Ultrasonic fingerprint sensing
Capture d'empreintes digitales à ultrasons

Each time the sound speed varies, for instance at an interface between two materials, a reflection/transmission occurs (the same as light). An ultrasonic wave is sent, and an echo is received later, depending on the sound speed. One problem is the multiple echoes.

Ultra-sound fingerprint reading was not common in the past, and required quite a big device with mechanical parts, and was quite expensive. Moreover, it took a few seconds to grab an image, and was not suited for large production volumes at low cost. Its main advantage is the possibility to read the derma, the sub-surface of the skin, rather than only the surface.

Several companies are working to make small solid-state ultrasonic sensors, and production started with UltraScan/Qualcomm in 2016.

In 2017, there is a big hype because ultrasound sensors may solve the "in-display" problem for smartphone makers, as they want to propose an edge-to-edge displays, and moreover, it looks more natural to put your fingerprint directly on the screen. (Fingerprint sensors on the back are less expensive, but this position is not natural although some people like that).

• (2019) A summary about this technology: Ultrasound Systems for Biometric Recognition (local copy).

• (1991) Live scan fingerprint imagery using high resolution C-scan ultrasonography / Schneider, J.K. & als / Niagara Technol. Lab. Buffalo
• (2001) Ultrasonic imaging systems for personal identification / Schneider, J.K. & als / Ultra-Scan
• This technology leads to pretty big sensors.

• (2007 Sep) Backed by a new $5 million investment from L-1 Identity Solutions, Ultra-Scan is working to develop and make a new fingerprint reader that is much smaller than current scanners and is able to scan four fingers, instead of just one.
• (2011 Nov) Ultrascan announces a new sensor design, including control electronics, with a very small profile, measuring 4.25” x 4.75” with a thickness of 0.25”, and an active image area of 3.75” x 3.75” at 500 dpi.

• (2017 June 28) Qualcomm announces advanced fingerprint scanning and authentication technology, Capable of Scanning Through Display, Thick Glass and Metal with Underwater Operation, Heartbeat and Blood Flow Detection. Indeed? All this through the display? First customer: Vivo smartphone.

• (2019 Dec) The 20x30mm sensor is unveiled. Announces 1 to 1 million FAR (like Apple for its FaceID), which could make sense when you acquire two fingers: the larger the sensing area, the better. Called "3D Sonic Max".
• About the Galaxy S10 disaster when using a cover:
  "It's practically impossible to try to predict what types of patterns will be available or what types of covers," Katouzian said. "We are constantly buying different covers and different materials to make sure the algorithm can tell the difference between a legitimate fingerprint and a spoof."

• (2021 Jan) Introducing Qualcomm 3D Sonic Sensor Gen 2
  Qualcomm 3D Sonic Sensor Gen 1 was 4x9mm (surface area 36mm²). Gen 2 will debut with a sensor that is 8x8 (64mm²).
• (2021 Jan) The sensor is released inside the Galaxy S21. Thank you JerryRigEverything for the teardown.
  This is not the very large 20x30mm sensor: likely too expensive.

• (2004 Aug) Ultrasonic imaging of fingerprints using acoustical impediography / Schmitt, R.M. (CrossMatch).
  "Authorizer prototype": 64x64 pixels @126 micron pitch (announced @250dpi, but this is 200 dpi).

• (Sonavation datasheet) The patented SonicTouch^TM technology used in Sonavation’s SonicSlide^TM sensors works very much like the ultrasound technology used in medical applications. The ridges and valleys of the fingerprint are acoustically measured to image the fingerprint in 256 shades of gray in order to discern the slightest fingerprint detail...
  The key imaging component of the sensor is the ceramic Micro-Electro Mechanical System (MEMS) piezoelectric transducer array that is made from a ceramic composite material. When this piezoelectric material is formed into a pillar 1/10th the diameter of a human hair, it has a unique set of properties that enable it to mechanically oscillate when an electric field is applied or create an electrical voltage when mechanically vibrated. The piezoelectric pillar is electrically vibrated at its natural ultrasonic resonant frequency. If a fingerprint ridge is directly above the pillar, much of the ultrasonic energy is absorbed by the skin and the signal impedance of the pillar is very high. If a valley is directly above the pillar, very little energy is absorbed and the impedance is very low. By arranging the pillars in a matrix of several thousand elements a two-dimensional image of a fingerprint can be created. The imaging ASIC electrically controls the pillar oscillation, imaging of the fingerprint and data management of the fingerprint information.

• (2013) The Swarm lab of Berkeley is developping an ultrasonic sensor. See also the sensor electronics research group. 8x24 pixels @ 250dpi.
• (2015) The Piezoelectric Micromachined Ultrasonic Transducers for Fingerprint Sensing Ph.D thesis : Yipeng Lu

• (2015 Jun) The Ultrasonic fingerprint sensor using a piezoelectric micromachined ultrasonic transducer array integrated with complementary metal oxide semiconductor electronics Lu & als. This paper presents an ultrasonic fingerprint sensor based on a 24x8 array of 22MHz AlN piezoelectric micromachined ultrasonic transducers (PMUTs) with 100um pitch, fully integrated with 180nm complementary metal oxide semiconductor (CMOS) circuitry through eutectic wafer bonding.
• (2015 Oct) Invensense announces UltraPrint™, its ultrasonic fingerprint imaging solution, manufactured on the proprietary InvenSense CMOS-MEMS Platform (ICMP), offering ramp to production in calendar year 2017.

• BEFS (Best Friend Solutions) is a subsidiary of Cammsys (2014).
• (2017 Jan) The BEFS applying for patents for commercializing of ultrasonic fingerprint identification sensor technology
• (2017 Apr) Development of a ceramic ultrasonic fingerprint recognition sensor: demo.

• (2017 Nov) Fingerprint Cards explains in their Technology Update why ultrasonic sensing is better for a full in-display fingerprint sensor. (local copy).
  Looks to work more or less like the Optel sensor.

• (2018 Sep) ultrasound fingerprint sensor prototype, PMUT based (AlN). Mass production expected early 2019.

• (1998) Fingerprint structure imaging based on an ultrasound camera / Wieslaw Bicz et al.
• Optel holographic ultrasonic camera for fingerprint recognition.

• (2009) High resolution ultrasonic method for 3D fingerprint recognizable characteristics in biometrics identification / Maeva & als.
• (2011) Data Acquisition System for Fingerprint Ultrasonic Imaging Device Moeen ud Din / University of Windsor
• (2012) High-speed biometrics ultrasonic system for 3D fingerprint imaging Roman G. Maev and Fedar Severin

• Cornell Research / SonicMEMS, a New Edge for Electronics / SonicMEMS Lab / GeeGah / A*STAR
• (2017 Jan) 64-Pixel solid state CMOS compatible ultrasonic fingerprint reader / Justin C. Kuo & al. + Intel
  linear array 64 pixels ultrasonic (AlN)
• (2017 Sep) Wideband material detection for spoof resistance in GHz ultrasonic fingerprint sensing / Justin C. Kuo; Amit Lal

• (2019 Jun) Cmos Controlled Ghz Ultrasonic Impedance Imager / Mamdouh Abdelmejeed ; Justin Kuo ; Adarsh Ravi ; Amit Lal
  single transducer.
• (2019 Dec) Monolithic 180nm CMOS Controlled GHz Ultrasonic Impedance Sensing and Imaging / Mamdouh Abdelmejeed & al.
  AlN on CMOS 180 nm chip, ultrasonic waves through the silicon. Transmit & receive transducers are 50x50 microns.

• (2017 May) Large-Scale and High-Density pMUT Array Based on Isolated Sol-Gel PZT Membranes for Fingerprint Imaging / Yuan-Quan Chen et al. (local copy)

• (2021 Jan) Under-Display Ultrasonic Fingerprint Recognition with Finger Vessel Imaging / Peng & al. / (North Carolina State University / supported in part by Goodix).
  One pixel moving / 500 dpi demonstrated. Based on PZT-5H. Detect a vessel @ 1 mm depth.
  Curiously, no real fingerprint image displayed !

• (2023 Jan) High Step-Up Ratio DC-AC Converter Using Fourth-Order LCLC Resonant Circuit for Ultrasonic Fingerprint-Sensor Drivers / Wei Liu & als. (local copy)

• (~2010) Tessonics is developping a new robust fingerprint identification technology based upon forming surface-subsurface (under skin) ultrasonic 3D images of the finger pads. (AM-1103)

• (2010) Aculab, the Acousto-Electronics Laboratory of the "Univeristà degli Studi Roma Tre", Rome, Italy, operates in the "Dipartimento di Ingegneria" in the field of ultrasonics-related research.
  Design and fabrication of a cMUT probe for ultrasound imaging of fingerprints / A. Savoia & als.
• (2011) A high frequency cMUT probe for ultrasound imaging of fingerprints
  Nicola Lambertia, Giosue Caliano, Antonio Iula, Alessandro Stuart Savoia

• (2012) Capacitive micromachined ultrasonic transducer (cMUT) for biometric applications PAVLO FESENKO / CHALMERS UNIVERSITY OF TECHNOLOGY, Göteborg, Sweden