Transducer device having coupled resonant elements

A transducer device includes a coupling cavity, a first resonant element and a second resonant element. The first resonant element is coupled to the coupling cavity and configured to send or receive acoustic signals. The second resonant element is coupled to the coupling cavity and configured to modify a frequency response of the first resonant element via the coupling cavity.

BACKGROUND

Generally, acoustic transducers convert received electrical signals to acoustic signals when operating in a transmit mode, and/or convert received acoustic signals to electrical signals when operating in a receive mode. The functional relationship between the electrical and acoustic signals of an acoustic transducer depends, in part, on the acoustic transducer's operating parameters, such as natural or resonant frequency, acoustic receive sensitivity, acoustic transmit output power and the like.

Acoustic transducers are manufactured pursuant to specifications that provide specific criteria for the various operating parameters. Applications relying on acoustic transducers, such as piezoelectric ultrasonic transducers and electro-mechanical system (MEMS) transducers, for example, typically require precise conformance with these criteria. In certain ultrasonic applications, for example, in which acoustic systems use frequency or phase modulation schemes, the bandwidth of the acoustic transducer may be engineered to improve performance. For example, multiple transducers with different resonant frequencies may be arranged in an array, so that the overall response of the transducer array is the desired frequency response. However, multiple designs are required to address each implementation, which may be time consuming and expensive. Also, a transducer array may require a relatively large physical layout in order to achieve the desired frequency response.

SUMMARY

In a representative embodiment, a transducer device includes a coupling cavity and first and second resonant elements. The first resonant element is coupled to the coupling cavity and configured to send or receive acoustic signals. The second resonant element is coupled to the coupling cavity and configured to modify a frequency response of the first resonant element via the coupling cavity.

In another representative embodiment, a transducer device includes a first resonant element including a first membrane arranged on a substrate and a first transducer structure stacked on the first membrane, and a second resonant element including a second membrane arranged on the substrate. The transducer device further includes a common coupling cavity configured to couple acoustic signals from the first and second resonant elements. The second resonant element may also include a second transducer structure stacked on the second membrane.

In another representative embodiment, a transducer device includes a first resonant element, a second resonant element and a mechanical coupler. The first resonant element is positioned on a substrate over a first cavity and has a first frequency response. The second resonant element is positioned on the substrate over a second cavity adjacent to the first resonant element and has a second frequency response. The mechanical coupler is in contact with the first and second resonant elements, causing each of the first and second resonant elements to oscillate at frequencies other than the first and second frequency responses, respectively.

DETAILED DESCRIPTION

Generally, it is understood that the drawings and the various elements depicted therein are not drawn to scale. Further, relative terms, such as “above,” “below,” “top,” “bottom,” “upper,” “lower,” “left,” “right,” “vertical” and “horizontal,” are used to describe the various elements' relationships to one another, as illustrated in the accompanying drawings. It is understood that these relative terms are intended to encompass different orientations of the device and/or elements in addition to the orientation depicted in the drawings. For example, if the device were inverted with respect to the view in the drawings, an element described as “above” another element, for example, would now be “below” that element. Likewise, if the device were rotated 90 degrees with respect to the view in the drawings, an element described as “vertical,” for example, would now be “horizontal.”

According to various embodiments, a coupled transducer device includes multiple resonant elements and a common coupling cavity for coupling the acoustic waves transmitted and/or received by the transducer device. The effect of the coupling cavity and the multiple resonant elements is to modify performance of one or more of the multiple resonant elements. The resonant elements may include multiple stacked transducer structures (two or more) arranged on thin plates or membranes that move or deform at predetermined frequencies. Alternatively, the resonant elements may include at least one transducer structure arranged on a membrane and at least one membrane (i.e., without a corresponding transducer structure). Also, according to various embodiments, a coupled transducer device includes multiple resonant elements and a mechanical coupling for coupling the acoustic waves transmitted and/or received by the transducer device. The coupled transducer device may be configured as an ultrasonic micro-electro-mechanical system (MEMS) device, for example.

A resonant transducer (e.g., one transducer structure) may be represented by a harmonic oscillator, for which displacement x is represented by Equation (1):

Solving Equation (1), it is determined that x=A sin(ω0t+δ), where ω0is resonant frequency, and A and δ are the amplitude and phase provided by the initial conditions.

When two harmonic oscillators (e.g., corresponding to two transducer structures) with the same resonant frequency are coupled together, the respective displacements x are represented by Equations (2) and (3), where the sub-index 1 and 2 refer to each harmonic oscillator and K is the coupling constant:

The general solution is in the form xi=A1sin(ω1t+δ1)+A2sin(ω2t+δ2) where i=1 or 2, ω12ω02+2K2and ω22=ω02. Consequently either of the two harmonic oscillators will incorporate an additional frequency of oscillation due to the coupling of the other oscillator.

Applying this basic principle to coupled transducer devices, the acoustic response of each transducer (e.g., including the frequency, amplitude and/or phase of oscillation) is modified by coupling another transducer or resonant element, as discussed below. Hence, the coupling enables design and controlled manipulation of the responses of two (or more) transducers or other resonant elements.

In an embodiment, both of the transducers may be is driven to achieve motion in both transducers. However, in alternative embodiments, only one of the transducers may be driven to achieve motion in both transducers. When only one of the transducers is driven, the resonant frequencies of the two transistors may be the same or different. When the resonant frequencies are different, the solution for the coupled transducer device includes more frequencies. For example, in the general case in which the two harmonic resonators have different resonant frequencies ω01and ω02, the general solution will involve frequencies represented by Equation (4):

FIG. 1Ais as top plan view illustrating a resonant element of a coupled transducer device, which includes a stacked transducer structure, according to a representative embodiment.FIG. 1Bis a cross-sectional diagram illustrating the resonant element of a coupled transducer device depicted inFIG. 1A, taken along line A-A′, according to a representative embodiment.

Referring toFIGS. 1A and 1B, resonant element110includes substrate105, on which thin plate or membrane130and transducer structure140are stacked. In the depicted embodiment, the membrane130and the transducer structure140are substantially circular in shape, and the transducer structure140forms an annular ring defining a center opening145, through which a center portion of a top surface of the membrane130is exposed. In alternative embodiments, the membrane130and/or the transducer structure140may be formed in different shapes, such as ovals, squares, rectangles and the like, without departing from the scope of the present teachings. Likewise, the shapes of the membrane130and the transducer structure140may be different from one another. For example, a substantially circular transducer structure140may be formed on a substantially rectangular membrane130, without departing from the scope of the present teachings.

As shown inFIG. 1B, the membrane130is positioned on the substrate105over a cavity120, which enables the mechanical movement of the exposed portion of the membrane130. The substrate105may be formed of various types of materials, including an insulating material, such as glass, sapphire, alumina or the like, or any semiconductor material compatible with semiconductor processes, such as silicon, gallium arsenide (GaAs), indium phosphide (InP) or the like. A semiconductor material is useful for integrating connections and electronics, thus reducing size and cost. The opening of the cavity120in the top surface of the substrate105is substantially circular, although it may have any of a variety of sizes and shapes, such as oval, square, rectangular and the like, without departing from the scope of the present teachings.

The membrane130may also be formed of various types of materials compatible with semiconductor processes, including polysilicon, silicon nitride, silicon carbide, boron silicate glass, or the like. The membrane130is thin enough to enable mechanical movement or vibrations in response to electrical and/or acoustic signals. For example, the membrane130may be about 0.5-2 microns thick at the exposed portion in order to vibrate at ultrasonic frequencies, although the thickness may vary to provide unique benefits for any particular situation or to meet application specific design requirements of various implementations, as would be apparent to one skilled in the art.

In the representative embodiment depicted inFIG. 1B, the transducer structure140includes multiple, stacked layers. In particular, a first electrode141is stacked on the top surface of the membrane130, a piezoelectric layer142is stacked on a top surface of the first electrode141, and a second electrode143is stacked on a top surface of the piezoelectric layer142. The first and second electrodes141and143are formed of an electrically conductive material, such as molybdenum, tungsten or aluminum or the like, and the piezoelectric layer142is formed of a thin film of aluminum nitride (AlN), zinc oxide (ZnO), or other film compatible with semiconductor processes. The thicknesses of the electrodes and piezoelectric layers may range from about 0.1 microns to about 1.5 microns, for example. A passivation layer144may be optionally included on a top surface of the second electrode143, in order to protect the other layers from humidity, debris and contaminants. The passivation layer144may be formed from silicon dioxide, silicon nitride, oxynitride, boron-silicate glass (BSG) or the like.

The first and second electrodes141and143are electrically connected to external circuitry via contact pads (not shown), which may be formed of a conductive material, such as gold, gold-tin alloy or the like. The contact pads may electrically connect with the first and second electrodes141and143through various electronic circuits (not shown), such as connectors passing through vias formed in the substrate105and/or the membrane130, trace patterns and the like.

As discussed above, the first and second electrodes141and143, the piezoelectric layer142and the passivation layer144may be substantially circular rings, which surround the suspended portion of the membrane130. In alternative embodiments, the first electrode141and the piezoelectric layer142may not include an opening, but rather may be formed over the entire surface of the membrane130. In this configuration, the top surface of the piezoelectric layer142is exposed through the opening in the transducer structure140, as opposed to the top surface of the membrane130, as shown inFIG. 1A. In a transmit mode (e.g., a speaker), an electrical input signal (e.g., excitation signal) may be input to the first and/or second electrodes141and143, via corresponding contact pads, and converted to a mechanical vibration (or resonance) having a frequency induced by the piezoelectric layer142and/or the membrane130. In a receive mode (e.g., a microphone), an acoustic input signal may be input to the piezoelectric layer142and/or the membrane130through the center opening145and/or the cavity120, and converted to a corresponding electrical output signal output by the first and/or second electrodes141and143, via the contact pads.

The resonant element110may be an ultrasonic transducer fabricated using MEMS technology, for example, known as a MEMS ultrasonic transducer (MUT). In this case, the membrane130moves or deforms at ultrasonic frequencies, which is translated into electrical signals available at the contact pads. In various embodiments, the translation may be made through a piezoelectric material (p-MUT), e.g., by the piezoelectric layer144and/or the membrane130, or through a capacitance variation (c-MUT). It is understood that other types and arrangements of membranes and/or transducer structures may be incorporated in the resonant element110, without departing from the scope of the present teachings.

FIG. 2Ais as top plan view illustrating a resonant element of a coupled transducer device, which includes a thin plate or membrane, according to a representative embodiment.FIG. 2Bis a cross-sectional diagram illustrating the resonant element of a coupled transducer device depicted inFIG. 2A, taken along line B-B′, according to a representative embodiment.

Referring toFIGS. 2A and 2B, resonant element210includes substrate205, on which thin plate or membrane230is stacked, without a transducer structure. In the depicted embodiment, the membrane230is substantially circular in shape, although in alternative embodiments, the membrane230may be formed in different shapes, such as ovals, squares, rectangles and the like, without departing from the scope of the present teachings.

As shown inFIG. 2B, the membrane230is positioned on the substrate205over a cavity220, which enables mechanical movement of the exposed portion of the membrane230. The substrate205may be formed of various types of materials, including an insulating material, such as glass, sapphire, alumina or the like, or any semiconductor material compatible with semiconductor processes, such as silicon, GaAs, InP, or the like. The membrane230may also be formed of various types of materials compatible with semiconductor processes, including polysilicon, silicon nitride, silicon carbide, boron silicate glass or the like. The membrane230is thin enough to enable mechanical movement or vibrations in response to pressure waves, e.g., acoustic signals. For example, the membrane230may be about 0.5-2 microns thick at the portion exposed over the cavity220in order to vibrate at ultrasonic frequencies, although the thickness may vary to provide unique benefits for any particular situation or to meet application specific design requirements of various implementations, as would be apparent to one skilled in the art.

As stated above, according to various embodiments, resonant elements, such as representative resonant elements110and210, are combined in various configurations to share a coupling cavity or a mechanical coupling, such that the two or more coupled resonant elements (referred to as a coupled transducer device) has a modified oscillation behavior, including a modified frequency response, different from that of each of the individual resonant elements. The frequency response of the resonant element combination may therefore be engineered to provide specific benefits or to meet application specific design requirements of various implementations. According to various embodiments, any number or type of resonant elements may be combined in alternative ways to share a coupling cavity, without departing from the scope of the present teachings.FIGS. 3A-6Bprovide specific non-limiting examples, using combinations of the representative resonant elements110and/or120, as discussed below.

ReferringFIG. 3A, coupled transducer device300A includes two vertically stacked resonator elements310-1and310-2, and a coupling cavity360formed between the vertically stacked resonator elements310-1and310-2. The bottom resonator element310-1includes transducer structure341stacked on membrane331, and the top resonator element310-2includes transducer structure342stacked on membrane332. The resonator elements310-1and310-2are thus configured to send or receive acoustic signals through the ambient environment, as well as through the coupling cavity360. In the depicted embodiment, the transducer structures341,342and the corresponding membranes331,332are substantially the same as the transducer structure140and the membrane130discussed above with reference toFIGS. 1A and 1B. The vertical arrangement of the resonator elements310-1,310-2and the coupling cavity360enables efficient use of space on the wafer (e.g., the substrate305).

The bottom resonator element310-1is arranged over cavity320of the substrate305, which enables mechanical movement or oscillation of the exposed portion of the membrane331. The substrate305may be formed of various types of materials, including glass, sapphire, alumina, silicon, GaAs, InP or the like. The top resonator element310-2is arranged on support structure303above and substantially in alignment with the bottom resonator element310-1.

The support structure303includes vertical walls extending from the top surface of the substrate305and a horizontal top surface, which includes and/or supports the membrane332of the top resonator element310-2. The coupling cavity360is formed by the inside surface of the support structure303and the top surface of the substrate305, as well as top and side portions of the first resonant element310-1and the exposed bottom portion of the second resonant element310-2. The coupling cavity360may include a vent (not shown), for example, traversing a portion of the support structure303or the substrate305. The vent creates a semi-sealed cavity, which provides pressure equalization and otherwise allows for pressure changes in the environment.

In an embodiment, the support structure303is formed of the same material as the membrane332, such as polysilicon, silicon nitride, silicon carbide, boron silicate glass or the like, in which case the support structure303may be one integrated piece, e.g., as discussed below with reference toFIGS. 7E-7I. Mechanical movement of the membrane332is enabled by the coupling cavity360and the center opening of the transducer structure342. Alternatively, the vertical walls and an outer peripheral portion of the horizontal top surface of the support structure303may be formed from a different material than the membrane332, in which case the membrane332may be stacked on a horizontal top surface of the support structure303over an opening formed therein (e.g., substantially the same size and shape as the opening of the cavity320) or attached to the edges of the opening, enabling mechanical movement of an exposed portion of the membrane332over the coupling cavity360. The support structure303may be formed, for example, using sacrificial layer semiconductor processes or through a microcap process, an example of which is described in U.S. patent application Ser. No. 12/430,966, filed Apr. 28, 2009, the subject matter of which is hereby incorporated by reference.

ReferringFIG. 3B, coupled transducer device300B includes two vertically stacked resonator elements310-1and310-3, and a coupling cavity360formed between the vertically stacked resonator elements310-1and310-3. The bottom resonator element310-1includes transducer structure341stacked on membrane331, and the top resonator element310-3includes only membrane333. In the depicted embodiment, the transducer structure341and the membranes331,333are substantially the same as the transducer structure140and the membrane130discussed above with reference toFIGS. 1A and 1B, and the membrane230discussed above with reference toFIGS. 2A and 2B. The vertical arrangement of the resonator elements310-1,310-3and the coupling cavity360enables efficient use of space on the wafer (e.g., the substrate305).

The bottom resonator element310-1is arranged over cavity320of substrate305, as discussed above with reference toFIG. 3A. The top resonator element310-3is arranged on support structure303above and substantially in alignment with the bottom resonator element310-1. The support structure303includes vertical walls extending from the top surface of the substrate305and a horizontal top surface, which includes and/or supports the membrane333of the top resonator element310-3. In an embodiment, the support structure303is formed of the same material as the membrane333, such as polysilicon, silicon nitride, silicon carbide, boron silicate glass, or the like, in which case the support structure303may be one integrated piece. Alternatively, the vertical walls and an outer peripheral portion of the horizontal top surface of the support structure303may be formed from a different material than the membrane333, in which case the membrane333may be stacked on a horizontal top surface of the support structure303over an opening formed therein (e.g., substantially the same size and shape as the opening of the cavity320) or attached to the edges of the opening, enabling mechanical movement of an exposed portion of the membrane333over the coupling cavity360.

InFIGS. 3A and 3B, pressure waves (e.g., acoustic signals) formed by oscillations of the bottom resonator element310-1and the top resonator element310-2or310-3are translated through the coupling cavity360, thus affecting the oscillation behavior of one another. Accordingly, the frequency response and other characteristics of the coupled transducer devices300A and300B are different from those of either the bottom resonator element310-1and the top resonator element310-2,310-3. The substantially enclosed nature of the coupling cavity360enables a relatively strong coupling response.

ReferringFIG. 4A, coupled transducer device400A includes two adjacent, horizontally arranged resonator elements410-1and410-2, and a coupling cavity460extending beneath cavities421and422of the resonator elements410-1and410-2. The left resonator element410-1includes transducer structure441stacked on membrane431, and the right resonator element410-2includes transducer structure442stacked on membrane432. Mechanical movements or oscillations of the membranes431and432are enabled by the cavities421and422, respectively. The resonator elements410-1and410-2are thus configured to send or receive acoustic signals through the ambient environment, as well as through the coupling cavity460. In the depicted embodiment, the transducer structures441,442and the corresponding membranes431,432are substantially the same as the transducer structure140and the membrane130discussed above with reference toFIGS. 1A and 1B.

The left resonator element410-1is arranged over the cavity421of substrate405and the right resonator element410-2is arranged over the cavity422of substrate405, which enables mechanical movement of the exposed portions of the membranes431,432, respectively. The substrate405may be formed of various types of materials, such as glass, sapphire, alumina, silicon, GaAs, InP or the like. Also, in another embodiment, the membranes431and432may be formed of the same membrane layer, extending continuously below the transducer structures441and442.

The coupling cavity460is defined by the substrate405and cavity structure403formed beneath the substrate405. The cavity structure403includes vertical walls extending from the bottom surface of the substrate405and a horizontal bottom portion, which defines a coupling cavity opening461. In an embodiment, the cavity structure403is formed of the same material as the substrate405, such as glass, sapphire, alumina, silicon, GaAs, InP or the like, in which case the cavity structure403and the substrate450may be one piece. The cavity structure403may be formed, for example, using sacrificial layer semiconductor processes or through a microcap process, an example of which is described in U.S. patent application Ser. No. 12/430,966, filed Apr. 28, 2009, the subject matter of which is hereby incorporated by reference.

In an embodiment, a gas permeable screen or mesh (not shown) may cover the coupling cavity opening461in order to provide additional protection of the internal components, including the exposed lower surfaces of the membranes431and432. For example, the screen or mesh may include multiple apertures sufficiently large to allow exposure to the ambient environment, yet small enough to limit the amount of debris, contaminates and moisture that can enter the coupling cavity opening461.

ReferringFIG. 4B, coupled transducer device400B includes two adjacent, horizontally arranged resonator elements410-1and410-3, and a coupling cavity460extending beneath cavities421and422of the resonator elements410-1and410-3. The left resonator element410-1includes transducer structure441stacked on membrane431, and the right resonator element410-3includes only membrane433, with no transducer structure. Mechanical movements or oscillations of the membranes431and433are enabled by the cavities421and422, respectively. In the depicted embodiment, the transducer structure441and the membranes431,433are substantially the same as the transducer structure140and the membrane130discussed above with reference toFIGS. 1A and 1B, and the membrane230discussed above with reference toFIGS. 2A and 2B.

The left resonator element410-1is arranged over the cavity421of substrate405and the right resonator element410-3is arranged over the cavity422of substrate405, which enables mechanical movement of the exposed portions of the membranes431,433, as discussed above with reference toFIG. 4A. Also, in another embodiment, the membranes431and433may be formed of the same membrane layer, extending continuously over the top surface of the substrate405, across opening of both cavities421,422and below the transducer structure441. The coupling cavity460is defined by the substrate405and cavity structure403formed beneath the substrate405, as discussed above with reference toFIG. 4A.

InFIGS. 4A and 4B, pressure waves (e.g., acoustic signals) formed by oscillations of the left resonator element410-1and the right resonator element410-2or410-3are translated through the coupling cavity460, thus affecting the oscillation behavior of one another. Accordingly, the frequency response and other characteristics of the coupled transducer devices400A and400B are different from those of either the left resonator element410-1and the right resonator element410-2,410-3.

FIG. 5Ais as top plan view illustrating a horizontally arranged coupled transducer device and coupling beam, according to a representative embodiment.FIG. 5Bis a cross-sectional diagram illustrating the horizontally arranged coupled transducer device ofFIG. 5A, taken along line C-C′, according to a representative embodiment.

ReferringFIGS. 5A and 5B, coupled transducer device500includes two adjacent, horizontally arranged resonator elements510-1and510-2. However, instead of a coupling cavity, in which acoustic signals are coupled in a gas coupling medium (e.g., air), the resonator elements510-1and510-2are coupled mechanically through a solid element, depicted as rectangular bar or coupling beam533. The coupling beam533works similarly to an air coupling medium, such as coupling cavities360and460, in order to couple resonant elements, accounting for differences in acoustic signal propagation. However, the coupling beam533may be formed in any shape, such as a rectangle, serpentine, wedge, or the like, to provide unique benefits for any particular situation or to meet application specific design requirements of various implementations, as would be apparent to one skilled in the art.

The coupling beam533extends between and contacts the membranes531and532of the resonator elements510-1and510-2. In the depicted embodiment, the coupling beam533is formed from the same layer as the membranes531and532, and thus is made of the same material, e.g., polysilicon, silicon nitride, silicon carbide, boron silicate glass, or the like. Alternatively, the coupling beam533may be formed separately from the membranes531and532, in which case the coupling beam533may be formed of the same or different material as the membranes531and532. The coupling beam533may be a hanging beam, for example, positioned over a gap523(e.g., air gap), which is formed between a bottom surface of the coupling beam533and a top surface of a center portion of the substrate505. The gap523may be formed as a recess or “swimming pool” in the substrate505, for example, using sacrificial layer semiconductor processes.

Referring toFIG. 5B, the left resonator element510-1includes transducer structure541stacked on membrane531, and the right resonator element510-2includes transducer structure542stacked on membrane532. Mechanical movements of the membranes531and532are enabled by the cavities521and522, respectively, and translated to one another via the coupling beam533. The resonator elements510-1and510-2are thus configured to send or receive acoustic signals through the ambient environment, as well as through the coupling beam533. In the depicted embodiment, the transducer structures541,542and the corresponding membranes531,532are substantially the same as the transducer structure140and the membrane130discussed above with reference toFIGS. 1A and 1B.

The left resonator element510-1is arranged over the cavity521of substrate505and the right resonator element510-2is arranged over the cavity522of substrate505, which enables mechanical movement of the exposed portions of the membranes531,532, respectively. The substrate505may be formed of various types of materials, such as glass, sapphire, alumina, silicon, GaAs, InP, or the like. Also, in another embodiment, the membranes531and532may be formed of the same membrane layer, extending continuously below the transducer structures541and542and including the coupling beam533, as stated above.

In an embodiment, a gas permeable screens or meshes (not shown) may cover the openings of cavities521and522in order to provide additional protection of the internal components, including the exposed lower surfaces of the membranes531and532. For example, the screen or mesh may include multiple apertures sufficiently large to allow exposure to the ambient environment, yet small enough to limit the amount of debris, contaminates and moisture that can enter the openings of cavities521and522.

FIG. 6Ais as top plan view illustrating a horizontally arranged coupled transducer device and coupling beam, according to a representative embodiment.FIG. 6Bis a cross-sectional diagram illustrating the horizontally arranged coupled transducer device ofFIG. 6A, taken along line D-D′, according to a representative embodiment.

ReferringFIGS. 6A and 6B, coupled transducer device600includes two adjacent, horizontally arranged resonator elements610-1and610-2, which are coupled mechanically through a solid element, depicted as rectangular bar or coupling beam633, instead of a coupling cavity. As discussed above with reference to coupling beam533inFIGS. 5A and 5B, the coupling beam633may be formed in any shape, such as a rectangle, serpentine, wedge, or the like, to provide unique benefits for any particular situation or to meet application specific design requirements of various implementations, as would be apparent to one skilled in the art. Also, the coupling beam633extends between and contacts the membranes631and632of the resonator elements610-1and610-2. In the depicted embodiment, the coupling beam633is formed from the same layer as the membranes631and632, and thus is made of the same material, e.g., polysilicon, silicon nitride, silicon carbide, boron silicate glass, or the like. Alternatively, the coupling beam633may be formed separately from the membranes631and632, in which case the coupling beam633may be formed of the same or different material as the membranes631and632. The coupling beam632is positioned over a gap623(e.g., air gap), which is formed between a bottom surface of the coupling beam633and a top surface of a center portion of the substrate605, as discussed above.

The left resonator element610-1includes transducer structure641stacked on membrane631, as discussed above with reference to left resonator element510-1. However, the right resonator element610-3includes only membrane632(with no stacked transducer structure). Mechanical movements of the membranes631and632are enabled by the cavities621and622, respectively, and translated to one another via the coupling beam633. The resonator elements610-1and610-2are thus configured to send or receive acoustic signals through the ambient environment, as well as through the coupling beam633. In the depicted embodiment, the transducer structure641and the membranes631,632are substantially the same as the transducer structure140and the membrane130discussed above with reference toFIGS. 1A and 1B, and the membrane230discussed above with reference toFIGS. 2A and 2B.

The left resonator element610-1is arranged over cavity621of substrate605and the right resonator element610-3is arranged over cavity622of substrate605, which may be formed of various types of materials, including an insulating material, such as glass, sapphire, alumina or the like, or any semiconductor material compatible with semiconductor processes, such as silicon, GaAs, InP, or the like. Also, in another embodiment, the membranes631and632may be formed of the same membrane layer, extending continuously below the transducer structure641and including the coupling beam633, as stated above. In an embodiment, a gas permeable screens or meshes (not shown) may cover the openings of cavities621and622in order to provide additional protection of the internal components, including the exposed lower surfaces of the membranes631and632.

As stated above, the coupled transducer devices of the various representative embodiments (e.g., coupled transducer devices300A,300B,400A,400B,500and600) may be fabricated in accordance with various techniques compatible with semiconductor processes. A non-limiting example of a fabrication process directed to transducer device300A depicted inFIG. 3Ais provided byFIGS. 7A-7I, using a surface micromachining approach, according to various embodiments. It is understood that all or part of the process depicted inFIGS. 7A-7Imay be applied to the fabrication of the other coupled transducer devices300B,400A,400B,500and600discussed herein.

Referring toFIG. 7A, a “swimming pool” or recess325is formed in a top surface of the substrate305, using by machining or by chemically etching the substrate305using photolithography, although various alternative techniques may be incorporated. In an embodiment, the recess325may be about 2-3 microns deep, for example. The recess is filled with a phosphosilicate glass (PSG) film, for example. A chemical mechanical polish (CMP) may be performed to create a planar top surface.

Referring toFIG. 7B, the resonant element310-1is formed on the top surfaces of the substrate305and PSG filled recess325. As discussed above, the resonant element310-1includes membrane331and stacked transducer structure341. The resonant element310-1may be fabricated by applying a layer of polysilicon, silicon nitride, silicon carbide, boron silicate glass or the like, to the top surfaces of the substrate305and PSG filled recess325as the membrane331. The transducer structure341may then be formed by applying a layer of an electrically conductive material, such as molybdenum, tungsten or aluminum or the like, as a first electrode, applying a piezoelectric thin film, such as AlN or ZnO, as a piezoelectric layer, applying another layer of the electrically conductive material as a second electrode, and optionally applying a passivation layer. The conductive layers may be respectively patterned, for example, using photolithography, although various alternative techniques may be incorporated, to provide the desired shapes of the bottom and top electrodes.

Referring toFIG. 7C, the substrate305and the resonant element310-1are covered with PSG layer326, which is then polished using CMP to create a planar top surface. The PSG layer326is masked and etched to the desired dimensions, as shown inFIG. 7D.

Referring toFIG. 7E, a membrane material303a, such as polysilicon, silicon nitride, silicon carbide, boron silicate glass or the like, is deposited over the PSG layer326and the substrate305. In an embodiment, the membrane material303ais the same material used to form the membrane331, and may be deposited using a plasma-enhanced chemical-vapor deposition (PECVD) process, for example. Unwanted membrane material303ais removed by etching, as shown inFIG. 7F, to form the membrane layer (or support structure)303. The etching includes removal of excess membrane material303afrom the top surface of the substrate305, as well as forming etch hole308. The etching may include chemically etching the membrane material303ausing photolithography, although various alternative techniques may be incorporated.

Referring toFIG. 7G, the resonant element310-2is formed on the top surface of the membrane material303. As discussed above, the resonant element310-2includes membrane332and stacked transducer structure342, which is fabricated according to substantially the same process described above with respect to the transducer structure341. In the depicted embodiment, the membrane332is integral with the membrane layer303, and therefore need not be formed in separate step.

Referring toFIG. 7H, back side etching is performed on a bottom surface of the substrate305to form preliminary cavity327directly below the PSG filled recess325, which serves as an etch stop. The back side etch may include using a dry etch process, such as a Bosch process, for example, although various alternative techniques may be incorporated without departing from the scope of the present teachings. The PSG material of the recess325and the PSG layer326is then chemically released or etched, for example, using a wet etch process including HF etch solution, for example. After the PSG material has been removed, cavity320is formed through the substrate305(by merging the recess325and the preliminary cavity327) and the coupling cavity360is formed within the membrane layer303, as shown inFIG. 7I. Also, the etch hole308becomes a vent for the coupling cavity360.

In an embodiment, the contact pads (not shown) may be formed by applying a gold layer to the outer surfaces of the substrate305and the membrane layer303, respectively, and patterning the gold layer, for example, using photolithography, although various alternative techniques may be incorporated. As stated above, the contact pads connect with the first and second electrodes of both transducer structures341and342by connectors (not shown) formed through corresponding via holes through the substrate305and/or the membranes331and332. The via holes may be formed prior to the formation of the transducer structures341and342and the contact pads, for example, using photolithography, although various alternative techniques may be incorporated. It is understood that, in other embodiments, the number, location and arrangement of the contact pads and corresponding connectors vary to provide unique benefits for any particular situation or to meet application specific design requirements of various implementations, as would be apparent to one skilled in the art.

According to various embodiments, the coupling transducer device eliminates the technical trade off between bandwidth and gain when only one transducer is used. Also, the he coupled transducer device is well suited for time-of-flight measurements that utilize frequency or phase modulation schemes.

The various components, materials, structures and parameters are included by way of illustration and example only and not in any limiting sense. In view of this disclosure, those skilled in the art can implement the present teachings in determining their own applications and needed components, materials, structures and equipment to implement these applications, while remaining within the scope of the appended claims.