Patent ID: 12199588

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

It will be understood 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 one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region 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.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

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 this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is 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 unless expressly so defined herein.

The present disclosure relates to acoustic wave devices, and particularly to interdigital transducer (IDT) and reflective structure arrangements for surface acoustic wave (SAW) devices. Representative SAW devices are described herein with reduced overall size while maintaining good quality factors. In certain embodiments, a SAW device may include an IDT arranged between reflective structures on a piezoelectric material. The reflective structures may include reflective IDTs that are configured to have a phase difference with the IDT to reflect and confine acoustic waves in the piezoelectric material. In certain embodiments, the reflective structures may be electrically connected to at least one of an input signal and an output signal. In this manner, the reflective structures may be configured with reduced size as compared to conventional reflective structures such as gratings, thereby providing a SAW device with reduced dimensions without a negative impact on device performance.

Before describing particular embodiments of the present disclosure further, a general discussion of SAW devices is provided.FIG.1is a perspective view illustration of a representative SAW device10. The SAW device10includes a substrate12, a piezoelectric layer14on the substrate12, an IDT16on a surface of the piezoelectric layer14opposite the substrate12, a first reflector structure18A on the surface of the piezoelectric layer14adjacent to the IDT16, and a second reflector structure18B on the surface of the piezoelectric layer14adjacent to the IDT16opposite the first reflector structure18A.

The IDT16includes a first electrode20A and a second electrode20B, each of which include a number of electrode fingers22that are interleaved with one another as shown. The first electrode20A and the second electrode20B may also be referred to as comb electrodes. A lateral distance between adjacent electrode fingers22of the first electrode20A and the second electrode20B defines an electrode pitch P of the IDT16. The electrode pitch P may at least partially define a center frequency wavelength λ of the SAW device10, where the center frequency is the primary frequency of mechanical waves generated in the piezoelectric layer14by the IDT16. For a single electrode IDT16such as the one shown inFIG.1, the center frequency wavelength λ is equal to twice the electrode pitch P. For a double electrode IDT16, the center frequency wavelength λ is equal to four times the electrode pitch P. A finger width W of the adjacent electrode fingers22over the electrode pitch P may define a metallization ratio, or duty factor, of the IDT16, which may dictate certain operating characteristics of the SAW device10.

In operation, an alternating electrical input signal provided at the first electrode20A is transduced into a mechanical signal in the piezoelectric layer14, resulting in one or more acoustic waves therein. In the case of the SAW device10, the resulting acoustic waves are predominately surface acoustic waves. As discussed above, due to the electrode pitch P and the metallization ratio of the IDT16, the characteristics of the material of the piezoelectric layer14, and other factors, the magnitude and frequency of the acoustic waves transduced in the piezoelectric layer14are dependent on the frequency of the alternating electrical input signal. This frequency dependence is often described in terms of changes in the impedance and/or a phase shift between the first electrode20A and the second electrode20B with respect to the frequency of the alternating electrical input signal. An alternating electrical potential between the two electrodes20A and20B creates an electrical field in the piezoelectric layer14which generate acoustic waves. The acoustic waves travel at the surface and eventually are transferred back into an electrical signal between the electrodes20A and20B. The first reflector structure18A and the second reflector structure18B reflect the acoustic waves in the piezoelectric layer14back towards the IDT16to confine the acoustic waves in the area surrounding the IDT16.

The substrate12may comprise various materials including glass, sapphire, quartz, silicon (Si), or gallium arsenide (GaAs) among others, with Si being a common choice. The piezoelectric layer14may be formed of any suitable piezoelectric material(s). In certain embodiments described herein, the piezoelectric layer14is formed of lithium tantalate (LT), or lithium niobate (LiNbO3), but is not limited thereto. In certain embodiments, the piezoelectric layer14is thick enough or rigid enough to function as a piezoelectric substrate. Accordingly, the substrate12inFIG.1may be omitted. Those skilled in the art will appreciate that the principles of the present disclosure may apply to other materials for the substrate12and the piezoelectric layer14. The IDT16, the first reflector structure18A, and the second reflector structure18B may comprise any metal or metal alloy. While not shown to avoid obscuring the drawings, additional passivation layers, frequency trimming layers, or any other layers may be provided over all or a portion of the exposed surface of the piezoelectric layer14, the IDT16, the first reflector structure18A, and the second reflector structure18B. Further, one or more layers may be provided between the substrate12and the piezoelectric layer14in various embodiments.

FIG.2Aillustrates an example SAW structure24that includes an IDT26arranged between two reflective structures28-1,28-2. An optional substrate (e.g.,12ofFIG.1) and/or piezoelectric layer or substrate (e.g.,14ofFIG.1) are not shown. The IDT26comprises a first electrode30that is electrically connected to an input signal and a second electrode32that is electrically connected to an output signal. The first electrode30comprises a plurality of first electrode fingers30A that are interdigitated with a plurality of second electrode fingers32A of the second electrode32. As previously described, the pitch between the first electrode fingers30A and the second electrode fingers32A is about equal to a center frequency wavelength λ for the SAW structure24. While only a certain number of first and second electrode fingers30A,32A are illustrated, in practice the IDT26can include many more alternating first and second electrode fingers30A,32A. Additionally, each of the reflective structures28-1,28-2comprises a plurality of reflective fingers28A that may be electrically shorted to one another within each of the respective reflective structures28-1,28-2. In other configurations, the reflective fingers28A may be electrically open to one another. A pitch of the reflective fingers28A within each of the reflective structures28-1,28-2may be configured similar to the pitch between the first electrode fingers30A and the second electrode fingers32A of the IDT26. In this manner, reflections from individual ones of the reflective fingers28A are in phase for a desired frequency within a resonant cavity between the two reflective structures28-1,28-2. In operation, a certain number of the reflective fingers28A are required to provide adequate confinement within the SAW structure24.FIG.2Billustrates an alternative configuration of an example SAW structure34where the IDT26is configured between the two reflective structures28-1,28-2and the number of reflective fingers28A within each of the two reflective structures28-1,28-2is reduced. InFIG.2B, the number of the reflective fingers28A are reduced to three reflective fingers28A in each of the reflective structures28-1,28-2(from five reflective fingers28A inFIG.2A) for illustrative purposes. In this manner, the alternative configuration of the SAW structure34inFIG.2Bhas reduced sized when compared withFIG.2A; however, device performance may be compromised. In operation, if the number of the reflective fingers28A is too low, a quality factor (Q factor) of the SAW structure34may be too low, indicating a high rate of energy loss. As configured inFIGS.2A and2B, the reflective structures28-1,28-1may also be referred to as gratings, or grating reflectors.

According to embodiments disclosed herein, a SAW device may comprise a piezoelectric material, an IDT on the piezoelectric material and electrically connected to an input signal and an output signal, and a first reflective structure and a second reflective structure on the piezoelectric material, wherein the IDT is arranged between the first reflective structure and the second reflective structure. The first reflective structure may comprise a first reflective IDT and the second reflective structure may comprise a second reflective IDT. In certain embodiments, the first reflective IDT and the second reflective IDT are configured to have a phase difference or be out of phase with the IDT in order to provide a resonant cavity with adequate confinement. In this manner, the first reflective IDT and the second reflective IDT can achieve similar reflection characteristics as larger conventional reflective structures, thereby providing a SAW device with decreased dimensions without a decrease in performance characteristics, such as Q factor.

FIG.3Aillustrates a SAW structure36that includes first and second reflective structures38-1,38-2that comprise reflective IDTs that have a phase difference with the IDT26according to embodiments disclosed herein. An optional substrate (e.g.,12ofFIG.1) and/or piezoelectric layer or substrate (e.g.,14ofFIG.1) are not shown, but may be provided to form a SAW device. InFIG.3A, the SAW structure36includes the IDT26with the first electrode30that is electrically connected to the input signal and the second electrode32that is electrically connected the output signal as previously described. The first electrode30comprises the plurality of first electrode fingers30A that are interdigitated with the plurality of second electrode fingers32A of the second electrode32. In this manner the plurality of first electrode fingers30A that are electrically connected to the input signal are alternated with the plurality of second electrode fingers32A that are electrically connected to the output signal to generate acoustic waves in response to an electrical signal as previously described. While only a certain number of the first and second electrode fingers30A,32A are illustrated, in practice the IDT26can include many more alternating first and second electrode fingers30A,32A. Each of the reflective structures38-1,38-2comprises a first reflective electrode40that is electrically connected to the input signal and a second reflective electrode42that is electrically connected to the output signal. The first reflective electrode40includes one or more first reflective electrode fingers40A, and the second reflective electrode40includes one or more second reflective electrode fingers42A. The one or more first reflective electrode fingers40A are alternated or interdigitated with the one or more second reflective electrode fingers42A to form reflective IDTs. As illustrated inFIG.3A, the IDT26is arranged between the first reflective structure38-1and the second reflective structure38-2such that an individual second reflective electrode finger42A is arranged closest to an individual second electrode finger32A of the IDT26, both of which are electrically connected to the output signal. In this manner, the alternating arrangement of electrode fingers30A,32A is interrupted by the reflective IDTs of the reflective structures38-1,38-2. The reflective IDTs are thereby configured to have a phase difference with the IDT26and accordingly, acoustic waves are reflected and confined within a resonant cavity that is formed between the reflective structures38-1,38-2on the piezoelectric material. In certain embodiments, the reflective IDTs are configured to be out of phase with the IDT26. Additionally, as the first reflective electrode40of each reflective structure38-1,38-2is electrically connected to the input signal and the second reflective electrode42of each reflective structure38-1,38-2is electrically connected to the output signal, the reflective structures38-1,38-2may also serve as IDT capacitors that may alter the overall static capacitance. In other embodiments, the individual second reflective electrode finger42A is arranged closest to the individual second electrode finger32A, and both may be electrically connected to the input signal to form reflective IDTs as previously described. Accordingly, a SAW device may include a reflective electrode finger of a reflective IDT that is arranged closest to an electrode finger of an IDT, and the reflective electrode finger and the electrode finger are both electrically connected to the same of either the input signal or the output signal. In contrast to the SAW structure36ofFIG.3A,FIG.3Billustrates a SAW structure44that includes the IDT26as previously described arranged between additional IDTs46-1,46-2that are configured to be in phase with the IDT26. Each of the additional IDTs46-1,46-2comprises a first electrode48with one or more first electrode fingers48A electrically connected with an input signal and a second electrode50with one or more second electrode fingers50A electrically connected with an output signal. The first electrode fingers48A and second electrode fingers50A of the additional IDTs46-1,46-2are arranged in an alternating manner that continues with the electrode fingers30A,32A of the IDT26. In this manner, the additional IDTs46-1,46-2are configured to be in phase with the IDT26and therefore do not serve to reflect and confine acoustic waves.

FIG.4Ais a graph plotting the admittance of four SAW devices with varying reflective structures. All of the four SAW devices, SAMPLES 1-4, are configured with a same IDT configured with a same center frequency wavelength λ. SAMPLE 1 is a SAW device that includes a structure similar to the SAW structure24ofFIG.2Awith an IDT (e.g.,26ofFIG.2A) length of about 112λ and a reflective structure (e.g.,28-1,28-2ofFIG.2A) length of about 14λ. SAMPLE 2 is a SAW device that includes a structure similar to the SAW structure34ofFIG.2Bwith an IDT (e.g.,26ofFIG.2B) length of about 112λ and a reflective structure (e.g.,28-1,28-2ofFIG.2B) length of about 3λ. SAMPLE 3 is a SAW device that includes a structure similar to the SAW structure36ofFIG.3Awith an IDT (e.g.,26ofFIG.3A) length of about 112λ and a reflective structure (e.g.,38-1,38-2ofFIG.3A) length of about 3λ. SAMPLE 4 is a SAW device that includes a structure similar to the SAW structure44ofFIG.3Bwith an IDT (e.g.,26ofFIG.3B) length of about 112λ and a reflective structure (e.g.,46-1,46-2ofFIG.3B) length of about 3λ. In this manner, SAMPLE 1 includes the IDT in between conventional reflective gratings, SAMPLE 2 illustrates the performance impact of reducing the length of conventional gratings, SAMPLE 3 includes the IDT in between reflective IDTs, and SAMPLE 4 illustrates the performance impact when adjacent IDTs are in phase with the IDT. The amplitude in decibels (dB) of admittance for each of the samples is plotted with respect to the frequency of an alternating electrical input signal. Notably, all four samples have a similar series resonant frequency (fs), or resonant frequency. The series resonant frequency represents the frequency where impedance is minimal. Differences between the four samples are more prominent at a parallel resonant frequency (fp), or antiresonant frequency. The parallel resonant frequency represents the frequency where impedance is highest.FIG.4Billustrates a magnified view of the dashed box ofFIG.4Awhere the parallel resonant frequencies of each of the samples differ. As illustrated, when the length of conventional gratings are reduced from a value of 14λ for SAMPLE 1 to a value of 3λ for SAMPLE 2, the parallel resonant frequency has a higher dB value which indicates the conventional gratings are less reflective with decreased length and therefore have a negative impact on the Q factor. In contrast, the parallel resonant frequency for SAMPLE 3 has a similar dB value to SAMPLE 1, indicating a similar reflectance performance and without a negative impact on the Q factor. The parallel resonant frequency for SAMPLE 3 does show a minor shift in frequency which indicates the reflective IDT structures of SAMPLE 3 have a minor coupling impact on bandwidth. This may be due to a minor increase in static capacitance as the reflective structure (e.g.,38-1,38-2ofFIG.3A) may also function as an IDT capacitor. SAMPLE 4 illustrates the largest change in the dB value at the parallel resonant frequency demonstrating the worst reflectance performance and largest impact on the Q factor.

SAW devices according to embodiments disclosed herein may be incorporated within larger devices and systems to provide simplified layouts or topologies.FIGS.5A,5B,6A, and6Billustrate representative radio frequency (RF) duplexing devices with various SAW devices as disclosed herein. RF duplexing devices typically are configured to receive signals and transmit signals of a different band using a common antenna. One of the primary challenges of duplexing is that RF transmission signals and RF receive signals can interfere with one another and accordingly, RF duplexing devices may employ one or more filters to improve isolation.

FIG.5Ais a block diagram of an RF duplexer52that includes conventional SAW resonators. The RF duplexer52includes a transmit (TX) port, a receive (RX) port, and an antenna (ANT) port. A TX filter54is positioned between the TX port and the antenna port, and an RX filter56is positioned between the RX port and the antenna port. The TX filter54is configured as a ladder filter with series resonators TX1, TX3, TX5and shunt resonators TX2, TX4, TX6, all of which may be configured with a structure similar to the SAW structure24ofFIG.2A. The RX filter56includes series resonators RX1, RX3, a shunt resonator RX2, a SAW coupled resonator filter (CRF) structure (5-IDT CRF) that includes five IDTs that alternate between input IDTs and output IDTs, and a capacitor58that is connected between the input and output of the 5-IDT CRF.FIG.5Bis a block diagram of an RF duplexer60that includes SAW resonators according to embodiments disclosed herein. The RF duplexer60includes the same RX filter54ofFIG.5Abetween the TX port and the antenna port, but a different TX filter62. In particular, the TX filter62includes shunt resonators TX2′, TX4′, TX6′ that are configured with a structure similar to the SAW structure36ofFIG.3A. In this regard, the shunt resonators TX2′, TX4′, TX6′ are configured with reflective IDTs that provide reduced die size without significant loss of performance.

FIG.6Ais a top view of a device layout of the RF duplexer52ofFIG.5A. As illustrated, the RF duplexer52includes the resonators TX1to TX6, the resonators RX1to RX3, the 5-IDT CRF, and the capacitor58as previously described as well as areas for RX, TX, antenna, and various ground connections.FIG.6Bis a top view of a device layout of the RF duplexer60ofFIG.5B. As illustrated, the RF duplexer60includes the resonators TX2′, TX4′, TX6′ in addition to the resonators TX1, TX3, TX5, the resonators RX1to RX2, and the 5-IDT CRF, and the capacitor58as previously described as well as areas for RX, TX, antenna, and various ground connections. Due to the configuration of the resonators TX2′, TX4′, TX6′ there is noticeably improved die space savings in these areas.

FIG.7Ais a top view illustration of the TX2resonator ofFIGS.5A and6A, andFIG.7Bis a top view illustration of the TX2′ resonator ofFIGS.5B and6B. In a non-limiting example, the TX2resonator comprises a length64of about 716.6 microns (μm) and a width66of about 141.2 μm while the TX2′ resonator comprises a length68of about 611.6 μm and a width70of about 141.2 μm. The size reduction from the length64of the TX2resonator to the length68of the TX2′ resonator is due to replacing conventional grating reflectors with reflective IDTs as previously described. In this manner, the TX2′ resonator demonstrates about a 14.65% reduction in die area.FIG.7Cis a top view illustration of the TX4resonator ofFIGS.5A and6A, andFIG.7Dis a top view illustration of the TX4′ resonator ofFIGS.5B and6B. In a non-limiting example, the TX4resonator comprises a length72of about 777.7 μm and a width74of about 93.9 μm while the TX4′ resonator comprises a length76of about 683.5 μm and a width78of about 93.9 μm. In this manner, the TX4′ resonator demonstrates about a 12.11% reduction in die area.FIG.7Eis a top view illustration of the TX6resonator ofFIGS.5A and6A, andFIG.7Fis a top view illustration of the TX6′ resonator ofFIGS.5B and6B. In a non-limiting example, the TX6resonator comprises a length80of about 652.8 μm and a width82of about 149.6 μm while the TX6′ resonator comprises a length84of about 555.1 μm and a width86of about 149.6 μm. In this manner, the TX6′ resonator demonstrates about a 14.966% reduction in die area. While the specific dimensions listed above are provided, relative resonator sizes may be dependent on the target frequency band that a specific resonator is configured to operate. In this regard, replacing conventional grating reflectors with IDT reflectors as described herein can save significant die area in SAW resonators configured for various operating bands.

FIGS.8A to8Iare simulation plots comparing the performance of the RF duplexer52ofFIGS.5A/6A with the RF duplexer60ofFIGS.5B/6B. InFIGS.8A to8I, Duplexer 1 refers to the RF duplexer52ofFIGS.5A/6A and Duplexer 2 refers to the RF duplexer60ofFIGS.5B/6B. The performance comparisons of Duplexer 1 and Duplexer 2 are useful to demonstrate that SAW devices, and in particular SAW resonators, as disclosed herein may have reduced die size without a significant impact on device performance.FIG.8Ais an S-parameters comparison plot representing passbands of Duplexer 1 and Duplexer 2. The S-parameter magnitude is plotted in decibels (dB) across a megahertz (MHz) frequency range. Insertion loss, or S2,1, is an indication of how much power is transferred between the TX port and the antenna port. For frequencies where S2,1is at or near 0 dB, then substantially all power from a signal is transferred. Accordingly, a TX passband is illustrated where the S2,1values are at or near 0 dB. On either side of the TX passband, or the shoulder regions, the S2,1values decrease rapidly. As the S2,1value becomes farther away from 0 dB, more and more power is rejected. As illustrated, the TX passbands for Duplexer 1 and Duplexer 2 are substantially the same.FIG.8Bis an S-parameters comparison plot representing a magnified view of the TX passbands ofFIG.8A. InFIG.8B, the comparison plot highlights the frequency range of 778 MHz to 808 MHz fromFIG.8A.FIG.8Cis a Smith chart comparing the antenna reflection impedance for the TX passband of Duplexer 1 and Duplexer 2. The chart illustrates the reflection scattering parameter (S1,1) at the antenna port in the TX passband frequency. Values at or near 1.0 in the center of the plot indicate the signal frequencies are passing through the TX filter54.FIG.8Dis an S-parameters comparison plot representing a zoomed out view of the TX passbands ofFIG.8A. InFIG.8D, the comparison plot illustrates a large frequency range from 100 MHz to 6000 MHz to show a similar rejection performance for frequencies well outside of the TX passbands.FIG.8Eis an S-parameters plot comparing return loss of Duplexer 1 and Duplexer 2. Return loss is an indication of voltage reflection, and S2,2represents how much power is reflected at the TX port. For frequencies where S2,2is at or near 0 dB, then substantially all power from a signal is reflected by the TX filter54.FIG.8Fis a Smith chart comparing the TX impendence for the TX passband of Duplexer 1 and Duplexer 2. The chart illustrates the reflection scattering parameter (S2,2) at the RX port in the TX passband frequency.FIG.8Gis a comparison plot for duplexer isolation in dB for Duplexers 1 and 2, where a lower dB value indicates better isolation. S3,2parameter values are plotted for Duplexers 1 and 2 to show isolation between the RX port and the TX port. S3,2values in the frequency range of about 756 MHz to about 770 MHz indicate how much power may be leaking from the TX port to the RX port, and S3,2values in the frequency range of about 786 MHz to about 800 MHz indicate how much power may be leaking from the RX port to the TX port. As illustrated, the dB values are at or near-60 dB for each of these frequency ranges, indicating good isolation and low power leakage.FIG.8His a zoomed out view of the comparison plot ofFIG.8G. InFIG.8H, the comparison plot illustrates a large frequency range from 100 MHz to 6000 MHz to show a similar isolation performance for frequencies well outside of the TX passbands.FIG.8Iis an S-parameters plot comparing antenna return loss of Duplexer 1 and Duplexer 2. As illustrated, the antenna return loss, plotted as S1,1, is similar between Duplexer 1 and Duplexer 2.

FIG.9illustrates a SAW structure88that includes reflective structures90-1,90-2that comprise reflective IDTs according to embodiments disclosed herein. An optional substrate (e.g.,12ofFIG.1) and/or piezoelectric layer or substrate (e.g.,14ofFIG.1) are not shown, but may be provided to form a SAW device. InFIG.9, the SAW structure88includes the IDT26with the first electrode30that is electrically connected to the input signal and the second electrode32that is electrically connected the output signal as previously described. The first electrode30comprises the plurality of first electrode fingers30A that are interdigitated with the plurality of second electrode fingers32A of the second electrode32. In this manner the plurality of first electrode fingers30A that are electrically connected to the input signal are alternated with the plurality of second electrode fingers32A that are electrically connected to the output signal to generate acoustic waves in response to an electrical signal as previously described. As with previous embodiments, while only a certain number of the first and second electrode fingers30A,32A are illustrated, in practice the IDT26can include many more alternating first and second electrode fingers30A,32A. Each of the reflective structures90-1,90-2comprises a first reflective electrode92that is electrically connected to ground and a second reflective electrode94that is electrically connected to the output signal. The first reflective electrode92includes one or more first reflective electrode fingers92A and the second reflective electrode94includes one or more second reflective electrode fingers94A. The one or more first reflective electrode fingers92A are alternated or interdigitated with the one or more second reflective electrode fingers94A to form reflective IDTs. As illustrated inFIG.9, the reflective structures90-1,90-2may be arranged on opposing sides of the IDT26such that an individual second reflective electrode finger94A is arranged closest to an individual second electrode finger32A of the IDT26, both of which are electrically connected to the output signal. In this manner, the alternating arrangement of electrode fingers30A,32A is interrupted by the reflective IDTs of the reflective structures90-1,90-2. The reflective IDTs are thereby configured to have a phase difference, and in some embodiments be out of phase with the IDT26and accordingly, acoustic waves are reflected and confined within a resonant cavity that is formed between the reflective structures90-1,90-2on the piezoelectric material. In other embodiments, the individual second reflective electrode finger94A is arranged closest to the individual second electrode finger32A, and both may be electrically connected to the input signal to form reflective IDTs as previously described. Additionally, as each reflective structure90-1,90-2is electrically connected to ground and at least one of the input signal or the output signal, the reflective structures90-1,90-2may also serve as IDT capacitors that may alter the overall static capacitance.

FIG.10illustrates a SAW structure96that includes an IDT98that is arranged between multiple reflective structures according to embodiments disclosed herein. An optional substrate (e.g.,12ofFIG.1) and/or piezoelectric layer or substrate (e.g.,14ofFIG.1) are not shown, but may be provided to form a SAW device. InFIG.10, the SAW structure98includes the IDT98with a first electrode100that is electrically connected to the input signal and a second electrode102that is electrically connected to the output signal as previously described. The first electrode100comprises a plurality of first electrode fingers100A that are interdigitated with a plurality of second electrode fingers102A of the second electrode102. In this manner the plurality of first electrode fingers100A that are electrically connected to the input signal are alternated with the plurality of second electrode fingers102A that are electrically connected to the output signal to generate acoustic waves in response to an electrical signal as previously described. As with previous embodiments, while only a certain number of first and second electrode fingers100A,102A are illustrated, in practice the IDT98can include many more alternating first and second electrode fingers100A,102A. In addition to first and second reflective structures104-1,104-2, additional reflective structure106-1,106-2are arranged on either side of the IDT98. Each of the first and second reflective structures104-1,104-2comprises a first reflective electrode108that is electrically connected to the input signal and a second reflective electrode110that is electrically connected to the output signal. In other embodiments, at least one of the first reflective electrode108and the second reflective electrode110may be electrically connected to ground while the other of the first reflective electrode108and the second reflective electrode110may be electrically connected to either the input signal or the output signal. The first reflective electrode108includes one or more first reflective electrode fingers108A that are alternated or interdigitated with one or more second reflective electrode fingers110A of the second reflective electrode110to form reflective IDTs as previously described. An individual second reflective electrode finger110A is arranged closest to an individual second electrode finger102A of the IDT98and both are electrically connected to the output signal, or the input signal in other embodiments. In this regard, the reflective structures104-1,104-2form reflective IDTs that have a phase difference with the IDT98, and acoustic waves may be reflected and confined within a resonant cavity that is formed between the first and second reflective structures104-1,104-2on the piezoelectric material. In certain embodiments, the reflective IDTs are out of phase with the IDT98. The additional reflective structures106-1,106-2are configured as reflective gratings to further reflect and confine acoustic waves within the resonant cavity. As illustrated inFIG.10, the reflective structures104-1,104-2are configured between the additional reflective structures106-1,106-2and the IDT98. In other embodiments, the order may be reversed such that the additional reflective structures106-1,106-2are configured between the reflective structures104-1,104-2and the IDT98.

FIG.11illustrates a SAW structure112that includes an IDT114that is arranged between multiple reflective IDTs according to embodiments disclosed herein. An optional substrate (e.g.,12ofFIG.1) and/or piezoelectric layer or substrate (e.g.,14ofFIG.1) are not shown, but may be provided to form a SAW device. InFIG.11, the SAW structure112includes the IDT114with a first electrode116that is electrically connected to the input signal and a second electrode118that is electrically connected the output signal as previously described. The first electrode116comprises a plurality of first electrode fingers116A that are interdigitated with a plurality of second electrode fingers118A of the second electrode118. In this manner the plurality of first electrode fingers116A that are electrically connected to the input signal are alternated with the plurality of second electrode fingers118A that are electrically connected to the output signal to generate acoustic waves in response to an electrical signal as previously described. As with previous embodiments, while only a certain number of the first and second electrode fingers116A,1118A are illustrated, in practice the IDT114can include many more alternating first and second electrode fingers116A,118A. First reflective structures120-1,120-2and second reflective structures122-1,122-2are arranged on either side of the IDT114. In certain embodiments, each of the first reflective structures120-1,120-2is arranged between the second reflective structures122-1,122-2. As illustrated inFIG.11, the first reflective structures120-1,120-2and the second reflective structures122-1,122-2are configured as reflective IDTs that are have a phase difference with the IDT114to reflect and confine acoustic waves as previously described. In certain embodiments, the reflective IDTs are out of phase with the IDT114. In certain embodiments, the first reflective structures120-1,120-2and the second reflective structures122-1,122-2are each electrically connected to both the input signal and the output signal. In other embodiments, the first reflective structures120-1,120-2and the second reflective structures122-1,122-2may each be electrically connected to ground and either the input signal or the output signal. The first reflective structures120-1,120-2and the second reflective structures122-1,122-2may be configured to reflect different frequency bands and may comprise different numbers of alternating electrodes fingers. In further embodiments, the SAW structure112may comprise additional reflective structures, including reflective IDTs and reflective gratings to further reflect and confine acoustic waves.

For simplicity, all of the embodiments disclosed herein are illustrated with unapodized IDTs where all of the IDT electrode fingers have a uniform length. In certain embodiments, one or more of the IDTs and reflective IDTs as previously described may comprise an apodized IDT where electrode fingers have different lengths at different positions along the apodized IDT that are configured for a particular response function. In certain embodiments, one or more of the IDTs as previously described may comprise a metallization ratio, or duty factor, of any range between 0 and 1 of a center wavelength A. In certain embodiments, the metallization ration is in a range of about 0.1 to about 0.9; or in a range of about 0.2 to about 0.8; or in a range of about 0.3 to about 0.7; or in a range of about 0.4 to about 0.5. In certain embodiments, the metallization ratio comprises a value of about 0.4, or a value of about 0.5.

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 within the scope of the concepts disclosed herein and the claims that follow.