Ultrasonic transducer array devices

Abstract

This invention relates to a multilayer structure for an ultrasonic transducer, comprising: a semiconductor layer stack defining a diode; a microfabricated ultrasonic transducer MUT layer stack electrically connected in series with said diode and including at least a first conductive layer disposed on the diode; and a cavity extending over a region including at least a portion of the semiconductor layer stack and the first conductive layer, wherein the MUT layer stack includes a membrane extending at least partially over said region. The multilayer structure for an ultrasonic transducer according to the invention can be used in sensor devices for measuring at least one characteristic of an object, wherein the sensor device is used for medical imaging, such as cardiac imaging, obstetric, gynecological, abdominal imaging, intravascular imaging, and mammography, or nondestructive testing (NDA), fingerprint sensors, rangefinders, gesture recognition, ultrasonic haptic feedback, ultrasonic communication, or MEMS speakers.

Description

Invention Field

[0001] This invention generally relates to the field of ultrasonic transducers, and more particularly to ultrasonic transducer array devices configured to transmit and receive ultrasonic signals, and methods for manufacturing such ultrasonic transducer array devices. Background of the Invention

[0003] Ultrasonic imaging, especially 3D ultrasound imaging, is a powerful imaging technique and is particularly useful in applications such as sonar, posture recognition, fingerprint sensors, medical imaging, and non-destructive testing (NDT). One way to acquire 3D images is by using a two-dimensional array of ultrasonic transducers, which eliminates the need for mechanical motors or manual movement of a one-dimensional array of transducers.

[0004] One of the main challenges in fabricating 2D transducer arrays is the wiring that connects the individual volume transducers. Individual volume transducers in a 2D array can be connected by directly combining or integrating a matrix of fully diced piezoelectric or capacitive transducers with front-end electronics (e.g., on top of a CMOS chip, i.e., CMOS integration). In this way, each piezoelectric or capacitive element can access its own front end and can be individually controlled. This requires the CMOS chip to be the same size as the transducer array device matrix, making the entire device extremely expensive, a barrier to fabricating very large 2D arrays. Furthermore, this technique cannot be used for flexible ultrasonic transducers, such as those fabricated on flexible substrates (e.g., silicon elastomers).

[0005] For high-resolution imaging applications, microfabricated ultrasonic transducers (MUTs) can be used. MUT technology is based on semiconductor materials and photolithography, and is becoming a major alternative to bulk PZT-based transducers in various applications. MUTs have a relatively simple manufacturing process and can be miniaturized to achieve better image resolution.

[0006] Typically, MUTs operate using two different mechanisms: capacitive force (called "capacitive MUT" or "cMUT") or piezoelectric (also known as "piezoelectric MUT" and "pMUT") induction actuation. Therefore, cMUT and pMUT are the commonly used types of MUTs.

[0007] CMUTs are based on two parallel membranes with a very small vacuum gap (approximately 200 nm) between them. The upper membrane is attracted to the lower membrane by an electrostatic force caused by a voltage applied to the membranes. CMUTs have several limitations, including the requirement for a high DC bias voltage, which is a particular disadvantage in applications where the transducer is part of a handheld device; malfunctions or performance drift due to charge buildup during the required high-voltage operation; and difficulty in generating sufficiently high sound pressure levels.

[0008] pMUTs comprise a thin film that vibrates due to an applied force generated by a thin piezoelectric layer. The piezoelectric layer is deposited on top of the film and is driven by an electrical signal. PMUTs suffer from low bandwidth and low output pressure due to their low electromechanical coupling factor, two significant factors in ultrasound imaging, particularly in medical and NDT applications. Low bandwidth makes it difficult to achieve the short pulse response required for high spatial resolution. Low output pressure results in low amplitude of emitted ultrasound, which can lead to a low signal-to-noise ratio. Therefore, there remains a need for ultrasound transducers that can be easily miniaturized and have sufficiently high output pressure and bandwidth.

[0009] Compared to conventional transducers, MUTs offer a simpler and cheaper manufacturing process. Furthermore, MUTs can be miniaturized to achieve better image resolution. For example, for small matrices, such as a 16×16 matrix arrangement of MUTs, individual wire bonding is still possible, allowing for individual access to all transducers in the matrix. Wire bonding is an inexpensive process that allows CMOS chips to be designed and manufactured independently of the matrix size. However, for larger matrices, and differing for both cMUTs and pMUTs, MUT technology faces the same problems as conventional techniques when manufacturing 2D arrays. Addressing via wire bond contacts becomes extremely difficult due to the density of elements in the transducer matrix.

[0010] The paper "Acoustical crosstalk in row-column addressed 2-D transducer arrays for ultrasound imaging" (T. Christiansen et al., Ultrasonics, Vol. 63, December 2015, pp. 174-178) describes a row-column addressed arrangement for reducing the number of contacts required in a cMUT 2D array. This reduces the number of electrical contacts required for an n×n array of transducers from n 2 Reduced to 2n.

[0011] However, row-column addressing in a MUT array is affected by cross-coupling: when a specific transducer is addressed by applying a signal to a row-column pair, that signal may capacitively couple to adjacent rows and columns, thus causing other transducers to be activated when not needed. Therefore, individual row-column addressing is an inefficient solution for 2D arrays of MUT arrays.

[0012] In addition to the need for ultrasonic transducers that can be easily miniaturized and have sufficiently high output pressure and bandwidth, there is still a need in the art for ultrasonic transducers and associated arrays that address at least some of the problems outlined above. Summary of the Invention

[0013] The objective of embodiments of the present invention is to provide an ultrasonic transducer array or ultrasonic transducer array device that allows for individual addressing of transducers (especially MUTs) while minimizing the number of electronic contacts and reducing cross-coupling between adjacent electrodes. This objective is achieved through the ultrasonic transducer array device and ultrasonic transducer multilayer structure according to the present invention.

[0014] An advantage of embodiments of the present invention is that it does not require state-of-the-art front-end electronics (e.g., CMOS chips) to access individual volume ultrasonic transducers with array configurations, which allows for the provision of devices that are relatively inexpensive compared to front-end electronics that include ultrasonic array devices.

[0015] Another advantage of embodiments of the present invention is that by using a first electrode for connecting an ultrasonic transducer in a first direction in an array configuration and a second electrode for connecting an ultrasonic transducer in a second direction in an array configuration, the number of required electrical contacts is significantly reduced.

[0016] Another advantage of embodiments of the present invention is that, for at least one ultrasonic transducer in the array configuration, the first electrode is connected to the second electrode via a diode connected in series with the respective ultrasonic transducer, thereby reducing capacitive cross-coupling between the electrodes.

[0017] Another advantage of embodiments of the present invention is that, since inexpensive off-the-shelf components are used and each ultrasonic transducer can be individually connected without expensive front-end electronics, the manufacturing process of the multilayer structure of the ultrasonic transducers and related array devices in the array configuration can be simple and inexpensive.

[0018] Another advantage of embodiments of the invention is that the cavity can support standing waves, which allows for adjustment of the bandwidth of the emitted ultrasound. Since the cavity frequency is combined with the diaphragm frequency, the bandwidth can be increased, thereby providing a transducer with multiple resonant frequencies and thus providing a wider bandwidth than a transducer that does not include a cavity capable of supporting standing waves.

[0019] Another advantage of embodiments of the invention is that at least one acoustically suitable medium in the cavity can help the vibration of the damping diaphragm, which helps to stop the ringing, without the need to provide damping layers on the diaphragm.

[0020] In one aspect, the present invention relates to an ultrasonic transducer array device configured to transmit and receive ultrasonic signals, comprising: a plurality of ultrasonic transducers arranged in an array configuration; at least one first electrode for connection to an ultrasonic transducer in the array configuration along a first direction; at least one second electrode for connection to an ultrasonic transducer in the array configuration along a second direction; wherein the at least one first electrode is connected to the at least one second electrode via a diode connected in series with a respective ultrasonic transducer, wherein, when in use, the direction from the anode to the cathode of the diode coincides with the direction from the high potential side to the low potential side of the respective ultrasonic transducer, and wherein the low potential side of the respective ultrasonic transducer is connected to the anode of the diode.

[0021] In some embodiments, the array configuration is an mn row-column configuration with m rows and n columns, where m and n are positive integers whose sum is equal to or greater than 3, and where the first direction corresponds to the direction along row m, and where the second direction corresponds to the direction along column n.

[0022] Each first electrode can be connected to each second electrode via a diode connected in series with the corresponding ultrasonic transducer, wherein, in use, the direction from the anode to the cathode of the diode coincides with the direction from the high-potential side to the low-potential side of the corresponding ultrasonic transducer, and wherein the low-potential side of the corresponding ultrasonic transducer is connected to the anode of the diode. Preferably, the plurality of ultrasonic transducers includes at least one micro-machined ultrasonic transducer (MUT), wherein the at least one MUT is a piezoelectric micro-machined ultrasonic transducer (pMUT) or a capacitive micro-machined ultrasonic transducer (cMUT).

[0023] Advantageously, the diode and the corresponding ultrasonic transducer connected in series with the diode are provided by a multilayer structure as described below.

[0024] The objective of embodiments of the present invention is to provide a multilayer structure for ultrasonic transducers in ultrasonic transducer array devices, which allows for individual addressing of transducers (particularly MUTs) while minimizing the number of electronic contacts and reducing cross-coupling between adjacent electrodes. This objective is achieved by the multilayer structure for ultrasonic transducers according to the present invention.

[0025] In one aspect, the present invention relates to a multilayer structure for an ultrasonic transducer, comprising: a semiconductor layer stack defining a diode; a microfabricated ultrasonic transducer (MUT) layer stack electrically connected in series with the diode and including a first conductive layer (e.g., a metal layer), the MUT layer stack being disposed at least partially on the diode; and a cavity extending over a region including at least a portion of the semiconductor layer stack and the first conductive layer, wherein the MUT layer stack includes a film extending at least partially over the region.

[0026] In another aspect, the present invention relates to a method of manufacturing an ultrasonic multilayer structure or ultrasonic transducer array device according to any embodiment of the foregoing aspects, comprising the steps of: providing a first wafer according to an array configuration, wherein the first wafer defines a semiconductor layer stack that defines a diode; providing a second wafer, preferably a silicon-based wafer comprising a SiO2 layer or a silicon nitride layer; bonding the first wafer to the second wafer to define a silicon-on-insulator (SOI) wafer, wherein the second wafer defines a buried oxide (BOX) layer of the SOI wafer; processing the first wafer to a predetermined thickness of the ultrasonic transducer array device; fabricating a MUT layer stack on the diode, the MUT layer stack comprising a first conductive layer; and generating a cavity extending over a region comprising at least a portion of the semiconductor layer stack and the first conductive layer.

[0027] The present invention also relates to the use of an ultrasonic transducer array device according to any embodiment of the first aspect in a sensor device for measuring at least one characteristic of an object, wherein the sensor device is used for medical imaging, such as cardiac imaging, obstetrics, gynecology, abdominal imaging, intravascular imaging and mammography, or non-destructive testing (NDA), fingerprint sensor, rangefinder, gesture recognition, ultrasonic haptic feedback, ultrasonic communication or MEMS speaker.

[0028] Another object of the present invention is to provide an ultrasonic transducer that can be easily miniaturized and has sufficiently high output pressure and bandwidth. This object is achieved by providing a microfabricated ultrasonic transducer comprising a cavity and a diaphragm with constructive interference acoustic coupling to provide additional driving force for the vibration of the diaphragm, thereby causing an increase in vibration amplitude compared to the case without constructive interference. Another advantage of embodiments of the invention is that the cavity can support standing waves, which allows for adjustment of the bandwidth of the emitted ultrasonic waves. Since the frequency of the cavity is combined with the frequency of the diaphragm, the bandwidth can be increased, thereby providing a transducer with multiple resonant frequencies and thus providing a wider bandwidth than a transducer that does not include a cavity capable of supporting standing waves.

[0029] Another advantage of embodiments of the invention is that at least one acoustically suitable medium in the cavity can help the vibration of the damping diaphragm, which helps to stop the humming sound, without the need to provide a damping layer on the diaphragm.

[0030] In one aspect, the present invention relates to a microfabricated ultrasonic transducer comprising an ultrasonic source including: at least one vibrating diaphragm having a diaphragm thickness defined along a first direction, and at least one means for inducing or detecting vibration of the at least one vibrating diaphragm to emit or receive ultrasonic waves; a cavity capable of supporting standing waves and defined by a first end, a second end, and sidewalls, wherein the first end is opposite to the second end along the first direction, and wherein the sidewalls extend between the first end and the second end; and wherein the at least one vibrating diaphragm is acoustically coupled to the cavity and closes the first end of the cavity.

[0031] In one embodiment, the microfabricated ultrasonic transducer includes an endwall disposed at a second end of the cavity, wherein the endwall has an endwall thickness defined along a first direction. The endwall thickness may be substantially greater than the thickness of the at least one membrane. In other embodiments, the endwall thickness is substantially less than the thickness of the at least one membrane.

[0032] In another embodiment, the sidewall has an acoustic impedance that is smaller than that of the endwall.

[0033] Advantageously, the microfabricated ultrasonic transducer also includes a first microchannel and possibly a second microchannel through the end wall. In some embodiments, the cavity has a cross-sectional dimension substantially the same as that of at least one vibrating diaphragm.

[0034] In another embodiment, the at least one vibrating diaphragm includes at least two adjacent vibrating diaphragms and at least two corresponding means for inducing or detecting vibration of the corresponding vibrating diaphragms in order to transmit or receive ultrasonic waves.

[0035] In one embodiment, the ultrasound source has a near-field distance, and the cavity has a cavity length smaller than the near-field distance.

[0036] Preferably, the cavity includes at least one acoustically suitable medium adapted to support standing waves and at least partially connected to at least one vibrating diaphragm, wherein the acoustically suitable medium is a gaseous, solid, or liquid medium, including air, helium, silicone oil, castor oil, gel, polyurethane, polyester, epoxy resin, foam plastic, foam metal, soft rubber, silicone rubber, sound-absorbing rubber, butyl rubber, glass wool, glass fiber, felt, silk, fabric, and microporous plate.

[0037] In a preferred embodiment, the ultrasound source and cavity are defined by a multi-layered structure as described above.

[0038] In another aspect, the present invention relates to an ultrasonic transducer array device configured to transmit and receive ultrasonic signals, comprising: a plurality of micro-machined ultrasonic transducers arranged in an array configuration according to at least one embodiment of the invention according to a first aspect; at least one first electrode for connecting the micro-machined ultrasonic transducers in the array configuration along a first direction; at least one second electrode for connecting the micro-machined ultrasonic transducers in the array configuration along a second direction; wherein the at least one first electrode is connected to the at least one second electrode via a diode connected in series with a respective micro-machined ultrasonic transducer, wherein, when in use, the direction from the anode to the cathode of the diode coincides with the direction from the high potential side to the low potential side of the respective micro-machined ultrasonic transducer, and wherein the low potential side of the respective micro-machined ultrasonic transducer is connected to the anode of the diode.

[0039] In another aspect, the present invention relates to the use of microfabricated ultrasonic transducers or ultrasonic transducer array devices as described above, wherein such use includes contacting at least one membrane with a liquid or gel as a transmission medium for ultrasonic waves generated by the microfabricated ultrasonic transducer or microfabricated ultrasonic transducer array.

[0040] In another aspect, the present invention relates to a method for manufacturing a micro-machined ultrasonic transducer as described above, comprising the steps of providing a wafer, forming a cavity on the back side of the wafer, and sealing a second end of the cavity.

[0041] For the purpose of summarizing the invention and its advantages over the prior art, certain objects and advantages of the invention have been described above. It should be understood, of course, that not all such objects or advantages may be achieved according to any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention can be embodied or practiced in a manner that achieves or optimizes one or more advantages as taught herein, without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0042] The above and other aspects of the invention will be apparent from the embodiments described below and will be illustrated with reference to the embodiments.

[0043] Brief description of the attached figures

[0044] The invention will now be further described by way of example with reference to the accompanying drawings, wherein the same reference numerals refer to the same elements in the various drawings.

[0045] Figure 1 A schematic diagram of an ultrasonic transducer array device according to various embodiments of the present invention has been explained.

[0046] Figure 2A simplified schematic electrical model of an ultrasonic transducer array device according to various embodiments of the present invention is depicted, wherein each ultrasonic transducer of the array device is connected in series with a corresponding diode.

[0047] Figure 3a A simplified schematic electrical model of an ultrasonic transducer array device excluding diodes according to various embodiments of the present invention has been explained.

[0048] Figure 3b A simplified schematic electrical model of the ultrasonic transducer array device according to various embodiments of the present invention has been explained.

[0049] Figure 4a This is a schematic cross-sectional side view illustrating a multilayer structure of a diode connected in series with a corresponding ultrasonic transducer according to various embodiments of the present invention, wherein the multilayer structure includes a pMUT layer stack.

[0050] Figure 4b This is a schematic cross-sectional side view illustrating a multilayer structure of a diode connected in series with a corresponding ultrasonic transducer according to various embodiments of the present invention, wherein the multilayer structure includes a pMUT layer stack.

[0051] Figure 5 Commentary Figure 4b The top view of the multi-layered structure shown in the image.

[0052] Figure 6 The diagram illustrates a schematic cross-sectional side view of a multilayer structure of a diode connected in series with a corresponding ultrasonic transducer according to various embodiments of the present invention, wherein the multilayer structure includes a stack of pMUT layers.

[0053] Figure 7 This is a schematic cross-sectional side view illustrating a multilayer structure of a diode connected in series with a corresponding ultrasonic transducer according to various embodiments of the present invention, wherein the multilayer structure includes a pMUT layer stack.

[0054] Figure 8 This is a schematic cross-sectional side view of a multi-layer structure according to another embodiment of the present invention.

[0055] Figure 9 This is a schematic cross-sectional side view of a multi-layer structure according to another embodiment of the present invention.

[0056] Figure 10 The diagram illustrates a schematic cross-sectional side view of a multilayer structure of a diode connected in series with a corresponding ultrasonic transducer, according to various embodiments of the present invention, wherein the multilayer structure includes a stack of cMUT layers.

[0057] Figure 11The diagram illustrates a schematic cross-sectional side view of a multilayer structure of a diode connected in series with a corresponding ultrasonic transducer, according to various embodiments of the present invention, wherein the multilayer structure includes a stack of cMUT layers.

[0058] Figure 12a This is a schematic cross-sectional side view in the zx plane of a "stationary" micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0059] Figure 12b This is a schematic cross-sectional side view of an "activated" micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0060] Figure 12c This is a schematic cross-sectional side view of an "activated" micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0061] Figure 13a This is a schematic cross-sectional side view of a microfabricated ultrasonic transducer including a first microchannel according to various embodiments of the present invention.

[0062] Figure 13b This is a schematic cross-sectional side view of a microfabricated ultrasonic transducer including a second microchannel according to various embodiments of the present invention.

[0063] Figure 14 This is a schematic cross-sectional side view of a micro-fabricated ultrasonic transducer including a piezoelectric layer according to various embodiments of the present invention.

[0064] Figure 15 This is a schematic cross-sectional side view of a micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0065] Figure 16a This is a schematic cross-sectional side view of an alternative micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0066] Figure 16b This is a schematic cross-sectional side view of an array of microfabricated ultrasonic transducers according to various embodiments of the present invention.

[0067] Figure 17a This is an illustrative cross-sectional side view of a method for manufacturing a micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0068] Figure 17b This is an illustrative top view of a method for manufacturing a micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0069] Figure 18a This is an illustrative cross-sectional side view of a method for manufacturing a micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0070] Figure 18b This is an illustrative top view of a method for manufacturing a micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0071] Figure 19a This is an illustrative cross-sectional side view of a method for manufacturing a micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0072] Figure 19b This is an illustrative top view of a method for manufacturing a micro-machined ultrasonic transducer according to various embodiments of the present invention.

[0073] Figure 20a and 20b This is an illustrative schematic diagram of the cavity according to various embodiments of the present invention.

[0074] Detailed Description of Explanatory Embodiments

[0075] The invention will be described with reference to specific embodiments and certain accompanying drawings, but the invention is not limited thereto but is defined only by the claims.

[0076] Furthermore, the terms "first," "second," etc., used in the specification and claims are used to distinguish between similar elements and are not necessarily used to describe an order in time, space, rank, or any other way. It should be understood that the terms thus used are interchangeable where appropriate, and the various embodiments of the invention described herein can operate in an order different from that described or illustrated herein.

[0077] It should be noted that the term "comprising" as used in the claims should not be construed as limiting itself to the means listed thereafter; it does not exclude other elements or steps. Therefore, the term should be interpreted as specifying the presence of the features, integers, steps, or components stated as mentioned, but does not exclude the presence or addition of one or more other features, integers, steps, or components, or groups thereof. Thus, the scope of a description of an apparatus comprising "A and B" should not be limited to an apparatus consisting solely of components A and B. This means that for the present invention, the only relevant components of the apparatus are A and B.

[0078] Throughout this specification, the reference to "an embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. Therefore, the phrase "in one embodiment" or "in an embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, but may refer to the same embodiment. Furthermore, in one or more embodiments, as will be apparent to those skilled in the art from this disclosure, particular features, structures, or characteristics may be combined in any suitable manner.

[0079] Similarly, it should be understood that in the description of exemplary embodiments of the invention, for the purpose of simplification and aiding in the understanding of one or more of the various inventive aspects, features of the invention are sometimes grouped together in a single embodiment, drawing, or description thereof. However, this approach to the disclosure should not be construed as reflecting an intention to claim more features than are expressly recited in each claim. Rather, as reflected in the appended claims, inventive aspects lie in fewer features than all the features of a single foregoing disclosed embodiment. Thus, the appended claims are explicitly incorporated into this detailed description, wherein each claim itself represents a separate embodiment of the invention.

[0080] Furthermore, although some embodiments described herein include some features included in other embodiments but not others, combinations of features from different embodiments are intended to fall within the scope of the invention and form different embodiments as will be understood by those skilled in the art. For example, any embodiment of the claimed embodiments in the appended claims may be used in any combination.

[0081] It should be noted that the use of specific terms in describing certain features or aspects of the invention should not be construed as implying that the term is redefined herein to be limited to any particular characteristic of the feature or aspect of the invention that includes the term and is associated with it.

[0082] Numerous specific details are set forth in the description provided herein. However, it should be understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description.

[0083] refer to Figure 1 An ultrasonic transducer array device 1, hereinafter also referred to as transducer array device 1, is shown according to various embodiments of the present invention. Figure 1 The configuration depicted corresponds to an array configuration of m rows and n columns located on a support surface. This support surface can be substantially flat or convex. Other array configurations are also possible, such as, for example, linear arrays, arrays in symmetric matrix form, arrays in asymmetric matrix form, curved arrays, or annular arrays, or combinations thereof, and are not limited thereto.

[0084] Transducer array device 1 includes a plurality of ultrasonic transducers 2 arranged in an array configuration (e.g., an m x n array configuration). Figure 1 , 2 (represented by capacitor symbols in 3a and 3b). Each individual transducer 2 within this configuration mnIt can be uniquely identified by its row m and column n positions.

[0085] The transducer array device 1 includes at least one first electrode 3 for connecting an ultrasonic transducer 2 along a first direction and at least one second electrode 4 for connecting an ultrasonic transducer 2 along a second direction.

[0086] For example, in an array configuration of m rows and n columns, the first electrode 3 can correspond to the row electrode 3. m The second electrode 4 can correspond to the column electrode 4. n 3 electrodes per row m Electrical connection along line m of ultrasonic transducer 2 mn 4 electrodes per column n Electrical connection along column n of ultrasonic transducer 2 mn .

[0087] For example, for Figure 2 The arrangement shown in the figure, when in use, is the row electrode 3 m Connect ultrasonic transducer 2 mn anode and column electrodes 4 n Connect ultrasonic transducer 2 mn The cathode, in which the ultrasonic transducer 2 mn High potential side and row electrode 3 m Connected and ultrasonic transducer 2 mn The low potential side and column electrode 4 n connect.

[0088] Figure 2 Each ultrasonic transducer 2 mn All are associated with the corresponding diode 5 mn Series connection, wherein the corresponding first electrode or row electrode 3 m via the corresponding ultrasonic transducer 2 mn The corresponding diodes in series 5 mn Connect to the corresponding second electrode or column electrode 4 n When in use, from the corresponding diode 5 mn The direction from the anode to the cathode is the same as that from the corresponding ultrasonic transducer 2 mn The direction from the high potential side to the low potential side is consistent, and the corresponding ultrasonic transducer 2 mn The low potential side and the corresponding diode 5 mn Anode connection. First electrode or row electrode 3 m It can be changed to connect to ultrasonic transducer 2 mn The cathode, and the second electrode or column electrode 4 n Can connect to ultrasonic converter 2 mn The anode, provided that... Figure 2 The direction of the diode shown in the image has been reversed.

[0089] By connecting the ultrasonic transducers 2 in this mn row-column configuration mn , with each of the 2 ultrasonic transducers mn Compared to the arrangement of unique, individual (e.g., wire-jointed) electrical contacts (requiring m×n connections), this approach is more efficient for achieving 2 connections per ultrasonic transducer. mn The number of electrical connections (m+n) required for individual addressing is greatly reduced.

[0090] According to various embodiments of the present invention, each first electrode or row electrode 3 m via the corresponding diode 5 mn Connected to each second electrode or column electrode 4 n Therefore, for example, in an ultrasonic transducer array 1 comprising four first electrodes or row electrodes 31, 32, 33, 34 and four second electrodes or column electrodes 41, 42, 43, 44, such as Figure 2 As shown, row electrode 33 is connected to diode 5 31 Connected to column electrode 41. The same row electrode 33 is connected via diode 5. 32 Connected to column electrode 42. The same row electrode 33 is connected via diode 5. 33 Connected to column electrode 43, and via diode 5 34 Connected to column electrode 44. However, it will be understood that the invention is not limited to four (4) first electrodes or row electrodes 3. m and four (4) second electrodes or column electrodes 4 n Furthermore, other numbers of row and column electrodes are also possible.

[0091] Each first electrode or row electrode 3 m In line electrode 3 m The first terminal has a voltage input V in,m 4 for each second electrode or column electrode n In column electrode 4 n The second terminal has a voltage output V g,n Diode 5 mn Arranged to allow current from row electrode 3 m The first end V in,m Through diode 5 mn and the corresponding transducer 2 mn Flow to column electrode 4 n The second end V g,n The premise is that at the first end V in,m Second end V g,n A suitable voltage difference is established between them. In other words, when using the ultrasonic transducer array device according to various embodiments of the present invention, the voltage difference between diode 5 and the transducer array is reduced. mn The direction from the anode to the cathode is the same as that of the corresponding ultrasonic transducer 2.mn The direction from the high potential side to the low potential side is consistent, and the corresponding ultrasonic transducer 2 mn The low potential side of diode 5 mn Anode connection.

[0092] For example, when a voltage is applied to the first electrode or the first terminal V of the row electrode 32 in,2 This makes the first terminal V of the first electrode or row electrode 32 in,2 The second terminal V of the middle and second electrode or column electrode 41 g,1 When there is a positive voltage difference, the current will flow through diode 5. 21 and transducer 2 21 At the first end V in,2 Second end V g,1 Flowing between.

[0093] Therefore, an advantage of the ultrasonic transducer array device 1 according to embodiments of the present invention is that diodes 5 are integrated through various embodiments of the present invention. mn This avoids activating non-target ultrasonic transducers through capacitive coupling. mn .

[0094] For example, refer to Figure 3a A transducer array device 1 according to various embodiments of the present invention is shown. This transducer array device 1 does not include, for example... Figure 2 Diode 5 shown mn In order to activate ultrasonic transducer 2 22 A voltage is applied to the first terminal V of the first electrode or row electrode 32. in,2 This causes a voltage difference to exist at the first terminal V of the first electrode or column electrode 32. in,2 With the second terminal V of the second electrode or column electrode 42 g,2 This causes current to flow along the first path P1 through the first electrode or row electrode 32 of the transducer 2. 22 And then flows through the second electrode or column electrode 42 to its second end V. g,2 However, due to capacitive coupling, a current is also induced to flow along the second path P2, which sequentially activates the ultrasonic transducer 2. 21 2 31 and 2 32 Additionally, an electric current is induced to flow along the third path P3, which sequentially activates the ultrasonic transducer 2. 22 2 13 and 2 12 . refer to Figure 3b In the transducer array device 1 according to various embodiments of the present invention, the second path P2 is connected by diode 5. 31 The circuit terminates, and therefore there is no closed circuit and current cannot flow through transducer 2.31 This prevents it from being activated. The third path P3 is connected to diode 5. 13 The circuit terminates, and therefore there is no closed circuit and current cannot flow through the ultrasonic transducer 2. 13 and 2 23 This prevents them from being activated. The first path P1 remains unchanged. Therefore, only the required transducer 2... 22 Activated. Although the foregoing embodiments of the invention have been described with or without reference to the ultrasonic transducer array device 1, wherein each ultrasonic transducer 2 is activated. mn With or without the corresponding diode 5 mn However, the embodiments of the present invention also cover not every ultrasonic transducer 2. mn All have corresponding diodes 5 mn The array configuration described herein still exists in the provision of corresponding ultrasonic transducers 2. mn At least one diode in series 5 mn In the ultrasonic transducer array device 1, for example Figure 3b Diode 5 in 31 In ultrasonic transducer 2 22 Even when targeted, activation of all three (3) ultrasonic transducers can still be prevented. Therefore, even including the individual ultrasonic transducers 2 mn One ultrasonic transducer is connected in series with only one diode 5 mn Multiple ultrasonic transducers 2 mn The ultrasonic transducer array device 1 can also provide access to the ultrasonic transducer 2 in this array configuration. mn Improved addressing selectivity. According to an embodiment of the invention, multiple ultrasonic transducers 2 mn (Hereinafter also referred to as reference numeral 2) includes at least one micro-machined ultrasonic transducer (also referred to as “MUT”), wherein the at least one MUT is a piezoelectric micro-machined ultrasonic transducer (also referred to as “pMUT”) or a capacitive micro-machined ultrasonic transducer (also referred to as “cMUT”).

[0095] According to various embodiments of the present invention, the ultrasonic transducer 2 and the corresponding diode 5 are connected in series. mn (Also referred to as 5 in the accompanying drawings) is provided as a multilayer structure. For example, depending on the conductivity type and concentration of the dopant in the semiconductor layer that is in direct contact with the conductive layer, the diode 5 may be provided at least in part by a stack of semiconductor layers and a conductive layer disposed on the stack of semiconductor layers to form a Schottky diode or a pn diode.

[0096] The conductive layer (e.g., a metal layer) and the semiconductor layer are part of the same multilayer structure as the ultrasonic transducer 2, wherein the ultrasonic transducer 2 may be defined by a stack of MUT layers at least partially disposed on the diode.

[0097] refer to Figure 4a A schematic cross-sectional side view of a first multilayer structure 10 defined by a diode connected in series with a corresponding ultrasonic transducer, according to an embodiment of the present invention, is described. The first multilayer structure 10 includes a substrate structure comprising a substrate 11 and an insulating layer 12. The substrate 11 may be a silicon substrate. The insulating layer 12 may be a silicon dioxide layer disposed on the substrate 11. A semiconductor layer stack 13 defining the diode 5 may be disposed on the substrate structures 11, 12. In some embodiments of the invention, the silicon dioxide layer 12 may be replaced by a silicon nitride layer. Preferably, the silicon substrate 11 and the silicon dioxide layer 12 are formed from a silicon-on-insulator (“SOI”) wafer, which preferably has a (111) device layer crystal orientation. In some embodiments of the invention, the insulating layer may be absent.

[0098] The semiconductor layer stack 13 of the diode 5 according to the above embodiments includes a first semiconductor layer 14 disposed on and in contact with an insulating layer 12, the insulating layer preferably being made of silicon dioxide. The first semiconductor layer 14 is heavily doped with a dopant of a first conductivity type. According to embodiments of the invention, the first semiconductor layer 14 is heavily n-doped. The first semiconductor layer 14 has a first thickness t1 measured in the z-direction in a first central region R1 of the first multilayer structure 10, and a second thickness t2 elsewhere that is less than the first thickness t1. The first central region R1 is measured in the x-direction.

[0099] The second layer 15 can be disposed above the first semiconductor layer 14, outside the first region R1, i.e., at a location in the xy plane where the thickness of the first semiconductor layer 14 is t2. The second layer 15 can be a semiconductor substrate doped with a dopant of a first conductivity type. Substrate doping means that it has a very low doping (or no doping) concentration, approximately 10% lower than the doping concentration of the third semiconductor layer 16. 2 Up to 10 3 (See below). According to other embodiments, layer 15 is an insulating layer, such as a polymer layer. The semiconductor layer stack 13 includes a third semiconductor layer 16 disposed above the first semiconductor layer 14 in a first central region R1, i.e., at a location in the xy plane where the thickness of the first semiconductor layer is t1. The third semiconductor layer 16 of the semiconductor layer stack 13 is weakly doped with a dopant of a first conductivity type. According to various embodiments of the invention, the third semiconductor layer 16 is n-doped and has a thickness preferably between 100 nanometers (nm) and 500 nanometers (nm).

[0100] The first multilayer structure 10 also includes a first conductive layer 17, which preferably comprises platinum, but other materials such as aluminum, molybdenum, chromium, gold and / or silver may also be used.

[0101] A first conductive layer 17 may be at least partially disposed over the third semiconductor layer 16 and the second semiconductor layer 15 of the semiconductor layer stack 13, wherein the first conductive layer 17 defines a conductive layer gap G (also referred to as gap G) such that the portion of the first conductive layer 17 disposed on the third semiconductor layer 16 is not connected to the portion of the first conductive layer 17 disposed on the second semiconductor layer 15. In other words, a first portion of the first conductive layer 17 is sandwiched between at least a portion of the third semiconductor layer 16 and the piezoelectric layer 18 over a first central region R1 within a first region X1, and a second portion of the first conductive layer 17 is disposed over at least a portion of the second semiconductor layer 15, such that the first portion and the second portion of the first conductive layer 17 define a first conductive layer gap G.

[0102] According to various embodiments of the present invention, the piezoelectric layer 18 may be, for example, lead zirconate titanate (PZT), aluminum nitride (AlN), scandium-doped aluminum nitride (Sc-AlN), PMN (chemical formula: Pb(Mg1 / 3Nb2 / 3)O3), PZN (chemical formula: Pb(Zn1 / 3Nb2 / 3O3)O3), PMN-PT, PZT-PMN, ZnO, ZnO2, or any other piezoelectric material that can be fabricated into a thin film. The piezoelectric layer 18 may be disposed on the conductive layer 17 and may fill one or more first conductive layer gaps G. The first multilayer structure 10 may also include a top electrode 19 disposed on the piezoelectric layer 18. The top electrode 19 may be a first electrode or a second electrode as previously described in various embodiments of the present invention. The first multilayer structure 10 also includes a recess P1 that may extend through the piezoelectric layer 18, the conductive layer 17, and the second semiconductor layer 15. A second electrode 20 may be disposed in the recess P1 on the first semiconductor layer 14.

[0103] According to various embodiments of the present invention, the multilayer structure 10 may include the above-mentioned... Figure 4a The described layers and features include a semiconductor layer stack 13 on top of which each layer may have more than one piezoelectric layer and a corresponding electrode, plus some insulating and protective layers between the piezoelectric layers and / or conductive layers and / or on top of the entire device. The insulating layer may be a polymer such as polyimide or a ceramic such as Al2O3, SiO2 or SiN, or a combination thereof, but is not limited thereto.

[0104] A Schottky junction is formed at the interface between the conductive layer 17 and the doped (preferably lightly doped) semiconductor layer. When referring to this interface, the metal / n-doped interface or anode is used. The other side is referred to as the metal / n+-doped interface or cathode.

[0105] A cavity C1 is provided through the silicon substrate 11 and the silicon dioxide layer 12, such that a first portion of a first multilayer structure comprising a semiconductor layer stack 13, a conductive layer 17, and a piezoelectric layer 18 is suspended over or covers the cavity C1 in a first region, wherein the first region X1 extends in the x-direction by a distance substantially corresponding to the width of the cavity C1 measured in the x-direction. Note that the cavity also extends in the y-direction, which is not shown in the figures.

[0106] The first portion extending over the first region X1 defines an ultrasonic source, which includes at least one membrane and at least one means for vibrating the at least one membrane to receive and emit ultrasonic waves. The at least one membrane extending over the first region X1 may include a first portion of a semiconductor layer stack 13 and a conductive layer 17, while the means for vibrating the membrane may include a portion of a piezoelectric layer 18. Therefore, the means for vibrating the membrane may include, for example, a piezoelectric material layer for forming a piezoelectric MUT (“pMUT”) or a multilayer structure together with a vacuum cavity for forming a capacitive MUT (“cMUT”). Each MUT can emit and receive sound waves. Sound waves are generated when a voltage difference is applied across a first electrode and a second electrode in contact with the means for vibrating the membrane. Conversely, arriving or detected sound waves induce motion within the MUT, thereby generating an electrical signal detected by the means. The first multilayer structure 10, together with electrodes 19 and 20, provides an ultrasonic transducer 2. However, as will be described in more detail below, in some embodiments, the ultrasonic transducer 2 is a cMUT, which is defined with… Figure 4a The cavity C1 described in the middle is different from the cavity. The piezoelectric layer 18 is capable of expanding and contracting when a voltage difference is applied between the high-potential electrode 19 and the low-potential electrode 20. This causes the piezoelectric layer 18 on the first region X1, as well as the suspended portion of the conductive layer 17 and the semiconductor layer stack 13, to vibrate in the z-direction (perpendicular to the plane of the multilayer structure 10), which causes the emission of ultrasonic waves. Conversely, the arriving or detected sound waves induce the movement of at least one membrane in the pMUT, thereby generating an electrical signal detected by the electrodes 19, 20.

[0107] The first electrode 19 (e.g., a high-potential electrode) can be connected to the row electrode 3 of the ultrasonic transducer array device 1 as described above, or form part of it. The second electrode 20 (e.g., a low-potential electrode) can be connected to the column electrode 4 of the ultrasonic transducer array device 1 as described above, or form part of it.

[0108] refer to Figure 4b The modified first multi-layer structure 10' and Figure 4a The first multilayer structure 10 is the same, except that the modified first multilayer structure 10' also includes a metal layer 22 to reduce the resistivity of the ground conductor between the semiconductor layer stack 13 and the insulating layer 12, wherein the insulating layer 12 may be a silicon dioxide (SiO2) layer 12. Figure 4a and Figure 4b The embodiments shown may have a protective insulating layer on top.

[0109] exist Figure 5 In, it is shown Figure 4b A top view of the multilayer structure. The first electrode 19 and the second electrode 20, as well as the metal layer 22, are visible. The region X1 defining the width of cavity C1 is also shown. Note that layers 18, 17, and 15 are not shown in this drawing to make layer 22 visible.

[0110] refer to Figure 6 A second multilayer structure 50 is shown, which can be included in the ultrasonic transducer array device 1 according to various embodiments of the present invention. Similar to... Figure 4a The first multilayer structure 10 depicted in the figure, and the second multilayer structure 50 include a second substrate structure, wherein the second substrate structure may include, for example, a second silicon substrate 51 and a second silicon dioxide layer 52 disposed on the silicon substrate 51. The second multilayer structure 50 also includes a second semiconductor layer stack 53 disposed on the silicon dioxide layer 52, a second conductive layer 56 (e.g., a metal layer) disposed on at least a portion of the second semiconductor layer stack 53, and a second piezoelectric layer 57 disposed on the second conductive layer 56.

[0111] The second semiconductor layer stack 53 of the second multilayer structure 50 may include a fourth semiconductor layer 60 disposed on and in contact with the second substrate structure (particularly the silicon dioxide layer 52). The fourth semiconductor layer 60 may be heavily doped with a dopant of a first conductivity type. Indeed, according to various embodiments of the invention, the fourth semiconductor layer 60 may be (silicon)n+ doped, having a conductivity of 10... 18 and 10 21 / cm 3 The relative concentrations between them.

[0112] Layer 61 may be disposed above the fourth semiconductor layer 60, except in the second central region R2. The second central region R2 includes at least a portion of the second multilayer structure 50 and extends in the x-direction, wherein the second top electrode 59 is connected to said at least a portion of the second multilayer structure 50. Layer 61 may be a fifth semiconductor layer with a very low doping concentration of a dopant of a first conductivity type, or even without any doping. According to some embodiments of the invention, the fifth layer 61 is a substrate doped with a dopant of a first conductivity type, preferably with a dopant concentration at least 10 lower than that of the sixth semiconductor layer 62. 2 (See next paragraph). According to other embodiments, layer 61 is an insulating layer, such as a polymer layer.

[0113] The second semiconductor layer stack 53 may further include a sixth semiconductor layer 62 disposed on the fourth semiconductor layer 60 in the second central region R2, and a seventh semiconductor layer 63 disposed on the sixth semiconductor layer 62 in the second central region R2. According to various embodiments of the invention, the sixth semiconductor layer 62 is n-doped, and the seventh semiconductor layer 63 is p+ doped. The combined thickness of the sixth semiconductor layer 62 and the seventh semiconductor layer 63 may be approximately one (1) to five (5) micrometers (μm), but is not limited thereto.

[0114] The doping concentration of the substrate doped region is typically about 10% lower than that of the n- (or p-) doped region. 2 Up to 10 3 The doping concentration of the n- (or p-) doped region is typically about 10 times lower than that of the n+ (or p+) doped region. 2 Up to 10 4 Factors.

[0115] The second multilayer structure 50 further includes a second piezoelectric layer 57 disposed on the second conductive layer 56 and filling the gap G between the second conductive layers. The second multilayer structure 50 also includes a second top electrode 59 disposed on the second piezoelectric layer 57 within the second central region R2. The second multilayer structure 50 further has a second recess P2 extending through the second piezoelectric layer 57, the second conductive layer 56, and partially through the second semiconductor layer stack 53. A second electrode 70 is disposed on the fourth semiconductor layer 60 in the recess P2. A pn ​​junction diode is formed at the boundary between the sixth and seventh semiconductor layers 62, 63. When a positive voltage difference is applied between the electrodes 59, 70, a depletion layer is formed at the pn junction, and current can flow between the electrodes 59 and 70. In a particular embodiment of the invention, where the capacitor between the electrodes 59 and 70 is not fully charged, when a positive voltage difference is applied between the electrodes 59, 70, a depletion layer is formed at the pn junction, and current can flow between the electrodes.

[0116] A second cavity C2 is provided through the second substrate (particularly the silicon substrate 51 and the silicon dioxide layer 52), such that a portion X2 of a layer structure including a portion of the semiconductor layer stack 53, the second conductive layer 56, and the piezoelectric layer 57 is suspended above the second cavity C2. This portion X2, together with electrodes 59 and 70, provides an ultrasonic transducer 2 capable of emitting and receiving ultrasonic waves, as described above regarding... Figure 4a The portion X2 of the second multilayer structure 50 covering or suspended above the second cavity C2 can define an ultrasonic source and receiver, which includes a membrane and means for vibrating the membrane to emit ultrasonic waves. The membrane may be defined by a portion of a semiconductor layer stack 53 and a second conductive layer 56 extending within the second region X2, while the means for vibrating the membrane may be defined by at least a portion of a piezoelectric layer 57 within the second region X2 and a top electrode 59.

[0117] The first electrode, top electrode, or positive electrode 59 may be connected to the row electrode 3 of the transducer array as described above, or form part of it. The second electrode, bottom electrode, or negative electrode 70 may be connected to the column electrode 4 of the transducer array as described above, or form part of it.

[0118] like Figure 6 Various embodiments of the second multilayer structure 50 shown include a diode structure referred to as a pn junction diode. This diode has a p+ / n- junction. The anode can be connected by connecting a conductive region or layer to the p+ region or layer. The n+ region or layer serves as a ground signal connector and is connected as a cathode by the conductive layer 70. The advantage of very low-doped or undoped regions is the reduction of all parasitic components.

[0119] like Figure 7 The multi-layered structure depicted in the text is similar to Figure 6 Furthermore, the second multilayer structure discussed earlier, in addition to the metal layer 89 beneath the semiconductor layer stack 83, is because n+ has a high resistivity, serving as a ground signal and is attached to the metal layer.

[0120] Further reference Figure 7 A third multilayer structure 80 is shown, which can be included in the ultrasonic transducer array device 1 according to various embodiments of the present invention. The third multilayer structure 80 is similar to the second multilayer structure 50 and includes a third substrate structure comprising a third substrate 81 and a third insulating layer, particularly a silicon dioxide layer 82 disposed on the third substrate 81. The third semiconductor layer structure 80 may further include a third semiconductor layer stack 83 disposed on the third substrate structures 81 and 82, a third conductive layer 86 disposed on at least a portion of the third semiconductor layer stack 83, and a third piezoelectric layer 88, at least a portion of the third piezoelectric layer 88 disposed on the third conductive layer 86.

[0121] The third multilayer structure 80 further includes a fourth conductive layer 89 disposed between the third insulating layer 82 (particularly the silicon dioxide layer) and the third semiconductor layer stack 83.

[0122] The third semiconductor layer stack 83 can be configured as follows. Layer 91 can be disposed on the fourth metal layer 89 in the z-direction, except for the third central region R3 between the top electrode 98 and the third substrate structures 81, 82. In some embodiments, layer 91 can be an eighth semiconductor layer 91 having a very low (or undoped) substrate doping concentration. According to other embodiments, layer 91 is an insulating layer, such as a polymer layer.

[0123] The third semiconductor layer stack 83 may further include ninth, tenth, and eleventh semiconductor layers 92, 93, and 94, which are disposed in this order above the second metal layer 89 in the third central region R3. That is, the ninth semiconductor layer 92 is adjacent to the fourth metal layer 89, the eleventh semiconductor layer 94 is adjacent to the third conductive layer 86, and the tenth semiconductor layer 93 is located between the ninth and eleventh semiconductor layers 92 and 94. The combined thickness of the tenth and eleventh semiconductor layers 93 and 94 is approximately one (1) to five (5) micrometers (μm).

[0124] According to various embodiments of the present invention, the ninth semiconductor layer 92 may be n+ doped. The tenth semiconductor layer 93 may be n- doped. The eleventh semiconductor layer 94 may be p+ doped. The operation of these features is related to... Figure 6 The corresponding layer in the text explains the same thing.

[0125] A third piezoelectric layer 88 is disposed on the third metal layer 86 and fills the gap G. The third multilayer structure 80 also includes a top electrode 98 disposed on the piezoelectric layer 88. The third multilayer structure 80 also has a third recess P3 extending through the third piezoelectric layer 88, the third metal layer 86 and through the third semiconductor layer 83. A negative voltage electrode 95 is disposed on the second metal layer 89 in the third recess P3.

[0126] The third cavity C3 is defined by a third substrate structure (particularly a silicon substrate 81 and a silicon dioxide layer 82), such that a portion X3 of a third multilayer structure comprising a fourth metal layer 89, a third semiconductor layer stack 83, a third metal layer 86, and a third piezoelectric layer 88 is suspended in the cavity C3. This third portion X3 may define at least one membrane and at least one means for vibrating the membrane to emit ultrasonic waves. In practice, this portion X3, together with electrodes 98 and 95, provides an ultrasonic transducer 2 capable of emitting ultrasonic waves, as described above with respect to FIG4.

[0127] Electrode 98 may be connected to the row electrode 3 of the ultrasonic transducer array device 1 as described above, or may form part of it. Electrode 95 may be connected to the column electrode 4 of the transducer array as described above, or may form part of it.

[0128] As described above, the diodes included in the array devices according to various embodiments of the present invention can be provided by Schottky diodes or pn diodes. However, other possibilities for providing diodes are also within the scope of the present invention. For example, field-effect transistors can be used as diodes to provide directional current flow.

[0129] refer to Figure 8 This illustrates another embodiment of the multilayer structure according to the present invention. Figure 8Embodiments include a mechanical layer 115, which may be another semiconductor layer (e.g., Si or SiC), a polymer, or a SiO2 or SiN layer. If it is a semiconductor layer, the layer may be doped, for example, with a substrate doped with a dopant of a first conductivity type, or it may not be doped at all. In some embodiments, layer 115 may be absent. The MUT layer includes a piezoelectric layer 18 and a first conductive layer 17. The first conductive layer is disposed on the mechanical layer 115. Figure 8 In the specific embodiment shown, a first portion of the conductive layer 17 is sandwiched between at least a portion of the piezoelectric layer 18 and the mechanical layer 115. Compared to the embodiment of FIG. 4, the positions of the heavily doped semiconductor layer 14 and the lightly doped semiconductor layer 16 are reversed: the heavily doped semiconductor is now farther from the cavity than the lightly doped semiconductor. Figure 8 At the top of the structure, a top electrode conductive rail 47 (e.g., a metal rail) is shown, which covers a portion of the insulating layer 125 and defines a semiconductor layer stack for the diode. In this embodiment, the semiconductor layer stack is placed on the conductive layer 119. The semiconductor stack is... Figure 8 The semiconductor layer stack has a thickness t8. Note that this semiconductor layer stack can be implemented as any semiconductor layer stack shown in other embodiments, provided that the different layers of the stack are placed in reverse order in the z-direction. In some embodiments, the conductive layer 119 may include multiple layers to form a multilayer structure. The insulating layer 125 protects the semiconductor layer, for example, from the influence of adjacent diodes in the array. In some embodiments, the semiconductor layer stack may include a semiconductor layer heavily doped with a dopant of a second conductivity type, sandwiched between a first portion of the first semiconductor layer and the first conductive layer within region R1.

[0130] The various embodiments of the multilayer structure of the present invention described above can be combined in various ways to produce, for example, multilayer structures having two or more cavities and / or additional semiconductor layer stacks and / or conductive rail (e.g., metal rail) stacks, and corresponding insulating layers. For example, Figure 9 and Figure 8 The same applies, but with a pMUT in regions X1 and X2, and two semiconductor multilayer stacks in regions R1 and R2. A first conductive rail 47 is also partially disposed in region R2 on the second semiconductor multilayer. A second conductive rail 48 is disposed on top of the first conductive rail 47 in the second region R2. The first conductive rail 47 and insulating layer 125 in region R1 are covered by insulating layer 126. A third conductive rail 49 (e.g., a metal rail) is shown as covering a portion of insulating layer 126 and the semiconductor layer stack defining the diode in region R2. The third conductive layer 49 acts as the top electrode of the second ultrasonic transducer in region X2. Similarly, more conductive rails can be disposed on top of each other by means of a middle insulating layer to avoid short circuits.

[0131] While the example multilayer structures described above include piezoelectric layers for forming the pMUT, these principles also apply to providing the cMUT. For example, see reference... Figure 10 A fourth multilayer structure 100 is shown, which can be included in an ultrasonic transducer array device 1 according to various embodiments of the present invention. The fourth multilayer structure 100 includes a fourth substrate structure 101 preferably made of silicon and a fourth semiconductor layer stack 103 disposed on the silicon substrate 101. The fourth semiconductor layer stack 103 in this cMUT diode configuration can be any of the semiconductor layer stacks 13, 53, and 83 described above. A fifth conductive layer 104 (e.g., a metal layer) is disposed on the fourth semiconductor layer stack 103. A first non-conductive layer 105 is disposed on at least a portion of the fifth conductive layer 104, excluding the fourth central region R4. A second non-conductive layer 106 is disposed on the first non-conductive layer 105 to form a cMUT cavity 107 in the fourth central region R4. The cMUT cavity 107 can be a vacuum cavity. An electrode 108 is disposed in the fourth central region R4 on the second non-conductive layer 106. A fourth recess P4 is provided through the second non-conductive layer 106, the first non-conductive layer 105, and the fifth conductive layer 104. Electrode 109 is disposed in the fourth recess P4 on the semiconductor layer 103. When an alternating voltage is applied between electrodes 108 and 109, the portion of the second non-conductive layer located in the fourth central region R4 (i.e., the portion suspended above the cMUT cavity 107) vibrates due to the alternating attraction and repulsion between electrodes 108 and the conductive layer 104. This causes ultrasonic waves to be emitted. Vibration may also occur due to the alternative electrostatic forces within the cMUT cavity 107, which functions as a capacitor, and between the two electrodes 104 and 108.

[0132] The non-conductive layers 105 and 106 may include, for example, polysilicon, SiN, SiO2, or other polymers.

[0133] like Figures 6 to 10 Each embodiment of the multilayer structure of the ultrasonic transducer shown in any of them may have a protective insulating layer on top.

[0134] exist Figure 11 In the previous section, another embodiment with cMUT was explained. For example, regarding... Figure 10 As explained, a cMUT cavity is created between conductive layer 104 and non-conductive layers 105 and 106. A fourth semiconductor layer stack 103 (as already mentioned, it can be any of the previously described semiconductor layer stacks 13, 53, and 83) now sits on top of electrode 108, but in reverse order in the z-direction. As in Figure 8In this configuration, a top electrode conductive rail 47 (e.g., a metal rail) is provided, which at least partially covers the semiconductor layer stack 103. The conductive layer 104 is provided with gaps G to prevent the bottom electrodes of the various MUTs from connecting to each other.

[0135] According to an embodiment of the present invention, the ultrasonic transducer array device further includes at least one power supply adapted to provide power to the ultrasonic transducer to keep the diodes conducting and activate the receiving function for ultrasonic signals. The power supply may be a DC power supply arranged in series with the ultrasonic transducer and the corresponding diodes.

[0136] According to another aspect of the present invention, a method for manufacturing an ultrasonic transducer array device according to any of the foregoing embodiments is provided below. The method includes the steps of: providing a first wafer according to an array configuration, wherein the first wafer defines a semiconductor layer stack; providing a second wafer, preferably a silicon-based wafer comprising a SiO2 layer or a silicon nitride layer; bonding the first wafer to the second wafer to define a silicon-on-insulator (SOI) wafer, wherein the second wafer defines a buried oxide (BOX) layer of the SOI wafer; and processing the first wafer to a predetermined thickness of the ultrasonic transducer array device.

[0137] Various embodiments of the present invention also include the present invention for manufacturing ultrasonic transducer array devices, including the steps of providing a substrate layer comprising a diode array and manufacturing an array of ultrasonic transducers on the substrate layer.

[0138] Specifically, embodiments of the method for manufacturing an ultrasonic transducer array device having a pMUT layer stack according to the present invention include the following steps: providing a first wafer according to a predetermined array configuration, wherein the first wafer defines a semiconductor layer stack according to at least one embodiment of the present invention described above; providing a second wafer, preferably a silicon-based wafer including a SiO2 layer or a silicon nitride layer; bonding the first wafer to the second wafer to define a silicon-on-insulator (SOI) wafer, wherein the second wafer defines a buried oxide (BOX) layer of the SOI wafer; and processing the first wafer to a predetermined thickness of the transducer array device layer.

[0139] The processing of the first wafer includes thinning and polishing steps.

[0140] Various embodiments of the method according to the present invention can provide a first ion-realized wafer. Ion realization can also be performed after the formation of the SOI wafer.

[0141] Various embodiments of the method according to the invention may include, but are not limited to, adding a conductive layer having a predetermined pattern corresponding to a predetermined array configuration on a first wafer before providing a second wafer using a deposition technique such as physical vapor deposition (PVD) or chemical vapor deposition (CVD).

[0142] The method also includes the following steps:

[0143] Deposit a second electrode or bottom electrode on the SOI wafer;

[0144] Deposit a piezoelectric layer on the SIO wafer and pattern it to connect to a ground electrode; deposit a first electrode or a top electrode on top of each film;

[0145] The film was fabricated on the back side of the second wafer using a deep reactive ion etching (DRIE) process; and

[0146] The BOX layer is removed by etching, where the etching process can be a hydrogen fluoride (HF) etching process, but is not limited to this.

[0147] According to various embodiments of the present invention, the first electrode or top electrode may be smaller than each membrane.

[0148] refer to Figures 12a to 12c The illustration shows microfabricated ultrasonic transducers (MUTs) according to various embodiments of the present invention. Both capacitive MUTs (hereinafter also referred to as "cMUTs" or "various cMUTs") and piezoelectric MUTs (hereinafter also referred to as "pMUTs" or "various pMUTs") are microelectromechanical systems (MEMS) devices manufactured using semiconductor mass production.

[0149] The transducer 801 includes an ultrasonic source 802 and a cavity 803 acoustically coupled to the at least one ultrasonic source 802. The cavity 803 may be a pMUT or cMUT cavity as described above with respect to the present invention.

[0150] The ultrasonic source 802 includes at least one vibrating membrane 804 having a film thickness defined along a first direction (z-direction) and at least one device 805 for vibrating the at least one vibrating membrane 804 to emit ultrasonic waves and / or for detecting the vibration of the at least one vibrating membrane to receive ultrasonic waves. The at least one vibrating membrane 804 may be at least a portion of a semiconductor layer stack defining a diode and a first conductive layer disposed on the semiconductor layer, as described above with respect to embodiments of the invention. The at least one device 805 for vibrating the at least one vibrating membrane 804 to emit ultrasonic waves and / or for detecting the vibration of the at least one vibrating membrane 804 to receive ultrasonic waves may be a portion of a MUT layer stack disposed on the first conductive layer and an electrode disposed on top of the MUT layer stack. As used herein and unless otherwise specified, when referring to at least one vibrating membrane, the term membrane 804 may also be used.

[0151] As used herein and unless otherwise indicated, when referring to at least one means for vibrating at least one vibrating diaphragm to emit ultrasonic waves and / or for detecting the vibration of at least one vibrating diaphragm to receive ultrasonic waves, reference may also be made to means for vibrating the diaphragm, or means 805.

[0152] Cavity 803 has a first end 806 and a second end 807, wherein the second end 807 is opposite to the first end 806 along a first direction (z-direction). Cavity 803 is defined by a sidewall 808, a membrane 804 at the first end 806, and an endwall 809 (hereinafter also referred to as the second endwall 809) at the second end 807. The membrane 804 is located at the first end 806 of the cavity and closes the first end 806 of the cavity. For example, the membrane may be bonded to the sidewall 808 at the first end of the cavity. Preferably, the sidewall 808 and the second endwall 809 are integral. This can help simplify the manufacture of transducer 801. In some embodiments, the sidewall 808 may be separately disposed from the second endwall 809 and may be fixed to the second endwall 809 by, for example, applying an adhesive or using an adhesive process.

[0153] As will be described in more detail below, at least one device 805 for vibrating the membrane may include, for example, a piezoelectric material layer for forming a pMUT or a multilayer structure together with a vacuum cavity for forming a cMUT. Each MUT can emit and receive sound waves. Sound waves are generated when a voltage difference is applied across a first electrode and a second electrode in contact with device 805. Conversely, arriving or detected sound waves induce motion within the MUT, thereby generating an electrical signal detected by device 805.

[0154] For details, please refer to the following: Figure 12a The figure depicts a schematic cross-sectional view of a transducer in a “stationary” configuration or state according to an embodiment of the invention in the zx plane, wherein the membrane 804 is undeformed.

[0155] refer to Figure 12b and 12c It depicts the transducer in an "active" configuration according to various embodiments of the invention. Figure 12a The same schematic cross-sectional view is shown, in which the membrane 804 is vibrated by the device 805, and the membrane 804 is periodically displaced in the z-direction and has a maximum displacement away from the cavity in the z-direction. Figure 12b ) and the maximum displacement in the cavity in the z-direction ( Figure 12c Move between ).

[0156] Sidewall 808 can be a single, continuous sidewall, for example, if cavity 803 has a cylindrical shape and therefore a circular cross-section cut in a plane parallel to the stationary membrane 804 (i.e., the xy-plane where the y-axis is perpendicular to the x and z axes shown in the figures). Sidewall 808 can be composed of several adjacent sidewalls, for example, if the cavity has a polygonal cross-section in the xy-plane. For example, cavity 803 can have a cuboid shape, and its cross-section can be square.

[0157] A membrane 804 is provided such that the first end 806 of the cavity is closed, which allows the transducer to be used in contact with liquids or gels without the risk of liquids or gels leaking into the cavity, which could alter the acoustic characteristics of the transducer and damage it.

[0158] The film may include ceramics such as SiO2, SiC or Al2O3; semiconductors such as silicon; polymers; carbon-based materials such as diamond films; glass or quartz; or other suitable films.

[0159] Cavity 803 is acoustically coupled to membrane 804 via at least one medium or material within the cavity, and is capable of supporting standing waves generated by membrane 804. At least one medium or material within cavity 804 is at least partially connected to membrane 804, and is a gaseous, solid, or liquid material, including but not limited to air, helium, silicone oil, castor oil, gel, polyurethane, polyester, epoxy resin, foam plastic, foam metal, soft rubber, silicone rubber, sound-absorbing rubber, butyl rubber, glass wool, glass fiber, felt, silk, fabric, and microporous plates. Periodic oscillations of membrane 804 cause corresponding periodic changes in pressure within cavity 803, provided that the oscillation frequency f of membrane 804 satisfies the relationship shown in equation (1):

[0160]

[0161] Where n is a positive integer, v is the speed of sound in cavity 803, and L is the length of the cavity. A standing wave can be established in cavity 803, having a node at the second end 807 and an antinode at membrane 804. The length L of cavity 803 is measured between the first end 806 and the second end 807 of cavity 803 when membrane 804 is undeformed. The resonant frequency of membrane 804 depends on its structural characteristics (such as geometry, thickness, diameter, etc.) and its mechanical properties, as well as the mechanical properties of the other layers on top of the membrane and their interactions, such as the effect of residual stress in one layer on another. If the ultrasonic source is a cMUT, meaning that membrane 804 is a membrane of the cMUT floating on a vacuum cavity embedded in device 805, then the resonant frequency also depends on the DC bias voltage of the cMUT.

[0162] To support standing waves, cavity 803 does not contain a vacuum and is filled with at least one acoustically suitable medium, such as a gaseous, solid, or liquid medium, including but not limited to air, helium, silicone oil, castor oil, gel, polyurethane, polyester, epoxy resin, foam plastic, foam metal, soft rubber, silicone rubber, sound-absorbing rubber, butyl rubber, glass wool, glass fiber, felt, silk, fabric, and microporous plates. This at least one acoustically suitable medium allows the standing waves to have a specific wavelength for a given length L of cavity 803 and the frequency from which the standing waves originate.

[0163] According to various preferred embodiments of the present invention, acoustically suitable materials can lead to damping and widening of the resonance bandwidth of the MUT.

[0164] The cavity 803 containing a vacuum cannot support standing waves. An acoustically suitable material is one that can compress and expand when subjected to forces caused by the movement of the diaphragm 804, ensuring that the diaphragm 804 does not lose contact with the material during vibration. If the cavity 803 is filled with a non-gaseous medium, the hardness and stiffness of the cavity filling material should be significantly less than the hardness or stiffness of the diaphragm 804 to avoid the cavity filling material inhibiting or limiting the vibration of the diaphragm 804 and unnecessarily altering the mechanical properties of the entire device. In some embodiments, for example, if the walls 808, 809 of the cavity 803 comprise a conductive material, the wall material can be selected to have a relatively low conductivity, thus not interfering with the manufacturing process.

[0165] Preferably, the acoustic impedance of the medium or material contained in cavity 803 is significantly different from the acoustic impedance of the second end wall 809 at the second end 807 of cavity 803. This has the advantage that a large portion of the ultrasonic waves in cavity 3 can be reflected back by the second end wall 809 at the second end 807, contributing to strong standing waves. The acoustic impedance of the medium contained in the cavity can be different from the acoustic impedance of the second end wall 809 at the second end 807. According to various embodiments of the invention, the acoustic impedance can be at least fifty (50) times smaller or larger than the acoustic impedance of the second end wall 809 at the second end 807, more preferably at least one hundred (100) times larger or smaller, and even more preferably at least five hundred (500) times larger or smaller or at least one thousand (1000) times larger or smaller.

[0166] When the membrane 804 is vibrated at a frequency that is not the resonant frequency of the cavity 803, compared to when the membrane 804 is vibrated at a frequency within the resonant frequencies of the cavity 803, the membrane 804 exhibits an increased amplitude of vibration. When the cavity length L is an odd integer multiple of λ / 4, where λ is the wavelength of the ultrasonic wave emitted in the cavity 803, maximum constructive interference of the emitted wave from the first end 806 and the reflected wave from the opposite second end 807 occurs at the interface between the cavity 803 and the membrane 804. This constructive interference provides an additional driving force for the vibration of the membrane 804, thus increasing the amplitude of vibration compared to the case where no constructive interference occurs. Therefore, by selecting an appropriate cavity length L, the output pressure of the transducer can be increased. The output ultrasonic wave is emitted in the direction R, and the direction R is typically in the z direction, as Figure 12b shown in

[0167] The cavity length L does not need to be exactly equal to λ / 4 to obtain an increased output pressure of the transducer. In fact, the length L of the cavity can be any odd multiple of λ / 4, with an error range of ±λ / 2. For example, a cavity length L of five (5) times λ / 4 or seven (7) times λ / 4 (where λ is a constant) is sufficient to support a standing wave with a resonant frequency of f = c / λ, where c is the speed of light in a vacuum. Any variation in the length L within ±λ / 2 may result in an error in the resonant frequency of the standing wave. The magnitude of the tolerance may depend on the application. For example, for imaging applications, a membrane with a resonant frequency underwater or under gel of one (1) to ten (10) megahertz (MHz) has a bandwidth of approximately 50 - 100% of the center frequency f0 (which depends on the application). Therefore, the frequency of the standing wave can be in the range. Therefore, the cavity length L can be between 0.8×L < L < 1.33×L, where L = n×λ / 4 and n is an odd number.

[0168] Another advantage of providing a cavity 803 that can support a standing wave is that this allows adjustment of the bandwidth of the emitted ultrasonic wave. Since the frequency of the cavity 803 combines with the frequency of the membrane 804, the bandwidth can be increased, thus providing a transducer 801 with multiple resonant frequencies and therefore providing a wider bandwidth than a transducer that does not include a cavity capable of supporting a standing wave.

[0169] Furthermore, at least one acoustically suitable medium in cavity 803 can aid in the vibration of damping diaphragm 804, which helps to suppress humming without requiring damping layers on diaphragm 804. Air, as the cavity filling material, provides some damping, and if the cavity filling material includes a permanent liquid such as oil or gel, it can provide even more damping. The cavity of transducer 801 according to the invention can also be filled with a solid material, such as a solid resin. A cavity filling material that provides significant damping can reduce diaphragm displacement and thus reduce output pressure, resulting in a lower signal-to-noise ratio, which can be compensated for, for example, by using a low-noise analog amplifier. Preferably, the solid material has a small amount of elasticity, which is greater than that of the diaphragm of the ultrasonic source. Therefore, according to various embodiments of the invention, since the diaphragm is completely attached to the solid material, it will be damped by the elasticity of the solid material.

[0170] Preferably, the bending stiffness of the second end wall 809 is greater than that of the membrane 804, which can be achieved by selecting the thickness t809 of the second end wall 809 in the z-direction to be substantially greater than the thickness t804 of the membrane 804. This can help reduce or avoid acoustic excitation of the second end wall 809, which would interfere with the standing waves in the cavity 803 and may introduce unwanted vibration modes in the transducer as a whole. The appropriate thickness depends on the mechanical properties of the materials of the membrane 804 and the second end wall 809, and can be determined, for example, experimentally by varying the thicknesses t1 and / or t2 and measuring the output modes of the transducer. For example, in some embodiments, the membrane 804 comprises silicon and has a thickness of five (5) micrometers (μm), and the second end wall 809 comprises stainless steel and has a thickness of 0.5 millimeters (mm).

[0171] For similar reasons, namely to prevent or reduce the acoustic excitation of the sidewall 808, preferably, the acoustic impedance of the sidewall 808 is significantly greater than the acoustic impedance of the material in the cavity 803.

[0172] refer to Figure 13a A cross-sectional view of a first modified transducer 9101 according to various embodiments of the present invention is described. The first modified transducer 9101 is similar to that associated with... Figures 12a to 12c The transducer 801 is described. In addition to the features of transducer 801, the first modified transducer 9101 includes a first microchannel 9120 passing through a second end wall 9109, the first microchannel having an opening at a second end 9107 of cavity 9103. The first microchannel 9120 connects cavity 103 to the external environment of the first modified transducer 9101.

[0173] refer to Figure 13b The second modified transducer 9201 according to various embodiments of the present invention. The second modified transducer 9201 is similar to that associated with Figures 12a to 12cThe transducer 801 is described. In addition to the features of transducer 801, the second modified transducer 9201 includes a second microchannel 9221 passing through a sidewall 9208. The second microchannel 9221 connects cavity 9203 to the external environment of the second modified transducer 9201. In some embodiments, the transducer may include both the first microchannel 9120 and the second microchannel 9221.

[0174] Microchannels 9120 and 9221 can provide means for regulating the pressure of the medium in cavities 9103 and 9203, preferably keeping the pressure within cavities 9103 and 9203 constant. Microchannels 9120 and 9221 can provide inlets for replenishing the medium in the cavities, for example, in the event of gradual leakage. Microchannels 9120 and 9221 can help provide a path for the medium to escape when the temperature of the medium has increased, causing the medium to expand and the pressure in cavities 9103 and 9203 to increase, thus helping to provide reliable performance of transducers 9101 and 9201 under varying temperatures.

[0175] For example, if the medium is air, microchannels 9120, 9221 can provide an escape path to the environment surrounding the transducer without requiring additional components. In some embodiments, such as if the medium comprises a gas not present in the environment surrounding the transducers 9101, 9201, or if the medium comprises a fluid, an overflow compartment (not shown) can be provided near the transducers 9101, 9201, which is connected to the microchannels 9120, 9221, for example via microfluidics, to allow the exchange of medium between the overflow compartment and cavities 9103, 9203.

[0176] Preferably, cavities 9103 and 9203 have cross-sectional dimensions that are substantially the same as those of membrane 804. These cross-sectional dimensions are measured in the xy-plane. This helps to prevent or reduce the divergence of acoustic waves generated by the transducer within the cavity in the direction of the measured cross-sectional dimension. By reducing this divergence, the amplitude of the standing wave can be increased.

[0177] More preferably, the cross-section of cavity 803 in the xy-plane is substantially the same as the cross-section of membrane 804 in the xy-plane. This allows for reduced divergence in more than one direction.

[0178] In embodiments where the cavity length L is comparable to the near field of the transducer (as defined below), the cavity cross-sectional dimensions or cross-section do not necessarily need to be substantially the same as the membrane cross-sectional dimensions or cross-section, because the cavity length L is small enough that far-field behavior cannot be achieved at the second end of the cavity.

[0179] The ultrasonic source 802 has a near-field distance D nf= A / πλ, where A is the area of ​​the 804 membrane, also known as the membrane area, and λ is the wavelength of the ultrasound waves in the cavity. The membrane area is measured in the xy-plane or in a plane parallel to the xy-plane. For example, for a circular membrane with radius a, the near-field distance is a. 2 / λ, where a is the radius of the membrane.

[0180] In some embodiments, the cavity length L is less than the near-field distance D. nf This configuration allows for high amplitude standing waves without requiring the membrane and cavity to be similar in size in the xy-plane, because the ultrasonic waves travel a shorter distance within the cavity before reflection than the near-field distance, and therefore do not exhibit significant divergence. The suitable cavity length L for this configuration depends on the frequency of the standing wave, which in turn depends on the material properties of the membrane and cavity filling materials as described above, and can be determined, for example, through simulation or experimentation.

[0181] In some embodiments, the cavity length L is greater than the near-field distance D. nf This allows for easier fabrication of transducers. Another advantage of this arrangement is the ability to achieve specific frequencies of ultrasound, which requires a greater near-field distance than D. nf A longer cavity length L. The appropriate cavity length L for this configuration depends on the frequency of the standing wave, which in turn depends on the material properties of the membrane and cavity filling material as described above, and can be determined, for example, through simulation or experimentation.

[0182] refer to Figure 14 The device 805 for vibrating the membrane 804 preferably includes a piezoelectric layer 8010, which is disposed on the membrane 804 and the first electrode 8011 and the second electrode 8012 respectively.

[0183] Suitable materials for forming the piezoelectric layer 8010 include lead zirconate titanate (PZT), aluminum nitride (AlN), magnesium lead niobate (PMN), PMN-PZT, polyvinylidene fluoride (PVDF), zinc oxide (ZnO), etc. A first electrode 8011 is disposed on the piezoelectric layer, and a second electrode 8012 is disposed between the piezoelectric layer 8010 and the film 804. By applying an AC voltage to the piezoelectric layer 8010 via the first electrode 8011 and the second electrode 8012, the piezoelectric layer 8010 can expand and contract at the frequency of the AC voltage. When the piezoelectric layer is attached to the film 804 through its lateral interface, its lateral expansion and contraction cause the film to vibrate.

[0184] In some embodiments, a piezoelectric layer 8010 is included in a film 804. For example, film 804 may include a multilayer stack including conductive layers and piezoelectric layers.

[0185] refer to Figure 15In some embodiments, device 805 includes a first conductive layer 8013, such as a metal layer, disposed on membrane 804, which is combined with a second conductive layer 8014 (such as a metal layer) and arranged such that membrane 804, located between the first conductive layer 8013 and the second conductive layer 8014 in the z-direction, forms a pair of electrodes that can be used as a capacitor. By applying an AC voltage across these electrodes, the membrane is caused to vibrate at the frequency of the AC voltage. The second conductive layer 8014 may be provided by, for example, a substrate 8015, which seals the second end 807 of cavity 803 and supports the sidewall 808. In some embodiments, substrate 8015 comprises a multilayer stack, and the second conductive layer 8014 may be provided by a layer in the multilayer stack (such as a titanium / platinum layer). In some embodiments, the second conductive layer 8014 may be provided by a buffer layer in a multilayer stack, such as in a SrRuO3 (SRO) / / La0.5Sr0.5CoO3 (LSCO) / / CeO2 / / Yttrium-stabilized zirconium oxide (YSZ) configuration.

[0186] The first conductive layer 8013 may include, for example, aluminum, silver, platinum, molybdenum, titanium, chromium, or other suitable metals. (See reference) Figure 16a An alternative transducer 301 according to various embodiments of the present invention is shown. The transducer 301 includes an ultrasonic source 302 and a cavity 303. The cavity 303 is defined at a first end 306 by a membrane 304, at a second end 307 by a second end wall 309, and by a side wall 308. The cavity 303 is formed by attaching the second end wall 309 to the side wall 308 and is capable of supporting standing waves as described above. The direction R of ultrasonic wave emission exits the membrane 304 from the side of the membrane 304 furthest from the second end wall 309. The membrane 304 is supported at its edge by a second side wall 310, which extends in the z-direction away from the membrane 304 and extends on the side of the membrane 304 furthest from the second end wall 309. The second sidewall 310 and the membrane 304 form the boundary of the opening 313, which is closed at the first end 314 by the membrane 304 and opens in the z-direction at the second end 315 opposite to the first end 314. By providing the second sidewall 310 and by attaching the second endwall 309 to the membrane 304 and the device 305, the cavity 303 can be protected from damage, including fragile components such as the membrane 304 and the device 305. Furthermore, this configuration allows for greater freedom in selecting the cavity size during manufacturing.

[0187] refer to Figure 16bIn the alternative transducer 401 according to various embodiments of the invention, at least one membrane 404 includes two adjacent membranes 4041, 4042, and corresponding means 4051, 4052 for inducing vibration of the corresponding membranes. Membranes 4041, 4042 are capable of transmitting ultrasonic waves into the same cavity 403. Membranes 4041, 4042 are adjacent to each other in the xy plane and may have the same or different coordinates in the z direction (i.e., the cavity length L may be the same or different at each membrane), and at least two corresponding means are used to induce vibration of the corresponding membranes. Cavity 403 is capable of supporting standing waves generated by at least one single membrane or by both membranes 4041, 4042. The standing waves generated by each membrane are independent of each other and may have different resonant frequencies depending on the resonant frequency of the corresponding membrane. The sidewalls 410 of the alternative transducer 401 provide first and second openings 4131, 4132, which help protect the ultrasonic source 402 from damage, as described above.

[0188] In some embodiments, three or more membranes that deliver ultrasound to the same cavity may be included in the transducer. The membranes may be arranged, for example, in an array configuration.

[0189] Although Figure 16b In the illustration, a multi-membrane configuration is shown in a transducer arrangement including an open cavity, but various embodiments of the invention include multi-membrane configurations that do not provide an open cavity, such as those similar to... Figure 16a The arrangement shown in the figure includes multiple membranes and devices supplied to the same cavity.

[0190] Various embodiments of the present invention provide an array composed of a plurality of transducers as described above. Such an array can be a one-dimensional array (i.e., a line) of transducers, suitable for obtaining two-dimensional ultrasound images. Such an array can also be a two-dimensional array of transducers, suitable for obtaining three-dimensional ultrasound images.

[0191] The use of an ultrasonic transducer or transducer array as described herein may include placing at least one membrane in contact with a liquid or gel, which serves as a transmission medium for the ultrasonic waves generated by the transducer or transducer array. (See above regarding...) Figure 12a-14 The ultrasonic transducer can be manufactured according to the following method. First, a substrate is provided. Then, a cavity is formed in the front side of the substrate, for example by deep reactive ion etching or wet etching on the top side of the substrate. Before or after realizing the cavity, a conductive layer and a piezoelectric layer are deposited on the film to form an ultrasonic source with a closed cavity.

[0192] As mentioned above Figure 15The ultrasonic transducer can be manufactured according to the following method. First, a substrate is provided. Then, a cavity is formed in the back side of the substrate, for example by deep reactive ion etching or wet etching on the back side of the substrate. Before or after realizing the cavity, a conductive layer and a piezoelectric layer are deposited on the top side of the substrate to form an ultrasonic source. Then, a second layer, wafer, or substrate is bonded or attached to the second end of the cavity by means of epoxy resin to form a closed cavity.

[0193] As mentioned above Figure 16a and 16b The ultrasonic transducer can be manufactured according to the following method. First, a substrate or wafer is provided. Then, an opening is formed in the back side of the wafer, for example by deep reactive ion etching (preferably for silicon or silicon-on-insulator substrates / wafers) or wet etching. Before or after realizing the cavity, a conductive layer and a piezoelectric layer are deposited on the top side of the film to form an ultrasonic source 802. Next, sidewalls enclosing the cavity are provided on another wafer or substrate, for example by depositing a thick conductive layer, a glass layer, and / or a silicon layer. Alternatively, both the cavity and the sidewalls can be formed by bonding a second wafer (substrate) to a first wafer, while the cavity has already been formed in the second substrate, for example by wet etching or deep reactive ion etching of a glass or silicon wafer. Finally, the cavity can be enclosed by bonding a second endwall to the sidewall of the cavity, or by etching the sidewalls already formed therein in the second substrate.

[0194] refer to Figure 17a (Cross-sectional side view of the transducer) and Figure 17b ( Figure 17a (Top view of a transducer), a method of manufacturing a transducer 801 according to various embodiments of the present invention, the transducer including a microchannel M in a sidewall 808 of the transducer near a film 804. The method includes the steps of: performing an additional etching step to form a microchannel M on the front side of the substrate or wafer before providing the film 804 on a substrate or wafer, the microchannel M extending outwardly from a cavity 8015. The film 804 is then provided by bonding a second wafer to the top of the substrate and optionally thinning the second wafer to an appropriate thickness. Finally, a further etching step is performed in the second wafer to form openings for the channels.

[0195] Alternatively, the cavity 803 can be provided on the back side of the substrate wafer via an etching process. The cavity 803 is achieved by etching through the back side of the SOI wafer. The cavity 803 is etched to a depth such that the remaining layer of the wafer at the closed end of the cavity has a thickness suitable for providing the film 804. The second end 807 of the cavity is then sealed by bonding a layer to the second end of the cavity. The microchannel is then provided on the front side of the wafer via an etching process.

[0196] Cavity 803 can be implemented using a back-side DRIE process on the SOI wafer. Cavity 803 should then be sealed with a second layer. The microchannel should be implemented on the front side of the SOI wafer using a DRIE process through the film / BOX, and, if necessary, through the handle layer of the SOI wafer (the BOX is a buried oxide layer and can be removed by another method besides DRIE). Then, except for opening 8015, the microchannel M should be sealed using some surface micromachining techniques.

[0197] refer to Figure 18a (Cross-sectional view of the transducer) and Figure 18b (Top view) A method of manufacturing a transducer 801 according to various embodiments of the present invention, the transducer including a microchannel M in a sidewall 808 of the transducer and remote from a membrane 804 in the z direction, the method comprising the steps of: providing a wafer; forming a cavity in the back side of the wafer by an etching process; forming a microchannel in the back side of the wafer by an etching process; and sealing the second end of the cavity by bonding a layer at the second end of the cavity.

[0198] refer to Figure 19a A method for manufacturing a transducer 801 according to various embodiments of the present invention, the transducer including a microchannel M in a second end wall 809 of the transducer, the method may include the following steps: first, providing a wafer; then, forming a cavity 803 on the front side of the wafer by an etching process; next, bonding a second wafer to the front side of the wafer for providing a film and optionally thinning the second wafer to an appropriate thickness. The microchannel M is then formed on the back side of the wafer by an etching process.

[0199] refer to Figure 19b A method for manufacturing a transducer 801 according to various embodiments of the present invention, the transducer including a microchannel M in a second end wall of the transducer, the method may include the following steps: first, providing a wafer; then forming a cavity on the back side of the wafer by an etching process; next, sealing the second end of the cavity by bonding or adhering a layer on the back side of the wafer; then forming the microchannel in a sealing layer 8016, for example by an etching process if the sealing layer 8016 comprises silicon, or by laser cutting if the sealing layer comprises, for example, steel or ceramic, or by any other suitable cutting method.

[0200] refer to Figure 20a and Figure 20bThe diagram illustrates a cavity 803 according to various embodiments of the invention, wherein the cavity 803 has a cross-sectional dimension measured in the xy plane, which varies in the z direction. According to a preferred embodiment of the invention, the cross-sectional dimension of the cavity 803 may not have a change of more than 10% compared to a reference cross-sectional dimension, wherein the reference cross-sectional dimension corresponds to the cross-sectional dimension of the membrane 804 measured in the xy plane. The dashed lines refer to... Figure 12a The manufacturing method shown in 14 indicates that the bottom can be integrated with the entire body or connected later as a separate layer.

[0201] It is understood that although preferred embodiments, specific structures and configurations, and materials have been discussed herein with respect to the device according to the invention, various changes or modifications in form and detail may be made without departing from the scope and technical teachings of the invention. For example, any molecular formulas given above represent only steps that may be used. Steps may be added to or removed from the methods within the scope of the invention.

[0202] By studying the accompanying drawings, this disclosure, and the appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plural. A single processor or other unit may perform the functions of several items recited in the claims. The mere fact that certain measures are stated in mutually different dependent claims does not imply that combinations of these measures cannot be advantageously used. Computer programs may be stored / distributed on suitable media (such as optical storage media or solid-state media supplied together with or as part of other hardware), but may also be distributed in other forms (such as via the Internet or other wired or wireless telecommunications systems). Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A multi-layer structure (10, 10', 50, 80, 100) for an ultrasonic transducer, comprising: Semiconductor layer stack (13, 53, 83), the semiconductor layer stack defining diode (5), A microfabricated ultrasonic transducer (MUT) layer stack is electrically connected in series with the diode and is at least partially disposed on the semiconductor layer stack. The MUT layer stack includes a conductive layer sandwiched between the semiconductor layer stack and the MUT layer stack for providing electrical contact with the diode and the MUT layer stack. Cavities (C1, C2, C3, 107) extending over regions (R1, R2, R3, R4) including at least a portion of the semiconductor layer stack and the conductive layer. The MUT layer stack includes a membrane that extends at least partially over the region.

2. The multi-layer structure of the ultrasonic transducer according to claim 1, characterized in that, Also includes: A substrate structure (101) is provided for supporting the multilayer structure. The first non-conductive layer (105) and the second non-conductive layer (106) are part of the MUT layer stack; The cavity (107) therein is a cMUT closed cavity defined by the sandwiched conductive layer, the first non-conductive layer and the second non-conductive layer.

3. The multi-layer structure of the ultrasonic transducer according to claim 2, characterized in that, It also includes a first electrode disposed in the region on at least a portion of the second non-conductive layer; and a second electrode (109) disposed in a recess in the semiconductor layer stack.

4. The multi-layer structure of the ultrasonic transducer according to claim 1, characterized in that, Also includes: A substrate structure (11) is provided to support the multilayer structure. The first semiconductor layer (14) of the semiconductor layer stack (13) is heavily doped with a dopant of a first conductivity type; The second layer is a semiconductor layer (15) or an insulating layer, wherein the semiconductor layer is a substrate doped with a dopant of the first conductivity type, and the dopant concentration is at least 10 lower than that of the first semiconductor layer. 2 times; The third semiconductor layer (16) of the semiconductor layer stack is weakly doped with a dopant of the first conductivity type; The cavity (C1) is a pMUT cavity defined by the substrate structure (11), and the region (R1) includes at least the portion of the semiconductor layer stack and the sandwiched conductive layer; as well as The MUT layer stack includes a piezoelectric layer.

5. The multi-layer structure of the ultrasonic transducer according to claim 3, characterized in that, A first portion of the sandwiched conductive layer (17) is located within the region (R1) between at least a portion of the first semiconductor layer (14) and the piezoelectric layer (18), and a second portion of the sandwiched conductive layer is disposed on at least a portion of the second semiconductor layer such that the first portion and the second portion of the sandwiched conductive layer define a first conductive layer gap (G); and the first semiconductor layer is sandwiched within the region between at least a portion of the third semiconductor layer and the first portion of the sandwiched conductive layer.

6. The multi-layer structure of the ultrasonic transducer according to claim 4, characterized in that, It also includes a fourth semiconductor layer stacked on top of the semiconductor layer, which is heavily doped with a dopant of the second conductivity type, wherein the fourth semiconductor layer is disposed on top of the third semiconductor layer, which is weakly doped with a dopant of the first conductivity type.

7. The multi-layer structure of the ultrasonic transducer according to claim 1, characterized in that, Also includes: A substrate structure (11) is provided to support the multilayer structure. The first semiconductor layer (14) of the semiconductor layer stack is heavily doped with a dopant of a first conductivity type; The second layer is an insulating layer (15); The third semiconductor layer (16) of the semiconductor layer stack is weakly doped with a dopant of the first conductivity type; The cavity (C1) is a pMUT cavity defined by the substrate structure (11), and the region includes at least the portion of the semiconductor layer stack and the sandwiched conductive layer; The MUT layer stack includes a piezoelectric layer (18) and one or more additional conductive layers.

8. The multi-layer structure of the ultrasonic transducer according to claim 4, characterized in that, The first portion of the sandwiched conductive layer (17, 56) is located between at least a portion of the piezoelectric layer and the mechanical layer (61) in the region, the mechanical layer (61) being a semiconductor layer or another insulating layer of a substrate doped with a dopant of the first conductivity type, and wherein the second portion of the sandwiched conductive layer is disposed on the mechanical layer such that the first portion and the second portion of the sandwiched conductive layer define a first conductive layer gap (G).

9. The multi-layer structure of the ultrasonic transducer according to claim 7, characterized in that, It also includes a fourth semiconductor layer stacked with the semiconductor layers heavily doped with a dopant of the second conductivity type, wherein the fourth semiconductor layer is disposed on top of the third semiconductor layer which is weakly doped with the dopant of the first conductivity type.

10. The multi-layer structure of the ultrasonic transducer according to claim 3, characterized in that, It also includes a second conductive layer (22) sandwiched between the substrate structure (11) and the semiconductor layer stack (13) outside the region.

11. The multi-layer structure of the ultrasonic transducer according to claim 3, characterized in that, The cavity is closed.

12. The multi-layer structure of the ultrasonic transducer according to claim 2, characterized in that, The substrate structure (101, 11) includes one or more of the following: a silicon wafer, a silicon-on-insulator (SOI) wafer, a silicon wafer or SOI wafer with an integrated circuit system, a semiconductor substrate, and a glass or polymer substrate with or without a thin-film transistor (TFT) circuit system.

13. The multi-layer structure of the ultrasonic transducer according to claim 1, characterized in that, The diode is provided by a field-effect transistor.

14. An ultrasonic transducer array device comprising a plurality of ultrasonic transducer multilayer structures according to any one of the preceding claims.

15. A method for manufacturing a multilayer structure of an ultrasonic transducer according to any one of claims 1 to 13, comprising the following steps: A first wafer is provided according to an array configuration, wherein the first wafer defines a semiconductor layer stack, and the semiconductor layer stack defines a diode; A second wafer is provided, the second wafer being a silicon-based wafer; The first wafer is bonded to the second wafer to define a silicon-on-insulator (SOI) wafer, wherein the second wafer defines a buried oxide (BOX) layer of the SOI wafer. The first wafer is processed to a predetermined thickness in the multilayer structure of the ultrasonic transducer; A MUT layer stack is fabricated on the diode, the MUT layer stack including a conductive layer sandwiched between the semiconductor layer stack and the MUT layer stack for providing electrical contact with the diode and the MUT layer stack; A cavity is generated over a region including at least a portion of the semiconductor layer stack and the sandwiched conductive layer.

16. Use of the ultrasonic transducer multilayer structure according to any one of claims 1 to 13 in a sensor device for measuring at least one characteristic of an object, wherein the sensor device is used for medical imaging, including cardiac imaging, obstetrics, gynecology, abdominal imaging, intravascular imaging and mammography, or for nondestructive testing of NDA, fingerprint sensor, rangefinder, gesture recognition, ultrasonic haptic feedback, ultrasonic communication or MEMS speaker.

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