Integrated MEMS-CMOS ultrasonic sensor

Abstract

Ultrasonic sensing methods with integrated MEMS-CMOS implementations are described. Embodiments include ultrasonic sensor arrays in which the PMUT structures of individual detector elements are at least partially integrated into a CMOS ASIC wafer. MEMS heating elements are integrated with the PMUT structures in the CMOS wafer by being integrated below and / or above the PMUT structures (e.g., in a protective layer). For example, embodiments can avoid wafer bonding and reduce other post-processing typically associated with fabrication of PMUT ultrasonic sensors, while also improving thermal response.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from the following applications, the entire contents of which are incorporated herein by reference:

[0003] U.S. patent application No. 17 / 477,498, filed September 16, 2021, entitled “INTEGRATED MEMS-CMOS ULTRASONIC SENSOR”;

[0004] U.S. provisional patent application with priority number 63 / 094,920, filed on October 22, 2020, and entitled “MEMS-CMOS ULTRASONIC SENSOR WITH THERMAL STABILIZATION.” Technical Field

[0005] The present disclosure relates to ultrasonic sensors, and more particularly, to integrating micro-electromechanical system (MEMS) and complementary metal-oxide semiconductor (CMOS) ultrasonic sensor components into an integrated MEMS-CMOS ultrasonic sensor element, for example, to implement a small fingerprint sensor for integration into portable electronic devices. Background Art

[0006] Various sensors can be implemented in electronic devices or systems to provide certain desired functions. Some sensors detect static types of user information such as fingerprints, iris patterns, etc. Other sensors detect dynamic types of user information such as body temperature, pulse, etc. Various types of sensors can be used for many different purposes. In some cases, such sensors help to achieve user authentication, for example, to protect personal data and / or prevent unauthorized access to user devices. In other cases, such sensors can help monitor changes in the user's physical and / or mental state, such as for health tracking, biofeedback, etc. To support these and other purposes, various types of sensors can communicate with, or even be integrated with, devices and systems such as portable or mobile computing devices (e.g., laptop computers, tablet computers, smart phones), gaming systems, data storage systems, information management systems, large-scale computer control systems, and / or other computing environments.

[0007] As one set of examples, authentication on an electronic device or system can be performed by one or more forms of biometric identifiers, which can be used alone or as a supplement to conventional password authentication methods. A common form of biometric identifier is a person's fingerprint pattern. A fingerprint sensor can be built into an electronic device to read the user's fingerprint pattern so that the device can only be unlocked by an authorized user of the device through authentication of the authorized user's fingerprint pattern. Another example of a sensor for an electronic device or system is a biomedical sensor in a wearable device such as a wristband device or watch, which detects biological properties of the user, such as the properties of the user's blood, heartbeat. Typically, different sensors can be provided in an electronic device to implement different sensing operations and functions. Such sensing operations and functions can be used as independent authentication methods and / or in combination with one or more other authentication methods such as password authentication.

[0008] Different types of sensors have been integrated with mobile electronic devices in different ways and to varying degrees. For example, many modern smartphones have integrated accelerometers, cameras, and even fingerprint sensors. However, each such sensor integration involves careful consideration and adherence to technical, design, and other constraints, such as limitations imposed on physical space, power, heat generation, cost, external access (e.g., for sensors that rely on physical contact or optical access), interference with interface elements (e.g., displays, buttons, etc.), and so on. Summary of the Invention

[0009] Systems and methods are provided for integrating microelectromechanical systems (MEMS) and complementary metal oxide semiconductor (CMOS) components into an integrated MEMS-CMOS ultrasonic sensor element. This integrated MEMS-CMOS sensor element design can avoid certain conventional wafer bonding and related issues by integrating some or all of the MEMS sensor components into a CMOS ASIC wafer. Some embodiments reduce or eliminate post-processing associated with forming PMUT detector elements. Some embodiments further include integrated temperature stabilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings, which are incorporated in and constitute a part of this document, illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the invention.

[0011] Figure 1 Shown is a block diagram of a sensor environment that serves as context for the various embodiments described herein.

[0012] Figure 2A and Figure 2BAn example of a portable electronic device with a sensing system integrated as an under-display sensor in accordance with various embodiments is shown.

[0013] Figure 3 Illustrative details of a conventional type of ultrasonic sensor are shown, which is used in some conventional ultrasonic fingerprint sensor embodiments.

[0014] Figures 4A to 4F Illustrative techniques for fabricating embodiments of an integrated micro-electromechanical systems and complementary metal oxide semiconductor (MEMS-CMOS) ultrasonic sensor element are shown, according to a first set of embodiments.

[0015] Figures 5A to 5C Illustrative techniques for fabricating embodiments of an integrated MEMS-CMOS ultrasonic sensor element according to a second set of embodiments are shown.

[0016] Figures 6A to 6C Illustrative techniques for fabricating embodiments of an integrated MEMS-CMOS ultrasonic sensor element according to a third set of embodiments are shown.

[0017] Figure 7 A flow chart is shown of an illustrative method for fabricating an integrated MEMS-CMOS ultrasonic sensor element according to various embodiments described herein.

[0018] Figure 8A and Figure 8B Shown are side and top views, respectively, of a first illustrative embodiment of a novel integrated MEMS-CMOS ultrasonic sensor element with integrated temperature stabilization.

[0019] Figure 9 A second illustrative embodiment of a novel integrated MEMS-CMOS ultrasonic sensor element with integrated temperature stabilization is shown.

[0020] Figure 10 A third illustrative embodiment of a novel integrated MEMS-CMOS ultrasonic sensor element with integrated temperature stabilization is shown.

[0021] Figure 11 A fourth illustrative embodiment of a novel integrated MEMS-CMOS ultrasonic sensor element with integrated temperature stabilization is shown.

[0022] Figure 12 A flow chart is shown of an illustrative method for fabricating a piezoelectric micromachined ultrasonic transducer (PMUT) according to various embodiments described herein.

[0023] In the drawings, similar components and / or features may have the same reference number. Furthermore, various components of the same type may be distinguished by following the reference number with a second reference number that distinguishes between the similar components. If only the first reference number is used in the specification, the description applies to any of the similar components having the same first reference number, regardless of the second reference number. DETAILED DESCRIPTION

[0024] In the following description, many specific details are provided to provide a thorough understanding of the present invention. However, it should be understood by those skilled in the art that the present invention can be practiced without one or more of these details. In other examples, features and techniques known in the art will not be described for brevity.

[0025] Steering Figure 1 , a block diagram of a sensor environment 100 is shown as context for various embodiments described herein. The sensor environment 100 is shown as including a processor-controlled system 120 and an ultrasonic sensor system 130. The processor-controlled system 120 is generally intended to represent any suitable system or systems for providing any suitable features of the sensor environment 100 in addition to the features of the ultrasonic sensor system 130. For example, in a smartphone, the processor-controlled system 120 may include subsystems for providing telephony and communication features, display features, user interaction features, application processing features, and the like. Embodiments of the sensor environment 100 may include one or more processors 110. In some embodiments, the one or more processors 110 are shared between the processor-controlled system 120 and the ultrasonic sensor system 130. In other embodiments, the processor-controlled system 120 uses the one or more processors 110, and the ultrasonic sensor system 130 has its own dedicated processor or processors 110.

[0026] An embodiment of the ultrasonic sensor system 130 includes a sensor array 140 and a sensor control circuit 150. The sensor array 140 can be implemented as an ultrasonic transducer array. Each ultrasonic transducer or each transducer group can be considered a detector element 142. The sensor control circuit 150 can direct the detector elements 142 to transmit and receive ultrasonic signals. In some embodiments, some or all of the sensor array 140 include acoustic transducers configured to serve as both acoustic wave sources (acoustic transmitters) and return acoustic signal receivers (acoustic receivers). In other embodiments, some or all of the sensor array 140 include acoustic wave transmitters and return acoustic signal wave receivers as separate ultrasonic transducers.

[0027] Each detector element 142 (or each acoustic receiver detector element 142) can detect a response to ultrasonic signaling, such as reflected acoustic signal information. For example, in the context of a fingerprint sensor, a finger is placed on a detection surface and bombarded with ultrasonic waves. Ultrasonic waves tend to pass through (e.g., be absorbed, scattered, etc.) the fingerprint skin in contact with the detection surface, but tend to be reflected when encountering air at the detection surface. Therefore, reflections tend to be weaker in the fingerprint ridge area (where the skin contacts the surface) than in the fingerprint groove area (where the skin does not contact the surface). By mapping the detector elements 142 to corresponding physical locations in the sensor array 140, the detected ultrasonic responses can be effectively used to generate a pixel (or group of pixels) of imaging information. The pixels of imaging information can be communicated by the sensor control circuitry 150 to the processor(s) 110 or otherwise used to generate useful output data, such as a fingerprint image.

[0028] For the sake of illustration, Figure 2A and Figure 2B An example of a portable electronic device 200 having a sensing system 130 integrated as an under-display sensor 230 is shown in accordance with various embodiments. The portable electronic device 200 may be Figure 1 Embodiments of the sensor environment 100 may be implemented, for example, by integrating the sensor environment 100 into a smartphone. For example, a single portable electronic device 200 may include one or more integrated ultrasonic sensor systems 130 as a fingerprint sensor, blood pressure or heart rate sensor, and / or for other purposes. Although illustrated as a smartphone, the portable electronic device 200 may be implemented as any suitable portable electronic device 200, such as a tablet computer, a laptop computer, an e-reader, a wrist-worn or other wearable device, and the like. Further, although illustrated as a portable device, the embodiments of the ultrasonic sensor described herein may also be implemented in non-portable devices, such as access control systems, automated teller machines, and the like.

[0029] As shown in the portable electronic device 200 ( Figure 2AAs shown in a top view of the portable electronic device 200 (indicated by reference numeral 200a in the figure), an embodiment of the portable electronic device 200 includes a housing 210 that integrates various features such as a display screen 220 and one or more physical buttons 235. Any other suitable interface elements may be included in the portable electronic device 200 and integrated with the housing 210 (or integrated within the housing). In this environment, the ultrasonic sensor system 130 can be implemented in any suitable location and / or integrated with any suitable components. For example, the ultrasonic sensor system 130 can be integrated with physical buttons at a dedicated location on the periphery of the display 220, on the underside or edge of the portable electronic device 200, etc. In some embodiments, as shown, the ultrasonic sensor system 130 is implemented as an under-display sensor 230. In this embodiment, the ultrasonic sensor system 130 is disposed below the display 220 and is configured to use a dedicated portion of the display 220 as a detection area 225.

[0030] For example, as the portable electronic device 200 (in Figure 2B As shown in the side view of FIG20 (indicated by reference numeral 200b in FIG20 ), the display screen 220 may include multiple layers, including multiple functional display layers 222 and a top cover layer 224. The multiple functional display layers 222 may implement any suitable type of display, such as a liquid crystal display (LCD), an organic light-emitting diode (OLED) display, a quantum light-emitting diode (QLED) display, a touch-sensitive display (e.g., to implement a capacitive touch screen), etc. The top cover layer 224 may be any suitable transparent and / or protective layer disposed above the multiple functional display layers 222. In some embodiments, the top cover layer 224 is configured to provide certain characteristics, such as transmissive and / or conductive properties, to support optical, acoustic, capacitive, pressure sensing, and / or other characteristics of the display screen 220. Embodiments of the under-display sensor 230 may be mounted below some or all of the multiple functional display layers 222. For example, the detector elements 142 of the sensor array 140 are configured to transmit ultrasonic waves in the direction of the detection area 225 through the functional display layer 222 and the top covering layer 224 (on which the finger 240 can be placed), and are configured to detect reflected ultrasonic wave information from the detection area 225 through the top covering layer 224 and the functional display layer 222.

[0031] Figure 3Illustrative details of a conventional ultrasonic sensor 300 are shown, which is used in some conventional ultrasonic fingerprint sensor embodiments. Examples of such conventional ultrasonic sensors 300, including descriptions of their fabrication and integration into portable electronic devices, are described in U.S. patent application Ser. No. 15 / 968,420, entitled “Ultrasound Fingerprint Sensing and Sensor Fabrication.” Such conventional ultrasonic sensors 300 are often manufactured by fabricating an application-specific integrated circuit (ASIC) (e.g., as a CMOS structured chip) and adding the MEMS ultrasonic sensor components to the ASIC. For example, the fabricated CMOS ASIC is finished with a passivation layer, etc., and the additional components are coupled to the wafer only via contacts (e.g., pads, etc.) intentionally exposed as part of the fabrication process. This subsequent addition of the sensor components to the fabricated ASIC is generally referred to in the art as “post-processing” the ASIC. In some such post-processing embodiments, the MEMS sensor wafer is fabricated separately, and the MEMS wafer is wafer-bonded (e.g., using eutectic bonding) to the CMOS ASIC to form the ultrasonic sensor 300. In other such post-processing embodiments, the MEMS component is directly bonded to the CMOS ASIC.

[0032] For example, by preparing electrodes for each transducer element on the ASIC, the ultrasonic transducer can be arranged into a sensing array built on a CMOS ASIC. A single piece or several large pieces of ultrasonic transducer material (e.g., piezoelectric material) are bonded or coated onto the ASIC. The corresponding electrodes can be connected. The transducer material is divided or etched to produce discrete ultrasonic transducer elements. This design can be configured to achieve the appropriate resonant frequency. The gaps between the discrete ultrasonic transducer elements can be filled with appropriate filling materials such as appropriate epoxy resins. The top electrodes of the discrete ultrasonic transducers can then be formed. Depending on the drive mode, each top electrode can include a single or several or a row or column of discrete ultrasonic transducer elements. When a high voltage is applied to the transducer, ultrasonic waves are generated. For example, a low voltage circuit is connected to the transducer to receive the electrical signal induced by the returned ultrasonic wave. For some embodiments using separate transmitting and sensing transducers, separate ultrasonic transducer layer structures can be manufactured (e.g., for generating ultrasonic signals and for sensing ultrasonic signals, respectively). For example, in some embodiments, the top structure is an acoustic signal receiver having an ultrasonic sensing transducer for detecting returning ultrasonic signals, while a separate bottom structure is an acoustic signal generator having an ultrasonic transmitter transducer for generating ultrasonic signals toward the top sensing area. Some embodiments (e.g., where the transducer is configured to both generate and sense ultrasonic signals) further include on-board circuitry (e.g., as part of the sensor control circuit 150) for controlling transmit and receive functions, such as including a multiplexed driver and receiver architecture.

[0033] Two cross-sectional images 350 of an illustrative conventional detector element of a conventional ultrasonic sensor 300 are shown. As shown in image 350a, the detector element includes a CMOS ASIC as a bottom layer. The MEMS sensor is then created by bonding a bottom electrode to the ASIC, building a piezoelectric material layer onto the bottom electrode, and building a top electrode onto the piezoelectric material layer. The MEMS sensor components form a PMUT detector element. In a typical application (e.g., by Figure 2A and Figure 2B In the illustrated application, the PMUT detector elements may be disposed beneath one or more device layers and a silicone layer (e.g., polydimethylsiloxane (PDMS)), etc. For context, the ridges of the fingertip are shown in contact with the top surface of the silicone layer.

[0034] As shown in image 350b, during transmission, an electric pulse is applied to the electrode, thereby mechanically deforming the piezoelectric material layer, thereby vibrating the air according to the ultrasonic acoustic signal. As can be seen in the two images 350, the PMUT is made to maintain or form a low pressure (e.g., vacuum) gap below the bottom electrode. This gap can help guide ultrasonic energy toward the silicone layer and away from the CMOSASIC. During reception, the reflected sound wave causes the mechanical deformation of the piezoelectric material layer, which induces an electrical signal. The generated electrical signal can then be processed to obtain the desired data. For example, as shown, the ultrasonic sensor 300 can convert analog electrical signals into digital data, which can be used to generate fingerprint images or any other suitable data.

[0035] Various problems can be attributed to the type of post-processing used by conventional approaches, such as the type of post-processing of the ultrasonic sensor 300. One such problem is that separate wafer processing is often performed by different manufacturers in different facilities. For example, a CMOS ASIC may be produced by a traditional CMOS foundry, while a PMUT is often produced by a specialized MEMS manufacturer. Separate manufacturing can cause misalignment and related problems, and resolving such problems can increase manufacturing costs and lead times, can force increased manufacturing tolerances, etc. Further, reliance on post-processing can increase the occurrence of bonding defects (particularly in mass production, and particularly in the case of separate wafer manufacturers). Further, separating the bonded wafers can create leakage in the low-voltage gap of the PMUT, the bonding material can increase resistance and / or other parasitics, and / or the bonding can otherwise degrade the performance of the sensor. Further, bonding can often increase the height of the sensor.

[0036] The embodiments described herein include various novel techniques for integrating MEMS and CMOS components into integrated MEMS-CMOS designs. This integrated MEMS-CMOS design can avoid wafer bonding and related issues by integrating some or all of the MEMS sensor components into the CMOS ASIC wafer. Some embodiments reduce or eliminate post-processing associated with the formation of PMUT detector elements.

[0037] Figures 4A to 4F illustrative techniques for fabricating an embodiment of an integrated MEMS-CMOS ultrasonic sensor element 400 according to a first set of embodiments are shown. The integrated MEMS-CMOS ultrasonic sensor element 400 may be Figure 1 Implementation of a detector element 142 of a sensor array 140. Typically, a MEMS sensor component includes a "bottom" electrode (e.g., of a first metal), a "top" electrode (e.g., of a second metal), and a piezoelectric transducer. Figures 4A to 4FIn the embodiment of the present invention, the integrated MEMS-CMOS ultrasonic sensor element 400 is manufactured by partially integrating the first and second electrode paths 410 into the CMOS substrate 405. For example, such integration is performed in a CMOS foundry or the like by depositing metal for the electrode paths 410 on a metal layer as part of an integrated circuit system of a CMOS wafer.

[0038] The integration of the electrode paths 410 includes patterning each electrode path 410 to couple with a corresponding electrode control circuit system (not shown). In some embodiments, the electrode control circuit system is also integrated with the CMOS wafer (as part of the integrated circuit chip), and the control terminal 412 of each electrode path 410 is electrically routed and coupled to its respective control circuit system via conductive paths and / or other components integrated with the CMOS substrate 405. In other embodiments, each electrode path 410 is electrically routed and coupled to one or more corresponding input / output nodes (e.g., exposed electrical contacts, electrical pads, pins, solder joints, etc.) via conductive paths and / or other components integrated with the CMOS substrate 405, and the electrode control circuit system can be electrically coupled to the electrode paths 410 via the corresponding input / output nodes. The integration of the electrode paths 410 also includes manufacturing each electrode path 410 to terminate at a respective exposed metal contact 414 at the end of processing of the CMOS wafer. After the CMOS wafer is processed (eg, by a CMOS foundry), there is a pair of exposed metal contacts 414 at the location of each integrated MEMS-CMOS ultrasonic sensor element 400 .

[0039] Steering Figure 4B After processing the CMOS wafer, post-processing can be performed to fabricate the remainder of the integrated MEMS-CMOS ultrasonic sensor element 400. As shown, a sacrificial layer 420 can be deposited on top of the CMOS substrate 405 in the region between the exposed metal contacts 414 of the two electrode paths 410. A first electrode 416a (the bottom electrode or lower electrode in the orientation of the drawing) is deposited by depositing a first metal on top of the sacrificial layer 420. The first metal is deposited such that a portion of the deposited metal is electrically coupled to the first exposed metal contact 414a. In some embodiments, the metal of the first electrode 416a is substantially the same as the metal of the exposed metal contact 414, such that the first electrode 416a is effectively an extension of the first electrode path 410a. In some embodiments, the first electrode 416a is deposited as a metal layer with a thickness between 0.5 and 1 micrometers, and the sacrificial layer 420 is deposited to a thickness of approximately 2 micrometers.

[0040] Steering Figure 4C, the sacrificial layer 420 can be removed to form the acoustic cavity 425, and the piezoelectric element 430 can be fabricated. The sacrificial layer 420 can be made of silicon oxide, silicon nitride, or any other suitable material to facilitate its removal to form the acoustic cavity 425 below the PMUT material. In some embodiments, the metal of the first electrode 416a is patterned to open small release holes for etching the underlying sacrificial layer 420, thereby forming the acoustic cavity 425 (e.g., using hydrofluoric acid, etc.).

[0041] In some embodiments, the acoustic cavity 425 is a "vacuum" cavity. In such embodiments, after etching the acoustic cavity 425, another layer of material is deposited on the first electrode 416a in the conformal layer to seal the release holes created for etching the sacrificial layer 420. In one such embodiment, the metal of the first electrode 416a is deposited as a conformal layer to seal the release holes created for etching the sacrificial layer. In another such embodiment, the piezoelectric film material (e.g., of the piezoelectric element 430) is deposited in the conformal layer to seal the release holes created for etching the sacrificial layer. The deposition of the conformal layer can be performed at low pressure to facilitate creating the acoustic cavity 425 as a "vacuum" cavity. As used herein, the term "vacuum cavity" is intended to include any cavity having a pressure low enough to provide desired acoustic properties according to specific design criteria, even if such a cavity may not be at a complete vacuum pressure (e.g., at zero pressure or negative pressure). For example, some etching processes are performed in a low pressure environment, and sealing the cavity in the same environment (eg, as part of the same manufacturing process) may maintain a sufficiently low pressure in the cavity to be considered a vacuum cavity herein.

[0042] The piezoelectric element 430 is formed by depositing a piezoelectric thin film on top of the first electrode 416a (and the acoustic cavity 425). The piezoelectric element 430 is patterned to form a piezoelectric transducer. In some embodiments, the active piezoelectric transducer is formed as a patterned thin film layer of aluminum nitride (AlN) or any other suitable material. In some embodiments, the piezoelectric element 430 is approximately one micron thick (e.g., substantially the same thickness as the first electrode 416a). In some embodiments, the piezoelectric element 430 helps seal the acoustic cavity 425.

[0043] Steering Figure 4D, a second electrode 416b is deposited by depositing a second metal on top of the piezoelectric element 430 (e.g., a top electrode or upper electrode in the orientation of the figure). The metals of the first and second electrodes 416 can be the same or different. The second metal is deposited so that a portion of the deposited metal is electrically coupled to the second exposed metal contact 414b (i.e., thereby electrically coupling the second electrode 416b to the second electrode path 410b). In some embodiments, the metal of the second electrode 416b is substantially the same as the metal of the second exposed metal contact 414b, so that the second electrode 416b is actually an extension of the second electrode path 410b. In some embodiments, the second electrode 416b is deposited as a metal layer with a thickness between 0.5-1 microns; substantially the same thickness as the first electrode 416a. Thus, the first electrode 416a and the second electrode 416b are patterned to form an electrode element, wherein the piezoelectric element 430 is sandwiched between the first electrode and the second electrode.

[0044] Steering Figure 4E In some embodiments, one or more additional layers (generally shown as additional layer 450) are deposited on the wafer. In some such embodiments, the one or more additional layers 450 include one or more protective layers. For example, in an embodiment configured for use as a fingerprint sensor, a protective layer having a matched acoustic impedance close to that of human skin can be deposited across the entire wafer. In some embodiments, the protective layer is made of polysilicon (e.g., PDMS) and is at least approximately 5-7 microns thick. In some embodiments, the surface of the sensor wafer is then planarized and / or otherwise finished.

[0045] Steering Figure 4F , showing that according to Figures 4A to 4E Illustrative simplified top view of a fabricated integrated MEMS-CMOS ultrasound sensor element 400. An illustrative overlap pattern can be seen in the top view, where the PMUT structures overlap to form a region directly above the acoustic cavity 425 where the piezoelectric element 430 is sandwiched between the first electrode 416a and the second electrode 416b.

[0046] Figures 5A to 5C illustrative techniques for fabricating an embodiment of an integrated MEMS-CMOS ultrasonic sensor element 500 according to a second set of embodiments are shown. The integrated MEMS-CMOS ultrasonic sensor element 500 may be Figure 1 Implementation of the detector elements 142 of the sensor array 140. Figures 4A to 4F As in , a MEMS sensor component typically includes a "bottom" electrode (e.g., of a first metal), a "top" electrode (e.g., of a second metal), and a piezoelectric transducer. Figures 5A to 5CIn the embodiment of the present invention, the integrated MEMS-CMOS ultrasonic sensor element 500 is manufactured by fully integrating the first electrode path 410 (including the first electrode 416a portion of the first electrode path 410) and partially integrating the second electrode path 410b into the CMOS substrate 405. For example, such integration is performed in a CMOS foundry or the like by depositing metal for the electrode path 410 on a metal layer as part of an integrated circuit system of a CMOS wafer.

[0047] Integration of the electrode paths 410 includes patterning each electrode path 410 to couple with corresponding electrode control circuitry (not shown), as shown in FIG. Figure 4A Similar to what is described. Figure 4A , Figure 5A The integration of the second electrode path 410b in the embodiment includes manufacturing the second electrode path 410b to terminate at the exposed metal contact 414b at the end of processing the CMOS wafer. Figure 4A Different, Figure 5A The fabrication of the complete first electrode path 410 (including the fabrication of the first electrode 416a) is shown as part of processing a CMOS wafer. As shown, during the fabrication of the CMOS wafer (e.g., at a CMOS foundry), the metal of the first electrode 416a is deposited and patterned in the last metal layer of the CMOS wafer. The integration of the first electrode 416a can include patterning a sacrificial layer (e.g., of silicon oxide, etc.), depositing the metal of the first electrode 416a over the sacrificial layer, patterning a release hole in the first electrode 416a, and etching the sacrificial layer using the release hole to form an acoustic cavity 425 below the first electrode 416a. As described above, in some embodiments, a conformal layer (e.g., of the metal of the first electrode 416a and / or the material of the piezoelectric element 430) can be used to seal the release hole to form the acoustic cavity 425 as a "vacuum" cavity. Therefore, after processing of the CMOS wafer is completed, there is a fully formed and exposed first electrode 416a (patterned over the acoustic cavity 425) of the first electrode path 410a and an exposed metal contact 414b of the second electrode path 410b at the location of each integrated MEMS-CMOS ultrasonic sensor element 500.

[0048] Steering Figure 5B and Figure 5C After processing the CMOS wafer, post-processing may be performed to fabricate the remaining parts of the integrated MEMS-CMOS ultrasonic sensor element 500 . Figure 5B and Figure 5C The rest of the process can be similar to the one described above. Figures 4C to 4EThe piezoelectric element 430 can be formed by depositing a piezoelectric thin film on top of the first electrode 416a (and the acoustic cavity 425) and patterning the thin film material to form a piezoelectric transducer. The second electrode 416b (e.g., the top electrode or upper electrode in the orientation of the figure) is deposited by depositing a second metal on top of the piezoelectric element 430, such that a portion of the deposited metal is electrically coupled to the second exposed metal contact 414b (i.e., thereby electrically coupling the second electrode 416b to the second electrode path 410b). Figure 5C One or more additional layers (generally shown as additional layer 450) are optionally deposited on the wafer. In some embodiments, the surface of the sensor wafer is then planarized and / or otherwise finished. The resulting integrated MEMS-CMOS ultrasonic sensor element 500 may be similar to Figures 4A to 4F The integrated MEMS-CMOS ultrasonic sensor element 400 is shown in FIG. 4 , wherein the PMUT structures overlap to form a region directly above the acoustic cavity 425 , with the piezoelectric element 430 sandwiched between the first electrode 416 a and the second electrode 416 b .

[0049] Figures 6A to 6C illustrative techniques for fabricating an embodiment of an integrated MEMS-CMOS ultrasonic sensor element 600 according to a third set of embodiments are shown. The integrated MEMS-CMOS ultrasonic sensor element 600 may be Figure 1 Implementation of the detector elements 142 of the sensor array 140. Figures 4A to 5C As in , a MEMS sensor component typically includes a "bottom" electrode (e.g., of a first metal), a "top" electrode (e.g., of a second metal), and a piezoelectric transducer. Figures 6A to 6C In the embodiment of the present invention, the integrated MEMS-CMOS ultrasonic sensor element 600 is manufactured by fully integrating the first electrode path 410 (including its first electrode 416a portion) and the second electrode path 410b (including its second electrode 416b portion) into the CMOS substrate 405. For example, such integration is performed in a CMOS foundry or the like by depositing metal for the electrode path 410 on a metal layer as part of an integrated circuit system of a CMOS wafer.

[0050] Integration of the electrode paths 410 includes patterning each electrode path 410 to couple with corresponding electrode control circuitry (not shown), as shown in FIG. Figure 4A described. Figure 4A Unlike in FIG, the electrode paths 410 are not fabricated to terminate at exposed metal contacts 414. Figure 5A , Figure 6AThe fabrication of the CMOS wafer in FIG. 4 includes the fabrication of the complete first electrode path 410a (including the fabrication of the first electrode 416a). As shown, during the fabrication of the CMOS wafer (e.g., in a CMOS foundry), the metal of the first electrode 416a is deposited and patterned in the last metal layer of the CMOS wafer. The integration of the first electrode 416a may include patterning a sacrificial layer (e.g., of silicon oxide, etc.), depositing the metal of the first electrode 416a over the sacrificial layer, patterning a release hole in the first electrode 416a, and etching the sacrificial layer using the release hole to form the acoustic cavity 425 below the first electrode 416a. As described above, in some embodiments, the release hole can be sealed using a conformal layer (e.g., of the metal of the first electrode 416a and / or the material of the piezoelectric element 430) to form the acoustic cavity 425 as a "vacuum" cavity. Figure 6A The fabrication of the CMOS wafer in FIG. 4 also includes the fabrication of the complete second electrode path 410 b (including the fabrication of the second electrode 416 b). Like the first electrode 416 a, the metal for the second electrode 416 b is deposited and patterned in the final metal layer of the CMOS wafer during fabrication. Thus, upon completion of the processing of the CMOS wafer, each integrated MEMS-CMOS ultrasonic sensor element 500 has a fully formed and exposed first electrode 416 a of the first electrode path 410 a (patterned above the acoustic cavity 425) and a fully formed and exposed second electrode 416 b of the second electrode path 410 b.

[0051] Steering Figure 6B and Figure 6C After processing the CMOS wafer, post-processing may be performed to fabricate the remaining parts of the integrated MEMS-CMOS ultrasonic sensor element 600 . Figure 6B and Figure 6C The rest of the process can be similar to the one described above. Figure 4C and Figure 4E The piezoelectric element 430 may be formed by depositing a piezoelectric thin film on top of the first electrode 416a (and the acoustic cavity 425) and the second electrode 416b and patterning the thin film material to form a piezoelectric transducer. Figure 6C One or more additional layers (generally shown as additional layer 450) are optionally deposited on the wafer. In some embodiments, the surface of the sensor wafer is then planarized and / or otherwise finished. The resulting integrated MEMS-CMOS ultrasonic sensor element 600 is Figures 4A to 5CThe ultrasonic sensor element of FIG. 60 differs from the integrated MEMS-CMOS ultrasonic sensor element in that the integrated MEMS-CMOS ultrasonic sensor element 600 has both the first electrode 416a and the second electrode 416b on the same side of the piezoelectric element 430. In this embodiment, as shown, the electrode 416 does not sandwich the piezoelectric transducer; rather, the electrode 416 is fabricated to contact the piezoelectric element 430 at multiple locations. For example, the first electrode 416a can be formed as a circular area, with the second electrode 416b formed as concentric rings around at least a portion of the first electrode 416a.

[0052] Figure 7 A flow chart is shown of an illustrative method 700 for fabricating an integrated MEMS-CMOS ultrasonic sensor element according to various embodiments described herein. The embodiment begins at stage 704 by depositing a first metal and a second metal in a set of integrated metal layers of a CMOS wafer, at least partially during processing of the CMOS wafer. At stage 708, the embodiment may pattern the first metal to form a first electrode path having a first control terminal configured to couple with electrode control circuitry and terminating at a first electrode disposed on top of a sacrificial material layer. At stage 712, the embodiment may pattern the second metal to form a second electrode path having a second control terminal configured to couple with electrode control circuitry and terminating at a second electrode.

[0053] At stage 716, embodiments may etch a layer of sacrificial material through the first electrode to form an acoustic cavity beneath the first electrode. At stage 720, embodiments may deposit a layer of piezoelectric film on top of at least the first electrode and pattern the piezoelectric film to form a piezoelectric element such that both the first electrode and the second electrode contact the piezoelectric element. Some embodiments may also include, at stage 722, depositing one or more protective layers on top of at least the piezoelectric element (e.g., and in embodiments where the second electrode is on top of the piezoelectric element, on top of the second electrode). Embodiments may also include flattening and / or otherwise finishing the sensor element.

[0054] In some embodiments, patterning the first metal at stage 708 includes patterning the first metal during processing of the CMOS wafer to form a first portion of a first electrode path that terminates at a first exposed metal contact on an uppermost metal layer of the CMOS wafer (e.g., Figure 4A Depositing an additional first metal of a first electrode path in a layer on top of the sacrificial material layer to electrically couple with the first exposed metal contact (e.g., as Figure 4B and patterning the additional first metal after depositing the additional first metal to form a first electrode (e.g., also as Figure 4BIn some such embodiments, after processing of the CMOS wafer and before depositing the additional first metal, a sacrificial metal layer may be deposited at stage 706, such as Figure 4B In some such embodiments, patterning the second metal at stage 712 includes patterning the second metal during processing of the CMOS wafer to form a first portion of a second electrode path that terminates at a second exposed metal contact on an uppermost metal layer of the CMOS wafer (e.g., Figure 4A Depositing an additional second metal of a second electrode path in a layer on top of the piezoelectric element to electrically couple with the second exposed metal contact (e.g., as Figure 4D and patterning the additional second metal after depositing the additional second metal to form a second electrode, thereby sandwiching the piezoelectric element between the first electrode and the second electrode (e.g., also as shown); Figure 4D shown).

[0055] In some embodiments, depositing the first metal at stage 704 includes depositing a portion of the first metal in an uppermost metal layer of the CMOS wafer; and patterning the first metal at stage 408 includes patterning the portion of the first metal during processing of the CMOS wafer to form a first electrode (e.g., as shown in FIG. 1 ) on the uppermost metal layer. Figure 5A or Figure 6A In some such embodiments, a sacrificial metal layer may be deposited in a CMOS wafer layer below the top metal layer prior to depositing the portion of the first metal in the top metal layer at stage 706; such that etching integrates the acoustic cavity in the CMOS wafer, e.g. Figure 5A or Figure 6A In some such embodiments, patterning the second metal at stage 712 includes patterning the second metal during processing of the CMOS wafer to form a first portion of a second electrode path that terminates at a second exposed metal contact on an uppermost metal layer of the CMOS wafer (e.g., Figure 5A Depositing an additional second metal of a second electrode path in a layer on top of the piezoelectric element to electrically couple with the second exposed metal contact (e.g., as Figure 5B and patterning the additional second metal after depositing the additional second metal to form a second electrode, thereby sandwiching the piezoelectric element between the first electrode and the second electrode (e.g., also as shown); Figure 5BIn other such embodiments, depositing the second metal in stage 704 includes depositing a portion of the second metal in an uppermost metal layer of the CMOS wafer; and patterning the second metal in stage 712 includes patterning the portion of the second metal during processing of the CMOS wafer to form a second electrode on the uppermost metal layer adjacent to the first electrode (e.g., as shown). Figure 6A In such an embodiment, depositing the piezoelectric film layer at stage 720 may be performed such that the piezoelectric element is patterned on top of both the first electrode and the second electrode (e.g., as shown). Figure 6B shown).

[0056] In some embodiments, etching the sacrificial material layer in stage 716 includes patterning release holes in the portion of the first metal that forms the first electrode, and etching the sacrificial material layer through the release holes to form the acoustic cavity. Some such embodiments may further include, in stage 718, depositing a conformal layer on top of the first electrode after etching in stage 716 to seal the release holes, thereby forming the acoustic cavity as a low pressure (e.g., vacuum) cavity. In some embodiments, the conformal layer is a first metal layer used to form the first electrode. In other embodiments, the conformal layer is a layer of piezoelectric thin film material (e.g., a separate layer of piezoelectric thin film material, or the piezoelectric element itself).

[0057] Temperature stability

[0058] One limitation of piezoelectric-based (i.e., PMUT-type) ultrasonic sensors is that the piezoelectric transducer (e.g., an active thin film layer of aluminum nitride) may be sensitive to temperature changes. As described above, the piezoelectric transducer in such a sensor operates by mechanical deformation. When transmitting, the piezoelectric transducer converts an electrical signal into a mechanical vibration, which produces an ultrasonic wave. When receiving (detecting), the piezoelectric transducer detects the reflected ultrasonic wave as a mechanical vibration and converts it back into an electrical signal. Typically, the reflected ultrasonic wave has relatively little energy and tends to produce a relatively weak signal. As the temperature of the piezoelectric transducer drops (e.g., in a cold environment), the piezoelectric material may harden. This can suppress the amount of mechanical deformation caused by the reflected ultrasonic energy, which can further weaken the detected signal.

[0059] Some embodiments may integrate MEMS heating elements into the ultrasonic sensor design to heat the sensor when and where appropriate. As described below, MEMS heating can be configured to gain and lose thermal energy very quickly, such as within a few milliseconds (e.g., or tens of milliseconds). Some embodiments may be configured to maintain the temperature of at least the piezoelectric transducer at around 10 degrees Celsius, and or provide heating when the temperature is detected to drop to a certain threshold level below 10 degrees Celsius (or above any desired temperature threshold). MEMS heating can also be configured to consume only a few milliwatts and operate within a very short time window to minimize the impact on power supply (e.g., on battery life) even across relatively large arrays.

[0060] Some embodiments implement MEMS heating by forming a MEMS heating element using a metal layer in a CMOS wafer. Other embodiments additionally or alternatively include a MEMS heating element above the piezoelectric transducer (such as in a protective layer). Some embodiments implement a separate MEMS heater as part of each (e.g., some or all) of the detector elements in the production sensor array. Other embodiments implement a single MEMS heater for a group of multiple detector elements (e.g., for zone heating). Some embodiments further include heating one or more additional layers near the sensor. For example, a PDMS layer, a top layer of glass, a display layer, etc. may also be affected by temperature changes that may affect the responsiveness, resonance, and / or other properties of the ultrasonic sensor. Therefore, some embodiments include heating elements to heat those additional layers.

[0061] Figure 8A and Figure 8B 1 and 2 show a side view and a top view, respectively, of a first illustrative embodiment of a novel integrated MEMS-CMOS ultrasonic sensor element 800 with integrated temperature stabilization. The integrated MEMS-CMOS ultrasonic sensor element 800 is substantially as described in reference Figure 4E The sensor element 400 is shown as described above, but with the addition of an integrated MEMS heating element 810. Although shown in this context, the MEMS heating element 810 may alternatively be used with any Figure 5C or Figure 6C In some embodiments, the MEMS heating element 810 is integrated with a conventional PMUT architecture, such as the embodiment shown in FIG. Figure 3 Those described.

[0062] As described herein, a MEMS ultrasonic sensor component generally includes a first electrode 416a (as part of a first electrode path 410a), a second electrode 416b (as part of a second electrode path 410b), a piezoelectric element 430, and an acoustic cavity 425. Figures 4A to 6C As described, some or all of the electrode paths 410 and / or the acoustic cavity 425 can be integrated during the manufacture of the CMOS wafer (e.g., integrated with one or both electrodes 416 in the top metal layer of the CMOS wafer). As described above, the cavity can be an air cavity, a low-pressure cavity, or a vacuum cavity. A piezoelectric film (piezoelectric element 430) can be deposited on top of at least the first electrode 416a. In some embodiments, the piezoelectric element 430 is also deposited on top of the second electrode 416b. In other embodiments, the second electrode 416b is deposited on top of the piezoelectric element 430 so that the piezoelectric element 430 is sandwiched between the first electrode 416a and the second electrode 416b. In some embodiments, one or more additional layers, such as one or more protective layers 450 (e.g., made of polysilicon), are deposited on the wafer; and the surface of the sensor wafer can then be flattened and / or otherwise finished.

[0063] The MEMS heating element 810 includes a metal deposited in a metal layer of a CMOS wafer and patterned to form a metal heating element. The metal heating element can be patterned into a heating wire, a heating coil, or any other suitable metal structure. The ends of the MEMS heating element 810 can be coupled to a heating control circuit system (not explicitly shown). The heating control circuit system can include any suitable electronic components to controllably heat the MEMS heating element 810. For example, the heating control circuit system can apply a voltage across the MEMS heating element 810, and the resistance of the MEMS heating element 810 can cause the metal heating element to heat up and radiate thermal energy. In some embodiments, the MEMS heating element 810 is patterned to terminate at one or more exposed electrical contacts that can be coupled to a non-integrated embodiment of the heating control circuit system. In other embodiments, some or all of the heating control circuit system is integrated with the CMOS wafer, and the MEMS heating element 810 is patterned to be electrically coupled to the integrated circuit system.

[0064] The MEMS heating element 810 may be located in any suitable position to provide heating to some or all of the piezoelectric elements 430. The illustrated embodiment shows the MEMS heating element 810 disposed directly below the piezoelectric element 430 and the acoustic cavity 425. Other embodiments of the MEMS heating element 810 may include one or more MEMS heating sub-elements disposed above and / or below some or all of the piezoelectric elements 430.

[0065] In the illustrated embodiment, the MEMS heating element 810 is implemented as a micro-serpentine metal coil embedded in a CMOS wafer. For example, the MEMS heater metal wire is formed in a serpentine path on a metal layer deposited during the fabrication of the CMOS wafer. Figure 8B An illustrative overlapping pattern can be seen in the top view of FIG. As shown, all PMUT structures overlap to form a region directly above the acoustic cavity 425, with the piezoelectric element 430 sandwiched between the first electrode 416a and the second electrode 416b; and a serpentine MEMS heater wire (MEMS heating element 810) can be seen disposed at least below the cavity (MEMS heating element 810 is drawn with a solid line for clarity, but is below the other structures shown in the top view). The heating wire can be deposited in any suitable shape or pattern. For example, the wire can be formed into a spiral shape rather than a serpentine shape.

[0066] According to different embodiments, the MEMS heating element 810 can be implemented in various ways. For example, Figure 9 A second illustrative embodiment of a novel integrated MEMS-CMOS ultrasonic sensor element 900 with integrated temperature stabilization is shown. The integrated MEMS-CMOS ultrasonic sensor element 900 is similar to the Figure 6C An integrated MEMS-CMOS ultrasonic sensor element 600 is shown. Figure 9 The MEMS heating element 810 is similar to Figure 8A The heating element is shown, but with an additional layer of MEMS heating wires (i.e., as multiple MEMS heating sub-elements). For example, the MEMS heater wires are formed from multiple metal layers deposited during the fabrication of the CMOS wafer, and multiple MEMS heater coils are connected in parallel or series to optimize heat transfer to the piezoelectric layer, thereby stabilizing its temperature. In such an embodiment, each layer can be patterned in the same or different manner. In one embodiment, each layer is patterned as a serpentine metal coil, where each layer is oriented differently relative to its adjacent layers and / or has differently spaced coils. In another embodiment, one layer is patterned as a serpentine coil and another layer is patterned as a spiral coil.

[0067] Figure 10 A third illustrative embodiment of a novel integrated MEMS-CMOS ultrasonic sensor element 1000 with integrated temperature stabilization is shown. The sensor element 1000 is similar to the CMOS ultrasonic sensor element 1000 except that the MEMS heating element 810 is formed above the piezoelectric element 430. Figure 9The illustrated sensor element 900. For example, a CMOS wafer is fabricated with one or more exposed contacts for a MEMS heating element 810, and the MEMS heating element 810 is deposited on top of the piezoelectric element 430 (e.g., directly, or with one or more material layers deposited between the MEMS heating element and the piezoelectric element) and patterned to electrically couple with the exposed contacts in post-processing. As with the MEMS heating element 810 implemented below the piezoelectric element 430, the MEMS heating element 810 implemented above the piezoelectric element 430 can be implemented in one or more layers, one or more shapes (e.g., serpentine, spiral, mesh, etc.), one or more thicknesses, one or more coil spacings, and / or any other suitable manner to optimize heat transfer to the piezoelectric element 430 and thereby stabilize its temperature.

[0068] Figure 11 A fourth illustrative embodiment of a novel integrated MEMS-CMOS ultrasonic sensor element 1100 with integrated temperature stabilization is shown. The sensor element 1100 is essentially Figure 9 and Figure 10 The MEMS heating element 810 is implemented as a plurality of MEMS heating sub-elements. A group of MEMS heating sub-elements of the MEMS heating element 810 is formed on a single metal layer below the PMUT structure (e.g., Figure 8A in) or on multiple metal layers (e.g., Figure 9 For example, the MEMS heater metal lines are formed from one or more metal layers deposited during fabrication of the CMOS wafer. The second set of MEMS heating subelements of the MEMS heating element 810 is deposited on top of the piezoelectric transducer (e.g., as Figure 10 As desired, multiple MEMS heater coils may be connected in parallel, in series, or in any suitable manner to heat the piezoelectric element 430.

[0069] Figure 12A flow chart of an illustrative method 1200 for fabricating a PMUT according to various embodiments described herein is shown. An embodiment of method 1200 may begin at stage 1204 by depositing a first metal to form a first electrode path, such that a portion of the first metal at one end of the first electrode path is deposited over a sacrificial material layer, and patterning the portion of the first metal to form a first electrode. At stage 1208, an embodiment may etch the sacrificial material layer to form an acoustic cavity below the first electrode. At stage 1212, an embodiment may deposit a piezoelectric film layer on top of at least the first electrode, and deposit the piezoelectric film to form a piezoelectric element. At stage 1216, an embodiment may deposit a second metal to form a second electrode path, and patterning a portion of the second metal at one end of the second electrode path to form a second electrode, such that the piezoelectric element is in electrical contact with the second electrode.

[0070] At stage 1220, an embodiment may deposit a third metal and pattern the third metal to form a MEMS heating element such that at least a portion of the MEMS heating element is positioned directly above and / or below the piezoelectric element, the MEMS heating element being further patterned to couple with a heating control circuit by which the heating element is selectively actuated to provide heating to the piezoelectric element. In some embodiments, the third metal is patterned to form the MEMS heating element to include at least one serpentine heating wire and / or at least one spiral heating wire. In some embodiments, the third metal is patterned to form the MEMS heating element to include: a first one or more MEMS heating sub-elements positioned below the acoustic cavity to provide heating to the piezoelectric element from below; and a second one or more MEMS heating sub-elements positioned above the acoustic cavity to provide heating to the piezoelectric element from above. In some embodiments, the third metal is patterned to form the MEMS heating element to include a stack of MEMS heating sub-elements positioned directly above and / or below the piezoelectric element.

[0071] In some embodiments, at stage 1222, a MEMS heating element (e.g., one or more MEMS heating sub-elements) is electrically coupled to a heating control circuit system. In some such embodiments, the heating control circuit is integrated into the CMOS wafer, and the deposited third metal is on one or more metal layers of the CMOS wafer, such that the MEMS heating element is integrated into the CMOS wafer. The MEMS heating element can be further patterned to couple to the heating control circuit via integrated electrical wiring (e.g., metal layer wiring, vias, etc.) of the CMOS wafer. In other such embodiments, the heating control circuit is integrated into the CMOS wafer and is electrically accessible via exposed metal contacts of the CMOS wafer, and the MEMS heating element can be electrically coupled to the heating control circuit via the exposed metal contacts.

[0072] Although this disclosure contains many details, these details should not be interpreted as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to a particular embodiment of a particular invention. Certain features described in this patent document in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, the various features described in the context of a single embodiment may also be implemented in multiple embodiments individually or in any suitable subcombination. Furthermore, although features may be described above as functioning in certain combinations and even initially claimed as such, one or more features from the claimed combination may in some cases be separated from the combination, and the claimed combination may be directed to a subcombination or variations of the subcombination.

[0073] Similarly, while operations are depicted in a particular order in the drawings, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desired results. Furthermore, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

[0074] Only a few implementations and examples are described, and other implementations, enhancements, and variations can be made based on what is described and illustrated in this patent document.

[0075] Unless specifically indicated to the contrary, references to "a," "an," or "the" are intended to mean "one or more." Ranges may be expressed herein as from "about" one specified value and / or to "about" another specified value. The term "about," as used herein, means approximately, within a certain range, roughly, or around. When the term "about" is used in conjunction with a numerical range, the term modifies the range by extending the limits above and below the stated numerical value. The term "about" is typically used herein to modify a numerical value above and below the stated value by 10%. When such a range is expressed, another embodiment includes from a specific value and / or to another specified value. Similarly, when a value is expressed as an approximation by using the antecedent "about," it is understood that the specified value forms another embodiment. It should be further understood that the endpoints of each range are included in the range.

[0076] All patents, patent applications, publications, and descriptions mentioned herein are incorporated by reference in their entirety for all purposes. No admission is made that any of the content is prior art.

Claims

1. A method for fabricating an integrated micro-electromechanical system (MEMS) and complementary metal oxide semiconductor (CMOS) ultrasonic sensor element, the method comprising: depositing a first metal and a second metal at least partially in a set of integrated metal layers of a CMOS wafer during processing of the CMOS wafer; patterning the first metal to form a first electrode path having a first control terminal configured to couple with electrode control circuitry and terminating at a first electrode disposed on top of a sacrificial material layer; patterning the second metal to form a second electrode path having a second control terminal configured to couple with the electrode control circuitry and terminating at a second electrode; etching the sacrificial material layer through the first electrode to form an acoustic cavity below the first electrode; as well as depositing a piezoelectric thin film layer on top of at least the first electrode, and patterning the piezoelectric thin film to form a piezoelectric element such that both the first electrode and the second electrode contact the piezoelectric element; Etching the sacrificial material layer includes: patterning a release hole in a portion of the first electrode formed of the first metal; etching the sacrificial material layer through the release hole to form the acoustic cavity; The method further includes: depositing a conformal layer of the first metal or depositing a conformal layer of the piezoelectric film on top of the first electrode after the etching to seal the release hole, thereby forming the acoustic cavity as a low-pressure cavity; A third metal is deposited and patterned to form a MEMS heating element such that at least a portion of the MEMS heating element is positioned above and / or below the piezoelectric element. The MEMS heating element is further patterned to couple with a heating control circuit.

2. The method according to claim 1, wherein Patterning the first metal includes: patterning the first metal during processing of the CMOS wafer to form a first portion of the first electrode path, the first portion terminating at a first exposed metal contact on an uppermost metal layer of the CMOS wafer; depositing an additional first metal of the first electrode path in a layer on top of the sacrificial material layer to electrically couple with the first exposed metal contact; and The additional first metal is patterned after depositing the additional first metal to form the first electrode.

3. The method of claim 2, further comprising: The sacrificial material layer is deposited after processing of the CMOS wafer and before depositing the additional first metal.

4. The method according to claim 2, wherein: Patterning the second metal includes: patterning the second metal during processing of the CMOS wafer to form a first portion of the second electrode path, the first portion terminating at a second exposed metal contact on an uppermost metal layer of the CMOS wafer; depositing an additional second metal of the second electrode path in a layer on top of the piezoelectric element to electrically couple with the second exposed metal contact; and The additional second metal is patterned after depositing the additional second metal to form the second electrode, thereby sandwiching the piezoelectric element between the first electrode and the second electrode.

5. The method of claim 1, wherein: Depositing the first metal includes depositing a portion of the first metal in an uppermost metal layer of the CMOS wafer; and Patterning the first metal includes patterning the portion of the first metal during processing of the CMOS wafer to form the first electrode on the uppermost metal layer.

6. The method of claim 5, further comprising: The sacrificial material layer is deposited in a layer of the CMOS wafer below the topmost metal layer before depositing the portion of the first metal in the topmost metal layer, such that the etching integrates the acoustic cavity in the CMOS wafer.

7. The method according to claim 5, wherein: Patterning the second metal includes: patterning the second metal during processing of the CMOS wafer to form a first portion of the second electrode path, the first portion terminating at a second exposed metal contact on an uppermost metal layer of the CMOS wafer; depositing an additional second metal of the second electrode path in a layer on top of the piezoelectric element to electrically couple with the second exposed metal contact; and The additional second metal is patterned after depositing the additional second metal to form the second electrode, thereby sandwiching the piezoelectric element between the first electrode and the second electrode.

8. The method of claim 5, wherein: Depositing the second metal includes depositing a portion of the second metal in an uppermost metal layer of the CMOS wafer; Patterning the second metal includes patterning the portion of the second metal during processing of the CMOS wafer to form the second electrode on the uppermost metal layer next to the first electrode; and The piezoelectric film layer is deposited such that the piezoelectric element is patterned on top of both the first electrode and the second electrode.

9. The method of claim 1, wherein: Patterning the second metal forms the second electrode that is not disposed on top of the sacrificial material layer.

10. The method of claim 1, wherein: The piezoelectric film layer is an aluminum nitride layer.

11. The method of claim 1 , further comprising: One or more protective layers are deposited on top of at least the piezoelectric element.

12. An integrated micro-electromechanical system and complementary metal oxide semiconductor (MEMS)-CMOS ultrasonic sensor element, comprising: a first electrode path at least partially integrated within a set of metal layers of a CMOS wafer, the first electrode path having a first control terminal configured to couple with electrode control circuitry, and the first electrode path terminating at a first electrode disposed on top of the acoustic cavity; The first electrode is patterned in the topmost metal layer of the CMOS wafer; and the acoustic cavity is formed by etching a sacrificial material layer below the first electrode through a release hole patterned in the first electrode, so that the acoustic cavity is integrated in the CMOS wafer; a piezoelectric film layer disposed on top of at least the first electrode and patterned to form a piezoelectric element; A conformal layer of the first electrode path or a conformal layer of the piezoelectric film is provided on top of the first electrode to seal the release hole; as well as a second electrode path at least partially integrated within the set of metal layers of the CMOS wafer, the second electrode path having a second control terminal configured to be coupled to the electrode control circuitry, and the second electrode path terminating at a second electrode in contact with the piezoelectric element; A MEMS heating element, at least a portion of which is positioned above and / or below the piezoelectric element, the MEMS heating element being patterned to be coupled to a heating control circuit.

13. The integrated MEMS-CMOS ultrasonic sensor element according to claim 12, wherein: The first electrode path includes: a first portion integrated within the set of metal layers of the CMOS wafer and terminating at an exposed metal contact in an uppermost metal layer of the CMOS wafer opposite the first control terminal; and A second portion is not integrated within the CMOS wafer, the second portion is electrically coupled to the exposed metal contact and is patterned to form the first electrode.

14. The integrated MEMS-CMOS ultrasonic sensor element according to claim 12, wherein: The second electrode is patterned in an uppermost metal layer of the CMOS wafer next to the first electrode; and The piezoelectric film layer is disposed on top of both the first electrode and the second electrode.

15. The integrated MEMS-CMOS ultrasonic sensor element according to claim 12, wherein: The first electrode contacts a bottom side of the piezoelectric element, and the second electrode contacts a top side of the piezoelectric element, such that the piezoelectric element is sandwiched between the first and second electrodes.

16. The integrated MEMS-CMOS ultrasonic sensor element according to claim 12, wherein: The first electrode and the second electrode are in contact with the same side of the piezoelectric element.

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