Lamb wave delay line with aluminum nitride piezoelectric layer

An acoustic wave element is disclosed. The acoustic wave element can include a piezoelectric layer that includes aluminum nitride. The acoustic wave element can also include a diamond like carbon layer. The acoustic wave element can further include an interdigital transducer electrode that is positioned on the piezoelectric layer. The piezoelectric layer is positioned between the interdigital transducer electrode and the diamond like carbon layer. The acoustic wave element is configured to generate a Lamb wave having a wavelength of λ.

CROSS-REFERENCE TO RELATED APPLICATION

Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet, or any correction thereto, are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

Technical Field

Embodiments of this disclosure relate to acoustic wave elements.

Description of Related Technology

Acoustic wave devices such as delay lines and acoustic wave resonators can be implemented in radio frequency electronic systems. For instance, a radio frequency front end of a mobile phone can include one or more delay lines and/or one or more acoustic wave filters that includes an acoustic wave resonator. A plurality of acoustic wave filters can be arranged as a multiplexer.

A delay line can include sets of interdigital transducer electrodes on a piezoelectric substrate. Example delay lines include Lamb wave delay lines and Rayleigh delay lines.

An acoustic wave filter can include a plurality of resonators arranged to filter a radio frequency signal. Example acoustic wave filters include surface acoustic wave (SAW) filters, bulk acoustic wave (BAW) filters, and Lamb wave filters. Example BAW resonators include film bulk acoustic wave resonators (FBARs) and solidly mounted resonators (SMRs). In BAW filters, acoustic waves propagate in a bulk of a piezoelectric layer. A SAW filter can include an interdigital transductor electrode on a piezoelectric substrate and can generate a surface acoustic wave on a surface of the piezoelectric layer on which the interdigital transductor electrode is disposed.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

In one aspect, an acoustic wave element is disclosed. The acoustic wave element can include a piezoelectric layer that includes aluminum nitride. The acoustic wave element can also include a diamond like carbon layer, and an interdigital transducer electrode positioned on the piezoelectric layer. The piezoelectric layer can be positioned between the interdigital transducer electrode and the diamond like carbon layer. The acoustic wave element can be configured to generate a Lamb wave having a wavelength of λ.

In an embodiment, the Lamb wave is a lowest-order antisymmetric mode Lamb.

In an embodiment, the acoustic wave element further includes a support layer under the diamond like carbon layer. The support layer can be a silicon layer. The silicon layer can have a thickness that is greater than 200λ. The support layer can include at least one of silicon dioxide, a ceramic, or sapphire.

In an embodiment, the piezoelectric layer is a doped aluminum nitride layer. The piezoelectric layer can be doped with scandium.

In an embodiment, the interdigital transducer electrode is an aluminum electrode.

In an embodiment, the piezoelectric layer is a thickness in a range from 0.1λ to 1λ.

In an embodiment, the diamond like carbon layer has a thickness in a range from 2 The diamond like carbon layer can have the thickness in a range from 2λ to 10λ.

In an embodiment, the acoustic wave element is a Lamb wave resonator.

In an embodiment, the acoustic wave element is included in a Lamb wave delay line.

In an embodiment, the acoustic wave element further includes a metal layer that is positioned between the piezoelectric layer and the diamond like carbon layer. The metal layer can include titanium. The metal layer can further include molybdenum. The acoustic wave element can further include a support layer under the diamond like carbon layer. The acoustic wave element can further include a silicon layer under the diamond like carbon layer.

In one aspect, an acoustic wave element configured to generate Lamb wave is disclosed. The acoustic wave element can include a piezoelectric layer that includes aluminum nitride. The acoustic wave element can also include a high acoustic velocity layer positioned under the piezoelectric layer. The high acoustic velocity layer has an acoustic velocity that is greater than an acoustic velocity of the piezoelectric layer. The acoustic wave element can further include an interdigital transducer electrode positioned over the piezoelectric layer. The acoustic wave element can be configured to generate a lowest-order antisymmetric mode Lamb wave that has a wavelength of λ.

In an embodiment, the acoustic wave element further includes a support layer positioned under the high acoustic velocity layer. The support layer can be a silicon layer. The silicon layer can have a thickness that is greater than 200λ.

In an embodiment, the piezoelectric layer is a doped aluminum nitride layer. The piezoelectric layer can be doped with scandium.

In an embodiment, the high acoustic velocity layer is a diamond like carbon layer.

In an embodiment, the high acoustic velocity layer is a diamond layer.

In an embodiment, the interdigital transducer electrode is an aluminum electrode.

In an embodiment, the acoustic wave element further includes a support layer that includes at least one of silicon dioxide, a ceramic, or sapphire.

In an embodiment, the piezoelectric layer has a thickness in a range from 0.1λ to 1λ.

In an embodiment, the high acoustic velocity layer has a thickness in a range from 2λ to 200λ. The high acoustic velocity layer can have the thickness in a range from 2λ to 50λ. The high acoustic velocity layer can have the thickness in a range from 2λ to 10λ.

In an embodiment, the acoustic wave element is a Lamb wave resonator.

In an embodiment, the acoustic wave element is included in a Lamb wave delay line.

In an embodiment, the acoustic wave element further includes a metal layer positioned between the piezoelectric layer and the diamond like carbon layer. The metal layer can include titanium. The metal layer can further include molybdenum. The acoustic wave element can further include a support layer under the diamond like carbon layer. The acoustic wave element can further include a silicon layer under the diamond like carbon layer.

In one aspect, an acoustic wave element that is configured to generate Lamb wave is disclosed. The acoustic wave element can include a piezoelectric layer that has an acoustic velocity of at least 10,000 meters per second. The acoustic wave element can also include a diamond like carbon layer that is positioned under the piezoelectric layer. The acoustic wave element can further include an interdigital transducer electrode that is positioned over the piezoelectric layer. The interdigital transducer electrode is configured to generate a Lamb wave having a wavelength of λ.

In an embodiment, a delay line includes the acoustic wave element. The delay line can have an operating frequency in a range from 5 gigahertz to 12 gigahertz. The delay line can have an operating frequency in a range from 8 gigahertz to 12 gigahertz.

In an embodiments, an acoustic wave filter includes the acoustic wave element.

In one aspect, a Lamb wave delay line is disclosed. The Lamb wave delay line can include an aluminum nitride piezoelectric layer, and a first interdigital transducer electrode that is positioned over the aluminum nitride piezoelectric layer. The first interdigital transducer electrode is configured to generate a second harmonic lowest-order antisymmetric mode Lamb wave that has a wavelength of λ. The aluminum nitride piezoelectric layer can have a thickness in a range from 0.1λ to 1λ. The Lamb wave delay line can also include a second interdigital transducer electrode positioned over the aluminum nitride piezoelectric layer. The second interdigital transducer electrode is coupled to the first interdigital transducer electrode. The first interdigital transducer electrode and the second interdigital transducer electrode are included in a delay line.

In an embodiment, the piezoelectric layer has a thickness in a range from 0.1λ to 0.5λ. The first interdigital transducer electrode can have a thickness in a range from 0.01λ to 0.1λ.

In an embodiment, the first interdigital transducer electrode has an aperture length in a range from 40λ to 60λ.

In an embodiment, the aluminum nitride piezoelectric layer is a doped aluminum nitride piezoelectric layer.

In an embodiment, the doped aluminum nitride piezoelectric layer is doped with scandium.

In an embodiment, the Lamb wave delay line has an operating frequency in a range from 5 gigahertz to 12 gigahertz. The Lamb wave delay line can have an operating frequency in a range from 8 gigahertz to 12 gigahertz. The Lamb wave delay line can have an operating frequency in a range from 8 gigahertz to 10 gigahertz.

In an embodiment, the second interdigital transducer electrode is configured to generate a second harmonic lowest-order antisymmetric mode Lamb wave.

In one aspect, a Lamb wave delay line is disclosed. The lamb wave delay line can include an aluminum nitride piezoelectric layer, and two sets of interdigital transducer electrodes over the aluminum nitride piezoelectric layer. The sets of interdigital transducer electrodes includes a first interdigital transducer electrode and a second interdigital transducer electrode. The first interdigital transducer electrode is configured to generate a second harmonic lowest-order antisymmetric mode Lamb wave having a wavelength of λ. The piezoelectric layer has a thickness in a range from 0.1λ to 1λ. The first interdigital transducer electrode and the second interdigital transducer electrode are included in a delay line. The delay line has an operating frequency in a range from 5 gigahertz to 12 gigahertz.

In an embodiment, the piezoelectric layer has a thickness in a range from 0.1λ to 0.5λ. The first interdigital transducer electrode has a thickness in a range from 0.01λ to 0.1λ.

In an embodiment, the first interdigital transducer electrode has an aperture length in a range from 40λ to 60λ.

In an embodiment, the aluminum nitride piezoelectric layer is a doped aluminum nitride piezoelectric layer. The doped aluminum nitride piezoelectric layer can be doped with scandium.

In an embodiment, the delay line matches a delay of a supply voltage to a corresponding delay arising from a phase difference between a radio frequency input signal processed by a carrier branch and a radio frequency input signal processed by a peaking branch.

In an embodiment, the delay line has an operating frequency in a range from 8 gigahertz to 12 gigahertz. The delay line can have an operating frequency in a range from 8 gigahertz to 10 gigahertz.

In one aspect, a method of operating the Lamb wave delay line described herein. The method can include receiving, by the Lamb wave delay line, a radio frequency signal, and providing, by the Lamb wave delay line, a delay for the radio frequency signal.

For purposes of summarizing the disclosure, certain aspects, advantages and novel features of the innovations have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, the innovations may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Acoustic wave elements can include acoustic wave resonators and acoustic wave delayer lines. Example acoustic wave elements disclosed herein include Lamb wave delay lines and Lamb wave resonators. A Lamb wave delay line can include two sets of interdigital transducers. A delay line can be used to provide a delay for a radio frequency (RF) signal. The delay line can provide phase rotation. Delay lines can be implemented in a variety of radio frequency applications. For example, delay lines can be used in a loop circuit coupled to the acoustic wave filter, in which the loop circuit is configured to generate an anti-phase signal to a target signal at a particular frequency. In some instances, a delay line can be implemented to reduce phase spreading.

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 include Lamb wave resonators. A Lamb wave resonator can generate a Lamb wave.

In general, high quality factor (Q), large effective electromechanical coupling coefficient (k2), high frequency ability, and spurious free response can be significant aspects for acoustic wave elements to enable low-loss filters, delay lines, stable oscillators, and sensitive sensors.

Aspects of this disclosure relate to an acoustic wave element that provides high frequency ability. Various embodiments disclosed herein can provide high frequency ability for lowest-order antisymmetric mode Lamb waves. Various embodiments disclosed herein can provide improved structural ruggedness for an acoustic wave element operable at a relatively high frequency, while maintaining a relatively high quality factor (Q) and a large effective electromechanical coupling coefficient (k2).

Embodiments of an acoustic wave element disclosed herein include a piezoelectric layer (e.g., an aluminum nitride (AlN) piezoelectric layer), and an interdigital transducer (IDT) electrode over the AlN piezoelectric layer. The acoustic wave element can also include a diamond like carbon (DLC) layer under the AlN piezoelectric layer, and a support layer (e.g., silicon (Si) layer) under the DLC layer. The acoustic wave element can further include a metal layer between the DLC layer and the AlN piezoelectric layer. In some applications, the IDT electrode can generate a second harmonic lowest-order antisymmetric mode Lamb wave having a wavelength of λ. A second harmonic lowest-order antisymmetric mode Lamb wave can be a largest resonance mode in such a device and/or have a relatively small dispersion under a substrate. Lamb wave elements disclosed herein can have relatively high resonant frequencies, such as resonant frequencies in a range from about 5 gigahertz (GHz) to 10 GHz.

Embodiments of this disclosure relate to a Lamb wave delay line that includes an aluminum nitride piezoelectric layer and interdigital transducer electrodes. The Lamb wave delay line can generate a second harmonic lowest-order antisymmetric mode Lamb wave having a wavelength of λ. A second harmonic lowest-order antisymmetric mode Lamb wave can be a largest resonance mode in such a device. The aluminum nitride piezoelectric layer can have a thickness in a range from 0.1λ to 1λ. In some embodiments, the thickness of the aluminum nitride piezoelectric layer can be less than 1 micron. The Lamb wave delay lines can have a relatively high operating frequency, such as an operating frequency in a range from 5 GHz to 10 GHz.

FIG.1Aillustrates a cross section of an acoustic wave element1according to an embodiment. The acoustic wave element1includes an aluminum nitride (AlN) piezoelectric layer10and an interdigital transducer (IDT) electrode12over the AlN piezoelectric layer10. The acoustic wave element1can be arranged to generate a second harmonic lowest-order antisymmetric mode Lamb wave having a wavelength. The material of the AlN piezoelectric layer10and a thickness H1of the AlN piezoelectric layer10are technical features that contribute to the acoustic wave element1being arranged to generate such a Lamb wave. In some embodiments, the AlN piezoelectric layer10can be formed by way of deposition. In some embodiments, the acoustic wave element1can include a cavity (e.g., an air cavity) below the AlN piezoelectric layer10.

The AlN piezoelectric layer10can be replaced with any suitable piezoelectric layer. For example, the AlN piezoelectric layer10can be replaced with any suitable electromechanical exchange material. The piezoelectric layer can include any suitable material that has an acoustic velocity of 10,000 meters per second (m/s) or greater, for example. In some embodiments, the AlN piezoelectric layer10can be doped with, for example, scandium (Sc).

A thickness H1of the AlN piezoelectric layer10can be selected based on a wavelength λ or L of an acoustic wave generated by the acoustic wave element1. The IDT electrode12has a pitch that sets the wavelength λ or L of the acoustic wave element1. The AlN piezoelectric layer10can be sufficiently thick to avoid significant frequency variation. In some embodiments, the thickness H1of the AlN piezoelectric layer can be in a range from 0.1λ to 1λ. In some instances, the thickness H1can be in a range from 0.1λ to 0.5λ. The thickness H1of the AlN piezoelectric layer10can be determined based at least in part on, for example, the mode of the operation frequency. For example, when the wavelength λ is 2 μm, the thickness H1of the AlN piezoelectric layer10can be in a range from 0.2 μm to 2 μm.

The IDT electrode12can include a bus bar and fingers that extend from the bus bar. The fingers of the IDT electrode12have an active region. The active region can a region between edge portions of the fingers and gap portions. This region can be referred to as an aperture. The IDT electrode12can include any suitable number of fingers. For example, in some applications, the IDT electrode12can include about 50 fingers. In some embodiments, the aperture of the IDT electrode can be in a range from 40λ to 60λ, for example, about 50λ.

The IDT electrode12can include any suitable IDT electrode material. In some embodiments, the IDT electrode12can include an aluminum (Al) IDT electrode. The IDT electrode12illustrated inFIG.1Ais a single layer IDT. However, the IDT electrode12can include a plurality of metal layers in some instances. The IDT electrode12may include one or more other metals, such as copper (Cu), Magnesium (Mg), tungsten (W), titanium (Ti), the like, or any suitable combination thereof. The IDT electrode12may include alloys, such as AlMgCu, AlCu, etc.

The IDT electrode12has a thickness H2. In some embodiments, the thickness H2of the IDT electrode12can be in a range from 0.01λ to 0.1λ. For example, when the wavelength λ is 2 μm, the thickness H2of the IDT electrode12can be in a range from 0.02μm to 0.2μm.

The illustrated acoustic wave element1is a Lamb wave element. The Lamb wave element can be included in a delay line in some embodiments. A Lamb wave delay line can include two sets of interdigital transducers. A delay-line can be used, for example, to match a delay of a supply voltage to a corresponding delay arising from a phase difference between an RF input signal processed by a carrier branch and an RF input signal processed by the peaking branch.

In some applications, the IDT electrode12can be configured to generate a second harmonic Lamb wave having a wavelength of λ. The second harmonic Lamb wave can be a lowest-order antisymmetric mode Lamb wave. In some embodiments, the acoustic wave element1can be included in an ultra-high frequency delay line. An operating frequency of the ultra-high frequency delay line can be in a range from 3 GHz to 20 GHz in certain applications. For example, the operating frequency can be in a range from 5 GHz to 12 GHz. As another example, the operating frequency can be in a range from 8 GHz to 10 GHz. In certain applications, the operating frequency of a delay line that include the Lamb wave element1is about 8.5 GHz. Using the lowest order antisymmetric Lamb wave mode can be beneficial in certain embodiments. The use of the lowest order antisymmetric Lamb wave mode can allow for higher frequency operation than other modes.

FIG.1Billustrates a displacement profile of the acoustic wave element1ofFIG.1A. The dashed lines betweenFIGS.1A and1Bshow relative positions of the AlN piezoelectric layer10.FIG.1Bindicates that larger displacement is concentrated between the fingers of the IDT electrode12and a smaller displacement below the fingers of IDT electrode12.

FIG.2Aillustrates a cross section of an acoustic wave element2according to another embodiment. The acoustic wave element2includes an aluminum nitride (AlN) piezoelectric layer10and an interdigital transducer (IDT) electrode12for removing cavity over the AlN piezoelectric layer10. The acoustic wave element2also includes a diamond like carbon (DLC) layer14under the AlN piezoelectric layer10, and a silicon (Si) layer16under the DLC layer14. The AlN piezoelectric layer10and the IDT electrode12illustrated inFIG.2Acan be generally similar or the same as the AlN piezoelectric layer10and the IDT electrode12, respectively, illustrated inFIG.1Ain certain embodiments.

In the acoustic wave element2, the AlN piezoelectric layer10can be replaced with any suitable piezoelectric layer. For example, the piezoelectric layer can include any suitable material that has an acoustic velocity of 10,000 m/s or greater. In some embodiments, the AlN piezoelectric layer10can be doped with, for example, scandium (Sc).

A thickness H1of the AlN piezoelectric layer10can be selected based on a wavelength λ or L of an acoustic wave generated by the acoustic wave element2. The IDT electrode12has a pitch that sets the wavelength λ or L of the acoustic wave element2. The AlN piezoelectric layer10can be sufficiently thick to avoid significant frequency variation. In some embodiments, the thickness H1of the AlN piezoelectric layer10can be in a range from 0.1λ to 1λ. In some instances, the thickness H1can be in a range from 0.1λ to 0.5λ. The thickness H1of the AlN piezoelectric layer10can be determined based at least in part on, for example, the mode of the operation frequency. For example, when the wavelength λ is 2 μm, the thickness H1of the AlN piezoelectric layer10can be in a range from 0.2 μm to 2 μm.

The IDT electrode12can include a bus bar and fingers that extend from the bus bar. The fingers of the IDT electrode12have an active region. The active region can a region between edge portions of the fingers and gap portions. This region can be referred to as an aperture. The IDT electrode12can include any suitable number of fingers. For example, in some applications, the IDT electrode12can include about 50 fingers. In some embodiments, the aperture of the IDT electrode can be in a range from 40λ to 60λ, for example, about 50λ.

The IDT electrode12can include any suitable IDT electrode material. In some embodiments, the IDT electrode12can include an aluminum (Al) IDT electrode. The IDT electrode12illustrated inFIG.1Ais a single layer IDT. However, the IDT electrodes12can include a plurality of metal layers in some instances. The IDT electrode12may include one or more other metals, such as copper (Cu), Magnesium (Mg), tungsten (W), titanium (Ti), the like, or any suitable combination thereof. The IDT electrode12may include alloys, such as AlMgCu, AlCu, etc.

The IDT electrode12has a thickness H2. In some embodiments, the thickness H2of the IDT electrode12can be in a range from 0.01λ to 0.1λ. For example, when the wavelength λ is 2 μm, the thickness H2of the IDT electrode12can be in a range from 0.02 μm to 0.2 μm.

By having a relatively high acoustic velocity material for the DLC layer14, the DLC layer14can trap acoustic energy in the AlN piezoelectric layer10, such that the quality factor (Q) can be generally maintained or unchanged as compared to an acoustic wave element without the DLC layer14. The DLC layer14can be replaced with any other suitable high acoustic velocity layer. For example, the high acoustic velocity layer can include any material that has an acoustic velocity that is higher than an acoustic velocity of a piezoelectric layer (e.g., the AlN piezoelectric layer10). In some embodiments, the high acoustic velocity layer can include any material that has an acoustic velocity greater than 10,000 m/s.

The DLC layer has a thickness H3. In some embodiments, the thickness H3of the DLC layer14can be greater than about 2λ. For example, the thickness H3of the DLC layer14can be in a range from 2λ to 200λ. In some applications, the thickness H3of the DLC layer14can be determined based, at least in part, on, for example, the mode of the operation frequency. In some applications, the DLC layer14that has the thickness H3equal to or greater than 2λ can have lower loss than the DLC layer14that has the thickness less than 2λ. In some applications, the DLC layer14can suppress an acoustic wave propagation in the Si layer16. This may allow the acoustic wave element2to maintain high velocity, high frequency operation with improved mechanical ruggedness as compared to an acoustic wave element without the DLC layer14.

The Si layer16can be replaced with any suitable support layer. In some embodiments, the support layer can include a relatively high thermal conductivity material. For example, the support layer can include a ceramic, silicon dioxide (SiO2), sapphire, etc.

The Si layer16has a thickness H4. The thickness H4of the Si layer16can be, for example, greater than 200λ. In some embodiments, the thickness H4of the Si layer16can be determined based at least in part on a desired final thickness of the acoustic wave element2.

The DLC layer14and the Si layer16can individually or in combination provide mechanical support for the AlN piezoelectric layer10. In some embodiments, the Si layer16may be omitted and only the DLC layer14may provide support for the AlN piezoelectric layer10. For example, a lowest order antisymmetric mode Lamb wave velocity of the acoustic wave element2can be about 10% higher than a similar acoustic wave element that does not include the DLC layer14.

The acoustic wave element2can be an acoustic wave resonator or an acoustic wave delay line. In some applications, the acoustic wave resonator can be included in an acoustic wave filer. In some embodiments, the acoustic wave element2can be a Lamb wave element. The Lamb wave element can be a Lamb wave resonator in certain instances. A Lamb wave resonator is a type of acoustic wave resonator. The Lamb wave element can be a delay line in some instances. A Lamb wave delay line can include two sets of interdigital transducers. A delay-line can be used, for example, to match a delay of a supply voltage to a corresponding delay arising from a phase difference between an RF input signal processed by a carrier branch and an RF input signal processed by the peaking branch.

In some applications, the IDT electrode12can be configured to generate a second harmonic Lamb wave having a wavelength of λ. The second harmonic Lamb wave can be a lowest-order antisymmetric mode Lamb wave. In some embodiments, the acoustic wave element2can include an ultra-high frequency delay line. An operation frequency of the ultra-high frequency delay line can be in a range from 3 GHz to 20 GHz in certain applications. For example, the operating frequency can be in a range from 5 GHz to 10 GHz. As another example, the operating frequency can be in a range from 8 GHz to 10 GHz. In certain applications, the operating frequency of a delay line that includes the Lamb wave element1is about 8.5 GHz. Using the lowest order antisymmetric mode Lamb wave can be beneficial in certain embodiments. The use of the lowest order antisymmetric mode Lamb wave can allow for higher frequency operation than other modes.

FIG.2Billustrates a displacement profile of the acoustic wave element2ofFIG.2A. The dashed lines betweenFIGS.2A and2Bshow relative positions of the components of the acoustic wave element2. As withFIG.1B,FIG.2Bindicates that larger displacement is concentrated between the fingers of the IDT electrode12and a smaller displacement below the fingers of the IDT electrode12.FIG.2Balso shows that the displacement propagates through at least a portion of the DLC layer14.

FIGS.3A to3Cillustrate simulated total displacement profile, electric potential, and stress of the acoustic wave element2at a resonance condition. The simulations are based on a lowest-order antisymmetric mode Lamb wave. The acoustic wave element2used for the simulation includes an aluminum nitride (AlN) piezoelectric layer10with a thickness H1of 0.3λ, an IDT electrode12formed of an aluminum (Al) IDT electrode with a thickness H2of 0.03λ, a diamond like carbon (DLC) layer14with a thickness H3of 2λ, and a silicon (Si) layer16with a thickness H4of 5λ.

FIG.3Ashows that the total displacement is distributed in the AlN piezoelectric layer10and at an upper portion (near a boundary between the AlN piezoelectric layer10and the DLC layer14) of the DLC layer14. The total displacement is propagated through about 1λ of the DLC layer14from the boundary between the AlN piezoelectric layer10and the DLC layer14. At a lower portion of the DLC layer14opposite the upper portion, there is no notable displacement. Therefore, there is no or almost no displacement in the Si layer16.

FIG.3Bshows that the electrical potential is concentrated at or near the boundary between the AlN piezoelectric layer10and the DLC layer14. High reflection can be assumed neat the boundary in such calculation results.FIG.3Cshows that stress is propagated in the AlN piezoelectric layer10and at the upper portion (near the boundary between the AlN piezoelectric layer10and the DLC layer14) of the DLC layer14.

FIGS.4A to4Cillustrate simulated admittance results for the acoustic wave element1and acoustic element2having various thicknesses H1(H1=0.2λ, 0.3λ, and 0.5λ) of the AlN piezoelectric layer10. The y-axes ofFIGS.4A to4Cshow the simulated admittance in decibel (dB) and the x-axes ofFIGS.4A-4Cshow the frequency in mega-hertz (MHz). The simulation is based on a lowest-order antisymmetric mode Lamb wave.

FIG.4Ashows the simulated result (1) for the acoustic wave element1and the simulated result (2) for the acoustic wave element2, when the thickness H1of the AlN piezoelectric layer10is 0.2λ. The acoustic velocity of the acoustic element2increased about 16% relative to the acoustic velocity of the acoustic element1. The coupling factor (K2) and the quality factor (Q) of the acoustic velocity of the acoustic element2are observed to be generally similar to the coupling factor (K2) and the quality factor (Q) of the acoustic velocity of the acoustic element1.

FIG.4Bshows the simulated result (1) for the acoustic wave element1and the simulated result (2) for the acoustic wave element2, when the thickness H1of the AlN piezoelectric layer10is 0.3λ. The acoustic velocity of the acoustic element2increased about 5% relative to the acoustic velocity of the acoustic element1. The coupling factor (K2) and the quality factor (Q) of the acoustic velocity of the acoustic element2are observed to be generally similar to the coupling factor (K2) and the quality factor (Q) of the acoustic velocity of the acoustic element1.

FIG.4Cshows the simulated result (1) for the acoustic wave element1and the simulated result (2) for the acoustic wave element2, when the thickness H1of the AlN piezoelectric layer10is 0.5λ. The acoustic velocity of the acoustic element2increased about 8% relative to the acoustic velocity of the acoustic element1. The coupling factor (K2) and the quality factor (Q) of the acoustic velocity of the acoustic element2are observed to be generally similar to the coupling factor (K2) and the quality factor (Q) of the acoustic velocity of the acoustic element1.

FIG.5illustrates a cross section of an acoustic wave element3according to another embodiment. The acoustic wave element3includes an aluminum nitride (AlN) piezoelectric layer10, an interdigital transducer (IDT) electrode12over the AlN piezoelectric layer10, a diamond like carbon (DLC) layer14under the AlN piezoelectric layer10, a silicon (Si) layer16under the DLC layer14, and a metal layer18between the AlN piezoelectric layer10and the DLC layer14. The AlN piezoelectric layer10, the IDT electrode12, the DLC layer14, and the Si layer16illustrated inFIG.5can each be generally similar or the same as the AlN piezoelectric layer10, the IDT electrode12, the DLC layer14, and the Si layer16, respectively, disclosed herein with respect to other embodiments. The acoustic wave element3with the DLC layer14may exclude a cavity that may be required for a similar conventional acoustic wave element that does not have a DLC layer.

As illustrated inFIG.5, the metal layer18can include a plurality of layers of different metals. For example, the metal layer18can include a titanium (Ti) layer18aon the DLC layer14and a molybdenum (Mo) layer18bbetween the Ti layer18aand the AlN piezoelectric layer10. In some applications, the metal layer18can help increase the coupling factor (K2) of the acoustic wave element3, and/or improve the quality factor (Q) of the acoustic wave element3. This can be due to the metal layer18trapping charge. The Ti layer18acan help increase the bonding strength between the metal layer18and the DLC layer14. The metal layer18can include any suitable metal or any material with a relatively low acoustic loss. For example, the metal layer18can include one or more of aluminum (Al), tungsten (W), gold (Au), silver (Ag), copper (Cu), iridium (Ir) and/or the like material. In some embodiments, the metal layer18may not affect acoustic performance of the acoustic wave element3. For example, the metal layer18can only affect electrical performance of the acoustic wave element3.

The metal layer18has a thickness H5. The thickness H5of the metal layer18can be less than 0.01λ. For example, the thickness H5of the metal layer18can be in a range from 0.002λ to 0.01λ. For example, when the wavelength λ is 2 μm, the thickness H5of the metal layer18can be in a range from 0.004 μm to 0.02 μm.

FIG.6is a graph showing simulation results of admittance of acoustic wave elements according to various embodiments. The y-axis ofFIG.6is for the admittance and the x-axis is for the frequency. The simulations were run for the acoustic wave element1, the acoustic element2, and the acoustic element3. The simulation results inFIG.6show that the thickness H5of the metal layer18of the acoustic element3affects the acoustic velocity. Further, when the metal layer18has the thickness H5that is less than 0.01λ, the reduction in acoustic velocity is relatively small. At the same time, the coupling factor (K2) is improved relative to those without the metal layer18.

FIGS.7A to7Cillustrate simulated total displacement profile, electric potential, and electrical field direction of the acoustic wave element3at an resonance condition. The simulations are based on a lowest-order antisymmetric mode Lamb wave. The acoustic wave element3used for the simulation includes an aluminum nitride (AlN) piezoelectric layer10, an IDT electrode12, a diamond like carbon (DLC) layer14, a silicon (Si) layer (not illustrated), and a metal layer18between the AlN piezoelectric layer10and the DLC layer14.

FIG.7Ashows that the total displacement is distributed in the AlN piezoelectric layer10, the metal layer18, and at an upper portion (near a boundary between metal layer18and the DLC layer14) of the DLC layer14. The total displacement is propagated through about 1λ of the DLC layer14from the boundary between the metal layer18and the DLC layer10. At a lower portion of the DLC layer14opposite the upper portion, there is no notable displacement.

FIG.7Bshows that the metal layer18affects the electrical potential distribution. This can allow for an increased quality factor (Q) of the acoustic wave element3as compared to a similar acoustic wave element without the metal layer18.FIG.7Cshows that the electrical field is concentrated near the metal layer18.

FIG.8illustrates a schematic top view of an acoustic wave delay line4with electrical connections thereof, according to one embodiment. The acoustic wave delay line4includes an aluminum nitride (AlN) piezoelectric layer10, and an interdigital transducer (IDT) electrode12over the AlN piezoelectric layer10. The acoustic wave delay line4can include one or more acoustic wave elements in accordance with any suitable principles and advantages disclosed herein. As illustrated inFIG.8, the acoustic wave delay line4can include two sets22aand22bof interdigital transducers that are longitudinally coupled to each other. A first set22aof the two sets of interdigital transducers is spaced apart along a longitudinal direction from a second set22bof the two sets of interdigital transducers. The first set22ais electrically connected to an input port and the second set22bis electrically connected to an output port. The first set22aand the second set22bare both electrically coupled and be grounded. The delay line4can include acoustic wave elements1in certain embodiments. The delay line4can include acoustic wave elements2in some other embodiments. The delay line4can have a relatively high operating frequency. The operating frequency of the delay line4can be in a frequency range from 3 GHz to 20 GHz in certain applications. For example, the operating frequency can be in a range from 5 GHz to 10 GHz. As another example, the operating frequency can be in a range from 8 GHz to 10 GHz. In certain applications, the operating frequency of a delay line4is about 8.5 GHz.

An acoustic path between the two sets22aand22bof interdigital transducers has a distance D. In some applications, such as in case of a single mode propagation, a delay in the acoustic wave delay line4can be calculated by dividing the distance D by the acoustic velocity. In some embodiments, the delay line4can include additional interdigital transducers positioned over the AlN piezoelectric layer10. For example, the delay line4can include another pair of interdigital transducer sets coupled to the two sets22aand22bof interdigital transducers.

FIG.9Ais a schematic diagram of an example transmit filter100that includes acoustic wave resonators according to an embodiment. The transmit filter100can be a band pass filter. The illustrated transmit filter100is arranged to filter a radio frequency signal received at a transmit port TX and provide a filtered output signal to an antenna port ANT. Some or all of the acoustic wave resonators TS1to TS7and/or TP1to TP5can be acoustic wave resonators in accordance with any suitable principles and advantages disclosed herein. For instance, one or more of the acoustic wave resonators of the transmit filter100can be an acoustic wave element2ofFIG.2Aor an acoustic wave element3ofFIG.5. Alternatively or additionally, one or more of the acoustic wave resonators of the transmit filter100can be any acoustic wave element disclosed herein. Any suitable number of series acoustic wave resonators and shunt acoustic wave resonators can be included in a transmit filter100.

FIG.9Bis a schematic diagram of a receive filter105that includes acoustic wave resonators according to an embodiment. The receive filter105can be a band pass filter. The illustrated receive filter105is arranged to filter a radio frequency signal received at an antenna port ANT and provide a filtered output signal to a receive port RX. Some or all of the acoustic wave resonators RS1to RS8and/or RP1to RP6can be acoustic wave resonators in accordance with any suitable principles and advantages disclosed herein. For instance, one or more of the acoustic wave resonators of the receive filter105can be a acoustic wave element2ofFIG.2Aor an acoustic wave element3ofFIG.5. Alternatively or additionally, one or more of the acoustic wave resonators of the receive filter105can be any acoustic wave resonator disclosed herein. Any suitable number of series acoustic wave resonators and shunt acoustic wave resonators can be included in a receive filter105.

Acoustic wave elements disclosed herein can be implemented in delay lines arranged to delay a radio frequency signal for a fifth generation (5G) technology application. Acoustic wave elements disclosed herein can be implemented in filters arranged to filter a radio frequency signal for a 5G technology application. Acoustic wave elements disclosed herein can operate at relatively high operating frequencies. Such acoustic wave elements can be used to delay and/or filter radio frequency signals having a frequency of at least 5 GHz that are within a 5G New Radio (NR) operating band within Frequency Range1(FR1). FR1can include a frequency range from 410 megahertz (MHz) to 7.125 gigahertz (GHz), for example, as specified in a current 5G NR specification. In certain implementations, acoustic wave elements disclosed herein can delay and/or filter radio frequency signals having frequencies above FR1. According to various implementations, acoustic wave elements disclosed herein can delay and/or filter radio frequency signals having frequencies above 6 GHz, such as radio frequency signals in a frequency range from 6 GHz to 10 GHz.

FIG.10Ais a schematic diagram of a radio frequency module175that includes an acoustic wave component176according to an embodiment. The illustrated radio frequency module175includes the acoustic wave component176and other circuitry177. The acoustic wave component176can include one or more acoustic wave elements with any suitable combination of features of the acoustic wave element disclosed herein. The acoustic wave component176can include an acoustic wave die that includes acoustic wave elements.

The acoustic wave component176shown inFIG.10Acan include acoustic wave elements178and terminals179A and179B. The acoustic wave elements178can include one or more acoustic wave elements with any suitable combination of features of the acoustic wave element disclosed herein. For example, one or more of the acoustic wave elements178can be an acoustic wave resonator included in an acoustic wave filter and implemented in accordance with any suitable principles and advantages of the acoustic wave element2ofFIG.2Aand/or any acoustic wave resonators disclosed herein The acoustic wave elements178can implement one or more delay lines. Alternatively or additionally, the acoustic wave elements178can be included in one or more acoustic wave filters and/or implement one or more acoustic wave filters.

The terminals179A and179B can serve, for example, as an input contact and an output contact. The acoustic wave component176and the other circuitry177are on a common packaging substrate180inFIG.10A. The package substrate180can be a laminate substrate. The terminals179A and179B can be electrically connected to contacts181A and181B, respectively, on the packaging substrate180by way of electrical connectors182A and182B, respectively. The electrical connectors182A and182B can be bumps or wire bonds, for example. The other circuitry177can 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 module175can include one or more packaging structures to, for example, provide protection and/or facilitate easier handling of the radio frequency module175. Such a packaging structure can include an overmold structure formed over the packaging substrate180. The overmold structure can encapsulate some or all of the components of the radio frequency module175.

FIG.10Bis a schematic diagram of a radio frequency module175′ that includes an acoustic wave component176′ according to an embodiment. The radio frequency module175′ can be generally similar to the radio frequency module175illustrated inFIG.10A. The illustrated radio frequency module175′ includes the acoustic wave component176′ and other circuitry177. The acoustic wave component176′ can include one or more acoustic wave elements with any suitable combination of features of the acoustic wave element disclosed herein. The acoustic wave component176′ can include an acoustic wave die that includes acoustic wave elements. The acoustic wave component176′ can include a delay line178′.

FIG.11is a schematic diagram of a radio frequency module184that includes an acoustic wave resonator according to an embodiment. As illustrated, the radio frequency module184includes duplexers185A to185N that include respective transmit filters186A1to186N1and respective receive filters186A2to186N2, a power amplifier187, a select switch188, and an antenna switch189. In some instances, the module184can include one or more low noise amplifiers configured to receive a signal from one or more receive filters of the receive filters186A2to186N2. The radio frequency module184can include a package that encloses the illustrated elements. The illustrated elements can be disposed on a common packaging substrate180. The packaging substrate can be a laminate substrate, for example.

The duplexers185A to185N 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 filters186A1to186N1can include one or more acoustic wave resonators in accordance with any suitable principles and advantages disclosed herein. Similarly, one or more of the receive filters186A2to186N2can include one or more acoustic wave resonators in accordance with any suitable principles and advantages disclosed herein. AlthoughFIG.11illustrates 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 amplifier187can amplify a radio frequency signal. The illustrated switch188is a multi-throw radio frequency switch. The switch188can electrically couple an output of the power amplifier187to a selected transmit filter of the transmit filters186A1to186N1. In some instances, the switch188can electrically connect the output of the power amplifier187to more than one of the transmit filters186A1to186N1. The antenna switch189can selectively couple a signal from one or more of the duplexers185A to185N to an antenna port ANT. The duplexers185A to185N can be associated with different frequency bands and/or different modes of operation (e.g., different power modes, different signaling modes, etc.).

FIG.12is a schematic block diagram of a module190that includes duplexers191A to191N and an antenna switch192. One or more filters of the duplexers191A to191N can include any suitable number of acoustic wave resonators in accordance with any suitable principles and advantages discussed herein. Any suitable number of duplexers191A to191N can be implemented. The antenna switch192can have a number of throws corresponding to the number of duplexers191A to191N. The antenna switch192can electrically couple a selected duplexer to an antenna port of the module190.

FIG.13Ais a schematic block diagram of a module210that includes a power amplifier212, a radio frequency switch214, and duplexers191A to191N in accordance with one or more embodiments. The power amplifier212can amplify a radio frequency signal. The radio frequency switch214can be a multi-throw radio frequency switch. The radio frequency switch214can electrically couple an output of the power amplifier212to a selected transmit filter of the duplexers191A to191N. One or more filters of the duplexers191A to191N can include any suitable number of acoustic wave resonators in accordance with any suitable principles and advantages discussed herein. Any suitable number of duplexers191A to191N can be implemented.

FIG.13Bis a schematic block diagram of a module215that includes filters216A to216N, a radio frequency switch217, and a low noise amplifier218according to an embodiment. One or more filters of the filters216A to216N can include any suitable number of acoustic wave resonators in accordance with any suitable principles and advantages disclosed herein. Any suitable number of filters216A to216N can be implemented. The illustrated filters216A to216N are receive filters. In some embodiments (not illustrated), one or more of the filters216A to216N can be included in a multiplexer that also includes a transmit filter. The radio frequency switch217can be a multi-throw radio frequency switch. The radio frequency switch217can electrically couple an output of a selected filter of filters216A to216N to the low noise amplifier218. In some embodiments (not illustrated), a plurality of low noise amplifiers can be implemented. The module215can include diversity receive features in certain applications.

FIG.14Ais a schematic diagram of a wireless communication device220that includes filters223in a radio frequency front end222according to an embodiment. The filters223can include one or more acoustic wave resonators in accordance with any suitable principles and advantages discussed herein. The wireless communication device220can be any suitable wireless communication device. For instance, a wireless communication device220can be a mobile phone, such as a smart phone. As illustrated, the wireless communication device220includes an antenna221, an RF front end222, a transceiver224, a processor225, a memory226, and a user interface227. The antenna221can transmit/receive RF signals provided by the RF front end222. Such RF signals can include carrier aggregation signals. Although not illustrated, the wireless communication device220can include a microphone and a speaker in certain applications.

The RF front end222can include one or more delay lines, 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 end222can transmit and receive RF signals associated with any suitable communication standards. The filters223can include one or more acoustic wave resonators that includes any suitable combination of features discussed with reference to any embodiments discussed above. Alternatively or additionally, the RF front end222can include one or more delay lines that include an acoustic wave element that includes any suitable combination of features discussed with reference to any embodiments discussed above.

The transceiver224can provide RF signals to the RF front end222for amplification and/or other processing. The transceiver224can also process an RF signal provided by a low noise amplifier of the RF front end222. The transceiver224is in communication with the processor225. The processor225can be a baseband processor. The processor225can provide any suitable base band processing functions for the wireless communication device220. The memory226can be accessed by the processor225. The memory226can store any suitable data for the wireless communication device220. The user interface227can be any suitable user interface, such as a display with touch screen capabilities.

FIG.14Bis a schematic diagram of a wireless communication device230that includes filters223in a radio frequency front end222and a second filter233in a diversity receive module232. The wireless communication device230is like the wireless communication device200ofFIG.14A, except that the wireless communication device230also includes diversity receive features. As illustrated inFIG.14B, the wireless communication device230includes a diversity antenna231, a diversity module232configured to process signals received by the diversity antenna231and including filters233, and a transceiver234in communication with both the radio frequency front end222and the diversity receive module232. The filters233can include one or more acoustic wave resonators that include any suitable combination of features discussed with reference to any embodiments discussed above. Alternatively or additionally, the diversity receive module232can include one or more delay lines that include an acoustic wave element that includes any suitable combination of features discussed with reference to any embodiments discussed above. In certain instances, the diversity receive module232can be considered part of a RF front end.

Any of the embodiments described above can be implemented in 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 cellular 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 having a frequency in a range from about 30 kHz to 300 GHz, such as a frequency in a 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 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 peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products.