Dmd And Principle Of Optical System - Sharp XG-NV7XU Service Manual

DMD AND PRINCIPLE OF OPTICAL SYSTEM

1. Outline of DMD
(Digital Micro Mirror Device)
The DMD is one of the ultra-micro electromechanical
systems called MEMS (Microeletromechanical System).
The DMD can be fabricated by employing the existing
0.8 micron rule, which is the established semiconduc-
tor manufacturing technology.
The DMD is an optical switch of semiconductor chip
fabricated by connecting several hundred thousand to
one million and several hundred thousand mirrors
(16µm X 16µm in size) onto the CMOS SRAM
semiconductor memory and these mirrors rotate
mechanically when digital electric signal is received.
In the DMD, the mirror rotates at an angle of ±10
degrees by the action of electrostatic field produced by
voltage which is generated on the SRAM memory. The
rotation of this mirror changes the direction of reflected
light, the principle of which is applied for the optical
switch. The gray scale (or color gradation) of reflected
light is achieved by controlling the response time (or
ON-time) of the mirror with digital signal (8-bit pulse
width modulation [PWM] signal) (Processing with 10-
bit PWM signal is now also available).
The gray scale has 256 tones. Hence, the total nµmber
of tones for RGB full primary colors counts as many as
256 X 256 X 256 = 16,700,000.
2. Structure of DMD Pixel
Figure 3. shows an exploded view of the DMD pixel.
The DMD monolithically consists of the four layers;
mirror, yoke and hinge, metal-3, and CMOS memory.
The mirror is made of 16 µm X 16 µm alµminµm plate.
The mirror is rigidly connected to the yoke below. The
yoke, in turn, is connected by two thin mechanically
compliant torsion hinges to the posts that are attached
to the PWB below. The address electrodes for the mirror
and yoke are connected to the complementary sides
of the PWB below. The yoke and mirror are connected
to the bias-reset bus formed on the metal-3 layer. The
bias-reset bus interconnects the yoke and mirrors of
each pixel to the bond pad around the chip.
When the digital signals [1] and [0] are written on the
CMOS SRAM, the mirror supported by the posts
inclines diagonally toward the PWB side. The angle of
inclination is ±10 degrees.
* DMD and DLP are the trademarks of Texas Instruments, Inc., U.S.A.
2 3 4 5 6
About 500,000 micro mirrors are found at the
central white part.
Figure 1. DMD (SVGA Specification)
Mirrors (each one of squares).
Area of a mirror is 16 µm X 16 µm. The space
between adjacent mirrors is 1 µm.
Figure 2. Microscopic View of DMD
Mirror
Landing Tip
Mirror
Address
Electrode
Yoke
Address
Electrode
Bias-Reset
Bus
Figure 3. DMD pixel exploded view
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7 8 9 10 11 12
(Layers)
Mirror
Torsion Hinge
Yoke
Yoke
and Hinge
Via 2 Contact
to CMOS
Metal-3
Landing
Site
CMOS
Memory