Ultrasonic sensor array and method of forming an ultrasonic transducer

Abstract

An ultrasonic sensor array includes a plurality of ultrasonic transducers, each transducer including a piezoelectric element. Each of the transducers includes an electret element, a receiving (Rx) layer configured to exhibit a first d33 resonant mode coefficient, and a transmitting (Tx) layer configured to exhibit a second d33 resonant mode coefficient, the first coefficient being different from the second coefficient. The transducers are disposed on a flexible substrate.

Description

[0001] Priority Statement

[0002] This application claims priority to U.S. non-provisional application filed June 27, 2019, entitled “ULTRASONIC SENSOR ARRAY”, serial number 16 / 455,472, which has been assigned to the assignee of this application and is expressly incorporated herein by reference. Technical Field

[0003] This disclosure relates to ultrasonic sensor arrays for biosensing, imaging and / or touch recognition, and more specifically, to sensor arrays having ultrasonic transducers configured with electret material layers exhibiting different electromechanical hysteresis characteristics, flexible substrates and / or separate transmitting and receiving layers. Background Technology

[0004] Ultrasonic sensor systems can use a transmitter to generate ultrasonic waves and transmit them through a transmission medium toward an object to be detected and / or imaged. The ultrasonic transmitter can be operatively coupled to an ultrasonic sensor array configured to detect portions of the ultrasonic waves reflected from the object. At each material interface where an ultrasonic pulse encounters it, a portion of the pulse may be reflected. In some implementations, ultrasonic pulses can be generated by starting and stopping the transmitter for short time intervals (e.g., less than 1 microsecond). Ultrasonic sensor systems can include biosensors, such as fingerprint or handprint sensors, and / or other ultrasonic imaging applications.

[0005] Thin-film piezoelectric acoustic transducers are attractive candidates for such applications, including biosensors such as fingerprint sensors, touch and gesture detection devices, and ultrasonic imaging devices. The piezoelectric layer can convert vibrations caused by the reflection of ultrasonic waves into an electrical output signal. In some implementations, the ultrasonic sensor system also includes a thin-film transistor (TFT) layer that may include an array of sensor pixel circuitry, which may, for example, amplify the electrical output signal generated by the piezoelectric layer. The piezoelectric layer may include one or more of leadzirconate titanate (PZT), single crystal lead magnesium niobate-lead titanate (PMN-PT), PZT ceramic, polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE), and / or another PVDF copolymer.

[0006] In some applications, a two-dimensional array of numerous transducer elements can be integrated with a pressure plate (“cover plate” or “cover glass”) of a display screen configured for user interaction, and disposed behind or “below” the pressure plate. For example, the display screen may provide a user touch interface and / or be integrated into a personal electronic device such as a mobile phone or tablet computer, and may comprise multiple layers of stacked glass, plastic, and / or adhesive layers.

[0007] For at least biosensing and touch and gesture detection, large-area (e.g., greater than 10 square inches) sensor arrays and / or flexible arrays are required. Such increased-area sensor arrays may be necessary for portable devices such as mobile phones and tablets, especially in applications where physical buttons need to be avoided. Without currently disclosed technologies, increased-area sensor arrays exhibit higher capacitance and require increased Tx / Rx sensitivity, or (adversely) high-voltage (>100 volts) transmitters operating at frequencies of 10 MHz or higher. Therefore, improved arrangements of ultrasonic transducers for such sensor arrays are needed. Summary of the Invention

[0008] The systems, methods, and apparatus disclosed herein each have some innovative aspects, and no single aspect is solely responsible for the desired properties disclosed herein.

[0009] One innovative aspect of the subject matter described in this disclosure relates to an ultrasonic sensor array comprising: a plurality of ultrasonic transducers, each transducer including a piezoelectric element. Each of the transducers includes an electret element, a receiving (Rx) layer configured to present a first d33 resonant mode coefficient, and a transmitting (Tx) layer configured to present a second d33 resonant mode coefficient, the first coefficient being different from the second coefficient. The transducers are disposed on a flexible substrate.

[0010] In some examples, the electret component is made of a fluoropolymer.

[0011] In some examples, the Tx layer includes the piezoelectric component and the Rx layer includes the electret component.

[0012] In some examples, the first d33 resonant mode coefficients have opposite signs to the second d33 resonant mode coefficients.

[0013] In some examples, the array further includes a flexible electronic layer, and the electret member is configured to be flexible. In some examples, the flexible electronic layer is a flexible organic light-emitting diode display.

[0014] In some examples, the piezoelectric component is formed of a ferroelectric material.

[0015] In some examples, the piezoelectric component is formed from a copolymer.

[0016] In some examples, at least some of the multiple transducers are electrically connected in series.

[0017] In some examples, the array has a surface area of ​​10 square inches or more.

[0018] According to some implementations, a method of forming an ultrasonic transducer includes: forming a receiving (Rx) layer; forming a transmitting (Tx) layer; and coupling the Rx layer to the Tx layer. The ultrasonic transducer is disposed on a flexible substrate and includes an electret member. The Rx layer is configured to exhibit a first d33 resonant mode coefficient, and the Tx layer is configured to exhibit a second d33 resonant mode coefficient, the first coefficient being different from the second coefficient.

[0019] In some examples, the electret component is made of a fluoropolymer.

[0020] In some examples, the Tx layer includes a piezoelectric member. In some examples, the piezoelectric member is formed of a ferroelectric material. In some examples, the piezoelectric member is formed of a copolymer.

[0021] In some examples, the first d33 coefficient has the opposite sign to the second d33 coefficient.

[0022] According to some implementations, an ultrasonic sensor array includes a plurality of ultrasonic transducers, each transducer including an electret member, and each of the transducers including a piezoelectric member. Each of the transducers includes a receiver (Rx) layer configured to present a first d33 resonant mode coefficient and a transmitter (Tx) layer configured to present a second d33 resonant mode coefficient, the first coefficient being different from the second coefficient. The transducers are disposed on a flexible substrate.

[0023] In some examples, the electret component is configured as an acoustic transducer.

[0024] In some examples, the piezoelectric component is made of ferroelectric material.

[0025] In some examples, the piezoelectric component is made of a copolymer.

[0026] In some examples, the Tx layer includes the piezoelectric component and the Rx layer includes the electret component.

[0027] In some examples, the first d33 resonant mode coefficients have opposite signs to the second d33 resonant mode coefficients.

[0028] In some examples, the array further includes a flexible electronic layer, and the electret member is configured to be flexible. In some examples, the flexible electronic layer is a flexible organic light-emitting diode display.

[0029] In some examples, at least some of the multiple transducers are electrically connected in series.

[0030] In some examples, the array has a surface area of ​​10 square inches or more. Attached Figure Description

[0031] Details of one or more implementations of the subject matter described herein are set forth in this disclosure and in the accompanying drawings. Other features, aspects, and advantages will become apparent upon reading this disclosure. Note that the relative dimensions of the drawings and other figures in this disclosure may not be drawn to scale. Dimensions, thicknesses, arrangements, materials, etc., shown and described in this disclosure are by way of example only and should not be construed as limiting. The same reference numerals and names in the various drawings indicate the same elements.

[0032] Figures 1A-1B show examples of piezoelectric ultrasonic transducers.

[0033] Figures 2A-2C show cross-sectional views of various configurations of the PMUT ultrasonic sensor array.

[0034] Figure 3A simplified cross-section of an ultrasonic transducer according to some implementations is shown.

[0035] Figure 4 A simplified cross-section of a touch sensor according to another implementation is shown.

[0036] Figure 5 A simplified cross-section of an ultrasonic sensor according to yet another implementation is shown.

[0037] Figure 6 A simplified cross-section of a hybrid ultrasonic transducer stack according to some implementations is shown.

[0038] Figure 7 Examples of techniques for improving Rx sensitivity are shown, based on some implementation methods.

[0039] Figure 8 An example of the process flow for manufacturing ultrasonic transducers is shown.

[0040] Figure 9 A front view of an example of an electronic device including an ultrasonic sensing system, according to some implementations, is shown.

[0041] Figure 10A A block diagram representation of the components of an example ultrasonic sensing system according to some implementations is shown.

[0042] Figure 10B A block diagram representation of components of an example electronic device according to some implementations is shown.

[0043] Specific implementation method

[0044] For the purpose of describing the innovative aspects of this disclosure, the following description pertains to certain implementations. However, those skilled in the art will readily recognize that the teachings herein can be applied in a variety of different ways. The described implementations can be implemented in any device, apparatus, or system including millimeter-wave band communication capabilities. Furthermore, the described implementations are contemplated to be included in or associated with a variety of electronic devices, such as, but not limited to: mobile phones, cellular phones supporting multimedia internet, mobile TV receivers, wireless devices, smartphones, smart cards, wearable devices such as bracelets, armbands, wristbands, rings, headbands, and patches, Bluetooth devices, personal data assistants (PDAs), wireless email receivers, handheld or portable computers, netbooks, notebooks, smartbooks, tablets, printers, copiers, scanners, fax machines, GPS receivers / navigators, cameras, digital media players (such as MP3 players), camcorders, game consoles, watches, clocks, calculators, television monitors, flat panel displays, e-readers, etc. Applications include: devices such as e-readers, mobile health devices, computer monitors, automatic displays (including odometer and speedometer displays), cockpit controls and / or displays, steering wheels, camera view displays (e.g., displays for rearview cameras in vehicles), electronic photographs, electronic billboards or signs, projectors, building structures, microwave ovens, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable storage chips, washing machines, dryers, washer / dryer systems, ATMs, parking timers, packages (e.g., in electromechanical systems (EMS) applications including microelectromechanical systems (MEMS) applications and non-EMS applications), aesthetic structures (e.g., displaying images on a piece of jewelry or clothing), and various EMS devices. The teachings herein can also be applied to applications such as, but not limited to, electronic switching devices, radio frequency filters, sensors, accelerometers, gyroscopes, motion sensing devices, magnetometers, inertial components for consumer electronics, components for consumer electronics, varactor diodes, liquid crystal devices, electrophoresis equipment, drive schemes, manufacturing processes, and electronic test equipment. Therefore, this teaching is not intended to be limited to the implementations described only in the accompanying drawings, but has broad applicability as will be readily apparent to those skilled in the art.

[0045] Referring to Figure 1A, a conventional piezoelectric ultrasonic transducer 100 can be configured to include a piezoelectric layer stack 110 and a mechanical layer 130, which are arranged to form a diaphragm (hereinafter referred to as a "PMUT diaphragm" or "deformable diaphragm") supported by an anchoring structure 170 on a cavity 120. The piezoelectric layer stack 110 includes a piezoelectric layer 115, a lower electrode 112, and an upper electrode 114. In the illustrated implementation, the lower electrode 112 is disposed below the piezoelectric layer 115 and close to the cavity 120, while the upper electrode 114 is disposed above the piezoelectric layer 115 and close to the surface of the piezoelectric layer 115 opposite to the cavity 120. The cavity 120 can be formed in or on a substrate 160. The substrate 160 can be or include, for example, a silicon wafer, a silicon-on-insulator (SOI) wafer, a silicon or SOI wafer with integrated circuits, a semiconductor substrate, or a glass or polymer substrate with thin-film transistor (TFT) circuitry. In some implementations, the substrate can be a flexible substrate, such as a thin layer of polyimide (PI), polyethylene naphthalate (PEN) or polyethylene terephthalate (PET), or a flexible substrate with InGaZnO (IGZO) circuitry.

[0046] Referring now to Figure 1B, during operation, the piezoelectric layer stack 110 and mechanical layer 130 can be bent and vibrated in response to a time-varying excitation voltage applied by transceiver circuitry 1010 across upper electrode 114 and lower electrode 112. Thus, one or more ultrasonic pressure waves 122 having frequencies, for example, in the ultrasonic band, can propagate into the propagation medium 124. In some implementations, the propagation medium 124 may include air, a pressure plate, a converge glass, a device housing, or an acoustic coupling or matching layer. The piezoelectric layer stack 110 can also receive reflected ultrasonic pressure waves from objects in the propagation medium and convert the received ultrasonic pressure waves into electrical signals that can be read by transceiver circuitry 1010. The deformable diaphragm on cavity 120 can be bent and vibrated in response to the impact of reflected ultrasonic pressure waves on the surface of the PMUT, thereby generating mechanical stress and strain in the PMUT diaphragm and surface charges on the surface of the piezoelectric layer that can be detected by the circuitry below. In some implementations, the lower electrode 112 (sometimes referred to herein as the reference electrode) may be grounded, connected to a constant bias voltage (e.g., a reference voltage), or connected to a multi-level bias signal, such as a receiver bias voltage that may be provided by the transceiver circuit 1010.

[0047] The PMUT array can be addressable for wavefront beamforming, beam control, receiver-side beamforming, and / or selective readout of the returned signal. For example, individual columns, rows, sensor pixels, and / or groups of sensor pixels can be individually addressable. The control system can control the transmitter array to generate a wavefront of a specific shape, such as a planar, circular, or cylindrical wavefront. The control system can control the amplitude and / or phase of the transmitter array to produce constructive or destructive interference at desired locations. For example, the control system can control the amplitude and / or phase of the transmitter array to produce constructive interference at one or more locations where a touch or gesture has been detected or may be detected.

[0048] In some implementations, and in some examples, the PMUT device may be co-fabricated on or within a thin-film transistor (TFT) circuit or CMOS circuitry on the same substrate, which may be a silicon, SOI, glass, or plastic substrate. The TFT substrate may include row and column addressing electronics, multiplexers, local amplification stages, and control circuitry. In some implementations, interface circuitry including driver and sensing stages may be used to stimulate the PMUT device and detect responses from the same device. In other implementations, a first PMUT device may function as an acoustic or ultrasonic transmitter, and a second PMUT device may function as an acoustic or ultrasonic receiver. In some configurations, different PMUT devices may be capable of low-frequency and high-frequency operation (e.g., for gesture and fingerprint detection). In other configurations, the same PMUT device may be used for both low-frequency and high-frequency operation. In some implementations, the PMUT may be fabricated using a silicon wafer with active silicon circuitry fabricated within the silicon wafer. The active silicon circuitry may include electronics for enabling the PMUT or PMUT array to function.

[0049] In some implementations, the PMUT array can be configured as an ultrasonic sensor array. Figures 2A-2C show cross-sectional views of various configurations of a conventional PMUT ultrasonic sensor array. Figure 2A depicts an ultrasonic sensor array 200a with PMUTs as transmitting and receiving elements, which can be used as, for example, an ultrasonic fingerprint sensor, an ultrasonic touchpad, or an ultrasonic imager. PMUT sensor elements 262 on the PMUT sensor array substrate 260 can emit and detect ultrasonic waves. As shown, ultrasonic waves 264 can be emitted from at least one PMUT sensor element 262. Ultrasonic waves 264 can travel through a propagation medium, such as an acoustic coupling medium 265, and a pressure plate 290a, toward an object 202, such as a finger or stylus, located on the outer surface of the pressure plate 290a. A portion of the ultrasonic waves 264 can be emitted through the pressure plate 290a and into the object 202, while a second portion can be emitted back from the surface of the pressure plate 290a toward the sensor element 262. The amplitude of the reflected wave can depend in part on the acoustic properties of the object 202. The reflected waves can be detected by sensor element 262, from which an image of object 202 can be acquired. For example, using a sensor array with a pitch of approximately 50 micrometers (approximately 500 pixels per inch), the ridges and valleys of a fingerprint can be detected. An acoustic coupling medium 265, such as an adhesive, gel, compliant layer, or other acoustic coupling material, can be provided to improve the coupling between the array of PMUT sensor elements 262 disposed on sensor array substrate 260 and the pressure plate 290a. The acoustic coupling medium 265 can facilitate the transmission of ultrasonic waves to and from sensor element 262. The pressure plate 290a may include layers of materials such as glass, plastic, sapphire, metal, metal alloy, or other pressure plate materials. An acoustic impedance matching layer (not shown) may be disposed on the outer surface of the pressure plate 290a. The pressure plate 290a may include a coating (not shown) on its outer surface.

[0050] Figure 2B depicts an ultrasonic sensor and display array 200b having PMUT sensor elements 262 and display pixels 266 co-fabricated on a sensor and display substrate 260. Sensor elements 262 and display pixels 266 may co-occur in each cell of the cell array. In some implementations, sensor elements 262 and display pixels 266 may be fabricated side-by-side within the same cell. In some implementations, a portion or all of sensor elements 262 may be fabricated above or below display pixels 266. A pressure plate 290b may be located above sensor elements 262 and display pixels 266 and may serve as or include a cover lens or cover glass. The cover glass may comprise one or more layers of material such as glass, plastic, or sapphire, and may include settings for a capacitive touchscreen. An acoustic impedance matching layer or coating (not shown) may be disposed on the outer surface of pressure plate 290b. Ultrasonic waves 264 may be emitted and received from one or more sensor elements 262 to provide imaging capability of an object 202, such as a stylus or finger, placed on pressure plate 290b. The pressure plate 290b is substantially transparent to allow a user to see the optical light emanating from the array of display pixels 266 through it. The user can selectively touch a portion of the pressure plate 290b, and this touch can be detected by the ultrasonic sensor array. For example, biometric information such as fingerprint information can be acquired when the user touches the surface of the pressure plate 290b. An acoustic coupling medium 265, such as an adhesive, gel, or other acoustic coupling material, can be provided to improve the acoustic, optical, and mechanical coupling between the sensor array substrate 260 and the cover glass. In some implementations, the coupling medium 265 can be a liquid crystal material, which can be used as part of a liquid crystal display (LCD). In LCD implementations, a backlight (not shown) can be optically coupled to the sensor and display substrate 260. In some implementations, the display pixels 266 can be part of an active-matrix organic light-emitting diode (AMOLED) or OLED display with luminescent display pixels. In some implementations, the ultrasonic sensor and display array 200b can be used for display purposes as well as for touch, stylus, or fingerprint detection.

[0051] Figure 2C depicts an ultrasonic sensor and display array 200c, where a sensor array substrate 260a is located behind a display array substrate 260b. An acoustic coupling medium 265a can be used to acoustically couple the sensor array substrate 260a to the display array substrate 260b. An optical and acoustic coupling medium 265b can be used to optically and acoustically couple the sensor array substrate 260a and the display array substrate 260b to a cover lens or cover glass 290c, which can also be used as a fingerprint sensor. An acoustic impedance matching layer or other coating (not shown) can be disposed on the outer surface of the cover glass 290c. Ultrasonic waves 264 emitted from one or more sensor elements 262 can travel through the display array substrate 260b and the cover glass 290c, be reflected from the outer surface of the cover glass 290c, and travel back towards the sensor array substrate 260a, where the reflected ultrasonic waves can be detected and image information acquired. In some implementations, the ultrasonic sensor and display array 200c can be used to provide visual information to the user, as well as to detect touch, stylus, or fingerprint from the user. Alternatively, a PMUT sensor array can be formed on the back side of the display array substrate 260b. Alternatively, a sensor array substrate 260a having the PMUT sensor array can be attached to the back side of the display array substrate 260b, wherein, for example, using an adhesive layer or adhesive material (not shown), the back side of the sensor array substrate 260a is directly attached to the back side of the display array substrate 260b.

[0052] This disclosure alleviates problems arising from the use of large-area sensor arrays for biosensing and touch and gesture detection. Such enlarged-area sensor arrays may be necessary for portable devices such as mobile phones and tablets, especially in applications where physical buttons must be avoided. Without the currently disclosed technology, enlarged-area sensor arrays exhibit higher capacitance and require increased Tx / Rx sensitivity, or (adversely) high-voltage (>100 volts) transmitters operating at frequencies of 10 MHz or higher. Therefore, improved arrangements of ultrasonic transducers for such sensor arrays are needed. One such arrangement disclosed below includes a hybrid piezoelectric-electret sensor with high sensitivity. In some implementations, the electret layer can be patterned to form an array of electret members. Further enhancement of receiving sensitivity can be obtained by cascading two or more such electret members. In some implementations, the electret members can be formed from a fluoropolymer such as polytetrafluoroethylene (PTFE) (e.g., Teflon™).

[0053] Furthermore, for some applications, flexible and / or wearable devices are desirable for more convenient human-computer interaction. To realize flexible and / or wearable devices, sensor arrays can be configured with flexible layers (including substrates) while simultaneously maintaining at least electromechanical coupling efficiency. Therefore, flexible electret microsensor arrays and flexible electronics are anticipated in some implementations.

[0054] In some implementations, the electret material can be configured as a passive layer in an array of micromechanical ultrasonic transducers. For example, a high-sensitivity hybrid sensor structure comprising a piezoelectric emitter layer and an electret receiver is anticipated.

[0055] Finally, in some implementations, each transducer includes a receiving layer exhibiting a first d33 resonant mode and a transmitting layer exhibiting a second d33 resonant mode, the first d33 resonant mode being different from the second d33 resonant mode.

[0056] Figure 3 A simplified cross-section of an ultrasonic transducer according to some implementations is shown. In the implementation shown, the ultrasonic transducer includes stacked layers including a transmitting (Tx) layer 301, a receiving (Rx) layer 303, a thin-film transistor (TFT) circuit substrate 305, and optionally, one or more acoustic matching layers 302.

[0057] Referring first to detail A, the ultrasonic transducer 300A includes a Tx layer 301 disposed above a TFT circuit substrate 305 near the outer surface of the sensor array. An Rx layer 303 is disposed between the Tx layer 301 and the TFT circuit substrate 305. Optionally, one or more acoustic matching layers 302 may be disposed between the Tx layer 301 and the Rx layer 303.

[0058] Referring now to detail B, the ultrasonic transducer 300B includes an Rx layer 303 disposed above a TFT circuit substrate 305 near the outer surface of the sensor array. The TFT circuit substrate 305 is disposed between the Rx layer 303 and the Tx layer 301. Optionally, one or more acoustic matching layers 302 may be disposed between the Tx layer 301 and the TFT circuit substrate 305.

[0059] Detail A and Detail B illustrate the "d33" resonant mode. The d33 resonant mode refers to an excitation mode in which an electrical signal applied in the vertical (Z) direction (across thickness 'T') results in resonant oscillation in the same (i.e., Z) direction. Accordingly, the d33 coefficient is a measure of the frequency response characteristics related to the size T of the resonator. The Tx layer 301 and the Rx layer 303 can each exhibit their own characteristic d33 coefficients. Advantageously, the corresponding characteristic d33 coefficient of the Tx layer 301 can differ from the corresponding characteristic d33 coefficient of the Rx layer 303.

[0060] Figure 4 A simplified cross-section of a touch sensor according to another implementation is shown. In the illustrated implementation, the touch sensor 400 includes a flexible electronics layer 405 disposed above a cavity 420. A flexible electret member 403 is disposed between the flexible electronics layer 405 and the sealed cavity 420.

[0061] As shown in detail C, the electret member 403 exhibits a nominal surface charge in the absence of pressure from a touch. Applied pressure (e.g., from a touch) can cause a change in surface charge (detail D). Therefore, the electret member 403 can be configured as a touch sensor. In some implementations, for example, the flexible electronics layer 405 can be a flexible organic light-emitting diode (OLED) display. Advantageously, when both the electret member 403 and the electronics layer 405 are configured to be flexible, the touch sensor 400 can be a wearable device or can be included in a wearable device. In some implementations, the electret member 403 or a second electret member (not shown) can also be used as an acoustic transducer. In this implementation, the piezoelectric Tx layer can be omitted. In some implementations, the cavity 420 can be evacuated. In other implementations, the cavity 420 can be filled with air or an inert gas, or filled with, for example, soft foam.

[0062] The inventors have realized that electret components can be expected to have significantly higher d33 coefficients and lower Tx quality factors compared to piezoelectric components, especially when the electret component is made of PTFE or the like and the piezoelectric component is a copolymer or formed from compounds such as lead zirconate titanate (PZT), aluminum nitride (AlN), or zinc oxide (ZnO). Therefore, a “hybrid” ultrasonic transducer in which the Rx layer comprises an electret component and the Tx layer comprises a piezoelectric component can be advantageous. More specifically, refer again... Figure 3 The Tx layer 301 can be advantageously formed from a piezoelectric material, while the Rx layer 303 can be advantageously formed from an electret material.

[0063] Figure 5 A simplified cross-section of an ultrasonic sensor according to yet another implementation is shown. In the illustrated implementation, the ultrasonic sensor 500 includes a Tx layer 501 comprising a piezoelectric member disposed on a cavity 520. An Rx layer 503, including an electret member, is disposed between the Tx layer 501 and the cavity 520. Advantageously, the Rx layer 503 also serves as a passive layer configured to improve the electromechanical coupling efficiency of the Tx layer 501. Detail E depicts the ultrasonic sensor 500 in the absence of external pressure or electrical excitation. Detail F depicts the ultrasonic sensor 500 during operation, such that the Tx layer 501 and Rx layer 503 have bent and / or vibrated in response to external pressure or a time-varying excitation voltage.

[0064] In some implementations, after polarization, the first coefficient d33 of the piezoelectric component has the opposite sign to the second coefficient d33 of the electret component. Figure 6 A simplified cross-section of a hybrid ultrasonic transducer stack according to several implementations is shown. In the illustrated implementation, an electret member 603 is disposed above a ferroelectric copolymer member 601. At least after polarization, the electret member 603 can have a first characteristic d33 coefficient with the opposite sign to the second characteristic d33 coefficient of the copolymer member 601. More specifically, the first characteristic d33 coefficient can be positive (that is, at least for common electret materials like PZT, AlN, ZnO, and porous polymers, an increase in thickness increases the dipole moment and thus increases the charge), while the second characteristic d33 can be negative (that is, for copolymers such as polyvinylidene fluoride (PVDF), an increase in thickness decreases the dipole moment and thus decreases the charge). Thus, improvements in differential Tx / Rx can be achieved.

[0065] Figure 7 Examples of techniques for improving Rx sensitivity according to some implementations are shown. In the illustrated example, individual pixel clusters (“superpixels”) forming part of a sensor array are connected in series. More specifically, in some implementations, as shown in detail G, the Rx layer and associated electrodes are patterned to form series connections between the individual pixels in each superpixel. In such an implementation, the sensor array (detail H) can be considered as a superpixel array. For the implementation shown, the inventors have found that Rx sensitivity is improved due to the reduced capacitance for a given amount of charge Q, resulting in improved electromechanical coupling.

[0066] Figure 8 An example of a process flow for manufacturing an ultrasonic transducer is shown. As described above, the ultrasonic transducer can be included in an ultrasonic sensor array. Method 800 includes, in block 810, forming an Rx layer of the ultrasonic transducer; in some implementations, the Rx layer may be or include an electret member. Method 800 may continue in block 820 to form a Tx layer of the ultrasonic transducer; the Tx layer may be or include a piezoelectric member. In block 830, the Rx layer and the Tx layer may be coupled. Advantageously, the Rx layer exhibits a first d33 resonant mode coefficient, and the Tx layer exhibits a second d33 resonant mode coefficient, the first coefficient being different from the second coefficient.

[0067] The aforementioned ultrasonic sensing array or system can be included in various electronic devices. Figure 9A front view illustrating an example of an electronic device 900 including an ultrasonic sensing system according to some implementations is shown. Electronic device 900 can represent, for example, various portable computing devices such as cellular phones, smartphones, multimedia devices, personal gaming devices, tablet computers, and laptop computers, as well as other types of portable computing devices. However, the various implementations described herein are not limited to applications in portable computing devices. In fact, the various techniques and principles disclosed herein can be applied to traditionally non-portable devices and systems, such as computer monitors, television displays, self-service terminals, vehicle navigation devices, and audio systems, among other applications.

[0068] In the illustrated implementation, electronic device 900 includes a housing (or "enclosure") 902 within which various circuits, sensors, and other electronic components can be housed. In the illustrated implementation, electronic device 900 also includes a display (which may be referred to herein as a "touchscreen display" or "touch-sensitive display") 904. Display 904 can generally represent any of a variety of suitable display types employing any of a variety of suitable display technologies. For example, display 904 can be a digital micro-shutter (DMS) based display, a light-emitting diode (LED) display, an organic LED (OLED) display, a liquid crystal display (LCD), an LCD display using LEDs as backlighting, a plasma display, an interferometric modulator-modulated display (IMOD), or another type of display suitable for use in conjunction with a touch-sensitive user interface (UI) system.

[0069] Electronic device 900 may include various other devices or components for interacting with or otherwise communicating information to or receiving information from a user. For example, electronic device 900 may include one or more microphones 906, one or more speakers 908, and in some cases one or more buttons 910 that are at least partially mechanical. Electronic device 900 may include various other components capable of implementing additional features, such as one or more video or still image cameras 912, one or more wireless network interfaces 914 (e.g., Bluetooth, WiFi, or cellular), and one or more non-wireless interfaces 916 (e.g., Universal Serial Bus (USB) interface or HDMI interface).

[0070] Electronic device 900 may include an ultrasonic sensing system 918 capable of imaging object signatures such as fingerprints, palm prints, or handprints. In some implementations, the ultrasonic sensing system 918 may serve as a touch-sensitive control button. In some implementations, the touch-sensitive control button may be implemented using a mechanical or voltage-sensitive system located beneath or otherwise integrated with the ultrasonic sensing system 918. In other words, in some implementations, the area occupied by the ultrasonic sensing system 918 may serve as both a user input button for controlling electronic device 900 and a sensor for enabling security features (such as user authentication) based on, for example, fingerprints, palm prints, or handprints.

[0071] Figure 10A A block diagram representation of the components of an example ultrasonic sensing system according to some implementations is shown. In the illustrated implementation, the ultrasonic sensing system 1000 includes a sensor system 1002 and a control system 1004 electrically coupled to the sensor system 1002. The sensor system 1002 is capable of scanning a target object and providing raw measurement image data, which can be used to obtain an object signature, such as that of a human appendage (e.g., one or more fingers or toes, palm, hand, or foot). The control system 1004 is capable of controlling the sensor system 1002 and processing the raw measurement image data received from the sensor system 1002. In some implementations, the ultrasonic sensing system 1000 may include an interface system 1006 capable of sending or receiving data such as raw or processed measurement image data to or from various components within or integrated with the ultrasonic sensing system 1000, or, in some implementations, sending or receiving data such as raw or processed measurement image data to or from various components, devices, or other systems outside the ultrasonic sensing system 1000.

[0072] Figure 10B A block diagram representation of components of an example electronic device according to some implementations is shown. In the illustrated example, electronic device 1010 includes the ultrasonic sensing system 1000 of FIG. 2A. For example, electronic device 1010 may be the one referenced above. Figure 9A block diagram representation of the electronic device 900 is shown and described. The sensor system 1002 of the ultrasonic sensing system 1000 of the electronic device 1010 can be implemented using an ultrasonic sensor array 1012. The control system 1004 of the ultrasonic sensing system 1000 can be implemented using a controller 1014 electrically coupled to the ultrasonic sensor array 1012. Although the controller 1014 is shown and described as a single component, in some implementations, the controller 1014 may be collectively referred to as two or more different control units or processing units that are electrically communicating with each other. In some implementations, the controller 1014 may include one or more of the following: a general-purpose single-chip or multi-chip processor, a central processing unit (CPU), a digital signal processor (DSP), an application processor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions and operations described herein.

[0073] Figure 10B The ultrasonic sensing system 1000 may include an image processing module 1018. In some implementations, raw measurement image data provided by the ultrasonic sensor array 1012 may be sent, transmitted, communicated, or otherwise provided to the image processing module 1018. The image processing module 1018 may include any suitable combination of hardware, firmware, and software configured, adapted to, or otherwise operable to process the image data provided by the ultrasonic sensor array 1012. In some implementations, the image processing module 1018 may include signal or image processing circuitry or circuit components, including, for example, amplifiers (such as instrumentation amplifiers or buffer amplifiers), analog or digital mixers or multipliers, switches, analog-to-digital converters (ADCs), passive or active analog filters, etc. In some implementations, one or more such circuitry or circuit components may be integrated within a controller 1014, for example, where the controller 1014 is implemented as a system-on-a-chip (SoC) or system-in-package (SIP). In some implementations, one or more such circuitry or circuit components may be integrated within a DSP included in or coupled to the controller 1014. In some implementations, the image processing module 1018 may be implemented at least partially by software. For example, one or more functions of one or more circuits or circuit components just described, or operations performed by one or more circuits or circuit components, may alternatively be performed by one or more software modules, for example, in the processing unit of the controller 1014 (such as in a general-purpose processor or DSP).

[0074] In some implementations, in addition to the ultrasonic sensing system 1000, the electronic device 1010 may include a separate processor 1020, a memory 1022, an interface 1016, and a power supply 1024. In some implementations, the controller 1014 of the ultrasonic sensing system 1000 can control the ultrasonic sensor array 1012 and the image processing module 1018, and the processor 1020 of the electronic device 1010 can control other components of the electronic device 1010. In some implementations, the processor 1020 communicates data, including, for example, instructions or commands, to the controller 1014. In some such implementations, the controller 1014 can communicate data, including, for example, raw or processed image data, to the processor 1020. It should also be understood that in some other implementations, the functionality of the controller 1014 may be implemented entirely or at least partially by the processor 1020. In some such implementations, a separate controller 1014 for the ultrasonic sensing system 1000 may not be necessary, as the functionality of the controller 1014 can be performed by the processor 1020 of the electronic device 1010.

[0075] Depending on the implementation, one or both of the controller 1014 and the processor 1020 may store data in the memory 1022. For example, data stored in the memory 1022 may include raw measurement image data, filtered or otherwise processed image data, estimated PSF or estimated image data, and final improved PSF or final improved image data. The memory 1022 may store processor-executable code or other executable computer-readable instructions that can be executed by one or both of the controller 1014 and the processor 1020 to perform various operations (or cause other components or modules, such as the ultrasonic sensor array 1012, the image processing module 1018, to perform operations), including any of the calculations, operations, estimations, or other determinations described herein (including those presented in any of the equations below). It should also be understood that the memory 1022 may be collectively referred to as one or more storage devices (or “components”). For example, depending on the implementation, the controller 1014 may access and store data in a storage device different from the processor 1020. In some implementations, one or more memory components may be implemented as NOR or NAND-based flash memory arrays. In some other implementations, one or more memory components may be implemented as different types of non-volatile memory. Additionally, in some implementations, one or more memory components may include an array of volatile memory, such as, for example, a type of RAM.

[0076] In some implementations, controller 1014 or processor 1020 may communicate data stored in memory 1022 or data received directly from image processing module 1018 via interface 1016. For example, such communicated data may include image data or data derived from or otherwise determined from image data. Interface 1016 may be collectively referred to as one or more interfaces of various types. In some implementations, interface 1016 may include a memory interface for receiving data from or storing data in external memory, such as a removable storage device. Additionally or alternatively, interface 1016 may include one or more wireless network interfaces or one or more wired network interfaces, enabling the transmission of raw or processed data to and from external computing devices, systems, or servers.

[0077] Power source 1024 can supply power to some or all of the components in electronic device 1010. Power source 1024 may include one or more of various energy storage devices. For example, power source 1024 may include a rechargeable battery, such as a nickel-cadmium battery or a lithium-ion battery. Additionally or alternatively, power source 1024 may include one or more supercapacitors. In some implementations, power source 1024 may be charged (or "rechargeable") using power drawn from, for example, a wall socket (or "power outlet") or a photovoltaic device (or "solar cell" or "solar cell array") integrated with electronic device 1010. Additionally or alternatively, power source 1024 may be wirelessly rechargeable.

[0078] As used below, the term "processing unit" refers to any combination of one or more of the controller of an ultrasonic system (e.g., controller 1014), an image processing module (e.g., image processing module 1018), or a separate processor (e.g., processor 1020) of a device including an ultrasonic system. In other words, the operations described below that are performed by or using the processing unit can be performed by one or more of the controller of the ultrasonic system, the image processing module, or a separate processor of a device including an ultrasonic sensing system.

[0079] Therefore, an improved ultrasonic sensor array has been disclosed. It should be understood that many alternative configuration and manufacturing techniques can be anticipated.

[0080] As used in this article, the phrase “at least one” in a list of entries refers to any combination of those entries, including a single member. For example, “at least one of a, b, or c” is intended to cover: a, b, c, ab, ac, bc, and abc.

[0081] The various illustrative logics, logic blocks, modules, circuits, and algorithmic processes described in conjunction with the implementation methods disclosed herein can be implemented as electronic hardware, computer software, or a combination of both. The interchangeability of hardware and software has been generally described in terms of functionality and illustrated in the aforementioned illustrative components, blocks, modules, circuits, and processes. Whether this functionality is implemented in hardware or software depends on the specific application and the design constraints imposed on the entire system.

[0082] Hardware and data processing apparatuses for implementing the various illustrative logics, logic blocks, modules, and circuits described in conjunction with the aspects disclosed herein may be implemented or performed by general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor or any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration. In some implementations, specific processes and methods may be performed by circuits specific to a given function.

[0083] In one or more aspects, the described functionality can be implemented in hardware, digital electronic circuits, computer software, firmware (including the structures disclosed in this specification and their equivalents) or any combination thereof. Implementation of the subject matter described in this specification can also be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a computer storage medium for execution by a data processing apparatus or for controlling the operation of the data processing apparatus.

[0084] If implemented in software, the functionality can be stored as one or more instructions or code on or transmitted over a computer-readable medium (such as a non-transitory medium). The processes of the methods or algorithms disclosed herein can be implemented in a processor-executable software module that may reside on a computer-readable medium. Computer-readable media include both computer storage media and communication media, including any medium capable of transferring a computer program from one place to another. Storage media can be any available medium accessible to a computer. By way of example and not limitation, non-transitory media can include RAM, ROM, EEPROM, CD-ROM or other optical disc storage, disk storage or other magnetic storage devices, or any other medium that can be used to store the required program code in the form of instructions or data structures and is accessible to a computer. Furthermore, any connection can be properly referred to as a computer-readable medium. The disks and discs used herein include high-compression optical discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks, and Blu-ray discs, where disks typically reproduce data magnetically, while optical discs reproduce data optically using lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, the operation of a method or algorithm may reside as one or any combination or set of code and instructions on a machine-readable medium and a computer-readable medium, which may be incorporated into a computer program product.

[0085] Various modifications to the implementations described in this disclosure will be apparent to those skilled in the art, and the general principles defined herein can be applied to other implementations without departing from the spirit or scope of this disclosure. Therefore, these claims are not intended to be limited to the implementations shown herein, but are consistent with the widest scope of this disclosure, the principles disclosed herein, and the novel features. Additionally, as will be readily understood by those skilled in the art, the terms “upper” and “lower,” “top” and “bottom,” “front” and “back,” as well as “above,” “cover,” “on,” “below,” and “below” are sometimes used to facilitate the description of the drawings and to indicate relative positions corresponding to the orientation of the drawings on a suitably oriented page, and may not reflect the suitably oriented device.

[0086] Some features described in this specification in the context of individual implementations may also be implemented in combination within a single implementation. Conversely, various features described in the context of a single implementation may also be implemented individually in multiple implementations or in any suitable sub-combination. Furthermore, although features may be described above as functioning in certain combinations, and even initially claimed in this way, in some cases, one or more features from the claimed combination may be removed from that combination, and the claimed combination may refer to a sub-combination or a variation of a sub-combination.

[0087] Similarly, although operations are depicted in a specific order in the accompanying drawings, this should not be construed as requiring these operations to be performed in the specific order or sequence shown, or to perform all shown operations to achieve the desired result. Furthermore, the drawings may schematically depict one or more example processes in the form of flowcharts. However, other operations not depicted may be combined with the schematically shown example processes. For example, one or more additional operations may be performed before, after, simultaneously with, or between any shown operations. In some cases, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the above implementations should not be construed as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated into a single software product or packaged into multiple software products. Furthermore, other implementations are within the scope of the following claims. In some cases, the actions listed in the claims may be performed in a different order and still achieve the desired result.

Claims

1. An ultrasonic sensor array, comprising: a plurality of ultrasonic transducers, each transducer comprising a piezoelectric member, wherein: each of the transducers comprises an electret member; each of the transducers comprises a receive (Rx) layer configured to exhibit a first d33 resonance mode coefficient and a transmit (Tx) layer configured to exhibit a second d33 resonance mode coefficient, the first d33 resonance mode coefficient being different from the second d33 resonance mode coefficient; and the transducers are disposed on a flexible substrate; wherein the first d33 resonance mode coefficient has an opposite sign relative to the second d33 resonance mode coefficient.

2. The ultrasonic sensor array of claim 1, wherein the electret member is composed of a fluoropolymer.

3. The ultrasonic sensor array of claim 1, wherein the Tx layer comprises the piezoelectric member and the Rx layer comprises the electret member.

4. The ultrasonic sensor array of claim 1, wherein the electret member is configured as an acoustic transducer.

5. The ultrasonic sensor array of claim 1, wherein the array further comprises a flexible electronic layer, the electret member being configured to be flexible.

6. The ultrasonic sensor array of claim 5, wherein the flexible electronic layer is a flexible organic light emitting diode display.

7. The ultrasonic sensor array of claim 1, wherein the piezoelectric member is formed of a ferroelectric.

8. The ultrasonic sensor array of claim 1, wherein the piezoelectric member is formed of a copolymer.

9. The ultrasonic sensor array of claim 1, wherein at least some of the plurality of transducers are electrically connected in series.

10. The ultrasonic sensor array of claim 1, wherein the array has a surface area of 64.516 square centimeters or greater.

11. A method of forming an ultrasonic transducer, the method comprising: forming a receive (Rx) layer; forming a transmit (Tx) layer; and coupling the Rx layer with the Tx layer; wherein: the ultrasonic transducer is disposed on a flexible substrate and comprises an electret member and a piezoelectric member; and the Rx layer is configured to exhibit a first d33 resonance mode coefficient and the Tx layer is configured to exhibit a second d33 resonance mode coefficient, the first d33 resonance mode coefficient being different from the second d33 resonance mode coefficient; wherein the first d33 resonance mode coefficient has an opposite sign relative to the second d33 resonance mode coefficient.

12. The method of claim 11, wherein the electret member is composed of a fluoropolymer.

13. The method of claim 11, wherein the Tx layer comprises a piezoelectric member.

14. The method of claim 13, wherein the piezoelectric member is formed of a ferroelectric.

15. The method of claim 13, wherein the piezoelectric member is formed of a copolymer.

16. The method of claim 11, wherein the electret member is configured as an acoustic transducer.

Images