Surface acoustic wave device

An acoustic wave device includes a piezoelectric substrate and an interdigital transducer disposed on the piezoelectric substrate, the interdigital transducer including a center region, first and second edge regions, and first and second gap regions, a temperature compensation layer covering the interdigital transducer, and a floating metal layer buried in the temperature compensation layer or disposed on top of the temperature compensation layer. The floating metal layer includes a plurality of floating metal blocks spaced apart from each other and overlapping at least the first and second edge regions of the interdigital transducer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on and claims priority to Chinese Patent Application No. 202410240146.7, filed on Mar. 4, 2024, the entire contents of which are hereby incorporated by reference.

FIELD

The present disclosure relates to the field of semiconductor devices and, in particular, to a surface acoustic wave device.

BACKGROUND

Surface acoustic wave (SAW) devices, such as SAW resonators and SAW filters, are used in many applications such as radio frequency (RF) filters. A typical SAW filter includes a plurality of interdigital transducers (IDTs) formed on a piezoelectric substrate, and each IDT may include a plurality of interdigital electrodes. In some applications, a thin layer of silicon oxide (SiO2) may be formed on the IDTs to obtain good temperature coefficient of frequency. Such a SAW device may be implemented as a temperature compensated-surface acoustic wave (TC-SAW) device.

SUMMARY

According to one aspect of the disclosure, an acoustic wave device is provided. The acoustic wave device includes a piezoelectric substrate and an interdigital transducer disposed on the piezoelectric substrate, the interdigital transducer including a center region, first and second edge regions, and first and second gap regions, a temperature compensation layer covering the interdigital transducer, and a floating metal layer buried in the temperature compensation layer or disposed on top of the temperature compensation layer. The floating metal layer includes a plurality of floating metal blocks spaced apart from each other and overlapping at least the first and second edge regions of the interdigital transducer.

DETAILED DESCRIPTION

The text below provides a detailed description of the present disclosure in conjunction with specific embodiments illustrated in the attached drawings. However, these embodiments do not limit the present disclosure. The scope of protection for the present disclosure covers changes made to the structure, method, or function by persons having ordinary skill in the art on the basis of these embodiments.

To facilitate the presentation of the drawings in the present disclosure, the sizes of certain structures or portions may be enlarged relative to other structures or portions. Therefore, the drawings in the present disclosure are only for the purpose of illustrating the basic structure of the subject matter of the present disclosure. The same numbers in different drawings represent the same or similar elements unless otherwise represented.

Additionally, terms in the text indicating relative spatial position, such as “top,” “bottom,” “upper,” “lower,” “above,” “below,” and so forth, are used for explanatory purposes in describing the relationship between a unit or feature depicted in a drawing and another unit or feature therein. Terms indicating relative spatial position may refer to positions other than those depicted in the drawings when a device is being used or operated. For example, if a device shown in a drawing is flipped over, a unit which is described as being positioned “below” or “under” another unit or feature will be located “above” the other unit or feature. Therefore, the illustrative term “below” may include positions both above and below. A device may be oriented in other ways (e.g., rotated 90 degrees or facing another direction), and descriptive terms that appear in the text and are related to space should be interpreted accordingly. When a component or layer is said to be “above” another member or layer or “connected to” another member or layer, it may be directly above the other member or layer or directly connected to the other member or layer, or there may be an intermediate component or layer.

A typical SAW resonator includes an interdigital transducer (IDT) formed on a piezoelectric substrate. One difficulty when designing a SAW resonator is the presence of transducer edge gap regions having an elastic wave velocity much higher than a transducer center region. The high velocity regions may result in generation of transverse mode signals in the SAW resonator, that may cause unwanted ripples in filter characteristics. A technical solution for suppressing the transverse mode is to create an edge region with a relatively slow velocity compared to the transducer center region. This may be achieved by providing a conductive stripe in the edge region. The conductive stripe may extend longitudinally across the entire length of a busbar of the interdigital transducer. The dimension of the conductive stripe is configured according to desirable characteristics and dimensions of the SAW resonator, and may not be varied. However, sometimes it might be desirable to vary the dimension of the conductive stripe.

According to embodiments of the present disclosure, a series of conductive metal blocks (hereinafter referred to as “floating metal blocks”) are provided at least in the edge region. The floating metal blocks may be individually formed, and thus the dimensions of the individual floating metal blocks may be varied.

FIG.1Aschematically illustrates a sectional view of a temperature compensated surface acoustic wave (TC-SAW) device1000, according to an embodiment of the present disclosure.FIG.1Bschematically illustrates a top view of TC-SAW device1000ofFIG.1A.FIG.1Cis a velocity profile of TC-SAW device1000ofFIG.1A. The dashed lines betweenFIGS.1A,1B, and1Cshow relative positions of the illustrated components of TC-SAW device1000. The sectional view ofFIG.1Ais taken along a section line A-A′ inFIG.1B.

As illustrated inFIGS.1A-1C, TC-SAW1000includes a piezoelectric substrate100, an interdigital transducer (IDT)200disposed on piezoelectric substrate100, a temperature compensation layer300covering IDT200, and a floating metal layer400buried in temperature compensation layer300. IDT200includes a center region C, first edge region E1, second edge region E2, first gap region G1, second gap region G2, first busbar region B1, and second busbar region B2. Floating metal layer400includes a plurality of floating metal blocks410and420spaced apart from each other and overlapping at least first and second edge regions E1and E2of IDT200, respectively.

More specifically, referring toFIGS.1B, IDT200includes a first busbar210, a second busbar220opposite first busbar210, a plurality of first fingers230extending from first busbar210and along a first direction (X-direction inFIGS.1A and1B), and a plurality of second fingers240extending from second busbar220and along the first direction. First fingers230and second fingers240are alternatively disposed along a second direction (Y-direction inFIGS.1A and1B) perpendicular to the first direction. Each finger among first fingers230and second fingers240has a width Wfalong the second direction (Y-direction inFIGS.1A and1B). The widths Wr of first fingers230may be the same as, or different from, each other. The widths Wfof second fingers240may be the same as, or different from, each other. A ratio between the width Wfof first or second fingers230or240and a distance between the centers of adjacent ones of first and second fingers230and240is defined as a duty cycle of IDT200. In the embodiments of the present disclosure, the duty cycle of IDT200may be, e.g., 0.5.

Each of first fingers230and second fingers240includes a first end201electrically connected to one of first busbar210and second busbar220and an opposite second end202having an edge portion250spaced from the other one of first busbar210and second busbar220to define a gap260. Edge portions250of first fingers230are disposed in first edge region E1. Edge portions250of second fingers240are disposed in second edge region E2. Gaps260defined between first fingers230and second busbar220are disposed in first gap region G1. Gaps260defined between second fingers240and first busbar210are disposed in second gap region G2.

Floating metal layer400includes a series of first floating metal blocks410and a series of second floating metal blocks420. The series of first floating metal blocks410are arranged along the second direction and spaced apart from each other, and overlap first edge region E1. The series of second floating metal blocks420are arranged along the second direction and spaced apart from each other, and overlap second edge region E2.

Each of first floating metal blocks410partially overlaps an edge portion250of one of first fingers230and a portion of one of second fingers240adjacent to the edge portion250of the first finger230. For example, as illustrated in FIG.,1B, a first floating metal block411partially overlaps an edge portion251of a first finger231and a portion of a second finger241adjacent to first finger231. Similarly, each of second floating metal blocks420partially overlaps an edge portion250of one of second fingers240and a portion of one of first fingers230adjacent to the edge portion250of the second finger240. The dimensions of first and second floating metal blocks410and420may be individually configured according to the structure of IDT200as well as performance parameter of TC-SAW device1000.

Each one of first and second floating metal blocks410and420has a thickness Dfmalong a direction perpendicular to a surface of piezoelectric substrate100(Z-direction inFIGS.1A and1B). The thicknesses Dfmof first floating metal blocks410may be the same as, or different from, each other. The thicknesses Dfmof second floating metal blocks420may be the same as, or different from, each other.

In an embodiment, each one of first and second floating metal blocks410and420may have, e.g., a rectangular shape with a width Wfmalong the first direction (X-direction inFIGS.1A and1B), and a length Lim along the second direction (Y-direction inFIGS.1A and1B). The widths Wfmof first floating metal blocks410may be the same as, or different from, each other. The widths Wfmof second floating metal blocks420may be the same as, or different from, each other. Width Wfmmay be substantially equal to, or less than, one wavelength (which is also referred to as “acoustic wavelength”) of the acoustic wave propagating within IDT200. For example, width Wfmmay be 1.0 L, where L is one acoustic wavelength (e.g., 4 μm). In another embodiment, each one of first and second floating metal blocks410and420may have a shape other than the rectangular shape.

The dimensions of first and second floating metal blocks410and420, such as width Wfm, length Lfm, and thickness Dfm, may be individually configured according to the structure of IDT200as well as performance parameter of TC-SAW device1000. For example, a width Wfmof each one of first and second floating metal blocks410and420is configured based on the widths Wt of one of first fingers230and one of second fingers240that the floating metal block partially overlaps. In the example ofFIG.1Bwhere first floating metal block411partially overlaps first finger231and second finger241, the width Wfmof first floating metal block411is configured based on the width Wfof first finger231and the width Wfof second finger241. For example, a length Lfmof each one of first and second floating metal blocks410and420is configured based on a pitch P1of first fingers230(i.e., the distance between adjacent first fingers230) and a pitch P2of second fingers240(i.e., the distance between adjacent second fingers240). For example, Ldm=(P1+P2)/2.

Each one of first gap region G1and second gap region G2has a width WGalong the first direction (X-direction). Width WGmay be substantially equal to, or slightly greater than one acoustic wavelength. For example, width WGmay be 1.5 L, where L is one acoustic wavelength (e.g., 4 μm). In some embodiments, width WGmay be less than one acoustic wavelength.

As described above, the series of first floating metal blocks410are spaced apart from each other along the second direction (Y-direction), and the series of second floating metal blocks420are spaced apart from each other along the second direction (Y-direction). A distance S between adjacent ones of first floating metal blocks410or second floating metal blocks420may be less than one acoustic wavelength. For example, distance S may be between 0.2 L to 0.6 L, where L is one acoustic wavelength.

In TC-SAW1000according to the embodiment of the present disclosure, piezoelectric substrate100may be formed of a piezoelectric material such as, for example, lithium niobate (LN) or lithium tantalate (LT). IDT200may be formed of a metal such as, for example, Ti, Cr, Ag, Cu, Mo, Pt, W, Al, Ti, or a stacked combination of two or more of those metal materials. Temperature compensation layer300may be formed of a dielectric material such as, silicon oxide (SiO2). In some embodiments, temperature compensation layer300may include a first temperature compensation layer disposed below floating metal layer400including floating metal blocks410and420, and a second temperature compensation layer disposed above floating metal layer400. The first and second temperature compensation layers may be formed of the same dielectric material. The thicknesses of the first and second temperature compensation layers may be the same or may be different.

Floating metal layer400(including first and second floating metal blocks410and420) may be formed of a metal material having a relatively high density compared to the metal material of IDT. For example, floating metal layer400may be formed of Ti, Cr, or Cu, or a stacked combination of two or more of those metal materials. Due to the presence of the high density floating metal blocks410and420in edge regions E1and E2, the elastic wave velocity in edge regions E1and E2is slower than that in the center region.

As further illustrated inFIG.1C, the elastic wave velocity in edge regions E1and E2is less than that in center region C, while the elastic wave velocity in gap regions G1and G2is greater than that in center region C.

In the embodiment illustrated inFIGS.1A-1C, first floating metal blocks410overlap only first edge region E1, and second floating metal blocks420overlap only second edge region E2. In some alternative embodiments, first floating metal blocks410may partially overlap first gap region G1, and second floating metal blocks420may partially overlap second gap region G2.FIGS.2A-2Cillustrates such an embodiment.

Specifically,FIG.2Aschematically illustrates a sectional view of a temperature compensated surface acoustic wave (TC-SAW) device2000, according to an embodiment of the present disclosure.FIG.2Bschematically illustrates a top view of TC-SAW device2000ofFIG.2A.FIG.2Cis a velocity profile of TC-SAW device2000ofFIG.2A.

As illustrated inFIGS.2A and2B, a right side of each of first floating metal blocks410extends into first gap region G1along the first direction (X-direction). That is, each first floating metal block410overlaps first edge region E1and a portion of first gap region G1. Similarly, a left side of each of second floating metal blocks420extends into second gap region G2along the first direction (X-direction). That is, each second floating metal block420overlaps second edge region E2and a portion of second gap region G2.

Each one of first floating metal blocks410or second floating metal blocks420includes a first portion401that overlaps first edge region E1or second edge region E2, and a second portion402that overlaps a portion of first gap region G1or second gap region G2. A dimension of first portion401along the first direction (X-direction) is a, and a dimension of second portion402along the first direction (X-direction) is b. Dimension a may be greater than dimension b. For example, dimension a is 0.8 L, and dimension b is 0.6 L, where L is one acoustic wavelength (e.g., 400 μm).

FIG.3Ais a graph showing a measurement of admittance of a TC-SAW resonator without floating metal blocks, according to a comparative example. In the graph, the label “Y” represents the admittance, and the label “real Y” represents the real part of the admittance. As shown inFIG.3A, a plurality of spurious responses (multiple smaller peaks) are observed between a resonant frequency around 905 MHz and an anti-resonant frequency around 940 MHz. Those spurious responses represent higher-order transverse modes.FIG.3Bis a graph showing a measurement of admittance of a TC-SAW resonator with floating metal blocks, according to an embodiment of the present disclosure. ComparingFIGS.3A and3B, it can be seen that the plurality of spurious responses between the resonant frequency around 905 MHz and the anti-resonant frequency around 940 MHz are significantly reduced, which means that the transverse modes generated in the SAW resonator with floating metal blocks are suppressed.

FIGS.4A-4Care graphs showing measurement of admittance of TC-SAW resonators with floating metal blocks, according to the embodiments of the present disclosure. Specifically, in the TC-SAW resonator ofFIG.4A, the distance S between adjacent ones of floating metal blocks410or420is 0.2 L, where L is one acoustic wavelength, and the thickness Dfmof floating metal blocks410and420is 34 nm. In the TC-SAW resonator ofFIG.4B, the distance S is 0.4 L, and the thickness Dfmis 47 nm. In the TC-SAW resonator ofFIG.4C, the distance S is 0.6 L, and the thickness Dfmis 103 nm. As shown inFIGS.4A-4C, in each one of the TC-SAW resonators, the transverse mode signals are suppressed.

FIG.4Dis a graph showing a relationship between the distance S between adjacent ones of the floating metal blocks, and the thickness D of the floating metal blocks, which can suppress transverse modes. As shown inFIG.4D, the distance S is positively related to the thickness D.

FIG.5is a graph showing measurement of admittance of two TC-SAW resonators with floating metal blocks, according to the embodiments of the present disclosure. In the graph, the dotted lines represent the admittance and real part of the admittance of a first TC-SAW resonator in which the floating metal blocks only overlap the edge regions, and the width Wfmof the floating metal blocks is 0.8 L. The solid lines represent the admittance and real part of the admittance of a second TC-SAW resonator in which the floating metal blocks overlap the edge regions and a portion of the gap region. The dimension a of a first portion of each floating metal block that overlaps the edge region is 0.2 L, and the dimension b of a second portion of each floating metal block that overlaps a portion of the gap region is 0.8 L. As shown inFIG.5, in both of the first and second TC-SAW resonators, the transverse mode signals are suppressed.

FIG.6Aschematically illustrates a sectional view of a temperature compensated surface acoustic wave (TC-SAW) device3000, according to an embodiment of the present disclosure.FIG.6Bschematically illustrates a top view of TC-SAW device3000ofFIG.6A.FIG.6Cis a velocity profile of TC-SAW device3000ofFIG.6A.

As illustrated inFIG.6A, floating metal layer400(including first floating metal blocks410and second floating metal blocks420) is formed on top of temperature compensation layer300. In other words, floating metal layer400is disposed on a top surface of temperature compensation layer300facing away from IDT200. Other than the location of floating metal layer400, the arrangement of components of TC-SAW device3000are the same as those of TC-SAW device2000, and thus detailed descriptions thereof are not repeated.

FIG.7Aschematically illustrates a sectional view of a temperature compensated surface acoustic wave (TC-SAW) device4000, according to an embodiment of the present disclosure.FIG.7Bschematically illustrates a top view of TC-SAW device4000ofFIG.7A.FIG.6Cis a velocity profile of TC-SAW device4000ofFIG.7A.

As illustrated inFIGS.7A and7B, floating metal layer400(including first floating metal blocks410and second floating metal blocks420) is formed on top of temperature compensation layer300. In addition, first floating metal blocks410overlap only first edge region E1, and second floating metal blocks420may overlap only second edge region E2. Other than the location of floating metal layer400, the arrangement of components of TC-SAW device4000are the same as those of TC-SAW device1000, and thus detailed descriptions thereof are not repeated.

In the TC-SAW devices according to embodiments of the present disclosure, a series of floating metal blocks410and420are provided to overlap at least edge regions E1and E2of IDT200. Therefore, the elastic wave velocity in edge regions E1and E2is less than that in center region C of IDT200, thus suppressing transverse modes.

In addition, the floating metal blocks are spaced apart from each other. Thus, the dimensions of the individual floating metal blocks may be configured according to the structure of IDT200as well as desired performance parameters of the SAW device. Consequently, the performance of the SAW device can be further improved.

The embodiments of the present disclosure provide an acoustic wave device. The acoustic wave device includes a piezoelectric substrate and an interdigital transducer disposed on the piezoelectric substrate, the interdigital transducer including a center region, first and second edge regions, and first and second gap regions, a temperature compensation layer covering the interdigital transducer, and a floating metal layer buried in the temperature compensation layer or disposed on top of the temperature compensation layer. The floating metal layer includes a plurality of floating metal blocks spaced apart from each other and overlapping at least the first and second edge regions of the interdigital transducer.

In one implementation, the interdigital transducer includes a first busbar, a second busbar opposite the first busbar, a plurality of first fingers extending from the first busbar and along a first direction, and a plurality of second fingers extending from the second busbar and along the first direction. The first fingers and the second fingers are alternatively disposed along a second direction perpendicular to the first direction. Each of the first fingers and the second fingers includes a first end electrically connected to one of the first busbar and the second busbar and an opposite second end having an edge portion spaced from the other one of the first busbar and the second busbar to form a gap. The edge portions of the first fingers are disposed in the first edge region, and the edge portions of the second fingers are disposed in the second edge region.

In one implementation, the plurality of floating metal blocks include a series of first floating metal blocks arranged along the second direction and overlapping at least the first edge region, and a series of second floating metal blocks arranged along the second direction overlapping at least the second edge region.

In one implementation, each of the first floating metal blocks partially overlaps an edge portion of one of the first fingers, and one of the second fingers adjacent to the first finger, and each of the second floating metal blocks partially overlaps an edge portion of one of the second fingers, and one of the first fingers adjacent to the second finger.

In one implementation, the first floating metal blocks have different thicknesses, and the second floating metal blocks have different thicknesses.

In one implementation, the first floating metal blocks have different widths along the first direction, and the second floating metal blocks have different widths along the first direction.

In one implementation, the plurality of first fingers have different widths along the second direction, and the plurality of second fingers have different widths along the second direction.

In one implementation, a width of each floating metal block among the first floating metal blocks and the second floating metal blocks is configured based on widths of one of the first fingers and one of the second fingers that the floating metal block partially overlaps.

In one implementation, the first floating metal blocks partially overlap the first gap region, and the second floating metal blocks partially overlap the second gap region.

In one implementation, a width of each one of the first gap region and the second gap region along the first direction is less than one acoustic wavelength.

In one implementation, a width of a space between adjacent first floating metal blocks or between adjacent second floating metal blocks is less than one acoustic wavelength.

In one implementation, the piezoelectric substrate is formed of lithium niobate (LN) or lithium tantalate (LT).

In one implementation, the interdigital transducer is formed of Ti, Cr, Ag, Cu, Mo, Pt, W, Al, Ti, or a stacked combination of two or more of those materials.

In one implementation, the temperature compensation layer is formed of a dielectric material.

In one implementation, the temperature compensation layer comprises a first temperature compensation layer disposed below the floating metal layer, and a second temperature compensation layer disposed above the floating metal layer.

In one implementation, the first and second temperature compensation layers are formed of the same dielectric material.

In one implementation, the floating metal layer is formed of a metal material having a relatively high density compared to a metal material of the interdigital transducer.

In one implementation, the floating metal layer is formed of Ti, Cr, or Cu, or a stacked combination of two or more of those metal materials.

In one implementation, a duty cycle of the interdigital transducer is 0.5.

In one implementation, a distance between adjacent ones of the floating metal blocks is positively related to a thickness of the floating metal blocks.

It is appreciated that certain features of the specification, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the specification, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the present disclosure. Certain features described in the context of various embodiments may not be essential features of those embodiments, unless noted as such.

It is appreciated that, although terms such as “first” and “second” are used herein for describing various elements, the elements should not be limited by these terms, which are only used for distinguishing the elements. For example, a first element may also be referred to as a second element, and similarly, the second element may also be referred to as the first element, without departing from the spirit and scope of the present disclosure.