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EP-3867797-B1 - ULTRASONIC FINGERPRINT SENSOR WITH FLEXIBLE SUBSTRATE

EP3867797B1EP 3867797 B1EP3867797 B1EP 3867797B1EP-3867797-B1

Inventors

  • LU, YIPENG
  • PANCHAWAGH, Hrishikesh Vijaykumar
  • DJORDJEV, Kostadin Dimitrov
  • SEO, JAE HYEONG
  • BUCHAN, NICHOLAS IAN
  • TSENG, CHIN-JEN
  • KAO, TSONGMING

Dates

Publication Date
20260513
Application Date
20190918

Claims (10)

  1. An ultrasonic fingerprint sensor system (1120, 1220, 1330) comprising: a flexible substrate (1221, 1331) having a plurality of sensor circuits; and an ultrasonic transceiver (1223, 1333) coupled to the flexible substrate and provided between the flexible substrate and a display (1227, 1338), wherein the ultrasonic transceiver comprises: a piezoelectric layer (1224, 1334), formed on the flexible substrate, and configured to generate ultrasonic waves and receive reflections of ultrasonic waves; and an electrically nonconductive acoustic layer (1226, 1336) disposed on an electrically conductive layer (1225, 1335b), the layers being adjacent to the piezoelectric layer and disposed on or over a side of the piezoelectric layer facing the display, characterized in that the electrically nonconductive acoustic layer includes a dielectric material having an acoustic impedance value greater than 8.0 MRayls, and wherein the electrically conductive layer includes a metal layer having a thickness between 10 nm and 2 µm, wherein the ultrasonic fingerprint sensor system is underlying the display and configured to attach to the display.
  2. The system of claim 1, wherein the electrically conductive layer is an electrode layer (1225) coupled to the piezoelectric layer.
  3. The system of claim 2, wherein the electrode layer includes silver ink.
  4. The system of claim 2, wherein the electrode layer is divided in a plurality of electrode segments.
  5. The system of claim 1, wherein the electrically conductive layer includes silver ink.
  6. The system of claim 1, wherein the metal layer includes aluminum, nickel, copper, or combinations thereof.
  7. The system of claim 1, wherein the electrically conductive layer is a routing layer (1335b) and the ultrasonic transceiver further comprises an electrode layer (1335a) and a photo-imageable epoxy layer (1337) between the electrically nonconductive acoustic layer and the piezoelectric layer, wherein the photo-imageable epoxy layer is sandwiched between the routing layer and the electrically conductive layer.
  8. The system of any one of claims 1-7, wherein the flexible substrate includes polyimide and has a thickness between 25 µm and 75 µm.
  9. The system of any one of claims 1-7, wherein the ultrasonic transceiver is overlying the flexible substrate so that the piezoelectric layer is between the flexible substrate and the display.
  10. The system of claim 9, further comprising: a backing layer disposed on and underlying the flexible substrate, wherein the flexible substrate has a thickness between 5 µm and 50 µm, wherein the backing layer has a thickness between 5 µm and 50 µm.

Description

TECHNICAL FIELD This disclosure relates generally to ultrasonic fingerprint sensor systems and more particularly to ultrasonic fingerprint sensor systems with flexible substrates. DESCRIPTION OF RELATED TECHNOLOGY In an ultrasonic sensor system, an ultrasonic transmitter may be used to send an ultrasonic wave through an ultrasonically transmissive medium or media and towards an object to be detected. The transmitter may be operatively coupled with an ultrasonic sensor configured to detect portions of the ultrasonic wave that are reflected from the object. For example, in ultrasonic fingerprint imagers, an ultrasonic pulse may be produced by starting and stopping the transmitter during a very short interval of time. At each material interface encountered by the ultrasonic pulse, a portion of the ultrasonic pulse is reflected. For example, in the context of an ultrasonic fingerprint imager, the ultrasonic wave may travel through a platen on which a person's finger may be placed to obtain a fingerprint image. After passing through the platen, some portions of the ultrasonic wave encounter skin that is in contact with the platen, e.g., fingerprint ridges, while other portions of the ultrasonic wave encounter air, e.g., valleys between adjacent ridges of a fingerprint, and may be reflected with different intensities back towards the ultrasonic sensor. The reflected signals associated with the finger may be processed and converted to a digital value representing the signal strength of the reflected signal. When multiple such reflected signals are collected over a distributed area, the digital values of such signals may be used to produce a graphical display of the signal strength over the distributed area, for example by converting the digital values to an image, thereby producing an image of the fingerprint. Thus, an ultrasonic sensor system may be used as a fingerprint imager or other type of biometric scanner. In some implementations, the detected signal strength may be mapped into a contour map of the finger that is representative of the depth of the ridge structure detail. Ultrasonic sensor systems can be incorporated in display devices as fingerprint sensor systems to authenticate a user. Advances in display devices have resulted in flexible displays, three-dimensional cover glasses, and bezel-less designs. Consequently, more and more display devices have limited space to incorporate a discrete button for a fingerprint sensor system or an under-glass fingerprint sensor system that is positioned peripherally to the display of the display device. An under-glass and under-display fingerprint sensor system may provide additional functionality and space to the display device and may open up additional authentication software applications for improved user interfaces. US 2017/364726 A1 discloses a fingerprint sensor device that includes a sensor substrate, a plurality of sensor circuits over a first surface of the sensor substrate, and a transceiver layer located over the plurality of sensor circuits and the first surface of the sensor substrate. US 2014/352440 A1 discloses an ultrasonic sensor with bonded piezoelectric layer. SUMMARY The devices, systems, and methods of this disclosure each have several aspects, no single one of which is solely responsible for the desirable attributes disclosed herein. The invention is defined in the independent claims. Optional features are set out in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, drawings and claims. Note that the relative dimensions of the following figures may not be drawn to scale. Like reference numbers and designations in the various drawings indicate like elements. Figure 1 shows a front view of a diagrammatic representation of an example mobile device that includes an ultrasonic sensing system.Figure 2A shows a block diagram representation of components of an example ultrasonic sensing system according to some implementations.Figure 2B shows a block diagram representation of components of an example mobile device that includes the ultrasonic sensing system of Figure 2A.Figure 3A shows a cross-sectional projection view of a diagrammatic representation of a portion of an example ultrasonic sensing system according to some implementations.Figure 3B shows a zoomed-in cross-sectional side view of the example ultrasonic sensing system of Figure 3A according to some implementations.Figure 4A shows an exploded projection view of example components of the example ultrasonic sensing system of Figures 3A-3B according to some implementations.Figure 4B shows an exploded projection view of example components of an ultrasonic transceiver array in an ultrasonic sensor system of Figures 3A-3B according to some implement