The DMD TM Projection Display Chip: A MEMS-Based Technology
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The DMD™ Projection Display Chip: A MEMS-Based Technology Larry J. Hornbeck Introduction
Technology Description
The possibility of an all-digital (sourceto-eye) projection display was realized in 1987 with the invention of the Digital Micromirror Device™ projection display chip at Texas Instruments (TI). The DMD™ chip is a microelectromechanical systems (MEMS) array of fast digital micromirrors, monolithically integrated onto and controlled by an underlying silicon memory chip. Digital Light Processing™ projection displays are based on the DMD chip. DLP™ projection displays present bright, seamless images to the eye that have high image fidelity, and stability. The first projectors based on DLP technology were introduced to the market in 1996. Today, DLP subsystems are supplied to more than 30 projector manufacturers, who then design, manufacture, and market projectors based on DLP technology. There are now over 50 products based on DLP technology sold in the following market segments: portable electronics, home entertainment, video walls, large-venue (highbrightness) applications, and digital cinema. The number of DLP subsystems shipped to manufacturers has nearly doubled in the year 2000 compared with 1999, with over 500,000 subsystems sold between the initial product introduction in 1996 and September 2000. Over the past four years, DLP technology-based projectors have won some of the audio-visual industry’s most prestigious awards, including an Emmy™ Award from the Academy of Television Arts & Sciences in 1998. More than 1.1 million people around the world have seen first-run movies projected with DLP Cinema™ technology.
Two pixels (picture elements) of a DMD chip are illustrated in Figure 1. The entire structure above the CMP (chemical– mechanical polishing) oxide layer is fabricated from aluminum and its alloys. Each aluminum micromirror is 16.2 m (or 13.0 m) on a side and can reflect light in
MRS BULLETIN/APRIL 2001
one of two distinct directions (10), depending on the state of the underlying SRAM (static random-access memory) cell. The electrostatic attraction produced by voltage differences across the air gaps of both the micromirror and the yoke relative to the memory cell causes the micromirror to tilt about a pair of thin, compliant torsion hinges. Mechanical stops limit the micromirror tilt angle to 10 depending on the digital state (1 or 0) of the underlying memory cell. Incident light from a projection source is reflected by the tilting action of each micromirror either into or out of the pupil of a projection lens. In this manner, each micromirror acts as a digital light switch, turning the light on or off at each pixel location on the screen. DLP projection displays combine one DMD chip (time-multiplexed color) or three DMD chips (spatially multiplexed color) with a suitable light source and projection optics, plus digital processing and formatting functions to produce bursts of digital light pulses that the eye interprets as color and gray scale. DLP-based projector products have resolu
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