UV Responsive CCD Image Sensors With Phosphor

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352 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 50, NO. 2, FEBRUARY 2003

UV-Responsive CCD Image Sensors With EnhancedInorganic Phosphor Coatings

Wendy A. R. Franks, Martin J. Kiik, Member, IEEE, and Arokia Nathan, Senior Member, IEEE

AbstractTypical polysilicon gate charge-coupled device (CCD)image sensors are unresponsive to ultraviolet (UV) light because ofthe high absorption of the radiation in polysilcon gate material,which leads to a short penetration depth ( 2 nm), and absorp-tion of the radiation in the gate material rather than within thechannel of the CCD. An inorganic phosphor coating to convert theUV radiation to visible has been developed. Although the coatingis similar to acrylics doped with organic laser dyes reported previ-ously [1][4], in this work the organic dye has been replaced witha more robust inorganic phosphor. In addition, a new depositionmethod has been developed to improve the photoresponse nonuni-formity (PRNU) of the coated sensor. The inorganic phosphor hasbeen selected over organic laser dyes because organic moleculesdegrade rapidly upon exposure to UV radiation, with exponentialdegradation rates as high as 3% perhour at an illumination levelof1 W/cm . Inorganic phosphors exhibit reduced degradation with90% of the degradation occurring within the first 2% of the ma-terials lifetime. It is this stabilization that improves the viabilityof phosphor-coated CCD image sensors for commercial applica-tions. The quantum efficiency observed was 12% at 265 nm. Theimproved deposition technique reduced the photoresponse nonuni-formity degradation fourfold, so the observed PRNU was only 0.4times greater than that of the uncoated sensor.

Index TermsInorganic phosphor, phosphor coating, UV-en-hanced charge couple devices (CCDs).

I. INTRODUCTION

S INCE charge coupled devices (CCDs) and digital imagecameras were first integrated into manufacturing applica-tions, researchers have been investigating designs to improve

their poor ultraviolet (UV) responsivity. The low responsivity is

because of the small penetration depth of UV in silicon. Most of

the radiation is absorbed in the polysilicon gate region and very

little penetrates into the buried channel region of the sensor to

generate a photoelectric signal. Two different approaches to im-

prove this limitation are: structural modifications to the CCD

and postprocessing deposited phosphor coatings. Structural de-

signs such as back-side thinned devices, pinned photodiodes

and ITO gated CCD sensors [5][7] exhibit good characteris-

tics but require complicated fabrication processes that may be

expensive to manufacture. Organic phosphor coatings to convert

Manuscript received August 23, 2002; revised November 15, 2002. The re-view of this paper was arranged by Editor J. Hynecek.

W. A. R. Franks was with the Department of Electrical and Computer Engi-neering, University of Waterloo, Waterloo, ON N2L 3G1, Canada. She is nowwith the Physical ElectronicsLaboratory,Swiss Federal Institute of Technology,CH-8093 Zrich, Switzerland.

M. J. Kiik is with DALSA Corporation, Waterloo, ON N2V 2E9 Canada(e-mail: [email protected]).

A. Nathan is with the Department of Electrical and Computer Engineering,University of Waterloo, Waterloo, ON N2L 3G1 Canada.

Digital Object Identifier 10.1109/TED.2003.809029

UV into visible radiation have been developed as a simpler, yet

effective solution. For example, Photometrics Ltd. has devel-

oped Metachrome II, a sputter-deposited coating based on the

organic coronene molecule [8][10]. Another coating approach

involves organic laser dye doped plastics [1][4]. While organic

coatings exhibit good initial responsivities, they photodegrade

to zero efficiency exponentially. For example, the organic laser

dye PPO degrades by 3% every hour under 1- W/cm radia-

tion [1]. In addition to efficiency considerations, image quality

must be preserved. Since the organic coatings aretypically fairly

thin ( 10 m ), the modulation transfer function (a measure

of the amount of light that incorrectly enters adjacent pixelsresulting in blurred images) and photoresponse nonuniformity

(PRNU) degradation is typically low. Photometrics reports that

the PRNU of the coated sensor increases by 200%300% [11].

The coatings presented in this work are similar to the organic

laser dye doped plastics. However, here the organic dye is

replaced by an inorganic phosphor. Inorganic phosphors have

been used for over a century as a light-conversion material

in fluorescent light tubes [12]. These materials are inherently

designed for long lifetime, high-intensity applications. Several

different phosphors were selected for initial testing. They

were deposited onto fused silica slides with an eye-dropper

[13].(as a proof-of-concept experiment), using conventional

spin-coaters, or with a new settle-coating deposition technique.The best results reported here used a commercial phosphor

(La,Ce,Tb)PO : Ce : Tb deposited in a two-layer coating with

a second pure acrylic plastic layer deposited over the phosphor.

The quantum efficiency of the coated sensor is 12% at an

illumination wavelength of 265 nm with a PRNU that is 1.6

times greater than the uncoated sensor. To reduce PRNU degra-

dation, the new settle deposition technique showed a reduction

in PRNU degradation by up to a factor of 4.4, compared to

conventional spin-coating techniques.

II. CRITICALPARAMETERS

The phosphor must be selected so that it is effective as a lightconverter without compromising CCD operation. The key ma-

terial parameters considered include photostability, conversion

efficiency, decay time, absorption and emission peak, particle

size and distribution, and film morphology. The importance of

these parameters is described below. In terms of photostability,

in most cases vendors cannot supply the needed information

regarding the phosphor photostability. However, one can pre-

dict this by examining its stability in other applications. For ex-

ample, inorganic phosphors are typically used to coat fluores-

cent tubes where the rated lifetime can be as long as 55 000 h

0018-9383/03$17.00 2003 IEEE
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FRANKSet al.: UV-RESPONSIVE CCD IMAGE SENSORS 353

TABLE ICOMMERCIALPHOSPHORSSELECTED FORCONVERSIONEFFICIENCYTESTING

* Phosphor Technology, Ltd., U.K.

Phosphor Technology has a product JL 49 that is supposed to be the fastest phosphor in the world. It met all the compliance criteria but was

too expensive to be selected for testing.

United Mineral and Chemical Corporation, Lyndhurst, NJ USA. Osram Sylvania, Ltd., Towanda, PA USA.

of operation [12]. While inorganic phosphors do exhibit some

photodegradation, this generally occurs within the first 100 h of

operation when the coating stabilizes [12].

The selected phosphor should have a conversion efficiency

as close to 100% as possible. This is of particular importance

because the luminescence mechanism is isotropic and 50% of

the fluorescence is emitted away from the sensor. A fraction of

this fluorescence will experience total internal reflection at the

filmair interface and will be directed back toward the sensor.

This fraction will improve the conversion efficiency, however,

it also contributes to resolution degradation since the reflected

light may be directed to neighboring pixels. It is essential that

the decay time is shorter than the sensor integration time so

that all of the fluorescing photons have been emitted before

the associated charge packet is cleared from the pixel; other-

wise image smear will be observed. The phosphor should be

selected so that its absorption peak matches the application il-

lumination wavelength. The emission peak should be selected

to match the peak responsivity wavelength of the CCD to max-

imize overall sensor quantum efficiency. The phosphor particle

size must be small enough to accommodate the desired coating

thickness; they should have a diameter that is smaller than the

required coating thickness. The phosphor crystal edges should

be smooth rather than jagged to reduce losses. Particle-size vari-

ations should be minimized to ensure coating uniformity. The

presence of crystals larger than the coating thickness will result

in gross nonuniformities and an increase in PRNU.

A coating efficiency figure of merit has been adapted from

[1]. Light incident on the phosphor coating will either be re-

flected scattered by the phosphor crystals or absorbed

. Light that is absorbed will be reemitted at a longer wave-

length according to the phosphor internal conversion efficiency

. The figure of merit simplifies the absorption

and emission spectrum to a single wavelength, and is defined as

follows:

(1)

where is the fraction of light lost due to scattering,

is the fraction of light reflected, is the fraction reflected

at the filmsensor interface, is the fraction absorbed by

the phosphor, is the incident wavelength, and is the emitted

wavelength. The fraction of light emitted back toward the light
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source (the radiation that is not captured by total internal reflec-

tion) is defined as

(2)

where is the index of refraction of the film . Under theideal case when , CE 100%, 1.0, and

is 1.5 (when the plastic film is ethyl methacrylate), then is

0.04, is 0, is 0.125 ,and the figure of merit gives an

efficiency of 84%.

Based on the critical material parameters, several materials

were selected for testing (see Table I) [11]. To date, the most

promising phosphor tested is (La,Ce,Tb)PO : Ce : Tb, which

has commercial name 2212 from Osram Sylvania [14]. This

phosphor is listed as a lamp phosphor. It has a theoretical con-

version efficiency of 86% at 254 nm, a peak excitation wave-

length of 254 nm, and a peak emission wavelength of 546 nm.

Neither the decay time nor the particle size were specified by

the vendor.

III. COATINGCOMPOSITION ANDDEPOSITION

The deposition of an inorganic phosphor is not trivial since

the fluorescence mechanism is a function of the crystal structure

that cannot be disturbed [12]. Depositions involving dissolution

or bond disruption (for example, sputtering) are therefore pre-

cluded. Our deposition technique involves suspending the phos-

phor in a dissolved acrylic solution and directly applying the

suspension to the sensor using a proof-of-concept experiment,

with an eyedropper, or more reproducibly with a spin-coater.

This method of applying the phosphor is similar to the tech-

nique first proposed by Viehmann [1], who incorporated laserdyes in a plastic coating.

The coating consists of three components: the acrylic

matrix, the phosphor, and an organic solvent. Three different

acrylic resins were investigated: methyl methacrylate, ethyl

methacrylate, and butyl methacrylate. In-house tests revealed

that the ethyl methacrylate had the highest transmission at

255 nm; optical power absorbed was 2%, 8%, and 13% for ethyl

methacrylate, methyl methacrylate and butyl methacrylate,

respectively. Reagent grade toluene was selected to dissolve the

acrylic although any organic solvent would suffice. Coatings

were deposited onto nonluminescing fused silica slides and

onto DALSA IA-D1-0256 area array CCD sensors [15].

It was established early in the project that coatings with a

high phosphor concentration produced results with the best ef-

ficiency. This was expected since there must be sufficient phos-

phor present to convert incident illumination. In addition, when

the plastic content is too low the efficiency dropped sharply. It

is postulated that this low conversion efficiency is due to scat-

tering losses caused by the roughness of the coating. Fig. 1

shows a topographical measurement from a coating containing

20 mg/ml of acrylic; this coating is clearly nonuniform. In an

attempt to smooth the coating surface, a two-layer coating was

developed in which the phosphor suspension layer was covered

with a second layer containing only plastic. Fig. 2(a) and (b)

Fig. 1. Topographical measurement of coating 2212-2 ((La,Ce,Tb)PO :Ce : Tb) deposited on a fused silica slide.

Fig. 2. SEM micrograph of a cross-section of the (a) two-layer phosphorcoating and (b) pure phosphor crystals. The arrow in (a) points to a regionwhere it is obvious that the plastic has smoothed over the phosphor crystals.

are SEM photographs showing cross sections of the two-layer

2212-2 phosphor coating and pure phosphor crystals, respec-

tively. From a comparison of the two photographs, it can be

seen that the second layer of plastic coating helps smooth the

phosphor crystal surfaces. In total, three coatings were tested:

2212-1 containing no plastic, 2212-2 containing 20 mg/ml of

plastic and the two-layer 2212-2 coating described above. The

composition of the two different phosphor coatings and the pure

plastic coating is listed in Table II.
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TABLE IICOMPOSITION OF THE TWOD IFFERENTP HOSPHOR COATINGSTESTED AND THE PURE P LASTICCOATING THAT WAS U SED

ALONGWITHCOATING 2212-2 TO MAKE ATHIRDCOATING

Fig. 3. Block diagram of the conversion efficiency experimental setup.

A new settle deposition method was also developed in an at-

tempt to improve coating uniformity, which directly impacts the

PRNU and image resolution. The suspension is formed as de-

scribed in above; however, instead of immediately applying it to

the substrate the suspension was allowed to settle. This is effec-

tively a simple method of filtering the crystal that has a size dis-

tribution of 1 to 8 m with an average particle size of 3.6 1.7

m. The solution is then transferred to another container con-

taining the substrate and allowed to evaporate, leaving behind

the uniform coating. It was not necessary to add a subsequent

layer of plastic, as described above, since a layer of plastic set-tled on top of the phosphor.

IV. CONVERSION ANDQUANTUMEFFICIENCIES

In this work, the conversion efficiency is retrieved from mea-

surements of the luminescing efficiency of a coated fused-silica

slide, while the quantum efficiency involves measurements with

a coated CCD sensor. To measure the conversion efficiency,

the experimental setup given in Fig. 3 was used. The UV light

source is an Oriel 200 W Hg bulb. The light was first colli-mated and then passed through a liquid IR filter. Interference

filters were used to create a narrow-band spectrum made up of

atomic mercury lines. A visible light filter (transmission 0from 400 to 1000 nm) was used to provide a much better de-

fined UV spectrum. A pinhole slide was used so that the con-

vertedlightcould be considered a point source. This is necessary

because the isotropic luminescence of the phosphor means that

light is emitted equally in all directions, so therefore some will

not be captured by the optical power meter. To account for this

loss, a solid angle correction factor was applied to the optical

power meter reading. The correction factor was determined as

the solid angle made by the pinhole and the circumference of the

optical power meter as a fraction of the entire hemispherical

solid angle. Fused silica was selected as the coating substrate

because it is transparent at the illumination wavelengths. The

Fig. 4. Conversion efficiency versus wavelength for the three coatings tested.As in Fig. 1, the coating has been deposited onto a fused silica slide.

long pass filter was used to block out any of the incident UV

light that may have passed though the coating. To measure the

sensor quantum efficiency, the same light source as described

above was used along with a DALSA CA-D1-0256 camera. The

camera was clocked in time delay and integration (TDI) mode

at a line rate and data rate of 18.3 kHz and 5.0 MHz, respec-

tively. For PRNU measurements, the camera was operated in

the normal area imaging mode.Fig. 4 contains a plot showing the conversion efficiency as

a function of wavelength for the three coatings tested. Inspec-

tion of the figure reveals that the additional pure plastic layer

almost doubles the efficiency at 265 nm, from 19% to 35% for

the 2212-2 and two-layer 2212-2 coatings, respectively [13]. An

SEManalysis performedon thetwo-layer coating shows that the

coating is 30 2 m thick.

The two-layer coating was deposited onto DALSA IA-D1-

0256 area array sensors. The coating was applied as a thick

and thin coating with an estimated thickness of less than 20

m and greater than 50 m, respectively. These estimates were

based on the measured absorption coefficient of a coated fused

silica slide, which was found, using Beers law, to be 151 m at 265 nm [13]. A simple calculation of the predicted

coated sensor quantum efficiency is given as the quantum effi-

ciency of the sensor at the phosphor emission wavelength, 0.40,

multiplied by the coating conversion efficiency, 0.35, to give

14%. A plot of the quantum efficiency of both the thick and

thin two-layer coating, and the uncoated sensor as a function

of wavelength is given in Fig. 5. The figure shows that the mea-

sured coated sensor quantum efficiency is 12% 0.8% at an

illumination wavelength of 265 nm. This improvement repre-

sents a 3.5x improvement in sensor quantum efficiency. (Note

that the nonzero quantum efficiency of the uncoated sensor is

due to the residual blue response of the uncoated sensor.)
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Fig. 5. Quantum efficiency of a DALSA IA-DA-0156 image sensor with atwo-layer 2212-1 coating as a function of wavelength.

TABLE IIIPRNU RESULTS OF ANUNCOATED ANDCOATEDSENSOR FOR THETWO-LAYER

THICK AND THIN 2212 COATING AND THESETTLEDEPOSITIONMETHOD

V. PRNU

PRNU is a measure of pixel-to-pixel variations in sensor re-

sponsivity. Ideally the PRNU is zero, meaning that under con-

stant flat field illumination every pixel will have the same re-

sponsivity. However, in reality, the PRNU of an uncoated sensor

is typically on the order of 5%10% [15]. The PRNU degrada-

tion due to the coating is a simple, nondestructive test that can be

used to quantify nonuniformities in the coating thickness. This

parameter is of particular importance for image sensors where

coating nonuniformity will contribute to resolution degradation.In this investigation, PRNU is defined as the standard % rms cal-

culation:

PRNU

where is the standard deviation of the difference between

pixel output and the average pixel output across the entire array

as measured at 50% of saturation, is the average output at

100% of saturation, and is the output at zero illumination.

For comparison purposes, the PRNU of the uncoated sensor was

first measured at the coating emission wavelength. The PRNU

of the sensor coated with the two-layer 2212 coating was7.0 and

1.6 times larger than the uncoated sensor for the thick and thin

coating, respectively (see Table III). Note that the signal output

of each pixel of the coated sensor was found to havea linear rela-

tionship with light intensity indicating that post-data processing

could be used to correct PRNU degradation. An improved depo-

sition technique was developed to reduce the amount of PRNU

degradation; these results are described in Section VIII.

VI. CONTRAST TRANSFER FUNCTION

ANDPHOTODEGRADATION

The contrast transfer function (CTF) quantifies the degree to

which a given spatial input frequency can be reproduced by the

Fig. 6. Simulated CTF of the coated sensor.

image sensor. It is a measure of the sensors ability to image

a pattern of equidistantly spaced black and white bar pairs. The

CTF differs from the modulation transfer function (MTF) in that

the CTF is the response to a square wave input rather than a

sinusoidal input pattern. The CTF is defined as

(4)

where output and output are the maximum and minimum

output signal, respectively, and input and input are the

maximum and minimum input signal. A CTF equal to one in-

dicates that the sensor can perfectly image the target (assuming

an optical transfer function equal to unity).

The CTF is one of the most difficult imaging parameters to

quantify. The following experiment was performed in an attempt

to determine an approximate CTF value for a thick and thin

two-layer coating 2212-2. A precision 100- m-wide slit was

imaged onto a coated DALSA IL-P1 line scan sensor at an il-

lumination wavelength of 265 nm. A lens of magnification 0.5was used to image the 100- m slit down to 50 m at the sensor.

The line rate and light intensity were adjusted to ensure that the

pixels did not reach their full-well capacity and spill charge into

neighboring pixels. A digital oscilloscope was used to measure

the analog signal generated at the illuminated pixels. Six pixels

were actually illuminated (four fully and two partially); an ap-

proximation that five pixels (with a pixel pitch of 10 m) were

illuminated was used for this analysis.

To quantify the CTF degradation of the coated sensors, the

normalized output signal was plotted as a function of the pixel

number. The CTF data of the coated sensors had a Gaussian

shape due to the scattering of light by the coating. A Gaussian

distribution was fitted to the observed data to simulate the re-sponse of the coated sensor to an alternating bar target with

50- m-wide light and dark regions. Fig. 6 gives the simulated

response for two thicknesses of coatings; coating 1 is estimated

to be less than 20 m thick and coating 2 greater than 20 m.

If the optical transfer function is assumed to be 1.0, meaning a

difference in the normalized input signal is 1.0 (a valid assump-

tion given that the spatial frequency is 100 lp/mm), then the CTF

for the thin and thick coating is 0.9 and 0.4, respectively. These

findings confirm that the thinner coating is better for imaging

applications.

The photostability of the 2212 phosphor was tested. The two-

layer 2212-2 coating was deposited onto a fused silica slide and
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Fig. 7. Phosphor conversion efficiency as a function of net incidentillumination by radiation at 255 nm. Note that radiation hardening to a constantlevel of conversion efficiency occurs within illumination by the first 1 mJ/cmof radiation.

(a)

(b)

Fig. 8. Image offlat-fieldillumination of a 128 2 128 pixel section of DALSAIA-D1-0256 image sensor captured at (a) 265 nm (coated sensor) and (b) thesame sensor before coating at the phosphor emission wavelength 540 nm. Theaverage signal level for both images is 128 DN.

illuminated with 255-nm radiation at the following intensities:

0.12 W/cm for 3 h,2.0 W/cm for 5 h,and 11.1 W/cm for

2.3 h. After each period of radiation, the conversion efficiency

was tested; the results are plotted in Fig. 7. It is apparent from

the results that the coating degrades to approximately 50% of

the peak efficiency, but then remains stable at this level. This

measured stabilization of the inorganic phosphor coating is a

considerable improvement over organic phosphor coatings thatexponentially degrade to zero efficiency [1].

VII. SETTLE-METHODDEPOSITIONRESULTS

The settle-method coating resulted in a quantum efficiency

of 12% at 300 nm and a PRNU degradation that was 0.36 times

higher than the PRNU of the uncoated sensor. This marks an im-

provement in the photoresponse nonuniformity degradation by a

factor of 4.4. Fig. 8(a) and (b) shows images from an uncoated

sensor illuminated at 540 nm and a coated sensor illuminated at

300 nm, respectively. The image from the coated sensor is gen-

erally quite uniform although some artifacts are visible.

VIII. CONCLUSION ANDRECOMMENDATIONS

The coatings presented here are a viable alternative to organic

phosphor coatings for enhanced UV responsivity of CCD image

sensors. The coating radiation hardens to 50% of the peak initial

efficiency within the first 5% of the test period. It is this char-

acteristic of the coating that improves its viability in continuous

manufacturing applications. The phosphor coating improves the

quantum efficiency of the sensor by as much as a factor of 3.5

at 265 nm. In general, thinner coatings exhibit better imaging

qualities; the PRNU and CTF are reduced by 75% and 56%, re-

spectively, when a thinner coating is applied.

The results of the settle-method deposition are promising as

they demonstrate that the PRNU can be decreased by improving

theuniformityofthecoating.Onewaytoimprovecoatingunifor-

mity is to filter the phosphor to decrease variance in the particle

size distribution. Once this is done coatings with a thickness of a

certain number of particles can be designed. Laser ablation can

also be used; however, this is only feasible if the laser ablates

relatively large pieces of the phosphor so as not to disturb the

crystal structure that is essential to the luminescing properties.

ACKNOWLEDGMENT

The authors wish to acknowledge DALSA Corporation and

the Natural Sciences and Engineering Research Council for

their generous support of this project as part of the DALSA-

NSERC Industrial Research chair at the University of Waterloo.

In addition, the authors would like to thank Dr. D. Dykaar and

Dr. G. Ingram for their valuable contribution via discussions

and suggestions.

REFERENCES

[1] W. Viehmann, Thin-film scintillators for extended ultraviolet responsesilicon detectors,Proc. SPIE, vol. 196, pp. 9095, 1979.[2] M. Cullum, S. Deiries, S. DOdorico, and R. Reisse, Spectroscopy to

the atmospheric transmission limit with a coated GEC CCD, Astron.Astrophys., vol. 153, pp. L1L3, 1985.

[3] L. B. Robinson, W. E. Brown, D. K. Gilmore, R. J. Stover, M. Z. Wei,andJ. C. Geary, Characteristics of large Fordand ReticonCCDs, Proc.SPIE, vol. 1235, pp. 315326, 1990.

[4] G. R. Sims and G. Fabiola, Improvements in CCD quantum efficiencyin the UV and near-IR, Proc. SPIE, vol. 1071, pp. 3142, 1989.

[5] M. P. Lesser, Recent charge-coupled devices operation results atSteward Observatory,Proc. SPIE, vol. 1242, pp. 164169, 1990.

[6] , CCD thinning, coating, and mounting research for astronomy,Proc. CCDs in Astronomy, vol. 8, pp. 6375, 1989.

[7] E. Meisenzahl et al., 3.2 million pixel full-frame true 2-phase CCDimage sensor incorporating transparent gate technology, Proc. SPIE,vol. 3965, pp. 164169, 2000.

[8] M. M. Blouke, M. W. Cowens, J. E. Hall, J. A. Westphal, and A. B.

Christensen, Ultraviolet downconverting phosphor for use with siliconCCD imagers,Appl. Opt., vol. 19, pp. 33183321, Oct. 1980.

[9] R. A. Bredthauer, C. E. Chandler, J. R. Janesick, T. W. McCurin, and G.R. Sims, Recent CCD Technology Developments, in Instrumentation

for Ground-Based Optical Astronomy, L. B. Robinson, Ed. New York:Springer-Verlag, 1987, pp. 486492.

[10] G. Nalettoet al., Fluorescence of Metachrome in the far and vacuumultraviolet spectral region,Proc. SPIE, vol. 2519, pp. 3138, 1995.

[11] A. Wisniewski, private communication, 1999.[12] K. H. Butler, Fluorescent Lamp Phosphors: Technology and

Theory. New York: Springer-Verlag, 1994.[13] W. A. R. Franks, M. J. Kiik, and A. Nathan, Inorganic phosphor coat-

ings for UV-Responsive CCD image sensors, Proc. SPIE, vol. 3965,pp. 3341, 2000.

[14] Datasheet, Osram Sylvania Ltd., Towanda, PA.[15] DALSA Inc.. 19981999 Databook, Waterloo, ON, Canada. [Online].

Available: www.dalsa.com
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Wendy A. R. Franks received the B. Appl. Sci.degree in chemical engineering and the M. Appl. Sci.degree in electrical engineering from the Universityof Waterloo, Waterloo, ON, Canada, in 1998 and2000, respectively. She is currently pursuing thePh.D. degree in the field of biosensors at the SwissFederal Institute of Technology, Zrich (ETHZ).

She completed her Masters research while in theInternal Research Group at DALSA Corporation,

Waterloo.

Martin J. Kiik(M96) received the B. Appl. Sci. de-gree and the M.S. and Ph.D. degrees from the Uni-versity of Toronto, Toronto, ON, Canada, in 1986,1989, and 1994, respectively, where his research in-volved the investigation of the dynamics of chemicalprocesses in rare-gas discharges in supersonic jet ex-pansions.

Since 1994, he has been working in the ImageSensor R&D group at DALSA Corporation, Wa-terloo, ON, Canada.

Dr. Kiik is a member of the Association of Profes-sional Engineers of Ontario, Canada.

Arokia Nathan (S84M87SM99) received thePh.D. degree in electrical engineering from the Uni-versity of Alberta, Edmonton, AB, Canada, in 1988,where he was engaged in research related to thephysics and numerical modeling of semiconductormicrosensors.

In 1987, he joined LSI Logic Corporation,Santa Clara, CA, where he worked on advancedmultichip packaging techniques and related issues.

Subsequently, he was at the Institute of QuantumElectronics, ETH Zrich, Switzerland. In 1989, hejoined the Department of Electrical and Computer Engineering, University ofWaterloo, Waterloo, ON, Canada, where he is currently a Professor. In 1995, hewas a Visiting Professor at the Physical Electronics Laboratory, ETH Zrich.His present research interests lie in amorphous and polycrystalline silicondevices, circuits, and systems on rigid and mechanically flexible substrates fordigital imaging and displays. His interests have more recently encompassedpolymer electronics, specifically on aspects related to the physics, technology,and applications of organic thin film transistors, displays, and sensors. Hecurrently holds the DALSA/NSERC industrial research chair in sensortechnology and is a recipient of the Natural Sciences and Engineering ResearchCouncil E.W.R. Steacie Fellowship. He has published extensively in the fieldof sensor technology and CAD and is a coauthor of the book, MicrotransducerCAD (New York: Springer, 1999).

UV Responsive CCD Image Sensors With Phosphor

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