Higher bandwidth micromachined transducer mixed with bias scheme

Abstract

Various methods and systems are provided for increasing the fractional bandwidth (618, 718, 518) of an ultrasound device for both low and high frequency applications. In one example, where the transducer array (300) comprises one or more transducer elements (310, 314, 352, 106, 304, 302), which comprise a plurality of capacitive micromachined ultrasonic transducers (cMUTs (251, 200, 302)), the fractional bandwidth (618, 718, 518) can be advantageously increased by applying different bias voltages to different groups of cMUTs (251, 302) within each transducer element (310, 352, 106, 304, 312). The ratio between the different bias voltages can be optimized to maximize the fractional bandwidth (618, 718, 518). In another example, the different bias voltages can be configured to operate a first packet (320) of cMUTs (251, 302) in a transmit mode and to operate a second packet (322) of cMUTs (251, 302) in a receive mode.

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] Microelectromechanical 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. The sound waves can be emitted by a transmitting transducer, and the reflections 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. For some types of MEMS devices used as transmitting transducers and / or receiving transducers, such as capacitive micromachined ultrasonic transducers (cMUTs), the cMUT may include a top electrode and a bottom electrode. The top electrode may move when receiving an electrical signal to generate a sound wave, or may move when receiving a sound wave to generate an electrical signal that can be processed.

[0004] For cMUTs that operate primarily at higher frequencies, very thin membranes are required to match the fractional bandwidth requirements of the target applications. Although academic breakthroughs have been achieved in manufacturing MUTs with sub-micron membrane thicknesses through surface micromachining, wafer bonding techniques, and parallel manufacturing processes, industrial foundries dedicated to the industrialization of MUTs generally face a lack of sub-micron membrane capabilities. This shortcoming is closely related to the structural reliability of micro-electromechanical systems (MEMS) and the wafer-level device scalability goals of the sensor and actuator industry. Especially for cMUTs, this constraint affects the bandwidth (e.g., fractional bandwidth) of devices used for higher frequency applications. Therefore, a method for increasing the fractional bandwidth of cMUTs for high-frequency applications without using sub-micron membranes would be desirable.

[0005] Methods for solving the problem of increasing the fractional bandwidth of a cMUT for high frequency applications without reducing the membrane thickness include using a cMUT with multiple membranes. For example, U.S. Patent Application 20070059858A1 to Caronti proposes mixing different transducer elements and / or element geometries to solve bandwidth constraints. However, the cMUT of Caronti is subject to geometry-related constraints, where a particular geometric configuration can be used to solve a first target fractional bandwidth, a second geometric configuration can be used to solve a second target fractional bandwidth, a third geometric configuration can be used to solve a third target fractional bandwidth, and so on. Summary of the invention

[0006] In one embodiment, a method for an ultrasound system includes: applying a first DC bias voltage to a first portion of a capacitive micromachined ultrasound transducer (cMUT) of a transducer element of a transducer array of an ultrasound probe of the ultrasound system during an ultrasound scan of a patient and during a transmit mode of the transducer element of the transducer array of the ultrasound probe of the ultrasound system; applying a second DC bias voltage to a second portion of the cMUT of the transducer element, the second DC bias voltage being different from the first DC bias voltage; applying an AC drive signal to the first portion of the cMUT to generate a first acoustic signal based on a first combination of the first DC bias voltage and the AC drive signal, thereby causing a first portion of the cMUT to transmit an acoustic signal; A membrane of a portion vibrates at a first resonant frequency defined by a first DC bias voltage; an AC drive signal is applied to a second portion of the cMUT to generate a second acoustic signal based on a second combination of the second DC bias voltage and the AC drive signal, the second combination causing the membrane of the second portion of the cMUT to vibrate at a second resonant frequency defined by the second DC bias voltage, the second resonant frequency differing from the first resonant frequency by a threshold difference; and the first acoustic signal and the second acoustic signal are combined to generate a higher bandwidth signal, the higher bandwidth signal being based on constructive interference between a first transmit transfer function of the first portion of the cMUT and a second transmit transfer function of the second portion of the cMUT. Similarly, during a receive mode of the transducer element, a higher bandwidth input electrical signal may be generated, wherein the higher bandwidth input electrical signal has a first component generated by applying a first receive transfer function based on the first DC bias voltage to the first resonant frequency, and a second component generated by applying a second receive transfer function based on the second DC bias voltage to the second resonant frequency, and the higher bandwidth input electrical signal is based on constructive interference between the first receive transfer function and the second receive transfer function.

[0007] Compared to methods such as Caronti, the methods disclosed herein can be used with various levels of mixing by applying different DC bias voltages to electrodes of different cMUTs and thereby causing constructive coupling of different transmit and receive transfer functions for generating acoustic output signals from electrical signals and input electrical signals from received acoustic waves. An advantage of the systems and methods disclosed herein is that a single ultrasonic device can be configured for use by multiple applications that may require different operating frequencies, including both lower and higher frequencies. A single ultrasonic device will facilitate the use of different applications, which will reduce the cost of the ultrasonic system. In addition, for higher frequency applications, unlike other alternative ultrasonic devices that do not utilize interference between two resonances to produce a wider fractional bandwidth signal, the bandwidth of the ultrasonic device described herein may not be constrained by the diameter of the cMUT included in the ultrasonic device and / or the thickness of the membrane of the cMUT. In addition, the systems and methods disclosed herein may allow two or more adjacent cMUTs to be configured such that a first group of cMUTs operates in a collapsed operation mode and a second group of cMUTs operates in a non-collapsed operation mode, wherein one of the first group and the second group is configured to transmit and the other of the first group and the second group is configured to receive. In such a configuration, the transmit and receive operating bands may be additionally extended.

[0008] 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 features or essential features of the claimed subject matter, the scope of which is uniquely 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

[0009] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0010] Figure 1 A block diagram of an exemplary ultrasound system that may be used for ultrasound imaging according to one or more embodiments of the present disclosure is shown;

[0011] Figure 2A shows an exemplary cross-sectional view of a cMUT as in the prior art;

[0012] Figure 2B is a schematic diagram of a single-element transducer array of a cMUT according to one or more embodiments of the present disclosure.

[0013] Figure 3A A schematic diagram showing a one-dimensional (1D) array of transducer elements according to one or more embodiments of the present disclosure is shown;

[0014] Figure 3B shows a schematic diagram of a two-dimensional (2D) array of transducer elements according to one or more embodiments of the present disclosure;

[0015] Figure 4A An exemplary method for increasing the fractional bandwidth of an acoustic signal generated by a transducer array by introducing different bias voltages to different cMUTs of the transducer array is shown in accordance with one or more embodiments of the present disclosure.

[0016] Figure 4B An exemplary method for applying different bias voltages to different cMUTs of a transducer array to convert a portion of the cMUTs into a transmitting unit and a second portion of the cMUTs into a receiving unit according to one or more embodiments of the present disclosure is shown;

[0017] Figure 5 showing a first transmit sensitivity graph indicating a first fractional bandwidth of acoustic signals generated by a plurality of cMUTs as in the prior art;

[0018] Figure 6 showing a second transmit sensitivity graph indicating a second fractional bandwidth of acoustic signals generated by a plurality of cMUTs in accordance with one or more embodiments of the present disclosure;

[0019] Figure 7 showing a third transmit sensitivity graph indicating a third fractional bandwidth of acoustic signals generated by a plurality of cMUTs in accordance with one or more embodiments of the present disclosure; and

[0020] Figure 8 A visualization of destructive interference between two transfer functions is shown in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0021] The ultrasound system may include one or more detector arrays having multiple micromachined ultrasound transducers (cMUTs). Although cMUTs can be used for medical imaging, in addition to ultrasound imaging of humans or animals, cMUTs can also be used for various other purposes such as ultrasound / acoustic sensing, nondestructive evaluation (NDE), ultrasound therapy (e.g., high-intensity focused ultrasound (HIFU)), etc. The basic structure of the cMUT includes a thin film and a supporting substrate separated by a vacuum cavity. Typically, a doped silicon substrate constitutes the bottom electrode of the capacitor, and the conductive film acts as the top electrode. The membrane vibrates when excited with an electrical AC signal. Conversely, when the membrane vibrates due to an impinging sound wave, an electrical signal is generated.

[0022] cMUTs were originally fabricated using a sacrificial release process. In this process, a silicon nitride membrane layer is deposited on a patterned sacrificial polysilicon layer. The polysilicon is subsequently removed via small channels, and the resulting gap is then vacuum sealed by a second silicon nitride layer deposited on top of the membrane. The final thickness of the membrane is established by etching back the second nitride layer. This technique has many inherent disadvantages, including: stiction problems that may prevent membrane release; stresses in the membrane that are very sensitive to deposition conditions; difficulty controlling membrane thickness due to sequential deposition and etching steps; and difficulty controlling gap height or thickness due to undesirable non-uniform nitride deposition in the cavity during sealing.

[0023] Recently, a cMUT manufacturing process using direct wafer bonding (e.g., fusion bonding) technology has been developed. In this technology, a vacuum cavity is formed by etching an oxide layer before bonding the wafer to a silicon-on-insulator (SOI) wafer in a vacuum chamber. After removing the buried oxide (BOX) layer of the handle wafer and the SOI wafer, the single crystal silicon layer remains as a cMUT membrane with good uniformity and no significant residual stress. However, for high frequency ultrasonic devices, the thickness of the membrane may constrain the bandwidth of the electrical signal generated by the membrane.

[0024] To solve this problem, a method is proposed in which the cMUT of the transducer element is divided into a plurality of groups, and a different bias voltage is applied to each of the plurality of groups to deliver a different electrical signal to the cMUT. Therefore, the cMUT can vibrate at different resonant frequencies. By utilizing constructive interference between different resonant frequencies, the fractional bandwidth of the combined acoustic signal of the plurality of cMUTs can be increased without relying on a thinner membrane.

[0025] The higher bandwidth may allow a single ultrasound device to be used for a greater number of higher and lower frequency applications. For purposes of the present disclosure, higher frequency applications include applications that rely on frequencies between 20 MHz and 50 MHz. For example, currently, a first ultrasound device may be used for lower frequency applications (e.g., cardiac imaging); a second, different ultrasound device may be used for higher frequency applications (e.g., tissue harmonic imaging), and a third ultrasound device may be used for the highest frequency applications (e.g., intravascular imaging). Using the hybrid biasing strategy described herein, a single device may be configured for lower frequency applications, higher frequency applications, and the highest frequency applications. By using a single device instead of a first device, a second device, and a third device, the cost of the ultrasound system may be reduced, and the efficiency of the radiologist's workflow may be improved.

[0026] Figure 1 An exemplary ultrasound system is shown. Figure 2A Shown in Figure 1 An example of a cross section of a cMUT used in an ultrasound system. Multiple cMUTs may be arranged in a single transducer element array of an ultrasound system, such as Figure 2B A transducer array as depicted in FIG. A one-dimensional (1D) transducer array may include rows of transducer elements, such as Figure 3A A two-dimensional (2D) transducer array may include a matrix of transducer elements, such as Figure 3B As shown. Figure 4A A first method for increasing the fractional bandwidth of a signal transmitted by a transducer array by vibrating different cMUTs of a transducer element at different resonant frequencies to exploit constructive interference is shown in FIG. Figure 4B A second method for converting a first portion of the cMUT of the transducer elements into a transmitting cMUT and converting a second portion of the cMUT of the transducer elements into a receiving cMUT is shown in FIG. Figure 5 A first transmit sensitivity graph is shown indicating a first fractional bandwidth of a first acoustic signal generated by a plurality of cMUTs, wherein the same electrical signal is generated at the plurality of cMUTs. Figure 7 A second transmit sensitivity graph is shown indicating a second fractional bandwidth of a second acoustic signal generated by a plurality of cMUTs in a hybrid bias configuration, wherein different electrical signals are generated at different groups of cMUTs. In the hybrid bias configuration, the transfer functions of the different groups may be attenuated by the coupling layer to smooth out sharp transitions during destructive interference. In various embodiments, the coupling layer may include a rubber-based polymer. Figure 3A An example of a coupling layer is shown in .

[0027] Now turning to the attached figure, Figure 1 1 is a block diagram of an exemplary ultrasound system 100 that may be used for ultrasound imaging according to various embodiments. 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 for a cMUT, and variations in the configuration of the circuit 111 are possible without departing from the scope of the present disclosure.

[0028] 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 a set of transducer elements 106 that may each include, for example, a plurality of cMUTs. The cMUTs may include, for example, a single cMUT, a 1D array of cMUTs, a 2D array of cMUTs, an annular (ring) array of cMUTs, and the like. In certain embodiments, the ultrasound probe 104 may be operable to acquire ultrasound image data covering, for example, at least a substantial portion 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.

[0029] 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.

[0030] 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.

[0031] 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 be performed concurrently. In such cases, the probe may include a transmitting transducer element and a receiving transducer element.

[0032] 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.

[0033] 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.

[0034] 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 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.

[0035] 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.

[0036] 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.

[0037] The signal processor 132 may include suitable logic components, circuits, interfaces and / or codes that are operable to process ultrasound scan data (e.g., 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.

[0038] 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.

[0039] The ultrasound system 100 may be 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 for storing 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.

[0040] 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.

[0041] 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.

[0042] 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".

[0043] As described above, a probe for an imaging system such as an ultrasound imaging system or another type of medical system that relies on data acquisition via acoustic signals may incorporate a cMUT for transmitting and receiving signals. The performance of the cMUT may rely on the vibration of the membrane. For cMUTs that operate primarily at higher frequencies, very thin membranes are required to match the fractional bandwidth requirements of the target application (e.g., sub-micron membrane thickness). Although such very thin membranes can be obtained through surface micromachining, wafer bonding techniques, and / or parallel manufacturing processes, due to the structural reliability of microelectromechanical systems (MEMS) and the wafer-level device scalability goals of the sensor and actuator industry, the industrial process for generating sub-micron film thicknesses may be expensive and inefficient.

[0044] Figure 2A An exemplary embodiment of a cMUT 200 is shown, which may be included in a transducer element of an ultrasound system, such as Figure 1 One of the transducer elements 106. The reference axis 201 is set to include the y-axis, the x-axis and the z-axis.

[0045] In various implementations, the cMUT 200 can have a cylindrical shape. Figure 2A 200 has a bottom side 202 and a top side 204. In other embodiments, the cMUT 200 can have different shapes. In one example, the radius of the cylindrical cMUT is 15 microns. It should be understood that the specific geometric shape used in this example is one configuration, and other embodiment cMUTs with different geometric configurations may be used without departing from the scope of the present disclosure.

[0046] The cMUT 200 includes a top electrode 206 at the top side 204. A membrane layer 210 may be in coplanar contact with and electrically coupled to the top electrode 206. In some examples, the membrane layer 210 may be formed of silicon. In one example, the membrane has a thickness of 2 microns. An insulating layer 212 may be in coplanar contact with a bottom surface 211 of the membrane layer 210. In some embodiments, the insulating layer 212 or a similar isolation layer may extend across the bottom surface 211. In one example, the insulating layer 212 has a thickness of 150 nm. A bottom electrode 214 at the bottom side 202 may be in coplanar contact with a bottom surface 215 of the insulating layer 212. In the depicted embodiment, the insulating layer 212 includes a cutout or a side pillar to support the membrane layer 210. In some embodiments, an insulating layer 222 may extend across the top surface of the bottom electrode 214. Further, in some embodiments, the cutout may be composed of a first material, and the insulating layer extending across the top surface of the bottom electrode 214 may be composed of a second material. In other words, the insulating layer 212 and / or 222 may be included at either or both of above and below the microcavity 220 and / or on one or both sides of the microcavity 220 .

[0047] The insulating layer 212 may not completely cover the bottom surface 211 of the membrane layer 210 and the top surface 216 of the bottom electrode 214, thereby forming a microcavity 220 enclosed by the membrane layer 210, the insulating layer 212, and the bottom electrode 214. The microcavity 220 may be evacuated or the microcavity 220 may include a certain amount of fluid. In some examples, the fluid may be air. In one example, the height 207 of the microcavity 220 (e.g., the gap between the bottom surface 211 and the top surface 216) is 75nm. The bottom surface 217 of the bottom electrode 214 may be in direct coplanar contact with the silicon substrate 230 (e.g., a wafer). When the cMUT 200 is observed from the bottom side 202, the silicon substrate 230 may be the outermost layer. In some embodiments, the silicon substrate 230 may include or serve as a bottom electrode and may be coupled to a common ground terminal.

[0048] The cMUT 200 may be electrically coupled to a drive circuit that applies a combination of a DC bias signal and an AC drive signal via the top electrode 206 and the bottom electrode 214. The drive circuit may provide an AC drive signal voltage between the first top electrode 206 and the bottom electrode 214, which may cause vibration of the membrane layer 210. Specifically, the DC bias voltage fixes the instantaneous resonant frequency, and the AC drive voltage causes the membrane layer 210 to vibrate. The vibration of the membrane layer 210 may then generate an acoustic wave that radiates away from the surface of the top electrode 206, which may be directed toward an imaging target, such as a patient's body. In some cases, the DC bias voltage may be less than a threshold voltage (e.g., a collapse voltage) at which the membrane layer 210 (and the top electrode 206) collapses (e.g., operating in a non-collapse mode). The collapse voltage is the DC bias voltage at which the bottom surface 211 of the membrane layer 210 contacts the top surface of the isolation layer 222. In one example, the collapse voltage is 87.75V. In other cases, the DC bias voltage may be equal to or greater than the collapse voltage (e.g., operating in a collapse mode).

[0049] A DC bias voltage is applied to the top electrode 206, wherein the bottom electrode 214 is connected to the ground terminal of the cMUT. Figure 8 Described in more detail, different DC bias voltages may be applied to different cMUTs of the transducer element so that the acoustic signals interfere in a manner that generates a wider bandwidth output signal. Specifically, a first DC bias voltage may be applied to a first cMUT so that a first membrane layer of the first cMUT vibrates at a first resonant frequency, and a second DC bias voltage may be applied to a second cMUT so that a second membrane layer of the second cMUT vibrates at a second different resonant frequency. In a transmit mode, when an AC drive signal is applied to the transducer element, the acoustic signal generated by the transducer element may have a wider bandwidth due to interference between a first transmit transfer function based on the first DC bias voltage and the AC drive signal and a second transmit transfer function based on the second DC bias voltage and the AC drive signal.

[0050] Similarly, in receive mode, when receiving an acoustic signal at the transducer element, a first receive transfer function based on the first cMUT at a first DC bias voltage and a second receive transfer function based on the second cMUT at a second DC bias voltage will interfere to generate an output electrical signal with a wider bandwidth.

[0051] In another embodiment, the first DC bias voltage may be greater than the breakdown voltage applied to the first cMUT, and the second DC bias voltage may be less than the breakdown voltage applied to the second cMUT. The first cMUT may be used in a transmit mode of the transducer element, and the second cMUT may be used in a receive mode of the transducer element, or vice versa.

[0052] Multiple cMUTs can be arranged in a transducer element, such as Figure 2B As shown. Then, the transducer array may include a plurality of transducer elements, which may be as shown Figure 3A Arranged in rows as shown, or as Figure 3B Shown are arranged as a 2D matrix.

[0053] Figure 2B A single-element transducer 250 is shown, wherein the single-element transducer 250 includes a plurality of cMUTs 251. In the depicted embodiment, the plurality of cMUTs 251 are arranged in a 4×3 matrix. The matrix includes a first column 260, a second column 262, a third column 264, and a fourth column 266; and a first row 270, a second row 272, and a third row 274. Each cMUT 251 may have a diameter 290, and each cMUT may be spaced apart from other adjacent cMUTs 251 by a horizontal distance (e.g., a pitch) 292 and a vertical distance 294. The horizontal distance 292 may be the same as the vertical distance 294, or the horizontal distance 292 may be different from the vertical distance 294. In one embodiment, the diameter 290 is 30 microns and the pitch is 5 microns.

[0054] The single element transducer 250 also includes a common ground terminal 282 that can ground the electrical connection to the cMUT 251, and first and second common electrodes 284 and 286 that are used to provide a drive (AC) signal and a bias (DC) signal to the cMUT 251. Each of the plurality of cMUTs 251 can have a first electrode (e.g., a first common electrode 284 or a second common electrode 286) that is electrically coupled to one of the first and second common electrodes 284 and 286. Figure 2A ), and a second electrode (eg, Figure 2A In the depicted embodiment, a first group of cMUTs in column 262 (depicted in white) and a second group of cMUTs in column 266 (depicted in white) are electrically coupled to the first common electrode 284 without being coupled to the second common electrode 286, and a third group of cMUTs in column 260 (depicted in black) and a fourth group of cMUTs in column 264 (depicted in black) are electrically coupled to the second common electrode 286 without being coupled to the first common electrode 284. Thus, the plurality of cMUTs may be divided into a first portion (depicted in white) powered by the first common electrode 284 and a second portion (depicted in black) powered by the second common electrode 286.

[0055] In a typical configuration of a single element transducer 250, a voltage difference is generated at each cMUT 251, which causes the membrane (e.g., membrane layer 210) to resonate. Typically, the voltage difference is a combination of an AC voltage and a DC bias voltage applied at a single common electrode ( Figure 2B In contrast, Figure 2B As shown, different DC bias voltages may be provided to different cMUTs 251 of the single element transducer 250 at common electrodes 284 and 286. In other words, a first DC bias voltage may be applied to the cMUTs of columns 260 and 264 via the first common electrode 284, and a second DC bias voltage may be applied to the cMUTs of columns 262 and 266 via the second common electrode 286. In other embodiments, additional different bias voltages may be applied to different groups of cMUTs in different columns of the single element transducer 250, for example. By applying different DC voltages to different cMUTs, different cMUTs may resonate at different frequencies. The frequency difference between different cMUTs may be utilized to increase the fractional bandwidth of the acoustic signal generated by the single element transducer 250.

[0056] Additionally or alternatively, different DC bias voltages may be applied to different groups of cMUTs 251 of the single-element transducer 250 to configure a first group of cMUTs as receiving units and a second group of cMUTs as transmitting units.

[0057] refer to Figure 3A , shows an exemplary 1D transducer array 300 of an ultrasound system, such as ultrasound system 100. The transducer array 300 includes a 1D array of transducer elements having a width 330 and a height or elevation 332, wherein the transducer elements may be similar to Figure 2B The transducer array 300 includes a plurality of transducer elements 304 arranged in rows, including transducer elements 310, 312, 314, 316, and 318. Each transducer element 304 has an elevation 334. In other embodiments, the transducer elements 304 may be arranged in a different configuration. For example, in other embodiments, the transducer array 300 may include a different total number of transducer elements 304, and / or the columns of the transducer array 300 may each include a different number of transducer elements 304 (e.g., in various configurations).

[0058] Each transducer element 304 may include multiple cMUTs 302, which may be Figure 2A 200. Each cMUT 302 can generate an acoustic signal based on the vibration of the membrane of the cMUT, as described above. Each cMUT 302 can be positioned within each transducer element 304 at a certain interval. For example, the interval can be 5 microns.

[0059] Additionally, isolation may be provided between the transmit and receive circuits of the transducer array 300 to protect the receive circuits from the high voltages used during transmit. In systems using a shared transmit driver, a low voltage connection (e.g., receive signal path) may be temporarily connected to a common ground terminal 306 at a first side 307 to protect the channel from high potentials, while a second side 308 of the transducer array 300, which typically serves as a shared ground during receive, is pulsed with a high voltage to generate a plane wave output from all cMUTs 302. This type of isolation is typically provided via a multiplexer switch to ground, or by disconnecting the receive circuits from the transducer elements during transmit.

[0060] In a typical transducer array of an ultrasound system, an electrical signal may be applied to each cMUT 302 to generate a voltage difference between the top electrode of the corresponding cMUT 302 and the bottom electrode of the corresponding cMUT 302, as described above with reference to Figure 2A The top electrode 206 and the bottom electrode 214 of the cMUT 200 are described. The electrical signal can be a combination of an AC signal and a DC bias signal. The voltage difference generates an acoustic wave via a first vibration of a membrane layer (e.g., membrane layer 210), which can be directed to the anatomical structure of the patient. The acoustic wave can be reflected back by various parts of the anatomical structure and can be received at the corresponding cMUT (or a different cMUT). The received acoustic wave can cause a second vibration of the membrane layer. The second vibration can be converted into an acoustic signal. The acoustic signal of the cMUT is converted into an electrical signal.

[0061] However, as referenced below Figure 4A Described in more detail, by applying different electrical signals to different cMUTs 302, different vibrations may be generated at different cMUTs 302. Different electrical signals may be generated by applying different bias voltages to different cMUTs 302. In other words, the cMUTs 302 of the transducer elements 304 may be divided into different groups electrically connected to different bias voltage pads (e.g., electrodes), so that each group may be assigned a different bias voltage.

[0062] For example, in the depicted embodiment, a first bias voltage may be applied to a first grouping 320 of cMUTs 302 of transducer elements 310 via a first bias voltage pad 340, and a second bias voltage may be applied to a second grouping 322 of cMUTs 302 of transducer elements 310 via a second bias voltage pad 341. Similarly, a third bias voltage may be applied to a first grouping of cMUTs 302 of transducer elements 312 via a third bias voltage pad 342, and a fourth bias voltage may be applied to a second grouping of cMUTs 302 of transducer elements 312 via a fourth bias voltage pad 343. In some embodiments, two different bias voltages may be used, wherein the third bias voltage may be equal to the first bias voltage, and the fourth bias voltage may be equal to the second bias voltage. In other embodiments, any or all of the first bias voltage, the second bias voltage, the third bias voltage, and the fourth bias voltage may be different. Similar bias voltage pads 344 , 345 , 346 , 347 , 348 , and 349 may be used to apply equal or different bias voltages to associated cMUT 302 groups of transducer elements 314 , 316 , and 318 .

[0063] In cases where bias-driven mixing between two cMUTs would require SOI-based bonding techniques for cell-level electrical isolation, the already inherent etch-based element isolation process can be used to connect alternating or adjacent cMUTs to one of the first bias voltage pad 324 and the second bias voltage pad 326. In some implementations, such as in advanced 2D arrays, the cMUT connections can be tied through the back side of the wafer (e.g., silicon substrate 230) with through-wafer via connections.

[0064] With respect to the transducer element 310, and thus for the other transducer elements of the transducer array 300, the membranes of the first group 320 of cMUTs 302 may resonate at a first resonance, and the membranes of the second group 322 of cMUTs 302 may resonate at a second resonance. The first resonance and the second resonance may be converted into acoustic signals and combined, thereby utilizing interference to produce a wider bandwidth acoustic signal through constructive coupling.

[0065] The transducer array 300 is depicted in the x- and y-dimensions, as indicated by reference axis 398 . Figure 3A A cross-sectional perspective view 301 of a transducer array 300 is included, wherein the transducer array is depicted in the x-dimension and the z-dimension. In various embodiments, as shown in the cross-sectional perspective view 301, a coupling layer 305 can cover the surface of the transducer array 300, which can be used to attenuate sharp frequency transitions in the transfer function generated from the destructive interference of two different transmit transfer functions originating from two DC bias voltages, as described below with reference to Figure 6 and Figure 7 For example, Figure 3A , where the electrical connections are not formed through the back side of the wafer via through wafer via technology, the coupling layer 305 may cover an area of ​​the transducer array 300 including a portion of the transducer elements 302 and the common ground terminal 306 but not including the voltage bias pads 340-349, as shown Figure 3A As shown in the dashed box.

[0066] The coupling layer 305 may be composed of a soft solid (e.g., rubber and / or polymer) that may reduce destructive interference between different groups of cMUTs caused by the membranes of the different groups of cMUTs resonating at different resonant frequencies due to receiving different bias voltages. For example, the first group 320 may resonate at a first resonant frequency due to receiving a first bias voltage via the first bias voltage pad 340, and the second group 322 may resonate at a second resonant frequency due to receiving a second bias voltage via the second bias voltage pad 341. By including the coupling layer 305, destructive interference between a first transmit transfer function of the first group 320 and a second transmit transfer function of the second group 322 may be reduced, as described below with reference to Figure 7 and Figure 8 Described in more detail.

[0067] Reference now Figure 3B , a 2D transducer array 350 is shown, wherein the 2D transducer array 350 includes a plurality of transducer elements 352 arranged in a matrix. In the depicted embodiment, the matrix has six columns, including a first column 360, a second column 362, a third column 364, a fourth column 366, a fifth column 368, and a sixth column 370. The matrix has three rows, including a first row 380, a second row 382, ​​and a third row 384. As shown in reference Figure 3A As described, each transducer element 352 of the 2D transducer array 350 may include various bias voltage pads or electrodes capable of delivering different bias voltages to different groups of cMUTs within the transducer element 352. For example, each transducer element 352 may include a first electrode 354 and a second electrode 356, wherein a first bias voltage may be applied to a first portion (depicted in white) of the cMUT of the corresponding transducer element 352 via the first electrode 354, and a second bias voltage may be applied to a second portion (depicted in black) of the cMUT of the corresponding transducer element 352 via the second electrode 356. All cMUTs of each transducer element may be electrically coupled to a common ground terminal 358 (e.g., Figure 2BIn this way, the membranes of different groups of cMUTs within various transducer elements 352 can be caused to resonate at different frequencies, as described above. For 2D array embodiments such as the 2D transducer array 350, all electrical connections can be made through the back side of the wafer via through-wafer via technology, as is well known in the art.

[0068] Figure 4A shows the use of increasing the Figure 1 An exemplary method 400 for determining the fractional bandwidth of acoustic signals generated by a plurality of cMUTs of an ultrasound system of an ultrasound system 100. The cMUTs may be Figure 2A A non-limiting example of a cMUT 200, and the cMUT may be similar to Figure 3A The transducer array 300 and / or Figure 3B The configuration of the 2D transducer array 350 is arranged within the transducer elements of the transducer array. To increase bandwidth, a first group of acoustic signals generated by a first grouping of cMUTs within a transducer element (e.g., a first grouping 320 of transducer elements 310) may be combined with a second grouping of acoustic signals generated by a second grouping of cMUTs within the same transducer element. The first group of acoustic signals is generated from a membrane of a first group of cMUTs vibrating at a first resonant frequency, and the second group of acoustic signals is generated from a membrane of a second group of cMUTs vibrating at a second resonant frequency. The method 400 may be performed by a signal processor of an ultrasound system, such as Figure 1 The signal processor 132 of the ultrasound system 100. The method 400 may be performed during scanning of a patient using the ultrasound system.

[0069] At 402, the method includes applying a first DC bias voltage to a first group (e.g., first group 320) of cMUTs of transducer elements of a transducer array. The transducer array may include a plurality of transducer elements that may be configured as follows: Figure 3A The 1D transducer array in Figure 3B The first bias voltage pad of the transducer element (such as Figure 3A A first bias voltage pad 324) is used to apply a first bias voltage.

[0070] At 404, the method includes applying a second DC bias voltage to a second grouping of cMUTs of transducer elements (e.g., second grouping 322), wherein the second bias voltage is different from the first bias voltage (e.g., wherein a difference between the second bias voltage and the first bias voltage is greater than a threshold voltage). The second bias voltage pads of the transducer elements (e.g., second grouping 322) may be connected to the transducer elements via the second bias voltage pads. Figure 3A The second bias voltage pad 326 of the embodiment of the present invention is used to apply the second bias voltage. Figure 6In more detail, the first bias voltage and the second bias voltage can be such that destructive interference from the two output signals can be substantially blocked by the coupling layer (eg, Figure 3A The coupling layer 305) is selected in an attenuation manner.

[0071] For example, in some embodiments, the cMUTs included in each transducer element of the transducer array may be divided into two groups. A first bias voltage may be applied to a first group of cMUTs of a first transducer element, a first group of cMUTs of a second transducer element, a first group of cMUTs of a third transducer element, and so on. A second bias voltage may be applied to a second group of cMUTs of a first transducer element, a second group of cMUTs of a second transducer element, a second group of cMUTs of a third transducer element, and so on. It should be understood that although method 400 is described for two groups of cMUTs of each transducer element, in other embodiments, a greater number of bias voltages may be applied to a corresponding greater number of groups of cMUTs. For example, a third bias voltage may be applied to a third group of cMUTs of a transducer element; a fourth bias voltage may be applied to a fourth group of cMUTs of a transducer element; and so on. In addition, in some embodiments, different bias voltages may be applied to different cMUTs at different transducer elements. For example, a first bias voltage and a second bias voltage may be applied to different groups of the first transducer elements; a third bias voltage and a fourth bias voltage may be applied to different groups of the second transducer elements; a fifth bias voltage and a sixth bias voltage may be applied to different groups of the third transducer elements; and so on.

[0072] Returning to the example of two DC bias voltages, in response to a first bias voltage, the membranes of a first group of cMUTs may resonate at a first resonance. A first DC bias voltage may be applied at an electrode of each cMUT of the first group of cMUTs such that the corresponding membranes of the first group may vibrate at a first resonance frequency in response to an applied AC drive signal. Similarly, a second DC bias voltage may be applied at an electrode of each cMUT of a second group of cMUTs such that the corresponding membranes of the second group may vibrate at a second resonance frequency in response to the same applied AC drive signal (wherein the difference between the second resonance frequency and the first resonance frequency is greater than a threshold difference). The electrode may be a top electrode of the cMUT (e.g., top electrode 206) or a bottom electrode of the cMUT (e.g., bottom electrode 214).

[0073] The resonant frequency of the micromachined membrane can be determined by the following equation 1:

[0074]

[0075] where k represents the intrinsic spring constant and m is the mass of the membrane. It can be seen that the resonant frequency of the membrane varies directly with the spring constant and is inversely proportional to the mass. Assuming a small signal model of the cMUT, its ideal structure includes a clamped membrane that can be applied to the electrodes of the cMUT (e.g., Figure 2A A DC bias voltage is applied to the top electrode 206 or the bottom electrode 214 of the membrane to produce a spring softening effect that reduces the effective stiffness of the membrane's resonant frequency by a factor as described in Equation 2 below:

[0076]

[0077] Among them, ε 0 , A, V DC and g eff are the dielectric constant of free space, the coupling area of ​​the electrode, the applied DC bias voltage, and the effective gap height of the cMUT device. 0 ) and the isolation layer (thickness (t i ) and the dielectric constant (ε)) can be expressed as:

[0078]

[0079] Therefore, the resonant frequency of the cMUT membrane related to the changed spring constant and thus the DC bias voltage can be expressed as:

[0080]

[0081] By applying a first DC bias voltage to a first electrode of a first transducer element, and applying a second, different DC bias voltage to a second electrode of a second transducer element, the spring softening effect of the first membrane may be different from the spring softening effect of the second membrane. Thus, the first membrane may have a first resonant frequency, and the second membrane may have a second, different resonant frequency.

[0082] At 406, the method 400 includes generating a higher bandwidth acoustic signal due to applying an AC drive voltage to both the first plurality of cMUTs and the second plurality of cMUTs. When the AC drive voltage is applied to the first plurality of cMUTs, a first electrical signal is generated based on the AC drive voltage and a first DC bias voltage. When the AC drive voltage is applied to the second plurality of cMUTs, a second different electrical signal is generated based on the AC drive voltage and the second DC bias voltage. Since the frequency responses of the two devices based on the first electrical signal and the second electrical signal are different, they result in two different transmit transfer functions. Therefore, the interference between the first transmit transfer function and the second transmit transfer function of the two different transmit transfer functions can be used to generate a higher bandwidth signal.

[0083] At 408, the method includes receiving reflected acoustic waves reflected back by the anatomical structure of the subject at a plurality of transducer elements and generating an ultrasound image. When the transducer elements are operated in a receive mode, the first plurality of cMUTs have been biased with a first DC bias voltage and the second plurality of cMUTs have been biased with a second DC bias voltage. Thus, the membranes of the first plurality of cMUTs may resonate at a first resonant frequency and the membranes of the second plurality of cMUTs may resonate at a second resonant frequency. A first receive transfer function generated by the acoustic signal at the first plurality of cMUTs and a second receive transfer function generated by the acoustic signal at the second plurality of cMUTs may interfere to generate an electrical output signal having a wider fractional bandwidth than an alternative fractional bandwidth obtainable when the first DC bias voltage is equal to the second DC bias voltage. In this way, benefits in terms of increased fractional bandwidth are obtained for both transmit and receive situations.

[0084] Figure 4B An exemplary method 450 is shown for advantageously providing an ultrasound system such as Figure 1 The invention relates to an ultrasound system 100 of the present invention, wherein different DC bias voltages are applied to different portions of a cMUT of one or more transducer elements within a transducer array to configure a first portion of the cMUT to transmit a first acoustic signal and to configure a second different portion of the cMUT to receive a second acoustic signal reflected from an anatomical structure of the patient. The cMUT may be Figure 2A A non-limiting example of a cMUT 200, and the cMUT may be similar to Figure 3A The transducer array 300 and / or Figure 3B The configuration of the 2D transducer array 350 is arranged within the transducer elements of the transducer array. The first acoustic signal is generated from the membrane of the first portion of the cMUT vibrating at the first resonant frequency. The second acoustic signal causes the membrane of the second portion of the cMUT to vibrate at the second resonant frequency, thereby generating an electrical signal that can be combined to generate an image. The method 450 can be performed by a signal processor of the ultrasound system, such as Figure 1 The signal processor 132 of the ultrasound system 100. The method 400 may be performed during scanning of a patient using the ultrasound system.

[0085] At 452, the method includes applying a first DC bias voltage to a first plurality of cMUTs (e.g., the first grouping 320) of transducer elements of the transducer array. The same DC bias voltage may be applied to each cMUT of the first plurality of cMUTs. The transducer array may include a plurality of transducer elements that may be configured as follows: Figure 3A The 1D transducer array in Figure 3B The first bias voltage pad of the transducer element (such as Figure 3AThe first bias voltage pad 340 of the cMUT is used to apply a first DC bias voltage. The first bias voltage may be greater than a breakdown voltage of the cMUT, or less than a breakdown voltage (e.g., a non-breakdown voltage) of the cMUT. When a first set of electrical signals is applied to the first plurality of cMUTs, the membranes of the first plurality of cMUTs may resonate at a first resonant frequency, thereby generating a first acoustic signal. The first acoustic signal may be directed to an anatomical structure of the patient during scanning.

[0086] At 454, the method includes receiving a second acoustic signal reflected from the anatomical structure of the patient at a second plurality of cMUTs, wherein the second plurality of cMUTs includes cMUTs different from the first plurality of cMUTs. When the second acoustic signal is received at the second plurality of cMUTs, the second plurality of cMUTs may have been biased with a second different DC bias voltage such that the membranes of the second plurality of cMUTs may resonate at a second different resonant frequency, thereby generating a set of electrical signals at the electrodes of the cMUTs, as described above. The second bias voltage pads (such as the first bias voltage pads) of the transducer elements may be provided to the transducer elements. Figure 3A The second bias voltage pad 341 of the first transducer element is used to apply the second bias voltage. The second bias voltage may be greater than the breakdown voltage of the cMUT, or less than the breakdown voltage of the cMUT. In other words, if the first bias voltage of the first plurality of cMUTs is greater than the breakdown voltage, the second bias voltage of the second plurality of cMUTs may be less than the breakdown voltage, and if the first bias voltage of the first plurality of cMUTs is less than the breakdown voltage, the second bias voltage of the second plurality of cMUTs may be greater than the breakdown voltage. In this way, different DC bias voltages may be advantageously used to configure different cMUTs of a single transducer element to act as a receiving cMUT or a transmitting cMUT.

[0087] At 456 , the method includes generating an ultrasound image of the anatomy of the subject based on the electrical signals generated by the second plurality of cMUTs at each transducer element of the transducer array, and the method 400 ends.

[0088] Figure 5 FIG. 4 shows that when a single AC drive voltage is applied to multiple cMUTs configured with the same DC bias voltage, the Figure 3A 500 of a combined acoustic signal 502 generated by a plurality of cMUTs of a transducer array 300). In the embodiment depicted in the first transmit sensitivity graph 500, a homogenous DC bias voltage of 80% of the collapse voltage of the cMUT is applied to the plurality of cMUT cells. For example, the collapse voltage may be 87.75V. The first transmit sensitivity graph 500 shows the variation of the output pressure of the plurality of cMUT cells as a function of frequency at 80% of the collapse voltage under liquid loading conditions. The cMUT may be Figure 2AA non-limiting example of a cMUT 200. The transmit sensitivity is shown on the y-axis of the first transmit sensitivity graph 500, and the resulting frequency is shown on the x-axis.

[0089] The acoustic signal 502 reaches a peak at point 504 corresponding to a maximum sensitivity of approximately 96 dB, as indicated by dashed line 506. A second dashed line 508 indicates that the sensitivity is reduced by 3 dB from the maximum sensitivity indicated by point 504. Therefore, the fractional bandwidth 518 of the acoustic signal 502 can be defined as the frequency range where the output sensitivity is 3 dB less than the peak sensitivity at point 504. The fractional bandwidth 518 can be calculated by measuring the frequency range between the lowest frequency (fL) indicated by a first point 514 where the dashed line 508 intersects the acoustic signal 502 and the highest frequency (fH) indicated by a second point 516 where the dashed line 508 intersects the acoustic signal 502. The fractional bandwidth 518 can be calculated according to the following formula:

[0090] 2*[(fH-fL) / (fH+fL)]×100(1)

[0091] In the first transmit sensitivity graph 500, fL is 15.5 MHz, as indicated by dashed line 510, and fH is 26 MHz, as indicated by dashed line 512, and the fractional bandwidth 518 is 51.47%. The center resonant frequency of the plurality of cMUTs at 80% collapse value under liquid loading conditions is about 20 MHz, as shown by the peak at point 504.

[0092] Figure 6 Shown by Figure 5 6, but with a mixed bias configuration, in which different DC bias voltages are applied to different cMUTs in the plurality of cMUTs. In other words, the plurality of cMUTs are divided into two parts, and the two parts can each include a similar number of cMUTs (e.g., Figure 3A In the depicted embodiment, a bias voltage of 90% of the breakdown voltage is applied to the first portion of the plurality of cMUTs, and a bias voltage of 70% of the breakdown voltage is applied to the second portion of the plurality of cMUTs. In other embodiments, different percentages of the breakdown voltage may be applied to the first portion and the second portion of the plurality of cMUTs, provided that they are different (e.g., where the difference between the bias voltages is greater than the threshold voltage).

[0093] A notch 605 is shown between 10 MHz and 20 MHz where a frequency transition occurs. This frequency transition is a sharp transition where the acoustic signal 602 rises to a peak 604 within a short frequency difference of approximately 15 MHz-16 MHz, then drops to a trough 620, and then rises again to a second peak 607. The notch 605 is caused by destructive interference between a first transmit transfer function applied to a first portion of the plurality of cMUTs and a second transmit transfer function applied to a second portion of the plurality of cMUTs. From a mechanical perspective, this can be viewed as the first and second portions of the cMUTs vibrating 180 degrees out of phase, as described below with reference to Figure 8 Due to destructive interference, when the fractional bandwidth 618 is calculated based on a 3dB reduction in amplitude from the peak 607, as shown by dashed lines 606 and 608, the depth of the notch 605 intervenes in the 3dB calculation path, thereby significantly reducing fL. Therefore, the fractional bandwidth can be reduced to less than Figure 5 To mitigate destructive interference and attenuate notches to smooth a combined transmit transfer function including the first transfer function and the second transfer function and / or to smooth a frequency band of interest, a coupling layer (e.g., Figure 3A Coupling layer 305), as described above with reference to Figure 3A described.

[0094] Brief reference Figure 8 , a three-dimensional (3D) visualization 800 of destructive interference shows membrane displacements in the z dimension according to a reference axis 830, corresponding to two cMUTs of a plurality of cMUTs, including a first cMUT of a first portion and a second cMUT of a second portion. Specifically, the 3D visualization 800 shows a first membrane 802 (quarter geometry) of a first cMUT of a first portion and a second membrane 804 of a second cMUT of a second portion of the same transducer element vibrating out of phase. This means that the two membranes 802 and 804 vibrate at this frequency with their respective displacement amplitudes but in opposite directions, thereby canceling the cumulative effect. This is in Figure 6 The first membrane 802 rises to a peak 807 in the positive direction along the z-axis, where the first vibration of the membrane 802 is strongest at the center of the first cMUT and weakest at the edge of the first cMUT (e.g., at point 840). Similarly, the second membrane 804 drops to a peak 820 in the negative direction along the z-axis, where the second vibration of the membrane 804 is strongest at the center of the second cMUT and weakest at the edge of the second cMUT indicated by curve 842.

[0095] Figure 7 Shown by Figure 5A third transmit sensitivity graph 700 of a combined acoustic signal 702 generated by a plurality of cMUTs having Figure 6 A mixed bias configuration in which a coupling layer has been added to reduce destructive interference. A bias voltage of 90% of the breakdown voltage is applied to a first portion of the plurality of cMUTs, and a bias voltage of 70% of the breakdown voltage is applied to a second portion of the plurality of cMUTs. Figure 7 In the example, the destructive interference between the first transmit transfer function and the second transmit transfer function causes Figure 6 The notch 605 has been attenuated to smooth the combined transmit transfer function and / or to increase the frequency band of interest.

[0096] Since the destructive interference is attenuated, the acoustic signal 702 peaks at point 704 corresponding to a maximum sensitivity of approximately 93 dB, as indicated by dashed line 706 . Figure 6 The notch 620 has been reduced to a valley 720. The second dashed line 708 indicates that the sensitivity is reduced by 3 dB from the maximum sensitivity indicated by point 704. Therefore, the fractional bandwidth 718 of the acoustic signal 702 can be calculated by measuring the frequency range between the lowest frequency (fL) indicated by the first point 714 where the second dashed line 708 intersects the acoustic signal 702 and the highest frequency (fH) indicated by the second point 716 where the second dashed line 708 intersects the acoustic signal 702. In the third transmit sensitivity graph 700, fL is 12.4 MHz and fH is 26.6 MHz, where the fractional bandwidth 718 is about 73%. Therefore, the fractional bandwidth 718 based on the hybrid bias configuration represents a 3 dB reduction compared to the fractional bandwidth based on the configuration used for Figure 5 The fractional bandwidth 518 of the homogeneous biasing of the two portions of the cMUT is shown to increase by 19%.

[0097] It should be understood that although bandwidths 518 and 718 are 3 dB bandwidths, other reference dB values ​​may be used in other embodiments. Figure 5 The fractional bandwidth of 518 is Figure 7 In the case of the relative difference between the fractional bandwidth 718, the bandwidths 518 and 718 are calculated based on a 1 dB reduction from the peak or a 6 dB reduction from the peak or in a different manner.

[0098] Thus, by applying different DC bias voltages to different groups of cMUTs within transducer elements in a plurality of transducer elements of an ultrasound probe, different groups of cMUTs may resonate at different frequencies when an AC drive signal is applied, resulting in constructive interference of their corresponding transfer functions. This interference may be advantageously used to increase the fractional bandwidth of the combined acoustic signal generated by different groups of cMUTs. Due to the flexibility of using different cMUTs at carefully selected resonant peak frequencies through different levels of spring softening conditions, an increase in fractional bandwidth may be achieved by mixing and matching various optimized bias ratios. For example, in Figures 5 to 7 In the example shown, the target design is a resonant frequency of approximately 20 MHz (fluid loaded) with a transmit fractional bandwidth of at least 70%. Figure 5 ), where 80% of the breakdown voltage is used for both groups, achieving a fractional bandwidth of 51%. In the mixed bias case, where 90% and 70% of the breakdown voltage are used for both groups, a fractional bandwidth of 73% is achieved. This 70 / 90 optimal DC bias ratio is used to fix the resonant frequency at the 20MHz level and ensure that the resonant frequency is kept constant by Figure 6 The height of notch 605 represents an amplitude difference (e.g., between 604 and 620) that is small enough to be attenuated by the coupling layer. In other words, an optimized DC bias ratio can be selected for a particular situation, where the constructive interference is large enough to maximize the fractional bandwidth, while the destructive interference (notch 605) remains small enough to be attenuated by the coupling layer.

[0099] By increasing the fractional bandwidth of the acoustic signal, the fractional bandwidth constraint imposed by current membrane thickness on higher frequency ultrasound applications can be removed, thereby reducing the reliance on thinner and more expensive membranes. The proposed method can be used for both lower frequency and higher frequency high bandwidth applications. Therefore, a single ultrasound probe relying on the hybrid biasing method described herein can be used for a wider range of clinical tasks than would otherwise be accomplished with a variety of probes. By using a single ultrasound probe for a wider range of clinical tasks, the cost of ultrasound systems can be reduced, and the efficiency of the radiologist's workflow can be improved.

[0100] An additional advantage of applying different DC bias voltages to different groups of cMUTs within transducer elements in a plurality of transducer elements of an ultrasound probe is that a first group can be configured to have a first DC bias voltage to transmit acoustic signals and a second group can be configured to have a second DC voltage to receive acoustic signals (e.g., reflected back from a patient).

[0101] A first technical effect of applying different DC bias voltages to different groups of cMUTs within the transducer elements of a transducer array is that different groups of cMUTs can be configured to resonate at different resonant frequencies when an AC drive signal is applied, which can interfere so that the fractional bandwidth of the acoustic signal generated by the transducer array can be increased, thereby allowing the transducer array to be used for a wider range of options for both low-frequency and high-frequency applications.

[0102] The present disclosure also provides support for a method for an ultrasound system, the method comprising: during an ultrasound scan of a patient: during a transmit mode of a transducer element of a transducer array of an ultrasound probe of the ultrasound system: applying a first DC bias voltage to a first portion of a capacitive micromachined ultrasound transducer (cMUT) of the transducer element; applying a second DC bias voltage to a second portion of the cMUT of the transducer element, the second DC bias voltage being different from the first DC bias voltage; applying an AC drive signal to the first portion of the cMUT to generate a first acoustic signal based on a first combination of the first DC bias voltage and the AC drive signal, thereby causing a first portion of the cMUT to transmit an acoustic signal; a first acoustic signal reflected from a subject being scanned, at both the first portion of the cMUT and the second portion of the cMUT; and a second acoustic signal generated at a first receiving transfer function generated at the first portion of the cMUT based on the first DC bias voltage and a second receiving transfer function generated at the second portion of the cMUT based on the first DC bias voltage. In a second example of the method, optionally including the first example, a first portion of the cMUT is electrically coupled to a first bias voltage pad of a transducer element, and a first DC bias voltage is applied to the first portion of the cMUT via the first bias voltage pad, a second portion of the cMUT is electrically coupled to a second bias voltage pad of the transducer element, and a second DC bias voltage is applied to the second portion of the cMUT via the second bias voltage pad. In a third example of the method, optionally including one or both of the first and second examples, the first portion of the cMUT and the second portion of the cMUT are bound with through-wafer via connectors through the back side of a wafer of a transducer array. In a fourth example of the method, optionally including one or more or each of the first to third examples, the transducer array includes a single transducer element. In a fifth example of the method, optionally including one or more or each of the first to fourth examples, the transducer array includes a plurality of transducer elements, each of the plurality of transducer elements including at least a first bias voltage pad and a second bias voltage pad.In a sixth example of the method, optionally including one or more or each of the first to fifth examples, the method further includes: applying a first DC bias voltage to a first plurality of first bias voltage pads of the plurality of transducer elements, and applying a second DC bias voltage to a second plurality of second bias voltage pads of the plurality of transducer elements. In a seventh example of the method, optionally including one or more or each of the first to sixth examples, the method further includes: applying an additional bias voltage to an additional bias voltage pad of each transducer element, the additional bias voltage pad being electrically coupled to an additional different portion of the CMUT of the corresponding transducer element. In an eighth example of the method, optionally including one or more or each of the first to seventh examples, the transducer array is one of a one-dimensional (1D) transducer array including rows of transducer elements and a 2D transducer array including a two-dimensional (2D) matrix of transducer elements. In a ninth example of the method, optionally including one or more or each of the first to eighth examples, the method further includes: attenuating a frequency transition in the higher bandwidth signal via a coupling layer covering the first portion of the cMUT and the second portion of the cMUT, the frequency transition originating from destructive interference between a first transfer function based on a first DC bias voltage and a second transfer function based on a second DC bias voltage. In a tenth example of the method, optionally including one or more or each of the first to ninth examples, the fractional bandwidth of the higher bandwidth signal is based on an optimized ratio of the first DC bias voltage to the second DC bias voltage, the optimized ratio maximizing constructive interference of the higher bandwidth signal while keeping destructive interference small enough to be attenuated by the coupling layer. In an eleventh example of the method, optionally including one or more or each of the first to tenth examples, the method further includes: using the ultrasound probe for both low-frequency and high-frequency ultrasound applications.

[0103] The present disclosure also provides support for an ultrasound system, the ultrasound system comprising: an ultrasound probe, the ultrasound probe comprising a transducer array, the transducer array comprising at least one transducer element, the at least one transducer element comprising a first portion of a capacitive micromachined ultrasound transducer (cMUT) electrically coupled to a first bias voltage pad of the at least one transducer element and a second portion of the cMUT electrically coupled to a second bias voltage pad of the at least one transducer element; a processor; and a non-volatile memory, the non-volatile memory comprising instructions that, when executed, cause the processor to: during a transmit mode of the at least one transducer element: apply a first DC bias voltage to the first portion of the cMUT of the at least one transducer element; apply a second DC bias voltage to the second portion of the cMUT of the at least one transducer element, the second DC bias voltage being different from the first DC bias voltage; DC bias voltage; applying an AC drive signal to a first portion of the cMUT to generate a first acoustic signal based on a first combination of the first DC bias voltage and the AC drive signal, thereby causing a membrane of the first portion of the cMUT to vibrate at a first resonant frequency defined by the first DC bias voltage; applying an AC drive signal to a second portion of the cMUT to generate a second acoustic signal based on a second combination of the second DC bias voltage and the AC drive signal, the second combination causing the membrane of the second portion of the cMUT to vibrate at a second resonant frequency defined by the second DC bias voltage, the second resonant frequency differing from the first resonant frequency by a threshold difference; and combining the first acoustic signal and the second acoustic signal to generate a higher bandwidth signal based on constructive interference between a first transmit transfer function of the first portion of the cMUT and a second transmit transfer function of the second portion of the cMUT. In a first example of the system, additional instructions are stored in a non-transitory memory, which when executed cause the processor to: during a receive mode of at least one transducer element: receive a second acoustic signal reflected from a scanned subject at both a first portion of the cMUT and a second portion of the cMUT; generate a wider bandwidth output electrical signal based on constructive interference between a first receive transfer function generated at the first portion of the cMUT based on a first DC bias voltage and a second receive transfer function generated at the second portion of the cMUT based on the first DC bias voltage. In a second example of the system, optionally including the first example, the transducer array includes a plurality of transducer elements, and additional instructions are stored in a non-transitory memory, which when executed cause the processor to: apply a first DC bias voltage to each first bias voltage pad of each transducer element of the plurality of transducer elements, and apply a second DC bias voltage to each second bias voltage pad of each transducer element of the plurality of transducer elements.In a third example of the system, optionally including one or both of the first and second examples, additional instructions are stored in a non-transitory memory, which when executed cause the processor to: apply an additional bias voltage to an additional bias voltage pad of each transducer element, the additional bias voltage pad being electrically coupled to an additional different portion of the CMUT of the corresponding transducer element. In a fourth example of the system, optionally including one or more or each of the first to third examples, the system further includes: a coupling layer, the coupling layer being included between at least a first portion of the cMUT of at least one transducer element and a second portion of the cMUT, and attenuating a frequency transition resulting from destructive interference between a first transfer function of the first DC bias voltage and a second transfer function of the second DC bias voltage. In a fifth example of the system, optionally including one or more or each of the first to fourth examples, the fractional bandwidth of the higher bandwidth signal is based on an optimized ratio of the first DC bias voltage to the second DC bias voltage, the optimized ratio maximizing the constructive interference of the higher bandwidth signal while keeping the destructive interference small enough to be attenuated by the coupling layer.

[0104] The present disclosure also provides support for a method for an ultrasound system, the method comprising: during an ultrasound scan of a subject: applying a first DC bias voltage to a first portion of a capacitive micromachined ultrasound transducer (cMUT) of a transducer element of a transducer array of an ultrasound probe of the ultrasound system, the first DC bias voltage being greater than a breakdown voltage of the first portion of the cMUT; applying a second DC bias voltage to a second portion of the cMUT of the transducer element, the second DC bias voltage being less than a breakdown voltage of the second portion of the cMUT; applying an AC drive signal to the first portion of the cMUT to generate a first acoustic signal based on a first combination of the first DC bias voltage and the AC drive signal, thereby causing a membrane of the first portion of the cMUT to vibrate at a first resonant frequency based on the first DC bias voltage; receiving a second reflected acoustic signal at the second portion of the cMUT; generating an electrical signal based on the membrane of the second portion of the cMUT vibrating at a second resonant frequency based on the second DC bias voltage applied to the second portion of the cMUT, the second resonant frequency being different from the first resonant frequency; and generating an ultrasound image based on the electrical signal. In a first example of the method, the first DC bias voltage is less than the breakdown voltage, and the second DC bias voltage is greater than the breakdown voltage.

[0105] This written description uses examples to disclose the invention, including the best mode, and also to enable a person skilled 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 skilled in the art. Such other examples are intended to be 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. A method for an ultrasound system, the method comprising: During an ultrasound scan of a patient: During a transmit mode of a transducer element of a transducer array of an ultrasound probe of the ultrasound system: applying a first DC bias voltage (402) to a first portion of a capacitive micromachined ultrasonic transducer (cMUT) of the transducer element; applying a second DC bias voltage (404) to a second portion of the cMUT of the transducer element, the second DC bias voltage being different from the first DC bias voltage; applying an AC drive signal (406) to the first portion of the cMUT to generate a first acoustic signal based on a first combination of the first DC bias voltage and the AC drive signal, thereby causing a membrane of the first portion of the cMUT to vibrate at a first resonant frequency defined by the first DC bias voltage; applying the AC drive signal (406) to the second portion of the cMUT to generate a second acoustic signal based on a second combination of the second DC bias voltage and the AC drive signal, the second combination causing a membrane of the second portion of the cMUT to vibrate at a second resonant frequency defined by the second DC bias voltage, the second resonant frequency differing from the first resonant frequency by a threshold difference; as well as The first acoustic signal and the second acoustic signal are combined to generate a higher bandwidth signal (406) based on constructive interference between a first transmit transfer function of the first portion of the cMUT and a second transmit transfer function of the second portion of the cMUT.

2. The method according to claim 1, further comprising: During a receive mode of the transducer element: receiving a second acoustic signal (454) reflected from the scanned subject at both the first portion of the cMUT and the second portion of the cMUT; A wider bandwidth output electrical signal is generated based on constructive interference between a first receive transfer function generated at the first portion of the cMUT based on the first DC bias voltage and a second receive transfer function generated at the second portion of the cMUT based on the first DC bias voltage (456).

3. The method according to claim 1, wherein: The first portion of the cMUT is electrically coupled to a first bias voltage pad of the transducer element, and the first DC bias voltage is applied to the first bias voltage pad via the first bias voltage pad. said first portion of the cMUT; The second portion of the cMUT is electrically coupled to a second bias voltage pad of the transducer element, and the second DC bias voltage is applied to the second bias voltage pad via the second bias voltage pad. The second portion of the cMUT. 4 . The method of claim 3 , wherein the first portion of the cMUT and the second portion of the cMUT are bound with through-wafer via connections through a back side of a wafer of the transducer array. The method of claim 3 , wherein the transducer array comprises a single transducer element. 6 . The method of claim 3 , wherein the transducer array comprises a plurality of transducer elements, each transducer element of the plurality of transducer elements comprising at least the first bias voltage pad and the second bias voltage pad.

7. The method of claim 6, further comprising applying the first DC bias voltage to a first plurality of first bias voltage pads of the plurality of transducer elements, and applying the second DC bias voltage to a second plurality of second bias voltage pads of the plurality of transducer elements.

8. The method of claim 7, further comprising applying an additional bias voltage to an additional bias voltage pad of each transducer element, the additional bias voltage pad being electrically coupled to an additional different portion of the CMUT of the corresponding transducer element.

9. The method of claim 6, wherein the transducer array is one of a one-dimensional (1D) transducer array comprising rows of transducer elements and a two-dimensional (2D) transducer array comprising a 2D matrix of transducer elements.

10. The method of claim 1 , further comprising attenuating a frequency transition in the higher bandwidth signal via a coupling layer covering the first portion of the cMUT and the second portion of the cMUT, the frequency transition originating from destructive interference between a first transfer function based on the first DC bias voltage and a second transfer function based on the second DC bias voltage.

11. The method of claim 10, wherein the fractional bandwidth of the higher bandwidth signal is based on an optimized ratio of the first DC bias voltage to the second DC bias voltage, the optimized ratio maximizing the constructive interference of the higher bandwidth signal while keeping the destructive interference small enough to be attenuated by the coupling layer.

12. The method of claim 1, further comprising using the ultrasound probe for both low frequency and high frequency ultrasound applications.

13. An ultrasound system (100), comprising: An ultrasound probe (104), the ultrasound probe comprising a transducer array (300), the transducer array comprising at least one transducer element (310, 352, 106, 304, 312), the at least one transducer element (310, 352, 106, 304, 312) comprising a first portion of a capacitive micromachined ultrasound transducer (cMUT (251, 302)) electrically coupled to a first bias voltage pad (340, 324) of the at least one transducer element (310, 352, 106, 304, 312) and a second portion of the cMUT (251, 302) electrically coupled to a second bias voltage pad (326, 341) of the at least one transducer element (310, 352, 106, 304, 312); processor; and a non-transitory memory comprising instructions that, when executed, cause the processor to: During a transmit mode of the at least one transducer element (310, 352, 106, 304, 312): applying a first DC bias voltage to the first portion of the cMUT (251, 302) of the at least one transducer element (310, 352, 106, 304, 312); applying a second DC bias voltage to the second portion of the cMUT (251, 302) of the at least one transducer element (310, 352, 106, 304, 312), the second DC bias voltage being different from the first DC bias voltage; applying an AC drive signal to the first portion of the cMUT (251, 302) to generate a first acoustic signal (502, 602, 702) based on a first combination of the first DC bias voltage and the AC drive signal, thereby causing a membrane of the first portion of the cMUT (251, 302) to vibrate at a first resonant frequency defined by the first DC bias voltage; applying the AC drive signal to the second portion of the cMUT (251, 302) to generate a second acoustic signal (502, 602, 702) based on a second combination of the second DC bias voltage and the AC drive signal, the second combination causing the membrane of the second portion of the cMUT (251, 302) to vibrate at a second resonant frequency defined by the second DC bias voltage, the second resonant frequency differing from the first resonant frequency by a threshold difference; and The first acoustic signal (502, 602, 702) and the second acoustic signal (502, 602, 702) are combined to generate a higher bandwidth signal based on constructive interference between a first transmit transfer function of the first portion of the cMUT (251, 302) and a second transmit transfer function of the second portion of the cMUT (251, 302).

14. The ultrasound system (100) of claim 13, wherein further instructions are stored in the non-transitory memory, the further instructions when executed causing the processor to: During a receive mode of the at least one transducer element (310, 352, 106, 304, 312): receiving a second acoustic signal (502, 602, 702) reflected from a scanned subject at both the first portion of the cMUT (251, 302) and the second portion of the cMUT (251, 302); A wider bandwidth output electrical signal is generated based on constructive interference between a first receive transfer function generated at the first portion of the cMUT (251, 302) based on the first DC bias voltage and a second receive transfer function generated at the second portion of the cMUT (251, 302) based on the first DC bias voltage.

15. The ultrasound system (100) of claim 13, wherein the transducer array (300) comprises a plurality of transducer elements (310, 314, 352, 106, 304, 302), and further instructions are stored in the non-transitory memory, the further instructions when executed causing the processor to: The first DC bias voltage is applied to each first bias voltage pad (340, 324) of the element (310, 352, 106, 304, 312), and the second DC bias voltage is applied to each second bias voltage pad (326, 341) of each transducer element (310, 352, 106, 304, 312) of the plurality of transducer elements (310, 314, 352, 106, 304, 302).

Images