PISTON MODE GENERATION IN THIN PLATE LAMB WAVE DEVICE

An acoustic wave resonator comprises a plurality of interdigital transducer (IDT) electrodes disposed on upper and lower sides of a piezoelectric film, the IDT electrodes on the upper side of the piezoelectric film being offset from the IDT electrodes on the lower side of the piezoelectric film by λ/4, λ being a wavelength of a main acoustic wave generated by the acoustic wave resonator to enable the acoustic wave resonator to generate piston mode acoustic waves responsive to electrical excitation of the plurality of IDT electrodes with an alternating current.

BACKGROUND

Technical Field

Embodiments of this disclosure relate to acoustic wave resonators and structures and devices including same.

Description of Related Technology

Acoustic wave devices, for example, surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices may be utilized as components of filters in radio frequency electronic systems. For instance, filters in a radio frequency front-end of a mobile phone can include acoustic wave filters. Two acoustic wave filters can be arranged as a duplexer.

SUMMARY

In accordance with one aspect, there is provided an acoustic wave resonator comprising a plurality of interdigital transducer (IDT) electrodes disposed on upper and lower sides of a piezoelectric film, the IDT electrodes on the upper side of the piezoelectric film being offset from the IDT electrodes on the lower side of the piezoelectric film by λ/4, λ being a wavelength of a main acoustic wave generated by the acoustic wave resonator to enable the acoustic wave resonator to generate piston mode acoustic waves responsive to electrical excitation of the plurality of IDT electrodes with an alternating current.

In some embodiments, the piezoelectric film includes aluminum nitride.

In some embodiments, the piezoelectric film has a thickness of between 0.1λ and 1.0λ.

In some embodiments, the piezoelectric film has a thickness of between 0.3λ, and 0.5λ.

In some embodiments, the plurality of IDT electrodes each have a thickness of between about 0.01λ and about 0.03λ.

In some embodiments, the acoustic wave resonator is included in an electrical module having a frequency generator and phase shifter that causes a phase of an excitation voltage applied to the IDT electrodes on the upper side of the piezoelectric film to be phase shifted from an excitation voltage applied to the IDT electrodes on the lower side of the piezoelectric film.

In some embodiments, the acoustic wave resonator is included in an electrical module having a frequency generator and phase shifter that causes a phase of an excitation voltage applied to the IDT electrodes on the upper side of the piezoelectric film to be phase shifted by 90° from an excitation voltage applied to the IDT electrodes on the lower side of the piezoelectric film.

In some embodiments, the acoustic wave resonator has a resonant frequency above 5 GHz.

In some embodiments, the acoustic wave resonator has a resonant frequency above 6.5 GHz.

In some embodiments, the acoustic wave resonator has a resonant frequency above one of 9 GHz or 9.2 GHz.

In accordance with another aspect, there is provided a method of generating piston mode acoustic waves in an acoustic wave resonator including a plurality of interdigital transducer (IDT) electrodes disposed on upper and lower sides of a piezoelectric film, the IDT electrodes on the upper side of the piezoelectric film being offset from the IDT electrodes on the lower side of the piezoelectric film by λ/4, λ being a wavelength of a main acoustic wave generated by the acoustic wave resonator. The method comprises applying an excitation voltage to the IDT electrodes on the upper side of the piezoelectric film that is phase shifted from an excitation voltage applied to the IDT electrodes on the lower side of the piezoelectric film.

In some embodiments, the method comprises applying an excitation voltage to the IDT electrodes on the upper side of the piezoelectric film that is phase shifted by 90° from an excitation voltage applied to the IDT electrodes on the lower side of the piezoelectric film.

In some embodiments, the method comprises generating piston mode acoustic waves in the acoustic wave resonator having a frequency above 5 GHz.

In some embodiments, the method comprises generating piston mode acoustic waves in the acoustic wave resonator having a frequency above 6.5 GHz.

In some embodiments, the method comprises generating piston mode acoustic waves in the acoustic wave resonator having a frequency above one of 9 GHz or over 9.2 GHz.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Acoustic wave elements or resonators may be classified as surface acoustic wave (SAW) elements or bulk acoustic wave (BAW) elements, depending upon whether a main acoustic wave generated by excitement of the acoustic wave element travels along a surface or through the bulk of the substrate of the element.

A Lamb wave resonator can combine features of a SAW resonator and a BAW resonator. A Lamb wave resonator typically includes an interdigital transducer (IDT) electrode similar to a SAW resonator. Accordingly, the frequency of the Lamb wave resonator can be lithographically defined. A Lamb wave resonator can achieve a relatively high quality factor (Q) and a relatively high phase velocity like a BAW resonator (e.g., due to a suspended structure). A Lamb wave resonator that includes an AlN piezoelectric layer can be relatively easy to integrate with other circuits, for example, because AlN process technology can be compatible with complementary metal oxide semiconductor (CMOS) process technology. AlN Lamb wave resonators can overcome a relatively low resonance frequency limitation and integration challenge associated with SAW resonators and also overcome multiple frequency capability challenges associated with BAW resonators.

One example of a Lamb wave resonator is illustrated in partial cross-sectional view inFIG. 1, indicated generally at10. As illustrated, the Lamb wave resonator10includes a piezoelectric layer15and interdigital transducer (IDT) electrodes20disposed on the upper and lower surfaces of the piezoelectric layer15. The piezoelectric layer15can be a thin film. The piezoelectric layer15can be an aluminum nitride layer. In other instances, the piezoelectric layer15can be any suitable piezoelectric layer. The frequency of acoustic waves generated in the Lamb wave resonator can be based on the geometry and spacing between the IDT electrodes20. Some of the IDT electrodes20can be grounded in certain instances. In some other instances, some of the IDT electrodes20can be floating. An air cavity (or vacuum cavity or a cavity filled with some other gas) is typically provided between the lower surface of the piezoelectric layer15and a substrate upon which the Lamb wave resonator is mounted to allow for acoustic waves to pass through the piezoelectric layer15.

Depending upon the voltages applied to the IDT electrodes20, the Lamb wave resonator may exhibit A0 (main mode), F0 (second harmonic), and/or F1 (second harmonic) acoustic wave excitation modes.FIG. 2illustrates the polarities that may be applied to the different IDT electrodes20to generate the A0, F0, and F1 acoustic wave excitation modes as well as a chart exhibiting the frequencies at which these modes are observed for an example device having an IDT electrode spacing λ/2 of 1 μm, an AlN layer thickness (Hs) of 0.3λ, and an IDT electrode20thickness (He, height) of 0.03λ, with λ being the wavelength of the main acoustic wave generated in the resonator.FIG. 2also illustrates the associated impedance parameter Y11 for the different excitation modes where the curves RE(+), IM(+), RE(−), and IM(−) represent the real and imaginary parts of the Y11curves with the different polarities applied to the IDT electrodes as shown in the upper part of the figure; the RE(+) and IM(+) curves generated from the polarities as illustrated with the same polarities applied to vertically corresponding IDT electrodes as shown in the left side polarity diagram inFIG. 2, the RE(−) and IM(−) curves generated from the polarities as illustrated with opposite polarities applied to vertically corresponding IDT electrodes as shown in the right side polarity diagram inFIG. 2.

It has been discovered that shifting the positions of the IDT electrodes20on the upper and lower surfaces of the piezoelectric layer15relative to one another and applying an electrical AC signal with 90 degree shifted phase relative to one another, may cause the Lamb wave resonator to exhibit an excitation mode characterized by piston mode acoustic waves (a third harmonic), similar to an excitation mode that might be observed for a film bulk acoustic wave resonator. Piston mode acoustic waves are characterized by waves that travel from the upper to the lower surface of the piezoelectric layer15and back, rather that in a direction parallel to the upper and lower surfaces. The piston mode may in some instances be preferable to any of the A0, F0, and/or F1 acoustic wave excitation modes due to a higher associated quality factor (Q) and a piezoelectric coupling coefficient K2 that is at least as good or superior to that associated with the A0, F0, and/or F1 acoustic wave excitation modes.

FIG. 3illustrates a partial cross-sectional view of a Lamb wave resonator100modified to generate a piston mode acoustic wave excitation mode. As illustrated, the positions of the IDT electrodes20on the upper and lower surfaces of the piezoelectric layer15are shifted by λ/4 relative to one another. InFIG. 3, the E2 and E1 arrows characterize the preferable electric field direction when the piston mode is exited. The relative shifting (shift of λ/4) of the upper and lower IDT electrodes provides for forming a homogeneous acoustic impedance type waveguide, where the upper and lower periodical surface acoustic impedances have an opposite distribution. In the illustrated device the piezoelectric layer15may be formed of AlN, although other piezoelectric materials may alternatively be used. The piezoelectric layer15may have a thickness Hsranging from 0.1λ to 1.0λ and IDT electrodes formed of Al or any other suitable metal, metal alloy, or metal stack and having a thickness Heranging from 0.01λ to 0.3λ. These dimensions are to be understood as only examples and may vary in different implementations according to design goals.

The piston mode acoustic wave excitation mode may be generated by applying alternating current to the IDT electrodes20as illustrated inFIG. 4. A high frequency alternating current, for example, at 8.5 GHz as illustrated inFIG. 4is applied to a first IDT electrode20on the upper surface of the piezoelectric film15and to a first IDT electrode20on the lower surface of the piezoelectric film15. The phase of the voltage applied to the first IDT electrode20on the upper surface of the piezoelectric film15is phase shifted by 90° relative to the voltage applied to the first IDT electrode20on the lower surface of the piezoelectric film15. IDT electrodes20adjacent to the first IDT electrode20on the upper surface of the piezoelectric film15and adjacent to the first IDT electrode20on the lower surface of the piezoelectric film15may be grounded, or in some instances, left floating, or held at a negative voltage. It should be understood thatFIG. 4only illustrates four IDT electrodes20. In practice, acoustic wave devices as disclosed herein may include a far greater number of IDT electrodes20. In such implementations, adjacently alternating IDT electrodes would have voltage applied and be grounded or left floating, respectively. In some implementations, the phase shift in voltage applied to the excited IDT electrodes20on the upper surface of the piezoelectric film15and the excited IDT electrodes20on the lower surface of the piezoelectric film15may be other than 90°, for example, any phase shift greater than zero degrees and up to 90° and the acoustic wave resonator100may still generate piston mode acoustic waves.

A frequency at which the piston mode excitation mode is observed as compared to the A0, F0, and F1 modes in a resonator similar to that illustrated inFIGS. 3 and 4in which λ=2 μm, Hs=0.3λ, and He=0.03λ is illustrated inFIG. 5.

The frequency at which the piston mode excitation mode is observed depends on the thickness of the piezoelectric film. Simulations were performed on a resonator similar to that illustrated inFIGS. 3 and 4in which λ=2 μm, He=0.03λ, and Hswas varied from 0.3λ to 0.5λ. The results of these simulations are shown inFIGS. 6A-6C. As can be observed, as the piezoelectric film thickness increased the piston mode resonance frequency (Fs) decreased from 9,254 MHz (for Hs=0.3λ) to 5,530 MHz (for Hs=0.5λ). The piston mode anti-resonance frequency (Fp) decreased from 9,260 MHz (for Hs=0.3λ) to 5,535 MHz (for Hs=0.5λ). The coupling coefficient K2 decreased from 0.4% (for Hs=0.3λ) to 0.2% (for Hs=0.4λ or 0.3λ).

In some embodiments, multiple resonators as disclosed herein may be combined into a filter, for example, an RF ladder filter schematically illustrated inFIG. 7and including a plurality of series resonators R1, R3, R5, R7, and R9, and a plurality of parallel (or shunt) resonators R2, R4, R6, and R8. As shown, the plurality of series resonators R1, R3, R5, R7, and R9are connected in series between the input and the output of the RF ladder filter, and the plurality of parallel resonators R2, R4, R6, and R8are respectively connected between series resonators and ground in a shunt configuration. Other filter structures and other circuit structures known in the art that may include acoustic wave devices or resonators as disclosed herein, for example, duplexers, baluns, etc., may also be formed including examples of acoustic wave devices or resonators as disclosed herein.

Examples of acoustic wave devices or discussed herein can be implemented in a variety of packaged modules. Some example packaged modules will now be discussed in which any suitable principles and advantages of the acoustic wave devices or discussed herein can be implemented.FIGS. 8, 9, and 10are schematic block diagrams of illustrative packaged modules and devices according to certain embodiments.

As discussed above, surface acoustic wave resonators can be used in acoustic wave RF filters. In turn, an RF filter using one or more acoustic wave elements may be incorporated into and packaged as a module that may ultimately be used in an electronic device, such as a wireless communications device, for example.FIG. 8is a block diagram illustrating one example of a module315including an acoustic wave element filter300. The acoustic wave element filter300may be implemented on one or more die(s)325including one or more connection pads322. For example, the acoustic wave element filter300may include a connection pad322that corresponds to an input contact for the acoustic wave element filter and another connection pad322that corresponds to an output contact for the acoustic wave element filter. The packaged module315includes a packaging substrate330that is configured to receive a plurality of components, including the die325. A plurality of connection pads332can be disposed on the packaging substrate330, and the various connection pads322of the acoustic wave element filter die325can be connected to the connection pads332on the packaging substrate330via electrical connectors334, which can be solder bumps or wirebonds, for example, to allow for passing of various signals to and from the acoustic wave element filter300. The module315may optionally further include other circuitry die340, for example, one or more additional filter(s), amplifiers, pre-filters, modulators, demodulators, down converters, and the like, as would be known to one of skill in the art of semiconductor fabrication in view of the disclosure herein. In some embodiments, the module315can also include one or more packaging structures to, for example, provide protection and facilitate easier handling of the module315. Such a packaging structure can include an overmold formed over the packaging substrate330and dimensioned to substantially encapsulate the various circuits and components thereon.

Various examples and embodiments of the acoustic wave element filter300can be used in a wide variety of electronic devices. For example, the acoustic wave element filter300can be used in an antenna duplexer, which itself can be incorporated into a variety of electronic devices, such as RF front-end modules and communication devices.

Referring toFIG. 9, there is illustrated a block diagram of one example of a front-end module400, which may be used in an electronic device such as a wireless communications device (e.g., a mobile phone) for example. The front-end module400includes an antenna duplexer410having a common node402, an input node404, and an output node406. An antenna510is connected to the common node402.

The antenna duplexer410may include one or more transmission filters412connected between the input node404and the common node402, and one or more reception filters414connected between the common node402and the output node406. The passband(s) of the transmission filter(s) are different from the passband(s) of the reception filters. Examples of the acoustic wave element filter300can be used to form the transmission filter(s)412and/or the reception filter(s)414. An inductor or other matching component420may be connected at the common node402.

The front-end module400further includes a transmitter circuit432connected to the input node404of the duplexer410and a receiver circuit434connected to the output node406of the duplexer410. The transmitter circuit432can generate signals for transmission via the antenna510, and the receiver circuit434can receive and process signals received via the antenna510. In some embodiments, the receiver and transmitter circuits are implemented as separate components, as shown inFIG. 9, however, in other embodiments these components may be integrated into a common transceiver circuit or module. As will be appreciated by those skilled in the art, the front-end module400may include other components that are not illustrated inFIG. 9including, but not limited to, switches, electromagnetic couplers, amplifiers, processors, and the like.

FIG. 10is a block diagram of one example of a wireless device500including the antenna duplexer410shown inFIG. 9. The wireless device500can be a cellular phone, smart phone, tablet, modem, communication network or any other portable or non-portable device configured for voice or data communication. The wireless device500can receive and transmit signals from the antenna510. The wireless device includes an embodiment of a front-end module400similar to that discussed above with reference toFIG. 9. The front-end module400includes the duplexer410, as discussed above. In the example shown inFIG. 10the front-end module400further includes an antenna switch440, which can be configured to switch between different frequency bands or modes, such as transmit and receive modes, for example. In the example illustrated inFIG. 10, the antenna switch440is positioned between the duplexer410and the antenna510; however, in other examples the duplexer410can be positioned between the antenna switch440and the antenna510. In other examples the antenna switch440and the duplexer410can be integrated into a single component.

The front-end module400includes a transceiver430that is configured to generate signals for transmission or to process received signals. The transceiver430can include the transmitter circuit432, which can be connected to the input node404of the duplexer410, and the receiver circuit434, which can be connected to the output node406of the duplexer410, as shown in the example ofFIG. 10.

Signals generated for transmission by the transmitter circuit432are received by a power amplifier (PA) module450, which amplifies the generated signals from the transceiver430. The power amplifier module450can include one or more power amplifiers. The power amplifier module450can be used to amplify a wide variety of RF or other frequency-band transmission signals. For example, the power amplifier module450can receive an enable signal that can be used to pulse the output of the power amplifier to aid in transmitting a wireless local area network (WLAN) signal or any other suitable pulsed signal. The power amplifier module450can be configured to amplify any of a variety of types of signal, including, for example, a Global System for Mobile (GSM) signal, a code division multiple access (CDMA) signal, a W-CDMA signal, a Long-Term Evolution (LTE) signal, or an EDGE signal. In certain embodiments, the power amplifier module450and associated components including switches and the like can be fabricated on gallium arsenide (GaAs) substrates using, for example, high-electron mobility transistors (pHEMT) or insulated-gate bipolar transistors (BiFET), or on a Silicon substrate using complementary metal-oxide semiconductor (CMOS) field effect transistors.

Still referring toFIG. 10, the front-end module400may further include a low noise amplifier module460, which amplifies received signals from the antenna510and provides the amplified signals to the receiver circuit434of the transceiver430.

The wireless device500ofFIG. 10further includes a power management sub-system520that is connected to the transceiver430and manages the power for the operation of the wireless device500. The power management system520can also control the operation of a baseband sub-system530and various other components of the wireless device500. The power management system520can include, or can be connected to, a battery (not shown) that supplies power for the various components of the wireless device500. The power management system520can further include one or more processors or controllers that can control the transmission of signals, for example. In one embodiment, the baseband sub-system530is connected to a user interface540to facilitate various input and output of voice and/or data provided to and received from the user. The baseband sub-system530can also be connected to memory550that is configured to store data and/or instructions to facilitate the operation of the wireless device, and/or to provide storage of information for the user. Any of the embodiments described above can be implemented in association with mobile devices such as cellular handsets. The principles and advantages of the embodiments can be used for any systems or apparatus, such as any uplink wireless communication device, that could benefit from any of the embodiments described herein. The teachings herein are applicable to a variety of systems. Although this disclosure includes some example embodiments, the teachings described herein can be applied to a variety of structures. Any of the principles and advantages discussed herein can be implemented in association with RF circuits configured to process signals in a range from about 30 kHz to 10 GHz, such as in the X or Ku 5G frequency bands.

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 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 microwave, a refrigerator, a vehicular electronics system such as an automotive electronics system, a stereo system, a digital music player, a radio, a camera such as a digital camera, a portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multi-functional peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products.