Patent Description:
A non-intrusive imaging system for imaging internal organs of a human body and displaying images of the internal organs transmits signals into the human body and receives signals reflected from the organ. Typically, transducers that are used in an imaging system are referred to as transceivers and some of the transceivers are based on photo-acoustic or ultrasonic effects. In general, piezoelectric transducers are used for imaging as well as other applications, such as medical imaging, flow measurements in pipes, speaker, microphone, lithotripsy, heating tissue for therapeutics, and highly intensive focused ultrasound (HIFU) for surgery.

Advances in micro-machining technologies allow sensors and actuators to be efficiently incorporated on a substrate. In particular, micromachined ultrasound transducers (MUTs), using capacitive transduction (cMUTs) or piezoelectric transduction (pMUTs), are particularly advantageous compared to the conventional bulk piezoelectric elements having a large form factor. Although the basic concepts for these transducers have been disclosed in the early <NUM>'s, commercial implementation of these concepts has met with a number of challenges. For instance, the conventional cMUT sensors are particularly prone to failure or drift in performance due to the dielectric charge build-up during operation. The conventional pMUTs have been a promising alternative but have issues related to transmission and receive inefficiencies. As such, there is a need for pMUTs that have enhanced efficiencies and can be applied to various sensing devices.

<CIT> describes an ultrasonic element that has a vibrating film and a piezoelectric element part. The piezoelectric element part has a lower electrode, a piezoelectric layer and an upper electrode. The vibrating film is provided so as to cover an opening. The opening is formed by etching the silicon substrate from the back side thereof.

<CIT> and <CIT> relate to a transceiver element comprising a substrate and a membrane with a constant thickness suspending from the substrate.

In embodiments, a transceiver element includes: a substrate; at least one membrane suspending from the substrate; and a plurality of transducer elements mounted on the at least one membrane, each of the plurality of transducer elements having a bottom electrode, a piezoelectric layer on bottom electrode, and at least one top electrode on the piezoelectric layer, each of the plurality of transducer element generating a bending moment in response to applying an electrical potential across the bottom electrode and the at least one top electrode and developing an electrical charge in response to applying a bending moment thereto.

In embodiments, an imaging system includes: a transceiver cell for generating a pressure wave and converting an external pressure wave into an electrical signal; and a control unit for controlling an operation of the transceiver cell. The transceiver cell includes: a substrate; at least one membrane suspending from the substrate; and a plurality of transducer elements mounted on the at least one membrane, each of the plurality of transducer elements having a bottom electrode, a piezoelectric layer on bottom electrode, and at least one top electrode on the piezoelectric layer, each of the plurality of transducer element generating a bending moment in response to applying an electrical potential across the bottom electrode and the at least one top electrode and developing an electrical charge in response to a bending moment due to the external pressure wave.

References will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

In the following description, for purposes of explanation, specific details are set forth in order to provide an understanding of the disclosure. It will be apparent, however, to one skilled in the art that the disclosure can be practiced without these details. Furthermore, one skilled in the art will recognize that embodiments of the present disclosure, described below, may be implemented in a variety of ways, such as a process, an apparatus, a system, or a device.

Elements/components shown in diagrams are illustrative of exemplary embodiments of the disclosure and are meant to avoid obscuring the disclosure. Reference in the specification to "one embodiment," "preferred embodiment," "an embodiment," or "embodiments" means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the disclosure and may be in more than one embodiment. The appearances of the phrases "in one embodiment," "in an embodiment," or "in embodiments" in various places in the specification are not necessarily all referring to the same embodiment or embodiments. The terms "include," "including," "comprise," and "comprising" shall be understood to be open terms and any lists that follow are examples and not meant to be limited to the listed items. Any headings used herein are for organizational purposes only and shall not be used to limit the scope of the description or the claims. Furthermore, the use of certain terms in various places in the specification is for illustration and should not be construed as limiting.

<FIG> shows an imaging system <NUM> according to embodiments of the present disclosure. As depicted, the system <NUM> may include: an imager <NUM> that generates and transmit pressure waves <NUM> toward an internal organ <NUM>, such as heart, in a transmit mode/process; and a device <NUM> that communicates signals to the imager through a communication channel <NUM>. In embodiments, the internal organ <NUM> may reflect a portion of the pressure waves <NUM> toward the imager <NUM>, and the imager <NUM> may capture the reflected pressure waves and generate electrical signals in a receive mode/process. The imager <NUM> may communicate the electrical signals to the device <NUM> and the device <NUM> may display images of the human organ on a display/screen <NUM> using the electrical signals.

It is noted that the imager <NUM> may be used to get an image of internal organs of an animal, too. It is also noted that the pressure wave <NUM> may be acoustic, ultrasonic, or photo-acoustic waves that can travel through the human/animal body and be reflected by the internal organs.

In embodiments, the imager <NUM> may be a portable device and communicate signals through the communication channel <NUM>, either wirelessly or via a cable, with the device <NUM>. In embodiments, the device <NUM> may be a mobile device, such as cell phone or iPad, or a stationary computing device that can display images to a user.

<FIG> shows a block diagram of the imager <NUM> according to embodiments of the present disclosure. In embodiments, the imager <NUM> may be an ultrasonic imager. As depicted in <FIG>, the imager <NUM> may include: a transceiver tile(s) <NUM> for transmitting and receiving pressure waves; a coating layer <NUM> that operates as a lens for focusing the pressure waves and also functions as an impedance interface between the transceiver tile and the human body <NUM>; a control unit <NUM>, such as ASIC chip, for controlling the transceiver tile(s) <NUM>; a microprocessor <NUM> for controlling the components of the imager <NUM>; a communication unit <NUM> for communicating data with an external device, such as the device <NUM>, through one or more ports <NUM>; a memory <NUM> for storing data; a battery <NUM> for providing electrical power to the components of the imager; and optionally a display <NUM> for displaying images of the target organs.

In embodiments, the device <NUM> may have a display/screen. In such a case, the display may not be included in the imager <NUM>. In embodiments, the imager <NUM> may receive electrical power from the device <NUM> through one of the ports <NUM>. In such a case, the imager <NUM> may not include the battery <NUM>. It is noted that one or more of the components of the imager <NUM> may be combined into one integral electrical element. Likewise, each component of the imager <NUM> may be implemented in one or more electrical elements.

In embodiments, the user may apply gel on the coating layer <NUM> so that the impedance matching between the coating layer <NUM> and the human body <NUM> may be improved, i.e., the power loss at the interface is reduced.

<FIG> shows a schematic diagram of an exemplary transceiver tile <NUM> according to embodiments of the present disclosure. While the number of cells <NUM> and the arrangement of the transceiver cells within the transceiver tile <NUM> can be arbitrary in nature, some typical arrangements may include a rectangular grid, hexagonal grid, annular grid, polar grid and so on. Purely for illustrative purposes, the transceiver tile <NUM> having nine transceiver cells <NUM> is shown in <FIG> A.

<FIG> shows top and side views of a transceiver array <NUM> that includes one or more transceiver tiles according to embodiments of the present disclosure. As depicted, the transceiver array <NUM> may include one or more transceiver tiles <NUM> arranged in a predetermined manner. For instance, the transceiver tiles (or, shortly tiles) <NUM> may be physically bent to further form a curved transceiver array and disposed in the imager <NUM>. It should be apparent to those of ordinary skill in the art that the imager <NUM> may include any suitable number of tiles and the tiles may be arranged in any suitable manner, and each tile <NUM> may include any suitable number of transceiver cells that are the same as or similar to the cell <NUM>. In embodiments, the transceiver array <NUM> may be a micro-machined array fabricated from a substrate.

<FIG> shows an enlarged view of the transceiver cell <NUM> according to embodiments of the present disclosure. As depicted, each cell includes one or more arbitrarily shaped membranes <NUM>. Three membranes in <FIG> are shown purely for the purpose of illustration, even though other suitable number of membranes may be included in the transceiver cell <NUM>. In embodiments, the transceiver cell <NUM> can be of any arbitrary geometrical shape, such as (but not limited to) rectangle, rhomboid, hexagon or circle.

In embodiments, one or more piezoelectric elements <NUM> may be mounted on each membrane <NUM>, where the membrane may be actuated by the piezoelectric elements <NUM> or by an external pressure. In embodiments, a combination of a membrane <NUM> and one or more piezoelectric elements <NUM> may be used to create a piezoelectric transducer that transmits ultrasound or acoustic waves and convert acoustic or ultrasound waves impinging on the membrane to electrical signals. In embodiments, each membrane <NUM> can be of arbitrary shape and can have different length and width. According to the invention the membrane has a variable thickness.

In embodiments, each membrane <NUM> may be actuated at one or more primary modes of vibration. The resonance frequency of the membrane may be determined by various parameters: physical geometry of the membrane, variation of the thickness of the membrane, etc. In embodiments, the variation in the thickness of the membrane <NUM> may be achieved by at least one of etching the membrane and selectively depositing materials on the membrane.

In embodiments, the actuation of the membranes <NUM> by the piezoelectric elements <NUM> to create an acoustic output, i.e., pressure wave, is known as a transmit mode/process and denoted by Tx. Similarly, the transduction of an external pressure on the membrane to a change in charge on the piezoelectric element is known as a receive mode/process and denoted by Rx. Hereinafter, the combination of the membrane <NUM> with the piezoelectric elements <NUM> is referred to as a transducer element <NUM>. In embodiments, the membrane <NUM> may be interpreted as mechanically resonating elements including, but not limited to cantilevers, simply supported beams, diaphragms, corrugated diaphragms, and other simply supported or encastered apparatus.

In embodiments, one or more electrical connections <NUM> may be made to the piezoelectric elements <NUM> by means of electrical wires. The electrical wires (not shown in <FIG>) may be deposited on the transceiver cell <NUM> by various techniques, such as micro-machining, wire bonding techniques, or connecting external electrical circuits to the cell via vertical interconnections.

<FIG> shows a cross sectional view of an exemplary piezoelectric element <NUM> according to embodiments of the present disclosure. As depicted, the piezoelectric element <NUM> may include: a bottom electrode <NUM>, one or more top electrodes <NUM>, and a piezoelectric layer <NUM> disposed between the top and bottom electrodes. While a unimorph piezoelectric element is shown in <FIG> purely for the purpose of illustration, in embodiments, a multi-layer piezoelectric element (multi-morph) composed of a plurality of piezoelectric sublayers and electrodes can be utilized. Also, in embodiments, the piezoelectric element <NUM> may include one or more top electrodes, even though <FIG> shows three top electrodes for the purpose of illustration. In embodiments, the piezoelectric layer <NUM> may include at least one of PZT, KNN, PZT-N, PMN-Pt, AIN, Sc-AIN, ZnO, PVDF, and LiNiO<NUM>.

In embodiments, the thickness of the piezoelectric layer <NUM> may be less than <NUM> pm and the electrical potential between the top and bottom electrodes in the Tx mode/process may be <NUM> ~ <NUM> V. In contrast, the electrical potential between the top and bottom electrodes of a conventional piezoelectric element ranges <NUM> ~ <NUM> V. Since the electrical power for driving the piezoelectric element <NUM> may be proportional to the square of voltage of the pulse or waveform driving the piezoelectric element, the power consumed by the piezoelectric element <NUM> may be significantly lower than the power consumed by the conventional piezoelectric element.

In embodiments, the piezoelectric element <NUM> may be a piezoelectric micromachined ultrasound transducer and fabricated by conventional techniques that are used in the semiconductor, MEMS or ultrasonic industry. Similarly, in embodiments, the other components in the transceiver array <NUM> may be fabricated by the conventional techniques in the semiconductor, MEMS or ultrasonic industry.

<FIG> shows a cross sectional view of the transceiver cell <NUM> in <FIG>, taken along the line <NUM>-<NUM>, according to embodiments of the present disclosure. As depicted, the membrane <NUM>, which may be the same as or similar to the membrane <NUM>, has a varying thickness and may be coupled with multiple piezoelectric elements 520a - 520c. In embodiments, the membrane <NUM> may suspend from the bottom substrate <NUM> (which may be the same as similar to the substrate <NUM> in <FIG>) by a suspension mechanism <NUM>.

In embodiments, the thickness of the membrane <NUM> may be varied by forming one or more of grooves <NUM>, corrugations and perforation/aperture <NUM> in a planar membrane. In embodiments, the thickness of the membrane <NUM> may be varied by forming only grooves and/or corrugations <NUM> in a planar membrane so that one or more hermetic cavities may be formed underneath the membrane. In embodiments, materials may be selectively deposited or deposited and patterned to form bumps <NUM> on the top and/or bottom surface of the membrane, where the bumps vary the thickness of the membrane. In embodiments, the thickness variation of the membrane <NUM> may be achieved by conventional wafer processing techniques, such as etching and deposition techniques.

In embodiments, one or more piezoelectric elements 520a - 520c may be disposed on the top and/or bottom surface of the membrane <NUM>. In embodiments, each of the piezoelectric elements 520a - 520c may have two or more terminals and have different sizes and geometries. For instance, the piezoelectric element 520a and 520b may have two terminals, while the piezoelectric element 520c may have three terminals (one bottom electrode and two top electrodes).

In embodiments, the piezoelectric elements 520a - 520c may be connected to electrical wires/conductors (now shown in <FIG>), where the electrical wires may be deposited on the membrane <NUM> by various techniques, such as micro-machining, patterning, wire bonding techniques, or connecting external electrical circuits to the cell via three dimensional interconnections.

In embodiments, the top substrate <NUM> may be an optional element. In embodiments, each pair of metal conductors <NUM> may include a top metal plate that is placed in proximity to a bottom metal plate to thereby form a capacitor. During operation, the deflection of the membrane <NUM> due to an external pressure wave may be measured by measuring the variation of the capacitance of the metal conductors <NUM>. In embodiments, a light source, such as laser, <NUM> may be placed in proximity to the membrane <NUM> so that the light emitted by the light source <NUM> may pass through the aperture/perforation <NUM> in the membrane <NUM>. In embodiments, the light from the aperture <NUM> may be used to align the top substrate <NUM> with respect to the bottom substrate <NUM> when the top substrate is bonded to the bottom substrate.

In embodiments, the top substrate <NUM> may be an ASIC chip, where the ASIC chip includes electrical, electronic, or photonic elements for controlling the piezoelectric elements 520a - 520c. The top substrate <NUM> may be connected to the electrical connections in the membrane <NUM> through a number of techniques including, but not limited to, electrical through vias, flip-chip bonding, eutectic bonding or other lead transfer techniques commonly used in micro-machined devices. In embodiments, the ASIC chip may include multiple bumps, and the bumps may be connected to electrical circuits on the membrane <NUM> by vertical interconnections or by wire bonding.

<FIG> show schematic cross sectional views of transceiver cells according to embodiments of the present disclosure. As depicted in <FIG>, the membrane <NUM> may suspend from a substrate <NUM> at both ends and maintain a spaced-apart relationship with the substrate <NUM> by one or more mechanical supports <NUM>. In embodiments, one or more piezoelectric elements 604a - 604c may be disposed on the top surface of the membrane. It is noted that one or more piezoelectric elements may be disposed on the bottom surface of the membrane <NUM>, as in <FIG>. Also, one or more grooves <NUM> or bumps may be formed on the top surface (and/or bottom surface) of the membrane so that the thickness of the membrane is varied.

In embodiments, one or more cavities 602a - 602c may be formed between the membrane <NUM> and the substrate <NUM>, and the gas pressures inside the cavities may be adjusted so that the vibrational motion of the corresponding portions of the membrane may be controlled. For instance, the cavity 602a may be in vacuum so that the portion 620a of the membrane can freely move in the vertical direction, while the cavity 602c may be filled with gas so that the vibrational motion of the portion 620c of the membrane may be damped by the gas.

In embodiments, the membrane <NUM> may be bonded to a substrate <NUM> using commonly used substrate bonding and attachment techniques, such as but not limited to, anodic bonding, silicon fusion bonding, eutectic bonding, glass-frit bonding, solder attach etc., to create a vacuum (e.g., 602a) or an air gaps (e.g., 602b and 602c) under the membrane <NUM>. The bonding may allow rapid attenuation of acoustic energy in the vacuum or air gap and protect the membrane from moisture or other reactants.

In embodiments, various types of active or passive elements may be incorporated in between transceiver cells to reduce the acoustic cross talk between the cells. For instance, the substrate <NUM> may include grooves (not shown in <FIG>) to attenuate the cross talk. In another example, the bonding of the membrane <NUM> to the substrate <NUM> may reduce the cross talk. In addition to these passive cross talk attenuation mechanisms, one or more of the piezoelectric elements 604a - 604c may be actuated to actively attenuate the cross talk. Such active crosstalk attenuation features may be electrically excited to physically dampen mechanical vibration of the supports of the membrane.

In <FIG>, the membrane <NUM> may suspend from a substrate <NUM> at both ends and maintain a spaced-apart relationship with the substrate <NUM> by one or more supports <NUM>. Also, one or more cavities 702a - 702c may be formed between the substrate <NUM> and the membrane <NUM>, where the cavities <NUM> may have similar functions as the cavities 602a - 602c. In embodiments, the membrane <NUM> may be bonded to a substrate <NUM> using commonly used substrate bonding and attachment techniques, such as but not limited to, anodic bonding, silicon fusion bonding, eutectic bonding, glass-frit bonding, solder attach etc. In embodiments, the substrate <NUM> may be an ASIC chip that includes electrical, electronic, or photonic elements for controlling the piezoelectric elements attached to the membrane <NUM>, and the substrate <NUM> may be electrically connected to the membrane <NUM> by vertical interconnections or by wire bonding.

<FIG> illustrates a mechanism to generate a bending moment in a piezoelectric element <NUM> according to embodiments of the present disclosure. As depicted, the piezoelectric element <NUM> may include a top electrode <NUM>, a piezoelectric layer <NUM> and a bottom electrode <NUM>, where the piezoelectric layer <NUM> may be polarized (indicated by arrows P) in either upward or downward direction. In embodiments, the electrical field (indicated by arrows E) may be generated when an electrical potential is applied across the top electrode <NUM> and the bottom electrode <NUM>. Depending on the polarization direction, the piezoelectric element <NUM> may generate different bending moments (indicated by arrows M). In the Tx mode/process, the bending moment generated by the piezoelectric element <NUM> may be transferred to the underlying membrane and cause the membrane to vibrate, generating pressure waves.

In embodiments, the polarization P of the piezoelectric layer <NUM> may be changed by a process called poling. In embodiments, the poling process may include application of a high voltage across the top and bottom electrodes at a temperature above the Curie point for a predetermine time period. In embodiments, depending on the thickness and material of the piezoelectric layer <NUM>, the voltage for the poling process may be changed. For instance, for a <NUM> pm thick piezoelectric layer, the voltage potential may be about <NUM> V.

In embodiments, a piezoelectric element may have more than two electrodes. For instance, the piezoelectric element 502c may have two top electrode and one bottom electrode. In embodiments, a first portion of the piezoelectric layer below the first top electrode may be poled in a first direction and a second portion of the piezoelectric layer below the second electrode may be poled in a second direction, where the first direction may be parallel or opposite to the second direction.

<FIG> illustrates a mechanism to develop an electrical charge on the piezoelectric element <NUM> according to embodiments of the present disclosure. As depicted, the piezoelectric element <NUM> may generate an electrical charge upon applying a bending moment M. In embodiments, the piezoelectric element <NUM> may be polarized in either upward or downward direction. Depending on the polarization direction, the electrical charge developed on each piezoelectric element <NUM> may have a different polarity. In embodiments, the bottom electrode <NUM> may be connected to the ground or a predetermined voltage bias.

In the Rx mode/process, the membrane may be bent by the external pressure waves, such as the pressure wave reflected from the internal organ <NUM>, and the bending of the membrane may be transferred to the piezoelectric element <NUM>, developing an electrical charge on the piezoelectric element. Using this electrical charge, the intensity of the pressure waves may be measured. Also, the electrical charges developed by multiple piezoelectric elements may be processed to get the image of the internal organ <NUM>.

According to the invention there is a further benefit in varying the thickness of a membrane, referred to as corrugating the membrane, to create regions where selective application of bending moments may further change the deflection profile of the membrane. This is referred to as "stress shaping. " In embodiments, the combination of stress shaping and selective arrangement or attachment of piezoelectric elements to different parts of the membrane may be used to deflect the membrane in a predetermined manner.

<FIG> show schematic diagrams of electrical connections to multiple piezoelectric elements according to embodiments of the present disclosure. For the purpose of illustration, the piezoelectric elements <NUM> and <NUM> are assumed to be two- terminal devices, i.e., each piezoelectric element has two electrodes, even though each piezoelectric element may have more than two electrodes. Also, the piezoelectric elements <NUM> and <NUM> may be electrically coupled to two electrical ports/terminals <NUM> and <NUM>.

In <FIG>, a top electrode <NUM> of a first piezoelectric element <NUM> may be connected to a bottom electrode <NUM> of a piezoelectric element <NUM> by means of an electrical connection <NUM>, and the top electrode <NUM> may be coupled to an electrical terminal <NUM>. Similarly, a bottom electrode <NUM> of the first piezoelectric element <NUM> may be connected to a top electrode <NUM> of a second piezoelectric element <NUM> by means of the electrical connection <NUM> and the bottom electrode <NUM> may be coupled to an electrical terminal <NUM>. In embodiments, this configuration of the electrical connection may allow different piezoelectric elements to be polarized in opposite directions by using two electrical terminals. In embodiments, the same two terminals <NUM> and <NUM> may also be used in the Tx and Rx modes. This technique can be easily expanded to multiple piezoelectric elements within a membrane or a cell to be operated via two terminals <NUM> and <NUM>.

In <FIG>, the polarization of each of the piezoelectric elements <NUM> and <NUM> may be opposite to the polarization of the corresponding piezoelectric element in <FIG>. As such, in the Tx mode/process, the piezoelectric elements <NUM> and <NUM> may generate a bending moment that is opposite to the bending moment generated by the piezoelectric elements <NUM> and <NUM>. Likewise, in the Rx mode/process, the piezoelectric elements <NUM> and <NUM> may develop an electrical charge that is opposite to the electrical charge developed by the piezoelectric elements <NUM> and <NUM>.

In embodiments, one advantage of the electrical configurations in <FIG> is that each of the piezoelectric elements may be operated as a "two-port" electrical device. In a two-port configuration, only two electrical ports/terminals <NUM> and <NUM> may be needed even if multiple separate piezoelectric elements may be disposed on the membrane. In embodiments, the two-port electrical configuration may significantly reduce the number of interconnects required to operate devices and be advantageous in creating large tiles in addition to simplification of transmit and receive mode electronics.

In embodiments, multiple membranes may be used in a single cell to increase the acoustic output from the cell. Alternately, some of the membranes in a cell may be designed to operate at a different resonant frequency. <FIG> shows a perspective view of a transducer element <NUM> according to embodiments of the present disclosure. <FIG> shows a cross sectional view of the transducer element in <FIG>, taken along the line <NUM>-<NUM>, according to embodiments of the present disclosure. As depicted, the transducer element <NUM> may include a membrane <NUM> coupled with multiple piezoelectric elements <NUM> and <NUM>. When viewed from the top, the inner piezoelectric element <NUM> may have a rectangular shape with rounded corners while the outer piezoelectric element <NUM> may have a shape of belt and surround the piezoelectric element <NUM>. In embodiments, the inner piezoelectric element <NUM> may be polarized downwardly, while the outer piezoelectric element <NUM> may be polarized upwardly. The membrane <NUM> may have one or more grooves <NUM> so that the thickness of the membrane is <NUM> changed. The membrane <NUM> may suspend from the substrate <NUM> and the substrate <NUM> may have a cavity <NUM> so that the membrane <NUM> may vibrate without touching the top surface of the substrate <NUM>. In embodiments, the cavity <NUM> may be in vacuum or filled with a gas at a predetermined pressure.

In embodiments, in the Tx mode/process, application of appropriate electrical signals across the piezoelectric elements <NUM> and <NUM> may generate a piston motion of the membrane <NUM>. <FIG> shows a numerical simulation of the membrane <NUM> in the Tx mode/process according to embodiments of the present disclosure. As depicted, the central portion of the membrane <NUM> may have a piston motion (i.e., move upwardly) when electrical fields are applied to the piezoelectric elements <NUM> and <NUM> on the corrugated membrane <NUM>. In embodiments, the piston motion may lead to a significant increase in the acoustic output since the pressure level is directly proportional to the volumetric displacement of the membrane <NUM>. Simulation results indicate that the piston motion may increase the acoustic transmission by <NUM> dB, compared to a simple bending motion of the membrane.

In embodiments, by adjusting a time delay or a phase delay between the electrical signals that activate the piezoelectric elements <NUM> and <NUM>, an increase in the displacement (gain) of the central portion of the membrane may be achieved. <FIG> shows a plot of gains of the membrane <NUM> as a function of time/phase delay according to embodiments of the present disclosure. As depicted, the displacement (gain) of the central portion of the membrane <NUM> may reach its maximum value when the phase delay between the electrical signals for driving the piezoelectric elements <NUM> and <NUM> is about <NUM> degrees.

In embodiments, in the Rx mode/process, opposite bending moments may be developed in different portions of the membrane <NUM>. Since the piezoelectric elements <NUM> and <NUM> are polarized in opposite directions, a charge of the same polarity may be developed on both piezoelectric elements. In embodiments, the electrical connections to the piezoelectric elements <NUM> and <NUM> may be arranged to collect the charges of the same polarity. According to simulation results, the use of two oppositely polarized elements may increase the charge development by about <NUM>%, compared to the case where only one polarization is used.

<FIG> shows a schematic diagram of a transceiver cell <NUM> having multiple membranes 1604a and 1604b that have different resonance frequency characteristics according to embodiments of the present disclosure. As depicted, the multiple membranes 1604a and 1604b may be disposed on a substrate <NUM>. In embodiments, the dimension of the membranes and the separation of the membranes may be maintained at a fraction of the principal wavelength of the emitted sound, which may increase the bandwidth of the transducer cell <NUM>.

<FIG> shows a plot of gains of the membranes 1604a and 1604b as a function of frequency according to embodiments of the present disclosure. In embodiments, the membranes 1604a and 1604b may have different resonance frequency characteristics <NUM> and <NUM>, respectively.

In embodiments, a transducer cell with increased bandwidth may be desirable as it may be operated in a harmonic imaging mode, i.e., a Tx mode frequency is different from an Rx mode frequency. In an embodiment that uses the harmonic imaging, a first pulse is sent to drive the piezoelectric elements followed by a second pulse, where the piezoelectric elements are driven by the second pulse in an anti-phase to the first pulse. This technique is commonly referred to as pulse-inversion.

In embodiments, multiple membranes in a transceiver cell may be designed to transmit or receive at different frequencies by changing one or more of the following design points: (<NUM>) the corrugation pattern of the membrane, (<NUM>) shape of the piezoelectric elements, (<NUM>) physical dimensions of the membrane, and (<NUM>) polarization of the piezoelectric elements.

<FIG> shows a schematic diagram of a transceiver cell <NUM> including a substrate <NUM> and multiple membranes 1804a - 1804c that have different resonance frequency characteristics according to embodiments of the present disclosure. <FIG> shows a plot of gains of the membranes 1804a - 1804c as a function of frequency according to embodiments of the present disclosure. In <FIG>, the curves <NUM>, <NUM> and <NUM> correspond to the membranes 1804a, 1804c and 1804b, respectively. As depicted, the frequency corresponding to the peak gain of the membrane 1804b may be separated from the frequencies corresponding to the peak gains of the membranes 1804a and 1804c.

In embodiments, the membranes 1804a and 1804c may be operated in both Tx and Rx mode while a membrane 1804b may be operated in the Rx mode only. The resonance frequencies of the membranes 1804a and 1804c may be designed to increase the bandwidth of the transducer by tuning the frequency-gain responses of the membranes 1804a and 1804c, while the membrane 1804b may be designed to operate in the Rx mode only and receive a harmonic response of the Tx mode.

<FIG> shows a schematic diagram of a transceiver cell <NUM> having multiple membranes 1902a - 1902c that have different frequency responses according to embodiments of the present disclosure. As depicted, the three membranes 1902a - 1902c may be disposed on a substrate <NUM>. <FIG> shows a plot of gains of the membranes in <FIG> as a function of frequency according to embodiments of the present disclosure. In <FIG>, the curves 1922a - 1922c may correspond to the membranes 1902a - 1902c, respectively. As depicted, the three membranes 1902a - 1902c may have different frequency responses and the frequencies at the maximum gains are separated from each other, increasing the bandwidth of the transducer cell. As the transducer cell <NUM> may have an increased bandwidth, the transducer cell may be operated in a harmonic imaging mode, i.e., a Tx mode frequency is different from an Rx mode frequency.

<FIG> shows a schematic diagram of a transceiver cell <NUM> having multiple transducer elements 2004a - 2004c according to embodiments of the present disclosure. As depicted, the transducer elements 2004a - 2004c may be disposed on a substrate <NUM>, and each transducer element may include a membrane, preferably a corrugated membrane, and multiple piezoelectric elements disposed on the membranes. As depicted, the polarization direction of each piezoelectric element on the membranes is indicated by an upward arrow <NUM> or a downward arrow <NUM>.

<FIG> shows a membrane actuated in a first mode of resonance according to embodiments of the present disclosure. As depicted, the transducer element 2004a may include a membrane <NUM> that may suspend from the substrate <NUM> by a suspension mechanism <NUM>. Multiple piezoelectric elements <NUM> may be disposed on the membrane <NUM>, where each piezoelectric element may be polarized either upwardly or downwardly, as indicated by the arrows P.

When a suitable electrical signal is applied to the piezoelectric elements <NUM> on the membrane <NUM>, the membrane <NUM> may vibrate in the first resonance mode. <FIG> shows the membrane <NUM> actuated in a first mode of resonance according to embodiments of the present disclosure. (For simplicity, the piezoelectric elements <NUM> are not shown in <FIG>).

In embodiments, the polarities of the piezoelectric elements on a membrane may be arranged so that the membrane may vibrate in a different resonance mode. <FIG> shows a cross sectional view of the transducer element 2004b according to embodiments of the present disclosure. <FIG> shows the membrane <NUM> actuated in a third mode of resonance according to embodiments of the present disclosure. The transducer element 2004b may be similar to the transducer element 2002b, with the difference that the piezoelectric elements <NUM> have different polarities from the piezoelectric elements <NUM>. As depicted in <FIG>, the membrane <NUM> may vibrate in the third mode of resonance when an electric field is applied to the piezoelectric elements <NUM>.

<FIG> shows a cross sectional view of a transducer element 2004c according to embodiments of the present disclosure. <FIG> shows a membrane <NUM> actuated in a fifth mode of resonance according to embodiments of the present disclosure. As depicted, the transducer element 2004c may be similar to the transducer element 2004a, with the difference that the piezoelectric elements <NUM> have different polarities from the piezoelectric elements <NUM>. As depicted in <FIG>, the membrane <NUM> may vibrate in the fifth mode of resonance when an electric field is applied to the piezoelectric elements <NUM>.

In embodiments, in the Rx mode/process, applications of external pressure waves of different frequencies may lead to excitations of the membranes at different modes. In embodiments, the polarization of the piezoelectric elements may be arranged so that the external pressure waves may create electrical charges having the same polarity across each membrane. One of the benefits of such a configuration is that it may allow unprecedented control over shaping the frequency responses of membranes in the Tx and Rx modes.

<FIG> show steps for fabricating an exemplary transceiver cell that has two membranes according to embodiments of the present disclosure. <FIG> shows a top view of the two membranes <NUM> disposed on a substrate <NUM> and <FIG> shows a cross sectional view of the membrane and substrate, taken along the line <NUM>-<NUM> according to embodiments of the present disclosure. As depicted, in embodiments, the membranes <NUM> may be formed by depositing a membrane layer <NUM> on the substrate <NUM> and two cavities <NUM> may be formed to remove portions of the substrate <NUM>, to thereby form the membranes <NUM> that may vibrate relative to the substrate <NUM> in a vertical direction. In embodiment, the cavities <NUM> may be formed by conventional wafer processing techniques, such as etching. In embodiments, the substrate <NUM> may be formed of the same material as the membrane layer <NUM>. In alternative embodiments, the substrate <NUM> may be formed of a different material from the membrane layer <NUM>. It is noted that the cavities <NUM> may be formed after the other components, such as top conductor (<NUM> in <FIG>), of the transducer cell is formed.

<FIG> shows bottom electrodes <NUM> and three bottom conductors 2504a - 2504c according to embodiments of the present disclosure. As depicted, each of the membranes <NUM> may have three bottom electrodes <NUM> and each of the bottom electrodes <NUM> may be electrically connected to one of the three bottom conductors 2504a - 2504c. In embodiments, the bottom electrodes <NUM> may be formed of a first metal and the bottom conductors 2504a - 2504c may be formed of a second metal, where the first metal may be the same as (or different from) the second metal.

<FIG> shows piezoelectric layers <NUM>, <NUM> and <NUM> disposed over the six bottom electrodes <NUM> and three bottom conductors 2504a - 2504c according to embodiments of the present disclosure. <FIG> shows top electrodes <NUM> and <NUM> disposed on the piezoelectric layers <NUM>, <NUM> and <NUM> according to embodiments of the present disclosure. As depicted, three top electrodes may be formed over each membrane <NUM>, i.e., each membrane <NUM> may include three piezoelectric elements. In embodiments, one of the top electrodes <NUM> and <NUM>, one of the piezoelectric layers <NUM>, <NUM> and <NUM>, and one of the bottom electrodes <NUM> may form a two-terminal piezoelectric element and may vibrate when an electrical potential is applied across the top and bottom electrodes.

<FIG> shows top conductors <NUM> and <NUM> that are electrically connected to the top electrodes <NUM> and <NUM> according to embodiments of the present disclosure. The top conductor <NUM> may be electrically connected to the two top electrodes <NUM> while the top conductor <NUM> may be electrically connected to the four top electrodes <NUM>. In embodiments, the top electrodes may be electrically connected to the bottom conductors 2504a and 2504b through vias. For instance, the vias <NUM> and <NUM> may electrically connect the four top electrodes <NUM> to the bottom conductor <NUM> while the vias <NUM> and <NUM> may electrically connect the two top electrodes <NUM> to the bottom conductors 2504b and 2504c.

<FIG> shows a schematic diagram of three transceiver cells 2902a - 2902c having different electrode patterns according to embodiments of the present disclosure. As depicted, each transceiver cell (e.g., 2902a) may have one membrane (e.g., 2904a) and four transducer elements (e.g., 2906a) disposed on the membrane. In embodiments, the gain of each transceiver cell may be a function of various factors: size, shape, and number of the transducer elements, size and shape of the top electrode of each transducer element, size and shape of each membrane, spacing between the transducer elements, polarization of each transducer element, so on.

For the purpose of illustration, in <FIG>, the projection area of the top electrode is changed to control the gain of the transducer cell. In embodiments, the top electrodes of the transducer elements 2904c is larger than the top electrodes of the transducer elements 2904b, and the top electrodes of the transducer elements 2904b is larger than the top electrodes of the transducer elements 2904a. While the other factors that affect the gain, such as size and number of transducer elements 2906a - 2906c and size of the membranes 2904a - 2904c, are the same in the transceiver cells 2902a - 2902c, the gain of the transceiver cells 2902a - 2902c varies depending on the size of the top electrode. <FIG> illustrates a plot of gains of the transceiver cells 2902a - 2902c as a function of frequency, where the curves <NUM>, <NUM>, and <NUM> may correspond to the transceiver elements 2902a - 2902c, respectively. As depicted, the gain of the transceiver cells decreases as the size of the top electrodes increases.

It should be apparent to those of ordinary skill in the art that, in embodiments: (i) each of the transceiver arrays, tiles, cells membranes, piezoelectric elements, and electrodes of a piezoelectric elements may have any suitable shape; (ii) the placement of tiles in a transceiver array, the placement of cells in a tile, the placement of membranes in a cell, the placement of piezoelectric elements on a membrane, and the placement of electrodes on the piezoelectric element, and the placement of capacitor pads may be arbitrary; (iii) the variation of the thickness of a membrane may be changed arbitrarily to enhance or change the performance of the membrane; (iv) the number of tiles in a transceiver array, the number of cells in a tile, the number of membranes in a cell, and the number of piezoelectric elements in a membrane can be varied by design; (v) the polarization of the piezoelectric elements may be varied during the operation of the device; (vi) the components in a transceiver array may be combined in a beneficial manner; (vii) the placement of perforations in a membrane that allows transmission of laser light may be arbitrary; and (viii) the interlayer dielectrics, electrical vias, electrical redistribution layers, acoustic impedance matching layers, moisture protection barriers, housings, and electrical interconnections may be formed of materials that are typically used in the semiconductor, MEMS, or ultrasound industries.

Claim 1:
A transceiver element, comprising:
a substrate (<NUM>);
a membrane (<NUM>) suspending from the substrate (<NUM>); and
a transducer element (<NUM>) mounted on the membrane (<NUM>) at an attachment area, the transducer element (<NUM>) having a bottom electrode, a piezoelectric layer on the bottom electrode, and a top electrode on the piezoelectric layer, the transducer element (<NUM>) generating a bending moment in response to applying an electrical potential across the bottom electrode and the top electrode and developing an electrical charge in response to applying a bending moment thereto;
wherein the membrane (<NUM>) has a first cross-sectional thickness in the attachment area and a second cross-sectional thickness in a deflection area of the membrane (<NUM>), the first cross-sectional thickness being different from the second cross-sectional thickness to permit a desired deflection profile of the membrane (<NUM>) for enhancing performance of the transducer element (<NUM>).