HKUST

A High-Resolution Projection Display Based on Silicon Light

Valves

P W Cheng, H C Huang and H S Kwok

Centre for Display Research

Department of Electrical and Electronic Engineering

The Hong Kong University of Science & Technology

HKUST

Outline

• Silicon Light Valve

• XGA Display Features

• Optical Engine

• Conclusion

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Characteristics and Topography

• Fine pixels on the top as reflective mirrors• All the electronics are beneath the mirrors• Light shield and surface planarization

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Silicon Advantages

• Full driver Integration and fine pixels

• High fill factor

• Mature silicon VLSI technology

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SEM Pictures of Fine Pixels

• 9.6 m pixels• 86% fill factor• Virtual Reality

• 13.8 m pixels• 91% fill factor• Projection

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Effect of Pixel Size on Optical Performance(Comparison between theory and experiment)

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Fabrication Flow

• Front-end for electrical functions– Full integration of display drivers– Pixels of high breakdown voltage– Standard 0.5 m CMOS process

• Back-end for optical performance– Surface planarization and light shield– Pixels of high fill factor– Modified 0.35 m process

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HKUST-XGA Panel Specifications

• Resolution: 1024 x 768,13.8mpixels• Fill factor: 91%• Reflectivity:90% (dielectric mirror)• Process: 0.5m FE/0.35m BE• Data driver: 6-bit, 2 channels• LC Mode: MTB NW or NB• Others: Built-in gamma corrections

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Functional Block Diagram

ODD-COLUMN DATA DRIVERS

D/A CONVERTERS

SC

AN

DR

IVE

RS

1024 x 768PIXEL ARRAY

QA1BIT1SHR

SCLKFLM

SCAN_DN

CLK1DISP1ODD_DATA (0:5)

V1, V2, V3, V4

VG1, VG2, VG3,VG4

VB1, VB2

FRAME

D/A CONVERTERS

EVEN-COLUMN DATA DRIVERSR

EF

ER

EN

CE

V

OL

TA

GE

G

EN

ER

AT

OR

CLK2DISP2EVEN_DATA (0:5)

VCC, VDD, VDD2GNDSHIELD

BIT2

SOUT

• Almost identical to TFT panel with full driver integration

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Fine and Resolvable Pixels

• Advantage of digital driving scheme

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Reflectance-vs-Voltage Curves

Contrast Ratios:Red 169:1Green 101:1Blue 68:1 White 108:1

• Wide-band MTB NW mode for three primary colors

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Gamma Correction

VG1 VG2

VG3 VG4

• Fine tune of linear gray scale for three primary colors

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Optical Engine

• Trichroic prism assembly (TPA)• 16o incident angle (patent pending)

MH Lamp

BD

AC

B-LCD

G-LCD

R-LCD

PBS

• H. S. Kwok etal, to be published on Applied Optics, 1999

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Good Color Fidelity for TPA - Experimental Results

• Negligible S-P Polarization Split

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Measured color coordinates

Includes the effects of the halogen light source and the TPA

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Good Color Saturation by the Optical Engine

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Linear Gray Scale by correction

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Projected Image on the Screen

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Projector Prototype Specifications

Parameter ValueResolution 1024 H x 768 VPixel Size 13.8mAperture Ratio 91%Array Area 14.1mm H x 10.6mm VLC mode Reflective NW MTB modeContrast Ratio 100:1, typicallyLight Source 50W MH LampLuminous Flux 100 lumensColor 262,144CIE Coordinates Red: x = 0.66, y = 0.34

Green: x = 0.30, y = 0.65Blue: x = 0.17, y = 0.12

Driving Scheme Frame InversionFrame Rate 30 Hz

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Conclusions

• Highly Integrated Silicon Light Valve– Front-end for electrical functions– Back-end for optical optimization

• XGA Projection Display Features– Fine and resolvable pixels– Linear gray scale– Good color saturation

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Acknowledgements

• Dr. Steve Yeung and Mr. George Lee of Varitronix (HK) for making LC cells

• Sponsored by Industry Department of Hong Kong Government

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END (of IDRC99)

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