Fingerprint sensing
techniques
0920 2007
Biometrics Tech. and Application
Dr. Hsu, Wen-Hsing
Fingerprint sensing techniques
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Optical readers
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Electro-optical readers
Capacitance
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Silicon chips
TFT
RF field - AC capacitance
Pressure
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Reflection
Transmission
Sweep, sweep with a roller
Touchless
TFT
Resistive membrane on silicon, TFT
Tactile MEMS
Thermal
Ultra-sound
Ink
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Ink and paper are the
tried-and-true way to
take fingerprints, but
technology has found
ways to eliminate
smudges and ink
stains.
Optical readers
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Reflection
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).
Optical readers -Reflection
Many companies are offering such devices, this is a common technology. .
Here is the example of the Compaq fingerprint
reader (CMOS camera, around 2000).
Generally, one fingerprint is taken at a time,
but some devices are able to acquire several
fingers at a time. (Rolling Fingerprint)
Nagoya University uses a micro-collimator instead of the fiber
optic, enabling direct fingerprint comparison.
Reflection with sweep
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Kinetic Sciences and Cecrop/Sannaedle have proposed sweep optical
sensors based on this principle. Cecrop seems to have abandonned this
device
Kinetic Sciences Paper describing the sensor
Cecrop/Sannaedle
Casio + Alps Electric uses a roller with the
sensor inside. The roller acts like the prism.
Casio
Alps Electric
As well as Digital Persona with the
Firefly
Digital Persona Firefly
Reflection touchless
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TST 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). Thales (formerly
Thomson-CSF) also proposed
the same, but with the use of a
special powder to put on the
finger. The BERC lab from
Yonsei University (Korea) also
developped a touchless
sensor (2004).
(2005) TBS launch a touchless
sensor with the "Surround
Imaging".
Transmission
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It is also possible to directly read the light transmitted
by the finger.
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Mitsubishi proposes to read the fingerprint with a regular
camera.
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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. Mitsumi & NEC proposes
the same but with a sweep sensor.
Delsy
NEC
Mitsumi
In July 2005, NanoIdent unveils a flexible fingerprint sensor using polymer/organic photodetector.
TFT optical / TFT optique
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.
Other companies proposing TFT fingerprint sensors:
Casio
SiliconImageWorks
Silicon Display Technology
Alps Electric
Mitsubishi
Seiko/Epson
Electro-optical readers
A variant of TFT devices is the use of capacitance
information instead of reflected light.
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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.
Ethentica
TesTech
Capacitance
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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).
Silicon chips + capacitance
Silicon chips can be seen as a variant of the CMOS
cameras: instead of using the light, another physical effect
is used.
Companies proposing (or having proposed) capacitance
sensing:
Veridicom, Fujitsu, Infineon, Sony, Upek, LighTuning,
Melfas, Atrua, NTT, Symwave, ...
Labs working (or having worked) on
silicon capacitance sensors:
Seoul University
 A 600-dpi Capacitive Fingerprint Sensor
Chip and Image-Synthesis Technique (Lee
& als, Seoul National University, 1998)
Kaist
 IML KAIST
NTT
 NTT Microsystem Integration Laboratories
 A Single-Chip Fingerprint Sensor and Identifier
(Shigematsu & als)
Capacitance + TFT
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Flat panel technology rather
than bulk silicon has been
studied by Philips Korea and
some others, using
capacitive sensing. This is
still at the laboratory stage.
A Capacitive Fingerprint
Sensor with LowTemperature Poly-Si TFTs
Mitsubishi Electric Corp.
(April 2004) Alps Electric
develops 2 fingerprint
sensors. One is transparent,
electrostatic (capacitive).
RF field - AC capacitance
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Sometimes confused with
capacitance sensing, the only
common point between RF
field sensing and capacitance
sensing is the "capacitance"
connection of the signal.
Companies proposing (or
having proposed) RF/ACcapacitance sensing:
Authentec, Fingerprint Cards
Labs working (or having worked) on RF
capacitance sensing:
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Labs working (or having worked) on RF capacitance sensing:
Validity / Philips Korea
An alternate solution consists in having connection through wires, so the finger is not
mandatory directly in contact with the silicon part.
 Validity
Pressure
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.
Several solutions, depending on the material, have been proposed:
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Conductive membrane on a CMOS silicon chip.
Conductive membrane on TFT.
Micro-electromechanical switches on silicon chip.
Conductive membrane on silicon
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Opsis (a french company) offered a device using a
conductive membrane deposited on a CMOS chip (July
1994).
Conductive membrane on TFT
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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).
Tactile MEMS
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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.
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NTT Microsystem
Integration Laboratories
NTT research group
 Michigan University (Wise)
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Tima homepage
N.Galy thesis page and the
thesis
• Leti, pressure sensors (Rey)
• LighTuning
Micron Technology: Tactile sensor using an insulated flexible matrix loaded with filler
particles US 6,561,044
Thermal
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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.
Atmel (formerly Thomson-CSF) proposes the FingerChip
Hunno Technologies & Hyung-Kew Lee (Korea, KAIST) have studied a thermal fingerprint
sensor in 1999, probably using bolometers.
Nagoya University has studied a thermal sensor based on MEMS, using a resistor to heat a
sensor above a cavity.
INO (Institut National d'Optique / Canada) has used bolometers to make a 160x120 pixel
fingerprint sensor (US patent 6,633,656). Bolometric FPA for fingerprint recording
Ultra-sound

Ultra-sound fingerprint reading is not common. It may be seen as a kind
of echography. Ultra-sound sensing requires quite a big device with
mechanical parts, and is quite expensive. Moreover, it takes a few
seconds to grab an image. It is not suited for large production volumes at
low cost. Its main advantage is the reading of the derma, the sub-surface
of the skin, rather than the surface.
Ultrascan
Optel is still at R & D stage
Surface impedance impediography
(2004) CrossMatch is developping a fingerprint sensor based on piezo-electric pillars glued in teflon and covered with
urethan, based on ultra-sound
Fingerprint: List of silicon
sensors
List of fingerprint sensors / sensing area / JF Mainguet 2005
( sweep sensor area sensor)
Company
Atmel
formerly
Thomso
n-CSF
Sensing
type
thermal
Brand
Finger
Chip
T
Part
number
Rele
ase
date
R
es.
dp
i
x
pi
xe
l
y
pi
xe
l
x
m
m
y
m
m
notes
FC8x8
1997
50
8
16
0
16
0
8.
0
8.
0
prototype
FC2x17
1997
50
8
35
0
40
17
.5
2.
0
prototype
FC15A1
40
1998
50
8
28
0
30
14
.0
1.
5
prototype
AT77C1
01B
2000
50
8
28
0
8
14
.0
0.
4
formerly FCD4B14
AT77C1
04
2004
50
8
23
2
8
11
.6
0.
4
navigation
AT77C
105
200
5
5
0
8
2
3
2
8
11
.6
0
.
4
navigation & low
voltage I/Os
pressure
-
prot
o
2004
-
-
-
-
-
-
optical TFT
-
prot
o
2004
-
-
-
-
-
-
Alps/Casio
optical roller
-
prot
o
2003 Feb
600
288
-
12.2
-
sweep rolling tube
Atrua
capacitive
-
AT
W1
00
2002
363
192
8
13.5
0.6
Alps
Formely I-Control / ICS-3000
FingerLoc
Authentec
spin-off
from Harris
RF modulation
AFS2
2000 May
250
128
128
13.0
13.0
-
AFS
8500
2002 May
250
96
96
9.75
9.75
Discontinued.
AFS
8600
2004 Jan
250
96
96
9.75
9.75
-
AES
4000
2000 Sep
250
96
96
9.75
9.75
-
AES
3500
2001 Oct
500
128
128
6.5
6.5
USB. Discontinued.
AES
3400
2002 Sep
500
128
128
6.5
6.5
-
AES
2500
2002 Nov
500
192
16
9.75
0.81
USB. Replaced by the AES2501.
AES
2501
2003 Dec
500
192
16
9.75
0.81
USB
AES
2502
2003 Dec
500
192
16
9.75
0.81
SSI
AES
2510
2004 Jun
500
192
16
9.75
0.81
serial, 8 bit-parallel
1510
2005 Mar
500
128
8
6.4
0.4
Entr壆ad
4bit-parallel, master SSI
BMF
Casio
Delsy
pressure TFT
BLP100
2002 Feb
438
256
384
14.8
22.2
BLP60
2003
508
192
192
9.6
9.6
-
prot
o
2004 Oct
423
368
368
22.08
22.08
-
prot
o
2004
500
200
240
10.0
12.0
-
CM
OS
2001
508
288
384
12
18
pixel pitch is 0.058mm (width/height not OK)
Hitachi
demonstrated over a LCD display / CEATEC 2004
optical TFT
optical trans.
Digital Persona
optical roller
Ethentica
electro-optical
Fidelica
pressure
Backlight
Discontinued?
-
CCD
2001
-
512
576
-
-
FireFly
Firefl
y
2003 May
600
345
-
14.5
-
TactileSense
TFPM
2001
403
225
306
14.2
19.3
Formerly Who?Vision
-
FIS3002
2004 Feb
508
256
256
12.8
12.8
-
600dpi max (500dpi sweep dir.) depends on speed.
Fingerprint Cards
Fujitsu
active
capacitive
capacitive
Idex
AC capacitive
Infineon
capacitive
INO
thermal
KAIST univ.
KSI / Cecrop
FPC
1010
2002
363
152
200
10.6
14.0
FPC1011
FPC
1030
2002
363
152
32
10.6
2.2
FPC1031
MBF
110
2001
500
300
300
15.0
15.0
(= Veridicom FPS110)
MBF
200
2001
500
256
300
12.8
15.0
USB. (= Veridicom FPS200)
MBF
300
2002 Mar
500
256
32
12.8
1.7
Discontinued.
MBF
310
2003 Jul
500
218
8
10.9
0.4
Replaces the MBF300.
-
2000
500
256
-
12.8
-
FingerTip
FTF
1100
2000
513
224
288
11.1
14.3
-
FPA
2003 Sep
488
160
120
8.3
6.2
Bolometers
-
proto
2002
500
210
100
10.5
5.0
-
-
proto
2005
462
200
160
11.0
8.8
integrated processor for recognition.
-
-
2000
900
-
3
19.1
-
-
-
SmartFinger
Sweep 1 line. Non-active pixels on silicon.
Discontinued in 2004.
capacitive
optical sweep
-
Leti
MEMS pressure
-
proto
2002
391
92
92
6.0
6.0
-
capacitive
-
LTT
C300
2003
313
192
128
15.4
10.3
-
capacitive
-
LTT
C500
2003
500
236
192
11.8
9.6
-
capacitive
-
LTT
S500
2004 Oct
500
200
16
10
0.8
sweep-type
LG-Philips
optical TFT
FingerTalk
proto
2000
300
240
256
20.1
26.8
Melfas
capacitive
-
MFCS
1000
-
400
150
-
9.6
-
-
Michigan univ.
tactile
-
proto
-
500
16
16
0.8
0.8
-
Optical TFT
-
proto
2003 feb
423
250
320
15.0
19.2
-
capacitive TFT
-
proto
2003 Feb
423
250
320
15.0
19.2
-
optical trans.
-
R&D
2003
-
-
-
-
-
-
Mitsumi
optical
-
SEFA1
2005 jun
600
256
-
10.8
-
Proto shown May 2004.
NanoIdent
photo-organic
-
proto
2005
250
256
256
-
-
(announced resolution is likely an error)
NEC
optical trans.
FingerThrough
2002 Oct
800
480
540
15
18
LighTuning
Mitsubishi
SA301
-10
backlight
(approximative values)
Fingerprint sweep sensing
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Fingerprint sweep (or swipe) sensors is a subcategory of fingerprint sensors, useful because of its
lower cost production compared to static (or area) sensors.
History of fingerprint sweep sensors
1997
May: Thomson-CSF (now Atmel) demonstrated the FingerChip FC2x17, at the CTST'97.
1998
May: Thomson-CSF demonstrated the FingerChip FC15A140.
May: Seoul University submits a paper about a capacitance swipe sensor (published April '99).
July: First prototype from Idex on its first sweep sensor.
1999
May: Sannaedle / Cecrop demonstrates MyFin, a swipe optical reader.
May: Kinetic Sciences demonstrates the KC-901 at the CTCT.
2000
May: Atmel unveils the FingerChip AT77C101.
May: Kinetic Sciences demonstrates a new version of their swipe optical sensor (K-1000?).
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2001
April: Idex & STm announce the development of SmartFinger.
Sept: Fingerprint Cards announces the FCP1030.
Nov: Citizen & IBM shows the WatchPad, the first watch with a built-in fingerprint reader, the FingerChip.
2002
Feb: Fujitsu announces the MBF300, and shows it at the CTST in May.
Summer: Tima publishes about a sweep tactile sensor.
Oct: I-Control promotes the ICS3000 / PDS3000
Nov: Authentec introduces the AES2500.
Nov: The HP iPAQ h5450 is the first PDA with a built-in fingerprint sensor, the FingerChip AT77C101 from Atmel.
Nov: STm unveils a TouchStrip prototype at the COMDEX.
2003
Feb: Alps Electrics + Casio unveiled their "rolling-tube head" scanner.
March: STm displays the TouchStrip on the web.
May: Digital Persona unveils the Firefly, a sweep optical fingerprint sensor using a roller.
Jul: Sharp announces the Mebius Muramasa, the first Tablet PC with a build-in sweep fingerprint sensor, the FingerChip.
Jul: Fujitsu announces the MBF310.
Sept: Melfas announces the MFCS1000.
Oct: YRP shows the Ubiquitous Communicator, a R&D study prototype, containing the Atrua sweep sensor.
Nov: Elsafe installs the first safe with a sweep fingerprint reader, the FingerChip.
2004
Feb: I-Control becomes Atrua and promotes "Atrua Wings" (ATW100).
Feb: Atmel announces the AT77C104, the FingerChip with integrated navigation.
Feb: Atmel announces the colored FingerChip.
Feb: The Fujitsu F900i cell phone contains the Authentec AES2500. (Japan only)
March: Upek becomes a spin-off from STm.
March: Fingerprint Cards announces the FPC1031B.
March: Validity unveils the VFS101 (USB), VFS131 (SPI) & FVS161 (LPC) (RF Fingerprint imaging on flexible tape)
March: Ritech announces the BioSlimDisk iCool containing the Upek TouchStrip.
March: Trek announces Thumdrive Swipe containing the Upek TouchStrip (to check).
April: Fujitsu announces the LOOX T series notebooks (t50H & T70H) with the Authentec AES2500.
April: Motion Computing announces the M1400 tablet PC with the Authentec AES2500.
April: MPC unveils the Transport X3000 with the Upek TouchStrip.
May: The Fujitsu F506i cell phone contains the Upek TouchStrip. (Japan only)
June: The F900it is the same as F900i, but with a twist screen.
June: The Gateway notebook 450XL contains the Upek TouchStrip.
June: Authentec announces the AES2510, a swipe sensor + navigation, available mid-June, $6.
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2005
Jan: Bionopoly unveilsBio-USB flash drive & Fingerprint Passcode Generator
using the Atmel FingerChip.
Feb: IBM announces a keyboard (and peripheral) with a swipe sensor.
Feb: Atmel releases the FingerChip AT77C105
Feb: Yulong announces the Coolpad 858F GSM with the Atrua swipe
fingerprint sensor.
March: Authentec unveils the Entr壆ad 1510, a swipe sensor + navigation, $5.
March: Sandisk unveils the Cruzer?Profile USB drive (using the Upek swipe
sensor?).
March: IRevo introduces the Gateman MB740 door lock using the Atmel
FingerChip
March: Atrua announces the ATW200. No photo.
March: G&D unveils the StarSign Bio Token containing the FingerChip sweep
sensor.
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March: The Fujitsu Stylistic ST5022 Tablet PC with the Authentec swipe sensor.
April: IBM unveils the ThinkPad X41 with the TouchStrip from Upek.
April: LG releases the LG-LP3550 cameraphone containing the Authentec AES2500.
April: Scandinavian Ecotechnologies presents a biometric card with an embedded swipe sensor likely from Fingerprint Cards.
April: Toshiba introduces the Libretto U100 with the Authentec AES2500.
April: Toshiba introduces the Portege R200 = the Dynabook SS SX/190 with the Authentec AES2500.
April: Tychi unveils the BioKnob (door knob)
April: MPC's Transport X3100 with the sweep-type Upek TouchStrip.
May: Ritech unveils the iDEA containing the Upek TouchStrip.
May: Ritech unveils the BioMouse with the Upek TouchStrip.
May: Motion Computing announces the M1600 tablet PC with the Authentec AES2500.
May: Fujitsu LifeBook S6240, S7020 & S7021 / B6000 with the Authentec swipe sensor.
June: IBM unveils the ThinkPad X41 Tablet with the TouchStrip from Upek.
June: Aratek Fingo Mouse / Fingo Reader / Fingo Lock using a swipe sensor from Authentec.
June: NEC Versa C250/M350/P550 with the Upek TouchStrip sweep sensor
June: LaCie unveils the SAFE Mobile Hard Drive using a Upek TouchStrip sensor.
June: HP nx6125 laptop with an Authentec 2501 swipe sensor.
June: Mitsumi announces an optical sweep fingerprint sensor, the SEF-A1
July: The Pantech & Curitel PT-K1200 cellphone containing an Authentec swipe sensor is unveiled.
July: Motion Computing unveils the LS800 A5 tablet PC with the Authentec AES2501.
July: Card Media announces the Storeguard with the AUthentec swipe sensor.
July: MPC's Transport T3100 with the Upek TouchStrip.
Aug: Fujitsu LifeBook P1500 with the Authentec swipe sensor.
Aug: More info about the Symwave capacitance sweep fingerprint sensor SW-6888
Aug: The Fujitsu Stylistic ST5032 Tablet PC with the Authentec swipe sensor.
Aug: Sony announces the Vaio BX series with the Upek swipe sensor.
Aug: The Lenovo ThinkPad R52 now offers a Upek fingerprint sensor (as an option).
Sep: Itronix announces the GoBook?VR-1 with the Upek swipe sensor.
Sep: Lenovo unveils the ThinkPad Z60m & Z60t with the Upek swipe sensor.
Sep: Toshiba announces the Tecra S3 M740 & M780
Sep: Willcom unveil a cellphone proto using the Fujitsu swipe fingerprint sensor.
Sep: HP released the HP iPAQ hx2790 with Windows Mobile 5.0 with the Atmel FingerChip.
Oct: Fujitsu Lifebook FMV P8210, T8210 & TB12 Tablet PCs with the Authentec swipe sensor.
Oct: Sony introduces the Vaio AX series (VGN-AX570G) with the Upek swipe sensor.
Oct: Samsung unveils the SCH S370 cellphone using the Authentec swipe sensor.
Oct: Amoi announces the M606, M616 and A717 notebook PCs with the Upek swipe sensor.
Oct: Medion introduces the MD 96500 notebook PC with the Authentec EntrePad 2501A swipe sensor.
Atmel

· Official homepage of
the FingerChip: Atmel
website
See also the (local)
FingerChip products page
for more information.


Seoul University
· A 600-dpi Capacitive
Fingerprint Sensor Chip
and Image-Synthesis
Technique
(Lee & als, Seoul
National University,
1998)
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Idex
· Homepage: Idex
· (1998) IFF120: first
sweep active AC
capacitance sensing
prototype, started with
Sintef.
· (2001) SmartFinger©:
development with ST.
IFF 120
SmartFinger©
Sannaedle / Cecrop / Kinetic Sciences
· Homepage: Cecrop/Sannaedle.
· Homepage: Kinetic Sciences (KSI).
· In 1999, Sannaedle (now Cecrop) offered a device called MyFin. At the same
time, KSI offered the KC-901, which was probably the same device.
· In 2002, Cecrop was offering the CFS2000, while KSI offered the K-1000.
· In 2004, KSI is still displaying the device on their web site, while there is
no more information about an optical sweep sensor on the Cecrop website.