Dual bias micromachined ultrasonic transducer

Abstract

Methods and systems are provided for an ultrasound probe comprising a piezoelectric micromachined ultrasound transducer (200) comprising a first top electrode (206), a second top electrode (207), and a bottom electrode (21). The ultrasound probe further includes a transmitter / receiver (434, 436) configured to apply a single drive signal to the bottom electrode (210) and a bias circuit (402) configured to apply a first bias voltage to the first top electrode (206) and a second bias voltage to the second top electrode (207).

Description

Technical Field

[0001] Embodiments of the subject matter disclosed herein relate to microelectromechanical systems (MEMS) devices, and more particularly, to micromachined ultrasonic transducers. Background Art

[0002] Micro-electromechanical system (MEMS) ultrasound devices (hereinafter, MEMS devices) can be used to image and / or treat targets such as organs and soft tissues in the human body and non-human targets. For example, in addition to ultrasound imaging of humans, animals, etc., MEMS devices can also be used for applications such as ultrasound / acoustic sensing, non-destructive evaluation (NDE), ultrasound therapy (e.g., high-intensity focused ultrasound (HIFU)), etc. The MEMS device can rely on the vibration of a membrane having a first electrode to receive and transmit signals.

[0003] MEMS devices can use real-time, non-invasive high-frequency (e.g., in the range of 100KHz to tens of MHz) sound waves to produce a series of two-dimensional (2D) images and / or three-dimensional (3D) images. Sound waves can be emitted by a transmitting transducer, and the reflection of the emitted sound waves can be received by a receiving transducer. The received sound waves can then be processed to display an image of the target. Some types of MEMS devices can be used as transmitting transducers and / or receiving transducers, such as micromachined ultrasonic transducers (MUTs). MUTs can be capacitive micromachined ultrasonic transducers (CMUTs) or piezoelectric micromachined ultrasonic transducers (PMUTs). CMUTs can include top and bottom electrodes coupled to a membrane. The membrane can move when receiving an electrical signal to generate sound waves, or can move when receiving sound waves to generate electrical signals that can be processed. PMUTs can include a thin layer of piezoelectric material. Piezoelectric materials can compress / expand (e.g., vibrate or deflect) in response to an applied electric field to generate sound waves, and can then generate an electric field in response to being vibrated by sound waves. Summary of the invention

[0004] In one embodiment, an ultrasound probe includes a piezoelectric micromachined ultrasonic transducer (PMUT) including a first top electrode, a second top electrode, and a bottom electrode; a transmitter / receiver configured to apply a single drive signal to the bottom electrode; and a bias circuit configured to apply a first bias voltage to the first top electrode and a second bias voltage to the second top electrode. In one example, the voltage applied to the piezoelectric layer at both ends of the PMUT at the first top electrode and the second top electrode can be polarized in opposite directions. When a single drive signal is applied, the opposite polarization directions can cause opposite deflections of the piezoelectric layer. In this way, the bandwidth of the PMUT can be increased without the need for two different drive signals. Increasing the bandwidth can make the MUT transducer more useful in applications requiring higher resolution, such as medical ultrasound.

[0005] It should be understood that the above brief description is provided to introduce in a simplified form selected concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0007] Figure 1 shows a block diagram of an exemplary ultrasound system that may be used for ultrasound imaging according to various embodiments; and

[0008] Figure 2A shows an exemplary cross-sectional view of a PMUT according to various embodiments; and

[0009] Figure 2B shows an exemplary cross-sectional view of a CMUT according to various embodiments; and

[0010] Figure 2C shows an exemplary top view of a MUT according to various embodiments; and

[0011] Figure 3A A graph showing an example of two drive signals with a common bias voltage as a prior art; and

[0012] Figure 3B A graph showing an example of a single drive signal with dual bias voltages according to various embodiments; and

[0013] Figure 4shows a schematic diagram of a drive circuit capable of delivering dual bias voltages according to various embodiments; and

[0014] Figure 5 a graph showing displacement as a function of the electric field of a piezoelectric transducer according to various embodiments; and

[0015] Figure 6 The use of various embodiments is shown Figure 4 A flowchart of an example of a method of driving a circuit; and

[0016] Figure 7 shows displacement and Figure 2A The graph of the functional relationship of the positions of the two ends of the cross section of the PMUT is shown. DETAILED DESCRIPTION

[0017] The following description relates to systems and methods for driving a micromachined ultrasonic transducer (MUT). The MUT may be, for example, Figure 1 Part of the ultrasound system shown. In some examples, the MUT can be capacitive (CMUT) or piezoelectric (PMUT). The MUT device can have a limited signal bandwidth, resulting in poor image quality. One method to widen the bandwidth is to pattern the MUT with two separate top electrodes and actuate (e.g., drive) the MUT with two different drive signals, one of which is applied to each of the two top electrodes. The two different drive signals can actuate different resonant frequencies under each of the two top electrodes. However, the two different drive signals may require two transmitters and two receivers coupled to each transducer element of the ultrasound probe. When the ultrasound probe may include a transducer array containing up to thousands of transducers, doubling the number of transmitters and receivers for each transducer may not be feasible from a cost and form factor perspective.

[0018] The diagram of MUT is as follows FIG. 2A to FIG. 2C shown. Figure 2A An example of a cross section of a PMUT is shown, Figure 2B shows an example of a cross section of a CMUT, and Figure 2C A top view of a MUT, which can be a PMUT or a CMUT, is shown. MUTs like CMUTs and PMUTs can be more cost-effective and more reliable than their non-micromachined bulk counterparts. However, when driven with a single drive signal, a MUT can vibrate with a limited bandwidth. Figure 3A An example of a dual drive signal that can be used to drive the MUT is shown, but this dual drive signal may not be practically implemented due to the number of transmitter and receiver components required to provide the dual drive signal. Figure 3BAn exemplary implementation of a single drive signal with dual bias voltages is shown. Figure 3B The common drive signal shown in FIG. 1 can be provided via Figure 4 The bias circuit including two capacitors schematically shown in FIG. 1 is applied to two different top electrodes. Using a common drive signal with dual bias voltages to drive the MUT can cause the active layer of the MUT to compress and expand in response to the applied electric field. Figure 5 The piezoelectric layer in the PDMS demonstrates this effect. Figure 5 A graph showing the displacement of the piezoelectric layer as a function of the electric field. Figure 6 The diagram shows the Figure 4 Flowchart of a method for an ultrasonic probe schematically shown in FIG. When the ultrasonic probe includes a PMUT, the effect of actuating the ultrasonic probe with a dual bias voltage may be to change the polarization direction of a portion of the piezoelectric layer. Figure 7 This effect is schematically illustrated in , along with a graph showing the change in deflection due to application of a single drive signal under dual bias.

[0019] Now go to Figure 1 , a block diagram of an exemplary ultrasound system 100 that may be used for ultrasound imaging according to various embodiments is shown. The ultrasound system 100 includes a transmitter 102, an ultrasound probe 104, a transmit beamformer 110, a receiver 118, a receive beamformer 120, an A / D converter 122, an RF processor 124, an RF / IQ buffer 126, a user input device 130, a signal processor 132, an image buffer 136, a display system 134, and an archive 138. The circuit 111 is a non-limiting example of a bias of a MUT, and variations in the configuration of the circuit 111 are possible without departing from the scope of the present disclosure.

[0020] The transmitter 102 may include suitable logic, circuitry, interfaces, and / or code that may be operable to drive the ultrasound probe 104. The ultrasound probe 104 may include, for example, a single element MUT, a 1D array of MUTs, a 2D array of MUTs, an annular (ring) array of MUTs, and the like. Thus, the ultrasound probe 104 may include a set of transducer elements 106, which may be, for example, MUTs. In certain embodiments, the ultrasound probe 104 may be operable to acquire ultrasound image data covering, for example, at least a majority of an anatomical structure, such as a heart, a blood vessel, or any suitable anatomical structure. Each of the transducer elements 106 may be referred to as a channel.

[0021] The transmit beamformer 110 may include suitable logic, circuitry, interfaces, and / or code operable to control the transmitter 102, which drives the set of transmit transducer elements 106 to transmit ultrasound transmit signals into an area of ​​interest (e.g., a person, an animal, an underground cavity, a physical structure, etc.). The transmitted ultrasound signals may be backscattered from structures (such as blood cells or tissue) in the object of interest to produce echoes. The transducer elements 106 may then receive the echoes. For example, one or more drive circuits 111 may be coupled to and drive or control electrodes of each transducer element 106. For example, one or more drive circuits may be coupled to separate AC voltage sources and DC voltage sources.

[0022] The set of transducer elements 106 in the ultrasound probe 104 may be operable to convert the received echoes into analog signals and transmit to the receiver 118. The receiver 118 may comprise suitable logic, circuitry, interfaces, and / or code that may be operable to receive the signals from the ultrasound probe 104. The analog signals may be transmitted to one or more of the plurality of A / D converters 122.

[0023] Thus, the ultrasound system 100 may be multiplexed so that ultrasound transmit signals are transmitted during certain time periods and echoes of these ultrasound signals are received during other time periods. Although not explicitly shown, various embodiments of the present disclosure may allow for the transmission of ultrasound signals and the reception of echoes from these signals to occur simultaneously. In such cases, the probe may include a transmitting transducer element and a receiving transducer element.

[0024] The plurality of A / D converters 122 may include suitable logic components, circuits, interfaces, and / or codes that are operable to convert analog signals from the receiver 118 into corresponding digital signals. The plurality of A / D converters 122 are disposed between the receiver 118 and the RF processor 124. Nevertheless, the present disclosure is not limited in this regard. Therefore, in some embodiments, the plurality of A / D converters 122 may be integrated within the receiver 118.

[0025] The RF processor 124 may include suitable logic components, circuits, interfaces and / or codes that are operable to demodulate the digital signals output by the plurality of A / D converters 122. According to an embodiment, the RF processor 124 may include a complex demodulator (not shown) that is operable to demodulate the digital signals to form I / Q data pairs representing corresponding echo signals. The RF data (which may be, for example, I / Q signal data, real-valued RF data, etc.) may then be transmitted to the RF / IQ buffer 126. The RF / IQ buffer 126 may include suitable logic components, circuits, interfaces and / or codes that are operable to provide temporary storage of RF or I / Q signal data generated by the RF processor 124.

[0026] Thus, various embodiments may cause, for example, the RF processor 124 to process real-valued RF data or any other equivalent representation of the data with an appropriate RF / IQ buffer 126. The receive beamformer 120 may include suitable logic, circuitry, interfaces, and / or code that may be operable to perform digital beamforming processing to, for example, sum delayed channel signals, phase-shifted channel signals, and / or weighted channel signals received from the RF processor 124 via the RF / IQ buffer 126 and output a beam summed signal. The delayed channel data, phase-shifted channel data, and / or weighted channel data may be summed to form a scan line output from the receive beamformer 120, where the scan line may be, for example, complex-valued or non-complex-valued. The specific delay of the channel may be provided, for example, by the RF processor 124 or any other processor configured to perform this task. The delayed channel data, phase-shifted channel data, and / or weighted channel data may be referred to as delay-aligned channel data.

[0027] The resulting processed information may be a beam-summed signal output from the receive beamformer 120 and transmitted to the signal processor 132. According to some embodiments, the receiver 118, the plurality of A / D converters 122, the RF processor 124, and the beamformer 120 may be integrated into a single beamformer, which may be a digital beamformer. In various embodiments, the ultrasound system 100 may include a plurality of receive beamformers 120.

[0028] The user input device 130 may be used to input patient data, scan parameters, settings, select protocols and / or templates, etc. In an exemplary embodiment, the user input device 130 is operable to configure, manage, and / or control the operation of one or more components and / or modules in the ultrasound system 100. In this regard, the user input device 130 is operable to configure, manage, and / or control the operation of the transmitter 102, the ultrasound probe 104, the transmit beamformer 110, the receiver 118, the receive beamformer 120, the RF processor 124, the RF / IQ buffer 126, the user input device 130, the signal processor 132, the image buffer 136, the display system 134, and / or the archive 138. The user input device 130 may include switches, buttons, rotary encoders, touch screens, motion tracking, voice recognition, a mouse device, a keyboard, a camera, and / or any other device capable of receiving user guidance. In certain embodiments, for example, one or more of the user input devices 130 may be integrated into other components such as the display system 134 or the ultrasound probe 104. For example, user input device 130 may include a touch screen display.

[0029] The signal processor 132 may include suitable logic components, circuits, interfaces and / or codes that are operable to process ultrasound scan data (i.e., summed IQ signals) to generate ultrasound images for presentation on a display system 134. The signal processor 132 is operable to perform one or more processing operations based on a plurality of selectable ultrasound modalities on the acquired ultrasound scan data. In an exemplary embodiment, the signal processor 132 may be used to perform display processing and / or control processing, etc. The acquired ultrasound scan data may be processed in real time during a scanning session as echo signals are received. Additionally or alternatively, the ultrasound scan data may be temporarily stored in the RF / IQ buffer 126 during a scanning session and processed in an online operation or an offline operation. In various embodiments, the processed image data may be presented at the display system 134 and / or stored at the archive 138. The archive 138 may be a local archive, a picture archiving and communication system (PACS), or any suitable device for storing images and related information.

[0030] The signal processor 132 may include one or more central processing units, microprocessors, microcontrollers, etc. For example, the signal processor 132 may be an integrated component, or may be distributed in various locations. In an exemplary embodiment, the signal processor 132 may be capable of receiving input information from the user input device 130 and / or the archive 138, generating output that may be displayed by the display system 134, and manipulating the output in response to the input information from the user input device 130, etc. For example, the signal processor 132 may be capable of executing any of the methods and / or instruction sets discussed herein according to various embodiments.

[0031] The ultrasound system 100 is operable to continuously acquire ultrasound scan data at a frame rate suitable for the imaging situation under consideration. Typical frame rates may be in the range of 20 to 120, but may be lower or higher. The acquired ultrasound scan data may be displayed on the display system 134 at a display rate that is the same as the frame rate, or at a display rate that is slower or faster than the frame rate. An image buffer 136 is included to store processed frames of acquired ultrasound scan data that are not scheduled for immediate display. Preferably, the image buffer 136 has sufficient capacity to store frames of ultrasound scan data for at least several minutes. The frames of ultrasound scan data are stored in a manner that is easy to retrieve from them according to their acquisition order or time. The image buffer 136 may be embodied as any known data storage medium.

[0032] The display system 134 may be any device capable of conveying visual information to a user. For example, the display system 134 may include a liquid crystal display, a light emitting diode display, and / or any suitable one or more displays. The display system 134 may be operable to present an ultrasound image and / or any suitable information.

[0033] The archive 138 may be one or more computer-readable memories, such as a picture archiving and communication system (PACS), a server, a hard disk, a floppy disk, a CD, a CD-ROM, a DVD, a compact memory, a flash memory, a random access memory, a read-only memory, an electrically erasable and programmable read-only memory, and / or any suitable memory, that are integrated with the ultrasound system 100 and / or communicatively coupled (e.g., via a network) to the ultrasound system 100. The archive 138 may include, for example, a database, a library, a collection of information, or other memory that is accessed by and / or in conjunction with the signal processor 132. For example, the archive 138 may be capable of storing data temporarily or permanently. The archive 138 may be capable of storing medical image data, data generated by the signal processor 132, and / or instructions readable by the signal processor 132, etc.

[0034] The components of the ultrasound system 100 may be implemented in software, hardware, firmware, etc. The various components of the ultrasound system 100 are communicatively connected. The components of the ultrasound system 100 may be implemented separately and / or integrated in various forms. For example, the display system 134 and the user input device 130 may be integrated as a touch screen display. In addition, although the ultrasound system 100 is described as including a receive beamformer 120, an RF processor 124, and a signal processor 132, various embodiments of the present disclosure may use various numbers of processors. For example, various devices that execute code may generally be referred to as processors. Various embodiments may refer to each of these devices including each of the RF processor 124 and the signal processor 132 as a processor. In addition, there may be other processors to additionally perform the tasks described as being performed by these devices including the receive beamformer 120, the RF processor 124, and the signal processor 132, and for ease of description, all of these processors may be referred to as "processors".

[0035] Such as Figure 1 A transducer such as the transducer 106 of the embodiment of the present invention may be a MUT such as a PMUT or a CMUT. In terms of manufacturing cost, a MUT may provide advantages over a bulk ceramic transducer, so that an ultrasound system using a MUT is more economical. In addition, a bulk ceramic transducer using lead zirconate titanate (PZT) as a piezoelectric material may cause environmental hazards due to the presence of lead. The CMUT does not include lead, and the amount of lead in the PMUT is 0.5% to 1% of the amount of lead in the bulk PZT transducer. However, when compared to a bulk ceramic transducer, the adoption of the MUT may be hindered by limited bandwidth. The bandwidth of the MUT may be increased by providing two different drive signals. However, providing two different drive signals may require that each transducer be coupled to two transmitters and two receivers, which may not be feasible, especially for a matrix array that may include up to thousands of transducers. As described in more detail herein, providing a single drive signal with dual bias (e.g., with a first bias and with a second bias) without doubling the transceiver and receiver for each transducer may result in a higher bandwidth.

[0036] Now turn to Figure 2C , shows a top view of MUT 280. MUT 280 may be a transducer element of an ultrasound system, such as Figure 1 A reference axis 201 is provided for comparison FIG. 2A to FIG. 2C The reference axes include a y-axis, an x-axis, and a z-axis. The MUT 280 includes an active layer 282. In an example where the MUT 280 is a CMUT, the active layer 282 may be a membrane layer. Figure 2BThe example in which the MUT 280 is a CMUT is further discussed. In an alternative example in which the MUT 280 is a PMUT, the active layer 282 may be a piezoelectric layer. Figure 2A The example in which the MUT 280 is a PMUT is further discussed. The active layer 282 is Figure 2C Shown as a square in FIG. 2 , however other shapes of the active layer 282 are contemplated.

[0037] The MUT 280 may include a first top electrode 206 and a second top electrode 207. In some examples, the first top electrode 206 may be shaped as a ring or annulus, wherein the first top electrode 206 surrounds the empty space 286. However, other shapes of the first top electrode 206 have been considered. In some examples, the shape of the first top electrode 206 may be selected based on the desired vibration of the active layer 282. The first lead 284 may be formed continuously with the first top electrode 206 and may extend from the outer edge of the first top electrode 206 and the outer edge 281 of the active layer 282.

[0038] The second top electrode 207 may be positioned within the empty space 286 defined by the first top electrode 206. In some examples, the second top electrode 207 may be shaped as a circle. In an alternative embodiment, the second top electrode 207 may be shaped as a ring or a loop. The second top electrode is completely spaced apart from the first top electrode 206. Both the first top electrode 206 and the second top electrode 207 are continuous. Alternative shapes and relative placements of the second top electrode 207 have been considered. In some examples, the shape and / or placement of the second top electrode 207 may be selected based on the desired vibration of the active layer 282. The second lead 288 may be formed continuously with the second top electrode 207 and may extend from the second top electrode 207 to the outer edge 281 of the active layer 282. The ring of the first top electrode 206 may be discontinuous at the location where the second lead 288 crosses the first top electrode 206. In this way, the first top electrode 206 is not in direct contact with the second top electrode 207.

[0039] In some examples, the first lead 284 and the second lead 288 can each be coupled to a distribution bus. The distribution bus can couple each transducer of a transducer array (e.g., transducer array 106) to a bias network. The distribution bus can be configured to have a minimum impedance. In this way, undesirable phase shifts of a single drive signal across the transducer array can be reduced or eliminated. The distribution bus can exist on the MUT device or on an interconnect structure such as a flexible circuit board, a silicon interposer, or a printed electrical trace; other connection methods can be used.

[0040] According to which MUT 280 is a PMUT ( Figure 2A ) and wherein the MUT 280 is a CMUT ( Figure 2B ) embodiment, the cross section AA' of MUT280 is Figure 2B and Figure 2C Now turn to Figure 2A , showing a cross-sectional view of PMUT 200. PMUT 200 may be Figure 2C 2. The PMUT 200 may include a first side 204. The first side 204 may be a side of the PMUT 200 that is placed on or pointed toward a target to be imaged by an ultrasound probe including the PMUT 200. The second side 202 of the PMUT 200 may be a side opposite to the side 202 along the y-axis and away from the object. The first side 204 may be Figure 2C The side shown in .

[0041] The PMUT 200 may include a first top electrode 206 positioned as the outermost layer of the PMUT 200. In some examples, the first top electrode 206 may be shaped as a ring or annulus. The PMUT 200 may also include a second top electrode 207. When the PMUT 200 is viewed from the first side 204 toward the second side 202, the first top electrode 206 and the second top electrode 207 may together comprise a first outermost layer. The side of the first top electrode 206 and the second top electrode 207 closest to the second side 202 may be in coplanar contact with the piezoelectric layer 208. The piezoelectric layer 208 may be formed of a piezoelectric material such as PZT, AlN, ScAlN, etc. The side of the piezoelectric layer 208 closest to the second side 202 may be in direct coplanar contact with the bottom electrode 210. In this way, the piezoelectric layer 208 may be sandwiched between the first top electrode 206 / second top electrode 207 and the bottom electrode 210. The side of the bottom electrode 210 closest to the second side 202 may be in direct coplanar contact with the first silicon layer 212. The side of the first silicon layer 212 closest to the second side 202 may be in direct coplanar contact with a silicon dioxide (SiO2) layer 214. The side of the silicon dioxide layer 214 closest to the second side 202 may be coplanar with a second silicon layer 216. When viewed from the first side 204 toward the second side 202, the second silicon layer 216 may be the last, outermost layer of the PMUT 200. The second silicon layer 216 and the silicon dioxide layer 214 may together enclose a microcavity 218. The microcavity 218 may be evacuated (e.g., under vacuum) or may include a certain amount of air or other gas.

[0042] The PMUT 200 may be electrically coupled to a device such as a Figure 1111 of the drive circuit. In the transmission mode, the drive circuit can supply drive signal voltages between the first top electrode 206 and the bottom electrode 210 and between the second top electrode 207 and the bottom electrode 210, each of which can induce a specific vibration mode in the piezoelectric layer 208. The vibration of the piezoelectric layer 208 can then generate an acoustic wave toward the imaging target. In some examples, adjusting the drive signal voltage can result in adjusting the vibration mode. By simultaneously exciting two different vibration modes of the piezoelectric layer 208, a first acoustic wave characteristic of the first vibration mode and a second acoustic wave characteristic of the second vibration mode can be simultaneously generated and emitted. In this way, the bandwidth of the PMUT 200 can be increased.

[0043] Now turn to Figure 2B , which shows an exemplary embodiment of CMUT 250. CMUT 250 may be Figure 2C 204. An exemplary embodiment of a MUT 280 shown in FIG. 205. When the CMUT 250 is viewed from the first side 204, the CMUT 250 includes a first top electrode 206 and a second top electrode 207 as the outermost layers. The membrane layer 254 may be in coplanar contact with the first top electrode 206 and the second top electrode 207 and electrically coupled. In some examples, the membrane layer 254 may be formed of silicon or silicon oxide. The insulating layer 256 may be in coplanar contact with the bottom side of the membrane layer 254 (e.g., the side closest to the second side 202). The bottom electrode 258 may be in coplanar contact with the bottom side of the insulating layer 256. The insulating layer 256 may not completely cover the bottom sides of the membrane layer 254 and the bottom electrode 258, thereby forming a microcavity 262 enclosed by the membrane layer 254, the insulating layer 256, and the bottom electrode 258. The microcavity 262 may be evacuated or may include a certain amount of air. The bottom side of the bottom electrode 258 may be in direct coplanar contact with the silicon substrate 260. When the CMUT 250 is viewed from the second side 202 , the silicon substrate 260 may be the outermost layer.

[0044] The CMUT 250 may be electrically coupled to a first top electrode 206 and a bottom electrode 258 and to a second top electrode 207 and a bottom electrode 258, such as Figure 1 The driving circuit 111 of the CMUT 250 can supply driving signal voltages between the first top electrode 206 and the bottom electrode 258 and between the second top electrode 207 and the bottom electrode 258, wherein each driving signal voltage can induce a characteristic vibration mode in the membrane layer 254 according to the applied driving signal. The membrane layer 254 of the CMUT 250 can behave like the piezoelectric layer 208 of the PMUT 200.

[0045] Now go to Figure 3A (Prior Art), graph 300 shows a MUT (e.g., Figure 2C280) of the MUT 280, the two drive signals are applied simultaneously to a single MUT, and each MUT requires two transmitters and two receivers. Curve 302 corresponds to the first drive signal, and curve 304 corresponds to the second drive signal. The first drive signal and the second drive signal can both oscillate sinusoidally between two voltages. The first drive signal 302 can have a different shape, such as a modulated Gaussian shaped pulse (not shown). The second drive signal will then have a modulated Gaussian pulse of a similar shape and opposite phase. Both curves 302 and curve 304 oscillate between 0V and -20V, but other voltage ranges are possible, such as oscillating between +10V and -10V. The first drive signal can be out of phase with the second drive signal. In other words, for any time period, curve 302 increases while curve 304 decreases, or vice versa. Phasing the drive signals in this way can result in an active layer of the transducer (e.g., Figure 2C The two different vibrations of the active layer 282 of the MUT are generated, resulting in an increase in the bandwidth of the MUT. However, providing two out-of-phase drive signals for an ultrasound probe including multiple transducers in this manner may require an impractical number of transmitters and receivers. Alternatively, the first drive signal and the second drive signal may be provided by an RF transformer coupled to a single transmitter / receiver. However, an RF transformer may be required for each transducer of the transducer array and may not be a cost and space effective solution.

[0046] Now go to Figure 3B , FIG. 350 shows a schematic diagram for a Figure 2C280 of MUT 280, an example voltage across the MUT device as a function of time. A single drive signal may require a single transmitter and receiver for each transducer element. Graph 350 includes curve 302, which corresponds to the voltage across the device from a single drive signal and a first bias. Graph 350 also includes curve 352, which corresponds to the voltage across the device from a single drive signal and a second bias. A single drive signal with a first bias may cause the voltage across the device to oscillate between 0V and +20V. A single drive signal with a second bias may cause the voltage across the device to oscillate in phase with the single drive signal at the first bias, and may offset the first bias. In other words, for any given time period, curve 302 and curve 352 are either increasing or decreasing. In the example of graph 350, curve 352 is offset by 20V relative to curve 302, however, other offsets have been considered. In addition, a sine wave may be an example of an embodiment of a single drive signal, but other waveforms of a single drive signal have been considered. The voltage offset between the drive signal having the first bias voltage and the drive signal having the second bias voltage may cause the piezoelectric layer (such as Figure 2A The piezoelectric layer 208 is polarized in opposite directions. In this way, the two active vibrations of the active layer are excited, similar to Figure 3A However, the dual bias offset Figure 3B The single drive signal does not require duplication of ultrasound transmitters and receivers.

[0047] Now go to Figure 4 , a schematic diagram 400 of a bias circuit 402 that can bias a single drive signal to a dual bias voltage applied to an electrode of a transducer array 404 is shown. The transducer array 404 may include a first transducer 406 and a second transducer 408. Although two transducers are shown in the schematic diagram 400, it should be understood that, depending on the embodiment, the transducer array may have N transducers. In addition, the transducer array may be arranged as a linear array, a 2D array, an annular array, and the like.

[0048] In one embodiment, the first transducer 406 and the second transducer 408 may each include a piezoelectric layer and be configured as a PMUT, such as Figure 2A In an alternative embodiment, the first transducer 406 and the second transducer 408 may each include a membrane and may be configured as a CMUT, such as Figure 2B CMUT 250. In a further example, the first transducer 406 may be configured as a PMUT, while the second transducer 408 is configured as a CMUT.

[0049] The first top electrode 410 and the second top electrode 412 may be directly coupled to the first transducer 406. The third top electrode 414 and the fourth top electrode 416 may be directly coupled to the second transducer 408. The first top electrode 410 and the third top electrode 414 may be equivalent to FIG. 2A to FIG. 2C The second top electrode 412 and the fourth top electrode 416 may be equivalent to FIG. 2A to FIG. 2C The first top electrode 410 and the third top electrode 414 are driven by the same bias voltage 422 , and the second top electrode 412 and the fourth top electrode 416 are driven by the same bias voltage 428 .

[0050] The first bottom electrode 418 may be directly coupled to the first transducer 406, and the second bottom electrode 420 may be directly coupled to the second transducer 408. The first bottom electrode 418 and the second bottom electrode 420 may be equivalent to Figure 2A The bottom electrode 210 and / or Figure 2B The bottom electrode 258 is formed on the surface of the substrate.

[0051] The bias circuit 402 may be configured to bias the single drive signal with a first bias voltage applied to the first transducer 406 via the first top electrode 410 and to the second transducer 408 via the third top electrode 414. In addition, the bias circuit 402 is configured to bias the single drive signal with a second bias voltage applied to the first transducer 406 via the second top electrode 412 and to the transducer 408 via the fourth top electrode 416.

[0052] The first bottom electrode 418 may be electrically coupled to the first transmitter / receiver 434, and the second bottom electrode 420 may be coupled to the second transmitter / receiver 436. In some examples, when the number of transducers N is large (e.g., ≥1000), it may be impractical to provide a cable to connect each transmitter / receiver to each transducer. To this end, N transmitters / receivers (including the first transmitter / receiver 434 and the second transmitter / receiver 436) may be positioned physically close to the N transducers (e.g., within the handle of the ultrasound probe). The first transmitter / receiver 434 may send a first single drive signal to the first transducer 406 via the first bottom electrode 418, and the second transmitter / receiver 436 may send a second single drive signal to the second transducer 408 via the second bottom electrode 420. In some examples, the first single drive signal and the second single drive signal may be equivalent.

[0053] In an example where the transducer array 404 includes N transducers, each bottom electrode of the N transducers may be coupled to a single transmitter / receiver. In some embodiments, an array of N transducers may include no more than N transmitters and no more than N receivers. Each of the N transducers may require a single transducer / receiver because a single drive signal is transmitted to each of the N transducers.

[0054] The bias circuit 402 may be coupled to the top electrode 411 of the transducer array 404. The first top electrode 410 and the third top electrode 414 may each be electrically coupled to a first bias input 422. In an example where the transducer array 404 includes N transducer elements, each of the N transducer elements may also be coupled to the first bias input 422. The first bias input 422 may be coupled to a first resistor 426. A first capacitor 424 may be coupled to the first bias input 422 between the first resistor 426 and the first top electrode of the transducer array (e.g., the first top electrode 410 and the third top electrode 414). One side 425 of the first capacitor 424 (e.g., the side not coupled to the first bias input 422) may be coupled to electrical ground or to an alternating potential with a low AC impedance.

[0055] The second top electrode 412 and the fourth top electrode 416 can each be electrically coupled to a second bias input 428. In an example where the transducer array 404 includes N transducer elements, each of the N transducer elements can also be coupled to the second bias input 428. The second bias input 428 can be coupled to a second resistor 430. A second capacitor 432 can be coupled to the second bias input 428 between the second resistor 430 and the second top electrode of the transducer array (e.g., the second top electrode 412 and the fourth top electrode 416). One side 433 of the second capacitor 432 can be configured similarly to the first capacitor 424 and can be coupled to electrical ground or to an alternating potential with a low AC impedance.

[0056] A dual voltage power supply 442 may be coupled to the first resistor 426 and the second resistor 430. The dual voltage power supply 442 may power the bias circuit 402. The dual voltage power supply 442 may output two separate voltages. One of the dual voltages may power the first bias input 422, while the other may power the second bias input 428. In a preferred embodiment, the bias voltages may have opposite polarities and similar magnitudes. In some embodiments, one of the dual bias voltages may be close to zero, while the other may be about a few volts or tens of volts. The dual voltage power supply 442 may be created by a commercially available voltage regulator or voltage divider.

[0057] The voltage applied across the active layers of the first transducer 406 and the second transducer 408 is the difference between a single drive signal supplied via the first transmitter / receiver 434 or the second transmitter / receiver 436 and the bias voltages supplied by the first bias input 422 and the second bias input 428. In some examples, the first bias voltage and the second bias voltage may be equal and opposite in sign. For example, the first bias voltage may be a positive voltage (e.g., +20V) and the second bias voltage may be a negative voltage (e.g., -20V). In alternative examples, the first bias voltage and the second bias voltage may be opposite in sign and unequal, or one of the bias voltages may be zero. For example, where the first bias voltage or the second bias voltage is zero; the corresponding capacitor (e.g., the first capacitor 424 for the first bias voltage or the second capacitor 432 for the second bias voltage) and the resistor (e.g., the first resistor 426 for the first bias voltage or the second resistor 430 for the second bias voltage) may be omitted. In examples where one or more transducers of the transducer array include a piezoelectric layer, application of the first bias voltage or the second bias voltage can result in a voltage across the piezoelectric layer that is greater than the coercivity of the piezoelectric layer. In this way, a portion of the piezoelectric layer directly beneath a first set of top electrodes (e.g., first top electrode 410 and third top electrode 414) coupled to first bias input 422 can have an opposite polarity than a portion of the piezoelectric layer directly beneath a second set of top electrodes (e.g., second top electrode 412 and fourth top electrode 416) coupled to second bias input 428.

[0058] The first capacitor 424 and the second capacitor 432 can each be physically located close to the transducer array 404. In this way, the connection impedance between the first capacitor 424 and the first top electrode 410 and the third top electrode 414 and the connection impedance between the second capacitor 432 and the second top electrode 412 and the fourth top electrode 416 can be minimized. Both the first capacitor and the second capacitor can be configured to have a capacitance of 1 to 20 times the combined transducer capacitance. The first capacitor 424 and the second capacitor 432 can each provide a low impedance path for transmission and reception signals from the first transmitter / receiver 434 and the second transmitter / receiver 436. The low ground impedance ensures low electrical crosstalk between the first transducer 406 and the second transducer 408.

[0059] The first resistor 426 and the second resistor 430 may be connected between the dual voltage power supply 442 and the corresponding first bias input 422 and the second bias input 428. In one example, the resistors are in the range of a few kOhms to hundreds of kOhms. The first resistor 426 and the second resistor 430 may charge the first capacitor 424 and the second capacitor 432 to a desired bias level, respectively. During operation of the ultrasound probe including the bias circuit 402, the first resistor 426 and the second resistor 430 may experience little current and little power dissipation. However, at power-up, the capacitor charging current may flow through the first resistor 426 and the second resistor 430. The capacitor charging current may cause a short but high-power pulse, and the first resistor 426 and the second resistor 430 may be selected to be able to withstand the pulse. In an alternative embodiment, the dual voltage from the dual voltage power supply 442 may rise gradually.

[0060] The bias circuit 402 may rely on cost-effective components, such as capacitors and resistors. Additionally, the number of capacitors and resistors may depend on the number of biases (e.g., dual bias, so two capacitors and two resistors) and not on N. To this end, the bias circuit 402 may be adaptable to large transducer arrays without increasing the cost or size of the bias circuit 402. However, it may be desirable to split the first capacitor 424 and the second capacitor 432 into a set of parallel-connected capacitors that may be spatially distributed so that each of the N transducer elements may be physically close to a capacitor.

[0061] The first transmitter / receiver 434 may include a first negative capacitance circuit 438, and the second transmitter / receiver 436 may include a second negative capacitance circuit 440. The first negative capacitance circuit 438 and the second negative capacitance circuit 440 may be configured to reduce or eliminate the parasitic shunt capacitance of the first transducer 406 and the second transducer 408, respectively. If not considered, the parasitic shunt capacitance may cause power loss in the first transmitter / receiver 434 and the second transmitter / receiver 436, especially in the example where the first transducer 406 and the second transducer 408 are PMUTs. In addition, the shunt capacitance may cause acoustic reflections of the transducer array 404. For this reason, N transmitters / receivers may require N negative capacitance circuits. By limiting the number of transmitters / receivers to at most equal to the number of transducers, the number of negative capacitance circuits may also be limited. In order to minimize the cost and complexity of the ultrasound system without sacrificing performance, it is desirable to limit the number of transmitters / receivers and corresponding negative capacitance circuits.

[0062] Now turn to Figure 5, a graph 500 showing the displacement of a piezoelectric layer as a function of an applied electric field is shown. An electric field is applied to the piezoelectric layer via a single top electrode and a single bottom electrode. Curve 502 corresponds to the displacement of the piezoelectric layer between the single top electrode and the single bottom electrode. Before the electric field is applied, the piezoelectric layer may be located at point 504 corresponding to 0 applied voltage and 0 deflection. Moving from point 504 to point 506 along curve 502, an increasing positive electric field is applied. As the positive electric field increases, the piezoelectric layer deflects an increasing amount in a first direction corresponding to a negative displacement along the y-axis of graph 500. When the electric field increases from a first voltage at point 506 to a second voltage at point 508, the electric field increases by more than the positive coercive field of the material, which causes the piezoelectric layer to reverse polarization. Reversing the polarization causes the piezoelectric layer to deflect in a second direction, corresponding to a positive deflection along the y-axis (e.g., between point 506 and point 508). Reducing the electric field between point 508 and point 510 causes the material to deflect again in the first direction. Continuing to reduce the electric field through point 510 in the negative direction along the x-axis may correspond to reducing the electric field through the negative coercive field of the material in the negative direction, which causes the piezoelectric layer to reverse polarization. Reversing polarization causes the piezoelectric layer to deflect in the second direction. The electric field is increased to a less negative value between 510 and 512, causing the piezoelectric layer to deflect in the first direction until zero displacement is reached at zero applied field at point 504.

[0063] based on Figure 5 , the piezoelectric material is in a first polarization between point 512 and point 506 and in a second reversed polarization between point 510 and point 508. Figure 2A In an example where a piezoelectric layer 208 of a piezoelectric layer 208 is driven by a single drive signal on a bottom electrode and biased to a first bias on a first top electrode and a second bias on a second top electrode, the first bias may maintain the piezoelectric layer in a first polarization under the first top electrode, and the second bias may be of opposite sign and stronger than the coercive field to maintain the piezoelectric layer in a second polarization under the second top electrode. In this way, when an increasing electrical drive signal is applied, the piezoelectric layer under the first top electrode may follow between point 512 and point 506 and deflect in a first direction, and the piezoelectric layer under the second top electrode may follow between point 510 and point 508 and deflect in a second direction. The opposite deflection directions may correspond to driving two different vibration frequencies simultaneously, thereby increasing the bandwidth of a transducer including the piezoelectric layer. Alternatively, the opposite deflection directions may increase the transmit or receive sensitivity of the pMUT.

[0064] Figure 6 It shows operations such as Figure 1 The method 600 may be performed by a signal processor of the ultrasound system, such as a Figure 1The ultrasound system 100 may include a signal processor 132 such as Figure 1 In one embodiment, the probe may include a transducer. In another example, the probe may include a transducer array consisting of N transducers. The transducer and / or the N transducers may be a MUT, such as Figure 2A PMUT 200 or Figure 2B 250 CMUTs.

[0065] At 602, method 600 includes applying a voltage across a transducer. Figure 4 As shown in the exemplary embodiment of , the transducer elements can be coupled to a single transmitter via a bottom electrode.

[0066] Step 602 of method 600 also includes steps 604, 606, and 608. Steps 604, 606, and 608 may occur simultaneously. At 604, method 600 includes applying a first bias voltage to a first top electrode of the transducer. For example, the first top electrode may be Figure 4 The first top electrode 410 and / or FIG. 2A to FIG. 2C At 606, method 600 includes applying a second bias voltage to a second top electrode of the transducer. For example, the second top electrode may be Figure 4 The second top electrode 412 or FIG. 2A to FIG. 2C The second top electrode 207. At 608, method 600 includes applying a single drive signal to the bottom electrode of the transducer. The bottom electrode may be, for example, Figure 4 The first bottom electrode 418, Figure 2A The bottom electrode 210 or Figure 2B The bottom electrode of the bottom electrode 258. The voltage applied across the transducer below the first top electrode can be in phase with the voltage applied across the electrode below the second top electrode.

[0067] The first bias voltage and the second bias voltage may be provided by a bias circuit (e.g., Figure 4 The bias circuit 402 of the embodiment of the present invention is supplied. In some examples, the first bias voltage and the second bias voltage may have opposite signs. For example, where the first bias voltage may be of a first sign (e.g., positive), the second bias voltage may be of a sign opposite to the first sign (e.g., negative). In this way, in an example where the probe includes a transducer array of N transducers, a single drive signal may be applied to the N transducers via at most N transmitters, and no more than N transmitters are required.

[0068] In addition, in an example where the transducer is a PMUT and includes a piezoelectric layer, step 602 may result in polarizing the piezoelectric layer of the transducer to a first polarization under the first top electrode and simultaneously polarizing the piezoelectric layer of the transducer to a second polarization opposite to the first polarization under the second top electrode. To this end, the voltage applied across the transducer through the first top electrode or the second top electrode may be greater than the coercive field of the piezoelectric layer and thus reverse the polarity of the piezoelectric layer. The piezoelectric layer polarized in the first direction and the piezoelectric layer polarized in the second direction may respond differently to the applied voltage, respectively.

[0069] At 610, method 600 includes transmitting an ultrasonic signal from a transducer toward a target. The ultrasonic signal may be a combination of a first active region of the MUT under a first top electrode vibrating at a first frequency in response to a single drive signal applied at a first bias voltage (the active region may correspond to a membrane of a CMUT or a piezoelectric layer of a PMUT) and a second active region of the MUT under a second top electrode vibrating at a second frequency in response to a single drive signal applied at a second bias voltage.

[0070] At 612, method 600 includes receiving the reflected ultrasound signal via a receiver coupled to the transducer. The received ultrasound signal may interact with the target before being reflected back to the transducer. In an example where the ultrasound probe includes a transducer array of N transducers, the received ultrasound signal generated by a single drive frequency may require at most N receivers, one receiver coupled to each of the N transducers of the transducer array, and no more than N receivers are required. Method 600 returns.

[0071] exist Figure 7 The effect of oppositely polarized parts of the piezoelectric layer is schematically shown in FIG. Figure 2A 200 is reproduced, including a first top electrode 206, a second top electrode 207, and a piezoelectric layer 208. A first arrow 702 and a second arrow 704 symbolically show the polarization direction when a single drive signal is transmitted to the piezoelectric layer. The first arrow 702 shows the polarization of a portion of the piezoelectric layer 208 directly below the first top electrode 206, which is directed to the first side 204 of the PMUT 200. The second arrow 704 shows the polarization of a portion of the piezoelectric layer 208 directly below the second top electrode 207, which is directed to the first side 204.

[0072] Graph 706 shows the deflection of the piezoelectric layer as a function of the position along the cross section of the PMUT 200. The cross section may correspond to the cross section of the PMUT 200 shown in the curve above 706. Line 710 shows the position along the position axis and the corresponding position on the PMUT 200, across which the polarization of the piezoelectric layer 208 changes from the first polarization to the second polarization. Curve 708 corresponds to the predicted deflection amount of the piezoelectric layer 208 relative to the position. Line 712 corresponds to the neutral position where the piezoelectric layer 208 is not deflected. Positive deflection may correspond to the flexure of the piezoelectric layer 208 toward the first side 204, and negative deflection may correspond to the flexure of the piezoelectric layer 208 toward the second side 202. Curve 708 may correspond to the deflection measured as a result of a single drive signal. As shown in curve 708, applying a single drive signal causes the piezoelectric layer 208 to deflect simultaneously in the positive and negative directions.

[0073] The technical effect of method 600 is to transmit a single drive signal to the transducer of the ultrasonic probe, which causes the active layer of the MUT to vibrate at two different frequencies at the same time. A drive voltage with a first bias can be applied to both ends of the MUT device, while a drive voltage with a second bias can be applied to both ends of the MUT device. The bottom electrode of the MUT can receive a single drive signal from a transmitter / receiver, while a first bias and a second bias are applied to a first top electrode and a second top electrode through a bias circuit. In this way, no more than N transmitters / receivers are used for N transducer arrays to actuate dual-frequency vibration, and the cost and physical size of the ultrasonic system are not significantly increased. In addition, the dual-frequency vibration is actuated using a single drive signal of a single phase. The bias circuit that provides the first bias and the second bias can be cost-effective and can be easily scaled to any N transducer arrays without increasing the number of circuit components.

[0074] The present disclosure provides support for an ultrasonic probe, including: a piezoelectric micromachined ultrasonic transducer (PMUT) including a first top electrode, a second top electrode, and a bottom electrode, a transmitter / receiver configured to apply a single drive signal to the bottom electrode, and a bias circuit configured to apply a first bias to the first top electrode and a second bias to the second top electrode. In a first example of the system, the voltage across the piezoelectric layer of the PMUT is the difference between the single drive signal and the first bias below the first top electrode and the difference between the single drive signal and the second bias below the second top electrode. In a second example of the system, optionally including the first example, the first bias is a positive voltage and the second bias is a negative voltage. In a third example of the system, optionally including one or both of the first and second examples, the PMUT includes a piezoelectric layer in coplanar contact with the first top electrode and the second top electrode, and the voltage across the piezoelectric layer below the first top electrode or below the second top electrode is greater than the coercive field of the piezoelectric layer. In a fourth example of the system, optionally including one or more or each of the first to third examples, the ultrasound probe further includes a plurality of PMUTs, and the bias circuit is configured to apply a first bias voltage to each first top electrode of each PUMT in the plurality of PMUTs, and to apply a second bias voltage to each second top electrode of each PMUT in the plurality of PMUTs. In a fifth example of the system, optionally including one or more or each of the first to fourth examples, the PMUTs are coupled to a single transmitter and a single receiver.

[0075] The present disclosure also provides support for a method of operating an ultrasonic probe, the method comprising: applying a first bias to a first top electrode of a transducer, and applying a second bias to a second top electrode of the transducer, while applying a single drive signal to a bottom electrode of the transducer, emitting an ultrasonic signal actuated by the transducer toward a target, and no longer receiving a reflected ultrasonic signal at a receiver coupled to the transducer. In a first example of the method, the transducer is a piezoelectric micromachined ultrasonic transducer (PMUT) or a capacitive micromachined ultrasonic transducer (CMUT). In a second example of the method, optionally including the first example, the sign of the first bias is opposite to the sign of the second bias. In a third example of the method, optionally including one or both of the first and second examples, the voltage applied across the transducer under the first top electrode is in phase with the voltage applied across the transducer under the second top electrode. In a fourth example of the method, optionally including one or more or each of the first to third examples, transmitting an ultrasonic signal comprises vibrating the transducer at a first frequency and vibrating the transducer at a second frequency. In a fifth example of the method, optionally including one or more or each of the first to fourth examples, the transducer is a PMUT and the polarization of a portion of the piezoelectric layer of the PMUT is reversed by applying a voltage across the transducer using a first bias voltage or a second bias voltage.

[0076] The present disclosure also provides support for an ultrasound probe, including: a transducer array including a transducer, a transmitter and a receiver coupled to the bottom electrode of the transducer, and a bias circuit coupled to a first top electrode and a second top electrode of each transducer in the transducer, wherein the bias circuit is configured to apply a first bias voltage to the first top electrode and a second bias voltage to the second top electrode. In a first example of the system, the bias circuit includes a first capacitor coupled to a first bias input and a second capacitor coupled to a second bias input. In a second example of the system, optionally including the first example, the first capacitor and the second capacitor are as close to the transducer as possible. In a third example of the system, optionally including one or both of the first example and the second example, the bias circuit includes a first resistor coupled to the first bias input and a second resistor coupled to the second bias input, and the first capacitor is positioned between the first resistor and the first top electrode, and the second capacitor is positioned between the second resistor and the second top electrode. In a fourth example of the system, optionally including one or more or each of the first to third examples, the transducer array includes N transducers and no more than N transmitters and no more than N receivers. In a fifth example of the system, optionally including one or more or each of the first to fourth examples, the receiver includes a negative capacitance circuit. In a sixth example of the system, optionally including one or more or each of the first to fifth examples, the first top electrode and the second top electrode are coupled to a distribution bus, and the distribution bus is configured to have a minimum impedance. In a seventh example of the system, optionally including one or more or each of the first to sixth examples, the bias circuit also includes a power supply.

[0077] In another representation, a method of operating an ultrasound probe includes transmitting a single drive signal biased with a first bias and a second bias across a piezoelectric micromachined ultrasound transducer (PMUT) of the ultrasound probe, wherein the single drive signal biased to one of the first bias or the second bias is greater than the coercive field of the piezoelectric layer of the PMUT. In a second example of the method, optionally including the first example, a portion of the piezoelectric layer under the first top electrode deflects in a first direction, while a portion of the piezoelectric layer under the second top electrode deflects in a second direction, the second direction being opposite to the first direction. In a third example of the method, optionally including one or both of the first and second examples, the method further includes transmitting an ultrasound signal toward a target, wherein a portion of the piezoelectric layer under the first top electrode transmits an ultrasound signal at a first frequency, and a portion of the piezoelectric layer under the second top electrode transmits an ultrasound signal at a second frequency. In a fourth example of the method, optionally including one or more or each of the first to third examples, the ultrasound probe includes N transducers, and transmitting a single drive signal includes transmitting a single drive signal using N transmitters coupled to the bottom electrodes of the N transducers. In a fifth example of the method, optionally including one or more or each of the first to fourth examples, the method further includes receiving the reflected ultrasound signals via N receivers coupled to the N transducers.

[0078] As used herein, the elements or steps listed in the singular and beginning with the word "one" or "a kind of" should be understood as not excluding a plurality of said elements or steps, unless such exclusion is explicitly stated. In addition, the reference to "one embodiment" of the present invention is not intended to be interpreted as excluding the existence of additional embodiments that also include the cited features. In addition, unless explicitly stated to the contrary, "comprising", "including" or "having" an embodiment of an element or multiple elements with a specific characteristic may include additional such elements that do not have the characteristic. The terms "including" and "in..." are used as the concise language equivalents of the corresponding terms "including" and "wherein". In addition, the terms "first", "second" and "third" etc. are only used as marks, and are not intended to impose numerical requirements or specific positional order on their objects.

[0079] Figure 2A , Figure 2B and Figure 2CAn exemplary configuration of relative positioning of each component is shown. In at least one example, if it is shown as directly contacting or directly coupling each other, such elements may be referred to as directly contacting or directly coupling, respectively. Similarly, in at least one example, the elements shown as being adjacent or adjacent to each other may be adjacent or adjacent to each other, respectively. For example, the components placed in coplanar contact with each other may be referred to as being in coplanar contact. For another example, in at least one example, the elements positioned to be spaced apart from each other and having only space therebetween without other components may be described and quoted as such. For another example, the elements shown as being located above / below each other, located on opposite sides of each other, or located on the left / right side of each other may be described and quoted as such relative to each other. In addition, as shown in the figure, in at least one example, the topmost element or the point of the element may be referred to as the "top" of the component, and the bottommost element or the point of the element may be referred to as the "bottom" of the component. As used herein, top / bottom, upper / lower, above / below may be relative to the vertical axis of the figure, and may be used to describe the positioning of the elements relative to each other in the figure. Thus, in one example, elements shown as being above other elements are positioned vertically above other elements. For another example, the shapes of the elements depicted in the figures may be referred to as having those shapes (e.g., such as being round, straight, planar, curved, rounded, chamfered, angled, etc.). In addition, in at least one example, elements shown as intersecting each other may be referred to as intersecting elements or intersecting each other. In addition, in one example, elements shown as being within another element or being shown as being outside another element may be described and referenced as such.

[0080] This written description uses examples to disclose the invention, including the best mode, and also to enable a person of ordinary skill in the relevant art to practice the invention, including making and using any devices or systems and performing any included methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to a person of ordinary skill in the art. Such other examples are intended to fall within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insignificant differences from the literal language of the claims.

Claims

1. An ultrasonic probe, comprising: A piezoelectric micromachined ultrasonic transducer (PMUT) (200) comprising a first top electrode (206), a second top electrode (207), and a bottom electrode (210); a transmitter / receiver (434, 436) configured to apply a single drive signal to the bottom electrode (210); and A bias circuit (402) is configured to apply a first bias voltage to the first top electrode (206) and a second bias voltage to the second top electrode (207).

2. The ultrasound probe of claim 1 , wherein the voltage across the piezoelectric layer of the PMUT is a difference between the single drive signal and the first bias voltage under the first top electrode and a difference between the single drive signal and the second bias voltage under the second top electrode. 3 . The ultrasound probe according to claim 1 , wherein the bias circuit comprises a power supply, and wherein the first bias voltage is a positive voltage and the second bias voltage is a negative voltage.

4. The ultrasound probe according to claim 1, wherein the PMUT includes a piezoelectric layer in coplanar contact with the first top electrode and the second top electrode, and the voltage across the piezoelectric layer under the first top electrode or under the second top electrode is greater than the coercive field of the piezoelectric layer.

5. The ultrasound probe according to claim 1, wherein the ultrasound probe further comprises a plurality of PMUTs, and the bias circuit is configured to apply the first bias voltage to each first top electrode of each PUMT of the plurality of PMUTs, and to apply the second bias voltage to each second top electrode of each PUMT of the plurality of PMUTs.

6. The ultrasound probe of claim 1, wherein the PMUT is coupled to a single transmitter and a single receiver.

7. The ultrasound probe of claim 1, wherein the bias circuit comprises a first capacitor coupled to a first bias input and a second capacitor coupled to a second bias input, and wherein the first capacitor and the second capacitor are positioned as close as possible to the PMUT.

8. An ultrasound probe according to claim 7, wherein the bias circuit includes a first resistor coupled to the first bias input and a second resistor coupled to the second bias input, and the first capacitor is positioned between the first resistor and the first top electrode, and the second capacitor is positioned between the second resistor and the second top electrode.

9. The ultrasound probe of claim 1, wherein the transmitter / receiver comprises a negative capacitance circuit, and wherein the first top electrode and the second top electrode are coupled to a distribution bus, and the distribution bus is configured to have a minimum impedance.

10. A method of operating an ultrasound probe, the method comprising: applying (604) a first bias voltage to a first top electrode of a transducer and applying (606) a second bias voltage to a second top electrode of the transducer while applying (608) a single drive signal to a bottom electrode of the transducer; transmitting (610) an ultrasonic signal actuated by the transducer toward a target; as well as The reflected ultrasound signal is no longer received (612) at a receiver coupled to the transducer.

11. The method of claim 10, wherein the transducer is a piezoelectric micromachined ultrasonic transducer (PMUT) or a capacitive micromachined ultrasonic transducer (CMUT). The method of claim 10 , wherein a sign of the first bias voltage is opposite to a sign of the second bias voltage.

13. The method of claim 10, wherein a voltage applied across the transducer beneath the first top electrode is in phase with a voltage applied across the transducer beneath the second top electrode.

14. The method of claim 10, wherein transmitting the ultrasonic signal comprises vibrating the transducer at a first frequency and vibrating the transducer at a second frequency.

15. The method of claim 10, wherein the transducer is a PMUT, and the voltage applied across the transducer using the first bias or the second bias reverses polarization of a portion of a piezoelectric layer of the PMUT.

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