Solid-State Finger

State Finger

Scanners Scanners

A Survey of Technolog

A Survey of Technolog

Philip D. Wasserman Philip D. Wasserman

Guest Researcher, NIST, Gaithersb

Guest Researcher, NIST, Gaithersb

December 26, 2005 December 26, 2005
Objectives Objectives

 Review solid state fingerprint s

Review solid state fingerprint s

technologies technologies

 Emphasize forensic requiremen

Emphasize forensic requiremen

 Present emerging, as well curren

Present emerging, as well curren

technologies technologies

 Discuss the future of solid Discuss the future of solid-state 

state 

scanners scanners
Solid-State Fingerprint S

State Fingerprint S

Technologies Technologies

 A live-scan fingerprint scanner measures 

scan fingerprint scanner measures 

property of a fingerprint and converts it to 

property of a fingerprint and converts it to 

ridge-valley image valley image

 Many technologies have been applied. A 

Many technologies have been applied. A 

representative vendor) include the follow

representative vendor) include the follow

 Capacitance (UPEK) Capacitance (UPEK) RF (Authentec) RF (Authentec) Thermal (Atmel) Thermal (Atmel) PiezoResistive (Fidelica) PiezoResistive (Fidelica)  Ultrasonic (Ultrascan) Ultrasonic (Ultrascan) Piezoelectric (Fraunhaufer with Piezoelectric (Fraunhaufer with Crossmatch Crossmatch) MEMS
Scanner Configurat

Scanner Configurat

 Sweep scanner Sweep scanner

 User sweeps finger across a nar

User sweeps finger across a nar

sensors. sensors.

 Area scanner Area scanner

 Contains an array of sensors wh

Contains an array of sensors wh

substantially cover the user’s fing

substantially cover the user’s fing

 Cost is higher than” sweep” scan

Cost is higher than” sweep” scan

larger sensor area. larger sensor area.
Sweep Scanners Sweep Scanners

 Single row (or a few rows) of sensor 

Single row (or a few rows) of sensor 

cost, size, and power. Intended for c

cost, size, and power. Intended for c

and laptop computer security. and laptop computer security.

 User sweeps finger across line of se

User sweeps finger across line of se

fingerprint is stitched together in soft

fingerprint is stitched together in soft

 Speed and direction of sweep must 

Speed and direction of sweep must 

• Naïve user may not produce usable prin

Naïve user may not produce usable prin

 Software stitching process may prod

Software stitching process may prod

• which are unacceptable in forensic qual

which are unacceptable in forensic qual
Area Scanners Area Scanners

 Captures one or more fingerprin

Captures one or more fingerprin

single impression. single impression.

 Usually flat, but rolled impressions 

Usually flat, but rolled impressions 

simulated by stitching multiple ima

simulated by stitching multiple ima

software. software.

 Image size must be sufficient to 

Image size must be sufficient to 

comparison accuracy requireme

comparison accuracy requireme
Fingerprint Size Fingerprint Size

 The NIST study NISTIR 7201, The NIST study NISTIR 7201, Effect of I

Compression on One-to-One Fingerprconcludes:

 “...image cropping quickly degrades matc “The conclusion from this study is that I

320 pixels by 320 pixels should not be use

 Relating to PIV requirements, NIST Spec

800-76, section 4.1 states: “The device of imaging an area of at least 16.5 mhorizontal and vertical directions.

 No commercially available single-fing

scanner meets these image size requirem

 Upek TCS1CD is the largest; 256 x 360 pixel
3.2” x 3” Silicon Finge

3.2” x 3” Silicon Finge

Scanner is Technically p

Scanner is Technically p

 Silicon CCD scanners as large as Silicon CCD scanners as large as 

have been produced. have been produced.

 Cost is now high Cost is now high Historically, demand and technology h

Historically, demand and technology h

dramatically reduced integrated circuit 

dramatically reduced integrated circuit 

 No commercially available solid s

meets the 3.2” x 3” size requiremfinger scanners

 Homeland Security 10-Print Captu

Scanner & Software Requirements DRAFT – September 29, 2005
Single-Finger Solid State 

Finger Solid State 

 All solid All solid-state scanner products 

state scanner products 

available are of the single available are of the single-finge

finge

 Targeted market is cell phones, 

Targeted market is cell phones, 

personal computers, access con

personal computers, access con
Optical Rolling Optical Rolling

-Tube Sc

Tube S

(Mitsumi) (Mitsumi)


Direct Optical Scanner 

Direct Optical Scanne

 The finger interior is illuminated fro

The finger interior is illuminated fro

around its periphery around its periphery 

 A fiber A fiber-optic light guide couples the 

optic light guide couples the 

CMOS camera the size of the finge

CMOS camera the size of the finge

 Mitsumi proposes the same techno

Mitsumi proposes the same techno

sweep scanner. sweep scanner. 
Active Capacitive Scanner

Active Capacitive Scanner

US Patent US Patent 5,973,623 5,973,623 (Assigned to 

(Assigned to 

 Each sensor cell (pixel) contai Each sensor cell (pixel) contains an active capac

ns an active capac

circuit whose effective capacitan circuit whose effective capacitance is decreased 

ce is decreased 

live skin close to the live skin close to the surface of the scanner. surface of the scanner. 

 A ridge intercepts fringing field lines between plate

A ridge intercepts fringing field lines between plate

the capacitance between them. the capacitance between them.

 The amplifier operates as an integrator The amplifier operates as an integrator

 Reset during phase 1 by shorting feedback capacit

Reset during phase 1 by shorting feedback capacit

 During phase 2, integrator receives a fixed increme

During phase 2, integrator receives a fixed increme

 This produces an output voltage E = This produces an output voltage E = 

ΔQ/Cf, where 

Q/Cf, where 

between top metal plates, as determined by skin p

between top metal plates, as determined by skin p

valley). valley).
Improved Improved 

Active Capacitive Se

Active Capacitive Se

US Patent #6,512,381 B2 (assigned 

US Patent #6,512,381 B2 (assigned 

 Greatly increases signal/nois Greatly increases signal/noise ratio e ratio External, synchronously driven conductor contact

External, synchronously driven conductor contact

 During phase 2, additional signal is provided thro

During phase 2, additional signal is provided thro

proportional to the proximity of live skin on a ridge

proportional to the proximity of live skin on a ridge

 Signal is than the sum of both internal and extern

Signal is than the sum of both internal and extern
RF Scanners (Authen

RF Scanners (Authen

 Sensor amps respond to RF coupl

Sensor amps respond to RF coupl

capacitance from finger to the sens

capacitance from finger to the sens
Non-Linearity of Solid 

Linearity of Solid 

Scanners Scanners

 Many solid state sensor tech

Many solid state sensor tech

have a non have a non-linear response to 

linear response to 

fingerprint property being mea

fingerprint property being me

 Capacitive sensors respond t

Capacitive sensors respond t

sensor capacitance, a non sensor capacitance, a non-linfunction of finger function of finger-sensor dista

sensor dista
Thermal Sensors (A

Thermal Sensors (A

 Measures the temperature differenc

Measures the temperature differen

ridge and valley. ridge and valley. 

 Temperature difference is transitory (la

Temperature difference is transitory (l

100ms)

 Consists of a silicon die tiled by pix

Consists of a silicon die tiled by pix

electric material sensitive to tempe

electric material sensitive to tempe

differences. differences. 

 The temperature difference appear

The temperature difference appear

pyro

-electric layer is transformed in

electric layer is transformed in

charges. These are amplified and 

charges. These are amplified and 

the underlying silicon circuitry the underlying silicon circuitry

 Only four bit gray scale from senso

Only four bit gray scale from senso
Pressure Scanner

Pressure Scanner

 Piezo

-electric electric Fraunhofer IKTS Fraunhofer IKTS

(Cr

Cr

 From Fraunhofer web site: “Realizatio

From Fraunhofer web site: “Realizatio

piezocomposites with ca. 25,000 indiv

piezocomposites with ca. 25,000 indiv

(diameter: 75 μm, pitch: 103 μm, heigh

(diameter: 75 μm, pitch: 103 μm, heig

demonstration of applicability in finger

demonstration of applicability in finger

(Cross Match and Fl)” (Cross Match and Fl)”

 U.S. Patents (Assigned to Cross M

U.S. Patents (Assigned to Cross M

 6,720,712 Scott , 6,720,712 Scott , et al. April 13, 2004 et al. April 13, 2004  6,812,621 Scott November 2, 2004 6,812,621 Scott November 2, 2004  6,844,660 Scott January 18, 2005 6,844,660 Scott January 18, 2005 
Micro

-electro electro

-mechanical 

mechanical 

(MEMS)

 MEMS are mechanical devices suc

MEMS are mechanical devices suc

embedded in semiconductor chips. embedded in semiconductor chips.

 Integrated circuits with moving parts. Integrated circuits with moving parts.

 Low potential cost due to semicond

Low potential cost due to semicond

processing methods. processing methods.

 A variety of technologies used to pr

A variety of technologies used to pr

of MEMS for fingerprint sensors of MEMS for fingerprint sensors

 pressure sensitive contacts pressure sensitive contacts variable capacitance variable capacitance piezoelectric piezoelectric piezoresistive piezoresistive pyroelectric (thermal) pyroelectric (thermal)
MEMS Capacitive Fing

S

Capacitive Fing

Sensor 

http://mtlweb.mit.edu/researchgroups/mems http://mtlweb.mit.edu/researchgroups/mems-salo

salo

%20Surface%20structure%20and%20fabrication%20for%20MEM

%20Surface%20structure%20and%20fabrication%20for%20MEM

sensor.pdf sensor.pdf

Experimental sensor has an array of 57 000 the area of 11.2 12.8 mm . Each pixel is a cpressure sensor that has a MEMS cavity stron a CMOS LSI. A sensing circuit is locatedjust below each MEMS cavity structure 
MEMS Capacitive Pressu

MEMS Capacitive Pressu

On Silicon (LITI) On Silicon (LITI)

http://www-leti.cea.fr/commun/AR-2002/09 2002/09-mems%20%26%20micro

mems%20%26%20micro
MEMS Resistive Sen

MEMS Resistive Se

Fidelica Fidelica

A resistive network and MEMS stru

cell location.

Upon the application of a fingerprin

under the ridges of the fingerprint edeflection, producing a resistance 
No Fully Acceptable So

No Fully Acceptable So

for Four for Four-Finger Live S

Finger Live S

 As stated in As stated in Homeland Security 10

User Group Scanner & Software RVersion 0.9 – DRAFT – September 

 “The size of the Scanner, power req

and speed of both the Software and have critical impacts on current facoperations. Although we are not awtechnology existing today that is abthese parameters ...”

 Solid

-state scanners provide the po

state scanners provide the po

satisfying these requirements satisfying these requirements
Can Multiple Smaller Scan

Can Multiple Smaller Scan

be Tiled to Simulate a Lar

be Tiled to Simulate a Lar

Proposed by Michael Garris, N

Proposed by Michael Garris, N

 Costs could be reduced if a multi Costs could be reduced if a multi

-finger s

finger s

implemented as a tiled array of small fing

implemented as a tiled array of small fing

chips

 There will be gaps between chips therefo

There will be gaps between chips therefo

regions will exist. regions will exist.

 The gaps can be filled by shifting the sen

The gaps can be filled by shifting the sen

and Y 

 Capture three images Capture three images  Combine them in software Combine them in software

 While retaining sensitivity, It is possible t

While retaining sensitivity, It is possible t

capacitive sensor array with a thin layer o

capacitive sensor array with a thin layer o

preferably Teflon, to reduce the coefficien

preferably Teflon, to reduce the coefficien

 US Patent # 6,512,381B2 US Patent # 6,512,381B2
Shifting the Sensor A

Shifting the Sensor A

 Capture a fingerprint image at a initial loc

Capture a fingerprint image at a initial loc

 Shift sensor array in X so image covers t

Shift sensor array in X so image covers t

Capture a second image. Capture a second image.

 Returning array to original position in X, s

Returning array to original position in X, s

Capture a third image. Capture a third image.

 Piezoelectric or magnetic actuators coul

Piezoelectric or magnetic actuators coul

move the sensor array. move the sensor array.

 There are many questions about this app

There are many questions about this app

 Can the sensors be made to slide smoothly u

Can the sensors be made to slide smoothly u

cover despite the finger pressure on top? cover despite the finger pressure on top? 

 Would the plastic cover excessively reduce se

Would the plastic cover excessively reduce se

resolution of the image? resolution of the image?

 Can the scanner be made durable? Can the scanner be made durable? Research will be required to Research will be required to answer these a

 answer these a
Connecting Multiple Scan

Connecting Multiple Scan

 The top surface or the array of scan

The top surface or the array of scan

must be planer and smooth if the co

must be planer and smooth if the c

slide easily. slide easily.

 Common lead bonding could not be us

Common lead bonding could not be u

 Flip

-chip techniques to connect the 

chip techniques to connect the 

circuitry to the substrate will allow t

circuitry to the substrate will allow t

placed more closely, reducing the r

placed more closely, reducing the r

 Through Through

-hole vias can connect the 

can connect the 

the front of the chip to capacitive se

the front of the chip to capacitive se

on the back. on the back. 

http://retina.et.tudelft.nl/data/art

http://retina.et.tudelft.nl/data/art

on/mems/520763576.pdf on/mems/520763576.pdf
Array Shifts To Cover 

Array Shifts To Cover 

Starting Position
Flip-Chip Struct

Chip Struct

Sic

Scanner Chi

Through-chip via

Sensing Capacitors

ProtectiveCoating

CS

Pi

Finger Contact

Surface (fixed)

The region between thesolder bumps may be filledwith epoxy. as well as the space between scanner chips to makea fully planar, smooth surface.
Flat Panel Display Tec

Flat Panel Display Tec

 Large feature size and substrate su

Large feature size and substrate su

panel display technology. panel display technology.

 Flat panel displays are now above 50” 

Flat panel displays are now above 50” 

 Greatly reduced cost per square inch 

Greatly reduced cost per square inch 

compared to silicon. compared to silicon.

 Highly refined manufacturing process Highly refined manufacturing process

 Thin

-film photo film photo

-detectors on glass

detectors on glass

 Could be capacitive for fingerprint sen

Could be capacitive for fingerprint sen

 Organic photo Organic photo

-detectors printed on 

detectors printed on 

(NanoIdent) (NanoIdent)
Capacitive Sensor With T

Capacitive Sensor With 

Panel Technology (Mits

Panel Technology (Mits

 Flat panel thin Flat panel thin

-film transistor technol

film transistor technol

rather than single rather than single

-crystal silicon crystal silicon 

 Potential for low cost, large area sca

Potential for low cost, large area sca

 Still in laboratory stage Still in laboratory stage  A Capacitive Fingerprint Sensor with 

A Capacitive Fingerprint Sensor with 

Temperature Poly Temperature Poly

-Si TFTs Si TFTs

http://ieeexplore.ieee.org/xpl/abs_fre

http://ieeexplore.ieee.org/xpl/abs_fre

er=1175508 er=1175508
Firms Developing Thin Firms Developing Thin

Transistor Fingerprint Se

Transistor Fingerprint Se

Glass Substrates Glass Substrates

 Casio

 SiliconImageWorks SiliconImageWorks Silicon Display Technology Silicon Display Technology Alps Electric Alps Electric Mitsubishi Mitsubishi
Silicon Integrated Circuit 

Silicon Integrated Circuit 

 As a semiconductor chip becomes 

As a semiconductor chip becomes 

goes down due to the defect densit

goes down due to the defect densit

 Costs go up exponentially above a 

Costs go up exponentially above a 

size.

 This critical die size has been incre

This critical die size has been incre

 Improved manufacturing processes ha

Improved manufacturing processes ha

defect density. defect density.

 Increased complexity has become 

Increased complexity has become 

because of increased die size, and 

because of increased die size, and 

feature size. feature size.
Silicon Integrated Circu

Silicon Integrated Circu

Moore’s Law Moore’s Law

 In the mid In the mid

-1960s, Intel co 1960s, Intel co

-founder G

founder G

Moore noticed that, largely as a res

Moore noticed that, largely as a res

size shrinkage size shrinkage, chip processing pow

, chip processing pow

roughly doubling every 18 months, 

roughly doubling every 18 months, 

concurrent reduction in cost. concurrent reduction in cost. 

 He extrapolated this trend in what p

He extrapolated this trend in what p

remarkably accurate estimate of se

remarkably accurate estimate of se

industry progress. The so industry progress. The so

-called “M

called “M

curve of industry progress is one of 

curve of industry progress is one of 

standards of the chip making world

standards of the chip making world
Silicon Chip Size and Co

Silicon Chip Size and Co

vs. Time (source INT

vs. Time (source INT
Roadmap, Semiconductor Industry Association, 2
Feasibility of 3.2” x 3.0

Feasibility of 3.2” x 3.0

(81.3mm x 76.2mm, 620

(81.3mm x 76.2mm, 620

 Cost

 2004

• $ 115

 2007

• $ 112

 Chip Size Chip Size

 Required chip area is 6200 mm Required chip area is 6200 mm

2

 Maximum chip area according to EIA Maximum chip area according to EIA

• 1000 mm

2 now 

• 1250 mm

2 in 2007 in 2007

 This has already been exceeded This has already been exceeded

• Kodak 1737 mm

2

• Dalsa 4032 mm

2

• Phillips Phillips 9246 mm

2

•
Large Silicon Integrated 

Large Silicon Integrated 

All CCD (Charge Coupled Device) Imag

All CCD (Charge Coupled Device) Imag

Convertible to capacitive scanners by r

Convertible to capacitive scanners by r

photodiodes with capacitor pla

photodiodes with capacitor pla

 3.2” x 3” Fingerprint Sensor would requ

3.2” x 3” Fingerprint Sensor would requ

 Kodak 39 megapixels megapixels, 6.8 micron pixe

, 6.8 micron pixe

50.7mm image area, 1.54” x 2.0”, 50.7mm image area, 1.54” x 2.0”, 3.08 

3.08 

 DALSA Inc., 26 Inc., 26 megapixels megapixels, 2.5” x 2.5

, 2.5” x 2.5

 Philips Philips, 66.236 , 66.236 megapixels megapixels, 12 micron 

, 12 micron 

4.24” x 3.38”, 4.24” x 3.38”, 14.36 in. 14.36 in.

2

 Pixel Size Pixel Size

 CCD < 20 micron CCD < 20 micron Fingerprint Sensor at 500dpi, pixel size 50.8 

Fingerprint Sensor at 500dpi, pixel size 50.8 
Conclusions Conclusions

 It is now technically feasible to mak

It is now technically feasible to mak

fingerprint scanner 3.2” x 3.0” fingerprint scanner 3.2” x 3.0”

 Current price could be competitive wit

Current price could be competitive wit

optical scanners. optical scanners.

 Can be linear extension of well develo

Can be linear extension of well develo

scanner technology scanner technology

 Glass substrates and thin Glass substrates and thin-film trans

film trans

another promising technology. another promising technology.

 Based on flat Based on flat-panel display technology panel display technolog Substrate and processing costs much 

Substrate and processing costs much 

silicon silicon

 Quality of transistors is poor Quality of transistors is poor No commercial product to date No commercial product to date
Suppliers of Solid State F

Suppliers of Solid State F

Scanners (A partial lis

Scanners (A partial lis

 Alps Electric Alps Electric  Atmel Atrua Authentec Authentec BMF  Casio  Casio + Alps Casio + Alps  Cecrop, KSI, Sannaedle Sannaedle Delsy Digital Persona Digital Persona  Ethentica Ethentica Fidelica Fidelica Fingerprint Cards Fingerprint Cards 

 Fujitsu Fujitsu  Idex Infineon Infineon (Sie

(Sie

 Melfas Mitsumi Mitsumi  NEC  NTT  NanoIdent NanoIdent Silicon Displa

Silicon Displa

 Sony  Symwave Symwave TesTech TesTech TST touchles

touchles

 Ultrascan Ultrascan Upek Validity Validity