based at least in part on reflectivity of the anti-reflection layer20and/or line widths, for instance, as explained below with respect toFIGS.4A to6. For example, when the anti-reflection layer20is an amorphous silicon layer, the thickness t5can be about 9 nm (e.g., 0.00225 L when the wavelength L is 4 μm), which can give a reflectivity of 0.07 in some embodiments. For example, when the anti-reflection layer20is a silicon oxynitride layer, the thickness t5can be about 110 nm, which can give a reflectivity of 0.17 in some embodiments.

The temperature compensation layer18can include any suitable material. For example, the temperature compensation layer18can be a silicon dioxide (SiO2) layer. The temperature compensation layer18can be a layer of any other suitable material having a positive temperature coefficient of frequency. For instance, the temperature compensation layer18can be a tellurium dioxide (TeO2) layer or a silicon oxyfluoride (SiOF) layer in certain applications. A temperature compensation layer can include any suitable combination of SiO2, TeO2, and/or SiOF.

The temperature compensation layer18can bring the temperature coefficient of frequency (TCF) of the SAW resonator2closer to zero relative to a similar SAW resonator without the temperature compensation layer18. The temperature compensation layer18together with a lithium niobate piezoelectric layer can improve the electromechanical coupling coefficient (k2) of the SAW resonator2relative to a similar SAW resonator with a lithium tantalate piezoelectric layer and without the temperature compensation layer18. Improved k2of the temperature compensation layer18can be more pronounced when the SAW resonator2includes a lithium niobate layer as the piezoelectric layer10. In certain embodiments, for example, as illustrated inFIGS.8B and8C, the temperature compensation layer18may be omitted.

The temperature compensation layer18has a thickness t4. In some embodiments, the thickness t4of the temperature compensation layer18can be in a range from 0.1 L to 0.5 L. For example, when the wavelength L is 4 μm, the thickness t4of the temperature compensation layer14can be 1200 nm.

FIG.3Ais a graph of a reference wiring resistance measurement and a wiring resistance measurement of the SAW resonator1illustrated inFIG.1B. A wiring resistance can be measured using a resistance wire test. A wiring resistance can also be referred to as an IDT resistance or electrode resistance. The reference wiring resistance can be a wiring resistance of a SAW resonator that does not include an anti-reflective material over an IDT electrode. The wiring resistance of the SAW resonator1is about 1.09 (e.g., 9% increase from the reference wiring resistance). This can result from the compound layer14′ degrading the performance of the SAW resonator1as compared to the reference SAW resonator that does not include the anti-reflective material.

FIG.3Bis a graph of a reference wiring resistance measurement and a wiring resistance measurement of the SAW resonator2illustrated inFIG.2B. The wiring resistance of the SAW resonator2is substantially the same or very similar to the reference wiring resistance. In other words, the anti-reflection layer20does not noticeably degrade the wiring resistance of the SAW resonator2as compared to the reference SAW resonator. Therefore, the SAW resonator2illustrated inFIG.2Bmay be a more desirable than the SAW resonator1illustrated inFIG.1Bin certain applications. The anti-reflection film20of the surface acoustic wave resonator2ofFIG.2Bcan contribute less than 2% of wiring resistance.

FIG.4Ais a graph of ellipsometer measurement results of reflectivity of an epoxy resin layer, a silicon oxynitride (SiON) layer, and an amorphous silicon (a-Si) layer for various thicknesses at a wavelength of 365 nm. These layers were deposited on a silicon substrate and then reflectivity was measured. The graph indicates that the thickness of these anti-reflection layers impacts reflectivity. A reflectivity of 1 can mean that 100% of light emitted from a light source is reflected back. A reflectivity of 0 can mean that 0% of the light emitted from the light source is reflected. A first measurement result30is a result of reflectivity of the epoxy resin layer. A second measurement result32is a result of the SiON layer. A third measurement result34is a result of the a-Si layer. The first result30shows that the reflectivity is between about 0.1 and about 0.15 for thicknesses of the epoxy resin layer larger than about 50 nm.

FIG.4Bis a table with the lowest reflectivity values of the second and third results32and34, respectively, ofFIG.4A. The second result32indicates that the lowest reflectivity can be obtained when the SiON layer has a thickness of about 110 nm. The third result34indicates that the lowest reflectivity can be obtained when the a-Si layer has a thickness of about 9 nm. The reflectivity of the anti-reflection layer can depend on a combination of a material of the anti-reflection layer and a thickness of the anti-reflection layer. The thickness of the anti-reflection layer can be selected to achieve a reflectivity that is no greater than a threshold value. For instance, the thickness of the anti-reflection layer can be selected such that the reflectivity is 0.2 or less for a given material of the anti-reflection layer.FIG.4Aindicates that a reflectivity of less than about 0.2 can be obtained with an amorphous silicon anti-reflection layer with a thickness in a range from about 5 nm to about 15 nm.FIG.4Aindicates that a reflectivity of less than about 0.2 can be obtained with an silicon oxynitride anti-reflection layer with a thickness in a range from about 105 nm to about 115 nm.

FIG.5Ais a graph of measurement results of line widths for different resist thicknesses of a resist film of a SAW resonator structure used in a lithography process. The SAW resonator structure used in the simulation ofFIG.5Adoes not include an anti-reflection layer between its IDT electrode and the resist film. A line width range r1from a bottom side to a top side of the measurement curve can be observed from this graph. The line width range r1of the measurement results ofFIG.5Ais about 0.15 nm.

FIG.5Bis a graph of measurement results of line widths for different resist thicknesses of a resist film of a SAW resonator structure used in a lithography process. The SAW resonator structure used in the measurement of FIG.5B includes an epoxy resin layer between its IDT electrode and the resist film. A line width range r2from a bottom side to a top side of the measurement curve can be observed from this graph. The line width range r2of the measurement results ofFIG.5Bis about 0.05 nm.

FIG.5Cis a graph of measurement results of line width values for different resist thicknesses of a resist film of a SAW resonator structure according to an embodiment used in a lithography process. The SAW resonator structure used in the measurement ofFIG.5Cincludes an amorphous silicon (a-Si) layer between its IDT electrode and the resist film. A line width range r3from a bottom side to a top side of the measurement curve can be observed from this graph. The line width range r3of the measurement results ofFIG.5Cis about 0.05 nm.

FIG.5Dis a graph of measurement results of line width values for different resist thicknesses of a resist film of a SAW resonator structure according to an embodiment used in a lithography process. The SAW resonator structure used in the measurement ofFIG.5Dincludes a silicon oxynitride (SiON) layer between its IDT electrode and the resist film. A line width range r4from a bottom side to a top side of the measurement curve can be observed from this graph. The line width range r4of the measurement results ofFIG.5Dis about 0.1 nm.

FIG.6is a graph of fit curves (also referred to as swing curves) of data points at the bottom sides of the measurement results curves illustrated inFIGS.5A-5D. The graph shows normalized line width in nanometer on y-axis and normalized resist thickness in nanometer on x-axis. These results may be used in determining the thickness t5of the anti-reflection layer20ofFIGS.2A and2Bthat meets a desired specification.

For example, a specification for a SAW resonator may specify a resist thickness variation to be within 1% (e.g., +/−1% or a total variation of 2%), a frequency shift to be below 1 megahertz (MHz) at a frequency of 2 gigahertz (GHz), and a frequency shift sensitivity to be 0.85 MHz/nm. This specification can be for a Band 25 filter. In such specification, at a frequency (f) of 2 GHz and velocity (V) of 4000 m/s, line width can be calculated to be 0.5 μm. Also, to satisfy such specification, the line width distribution should be lower than about 1.18 nm (1 MHz frequency shift/0.85 MHz/nm frequency shift sensitivity), which is about 0.236% of the line width. Accordingly, with a line width distribution of 0.2% or less, stringent SAW resonator specifications can be met.

FIG.7illustrates a cross section of a surface acoustic wave resonator3according to an embodiment. The illustrated SAW resonator3includes a piezoelectric layer10, an interdigital transducer (IDT) electrode12′ over the piezoelectric layer10, an anti-reflection layer20over the IDT electrode12′, and a temperature compensation layer18over the anti-reflection layer20. The SAW resonator3illustrated inFIG.7is generally similar to the SAW resonator2illustrated inFIG.2B. However, unlike the SAW resonator2, the IDT electrode12′ of the SAW resonator3is a multi-layer IDT electrode (e.g., includes two layers). As illustrated, the IDT electrode12′ includes an upper layer24and a lower layer22positioned between the upper layer24and the piezoelectric layer10. The upper layer24can be an aluminum layer. The lower layer22can be a molybdenum layer, a tungsten layer, a gold layer, a tantalum layer, a platinum layer, a silver layer, or a ruthenium layer, for example. SAW resonators can include a multi-layer IDT electrode that includes three or more layers in some other embodiments. Any suitable principles and advantages disclosed herein can be applied to single layer IDT electrodes or multi-layer IDT electrodes that include two or more IDT layers.

FIG.8Aillustrates a cross section of a surface acoustic wave resonator4according to an embodiment. The illustrated SAW resonator4includes a support layer26, a piezoelectric layer10over the support layer26, an IDT electrode12over the piezoelectric layer10, an anti-reflection layer20over the IDT electrode12, and a temperature compensation layer18over the anti-reflection layer20.FIG.8Aillustrates that the anti-reflection layers disclosed herein can be implemented in acoustic wave resonators that include multi-layer piezoelectric substrates. The SAW resonator4illustrated inFIG.8Ais generally similar to the SAW resonator2illustrated inFIG.2B. However, unlike the SAW resonator2, the SAW resonator4includes the support layer26. By including the support layer26, higher order spurious modes can be suppressed. In some embodiments, the support layer26can have a relatively high acoustic impedance. An acoustic impedance of the support layer26can be higher that ac acoustic impedance of the piezoelectric layer10. The support layer26can be a silicon layer, a spinel layer, a magnesium oxide spinel layer, a quartz layer, a ceramic layer, a glass layer, a sapphire layer, a silicon nitride layer, an aluminum nitride layer, a diamond layer such as synthetic diamond layer, or the like. In some other embodiments (not illustrated), one or more additional layer can be included between the substrate layer and the piezoelectric layer. The one or more additional layers can include a silicon dioxide layer or a silicon nitride layer, for example.

FIG.8Billustrates a cross section of a surface acoustic wave resonator5according to an embodiment. The illustrated SAW resonator5includes a piezoelectric layer10, an IDT electrode12over the piezoelectric layer10, and an anti-reflection layer20over the IDT electrode12. The surface acoustic wave resonator5is like the surface acoustic wave resonator2ofFIG.2B, except that the SAW resonator5does not include the temperature compensation layer18. In certain embodiments, a lithium tantalate layer may be a more suitable piezoelectric material than the lithium niobate layer when there is no temperature compensation layer present in the SAW resonator. A SAW resonator without a temperature compensation layer over an IDT electrode can include a multi-layer IDT electrode in certain instances. Alternatively or additionally, a SAW resonator without a temperature compensation layer over the IDT electrode can include a multi-layer piezoelectric substrate.

FIG.8Cillustrates another cross section of the surface acoustic wave resonator5illustrated inFIG.8B. The illustrated SAW resonator5includes the piezoelectric layer10, the IDT electrode12over the piezoelectric layer10, the anti-reflection layer20over the IDT electrode12. The IDT electrode12includes a first IDT electrode finger12xextending from a first bus bar (not shown) and a second IDT finger12yextending from a second bus bar (not shown). The first IDT electrode finger12xand the second IDT electrode finger12yare spaced apart from each other by a gap36. The gap36can be free from the anti-reflection layer20. The portion of the piezoelectric layer10under the gap36is free from the anti-reflection layer20.

In some embodiments, the anti-reflection layer20can be patterned such that the anti-reflection layer20substantially covers an upper surface of IDT fingers of the IDT electrode12. A width W1of the anti-reflection layer20over IDT electrode finger12xand a width W2of the IDT electrode finger12xcan be generally similar. In some embodiments the width W1of the anti-reflection layer20over the IDT electrode finger12xcan be the same as or shorter than the width W2of the IDT electrode finger12x. In some embodiments, a side wall12bof the IDT electrode finger12xthat extends from a lower surface of the IDT electrode finger12xto the upper surface of the IDT electrode finger12x, can be perpendicular with an upper surface of the piezoelectric layer10, or tapered. The side wall12bof the IDT electrode finger12xcan be free from the anti-reflection layer20. The anti-reflection layer20can have a footprint that corresponds to a footprint of IDT electrode fingers of the IDT electrode12in the acoustically active part of the SAW resonator5. The SAW resonator5and/or any other SAW resonators disclosed herein can include part of the anti-reflection layer20over a bus bar of the IDT electrode12. In some other embodiments, a bus bar can be free from the anti-reflection layer20. In some other embodiments, a bus bar can partly covered by the anti-reflection layer20and partly free from the anti-reflection layer20.

FIG.9Aillustrates a cross section of a Lamb wave device7according to an embodiment. The Lamb wave device7can be a Lamb wave resonator. The Lamb wave device7includes a piezoelectric layer10, an IDT electrode12over the piezoelectric layer10, an anti-reflection layer20over the IDT electrode12, and a temperature compensation layer18over the piezoelectric layer10. The Lamb wave device7also includes a substrate35, and an air cavity37between the piezoelectric layer10and the substrate35. The substrate35can include any suitable material. For example, the substrate35can be a semiconductor substrate, such as a silicon substrate. As illustrated, the Lamb wave device7includes part of the anti-reflection layer20over a bus bar of the IDT electrode12. In some other embodiments (not illustrated), a bus bar can be free from the anti-reflection layer. In some other embodiments (not illustrated), a bus bar can partly covered by the anti-reflection layer and partly free from the anti-reflection layer.

FIG.9Billustrates a cross section of a Lamb wave device8according to another embodiment. The Lamb wave device8can be a Lamb wave resonator. The Lamb wave device8is like the Lamb wave device7ofFIG.9Aexcept that the Lamb wave device8includes a solid acoustic mirror29and a substrate41in place of the substrate35and the cavity37. The solid acoustic mirror29can include acoustic Bragg reflectors. For instance, the solid acoustic mirror29can include alternating layers of a low impedance layer29aand a high impedance layer29b. As one example, the low impedance layer29acan be a silicon dioxide layer and the high impedance layer29bcan be a tungsten layer. As another example, the low impedance layer29acan be a silicon dioxide layer and the high impedance layer29bcan be a molybdenum layer. The substrate41can include any suitable material. For example, the substrate41can be a semiconductor substrate, such as a silicon substrate.

A method of manufacturing an acoustic wave device according to an embodiment will now be described. The method can include providing a piezoelectric layer and forming (e.g., depositing) an interdigital transducer electrode material over the piezoelectric layer. The interdigital transducer electrode material can include aluminum. The method can include forming (e.g., depositing) an anti-reflection layer over the interdigital transducer electrode material. The anti-reflection material can remain distinct from the interdigital transducer material after a heating process. The anti-reflection material can reduce reflections from the interdigital transducer material during photolithography. The method can include forming (e.g., depositing) a resist film over the anti-reflection layer. The resist film can be patterned, for example, by a stepper. The method can include patterning (e.g., etching) the interdigital transducer electrode material to form an interdigital transducer electrode. The method can include removing the resist film. The method can include forming (e.g., depositing) a temperature compensation layer over at least a portion of the piezoelectric layer, the interdigital transducer electrode, and/or the anti-reflection layer.

A SAW device including any suitable combination of features disclosed herein be included in a filter arranged to filter a radio frequency signal in a fifth generation (5G) New Radio (NR) operating band within Frequency Range 1 (FR1). A filter arranged to filter a radio frequency signal in a 5G NR operating band can include one or more SAW devices disclosed herein. FR1 can be from 410 MHz to 7.125 GHz, for example, as specified in a current 5G NR specification. One or more SAW devices in accordance with any suitable principles and advantages disclosed herein can be included in a filter arranged to filter a radio frequency signal in a 4G LTE operating band and/or in a filter having a passband that includes a fourth generation (4G) Long Term Evolution (LTE) operating band and a 5G NR operating band.

Acoustic wave devices disclosed herein can be implemented in a standalone filter. Acoustic wave devices disclosed herein can be implemented in one or more filters of multiplexer (e.g., a duplexer) with fixed multiplexing. Acoustic wave devices disclosed herein can be implemented in one or more filters of multiplexer with switched multiplexing. Acoustic wave devices disclosed herein can be implemented in one or more filters of a multiplexer with a combination of fixed multiplexing and switched multiplexing.

FIG.10Ais a schematic diagram of an example transmit filter45that includes surface acoustic wave resonators of a surface acoustic wave component according to an embodiment. The transmit filter45can be a band pass filter. The illustrated transmit filter45is arranged to filter a radio frequency signal received at a transmit port TX and provide a filtered output signal to an antenna port ANT. The transmit filter45includes series SAW resonators TS1, TS2, TS3, TS4, TS5, TS6, and TS7, shunt SAW resonators TP1, TP2, TP3, TP4, and TP5, series input inductor L1, and shunt inductor L2. Some or all of the SAW resonators TS1, TS2, TS3, TS4, TS5, TS6, and TS7and/or TP1, TP2, TP3, TP4, and TP5can be a SAW resonators with an anti-reflection layer in accordance with any suitable principles and advantages disclosed herein. For instance, one or more of the SAW resonators of the transmit filter45can be a surface acoustic wave resonator2ofFIG.2B. Alternatively or additionally, one or more of the SAW resonators of the transmit filter45can be any surface acoustic wave resonators disclosed herein (e.g., a surface acoustic wave resonator3ofFIG.7, a surface acoustic wave resonator4ofFIG.8A, or a surface acoustic wave resonator5ofFIGS.8B and8C). Any suitable number of series SAW resonators and shunt SAW resonators can be included in a transmit filter45.

FIG.10Bis a schematic diagram of a receive filter50that includes surface acoustic wave resonators of a surface acoustic wave component according to an embodiment. The receive filter50can be a band pass filter. The illustrated receive filter50is arranged to filter a radio frequency signal received at an antenna port ANT and provide a filtered output signal to a receive port RX. The receive filter50includes series SAW resonators RS1, RS2, RS3, RS4, RS5, RS6, RS7, and RS7, shunt SAW resonators RP1, RP2, RP3, RP4, and RP5, and RP6, shunt inductor L2, and series output inductor L3. Some or all of the SAW resonators RS1, RS2, RS3, RS4, RS5, RS6, RS7, and RS8and/or RP1, RP2, RP3, RP4, RP5, and RP6can be SAW resonators with an anti-reflection layer in accordance with any suitable principles and advantages disclosed herein. For instance, one or more of the SAW resonators of the receive filter50can be a surface acoustic wave resonator2ofFIG.2B. Alternatively or additionally, one or more of the SAW resonators of the receive filter50can be any surface acoustic wave resonator disclosed herein (e.g., a surface acoustic wave resonator3ofFIG.7, a surface acoustic wave resonator4ofFIG.8A, or a surface acoustic wave resonator5ofFIGS.8B and8C). Any suitable number of series SAW resonators and shunt SAW resonators can be included in a receive filter50.

FIG.11is a schematic diagram of a radio frequency module75that includes a surface acoustic wave component76according to an embodiment. The illustrated radio frequency module75includes the SAW component76and other circuitry77. The SAW component76can include one or more SAW resonators with any suitable combination of features of the SAW resonators and/or acoustic wave devices disclosed herein. The SAW component76can include a SAW die that includes SAW resonators.

The SAW component76shown inFIG.11includes a filter78and terminals79A and79B. The filter78includes SAW resonators. One or more of the SAW resonators can be implemented in accordance with any suitable principles and advantages of the surface acoustic wave resonator2ofFIG.2Band/or any surface acoustic wave resonator disclosed herein. The filter78can be a TC-SAW filter arranged as a band pass filter to filter radio frequency signals with frequencies below about 3.5 GHz in certain applications. The terminals79A and78B can serve, for example, as an input contact and an output contact. The SAW component76and the other circuitry77are on a common packaging substrate80inFIG.11. The package substrate80can be a laminate substrate. The terminals79A and79B can be electrically connected to contacts81A and81B, respectively, on the packaging substrate80by way of electrical connectors82A and82B, respectively. The electrical connectors82A and82B can be bumps or wire bonds, for example. The other circuitry77can include any suitable additional circuitry. For example, the other circuitry can include one or more one or more power amplifiers, one or more radio frequency switches, one or more additional filters, one or more low noise amplifiers, the like, or any suitable combination thereof. The radio frequency module75can include one or more packaging structures to, for example, provide protection and/or facilitate easier handling of the radio frequency module75. Such a packaging structure can include an overmold structure formed over the packaging substrate75. The overmold structure can encapsulate some or all of the components of the radio frequency module75.

FIG.12is a schematic diagram of a radio frequency module84that includes a surface acoustic wave component according to an embodiment. As illustrated, the radio frequency module84includes duplexers85A to85N that include respective transmit filters86A1to86N1and respective receive filters86A2to86N2, a power amplifier87, a select switch88, and an antenna switch89. The radio frequency module84can include a package that encloses the illustrated elements. The illustrated elements can be disposed on a common packaging substrate80. The packaging substrate can be a laminate substrate, for example.

The duplexers85A to85N can each include two acoustic wave filters coupled to a common node. The two acoustic wave filters can be a transmit filter and a receive filter. As illustrated, the transmit filter and the receive filter can each be band pass filters arranged to filter a radio frequency signal. One or more of the transmit filters86A1to86N1can include one or more SAW resonators in accordance with any suitable principles and advantages disclosed herein. Similarly, one or more of the receive filters86A2to86N2can include one or more SAW resonators in accordance with any suitable principles and advantages disclosed herein. AlthoughFIG.12illustrates duplexers, any suitable principles and advantages disclosed herein can be implemented in other multiplexers (e.g., quadplexers, hexaplexers, octoplexers, etc.) and/or in switch-plexers.

The power amplifier87can amplify a radio frequency signal. The illustrated switch88is a multi-throw radio frequency switch. The switch88can electrically couple an output of the power amplifier87to a selected transmit filter of the transmit filters86A1to86N1. In some instances, the switch88can electrically connect the output of the power amplifier87to more than one of the transmit filters86A1to86N1. The antenna switch89can selectively couple a signal from one or more of the duplexers85A to85N to an antenna port ANT. The duplexers85A to85N can be associated with different frequency bands and/or different modes of operation (e.g., different power modes, different signaling modes, etc.).

FIG.13Ais a schematic block diagram of a module90that includes a power amplifier92, a radio frequency switch93, and duplexers91A to91N in accordance with one or more embodiments. The power amplifier92can amplify a radio frequency signal. The radio frequency switch93can be a multi-throw radio frequency switch. The radio frequency switch93can electrically couple an output of the power amplifier92to a selected transmit filter of the duplexers91A to91N. One or more filters of the duplexers91A to91N can include any suitable number of surface acoustic wave resonators with an anti-reflection layer in accordance with any suitable principles and advantages discussed herein. Any suitable number of duplexers91A to91N can be implemented.

FIG.13Bis a schematic block diagram of a module90′ that includes filters91A′ to91N′, a radio frequency switch93′, and a low noise amplifier96according to an embodiment. One or more filters of the filters91A′ to91N′ can include any suitable number of acoustic wave resonators in accordance with any suitable principles and advantages disclosed herein. Any suitable number of filters91A′ to91N′ can be implemented. The illustrated filters91A′ to91N′ are receive filters. In some embodiments (not illustrated), one or more of the filters91A′ to91N′ can be included in a multiplexer that also includes a transmit filter. The radio frequency switch93′ can be a multi-throw radio frequency switch. The radio frequency switch93′ can electrically couple an output of a selected filter of filters91A′ to91N′ to the low noise amplifier96. In some embodiments (not illustrated), a plurality of low noise amplifiers can be implemented. The module90′ can include diversity receive features in certain applications.

FIG.14is a schematic block diagram of a module95that includes duplexers91A to91N and an antenna switch94. One or more filters of the duplexers91A to91N can include any suitable number of surface acoustic wave resonators with an anti-reflection layer in accordance with any suitable principles and advantages discussed herein. Any suitable number of duplexers91A to91N can be implemented. The antenna switch94can have a number of throws corresponding to the number of duplexers91A to91N. The antenna switch94can electrically couple a selected duplexer to an antenna port of the module95.

FIG.15Ais a schematic diagram of a wireless communication device100that includes filters103in a radio frequency front end102according to an embodiment. The filters103can include one or more SAW resonators in accordance with any suitable principles and advantages discussed herein. The wireless communication device100can be any suitable wireless communication device. For instance, a wireless communication device100can be a mobile phone, such as a smart phone. As illustrated, the wireless communication device100includes an antenna101, an RF front end102, a transceiver104, a processor105, a memory105, and a user interface107. The antenna101can transmit RF signals provided by the RF front end102. Such RF signals can include carrier aggregation signals. Although not illustrated, the wireless communication device90can include a microphone and a speaker in certain applications.

The RF front end102can include one or more power amplifiers, one or more low noise amplifiers, one or more RF switches, one or more receive filters, one or more transmit filters, one or more duplex filters, one or more multiplexers, one or more frequency multiplexing circuits, the like, or any suitable combination thereof. The RF front end102can transmit and receive RF signals associated with any suitable communication standards. The filters103can include SAW resonators of a SAW component that includes any suitable combination of features discussed with reference to any embodiments discussed above.

The transceiver104can provide RF signals to the RF front end102for amplification and/or other processing. The transceiver104can also process an RF signal provided by a low noise amplifier of the RF front end102. The transceiver104is in communication with the processor105. The processor105can be a baseband processor. The processor105can provide any suitable base band processing functions for the wireless communication device100. The memory106can be accessed by the processor105. The memory106can store any suitable data for the wireless communication device100. The user interface107can be any suitable user interface, such as a display with touch screen capabilities.

FIG.15Bis a schematic diagram of a wireless communication device110that includes filters103in a radio frequency front end102and second filters113in a diversity receive module112. The wireless communication device110is like the wireless communication device100ofFIG.15A, except that the wireless communication device120also includes diversity receive features. As illustrated inFIG.15B, the wireless communication device120includes a diversity antenna111, a diversity module112configured to process signals received by the diversity antenna111and including filters113, and a transceiver104in communication with both the radio frequency front end102and the diversity receive module112. The filters113can include one or more SAW resonators that include any suitable combination of features discussed with reference to any embodiments discussed above.

Although embodiments disclosed herein relate to surface acoustic wave resonators, any suitable principles and advantages disclosed herein can be applied to other types of acoustic wave resonators and/or acoustic wave devices, such as Lamb wave resonators and/or boundary wave resonators. For example, any suitable combination of features of an anti-reflection layer over an IDT electrode disclosed herein can be applied to a Lamb wave resonator and/or a boundary wave resonator.

Any of the embodiments described above can be implemented in association with mobile devices such as cellular handsets. The principles and advantages of the embodiments can be used for any systems or apparatus, such as any uplink wireless communication device, that could benefit from any of the embodiments described herein. The teachings herein are applicable to a variety of systems. Although this disclosure includes some example embodiments, the teachings described herein can be applied to a variety of structures. Any of the principles and advantages discussed herein can be implemented in association with RF circuits configured to process signals in a frequency range from about 30 kHz to 300 GHz, such as in a frequency range from about 450 MHz to 8.5 GHz.

Aspects of this disclosure can be implemented in various electronic devices. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products such as die and/or acoustic wave components and/or acoustic wave filter assemblies and/or packaged radio frequency modules, uplink wireless communication devices, wireless communication infrastructure, electronic test equipment, etc. Examples of the electronic devices can include, but are not limited to, a mobile phone such as a smart phone, a wearable computing device such as a smart watch or an ear piece, a telephone, a television, a computer monitor, a computer, a modem, a hand-held computer, a laptop computer, a tablet computer, a personal digital assistant (PDA), a microwave, a refrigerator, an automobile, a stereo system, a DVD player, a CD player, a digital music player such as an MP3 player, a radio, a camcorder, a camera, a digital camera, a portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multi-functional peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” “include,” “including” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Likewise, the word “connected”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

Moreover, conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. For example, while blocks are presented in a given arrangement, alternative embodiments may perform similar functionalities with different components and/or circuit topologies, and some blocks may be deleted, moved, added, subdivided, combined, and/or modified. Each of these blocks may be implemented in a variety of different ways. Any suitable combination of the elements and acts of the various embodiments described above can be combined to provide further embodiments. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.