Apparatus configured for near field ultrasound imaging

Abstract

Some disclosed devices include a display system having a display stack, an ultrasonic fingerprint sensor system including an ultrasonic fingerprint sensor system stack, and a reinforcement layer residing between the display stack and the ultrasonic fingerprint sensor system stack. In some examples, a reinforcement layer thickness of the reinforcement layer may allow the ultrasonic fingerprint sensor system to operate in a near field mode. According to some examples, operation in the near field mode may involve transmitting ultrasound having a peak frequency in the range of 1 megahertz (MHz) to 6 MHz.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 494,152, filed April 4, 2023, entitled “DEVICES CONFIGURED FOR NEAR-FIELD ULTRASONIC IMAGING,” and U.S. Application No. 18 / 611,365, filed March 20, 2024, entitled “DEVICES CONFIGURED FOR NEAR-FIELD ULTRASONIC IMAGING,” both of which are assigned to the assignee hereof and the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD

[0003] The present disclosure relates generally to devices including ultrasonic fingerprint sensor systems. BACKGROUND

[0004] Biometric authentication can be an important feature for controlling access to devices and the like. Many existing products include some type of biometric authentication, including but not limited to fingerprint-based authentication. While some existing fingerprint-based authentication methods and devices can provide satisfactory performance, improved methods and devices are still desired. SUMMARY

[0005] The systems, methods, and devices of the present disclosure each have several innovative aspects, none of which is, by itself, solely responsible for the desirable attributes disclosed herein.

[0006] One innovative aspect of the subject matter described in this disclosure can be implemented in an apparatus. In some examples, the apparatus can be or can include a foldable display device. The apparatus can include a display system including a display stack, an ultrasonic fingerprint sensor system including an ultrasonic sensor system stack, and a reinforcement layer residing between the display stack and the ultrasonic sensor system stack. According to some examples, the apparatus can be configured to allow the ultrasonic sensor system to operate in a near-field mode. In some examples, when operating in the near-field mode, the ultrasonic sensor system can transmit ultrasonic waves having a peak frequency in a range of 1 megahertz (MHz) to 6 MHz. According to some examples, a thickness of the reinforcement layer can be configured to allow the ultrasonic fingerprint sensor system to operate in the near-field mode. In some such examples, the reinforcement layer thickness can be less than one-fifth of a wavelength corresponding to the peak frequency.

[0007] According to some examples, operation of the ultrasonic fingerprint sensor system in the near-field mode can provide a resolution of at least 3 wire pairs per millimeter. In some examples, the stiffener layer thickness can correspond to a transmission coefficient in a range of 10% to 30% for ultrasonic waves in a range of 1 MHz to 6 MHz. According to some examples, the stiffener layer can include stainless steel, titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), or a combination thereof. In some examples, the stiffener layer can include a stainless steel layer, a titanium layer, a CFRP layer, or a GFRP layer having a thickness in a range of 30 micrometers to 200 micrometers, or an aluminum layer having a thickness in a range of 100 micrometers to 300 micrometers.

[0008] In some examples, the foldable display device can include an adhesive layer residing on a side of the stiffener layer proximate the display stack. The adhesive layer can have a thickness less than 100 micrometers. According to some examples, the display stack can include a display glass layer residing between the stiffener layer and an outer surface of the foldable display device. The display glass layer can include glass, transparent plastic, or a combination thereof. In some examples, a first acoustic resonator can be bounded by the stiffener layer and the display glass layer. According to some examples, the first acoustic resonator can be configured to induce a first local maximum of ultrasonic wave transmission. In some examples, the first acoustic resonator can include at least one first resonator flexible optical clear adhesive (OCA) layer. In some such examples, the at least one first resonator flexible OCA layer can have a thickness substantially an odd or even multiple of one-eighth of a wavelength of an ultrasonic wave in a range of 1 MHz to 14 MHz, where substantially indicates within ±10%.

[0009] According to some such examples, the foldable display device can include one or more layers residing between the display glass layer and the outer surface of the foldable display device. In some such examples, a second acoustic resonator can include the one or more layers and the display glass layer. According to some such examples, the one or more layers can include a second resonator flexible optical clear adhesive (OCA) layer having a thickness in a range of 5 micrometers to 180 micrometers.

[0010] In some examples, an ultrasonic fingerprint sensor system can include a thin film transistor (TFT) layer or a semiconductor layer. According to some examples, an acoustic resonator can include the stiffener layer and the TFT layer or the semiconductor layer. The acoustic resonator can be configured to induce a first local maximum of ultrasonic wave transmission.

[0011] According to some examples, the ultrasonic fingerprint sensor system can include a thin film transistor (TFT) layer, a piezoelectric layer, and a backing layer. In some examples, an acoustic resonator can include the TFT layer, the piezoelectric layer, and the backing layer. The acoustic resonator can be configured to cause a first local maximum of ultrasonic wave transmission.

[0012] In some examples, the display stack can include one or more display stack layers having a speed of sound above a speed of sound threshold. A respective thickness of the one or more display stack layers can be less than one fifth of a wavelength corresponding to the peak frequency. According to some examples, the speed of sound threshold can be in a range of 2000 meters per second to 2500 meters per second.

[0013] According to some examples, the apparatus can include a control system configured for communication with the ultrasonic fingerprint sensor system and the display system. The control system can include one or more general purpose single- or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or combinations thereof. In some implementations, a mobile device such as a wearable device, a cellular phone, or the like can be at least a portion of or can include at least a portion of the apparatus.

[0014] According to some examples, the control system can be configured to control the ultrasonic fingerprint sensor system to obtain ultrasonic image data from one or more objects in contact with an outer surface of the foldable display device and to perform an authentication process based at least in part on the ultrasonic image data. In some examples, the one or more objects can include one or more fingers, and the authentication process can be a fingerprint-based authentication process.

[0015] According to some examples, a foldable display device can include an ultrasonic fingerprint sensor system configured to operate in a near-field mode with a peak frequency in a range of 1 megahertz (MHz) to 6 MHz. The ultrasonic fingerprint sensor system can include an ultrasonic fingerprint sensor system stack. In some examples, the foldable display device can include a reinforcement layer residing between the display stack and the ultrasonic fingerprint sensor system stack. A reinforcement layer thickness of the reinforcement layer can be less than one fifth of a wavelength corresponding to the peak frequency. According to some examples, the display stack can include one or more display stack layers having a speed of sound above a speed of sound threshold. In some examples, the speed of sound threshold can be in a range of 2000 meters per second to 2500 meters per second. A respective thickness of the one or more display stack layers can be less than one fifth of a wavelength corresponding to the peak frequency.

[0016] In some examples, the stiffener layer thickness can correspond to a transmission coefficient in a range of 10% to 30% for ultrasonic waves in a range of 3 MHz to 6 MHz. According to some examples, operation of the ultrasonic fingerprint sensor system in the near-field mode can provide a resolution of at least 3 wire pairs per millimeter.

[0017] According to some examples, the stiffener layer can include stainless steel, titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), or a combination thereof. In some examples, the stiffener layer can include a stainless steel layer, a titanium layer, a CFRP layer, or a GFRP layer having a thickness in a range of 30 micrometers to 200 micrometers, or an aluminum layer having a thickness in a range of 100 micrometers to 300 micrometers.

[0018] In some examples, the apparatus can include an adhesive layer residing on a side of the stiffener layer proximate the display stack. In some such examples, the adhesive layer can have a thickness less than 100 micrometers.

[0019] According to some examples, the apparatus can include a display cover layer residing between the display stack and an outer surface of the foldable display device. In some examples, the display cover layer can be or can include glass, transparent plastic, or a combination thereof. According to some examples, a first acoustic resonator can include the stiffener layer, the display stack, and the display cover layer. The first acoustic resonator can be configured to induce a first local maximum of ultrasonic wave transmission.

[0020] In some examples, the first acoustic resonator can include at least one first resonator flexible optical clear adhesive (OCA) layer. According to some examples, a thickness of the at least one first resonator flexible OCA layer can be substantially an odd multiple or an even multiple of one-eighth of a wavelength corresponding to ultrasonic waves in a range of 1 MHz to 14 MHz, where substantially indicates within ±10%. In some such examples, the one or more layers can include a second resonator flexible optical clear adhesive (OCA) layer having a thickness corresponding to an odd multiple of one-eighth of a wavelength corresponding to ultrasonic waves in a range of 1 MHz to 14 MHz ±10%.

[0021] Other innovative aspects of the subject matter described in this disclosure can be implemented in a method. In some examples, the method can involve controlling, by a control system, an ultrasonic fingerprint sensor system to operate in a near-field mode having a peak frequency in a range of 1 megahertz (MHz) to 6 MHz. According to some examples, the method can involve controlling, by the control system, the ultrasonic fingerprint sensor system to obtain ultrasonic image data from one or more objects in contact with an outer surface of a device that includes the ultrasonic fingerprint sensor system. In some examples, the method can involve performing, by the control system, an authentication process based at least in part on the ultrasonic image data.

[0022] Some or all of the operations, functions, and / or methods described herein can be performed by one or more devices in accordance with instructions (e.g., software) stored on one or more non-transitory media. Such non-transitory media can include memory devices such as those described herein, including but not limited to random access memory (RAM) devices, read-only memory (ROM) devices, etc. Thus, some innovative aspects of the subject matter described in this disclosure can be implemented in one or more non-transitory media having software stored thereon.

[0023] For example, the software can include instructions for controlling one or more devices to perform a method. According to some examples, the method can involve controlling, by a control system, an ultrasonic fingerprint sensor system to operate in a near-field mode having a peak frequency in a range of 1 megahertz (MHz) to 6 MHz. According to some examples, the method can involve controlling, by the control system, the ultrasonic fingerprint sensor system to obtain ultrasonic image data from one or more objects in contact with an outer surface of a device that includes the ultrasonic fingerprint sensor system. In some examples, the method can involve performing, by the control system, an authentication process based at least in part on the ultrasonic image data. BRIEF DESCRIPTION OF DRAWINGS

[0024] The details of one or more specific implementations of the subject matter described in this specification are set forth in the accompanying drawings and description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following drawings can not be drawn to scale. Like reference numbers and designations in different drawings indicate like elements.

[0025] Figure 1 is a block diagram illustrating example components of a device, in accordance with some disclosed implementations.

[0026] Figure 2 illustrates example components of a device, in accordance with some disclosed implementations.

[0027] Figure 3is a graph showing examples of how the transmission coefficient of an ultrasonic wave in stainless steel (SUS) varies according to the thickness of the SUS and the peak frequency of the ultrasonic wave.

[0028] Figure 4 Example components of a device, in accordance with some disclosed implementations, are shown.

[0029] Figure 5 is a flowchart presenting examples of operations in accordance with some disclosed methods. DETAILED DESCRIPTION

[0030] For purposes of describing the innovative aspects of the present disclosure, the following description relates to certain implementations. Those of ordinary skill in the art, however, will readily recognize that the teachings herein can be applied in a multitude of different ways. The described implementations can be implemented in any device, apparatus, or system that includes a biometric system as disclosed herein. Furthermore, it is contemplated that the described implementations can be included in or associated with a variety of electronic devices such as, but not limited to: mobile telephones, multimedia Internet enabled cellular telephones, mobile television receivers, wireless devices, smartphones, smart cards, wearable devices such as bracelets, armbands, wristbands, rings, headbands, patches, etc., Bluetooth® devices, personal data assistants (PDAs), wireless electronic mail devices, and a computer system that includes means for establishing communications over a wireless link. Further, it is contemplated that some of the described implementations can provide multiple functions. Yet further, it is contemplated that the described implementations can be used in combination with one another in an embedded manner. ®devices, personal digital assistants (PDAs), wireless electronic mail receivers, hand-held or portable computers, netbooks, notebooks, smartbooks, tablets, printers, copiers, scanners, facsimile devices, global positioning system (GPS) receivers / navigators, cameras, digital multimedia players (such as MP3 players), camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, electronic reading devices (e.g., e-readers), mobile health devices, computer monitors, automobile displays (including odometer and speedometer displays, etc.), cockpit controls and / or displays, camera view displays (such as displays of rear view 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 memory chips, laundry machines, dryers, washer / dryers, parking meters, packaging (such as in electromechanical systems (EMS) applications including microelectromechanical systems (MEMS) applications, as well as non-EMS applications), aesthetic structures (such as display of images on a piece of jewelry or clothing), and various other EMS devices. The teachings herein also can be used in 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, parts of consumer electronics, steering wheels or other automobile components, varactors, liquid crystal devices, electrophoretic devices, driving schemes, manufacturing processes, and electronic test equipment, etc. Thus, the teachings are not intended to be limited to the specifically depicted embodiments as such can vary widely, as would be known by one ordinarily skilled in the art.

[0031] Many devices, including but not limited to mobile devices such as cellular phones, are configured to implement fingerprint-based authentication using an ultrasonic fingerprint sensor system. In many modern devices, a display stack can reside between an active area of the ultrasonic fingerprint sensor system and an outer surface of the device on which a user will place a finger for an authentication attempt. The active area may, for example, be an area in which an array of ultrasonic fingerprint sensor pixels, such as receiver pixels, reside.

[0032] It has proven challenging to provide foldable display devices with such “under-the-screen” configurations. One challenge is caused by a reinforcing layer that resides between a display stack and an ultrasonic sensor system stack in a foldable display device. In some cases, the reinforcing layer can reduce the energy of a transmitted ultrasonic wave by about 75% as compared to the energy transmitted through an overlying layer of a display device that lacks the reinforcing layer. Generally, the energy of a transmitted ultrasonic wave that passes through a display stack becomes relatively low at relatively high frequencies, such as frequencies in the range of 8 megahertz (MHz) to 12 MHz that are known to provide acceptable resolution for ultrasonic fingerprint imaging. Lower ultrasonic frequencies of longitudinal and transverse waves, such as longitudinal and transverse waves with ultrasonic frequencies in the range of 1 MHz to 6 MHz, have higher transmitted energy but have been proven to provide unacceptable resolution for fingerprint imaging.

[0033] Some disclosed devices provide an ultrasonic sensor system configured to operate in a near-field mode of a transmitted ultrasonic wave with a peak frequency in the range of 1 megahertz (MHz) to 6 MHz. In some such examples, operation of the ultrasonic sensor system in the near-field mode provides a resolution of at least 3 line-pairs per millimeter (LPMM). According to some examples, a foldable display device can include a reinforcing layer that resides between a display stack and an ultrasonic sensor system stack. A thickness of the reinforcing layer can be selected to allow the ultrasonic sensor system to operate in the near-field mode. The reinforcing layer thickness can be less than one-fifth of a wavelength corresponding to the peak frequency.

[0034] Particular aspects of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. Some disclosed foldable display device implementations configured for ultrasonic sensor system operation in a near-field mode can provide improved ultrasonic energy transmission as compared to ultrasonic energy transmission provided by ultrasonic sensor systems of previously deployed foldable display devices. Alternatively or additionally, some disclosed foldable display device implementations configured for ultrasonic sensor system operation in a near-field mode can provide higher resolution for ultrasonic image data obtained from ultrasonic wave transmissions with a peak frequency in the range of 1 MHz to 6 MHz as compared to resolutions provided by previously deployed foldable display devices.

[0035] Figure 1is a block diagram illustrating example components of a device, in accordance with some disclosed implementations. In this example, the device 101 includes a fingerprint sensor system 102, a reinforcing layer 103, and a display system 110. Some implementations can include an interface system 104, a memory system 108, a control system 106, a microphone system 112, a speaker system 114, a touch sensor system 116, or a combination thereof. In some examples, the device 101 can be a foldable display device. As with other disclosed examples, alternative implementations of the device 101 can include a different number of elements, different types of elements, or a combination thereof.

[0036] In this example, the fingerprint sensor system 102 is or includes an ultrasonic fingerprint sensor system. In some implementations, the fingerprint sensor system 102 can also include another type of fingerprint sensor, such as an optical fingerprint sensor, a capacitive fingerprint sensor, a thermal fingerprint sensor, etc. In some examples, the ultrasonic fingerprint sensor system can include a separate ultrasonic transmitter and an ultrasonic receiver. In some such examples, the ultrasonic transmitter can include an ultrasonic plane wave generator. However, various examples of ultrasonic fingerprint sensors are disclosed herein, some of which can include a separate ultrasonic transmitter and some of which can not. For example, in some implementations, the fingerprint sensor system 102 can include a piezoelectric receiver layer, such as a polyvinylidene fluoride (PVDF) polymer layer or a polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) copolymer layer. In some implementations, a separate piezoelectric layer can be used as an ultrasonic transmitter. In some implementations, a single piezoelectric layer can be used as both a transmitter and a receiver. In some examples, the fingerprint sensor system 102 can include an array of ultrasonic transducer elements, such as an array of piezoelectric micromachined ultrasonic transducers (PMUTs), an array of capacitive micromachined ultrasonic transducers (CMUTs), etc. In some such examples, the PMUT elements in a single layer array of PMUTs or the CMUT elements in a single layer array of CMUTs can be used as both ultrasonic transmitters and ultrasonic receivers.

[0037] Data received from the fingerprint sensor system 102 can sometimes be referred to herein as “fingerprint sensor data,” “ultrasonic fingerprint sensor data,” “fingerprint image data,” “ultrasonic wave image data,” etc., whether or not the received data corresponds to an actual finger or another object from which the fingerprint sensor system 102 has received data. Such data will typically be received from the fingerprint sensor system in the form of electrical signals. Thus, without additional processing, such image data can not be perceptible as an image by a human. As noted elsewhere herein, the word “finger” as used herein can correspond to any finger, including a thumb. Thus, a thumbprint is a type of fingerprint.

[0038] In some examples, the display system 110 can include a foldable display device. In some such examples, the display system 110 can include a display device that is foldable along a fold axis. In some examples, the display system 110 can include a display device that is foldable along a fold axis and a hinge axis. In some examples, the display system 110 can include a display device that is foldable along a fold axis, a hinge axis, and a third axis. In some examples, the display system 110 can include a display device that is foldable along a fold axis, a hinge axis, and a third axis, and a fourth axis. In some examples, the display system 110 can include a display device that is foldable along a fold axis, a hinge axis, and a third axis, and a fourth axis, and a fifth axis. In some examples, the display system 110 can include a display device that is foldable along a fold axis, a hinge axis, and a third axis, and a fourth axis, and a fifth axis, and a sixth axis. In some examples, the display system 110 can include a display device that is foldable along a fold axis, a hinge axis, and a third axis, and a fourth axis, and a fifth axis, and a sixth axis, and a seventh axis. In some examples, the display system 110 can include a display device that is foldable along a fold axis, a hinge axis, and a third axis, and a fourth axis, and a fifth axis, and a sixth axis, and a seventh axis, and an eighth axis. Figure 1In the example shown in FIG. 1, the device 101 includes a reinforcement layer 103. In some examples, the reinforcement layer 103 can reside between the active area of the fingerprint sensor system 102 (e.g., the area in which an ultrasonic sensor pixel array, such as an ultrasonic receiver pixel array, resides) and the display stack of the display system 110. Various types and thicknesses of reinforcement layers 103 are disclosed herein. In some examples, the reinforcement layer 103 can include stainless steel, titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), or a combination thereof. According to some examples, the reinforcement layer 103 can be or can include a stainless steel layer, a titanium layer, a CFRP layer, or a GFRP layer having a thickness in a range from 30 micrometers to 200 micrometers. In some examples, the reinforcement layer 103 can be or can include an aluminum layer having a thickness in a range from 100 micrometers to 300 micrometers. According to some examples, the thickness of the reinforcement layer 103 can be less than one fifth of a wavelength corresponding to a peak frequency of ultrasonic waves transmitted by the fingerprint sensor system 102, thereby allowing the fingerprint sensor system 102 to operate in a near-field mode. In some examples, the peak frequency of ultrasonic waves transmitted in the near-field mode can be in a range from 1 MHz to 6 MHz.

[0039] In some examples, the interface system 104 can include a wireless interface system. In some implementations, the interface system 104 can include a user interface system, one or more network interfaces, one or more interfaces between the control system 106 and the fingerprint sensor system 102, one or more interfaces between the control system 106 and the touch sensor system 116, one or more interfaces between the control system 106 and the memory system 108, one or more interfaces between the control system 106 and the display system 110, one or more interfaces between the control system 106 and the microphone system 112, one or more interfaces between the control system 106 and the speaker system 114, one or more interfaces between the control system 106 and the gesture sensor system 116, and / or one or more interfaces between the control system 106 and one or more external device interfaces (e.g., ports or application processors).

[0040] The interface system 104 can be configured to provide communication between components of the device 101, which can include wired or wireless communication, electrical communication, radio communication, etc. In some such examples, the interface system 104 can be configured to provide communication between the control system 106 and the fingerprint sensor system 102. According to some such examples, the interface system 104 can couple at least a portion of the control system 106 to the fingerprint sensor system 102, and the interface system 104 can couple at least a portion of the control system 106 to the touch sensor system 116, e.g., via electrically conductive material (e.g., via electrically conductive metal wires or traces). According to some examples, the interface system 104 can be configured to provide communication between the device 101 and other devices and / or humans. In some such examples, the display system 110, the microphone system 112, the speaker system 114, the gesture sensor system 116, or a combination thereof can be considered components of the interface system 104, even though these components are shown in Figure 1 FIG. 1 as separate blocks. In some examples, the interface system 104 can include one or more user interfaces, haptic feedback devices, etc. In some examples, the interface system 104 can include one or more network interfaces and / or one or more external device interfaces, such as one or more universal serial bus (USB) interfaces or serial peripheral interface (SPI).

[0041] The control system 106 can include one or more general purpose single- or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or combinations thereof. According to some examples, the control system 106 can also include one or more memory devices, such as one or more random access memory (RAM) devices, read-only memory (ROM) devices, etc. In this example, the control system 106 is configured to communicate with and control the fingerprint sensor system 102. In implementations where the device includes a touch sensor system 116, the control system 106 can be configured to communicate with and control the touch sensor system 116. In implementations where the device includes a memory system 108 that is separate from the control system 106, the control system 106 can also be configured to communicate with the memory system 108. In implementations where the device includes a display system 110, the control system 106 can be configured to communicate with and control the display system 110. In implementations where the device includes a microphone system 112, the control system 106 can be configured to communicate with and control the microphone system 112. In implementations where the device includes a speaker system 114, the control system 106 can be configured to communicate with and control the speaker system 114. According to some examples, the control system 106 can include one or more specialized components configured to control the fingerprint sensor system 102, the touch sensor system 116, the memory system 108, the display system 110, the microphone system 112, and / or the speaker system 114.

[0042] Accordingly, some examples of the device 101 can include specialized components configured to control at least a portion of the fingerprint sensor system 102, to process fingerprint image data received from the fingerprint sensor system 102, or a combination thereof. Although the control system 106 and the fingerprint sensor system 102 are shown as separate components in the example of FIG. 1, in some examples, the control system 106 and the fingerprint sensor system 102 can be implemented as a single component. Figure 1The control system 106 is shown as a separate component, but in some implementations at least a portion of the control system 106 and at least a portion of the fingerprint sensor system 102 can be co-located. For example, in some implementations one or more components of the fingerprint sensor system 102 can reside on an integrated circuit or "chip" of the control system 106. According to some implementations, the functionality of the control system 106 can be divided among one or more controllers or processors, such as between a dedicated sensor controller and an application processor of the device (also referred to herein as a "host" processor), such as a host processor of a mobile device. In some such implementations, at least a portion of the host processor can be configured for fingerprint image data processing, determining whether currently acquired fingerprint image data matches previously obtained fingerprint image data (such as fingerprint image data obtained during an enrollment process), and the like.

[0043] In some examples, the control system 106 can be configured to control the ultrasonic sensor system 102 to obtain ultrasonic image data from one or more objects in contact with an outer surface of the device 101. In some such examples, the control system 106 can be configured to perform an authentication process based at least in part on the ultrasonic image data. According to some examples, the one or more objects can include one or more fingers, and the authentication process can be a fingerprint-based authentication process.

[0044] In some examples, the memory system 108 can include one or more memory devices, such as one or more RAM devices, ROM devices, and the like. In some implementations, the memory system 108 can include one or more computer-readable media, storage media, and / or storage mediums. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media can be any available media that can be accessed by a computer. In some examples, the memory system 108 can include one or more non-transitory media. By way of example, and not limitation, non-transitory media can include RAM, ROM, electrically erasable programmable read-only memory (EEPROM), compact disk ROM (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry desired program code in the form of instructions or data structures and that can be accessed by a computer.

[0045] In this example, the device 101 includes a display system 110, which can include one or more displays. In some examples, the display system 110 can be, or can include, a light-emitting diode (LED) display, such as an organic light-emitting diode (OLED) display. In some examples, the display system 110 can be, or can include, a color on encapsulation (COE) display. According to this example, the display system 110 includes layers that can be collectively referred to as a “display stack.” In some examples, the display stack can include one or more display stack layers having a sound velocity that is above a sound velocity threshold. In some such examples, the one or more display stack layers each having a sound velocity that is above the sound velocity threshold can have a thickness that is less than one-fifth of a wavelength corresponding to a peak frequency of ultrasound transmitted by the fingerprint sensor system 102.

[0046] In some implementations, the device 101 can include a microphone system 112. The microphone system 112 can include one or more microphones, one or more types of microphones, or a combination thereof.

[0047] According to some implementations, the device 101 can include a speaker system 114. The speaker system 114 can include one or more speakers, one or more types of speakers, or a combination thereof.

[0048] The optional touch sensor system 116 can be, or can include, a resistive touch sensor system, a surface capacitive touch sensor system, a projected capacitive touch sensor system, a surface acoustic wave touch sensor system, an infrared touch sensor system, or any other suitable type of touch sensor system. In some implementations, an area of the touch sensor system 116 can extend over a majority or all of a display portion of the display system 110.

[0049] The device 101 can be used in a variety of different contexts, some examples of which are disclosed herein. For example, in some implementations, a mobile device can include at least a portion of the device 101. According to some implementations, the device 101 can be, or can include, a foldable display device, such as a foldable mobile phone. In some implementations, a wearable device can include at least a portion of the device 101. The wearable device can be, for example, a bracelet, a watch, an armband, a wristband, a ring, a headband, an earbud, or a patch. In some implementations, the control system 106 can reside in more than one device. For example, a portion of the control system 106 can reside in a wearable device, and another portion of the control system 106 can reside in another device, such as a mobile device (e.g., a smartphone). In some such examples, the interface system 104 can also reside in more than one device.

[0050] Figure 2 Example components of a device according to some disclosed implementations are shown. As with other disclosed implementations, the types, numbers, and arrangements of elements and the sizes of elements are merely examples. According to this example, the device 101 is configured to perform at least some of the methods disclosed herein. In this implementation, the device 101 includes a fingerprint sensor system 102, a reinforcing layer 103, and a display system 110.

[0051] In this implementation, the fingerprint sensor system 102 is an ultrasonic fingerprint sensor system. Thus, the fingerprint sensor system 102 can be referred to as an ultrasonic fingerprint sensor system 102. In this implementation, the ultrasonic fingerprint sensor system 102 includes an ultrasonic transducer layer 201, an electrode layer 209 on one side of the ultrasonic transducer layer 201, a sensor pixel array 206 on a second, opposite side of the ultrasonic transducer layer 201, and a TFT layer 208. In this implementation, the ultrasonic transducer layer 201 includes one or more piezoelectric polymers. In other implementations, the ultrasonic transducer layer 201 can include one or more other types of piezoelectric materials, such as piezoelectric composites.

[0052] According to this example, the electrode layer 209 resides between a passivation layer 212 and the ultrasonic transducer layer 201. According to some examples, the electrode layer 209 can include a metal ink, such as a silver ink. In some examples, the passivation layer 212 can include an adhesive, such as an epoxy film, a die attach film (DAF) layer, a polymer layer such as a polyethylene terephthalate (PET) layer, or the like.

[0053] In this example, the TFT layer 208 includes a TFT substrate and circuitry for the sensor pixel array 206. The TFT layer 208 can be a type of metal-oxide-semiconductor field-effect transistor (MOSFET) fabricated by depositing active semiconductor thin-film layers, as well as dielectric layers and metal contacts, on a TFT substrate. In some examples, the TFT substrate can be a non-conductive material, such as glass. In some alternative examples, the device 101 can include a semiconductor layer instead of the TFT layer 208.

[0054] In some examples, the reinforcement layer 103 can include stainless steel, titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), or a combination thereof. According to some examples, the reinforcement layer 103 can be or can include a stainless steel layer, a titanium layer, a CFRP layer, or a GFRP layer having a thickness in a range from 50 micrometers to 200 micrometers. In some examples, the reinforcement layer 103 can be or can include an aluminum layer having a thickness in a range from 100 micrometers to 300 micrometers. According to some examples, the thickness of the reinforcement layer 103 can be less than one fifth of a wavelength corresponding to a peak frequency of ultrasonic waves transmitted by the ultrasonic fingerprint sensor system 102, thereby allowing the fingerprint sensor system 102 to operate in a near-field mode. In some examples, the peak frequency of the ultrasonic waves transmitted when operating in the near-field mode can be in a range from 1 MHz to 6 MHz, such as 1 MHz, 2 MHz, 3 MHz, 4 MHz, 5 MHz, 6 MHz, or another peak frequency within the range. In some examples, operation of the ultrasonic fingerprint sensor system 102 in the near-field mode can provide a resolution of at least 3 line pairs per millimeter (LPMM). According to some examples, the resolution can be greater than 3 LPMM, such as 3.1 LPMM, 3.2 LPMM, 3.3 LPMM, 3.4 LPMM, 3.5 LPMM, etc.

[0055] According to this example, the display system 110 includes multiple layers, which are collectively referred to as a display stack 210. In this example, the display stack 210 includes a high-sonic velocity layer 219. The sonic velocity in the high-sonic velocity layer 219 is relatively high compared to the sonic velocities in other layers of the display stack 210. In some examples, the high-sonic velocity layer 219 can be or can include a glass layer. The high-sonic velocity layer 219 can also be referred to herein as a “display glass layer,” although in some examples, the “display glass layer” can include materials other than glass, such as a hard plastic material. Sound propagates at different speeds in various types of glass, ranging from approximately 2000 meters / second (m / s) to 6000 m / s. According to some examples, the sonic velocity in the high-sonic velocity layer 219 can be above a sonic velocity threshold, which can be 2000 m / s, 2500 m / s, 3000 m / s, etc. In some examples, the sonic velocity threshold can be in a range of 2000 m / s to 2500 m / s, such as 2000 m / s, 2100 m / s, 2200 m / s, 2300 m / s, 2400 m / s, 2500 m / s, etc. In some examples, sound can propagate at a relatively lower velocity in other layers of the display stack 210 than the sonic velocity in the high-sonic velocity layer 219. Such other layers of the display stack 210 may, for example, include one or more types of optical clear adhesive (OCA), pressure sensitive adhesive (PSA), polyethylene terephthalate (PET), etc. However, in some implementations, the display stack 210 can include more than one high-sonic velocity layer 219. In some implementations, the acoustic impedance of the high-sonic velocity layer 219 can also be higher than the acoustic impedance of most or all other layers in the display stack 210.

[0056] According to some examples, the thickness of both the high-sonic velocity layer 219 and the reinforcement layer 103 is less than one-fifth of a wavelength corresponding to a peak frequency of the ultrasonic waves transmitted by the ultrasonic fingerprint sensor system 102. In some such examples, the ultrasonic fingerprint sensor system 102 can operate in a near-field mode. In some such examples, the peak frequency of the ultrasonic waves transmitted during operation in the near-field mode can be in a range of 1 MHz to 6 MHz.

[0057] According to this example, the acoustic resonator 1 includes an ultrasonic transceiver layer 201, an electrode layer 209, and a passivation layer 212, and is bounded on one side by a TFT layer 208 (or a semiconductor layer, depending on the particular implementation). The acoustic resonator 1 can be configured to cause a local maximum of ultrasonic wave transmission. In some such examples, the thickness of the acoustic resonator 2 can correspond to a multiple of a quarter wavelength at a frequency in a range of 1 MHz to 15 MHz. The multiple can be 1, 2, 3, or another integer.

[0058] In this example, the reinforcement layer 103 resides between the ultrasonic fingerprint sensor system 102 and the display stack 210. Although Figure 2Not shown, but in some examples, one or more layers can reside between the TFT layer 208 and the reinforcement layer 103 (or between the semiconductor layer and the reinforcement layer 103). The one or more layers can include an adhesive layer, a double-sided tape (DST) layer, and the like.

[0059] In this example, the acoustic resonator 4 is bounded by the high acoustic velocity layer 219 and the outer surface 222 of the device 101. The acoustic resonator 4 includes one or more layers of the display stack 210 that reside between the high acoustic velocity layer 219 and the outer surface 222. In some examples, the one or more layers may, for example, include at least one flexible optically clear adhesive (OCA) layer. In some such examples, the thickness of the flexible OCA layer can be in the range of 5 micrometers to 180 micrometers. The acoustic resonator 4 can be configured to induce a local maximum of ultrasonic wave transmission. In some such examples, the thickness of the acoustic resonator 4 can correspond to a multiple of a quarter wavelength at a frequency in the range of 1 MHz to 15 MHz. Figure 2 In accordance with this example, the acoustic resonator 3 is bounded by the reinforcement layer 103 and the high acoustic velocity layer 219, and includes layers of the display stack 210 that reside between the reinforcement layer 103 and the high acoustic velocity layer 219. The acoustic resonator 3 can be configured to induce a local maximum of ultrasonic wave transmission. In some such examples, the thickness of the acoustic resonator 3 can correspond to a multiple of a half wavelength at a frequency in the range of 1 MHz to 15 MHz.

[0060] In this example, the acoustic resonator 4 is bounded by the high acoustic velocity layer 219 and the outer surface 222 of the device 101. The acoustic resonator 4 includes one or more layers of the display stack 210 that reside between the high acoustic velocity layer 219 and the outer surface 222. In some examples, the one or more layers may, for example, include at least one flexible optically clear adhesive (OCA) layer. In some such examples, the thickness of the flexible OCA layer can be in the range of 5 micrometers to 180 micrometers. The acoustic resonator 4 can be configured to induce a local maximum of ultrasonic wave transmission. In some such examples, the thickness of the acoustic resonator 4 can correspond to a multiple of a quarter wavelength at a frequency in the range of 1 MHz to 15 MHz.

[0061] In accordance with this implementation, the TFT layer 208, the sensor pixel array 206, and the electrode layer 209 are electrically coupled to at least a portion of the control system 106 and one side of the ultrasonic transceiver layer 201 via a portion of the interface system 104, which in this instance includes a conductive material and a flexible printed circuit (FPC).

[0062] In this example, the device 101 is configured to perform at least some of the methods disclosed herein. In this example, the control system 106 is configured to control the ultrasonic sensor system to transmit ultrasonic waves 213. In some examples, in addition to

[0063] Figure 2 ​The control system 106 can also include one or more other components in addition to the application-specific integrated circuit (ASIC) shown. According to this example, the ultrasonic waves 213 are transmitted through the TFT layer 208, the reinforcing layer 103, and the layers of the display stack 210. According to this example, the reflections 214 of the ultrasonic waves 213 are caused by an acoustic impedance contrast at (or near) the interface 215 between the outer surface 222 and whatever is in contact with the outer surface 222, which can be air or a surface of a target object, such as ridges and valleys of a fingerprint, etc. (As used herein, the term "finger" can refer to any finger, including the thumb. Thus, a thumbprint would be considered a type of "fingerprint.")

[0064] According to some examples, the reflections 214 of the ultrasonic waves 213 from air, a target object, or a combination thereof can be detected by the sensor pixel array 206. Corresponding ultrasonic signals can be provided to the control system 106. In some such implementations, the ultrasonic signals used by the control system 106 to perform fingerprint-based authentication can be based on reflections 214 from a target object that are detected by the sensor pixel array 206. In some implementations, reflections 214 corresponding to the outer surface 222 / air interface can be detected by the sensor pixel array 206, and corresponding background ultrasonic signals can be provided to the control system 106.

[0065] Figure 3 is a plot showing examples of how the transmission coefficient of ultrasonic waves in stainless steel (SUS) varies as a function of SUS thickness and peak frequency of the ultrasonic waves. Referring to the plot 300, it can be observed that, in general, the transmission coefficient decreases as the SUS thickness increases. One exception is the local maximum of the 12 MHz ultrasonic wave that appears at 240 microns, which is caused by the SUS layer acting as an acoustic resonator for the 12 MHz ultrasonic wave at that thickness. However, within the range of SUS thicknesses of interest, such as 30 microns to 250 microns, the transmission coefficient decreases as the SUS thickness increases, as opposed to the 12 MHz ultrasonic wave.

[0066] It can also be observed that, at higher frequencies, the transmission coefficient decreases more rapidly as the SUS thickness increases. For example, at a SUS thickness of approximately 40 microns, the transmission coefficient of the SUS for the 12 MHz ultrasonic wave is approximately 20%, whereas for the same SUS thickness, the transmission coefficient of the 4 MHz ultrasonic wave is approximately 50%. For a SUS thickness of approximately 120 microns, the transmission coefficient of the 4 MHz ultrasonic wave is approximately 20%, and for smaller thicknesses, it is greater than 20%. For a range of SUS thicknesses from approximately 260 microns to 75 microns, the transmission coefficient of the 4 MHz ultrasonic wave ranges from approximately 10% to 30%.

[0067] In general, it can be observed from the graph 300 that, except for the thickness corresponding to resonance, the transmission coefficient of SUS increases as the thickness of the SUS decreases, but the increase is relatively faster for relatively lower frequencies. Thus, if the reinforcing layer 103 is made of SUS, the amount of ultrasonic energy available for a fingerprint image can be increased by decreasing the thickness of the reinforcing layer 103, by decreasing the peak frequency of the transmitted ultrasonic waves, or both. The present inventors have found that the same principle applies to other materials used to form the reinforcing layer 103, such as titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), and the like.

[0068] Figure 4 Example components of a device, in accordance with some disclosed implementations, are shown. As with other disclosed implementations, the types, numbers, and arrangements of elements, and the sizes of elements, are merely examples. Note that Figure 4 Not drawn to scale, so Figure 4 The relative thicknesses of the layers shown can not be accurate. In this example, the device 101 is a foldable display device or includes a foldable display device, Figure 4 Not all of the foldable display device is shown in the middle. According to this example, the device 101 is configured to perform at least some of the methods disclosed herein. In this implementation, the device 101 includes an ultrasonic fingerprint sensor system 102, a reinforcing layer 103, and a display system 110.

[0069] In some examples, the reinforcing layer 103 can include stainless steel, titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), or a combination thereof. According to some examples, the reinforcing layer 103 can be or can include a stainless steel layer, a titanium layer, a CFRP layer, or a GFRP layer having a thickness in a range from 50 micrometers to 200 micrometers. In some examples, the reinforcing layer 103 can be or can include an aluminum layer having a thickness in a range from 100 micrometers to 300 micrometers. According to some examples, the thickness of the reinforcing layer 103 can be less than one fifth of a wavelength corresponding to a peak frequency of the ultrasonic waves transmitted by the ultrasonic fingerprint sensor system 102, thereby allowing the ultrasonic fingerprint sensor system 102 to operate in a near-field mode. In some examples, the peak frequency is in a range from 1 MHz to 6 MHz. In some examples, operation of the ultrasonic fingerprint sensor system 102 in the near-field mode can provide a resolution of at least 3 lines per millimeter.

[0070] According to this example, the display system 110 includes a plurality of layers, which are collectively referred to as a display stack 210. In this example, the display stack 210 includes a cover glass layer 419, which is a cover glass layer as described herein with reference to FIG. 2, a polarizer layer 421, a color filter layer 423, a thin film transistor (TFT) layer 425, and a backplane layer 427. Figure 2An example of a high acoustic velocity layer 219 is described. As noted in this description, in some examples, the display glass layer 219 can include or be formed entirely of glass. However, in some examples, the display glass layer 219 can include materials other than glass, such as hard plastic materials, e.g., polyethylene terephthalate (PET).

[0071] According to some examples, the thickness of both the display glass layer 419 and the reinforcement layer 103 is less than one fifth of a wavelength corresponding to a peak frequency of ultrasonic waves transmitted by the ultrasonic fingerprint sensor system 102. In some such examples, the ultrasonic fingerprint sensor system 102 can operate in a near-field mode. In some such examples, the peak frequency can be in a range of 1 MHz to 6 MHz.

[0072] In this example, the reinforcement layer 103 resides between the ultrasonic fingerprint sensor system 102 and the display stack 210. According to this example, a double-sided tape (DST) layer 405 resides between the ultrasonic fingerprint sensor system 102 and the reinforcement layer 103.

[0073] The acoustic resonator 3 can be configured to cause a local maximum of ultrasonic wave transmission. In some such examples, the thickness of the acoustic resonator 3 can correspond to a multiple of a half- wavelength at a frequency in a range of 1 MHz to 15 MHz.

[0074] According to this example, the acoustic resonator 3 is bounded by the reinforcement layer 103 and the display glass layer 419, and includes layers of the display stack 210 that reside between the reinforcement layer 103 and the display glass layer 419. In this example, these layers include an optically clear adhesive layer (OCA) 407 that resides between the reinforcement layer 103 and two back film (BF) layers, one of which is a polyethylene terephthalate (PET) back film (BF / PET) layer 410, and the other of which is a pressure sensitive adhesive back film (BF / PSA) layer 415. According to this example, a PET display panel layer (PNL / PET) layer 420 resides between the BF layers and two polarizer (POL) layers: a PET polarizer layer (POL / PET) layer 430 is attached to the display panel layer by a PSA polarizer layer (POL / PSA) layer 425. In this example, the cover glass layer 419 is attached to the POL / PET layer by an OCA layer 435. In some implementations, one or both of the OCA layer 407 and the OCA layer 435 can be or can include a flexible OCA layer. According to some examples, one or both of the OCA layer 407 and the OCA layer 435 can be or can include an OCA provided by 3M ™ Optical Clear Adhesive, such as 3M ™Contrast enhancement film CEF30XXAS series. In some such examples, the flexible OCA layer can have material properties that vary significantly with temperature. One such flexible OCA material has a longitudinal wave speed of approximately 2184 meters / second (m / s) at -4.7 degrees Celsius, but only approximately 1719 m / s at 38.7 degrees Celsius. The same type of flexible OCA material has a Young’s modulus of approximately 1668 at -4.7 degrees Celsius, but only approximately 1190 at 38.7 degrees Celsius. In some such examples, the thickness of one or both of OCA layer 407 and OCA layer 435 can be an odd multiple of 25 microns or substantially an odd multiple of 25 microns (such as 25 microns, 75 microns, 125 microns, etc.). In this context, “substantially” can mean within ±10%. Such embodiments can enhance resonant modes at 5 MHz. However, according to some alternative examples, the thickness of one or both of OCA layer 407 and OCA layer 435 can be an even multiple of 35 microns or substantially an even multiple of 35 microns (such as 70 microns, 140 microns, etc.). In this context, “substantially” can mean within ±10%. Such embodiments can enhance resonant modes in the range of 6 MHz to 7 MHz. More generally, in some examples, acoustic resonator 3 can include at least one flexible OCA layer having a thickness that is substantially an odd or even multiple of one-eighth of a wavelength of an ultrasonic wave in the range of 1 MHz to 14 MHz. In this context, “substantially” means within ±10%.

[0075] In this example, the acoustic resonator 4 is bounded by a display glass layer 419 and an outer surface 422 of the device 101. The acoustic resonator 4 includes a protective film layer 445 and an OCA layer 440, both of which reside between the display glass layer 419 and the outer surface 422. The protective film layer 445 can for example include colorless polyamide (CPI), polymethyl methacrylate (PMMA), or the like. The acoustic resonator 4 can be configured to induce a local maximum of ultrasonic wave transmission. In some such examples, the thickness of the acoustic resonator 4 can correspond to a multiple of a quarter wavelength at a frequency in the range of 1 MHz to 15 MHz. If a flexible OCA material such as those described above is used as the OCA layer 440, then an OCA layer 440 thickness in the range of 10 microns to 40 microns (such as 20 microns, 21 microns, 22 microns, 23 microns, 24 microns, 25 microns, 26 microns, 27 microns, 28 microns, 29 microns, 30 microns, etc.) can improve performance in some temperature ranges (such as for relatively lower temperatures). Further, if such a flexible OCA material is used as the OCA layer 440, then an OCA layer 440 thickness in the range of 60 microns to 90 microns (such as 70 microns, 71 microns, 72 microns, 73 microns, 74 microns, 75 microns, 76 microns, 77 microns, 78 microns, 79 microns, 80 microns, etc.) can improve performance in some temperature ranges. More generally, in some examples, the acoustic resonator 4 can include at least one flexible OCA layer having a thickness that substantially corresponds to an odd or even multiple of one-eighth of a wavelength of an ultrasonic wave in the range of 1 MHz to 14 MHz. In this context, “substantially” means within ±10%. In some examples, the thickness of the flexible OCA layer can be in the range of 5 microns to 180 microns.

[0076] In some examples, the device can also include a reference Figure 2 The acoustic resonator 1 described, the reference Figure 2 The acoustic resonator 2 described, or both.

[0077] The inventors have determined that there is an inverse relationship between the thickness of the OCA layer 407 and the OCA layer 440 and the resolution of the ultrasonic image data obtained by the ultrasonic fingerprint sensor system 102. In other words, a decrease in the thickness of the OCA layer 407 and the OCA layer 440 results in an increase in resolution.

[0078] Figure 5 is a flowchart that presents an example of operations in accordance with some disclosed methods. Figure 5 The blocks of can be performed by a device that includes at least an ultrasonic fingerprint sensor system and a control system. For example, Figure 5 The blocks of can be performed by Figure 1 The device 101 of B or a similar device. For example, in some implementations, Figure 1The control system 106 of the B can be configured to perform, at least in part, the operations described herein with reference to Figure 5 In some examples, the device can be a mobile device, such as a cellular phone. However, in other examples, the device can be another type of device, such as a tablet, a laptop, a car or component thereof, a door access control device, a wearable device, etc. As with other methods disclosed herein, Figure 5 The methods summarized in the numbered clauses below can include more or fewer blocks than indicated. Additionally, the blocks of the methods disclosed herein do not necessarily have to be performed in the order indicated. In some implementations, one or more blocks can be performed concurrently.

[0079] According to this example, the method 500 involves controlling a device that includes an ultrasonic fingerprint sensor system. In some examples, the method 500 can involve controlling Figure 1 The device 101 shown, Figure 2 The device 101 shown, Figure 4 The device 101 shown, or a similar device. In this example, block 505 involves controlling, by the control system, the ultrasonic fingerprint sensor system to operate in a near field mode. In some examples, at block 505, Figure 1 or Figure 2 The control system 106 shown can control the fingerprint sensor system 102. According to this example, block 505 involves controlling the ultrasonic fingerprint sensor system to transmit ultrasonic waves in a range of 1 MHz to 6 MHz.

[0080] In this example, block 510 involves controlling, by the control system, the ultrasonic fingerprint sensor system to obtain ultrasonic image data from one or more objects in contact with an outer surface of the device that includes the ultrasonic fingerprint sensor system. According to some examples, block 510 can involve obtaining ultrasonic wave image data from one or more fingers in contact with an outer surface of the device 101.

[0081] According to this example, block 515 involves performing, by the control system, an authentication process based at least in part on the ultrasonic image data. Block 515 can involve a fingerprint-based authentication process. For example, block 515 can involve obtaining fingerprint features (such as fingerprint minutiae) from the ultrasonic image data and comparing the fingerprint features to previously obtained fingerprint features. The previously obtained fingerprint features may, for example, have been obtained during a registration process.

[0082] Implementation examples are described in the following numbered clauses:

[0083] 1. A foldable display device, the foldable display device comprising: a display system comprising a display stack; an ultrasonic fingerprint sensor system comprising an ultrasonic fingerprint sensor system stack; and a reinforcement layer residing between the display stack and the ultrasonic fingerprint sensor system stack, a reinforcement layer thickness of the reinforcement layer configured to allow the ultrasonic fingerprint sensor system to operate in a near-field mode with a peak frequency in a range of 1 megahertz (MHz) to 6 MHz.

[0084] 2. The foldable display device of clause 1, wherein operation of the ultrasonic fingerprint sensor system in the near-field mode provides a resolution of at least 3 wire pairs per millimeter.

[0085] 3. The foldable display device of clause 1 or clause 2, wherein the reinforcement layer thickness corresponds to a transmission coefficient in a range of 10% to 30% for ultrasonic waves in the range of 1 MHz to 6 MHz.

[0086] 4. The foldable display device of any of clauses 1 to 3, wherein the reinforcement layer comprises stainless steel, titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), or a combination thereof.

[0087] 5. The foldable display device of clause 4, wherein the reinforcement layer comprises a stainless steel layer, a titanium layer, a CFRP layer, or a GFRP layer having a thickness in a range of 30 micrometers to 200 micrometers, or an aluminum layer having a thickness in a range of 100 micrometers to 300 micrometers.

[0088] 6. The foldable display device of any of clauses 1 to 5, further comprising an adhesive layer residing on a side of the reinforcement layer proximate to the display stack, the adhesive layer having a thickness less than 100 micrometers.

[0089] 7. The foldable display device of any of clauses 1 to 6, wherein the display stack comprises a display glass layer residing between the reinforcement layer and an outer surface of the foldable display device, the display glass layer comprising glass, transparent plastic, or a combination thereof, wherein a first acoustic resonator is bounded by the reinforcement layer and the display glass layer, the first acoustic resonator configured to induce a first local maximum of ultrasonic wave transmission.

[0090] 8. The foldable display device of clause 7, wherein the first acoustic resonator comprises at least one first resonator flexible optical clear adhesive (OCA) layer having a thickness that is substantially an odd or even multiple of one-eighth of a wavelength corresponding to an ultrasonic wave in a range of 1 MHz to 14 MHz, wherein substantially indicates within ±10%.

[0091] 9. The foldable display device of clause 7, further comprising one or more layers residing between the display glass layer and the outer surface of the foldable display device, wherein a second acoustic resonator comprises the one or more layers and the display glass layer.

[0092] 10. The foldable display device of clause 9, wherein the one or more layers comprise a second resonator flexible optical clear adhesive (OCA) layer having a thickness in a range of 5 micrometers to 180 micrometers.

[0093] 11. The foldable display device of any one of clauses 1 to 10, wherein the stiffener layer thickness is less than one-fifth of a wavelength corresponding to the peak frequency.

[0094] 12. The foldable display device of any one of clauses 1 to 11, wherein the display stack comprises one or more display stack layers having a sound speed above a sound speed threshold, each of the one or more display stack layers having a thickness that is less than one-fifth of a wavelength corresponding to the peak frequency.

[0095] 13. The foldable display device of clause 12, wherein the sound speed threshold is in a range of 2000 meters per second to 2500 meters per second.

[0096] 14. The foldable display device of any one of clauses 1 to 13, further comprising a control system configured to: control the ultrasonic fingerprint sensor system to obtain ultrasonic image data from one or more objects in contact with an outer surface of the foldable display device; and perform an authentication process based at least in part on the ultrasonic image data.

[0097] 15. The foldable display device of clause 14, wherein the one or more objects comprise one or more fingers, and wherein the authentication process is a fingerprint-based authentication process.

[0098] 16. A foldable display device, the foldable display device comprising: a display system comprising a display stack; an ultrasonic fingerprint sensor system configured to operate in a near-field mode with a peak frequency in a range of 1 megahertz (MHz) to 6 MHz, the ultrasonic fingerprint sensor system comprising an ultrasonic fingerprint sensor system stack; and a reinforcement layer residing between the display stack and the ultrasonic fingerprint sensor system stack, a reinforcement layer thickness of the reinforcement layer being less than one fifth of a wavelength corresponding to the peak frequency.

[0099] 17. The foldable display device of clause 16, wherein the display stack comprises one or more display stack layers having a sound speed above a sound speed threshold, a thickness of each of the one or more display stack layers being less than one fifth of the wavelength corresponding to the peak frequency.

[0100] 18. The foldable display device of clause 17, wherein the sound speed threshold is 2500 meters per second.

[0101] 19. The foldable display device of any of clauses 16 to 18, wherein operation of the ultrasonic fingerprint sensor system in the near-field mode provides a resolution of at least 3 wire pairs per millimeter.

[0102] 20. The foldable display device of any of clauses 16 to 19, wherein the reinforcement layer thickness corresponds to a transmission factor in a range of 10% to 30% for ultrasonic waves in a range of 3 MHz to 6 MHz.

[0103] 21. The foldable display device of any of clauses 16 to 20, wherein the reinforcement layer comprises stainless steel, titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), or a combination thereof.

[0104] 22. The foldable display device of any of clauses 16 to 21, wherein the reinforcement layer comprises a stainless steel layer, a titanium layer, a CFRP layer, or a GFRP layer having a thickness in a range of 30 micrometers to 200 micrometers, or an aluminum layer having a thickness in a range of 100 micrometers to 300 micrometers.

[0105] 23. The foldable display device of any of clauses 16 to 22, further comprising an adhesive layer residing on a side of the reinforcement layer proximate the display stack, a thickness of the adhesive layer being less than 100 micrometers.

[0106] 25. The foldable display device of clause 24, wherein the first acoustic resonator comprises at least one first resonator flexible optically clear adhesive (OCA) layer having a thickness that is substantially an odd or even multiple of one-eighth of a wavelength corresponding to an ultrasonic wave in a range of 1 MHz to 14 MHz, wherein substantially indicates within ±10%.

[0107] 27. The foldable display device of clause 26, wherein the one or more layers comprise a second resonator flexible optically clear adhesive (OCA) layer having a thickness that corresponds to an odd multiple of one-eighth of a wavelength corresponding to an ultrasonic wave in a range of 1 MHz to 14 MHz ±10%.

[0108] 26. The foldable display device of any of clauses 16-25, wherein the ultrasonic fingerprint sensor system comprises a thin film transistor (TFT) layer or a semiconductor layer, wherein an acoustic resonator comprises the stiffener layer and the TFT layer or the semiconductor layer, the acoustic resonator being configured to cause a first local maximum of ultrasonic wave transmission.

[0109] 27. The foldable display device of any of clauses 16-26, wherein the ultrasonic fingerprint sensor system comprises a thin film transistor (TFT) layer, a piezoelectric layer, and a backing layer, wherein an acoustic resonator comprises the TFT layer, the piezoelectric layer, and the backing layer, the acoustic resonator being configured to cause a first local maximum of ultrasonic wave transmission.

[0110] 28. The foldable display device of any of clauses 16-27, further comprising a control system configured to: control the ultrasonic fingerprint sensor system to obtain ultrasonic image data from one or more objects in contact with an outer surface of the foldable display device; and perform an authentication process based at least in part on the ultrasonic image data.

[0111] 29. The foldable display device of clause 28, wherein the one or more objects comprise one or more fingers, and wherein the authentication process is a fingerprint-based authentication process.

[0112] 30. A method comprising: controlling, by a control system, an ultrasonic fingerprint sensor system to operate in a near-field mode with a peak frequency in a range of 1 megahertz (MHz) to 6 MHz; controlling, by the control system, the ultrasonic fingerprint sensor system to obtain ultrasonic image data from one or more objects in contact with an outer surface of a device comprising the ultrasonic fingerprint sensor system; and performing, by the control system, an authentication process based at least in part on the ultrasonic image data.

[0113] As used herein, the phrase referring to at least one of a list of items refers to any combination of those items, including single members. As an example, "at least one of a, b, or c" is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c.

[0114] The various illustrative logics, logical blocks, modules, circuits and algorithm processes described in connection with the implementations disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. The interchangeability of hardware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware or software depends on the particular application and design constraints imposed on the overall system.

[0115] The hardware and data processing apparatus used to implement the various illustrative logics, logical blocks, modules and circuits described in connection with the aspects disclosed herein can be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor can be a microprocessor, but, in the alternative, can be any conventional processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, particular processes and methods can be performed by an electrical circuitry specifically designed and constructed for the performance of the particular process and method.

[0116] In one or more aspects, the functions described can be implemented in hardware, digital electronic circuitry, computer software, firmware, including the structures disclosed in this specification and their structural equivalents, or in any combination thereof. Implementations of the subject matter described in this specification also can 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, or to control the operation of, data processing apparatus.

[0117] If implemented in software, the functions can be stored on or transmitted over as one or more instructions or code on a computer-readable medium such as a non-transitory medium. The processes of a method or algorithm disclosed herein can be implemented in a processor-executable software module which can reside on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that can be enabled to transfer a computer program from one place to another. Storage media can be any available media that can be accessed by a computer. By way of example, and not limitation, non-transitory media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection can be properly termed a computer-readable medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, the operations of a method or algorithm can reside in one or any combination of the machine-readable media used for the storage of software whereby the instructions for the operation of the method or algorithm are carried on the machine-readable media.

[0118] Various modifications to the specific implementations described herein will be readily apparent to those of ordinary skill in the art, and the generative principles defined herein can be applied to other implementations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the implementations shown herein but is to be accorded the widest scope consistent with the claims, the principles and the novel features disclosed herein. The word “exemplary” (if used herein) is used herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations.

[0119] While several inventive embodiments have been described and illustrated, it is understood that these embodiments are merely hypothetical examples of mechanisms embodying the application and that numerous mechanical modifications have been and can be made by those of ordinary skill in the art, and that such modifications are contemplated to be within the scope of the present application. Accordingly, it is not intended that the application be limited by the above described embodiments but rather that these embodiments be understood to provide practical examples of the present application. Other substitutions, modifications, changes, and omissions can be made by those of ordinary skill in the art to which the application relates without departing from the spirit and scope of the application.

[0120] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring such an order nor that all illustrated operations be performed to achieve desirable results. In certain circumstances, multitasking and parallel processing can be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

[0121] It is understood that, except for any operational features explicitly identified as incompatible with each other, or the surrounding context implies that they are mutually exclusive and not readily combined in a complementary and / or supportive sense, the present disclosure contemplates and envisions that particular features of those complementary implementations can be selectively combined to provide one or more overall but slightly different technical solutions. It is therefore also understood that the above description is given solely as an example and can be modified in detail within the scope of the present disclosure.

Claims

1. A foldable display device, the foldable display device comprising: a display system comprising a display stack; an ultrasonic fingerprint sensor system comprising an ultrasonic fingerprint sensor system stack; and a reinforcement layer residing between the display stack and the ultrasonic fingerprint sensor system stack, a reinforcement layer thickness of the reinforcement layer configured to allow the ultrasonic fingerprint sensor system to operate in a near-field mode with a peak frequency in a range of 1 megahertz (MHz) to 6 MHz.

2. The foldable display device of claim 1, wherein the operation of the ultrasonic fingerprint sensor system in the near-field mode provides a resolution of at least 3 wire pairs per millimeter.

3. The foldable display device of claim 1, wherein the reinforcement layer thickness corresponds to a transmission coefficient in a range of 10% to 30% for ultrasonic waves in the range of 1 MHz to 6 MHz.

4. The foldable display device of claim 1, wherein the reinforcement layer comprises stainless steel, titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), or a combination thereof.

5. The foldable display device of claim 4, wherein the reinforcement layer comprises a stainless steel layer, a titanium layer, a CFRP layer, or a GFRP layer with a thickness in a range of 30 micrometers to 200 micrometers, or an aluminum layer with a thickness in a range of 100 micrometers to 300 micrometers.

6. The foldable display device of claim 1, further comprising an adhesive layer residing on a side of the reinforcement layer proximate to the display stack, a thickness of the adhesive layer being less than 100 micrometers.

7. The foldable display device of claim 1, wherein the display stack comprises a display glass layer residing between the reinforcement layer and an outer surface of the foldable display device, the display glass layer comprising glass, transparent plastic, or a combination thereof, wherein a first acoustic resonator is bounded by the reinforcement layer and the display glass layer, the first acoustic resonator configured to induce a first local maximum of ultrasonic wave transmission.

8. The foldable display device of claim 7, wherein the first acoustic resonator comprises at least one first resonator flexible optical clear adhesive (OCA) layer, a thickness of the at least one first resonator flexible OCA layer being substantially an odd or even multiple of one eighth of a wavelength of ultrasonic waves in a range of 1 MHz to 14 MHz, wherein substantially indicates within ±10%.

9. The foldable display device of claim 7, further comprising one or more layers residing between the display glass layer and the outer surface of the foldable display device, wherein a second acoustic resonator comprises the one or more layers and the display glass layer. ​ 10. The foldable display device of claim 9, wherein the one or more layers comprise a second resonator flexible optical clear adhesive (OCA) layer having a thickness in a range of 5 micrometers to 180 micrometers.

11. The foldable display device of claim 1, wherein the stiffener layer thickness is less than one fifth of a wavelength corresponding to the peak frequency.

12. The foldable display device of claim 1, wherein the display stack comprises one or more display stack layers having a sound speed above a sound speed threshold, each of the one or more display stack layers having a thickness less than one fifth of a wavelength corresponding to the peak frequency.

13. The foldable display device of claim 12, wherein the sound speed threshold is in a range of 2000 meters per second to 2500 meters per second.

14. The foldable display device of claim 1, further comprising a control system configured to: control the ultrasonic fingerprint sensor system to obtain ultrasonic image data from one or more objects in contact with an outer surface of the foldable display device; and perform an authentication process based at least in part on the ultrasonic image data.

15. The foldable display device of claim 14, wherein the one or more objects comprise one or more fingers, and wherein the authentication process is a fingerprint-based authentication process.

16. A foldable display device, comprising: a display system comprising a display stack; an ultrasonic fingerprint sensor system configured to operate in a near-field mode at a peak frequency in a range of 1 megahertz (MHz) to 6 MHz, the ultrasonic fingerprint sensor system comprising an ultrasonic fingerprint sensor system stack; and a stiffener layer residing between the display stack and the ultrasonic fingerprint sensor system stack, the stiffener layer having a stiffener layer thickness less than one fifth of a wavelength corresponding to the peak frequency.

17. The foldable display device of claim 16, wherein the display stack comprises one or more display stack layers having a sound speed above a sound speed threshold, each of the one or more display stack layers having a thickness less than one fifth of a wavelength corresponding to the peak frequency.

18. The foldable display device of claim 17, wherein the sound speed threshold is 2500 meters per second.

19. The foldable display device of claim 16, wherein operation of the ultrasonic fingerprint sensor system in the near-field mode provides a resolution of at least 3 lines per millimeter.

20. The foldable display device of claim 16, wherein the stiffener layer thickness corresponds to a transmission factor in a range of 10% to 30% for ultrasonic waves in a range of 3 MHz to 6 MHz.

21. The foldable display device of claim 16, wherein the stiffener layer comprises stainless steel, titanium, aluminum, carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), or a combination thereof.

22. The foldable display device of claim 16, wherein the reinforcement layer comprises a stainless steel layer, a titanium layer, a CFRP layer, or a GFRP layer having a thickness in a range of 30 micrometers to 200 micrometers, or an aluminum layer having a thickness in a range of 100 micrometers to 300 micrometers.

23. The foldable display device of claim 16, further comprising an adhesive layer residing on a side of the reinforcement layer proximate to the display stack, the adhesive layer having a thickness less than 100 micrometers.

24. The foldable display device of claim 16, further comprising a display cover layer residing between the display stack and an outer surface of the foldable display device, the display cover layer comprising glass, transparent plastic, or a combination thereof, wherein a first acoustic resonator comprises the reinforcement layer, the display stack, and the display cover layer, the first acoustic resonator configured to cause a first local maximum of ultrasonic wave transmission.

25. The foldable display device of claim 24, wherein the first acoustic resonator comprises at least one first resonator flexible optically clear adhesive (OCA) layer having a thickness substantially an odd or even multiple of one-eighth of a wavelength corresponding to an ultrasonic wave in a range of 1 MHz to 14 MHz, wherein substantially indicates within ±10%.

26. The foldable display device of claim 24, further comprising one or more layers residing between the display cover layer and the outer surface of the foldable display device, wherein a second acoustic resonator comprises the one or more layers and the display cover layer.

27. The foldable display device of claim 26, wherein the one or more layers comprise a second resonator flexible optically clear adhesive (OCA) layer having a thickness corresponding to an odd multiple of one-eighth of a wavelength corresponding to an ultrasonic wave in a range of 1 MHz to 14 MHz ±10%.

28. The foldable display device of claim 16, wherein the ultrasonic fingerprint sensor system comprises a thin film transistor (TFT) layer or a semiconductor layer, wherein an acoustic resonator comprises the reinforcement layer and the TFT layer or the semiconductor layer, the acoustic resonator configured to cause a first local maximum of ultrasonic wave transmission.

29. The foldable display device of claim 16, wherein the ultrasonic fingerprint sensor system comprises a thin film transistor (TFT) layer, a piezoelectric layer, and a backing layer, wherein an acoustic resonator comprises the TFT layer, the piezoelectric layer, and the backing layer, the acoustic resonator configured to cause a first local maximum of ultrasonic wave transmission.

30. A method, the method comprising: controlling, by a control system, an ultrasonic fingerprint sensor system to operate in a near-field mode having a peak frequency in a range of 1 megahertz (MHz) to 6 MHz; controlling, by the control system, the ultrasonic fingerprint sensor system to obtain ultrasonic image data from one or more objects in contact with an outer surface of a device that includes the ultrasonic fingerprint sensor system; and performing, by the control system, an authentication process based at least in part on the ultrasonic image data.

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