EXHIBIT F

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 1 of 10
Charge-transfer-plate spatial light modulators

Cardinal Warde, Craig M. Schiller. Jeffrey Bounds, Thomas N. Horsky, George Melnik,

and Robert Dillon

Charge-transfer-plate spatial light modulators (CTPSLM's) are a class of devices that employ chargetransfer plates as the interface between the charge-generation element and the light-modulation

element. Both optically addressed and electrically addressed devices have been built. Chargegenerating elements for the optically addressed devices include photoconductors, photodiode and

phototransistor arrays, optoelectronic integrated circuit chips, and photocathode-microchannel-plate

assemblies. For electrically addressed devices, electron guns, very large-scale integrated circuits,

thin-film transistors, and matrix electrodes are among the possible charge-generation elements. Lightmodulation elements used in CTPSLM's include liquid crystals, electro-optic organic and inorganic

crystals, polymers, deformable membrane mirrors, oil films, multilayer dielectric films, and electroluminescent films. In principle, all combinations of charge-generation elements and light-modulating

elements are possible. This paper explores the fundamental performance limitations ofCTP technology,

and describes the design, operation, and applications of five different CTPSLM's (three based on

membrane-mirrortechnology and two on liquid-crystal technology).

1. Introduction

Two-dimensional spatial light modulators (SLM's)

are the building blocks of optical information processors.1

SLM's modify the amplitude, phase, polarization, or intensity of a readout light beam in response

to eitherthe intensity ofa second write-light beam or

to a two-dimensional electrical voltage or current

pattern. Devices ofthe firsttype are called optically

addressed SLM's and devices of the second type are

called electrically addressed SLM's, respectively.

Charge-transfer-plate spatial light modulators

(CTPSLM's) are a relatively new class ofdevicesthat

employ the structure shown in Fig. 1, in which a

charge-transfer plate (CTP) is used as the interface

between the charge-generation element and the lightmodulation element. The general CTPSLM may

also contain an optional gain element, as shown in

Fig. 1.

When the work was performed the authors were with Optron

Systems, Inc., 3 Preston Court, Bedford, Massachusetts 01730.

C. Warde's permanent address is the Department of Electrical

Engineering and Computer Science, Massachusetts Institute of

Technology, Cambridge, Massachusetts 02139. J. Bounds is now

with the Department of Electrical Engineering and Computer

Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. R. Dillon is presently with Sparta, Inc., 24

Hartwell Avenue, Lexington, Massachusetts 02173.

Received 28 August 1991.

0003-6935/92/203971-09$05.00/0.

© 1992 Optical Society ofAmerica.

As illustrated in Fig. 2, a CTP is essentially a dense

array of longitudinally oriented conducting pins embedded in a wafer of electrically insulating material.

The CTP derivesits name from its ability to serve as a

high-densitymultifeedthroughvacuum interface that

can transfer a two-dimensional charge distribution

from vacuum to air. CTP's that are 25 mm in

diameter with 50-|im-diameter conducting pins on

70-jj.m centers, and with 10-p.m-diameter conductors

on 14-jAm centersin hexagonal close-packed patterns,

have been builtin thicknesses up to 5 mm. Thusthe

ratio of a collective pin cross-sectional area to the

total CTP area is ~ 50%. The surfaces of the CTP

can be highly polished to an optical flatness ofX/10.

Charge-generating elements for the optically

addressed CTPSLM's include photoconductors, photodiode and phototransistor arrays, optoelectronic

integrated circuit chips, and photochathode-microchannel-plate (MCP) assemblies. On the otherhand,

electron guns, very large-scale integrated (VLSI) circuits, thin-film-transistors, and matrix electrodes are

among the possible charge-generation elements for

electrically addressed devices. Light-modulation elements that can be used in CTPSLM's include liquid

crystals, electro-optic organic and inorganic ciystals,

polymers, deformable membrane mirrors, oil films,

multilayer dielectric films, and electroluminescent

films. In principle, all combinations of chargegeneration elements and light-modulating elements

are possible.

10 July 1992 / Vol. 31, No. 20 / APPLIED OPTICS 3971

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 2 of 10
Minar Ughl Modulailon

, Element

Readout Ught

Gam Charge Element OTP Generafion Element

Wnla Ughl S—

O— G>—

vtodulaled Ught

Fig, 1. ArchitectureofCTPSLM's.

This paper describes the characteristics of CTP's

and structure, principles of operation, and applications of five different CTPSLM's (three based on

membrane-mirrortechnology and two based on liquidcrystaltechnology).

2. CTP Characteristics

A. CTP-Limited Spatial Resolution

The spatial resolution of a light modulator with the

architecture shown in Fig. 1 may be limited by the

spatial rsolution ofany ofits constituents(the charge

generation, gain, CTP, or light-modulation element).

We are concerned here with only the influence ofthe

CTPon the resolution ofthe SLM.

The spatial resolution of the CTP is determined

primarily by CTP thickness, interpin separation, pin

diameter, pin array pattern, and the CTP insulator

material resistivity and dielectric constant. These

parameters detemine the interpin capacitance and

resistance, and therefore the extenttowhich a charge

placed ononepin raisesthevoltage on thatpinas well

as on the neighboringpins. The spatial resolution of

the CTP has been studied by electrostatic modeling

techniques and confirmed by experiments involving

the transfer of voltage longitudinally through the

CTPto thin liquid-crystallayers.

In the electrostatic model, only two dimensions

were considered, so that fringing effects atthe face of

the platewere neglected. The fringingeffectsshould

be negligible, considering the pin geometry. By treating theCTPcharge-to-voltage response with a linearsystems analysis, we may use a spatial point-spread

function representation to characterize the spatial

<3> o cu o o

(S><3>e>OiO<3>OOCDG5

iS>C0<I>G>G>OC3»CZ>G>OGE5OCZ>'

CI5CE> O O <S> ®

CjDOCDOcSiOCDOOeSCOOiCiXZJ G>\

0CI><E5G|>CDCI><Z>00<3>CCie>e>

<T5 CD CD<SICZ><Z><Z>G>0<D><Z>CZ>CDCD

CD CE> dD CD O O O CD CD CDs

CD CD CD

INSULATING

MAT MIX CONDUCTORS

resolution ofthe CTP. Thus the voltage on any pin

can be determined from a superposition of all contributions arising from charge on the other pins plusthe

component, because ofthe self-capacitance ofthe pin

itself.

The generalized distributed capacitance problem

can be modeled by the equation

V=W q. (1)

where q and V are vectors representing the charge

and voltage respectively on each pin, and "

1

is the

inverted capacitance matrix. Alternatively, we may

write

<7n

'ii 'In

'nl

V!

V„

(2)

Fig. 2. CTP is a close-packed array ofconductors embedded in an

insulatingmatrix.

Because the CTP pins are hexagonaliy packed, we

need only solve for fields in one-sixth of the plate.

Thus we determined the capacitance matrix by using

a two-dimensional finite-difference numeric field approximation that solved Poisson's equation with a

relaxation technique over an equilateral triangular

mesh. The main difficulty with thistechnique, aside

from the length of computation time, was the bookkeeping involved in translating from the triangular

mesh to the inherent Cartesian coordinate structure

ofa matrix.

The procedure for calculating the capacitance matrix was as follows. One pin was assigned apotential

with respect to a reference (ground) at infinity, and

the relaxation method was used to solve for charge

distributions resulting from the imposed potential.

We supplied the algorithm with a series of unit test

voltage vectors (Vj to Vn)to obtain approximationsto

each column of the capacitance matrix. For example,

(3)

Thus we obtained the ^ matrix, which, when inverted, allowed usto compute thevoltagedistribution

developed on thepinsin response to an applied charge

distribution. Specifically, by applying charge to only

one pin, we found the spatial point-spread function,

which is illustrated in Fig. 3, from the model. The

lower part ofFig. 3 showsthe voltages onthe charged

pin (pin 0) and two adjacent uncharged pins (pin 1

and pin 2) on a sectional cut along the x axis. From

1

0 Cu

Vi = - qCVj) =

0 cnI

3972 APPLIED OPTICS / Vol. 31. No. 20/10 July 1992

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 3 of 10
VoHage on pin v

VrSBX

Netchaigeon P'"^ X^/

f

r) @ Co561

©

Wc»D

v Q

10-.

4- -LSiFi-L

Pig, 3. Calculated normalized pin voltages that are due to capacitance coupling for a hexagonally packed CTP in response to a

charge q placed on one pin.

Fig. 3 we see that if V is the voltage developed on a

CTP pin in response to a charge q placed on that pin,

the voltage developed on the neighboring pins is of

the order of V/3, and ~V/10 on the next-nearestneighbor pins. Note also that for a 4-mm-thick CTP

with 50-|xm conducting pins on 70-pm centers the

CTPpin self-capacitance is found to be approximately

0.4 pF.

In practice, CTP's may exhibit fixed-pattern noise

arising from irregularities in the packing ofthe pins,

and these irregularities may be evident in the modulated outputimage. This would be true especially in

systems that do not spatially filter the diffraction

pattern from themodulator before reimaging to form

the output image. A liquid-crystal CTPSLM thatis

read out between crossed polarizers is an example.

Of course, the ideal system is one in which the CTP

resolution is atleast a factor of 2 higher than that of

the element with the next-highest resolution.

B. Secondary Electron Emission Characteristics of the

CTP

Two charge-generation elements that are of special

interest are the electron gun and the photocathodeMCP assembly. These components perform electron addressing ofthe CTP and therefore rely on the

secondary electron emission characteristics of the

target to deposit bipolar charge patterns. The secondary electron emission characteristic of a material

is a plot ofthe ratio 8(£k) ofthe number ofsecondary

electrons (sec. elec.) emitted from the surface to the

number of incident primary electrons (pri. elec.) as a

function ofprimary electron energyEp, thatis,

where

No. sec. elec.

8(£Jp = ^r—No. pn. elec.

Ep = eCV* - V.).

(4)

(5)

Vk is the effective cathode voltage and V", is the

effective CTP surface voltage. The secondary electron emission characteristic of a CTP has been measured and the resultant curve is plotted in Fig. 4.

When a CTPSLM is operated below the first crossover point of the characteristic, where 8 < 1, the

surface ofthe material will charge negatively because

of net electron accumulation. On the other hand,

when the device is operated between the first and the

second crossover points, where 8 > 1, itis possible to

charge the surface either positively or negatively.

Positive charging is achieved by collecting the secondary electrons with a collector grid placed in close

proximity to the CTP, whereas negative charging is

achieved by simply permitting the emitted secondary

charge to fall back to the surface.

From Fig. 4 we see that, for a bare CTP, 8 has a

peak value of 1.3 at Ep = 200 eV. To increase the

effective 8, the CTP may be overcoated with a secondary electron enhancer coating, such as MgO, which

will also typically increase the value ofEp at which 5

peaks. For electron-beam-addressed devices, increasing the value of Ep, up to a point, increases the

sharpness of the electron image deposited on the

CTP, and therefore improves the spatialresolution of

the device.

C. Charge-Transfer Efficiency and Storage Time

Given the capacitive coupling between the CTP pins,

it is clear that there is a loss of charge sensitivity

when a CTP is used in an SLM compared with the

case for a non-CTP-based SLM. The charge sensitivity may be defined as

7 =

Vm (with CTP)

(without CTP):

(6)

where Vm isthe longitudinal componentofthevoltage

developed across a pixel of the light-modulating elementthatis due to a char-ge q on that pixel. Clearly

!.0 BM

V,

0.5

l),6 -C

O.'l

200 JOO 600

E„ (.V)

Fig. 4. Measured secondary electron emission characteristic of a

CTP.

10 July 1992 / Vol. 31, No. 20 / APPLIED OPTICS 3973

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 4 of 10
7 <1 1 for all practical cases. Thin OTP's with large

interpin separationswill optimize the charge-transfer

efficiency but atthe expense ofthe spatial resolution.

Long-term (hours) storage of charge by the OTP

itselfis necessary ifCTPSLM's are to exhibit image

storage. This means that lateral spreading of the

charge frompin topinmustbe minimized. Thusthe

interpin RC value must be maximized. It is therefore necessary thathigh-resistivity insulating materials be used for the OTP substrate for the case in

which long-term storage is required. The typical

resistivity of the insulating material used in our

OTP'sis ~1014 Q cm, and charge storage times ofthe

order of60 s have been observed.

3. Charge-Transfer Plate Membrane-Mirror Light

Modulators

Like various types of membrane light modulators given

in related works of others,2-10 charge-transfer-plate

membrane-mirror light modulators (CTPMLM's)

employ a thin deformable membrane mirror as the

light-modulating element. However, the CTPMLM's

differ from the previous devices in thatthe CTPMLM's

employ a OTP as the support substrate for the membrane. The characteristics of three types of membrane-mirror devices are discussed: (1) ahardwired

matrix-electrode-addressed device in which an array

ofelectrodesis deposited on the addressing side ofthe

OTPand driven by abankofvoltage amplifiers, (2) an

optically addressed device (which is photocathodeMCP driven), and (3) an electron-beam-addressed

device in which ahigh-resolutionelectron gun is used

asthe charge-generation element. All three ofthese

devices employ the same basic OTP-membrane anode

structure as shown in Fig. 5.

A. CTP-Membrane Anode Fabrication

In order to fabricate the OTP-membrane anode

assembly, itis necessary firstto create the pixel wells

into which the membrane mirror deforms when

addressed. Two approaches are used: the etchedpin method, and the etched-overcoat method. With

the etched-pin method, the pins on one side of the

OTP are etched back ~ 3 pm to form shallow wells.

The polymeric membrane is then bonded onto the

OTP surface that contains the wells such that a

reliable bond between the two dielectric surfaces is

established by van der Waals forces. The resultant

membrane pixels appear in a hexagonal close-packed

array thatmatchesthat oftheOTPconductors. The

exposed surface ofthe membrane is then metallized

to convertit to a flexible mirror as well as to provide

an electrode to which a potential Vm(0 can be applied

during operation. This approach yields one well per

pixel.

With the etched-overcoat approach, an insulating

layer is first deposited over one face ofthe CTP and

the wells are etched out ofthe insulating layer. The

approach offerstremendousflexibility in the design of

thepixel pitch, pixel diameter, and membrane tension.

This is because the membrane tension is determined

Etched Well

v

Metallized Mirror

Membrane Beclrode

|\ |

"V I

Conciucling

Pin

Insulaling Matrix

(a)

Charge-Generation Element

(e.g., e-beam, electrode matrix, or VLSI Chip)

(b)

Fig. 5, Deformable membrane mirror stretched over the wells of

the CTP: (a) membrane in the unaddressed state, (b) membrane

deformation in response to a charge pattern on theCTP.

almost exclusively by the materials used for the

membrane and the insulating well layer. When photolithographic techniques are used to etch the wells,

extremely high spatial uniformity can be achieved,

thereby leading to the SLM's with low fixed-pattern

noise. Of course, this approach also permits the

possibility of oversampling each pixel with several

pins, which is importantfor some applications.

The lifetime ofthe polymeric membrane was found

to be excellent when it was encapsulated in a hermetically sealed vacuum chamber at the readout face of

the device. In fact, one ofourfirst membranes to be

operated within the hermetically sealed chamber was

still functioning normally (with minimal degradation) after more than oneyear ofintermittent use.

B. Principles of Operation

Thebasic operation oftheCTPMLM'sissuchthat, in

the unaddressed state, the membrane mirror, which

is under a slight tension, is flat [see Fig. 5(a)] and all

the readoutlightis reflected into the zero order. In

the optically addressed and electron-beam-addressed

devices, for example, images arewritten by depositing

a charge pattern ty[x,y) on the addressing face ofthe

CTP. This pattern of charge generates electrostatic

forcesthat deform the membrane (in a corresponding

pattern) into the underlying wells [see Fig. 5(b)].

3974 APPLIED OPTICS / Vol. 31. No. 20/10 July 1992

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 5 of 10
Thus the readout light that reflects from the membrane mirror is phase modulated. The amount of

deformation increases as the accumulated charge

density on the CTP pins increases, leading to grayscale phase modulation of the readout light. The

spatially periodic (hexagonal) phase modulation of

the readout wave front causes light to be scattered

out ofthe zero orderinto higher orders.

The electrostatic force attracting the membrane

into a pixel well is easily seen by considering a net

charge q deposited onto the correspondingpin. Ifwe

assume, for simplicity, that the separation between

the membrane and the pin (well depth) is approximately uniform and is much less than the diameter of

the pin, the situation resembles that of a parallel

plate capacitor, and the force Fattracting the membrane to the pin is therefore approximately given by

F = qV/2S =

2€0A

(7)

where Visthe voltage between the membrane and the

pin,Sisthe well depth,A isthe area ofthe well, and eo

is the permittivity offree space. As charge is added

to the pin, the membrane deforms into the well until

the restoring force exerted by the tension on the

membrane exactly cancelsthe attractive force.

Altering device parameters such as well diameter a

and well depth S has a profound effect on the voltage

required to deflectthe membrane. Ithasbeen shown

that the membrane deflection d is given by the

equation5

d = (a2e0y

2

)/(32TS2), (8)

where T is the membrane tension. Thus it is seen

that for a voltage-driven device, the operatingvoltage

scales as the ratio of well depth to well diameter

[Vw (S/aKTrf)1'

2

], whereas for a current-driven device the required charge scales as the well diameter a

and is independent of the well depth [q « a(Td)1'

2

'].

Hence the gray-scale modulation is a nonlinear function ofthe accumulated CTP surface charge.

When the device is read out with coherent laser

light and a classical two-lens spatial filtering system

is used to manipulate the light modulated by the

membrane, thepattern oflightin the Fourierplane of

the system also exhibits the hexagonal symmetry of

the membrane mirror pixels. By employing a variety of different spatial filters in the Fourier plane,

many different operations can be performed. For

example, (1) spatially sampled phase-onlymodulation

of the readout light is achieved if no spatial filter is

used, and (2) intensity modulation is achieved through

the use ofsimple Fourier-plane filters, such as those

shown in Fig. 6. With a low-pass (zero-order) filter

[see Fig. 6(a)] a negative ofthe write image is formed,

and with the special high-pass filter of Fig. 6(b) a

positive image is formed. The filter in Fig. 6(b) is

essentially a zero-order stop combined with a set of

bandpass subfilters centered on the signal-carrying

diffracted beams. The bandpass filter [Fig. 6(b)]

(a) (b)

Fig. 6. Amplitude modulation spatial filters; (a) low-pass, zeroorderfilter; (b) special bandpass Fourier-plane spatial filter.

offers the higher contrast ratio in the output image,

Assuming the membrane remains flatin its OFF state.

To gain further insight into the diffraction properties of the membrane, we considered the twodimensional hexagonal sampling of the membrane

mirror and computed the two-dimensional fast Fourier transform of the spatial phase function associated with the deformed mirror. In the model, we

assumed a uniform distribution of charge on the

CTP, and we assumed that the membrane over each

pore is deflected parabolically (a good approximation

to the experimentally observed profile). From this

exercise, we determined the intensity in the various

orders of the diffracted light. Further theoretical

and experimental details are given in the paper by

Horsky et al.nin thisissue.

C. Hardwired Matrix-Electrode-Addressed CTPMLM

The hardwire-addressed CTPMLM, which is also

called the W-MLM for brevity, has the architecture

shown in Fig. 7. As can be seen it consists of a

CTP-membrane anode assembly with a two-dimensional array of electrodes deposited on the addressing

side of the CTP. Each electrode is driven by a

separate high-bandwidth, high-current amplifier.

An electrode may address either one or several pins,

depending on the design and the intended application

of the device. Assuming the amplifiers are not currentlimited, this hardwired device can be driven up to

READOUT PROCESSED

UGHT UGHT METALLIZED METAL WELL MEMBRANE

ELECTRODE

INSULATING

SPACER

CTP

ELECTRONIC CONTROLLER NPUT

SIGNAL

Fig. 7. Architecture ofthe W-MLM.

10 July 1992 / Vol. 31, No. 20 / APPLIED OPTICS 3975

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 6 of 10
the ultimate practical speed ofresponse ofthe membrane, which is limited by only the first resonant

frequency ofthe membrane (which is estimated to be

several megahertz for our devices, based on simple

geometric considerations). A2 x 2 matrix-electrodeaddressed MLM was built and a membrane response

time on the order ofI ps was observed, as can be seen

in the oscilloscope traces of Fig. 8. Applications of

the W-MLM include real-time wave-front phase correction for communication and imaging through turbulence, correction of aberrations in optical instruments, and phase-only Fourier-plane spatial filtering.

This device can also function as an array of electrically controlled dynamic focusing mirrors.

D. Optically addressed CTPMLM

One of the optically addressed configurations ofthe

CTPMLM isshown inFig. 9. This particular configurationissimilartothatofthe microchannelSLM.12-14

Itis a high-gain, high-sensitivity device that employs

the standard CTP-membrane anode, a collector grid,

and a photocathode-MCP assembly as the chargegeneration element. We also call this device the

O-MM for brevity.

In operation, the write-light image incident on the

photocathode liberates electronsthat are amplified by

the MCP's before bombarding the addressing face of

the CTP. The purpose of the collector grid is to

control the collection of secondary electrons emitted

by the CTP surface so that the secondary emission

process can be exploited to selectively remove electrons from or deposit electrons onto the CTP, as

discussed above. The landingenergy ofthe primary

electrons is determined by the effective MCP cathode

potential Vk (which tendstobe lessthan ~ 100 V), the

membrane voltage Vm, and the state of charge of the

CTPsurface.

OPTICAL CONTROL BEAM

-337.5mV

lOmv

i

Inot

!/

a

-437.SmV- -20^0 lu 8Q>i9

s ^

hi

phoiocaihoci:

MCP

PMCP QRJO ENMANCCfl COAT1

,MO

OTP

INSIAATOQ LAYER

WEU.

klETAEUZED MEMBRANE MIRROR INDOW

READOUT UGHT PHASE MODULATED

Fig. 8. Optical response (top trace) caused by a voltage step

(bottom trace) on one electrode ofa W-MLM, indicating a noncurrent-liraited membrane response time of ~ 1 ps. The electrode

addressed several pins.

Fig. 9. Structure of the optically addressed photocathode-MCP

membrane-mirrorlightmodulator.

In a preliminary vacuum-demountable device that

was built without a photocathode and operated with

UV write light (the MCP input face acted as an UV

photocathode), we demonstrated a spatial resolution

of 2 line pairs/mm, and a framing speed of 500 Hz

with it radians ofphase-modulation depth at 633 nm.

Because ofits bipolar charging characteristics and

thresholding capability, the O-MLM, like the microchannel SLM, can perform a wide variety of image

processing functions. These include image addition,

subtraction, and logic operations. Like the W-MLM,

applications of the O-MLM include real-time wavefront phase correction for communication and imaging through turbulence, correction of aberrations in

optical instruments, phase-only Fourier-plane spatial

filtering, and arrays of optically controlled dynamic

focusing mirrors.

E. Electron-Beam-Addressed MLM

The structure of the electron-beam-addressed MLM

(e-MLM) is illustrated in Fig. 10. It consists of a

high-current, high-resolution electron gun, and a

CTP/membrane anode assembly. The electron gun

converts the control signals from the electronic controller into a charge image that is deposited on the

addressing face ofthe CTP asthe electron beam scans

the surface. The advantages of electron-beam addressing include essentially wireless operation, and

freedom from the fixed-pattern noise that is associated with most other addressing structures. This

device offers flickerless gray-scale operation, a

high readout light efficiency, a high contrast ratio

Iiniuli enMNDQW : 11' /

R£ADQUT uQm

—C^E- XAHOin MU II

5C«Otf?ET^CTCfl METM117F1> cowpuren Ml CJUIANIFig. 10. Structure ofthee-MLM.

3976 APPLIED OPTICS / Vol. 31. No, 20 / 10 July 1992

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 7 of 10
(> 100:1), a potentially large number of pixels (106

),

and readout over a broad wavelength range (UV to

long-wave IR).

Applications of the e-MLM are expected to include

large-screen projection displays, infraredscene projectors, a computer-generated holographic display, and

amplitude andphase-onlymasksin optical processors.

Further details of the e-MLM can be found in the

paper by Horsky etal.nas well as elsewhere.15,16

4. Liquid-Crystal CTP light Modulators

A, E-Beam Liquid Crystal CTPSLM's

The structure of electron-beam liquid-crystal

CTPSLM's, which are called e-LCLM's for brevity, is

shown in Fig. 11. It consists of an electron gun that

scans a focused electron beam across a special CTPliquid-crystal anode that forms the faceplate of the

electron gun. Withoutsome kindofinterface component, such asthe CTP, electron-beam addressing of a

liquid-crystal layer would be impossible. Related

e-LCLM's that employ some kind of charge-transfer

component are discussed elsewhere.17-19

In particular, because CTP's can be polished to an

optical flatness of X/10 or better, and liquid-crystal

alignment layers can be deposited on them by standard techniques, a high-quality liquid-crystal light

modulation cell can be readily formed on the CTP by

using a glass flat as the second confining surface.

Electron-beam-addressed prototypes of both 45°-

twist nematic cells for amplitude modulation and

parallel aligned nematic cells for phase modulation

have been built. The amplitude modulation cells are

~ 3 (J.m thick, while very thick cells (~20 p,m) were

used for the phase modulators.

A novel electron-beam-addressing scheme that exploitsthe secondary electron emission characteristics

of the CTP was employed to ensure that the timeaveraged addressing voltage acrossthe CTP was zero.

Liquid crystals undergo electrochemical degradation

when exposed to long-term dc fields. By writing the

appropriate charge distributions on the CTP surface,

dynamic lenses ofvarying focal lengths were demonstrated with the phase-modulating e-LCLM's.

Coherent light amplitude image generation with a

contrast ratio of 200:1 and a spatial resolution of 3

line pairs/mm was also demonstrated. Further details of work on the above-mentioned e-LCLM's can

be found in the paper by Melnik et air® and elsewhere.21,22

nwrtPAACMr

EWANCER CavSTAJ./ POtAfOWa / / atAU SPUTTER

T d

OTP

WINDOW

Muoma

hE3i!

Applications of the phase-only e-LCLM include

programmable general-purpose optical elements,

nearly real-time computer-generated holographic displays, phase-only spatial filters, wave-front phase

correction for communication and imaging through

turbulence, and the correction of aberrations in optical instruments. The amplitude device will find

applications in projection displays and as an inputplane transducer or Fourier-plane filter in optical

processors.

B. Optoelectronic VLSI Liquid-Crystal CTPSLM's

Currently we are investigating both electrically addressed and optically addressed optoelectronic silicon

VLSI circuitliquid-crystalCTPSLM's(VLSILCLM's).

These devices have the general structures shown in

Fig. 12, in which VLSI chips are bump bonded to

CTP—liquid-crystal anode assemblies to form SLM's.

The optically addressed devices employ either photodiodes or phototransistors as the charge-generation

element. In both devices, extra circuitry added at

each pixel along with short-range electricalinterpixel

communication convertsthese devicesto smartSLM's.

Devices that emply both nematic and ferroelectric

liquid crystals are beinginvestigated.

The designs shown here have several advantages

over the initial approaches pursued by others,23-30 in

which the liquid crystal is in direct contact with the

Readout Light Modulated Ught

Uquid Crystal

Alignmonl Layer

Wiido-.v

Vk —

Edge Seal

CTP

polyimico Bump Bonds Metaled Silicon

Input I.e.

Unas

Readout Light Modulated Ught

Liquid Crystal

vVirGcw

Edge Seal

CTP

Write Ught

Alignment

Layer

Bump Bonds VLSIChip with Phololranslstor

Anay

(b)

Fig. 11. Architecture ofthe e-LCLM.

Fig 12. (a) Architecture ofthe electrically-addressedVLSI LCLM,

(b) architecture ofthe optically addressed VLSI LCLM.

10 July 1992 / Vol. 31, No. 20 / APPLIED OPTICS 3977

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 8 of 10
VLSI chip. These initial devices had to be built

without an alignment layer on the chip because of

possible damage to the chip by alignment layer processing. The specific advantages ofusing a CTP are

(1) no possible damage to the chip from alignment

layer deposition and processing, (2) the CTPpermits

the use of two liquid-crystal alignmentlayers and so

there is no loss of contrast ratio in the CTP-based

devices, and (3) excellent spatial uniformity can be

achieved in the liquid-crystal cell because the CTP

can be polished flatto X/10. These devicesshould be

ideal for optical signal processing and computing

applications.

5. Summary

CTP's permit the development of a rich class of

SLM's. The SLM's that are discussed here include

membrane mirrors and liquid crystals, and driving

schemesinclude electron beams, hardwire electrodes,

and VLSI chips. Clearly, polymers, oil films, organic

and inorganic crystals are also potentiallight modulation materials that mate well with CTP's. The

advantages of using a CTP in a SLM structure

include repairability ofthe SLM in the sense thatthe

light-modulation element may be changed at will

without interfering with the charge-generation element, and the versatility of being able to mate any

charge-generation element with anylight-modulation

material. The disadvantages include the loss of

charge efficiency because of the added capacitance of

theCTP, and a possible loss ofspatial resolution ifthe

CTPresolution is notsufficiently high.

The goal of future research in this area is to

increase the spatial resolution and decrease the interpin capacitance of the CTP's, as well as to develop

large-area (~ 100-mm-diameter) CTP's and increase

the leak-tightness yield. This will permit the development oflow-cost CTPSLM's with millions ofpixels

that could find applications in areas such as largescreen, high-definition projection displays, infrared

scene projectors, and industrial inspection systems.

This paper is an outgrowth ofresearch that spans

1987-1991 that has been sponsored, in part, by the

U.S. Air Force under contract F30602-86-C-0209, the

U.S. Army Strategic Defense Command under contract DASG60-87-C-0039, the U.S. Naval Research

Laboratory under contracts N00014-87-C-2290 and

N00014-89-C-2021, the U.S. Army Missile Command

under contract DAAH01-89-C-A014, NASA under

contractNAS9-18322, and the NationalScienceFoundation under grantISI-89-61378.

6. References

1. C. Warde and A. D. Fisher, "Spatial light modulators:

applications and functional capabilities," in Optical Signal

Processing, J. Horner, ed. (Academic, New York, 1987), pp.

477-523.

2. K. Preston,Jr., "An arrayoptical spatial phasemodulator," in

Proceedings ofthe International Solid State Circuits Conference (Institute of Electrical and Electronics Engineers, New

York, 1968). p. 100.

3. K. Preston, Jr., Coherent Optical Computer (McGraw-Hill,

NewYork, 1972).

4. 3. A. van Raalte, "A new schlieren light valve for television

projection," Appl. Opt. 9,2225-2230 (2970),

5. F. Reizman, "An optical spatial phase modulator array, activated by optical signals," in Proceedings 1969Electro-Optical

Systems Design Conference, (Institute of Electrical and Electronics Engineers, New York, 1969), pp. 225-230.

6. L. B. Somers, "The photoemitter membrane light modulator

image transducer," in Advances in Electronics and Electron

Physics (Academic, New York, 1972), Vol. 33A, p. 493.

7. A. D. Fisher, L. C. Ling, J. N. Lee, and R. C. Pukuda,

"Photoemitter membrane light modulator," Opt. Eng. 25,

261-268 (1986).

8. P.B. Rolsma,J. N. Lee, T. K. Oh, and L.-C. Ling, "Experimental parameters of the photoemitter membrane spatial light

modulator," Appl. Opt. 28, 4816-1825 (1989).

9. D. E. Pape, "Optically addressed membrane spatial light

modulator," Opt. Eng. 24,107-110 (1985).

10. D. R. Pape and L. J. Hornbeck, "Characteristics of the

defortnable mirror device for optical information processing,"

Opt, Eng. 22,675-681 (1983).

11. T. N. Horsky, C. M. Schiller, G. J. Genetti, T. N. Tsakiris,

D, M. O'Mara, R. Jurgilewicz, and S.-D. Lee, and C. Warde,

"Electron-beam-addressed membrane mirror lightmodulator

for projection display," Appl. Opt. 31,3980-3990 (1992).

12. C. Warde, A. M. Weiss, A. D. Fisher, and J. I. Thackara,

"Optical information processing characteristics of the microchannel spatial light modulator," Appl. Opt, 20, 2066-2074,

1991.

13. C. Warde and J. I.Thackara, "Oblique-cut LiNbOj microchannol spatiallightmodulator," Opt. Lett. 7,344-346 (1982).

14. C. Warde and J. I. Thackara, "Operating modes of the

microchannel spatiallightmodulator," Opt, Eng. 22,295-702

(1983).

15. T. N. Horsky, G.J. Genetti, D. M. O'Mara, C. M. Schiller, and

C. Warde, "Electron beam-addressed membrane light

modulator," in Spatial Light Modulators and Their Applications, Vol. 14 of 1990 OSA Technical Digest Series, (Optical

Society ofAmerica, Washington, D.C., 1990), pp. 170-173.

16. T. N. Horsky,C. M. Schiller, G.J.Genetti, D.M. O'Mara, W. S.

Hamnett, and C. Warde, "Electron-beam addressed membrane light modulator for 1R scene projection," in Infrared

Technology XVII, B. F. Andresen and I. J. Spiro, eds., Proc.

Sec. Photo-Opt. Instrum. Eng. 1540,527-532 (1991).

17. J.-A. Zhao, S.-S. Tung, and L. Ruan, "A study ofliquid crystal

light valve for large-screen projection TV," Displ. Technol. 1,

151-168(1986).

18. T. S. Buzak, R. S. Vatne, G. A. Nelson, and D, E. Whitlow,

"Eiectron-beam-addressed light valve operating modes and

performance," in 1987 SID International Symposium Digest

ofTechnical Papers (Society for Information Display, Playa

Del Rey,Calif.,Vol. 1987), pp. 64-67.

19. W. C. Nixon and C. E. Bryan, "Light value," British patent

WO85/01362 (28 March 1985).

20. G. A. Melnik, G. C. Gilbreath, T. N. Tsakiris, R. Jurgilewicz,

D. M. O'Mara, T. N. Horsky, and C. Warde, "Operating modes

of the charge-transfer-plate liquid-crystal phase modulator,"

Appl. Opt. 31,3892-3897 (1992),

21. G. A. Melnik, G.J. Genetti, T. N. Horsky, D. M. O'Mara, T. N.

Tsakiris, C. Warde, and C. G. Gilbreath, "Electron beamaddressed liquid crystal phase modulator," in Spatial Light

Modulators and Their Applications, Vol. 14 of 1990 OSA

Technical Digest Series (Optical Society of America, Washington, D.C., 1990), pp. 185-1988.

22. P. W. Hirsch, I. Farber, and C. Warde, "Development of an

e-beam charge-transfer liquid crystal light modulator," in

Spatial Light Modulators and Applications, Vol. 8 of 1988

3978 APPLIED OPTICS / Vol. 31. No. 20/10 July 1992

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 9 of 10
OSA Technical Digest Series (Optical Society of America,

Washington, D,C., 1988), pp. 11-14.

23. D.A.Jaredand K.M.Johnson, "Opticallyaddressed thresholding very-large-scale-integration/liquid-crystal spatial light

modulators," Opt. Lett. 16,967-969 (1991).

24. D. A. Jared, R. Turner, and K. M. Johnson, "Electricallyaddressed spatial light modulator that uses a dynamic

memory," Opt. Lett. 16.1765-1767 (1991).

25. T. J. Drabik and M. A. Handshy, "Silicon VLSI/ferroelectric

liquid crystaltechnologyformicropower optoelectronic computing devices," Appl. Opt. 29,5220-5225 (1990).

26. M. A. Handshy, T. J. Drabik, L. K. Cotter, and S. D. Gaalema,

"Fast ferroelectric-liquid-crystal spatial light modulator with

silicon-integrated-circuit active backplane," in Optical and

Digital Gallium Arsenide Technologies for Signal Processing

Applications, (M. P. Bendett, D. H, Butler, A. Prabhakar, and

A. Yang, eds., Proc. Soc. Photo-Opt. Instrum. Eng. 129],

158-164(1990).

27. L- K. Cotter, T. J. Drabik, R. J. Dillon, and M. A. Handshy,

"Ferroelectric-liquid-crystal/silicon-integrated-circuit spatial

lightmodulator," Opt. Lett. 15,291-293 (1990).

28. D. J. McKnight, D. G. Vass, and R. M. Sillitto, "Development

of a spatial light modulator—a randomly addressed liquid

crystaloverMOSarray," AppL Opt. 28,4757-4762 (1989).

29. I. Underwood, D. G. Vass, andR. M. Sillitto, "Evaluation ofan

nMOS VLSI array for an adaptive liquid-crystal spatial light

modulator," Proc. Inst. Electr.Eng. 133, 77 (1986).

30. W. A. Crossland, M. J, Birch, D. G. Vass, I. Underwood, S. A.

Reid, and S. G. Latham, "Silicon active backplane spatial light

modulators using ferroelectric liquid crystals," in Spatial

LightModulators and TheirApplications, Vol. 14 of1990 OSA

Technical Digest Series (Optical Society ofAmerica, Washington D.C.. 1990), pp. 94-97.

10 July 1992 / Vol. 31, No. 20 / APPLIED OPTICS 3979

Case 6:20-cv-00455-ADA Document 45-6 Filed 01/08/21 Page 10 of 10