Fingerprint sensing techniques
Techniques de capture d'empreintes digitales




Ink

Ink and paper are the tried-and-true way to take fingerprints, but technology has found ways to eliminate smudges and ink stains.

L'encre et le papier a longtemps été la méthode traditionelle pour collecter les empreintes, mais la technologie a vite permis d'éliminer les tâches.

Fortunately, some inkless techniques exist :)

Fingerprinting Fingerprinting ink Fingerprinting inkless

Optical readers / La lecture optique

Reflection with contact / Réflexion avec contact

The oldest 'live-scan' readers use frustrated refraction over a glass prism (when the skin touches the glass, the light is not reflected but absorbed). The finger is illuminated from one side with a LED while the other side transmits the image through a lens to a camera. (FTIR: frustrated total internal reflection).

La plus ancienne technique de capture d'empreinte "live" est l'usage de la réflexion totale sur un prisme en verre (lorsque la peau touche le verre, la lumière n'est plus réfléchie, elle est absorbée). Le doigt est éclairé à l'aide d'une DEL (diode électroluminescente) par un coté du prisme, tandis que l'image est récupérée de l'autre coté avec une lentille et un capteur d'image.
(Ce schéma date de 1996, les capteurs CMOS étaient fort rares...)

  • (2000) Here is the example of the Compaq fingerprint reader (CMOS camera).
Optical sensor with red LEDs

Generally, one fingerprint is taken at a time, but some devices are able to acquire several fingers at a time (slap).

Généralement, une seule empreinte est prise à la fois, mais certains appareils peuvent capturer plusieurs empreintes à la fois.

Many companies are offering such devices, this is a common technology. Some are offering some variants less common.

Cette technologie de capture est très courante, et de nombreuses compagnies l'utilisent. Quelques-unes offrent des variantes moins courantes.

Nagoya micro-collimator
  • Nagoya University uses a micro-collimator instead of the fiber optic, enabling direct fingerprint comparison.
    L'université de Nagoya utilise un micro-collimateur à la place de la fibre optique, afin de réaliser une comparaison directe de l'empreinte.

    (1999) Fingerprint Sensor with Micro Collimator (Nagoya Univ.)

TFT optical / TFT optique

(1997) Philips replaces the CMOS sensor by a TFT display, used as sensor. Philips has also worked with Ethentica to combine their technologies, but without known product. LG has also studied a TFT sensor.
(1997) Philips remplace le capteur CMOS par un afficheur TFT, utilisé comme capteur. Philips a également travaillé avec Ethentica pour combiner leur technologies. LG a aussi fait des recherches sur les capteurs TFT.

Other companies proposing TFT fingerprint sensors:

Philips TFT
Casio Casio sensor SiliconImageWorks
  • (2005 Jul) NanoIdent unveils a flexible fingerprint sensor using a polymer organic photodetector.
  • Note: a variant of TFT devices is using the capacitance information instead of reflected light.


    Pinhole / Sténopée


  • (2015) Vkansee introduces a 2000dpi reader, UTFIS, using advanced pinhole imaging techniques to take a high-resolution image.

  • Reflection with sweep / Réflexion avec balayage


  • (1999) Kinetic Sciences and Cecrop/Sannaedle have proposed sweep optical sensors.
    Kinetic Sciences et Cecrop/Sannaedle ont proposé des capteurs optiques à balayage.
    Paper describing the sensor (dead link):
    http://www.smta.org/files/telecom_solutions02_immega.pdf
  • Kinetic Sciences Kinetic Sciences
  • Casio + Alps Electric uses a roller with the sensor inside. The roller acts like the prism.
    Casio + Alps Electric utilise une roulette contenant le capteur. La roulette agit comme prisme.
  • Casio + Alps optical roller
  • As well as Digital Persona with the Firefly
    Ainsi que Digital Persona et son Firefly
  • Digital Persona Firefly

    Reflection touchless / Réflexion sans contact


    Instead of touching a platen, the idea is to acquire directly the fingerprint image with an adapted camera.

  • (2003) TST Touchless Sensor Technology removed the prism by directly reading the fingerprint, so the finger does not touch anything (but still need a guide to get the right optical distance).
  • acquisition TST sensor fingerprint captured with TST sensor
  • (2004) The BERC lab from Yonsei University (Korea) also developped a touchless sensor.
  • BERC touchless
  • (2005) TBS launches a touchless sensor with the "Surround Imaging".
  • TBS touchless
  • (2011 Jan) AOS Advanced Optical Systems develops AIRprint, a device that detects fingerprints by shining polarized light onto a person's hand and analyzing the reflection using two cameras configured to detect different polarizations, able to scan fingerprints from up to two meters away.
  • (2013) OnePrint & IDAir
  • (2015) AOS Advanced Optical Systems installs at Schiphol its zero contact fingerprint sensor (ANDI OTG).
  • (2009 Sep) FlashScan3D and TBS Holding unveils a new touchless fingerprint sensor technology using Structured Light Illumination (SLI) developped by two universities (University of Kentucky and Carnegie Mellon).
  • More info about structured light and fingerprint on the Saleh Mosaddegh website
  • FlashScan3D
  • (2014 Aug) Finger On the Fly® from Safran/Morpho is using structured light.
  • (2014 Sep) Compact touchless fingerprint reader based on digital variable-focus liquid lens C.W. Tsai ; P.J. Wang ; J.A. Yeh .
  • C. W. Gary Tsai founded Lustrous Electro-Optics Inc. Hsinchu, Taiwan. See Digital liquid lens for fast scanning technologies


  • Reflection with a gel / Réflexion sur un gel


  • (2009) GelSight, Inc. provides extremely detailed and rapid surface measurements through the GelSight sensor technology. [2009 SIGGRAPH Emerging Technologies]
  • This is not a sensor specifically for fingerprint. But a very original method, close to the touchless reading in fact.
  • Microgeometry Capture using an Elastomeric Sensor
  • Retrographic sensing for the measurement of surface texture and shape


  • Transmission


  • It is also possible to directly read the light transmitted by the finger.
    On peut aussi utiliser la lumière transmise par le doigt.
  • Transmission through the finger
  • Mitsubishi proposes to read the fingerprint with a regular camera.
    Mitsubishi propose de lire l'empreinte avec une caméra normale.
  • (2005 Sep) Mitsubishi launches the Mitsubishi Finger Transmission Authentication Device
  • Mitsubishi sensor
  • NEC and Delsy (and Secom?) use a CMOS camera which is the size of the finger, with a fiber optic in-between, the light is coming from the edges in this case.
    NEC et Delsy (et Secom?) utilisent un capteur optique CMOS qui est nécessairement de la taille du doigt, avec une fibre optique déposée sur le capteur, la lumière provenant des bords dans ce cas.
  • (2015 Dec) Holtek is using this principle with the GH8111
  • Using fiber optics Delsy sensor
  • Mitsumi, NEC Elecvision proposes the same but with a sweep sensor.
    Mitsumi, NEC & Elecvision propose le même principe, mais avec un procédé à balayage.
  • Mitsumi SEF-A1

    Optical coherence tomography

    Fingerprint detection using full-field swept-source optical coherence tomography
    Appl. Phys. Lett. 91, 181106 (Published Date: 30 October 2007).
    Satish Kumar Dubey, Tulsi Anna, Chandra Shakher, and Dalip Singh Mehta
    Laser Applications and Holography Laboratory, Instrument Design Development Centre, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India

    We report the application of full-field swept-source optical coherence tomography for fingerprint detection. This system consists of a superluminescent diode as broadband light source and an acousto-optic tunable filter as wavelength-tuning device. The conventional optical coherence tomographic system was modified by coating aluminum oxide on one side of the beam splitter which is used as reference mirror and fingerprints on the glass slide as object. Low-coherence interferometry, nonmechanical scanning, and compactness are the main advantages of the proposed system over conventional fingerprint detection techniques. The present technique is noninvasive in nature and does not require any physical or chemical processing.

    Langevin Institute

  • (2015 Oct) The Langevin Institute has made an OCT (optical coherence tomography) device specifically to acquire fingerprints.
    Fingerprint imaging from the inside of a finger with full-field optical coherence tomography Egidijus Auksorius and A. Claude Boccara.

  • Electro-optical readers / La lecture électro-optique

    Ethentica TesTech

    Some polymers are able to emit light when properly excited with the proper voltage (generally quite a high voltage is required. This polymer is directly contacting a CMOS camera, which is necessarily the size of the finger. Generally, the finger acts as the ground, and the polymer emits light where the ridges touch. Ethentica and TesTech propose such a solution.
    Certains polymères sont capables d'émettre de la lumière lorsqu'ils sont convenablement polarisé (généralement une assez haute tension est requise). Ce polymère est directement déposé sur une caméra CMOS, qui est nécessairement de la taille du doigt. En général, le doigt sert de masse, et le polymère émet de la lumière là où les crêtes touchent. Ethentica et TestTec propose ce genre de capteur.


    Capacitance / Capacité

    Passive Capacitance / Capacité passive

    After optical sensing, the measurement of the capacitance between the skin and the pixel is the most physical effect used to acquire fingerprints. Where there is a ridge or a valley, the distance varies, as does the capacitance. Because an electrical field is measured and the distance between the skin and the pixel must be very low to provide enough sensitivity, the coating must be as thin as possible (a few microns). A significant drawback is vulnerability to strong external electrical fields, the most dangerous being ESD (Electro-Static Discharge).
    Après la lecture optique, la mesure de la capacité électrique entre la peau et le pixel est l'effet physique le plus souvent mis en oeuvre: la capacité électrique varie comme l'inverse de la distance, ce qui permet de distinguer crêtes et vallées. Comme le champ électrique mesuré entre la peau et le pixel est très faible, la protection surfacique doit être très mince (quelques microns) afin d'obtenir une sensiblité correcte. Un défaut connu est la sensibilité aux forts champs électriques, comme ceux provoqués par les décharges électrostatiques ESD.

    Silicon chips / puces silicium

    Silicon chips can be seen as a variant of the CMOS cameras: instead of using the light, another physical effect is used.
    Les puces silicium (électroniques) peuvent être vues comme une variante des cameras CMOS: au lieu d'utiliser les photons, un autre effet physique est utilisé.

    Companies proposing (or having proposed) capacitance sensing:
    Compagnies proposant (ou ayant proposé) des capteurs d'empreintes capacitifs:

  • Veridicom, Fujitsu, Infineon, Sony, Upek, Hitachi, LighTuning, Melfas, Atrua, NTT, Symwave, ...
  • Labs working (or having worked) on silicon capacitance sensors:
    Laboratoires travaillant (ou ayant travaillés) sur les capteurs d'empreintes capacitifs:
    Seoul University (1999)
  • (1999) Seoul University A 600-dpi Capacitive Fingerprint Sensor Chip and Image-Synthesis Technique (Lee & als, Seoul National University, 1998)
  • Kaist
  • (2002) Kaist IML KAIST
  • NTT Low Energy Labs (1999)
  • (1999) NTT NTT Microsystem Integration Laboratories
  • A Single-Chip Fingerprint Sensor and Identifier (Shigematsu & als)
  • (2008) Low Parasitic Capacitance and Low-Power CMOS Capacitive Fingerprint Sensor Department of Electrical Engineering / National Chi Nan University /Puli, Nantou, 545 Taiwan
    500 dpi, 32x32 pixels.
  • (2013) Design of Low Power and High Speed CMOS Fingerprint Sensor School of Information and Telecommunication, Hanshin University, Osan, Korea
    160x192 pixels.


  • Capacitance + TFT / capacitif + TFT

    Flat panel technology rather than bulk silicon has been studied by Philips Korea and some others, using capacitive sensing.

    La technologie des écrans plats a été étudiée par Philips comme substitut du silicium, en utilisant un effet capacitif.

  • (2003) Mitsubishi Electric Corp.
  • (2004 Apr) Alps Electric develops 2 fingerprint sensors. One is transparent, electrostatic (capacitive).
    Alps Electric développe 2 capteurs d'empreinte. L'un d'eux est transparent, électrostatique (capacitif).
  • Alps Electric, electrostatic reading Alps Electric, transparent sensor

    RF field - Active capacitance / transmission RF - capacitif actif

    Sometimes confused with capacitance sensing, the common point between RF field sensing and capacitance sensing is the "capacitance" connection of the signal.
    Parfois confondu avec les capteurs capacitifs, le seul point commun entre un capteur RF et un capteur capacitif est la liaison électrique "capacitive" du signal.

    A low radio frequency (RF) signal is injected into the finger, then read by the pixels on the silicon acting like antennas. The signal strenght depends on the capacitance/resistive connection, so from the distance between the skin and the pixel.
    Un faible signal radiofréquence est injecté dans le doigt, puis lu par les pixels sur le silicium qui agissent comme des antennes. La puissance du signal lu dépend de la liaison capacitive/résistive, donc de la distance entre la peau et le pixel.

    When the frequency is zero = a constant voltage, this is the simple impedance/resistance that is used.
    Lorsque la fréquence est zero = du courant continu, c'est la simple impédance/résistance qui est utilisée.

  • (1999) Proposé par G.Olavarrieta Fritsche / SEPI-ESIME [Mexico]: A simple fingerprint sensor based on ridge conductivity.
  • (2007 Mar) Imtek and Cross-Match are developping a foil sensor based on passive impedance.
  • Companies proposing (or having proposed) RF/AC-capacitance sensing:
    Compagnies proposant (ou ayant proposé) des capteurs d'empreintes RF:

    Labs working (or having worked) on RF capacitance sensing:
    Laboratoire travaillant (ou ayant travaillé) sur les capteurs d'empreintes RF:

    An alternate solution consists in having connection through wires, so the finger is not mandatory directly in contact with the active silicon part.
    Une solution alternative consiste à avoir les connexions via des fils, ce qui évite d'avoir le doigt directement en contact avec le silicium actif.
    Validity Chip-On-Film. Click to enlarge
  • Validity (now Synaptics) is offering a technology called High Frequency Co-Planar Amplitude Modulated RF Fingerprint Sensing which is using Kapton with interconnection lines for the sensing area.
  • Idex is using a piece of silicon to make the connections.

  • Pressure / Pression

    This is one of the oldest ideas, because when you put your finger on something, you apply a pressure. Piezo-electric material has existed for years, but unfortunately, the sensitivity is very low. Moreover, when you add a protective coating, the resulting image is blurred because the relief of the fingerprint is smoothed.
    These problems have been solved, and now some devices using pressure sensing are available.
    C'est une des plus anciennes idées, car lorsque vous posez votre doigt, vous appliquez une pression. Les matériaux piézo-électriques sont connus depuis longtemps, mais malheureusement leur sensibilité est très faible. De plus, lorsque vous ajoutez une protection surfacique, l'image résultante est floue car le relief de l'empreinte est atténué.
    Ces problèmes ont été résolus, et maintenant quelques dispositifs utilisant la pression sont disponibles.

    Several solutions, depending on the material, have been proposed:

    Conductive membrane on silicon / Membrane conductrice sur silicium

    (1994 Jul) Opsis (a french company) offered a device using a conductive membrane deposited on a CMOS chip.
    Opsis (France) a offert un dispositif utilisant une membrane conductrice déposée sur une puce CMOS (juillet 1994).

    Conductive membrane on TFT / Membrane conductrice sur TFT

    Alps Electric, pressure Alps Electric, pressure prototype
  • Since 2002, BMF is offering a product using a TFT substrate (developed with Sanyo)
  • Fidelica offers since mid-2004 the FIS-3002, also using a TFT substrate from Sanyo.
  • (April 2004) Alps Electric develops 2 fingerprint sensors. One is based on pressure.
  • The Fraunhofer IKTS is working on 1-3 piezocomposites to create a fingerprint sensor (for CrossMatch, 2004).
  • Micron Technology: Tactile sensor using an insulated flexible matrix loaded with filler particles US 6,561,044
  • Tactile MEMS

    Micro electro-mechanical devices allow engineers to make extremely tiny silicon switches. When a ridge touches a switch, it closes. But the coating remains a significant problem, and moreover, a binary image is the result, leading to minimal information. No further development has been done with this technique beyond the laboratory.
    Les dispositifs micro-usinés permettent la réalisation de très petits interrupteurs. Lorsque qu'une crête touche un interrupteur, elle le ferme. Mais la protection surfacique reste un problème délicat, et de plus on obtient une simple image binaire, contenant peu d'information. Il n'existe pas encore de développement ayant dépassé le stade du laboratoire.
  • (2001) NTT Microsystem Integration Laboratories
  • NTT research group
  • NTT
  • (1997) Very high density bulk micromachined capacitive tactile imager Michigan University (Wise)
  • Michigan university
  • Tima homepage
  • La thèse de Fabien Parrain (2002)
  • N.Galy thesis page and the thesis
  • CNRS: zoom sur le micro et nano systèmes: Tima
  • Tima Tima tactile chip
  • (2010) TIMA & Department of Electronic & Computer Engineering HKUST HONG KONG The Design, Fabrication and Characterization of a Piezoresistive Tactile Sensor for Fingerprint Sensing. 1 pixel, 100 to 250 microns
  • (1997) Leti, pressure sensors (Rey)
  • Leti
  • (2004) LighTuning
  • LighTuning MEMS

    Universiti Kebangsaan Malaysia / Mitra Damghanian, Burhanuddin Yeop Majlis

  • Institute of Microengineering and Nanoelectronics (IMEN) (2006) (simulations) Design of a High Sensitivity Structure for MEMS Fingerprint Sensor / ICSE2006 Proc. 2006, Kuala Lumpur, Malaysia
  • (2009) (simulations) Analysis and design of a wide micro beam as a pressure gauge for high sensitivity MEMS fingerprint sensors
  • IMEN

    National Tsing Hua University, Hsinchu, Taiwan:

  • (2006) A Highly Sensitive CMOS-MEMS Capacitive Tactile Sensor. 1 pixel, 200 microns.
  • (2006) A CMOS Micromachined Capacitive Tactile Sensor With High-Frequency Output. idem
  • (2011) A CMOS capacitive pressure sensor chip for fingerprint detection. 8x32pixels, 65 microns.
  • (2013) Fidelica is now part of Lenovo.
  • (2014) Lenovo proposes some MEMS to make fingerprint sensors: Mems on alternate substrates.
  • Piezo-led

  • (2013 Feb) High-resolution electroluminescent imaging of pressure distribution using a piezoelectric nanowire LED array (Georgia Institute of Technology).
    When pressure is applied to the nanowires, piezoelectricity is generated, which stimulates the production of photons at the root of the nanowire — where the n-type ZnO meets the p-type GaN. The harder you press, the stronger the current, the brighter the light. These LED nanowires have a spatial resolution of just 2.7 micrometers (micron), resulting in a pixel density of 6350 dpi.

  • Thermal / Thermique

    Pyro-electric material is able to convert changes in temperature into a specific voltage. This effect is quite large, and is used in infrared cameras. This type of sensor doesn't measure the difference of temperature between the skin in the ridges and valleys, because the difference is negligible. In fact, as the finger is directly placed on the material, the ridge's temperature is what's measured, as it's in contact. The valleys don't make contact, so the temperature of the pyro-electric material under the valleys remains almost unchanged. A drawback of the technique is that the image disappears quickly. When you place your finger on the sensor, there is a big change of temperature, and therefore signal, but after a short period (less than a tenth of a second), the image vanishes. The finger and the chip have reached thermal equilibrium, and as there is no change in temperature, there is no signal. This effect disappears when you sweep your finger over the sensor, because of the touch/no touch of ridge/valley.
    Les matériaux pyro-électriques convertissent un changement de température en charges électriques. Cet effet est assez important, et largement utilisé dans les caméras infrarouges. Ce type de capteur ne mesure pas la différence de température de la peau des crêtes et vallées, qui est négligeable. En fait, lorsque le doigt est posé en contact avec le matériau, la température des crêtes est mesurée, car elle est en contact, à la différence des vallées qui ne le sont pas, et donc n'apporte pas de changement de température. Lorsque le doigt est placé sur le capteur, une très grosse variation de température est induite, donc on obtient beaucoup de signal, mais celui-ci disparait assez vite car l'équilibre thermique est vite atteint. Cet effet (néfaste dans le cas où on ne bouge pas) disparaît lorsque l'on balaye le doigt à la surface du capteur, car la succession des crêtes et vallées induit le changement de température du matériau.

    Thermal sensing
    Imtek
  • (2005) IMTEK & Schippers propose a thermal fingerprint sensor based on a similar technique than Nagoya Univ., adapted for a smart card.
  • (2008) Hirobumi Han from the Wakayama university proposes a thermal sensor using micro-heaters on a polyimide substrate. Characteristics of thermal-type fingerprint sensor.
  • (2016 Apr) Survey of Biometric Authentication and Proposal of and Proposal of New Sensing Mechanism / Hirofumi Miki, Shigeki Tsuchitani (Department of Systems Engineering, Wakayama University).
    New? seems to be active sensing using polyimide, like the previous paper.
  • (2013 Dec) Next Biometrics unveils a new active thermal sensor, composed of an area sensor (LTPS -Low Temperature Poly Silicon- TFT -Thin Film Transistors- and Devices) on glass + a silicon companion chip to drive and read the sensor.
    Active thermal sensing uses a heat pulse to break the thermal equilibrium when there is no move, enabling static acquisition.

  • Ultra-sound / Ultrasons

    Ultra-sound fingerprint reading was not common. It may be seen as a kind of echography. In the past, ultra-sound sensing required quite a big device with mechanical parts, and was quite expensive. Moreover, it takes a few seconds to grab an image. It 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.

    Ultrascan > 2013 > Qualcomm

  • (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.
  • Ultrascan
  • (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.
  • Optel

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

    CrossMatch >> Sonavation

  • (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 SonicTouchTM technology used in Sonavation’s SonicSlideTM 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.
  • Sonavation MEMS

    UC Berkeley Swarm lab >> Invensense

  • (2013) The Swarm lab of Berkeley is developping an ultrasonic sensor. See also the sensor electronics research group. 8x24 pixels @ 250dpi.
  • (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.
  • University of Windsor [Canada]

  • (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

  • Some other ultrasonic fingerprint sensor studies

  • (~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)
  • Tessonics

  • (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.

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

  • Photonic crystals

    (2006) University of Toronto
    "You can elastically deform these crystals and produce different colours," says lead author André Arsenault, a PhD candidate in the laboratory of Geoffrey Ozin, a University Professor in the Department of Chemistry and a Canada Research Chair in materials chemistry.
    Photonic crystals are a relatively new development in the scientific quest to control light. Ozin's lab first created photonic crystals in 2002, using spherical particles of silica mere micrometers in diameter that self-assemble into neat layers, creating what's known as an opal. After filling the space between the spheres with silicon, they used acid etching to remove the silica balls. This left an ordered sponge of air bubbles in silicon known as an inverse opal. This photonic crystal material, the first of its kind, did indeed trap light. These photonic crystals can produce color based on how an electromagnetic wave interacts with the structure -- meaning that it could be tuned to produce any color.
    In the new study, the team injected an elastic compound between the spheres, which were then etched away, leaving an orderly and compressible elastic foam that can be transferred onto virtually any surface, such as glass, metal or plastic. The material changes color based on how far the spheres are separated.