1

Grating Electromechanical Systems (GEMS),

Laser Displays, and Related Doodles

Marek W. Kowarz*Infotonics Technology Center

* Major portions of this work were performed when the

author was with Eastman Kodak Company.

The Institute of Optics Colloquium,

University of Rochester, April 20, 2009.

2

Device ON

Incident

Beam

Diffracted

Beams

Diffracted

Beams

ΛΛΛΛ Sapphire Display

1080 X 1920

Monochrome Display

256 X 455

RGB Laser Display

256 X 455

Invention of

GEMS Device

1st Operational

GEMS Device

Base Device

Patent (6,307,663)

Base Display

Patent (6,411,425)

Spectral Imager

Device & System

2007

2008

Spectral Imager

6-Band Demo

XGA Display

Evaluation Kit

GEMS Technology: Timeline and Milestones

Grating ElectroMechanical System

GEMS Project

GEMS Display

Project

3

Device OFF

RibbonIncident

Beam

Reflected

BeamIntermediate

Support

Silicon

Substrate

Reflective (Off) State

Device OFF

RibbonIncident

Beam

Reflected

BeamIntermediate

Support

Silicon

Substrate

Reflective (Off) State

GEMS Device

ΛΛΛΛ

Intermediate

Supports

Device ON

Incident

Beam

Diffracted

Beams

Diffracted

Beams

ΛΛΛΛ

+1st

+2nd

−1st

−2nd

Diffracted

OrdersDiffracted

OrdersArr

ay

Directi

on

Diffractive (On) State

ΛΛΛΛ

Intermediate

Supports

Device ON

Incident

Beam

Diffracted

Beams

Diffracted

Beams

ΛΛΛΛ

+1st

+2nd

−1st

−2nd

Diffracted

OrdersDiffracted

OrdersArr

ay

Directi

on

Diffractive (On) State

Device Features

Very wide active area

⊥⊥⊥⊥ grating (ΛΛΛΛ) direction

Digital operation

>2000:1 contrast

>60% multiorder efficiency

Typical Dimensions

Grating period = 15 to 50 µµµµm

Actuation depth = 150 to 200 nm

4

GEMS Device Structure and Operation

The GEMS device consists of a linear array of pixels with electromechanical

ribbons suspended above a hidden grating

Typically

Pitch = 15 to 50 µµµµm

Actuation Depth = 150 to 200 nm

Metal

Die

lec

tric

s

Silicon Substrate

Periodic

Support

Cross-Sectional View

Grating ElectroMechanical System

5

GEMS Device Wafer

6" GEMS Wafer

Stitched Linear Array

(1 mm active area width)

Scalable

Resolution

1080

2160

3240

Very Wide Active Area Device

(10 mm x 20 mm active area)

18 µµµµm

36 µµµµm

or Pixel Size

Flexibility

Array Direction

Gra

tin

g (

ΛΛ ΛΛ)

Dir

ecti

on

Active Area

1080-Pixel GEMS Linear Array

ΛΛΛΛ = 36 µµµµm

6

Pixel #1 ON . . . . .

Pixel #2 OFF. . . . . .

Pixel #3 ON. . . . . . .

Pixel #4 OFF . . . . . .

Incident Beam

Line Illumination

� ON pixels diffract light and the diffractive orders are

collected to form a line image

Optical Stop

� OFF pixels reflect light, which is blocked by an optical stop

Optical System Principles

7

-0.4

0

0.4

0.8

1.2

1.6

2

-45

-30

-15

0

15

30

45

-0.4 0 0.4 0.8

1st-

Ord

er

Inte

nsity (

V)

Input (V

)

Time (µs)

RibbonVoltage

Intensity

Response to High-Speed Input Signal

The fast switching speeds of the GEMS device enable a 2D display

with a 1D linear array

~30 nanosecond digital operation

GEMS Device High-Speed Response

8

225

ns

0th

Order

1st Order

0 V

25 V

−25 V

1 µs

Rib

bo

n

Vo

ltag

e

Inte

nsit

y

(arb

. u

nit

s)

Inte

nsit

y

(arb

. u

nit

s)

25 ns

Increment

0th Order

1st Order

Enlarged

Example of Response to

Random PWM Data Stream

Response times ~30 ns

and jitter <0.5 ns

The fast switching speeds allow for the generation of gray scale

through pulse width modulation (PWM)

PWM Gray Scale Generation

9

Device OFF

RibbonIncident

Beam

Reflected

BeamIntermediate

Support

Silicon

Substrate

Metal

Dielectrics

Reflective (Off) State Λ

h

bs

bc

Diffractive (On) State

Device ON

Incident

Beam

Diffracted

Beams

Diffracted

Beams

ΛΛΛΛ

+1st

+2nd

−1st

−2nd

Diffracted

OrdersDiffracted

Orders

Opto-Electromechanical Device Model

Standoffs

Red: Si3N4

Blue: SiO2

• GEMS period (Λ)

• Support width (bS)

• Channel depth (h)

• Ribbon width

• Ribbon gap

• Ribbon dielectric thickness

• Ribbon metal reflector

• Standoff separation

• Standoff height

1. Pull-down &

operating voltage

2. Ribbon profile

3. Diffraction efficiency

Opto-Electromechanical

Model

10

h

1t1ε

x2/L− 2/L

)( profile xy⇒V

Stress-Limit Ribbon Deformation Model

unit widthper force tensile ⇒= ∑n

nntS σ

gap ticelectrosta effective ⇒+= ∑q

q

qtht

ε

Stressed ribbon differential equation:

where

layer th of stress nn ⇒σ

layer th ofty permittivi relative qq ⇒ε

widthribbon length, ribbon ⇒⇒ wL

space free ofty permittivi ⇒oε

2

2

2

2

4

4

)(2

yt

wV

dx

ydSw

dx

ydEI o

−=−

ε

tension

electrostatic

attractionbending

Analytical solution for ribbon profile and critical voltages

Device Model: Critical Voltages, Contact Length & Efficiency

ΛΛΛΛ

h

bs

bc

oPD

St

LV

ε

3673.1 =

( ) ( )

−

+−+−=

ht

hthtthht

S

LV

oRL ln

2

2/3

ε

Pull-down voltage:

Release voltage:

Contact length: ( ) VVVLb RLc voltageoperating @ 1 −=

2

0

2)(4 1

∫Λ

Λ−

Λ= dxee mxixyi

mπλπη

Diffraction Efficiency:

Nearly trapezoidal grating profile

12

0

5

10

15

20

25

30

20 40 60 80 100 120 140 160

Pull-D

own Voltage [V

]

Ribbon Length [µm]

Wafer Lot 3

Wafer Lot 2

Wafer Lot 1

−180

−160

−140

−120

−100

−80

−60

−40

−20

0

20

−30 −20 −10 0 10 20 30Deflection (nm)

x (µm)

20V

18V

12V

16V

Ribbon Shape

(AFM)

Pull-Down Voltage

Stress-Limit Model

Versus Experiment

13

Laser Display

14

RGB Display Lasers (early 2000s)

15

Compact RGB Display Lasers (now)

And many others

in development(OSRAM, Mitsubishi, �)

Novalux Necsel(now Necsel)

Multi-Watt

Corning Green Laser(waveguide SHG)

100–300 mW

Nichia Blue Laser Diode

50 mW–1 W

16

Laser Projection Display

� Realization of low-cost, high-power RGB lasers enables

• Projected images with large-screen diagonal (front or rear)

• Color with extreme saturation, when desirable

• Light source having long lifetime

• Low cost per diagonal inch

• Efficient use of light

• High energy efficiency

• Compact, lightweight systems

� A low-cost, high-performance light modulator is also

required

17

Modulator Options

� 2D Spatial Light Modulator and no scanner – e.g., DMD

• Example: Mitsubishi Laservue TV (see laservuetv.com)

• Challenging to achieve full HD resolution without artifacts at low cost

� No Spatial Light Modulator and 2D laser scanner – e.g., MEMS raster scanner with direct diode modulation

• Example: Microvision pico-projector (see www.microvision.com)

• Low-cost solution

• Full HD challenged by scanner resolution and laser modulation speed

• Difficulties with speckle reduction and laser power scalability

� 1D Spatial Light Modulator and 1D scanner

• Resolution is easily scalable

• Excellent image quality

• Low-cost solution at high resolution

18

LaserCantilever Array

History: MEMS Cantilevers (1978)

K. E. Petersen, IEEE Trans.

Electron Devices 25 (1978)

Lamp

History: Scophony (1938)

Liquid Light

Modulation

Scophony Projection Television Manual

(www.tvhistory.tv)

Laser

GLV Pixel

History: Grating Light Valve (1992 – Present)

Grating Light Valve Display Device, (Sony Corporation, 2002)

D. Corbin et al., Grating Light Valve and Vehicle Displays, (www.siliconlight.com)

Three-Chip Front-Projection Laser Display PrototypeGEMS

GEMS

GEMS

Patterned

Turning Mirror

Projection

Lens

X-cube

Red

Laser BeamTo Screen

Green

Laser Beam

Blue

Laser Beam

G

R

B

GEMS

GEMS

GEMS

Patterned

Turning Mirror

Projection

Lens

X-cube

Red

Laser BeamTo Screen

Green

Laser Beam

Blue

Laser Beam

G

R

B

Galvanometer

Mirror

Screen

Resolution 1920 (H)

1080 (V)

Frame Rate 60 Hz

Screen Size 115 inch

Native Bit Depth 11 bit/color

(PWM)

System Contrast

Frame-sequential >1500:1

ANSI Checkerboard >250:1

20

GEMS Front-Projection Prototype:

Photograph of Scene from Scanned Motion Picture Film

Image Color Setting: Natural Mode

21

GEMS Laser Display (color filled)

TV Standard (ITU 709) (dotted)

High End LCOS (solid)

High End DMD (dashed)

Color Gamut

Photograph of Computer-Generated Imagery

Image Color Setting: Full Gamut Mode

Three-Chip Front-Projection Laser Display Prototype

GEMS

GEMS

GEMS

Patterned

Turning Mirror

Projection

Lens

X-cube

Red

Laser BeamTo Screen

Green

Laser Beam

Blue

Laser Beam

G

R

B

GEMS

GEMS

GEMS

Patterned

Turning Mirror

Projection

Lens

X-cube

Red

Laser BeamTo Screen

Green

Laser Beam

Blue

Laser Beam

G

R

B

Galvanometer

Mirror

Cables from

Electronics Rack

GEMS

Galvo

Mirror

X-cube

GEMS

GEMS

23

Propagation of Diffracted Light BeamsNear GEMS Array

Before Patterned M

irror

After Patterned M

irror

After Lens

Near Scanning M

irror

GEMS

Laser Beam

Scanning

Mirror

Projection Lens

Patterned

Mirror

� Perpendicular orientation of GEMS grating period enables

(a) Diffracted beams to be separated throughout system (except at image plane)

(b) On-axis illumination path before projection lens

(c) Collection of multiple diffracted beams with relatively small projection lens

� Small scanning mirror is placed near Fourier transform plane of projection lens

Light Propagation Model

Near GEMS Array

Before Patterned M

irror

After Patterned M

irror

After Lens

Near Scanning M

irror

24

To separate diffracted orders: sin θθθθI < λ/Λλ/Λλ/Λλ/Λ

For a Gaussian laser beam: FWHM ≈ 0.55 λλλλ/sin(θθθθI /2)

Therefore, FWHM > 1.1 ΛΛΛΛ [In practice FWHM ≈ 1.5 ΛΛΛΛ]

Separation of Diffracted Orders

+2nd

0th

+1st −1st −2nd

Diffracted

Orders

FWHM

Λ

h

FWHM

Incident

Beam

Patterned

Mirror

Λ

h

θI

25

Patterned

Turning Mirror

Green

Laser

GalvanometerMirror

Projection

Lens

Red

Laser

Blue

Laser

GEMS

GEMS

GEMS

Laser Projector Architecture 1: Three-Chip System

26

Combines advantages of three-chip architecture with those of single-

chip architecture

� Simple optical architecture

� Maximum laser power utilization and brightness

� Best image quality

Trilinear Array

(front view)

Galvanometer

Mirror

Trilinear

GEMS array

Patterned

Mirror Projection Lens

RGB

Laser Beams

Enlarged

Area

R

G

B

Trilinear

GEMS Array

Laser Projector Architecture 2: Multilinear Array System

27

Galvanometer Patterned

Turning Mirror

Red & Green

Lasers Projection

Lens

Blue & Cyan

Lasers Bilinear GEMS

Bilinear

GEMS

Mirror

Dichroic

Beamsplitter Enlarged

Area

R

G

Four-Color System with Two Bilinear GEMS Arrays

Laser Projector Architecture 3:

28

GEMS Device Efficiency Model

Optimized GEMS System Collects: 4 or 6 orders for Red (curve b or c)

6 orders for Green (curve c)

6 or 8 orders for Blue (curve c or d)

0.4 0.45 0.5 0.55 0.6 0.65 0.7

Wavelength − Microns

30

40

50

60

70

80

90

±1 orders

±1 & ±2 orders

±1, ±2 &

±3 orders

±1, ±2, ±3 & ±4 orders

Wavelength (µm)

Diffraction Efficiency (

%)

(a)

(b)

(c)

(d)

8.5 µm ribbon width

0.5 µm ribbon gap

170 nm depth

29

Efficient GEMS device can be fabricated using the same design for

all three colors

Note: RGB wavelengths are 630 nm, 530 nm, and 450 nm for model

Device Efficiency Model for RGB System

0.15 0.16 0.17 0.18 0.19

Depth − Microns

30

40

50

60

70

80

90

ycneiciffE

−% B

G

R

Orders Collected

±1, ±2, and ±3 orders for Red and Green

±1, ±2, ±3, and ±4 orders for Blue

8.5 µm ribbon width

0.5 µm ribbon gap

Actuation Depth (µm)

Diffraction Efficiency (

%)

30

Vertical Resolution (device pixels) 1080 2K – 4K

Horizontal Resolution (scan) 1920 4K – 8K

Frame Rate 60 Hz 60 Hz

Display Bit Depth (per color) 11 bit >11 bit native

System Contrast (ANSI) 250:1 >500:1

System Contrast (frame-sequential) 1500:1 >5000:1

Data Stream Content interlaced progressive

Performance Demo Ultimate

GEMS Laser Projection System

High Image Quality

� Laser primaries for wide color gamut with bright, saturated colors

� Extremely high and scalable resolution for sharp, crisp images

� High native bit depth for billions of noise-free colors per pixel

� Reduced pixelization

� No motion artifacts

Simple GEMS-Based Design

� Alignment and defect tolerant design

� Digital operation

� Compact optical components

� Low-cost modulator and optics

Extendable System

� Easily scalable linear array

� Programmable aspect ratio

� Flexible frame rate

System Architecture Options

� Single chip or three chip

� Multilinear arrays for high performance at low cost

Technology Benefits

32

Potential Applications

GEMS Laser Display

� Front projection

� Rear projection laser TV

� Data visualization and simulation

� Command and control

� Panoramic workstations

� Heads-up displays

� Mobile projectors

Other Systems

� Laser printing

� Maskless lithography

� Light modulation

� Programmable spectral imaging

� OFlight Training Simulator

33

PROGRAMMABLE

SPECTRAL IMAGING

34

Multispectral imaging systems are used in a variety of applications where

conventional RGB imaging does not adequately reveal spectral features of interest.

� Application areas: remote sensing, medical, and biological imaging, �

For example, the 4-band multispectral image below shows vegetation regions (false red) that

are not visible in the natural color image.

Challenge: Create an imaging system with a programmable spectral

transmission function that provides high-resolution line-scanned imaging.

Multispectral Imaging: Introduction

3-Band Natural Color

Image of Forest Fire

4-Band Image of Forest Fire

with False Color Infrared

DigitalGlobe DigitalGlobe

35

Line

Image Dispersive

Element

(grating)

Filtered

Line Image

Linear

CCD

De-dispersive

Element

(grating)

GEMS acts as an optical “switch” that

passes (or extinguishes) narrow spectral

channels

System Concept

� Spectral band selection approach:

� Line image dispersed by a grating onto a Spatial Light Modulator (SLM)

� Electronic control of SLM provides selection of wavelength bands for imaging

� Selected bands are de-dispersed and re-imaged on a detector array

� 2D image is captured by line scanning across object of interest

36

GEMS

DeviceInput

Slit

TransmissionGrating

Patterned

Mirror

Image

SensorScale: 40 x 25 cm

GEMS

DeviceInput

Slit

TransmissionGrating

Patterned

Mirror

Image

SensorScale: 40 x 25 cm

0th 1st 2nd−1st−2nd

Diffracted Orders

ClearMirror

Patterned MirrorOptical System

Transmissive

Double-Pass

Spectrometer

Key Features� High-speed spectral tuning

� Excellent image quality

� 32 spectral bands (current configuration) 450–566 nm: 12 bands with ~10 nm bandwidth566–634 nm: 14 bands with ~5 nm bandwidth634–692 nm: 6 bands with ~10 nm bandwidth

GEMS-Based Programmable Spectral Imager

GEMS acts as a

“spectral switch”

37

Spectral Imager Breadboard

Test

Object

Camera

GEMS

device

Volume Phase

Grating

Lens Lens Patterned

Mirror

Lens

Test

Object

Camera

GEMS

device

Volume Phase

Grating

Lens Lens Patterned

Mirror

Lens

Imaging Axis

Spectral Axis

Active Area: 10.8 mm x 19.44 mm

Imaging Axis

Spectral Axis

Active Area: 10.8 mm x 19.44 mm

38

Entire Image

(17 mm of 19.44 mm)

Enlarged 4X

Enlarged 16X

Test Object

Ronchi ruling (12 lp/mm)

Camera

Olympus E-1 (5 megapix)

Breadboard Image Quality

39

All Bands

Blue Band

(20 nm)

Red & Blue Bands

(20 nm each)

Red Band

(20 nm)

Green Band

(20 nm)

Spectral Selection with Slide Translation

40550 560 570 580 590 600 610 620 630 640 650

Wavelength (nm)

Intensity (arb. units)

Single 90 nm

Dual 40 nm

Dual 30 nm

Dual 20 nm

Dual 10 nm

550 560 570 580 590 600 610 620 630 640 650

Wavelength (nm)

Intensity (arb. units)

Single 90 nm

Dual 40 nm

Dual 30 nm

Dual 20 nm

Dual 10 nm

555 560 565 570 575 580 585 590 595 600 605 610 615

Wavelength (nm)Intensity (arb. units)

5 nm

40 nm

Fully Programmable Spectral Bands

Programmable

Bandwidth

Multiple Programmable

Spectral Bands

41

An Interesting CombinationO

Programmable Spectral Imaging and Broad Gamut Display

Both with GEMS-based Systems

42

Device ON

Incident

Beam

Diffracted

Beams

Diffracted

Beams

ΛΛΛΛ Sapphire Display

1080 X 1920

Monochrome Display

256 X 455

RGB Laser Display

256 X 455

Invention of

GEMS Device

1st Operational

GEMS Device

Base Device

Patent (6,307,663)

Base Display

Patent (6,411,425)

Spectral Imager

Device & System

2007

2008

Spectral Imager

6-Band Demo

XGA Display

Evaluation Kit

GEMS Technology: Timeline and Milestones

Grating ElectroMechanical System

GEMS Project

GEMS Display

Project

Ultratech Nano160

(1X projection; backside alignment) TEL Mark VII Coat/

Develop Track

LPCVD and Atmospheric

Furnace Processes

Chemical-

Mechanical

Polishing

and GrindingVeeco 3-Chamber Sputter Tool

Ultratech XLS

Stepper

(4X projection;

0.35 µm

resolution)

ITC MEMS Wafer Fab

Leybold Reactive Evaporator

for Optical Glasses

Xactix XeF2 Sacrificial EtchSTS Si

Deep RIELAM Alliance

Cluster Tool

ITC MEMS Wafer Fab

45

Suss ABC200 Automated Wafer Bond Cluster Plating Bench

Asymtek Automated Fluid

Dispensing system Ohmcraft Micropen

Flip Chip

Bonders

SEC 860 Omnibonder

Suss FC150

Hesse & Knipps Automated

Wedge Wirebonder

ADT 7200 Automated

Dicing Saw

ITC MEMS Packaging

46

ITC Laser Microscopy System for GEMS Device Screening

He-Ne

De

tec

tor

Mic

ros

co

pe

GEMS Diffracted Orders

Near Detector

Laser, Optics

& Detector

Laser, Optics & Detector

• Custom-modified high-quality

microscope with laser probe beam

for initial device screening

• System is configured to measure

GEMS diffracted orders

• Provides feedback on device

fabrication & packaging processes

47

GEMS Wafer from ITC

48

Thank You !

e-mail: marek.kowarz@itcmems.com

website: www.itcmems.com

49

1) M. W. Kowarz, J. C. Brazas and J. G. Phalen, “Conformal Grating Electromechanical Systems

(GEMS) for High-Speed Digital Light Modulation,” IEEE 15th International MEMS Conference Digest,

pgs. 568-573 (2002).

2) J. D. Newman, M. W. Kowarz, J. G. Phalen, P. P. Lee and A. D. Cropper, “MEMS Programmable

Spectral Imaging System for Remote Sensing,” Spaceborne Sensors III, SPIE Proc. Vol. 6220, pgs.

53-61 (2006).

3) M. W. Kowarz, J. G. Phalen and C. J. Johnson, “Line-Scanned Laser Display Architectures Based

on GEMS Technology: From Three-Lens Three-Chip Systems to Low-Cost Optically Efficient Trilinear

Systems,” SID Symposium Digest, Vol. 37, pgs. 1908-1911 (2006).

4) J. Agostinelli, M. W. Kowarz, D. Stauffer, T. Madden, and J. G. Phalen, “GEMS: A Simple Light

Modulator for High-Performance Laser Projection Display,” ITE/SID 13th International Display

Workshops (IDW’06), pgs. 1579-1582 (2006).

References