Abstract—The Technology of Micro Electro Mechanical

Systems (MEMS) is revolutionizing the architecture of Sensors,

Mobile Multimedia Phones, Media Tablets, Laptops, Projectors,

Cinema Screens and High Definition Television (HDTV),

amongst, countless other applications in many fields of

engineering. This paper deals with MEMS-based Technologies for

Mobile Multimedia Displays and HDTV. Basic concepts of

Liquid Crystal Display (LCD) Technology are discussed. MEMS-

based display technologies namely Digital Light Processing (DLP)

of Texas Instruments, Digital Micro Shutter (DMS) of Pixtronix

and Interferometric Modulation (IMOD) of Qualcomm MEMS

Technologies are introduced. The architecture of the DLP light

switch MEMS chip containing two million hinge-mounted

mirrors of about 10X10 µm² each is presented. The design

concepts of ultra low power consumption, exceptional image

quality and sunlight-viewable MEMS-based technology for mobile

multimedia applications are discussed. Design Methodology of

MEMS is briefly touched standing on the shoulders of the VLSI

technology.

I. INTRODUCTION

Recent developments in MEMS-based technologies provide

products of exceptional qualities with significant reduction in

cost and energy consumption, thus, setting unprecedented

paradigm for the market forces. Recently, display intensive

devices such as Laptops, Media Tablets, Mobile Multimedia

Phones, Gaming Gadgets, portable GPS, for exemple, are

flooding the market; however, the present Liquid Crystal

Display (LCD) technology needs improvements in image

quality and power consumption. Better image quality

products can be designed; however, solutions demand more

power consumption, resulting in less autonomy of viewing

per battery charge. Likewise, the improvements in video

quality of large High Definition TV or Projector or Cinema

Screen require innovative solutions of optimum performance.

Thanks to advances in MEMS Technologies, the

manufacturing the low- cost consumer electronics

multimedia devices with high optical transmission, wide color

gamut, high brightness, high contrast ratio, wide viewing

angles, excellent video controls and ultra low power

consumption is easily realizable.

The application of MEMS Technologies in the fields of

display systems and RF communication circuits permits

designer to achieve excellent performance beyond the over

stretched limits of the Moore Law. It should be emphasized

that RF MEMS for communication or Optical MEMS for

video transmission require an intimate knowledge of inter-

action among device design, fabrication process and multi-

physics all along the system design and development cycles.

Thus, by training and design experience, the RF MEMS or

Optical MEMS Engineers have the ability to simultaneously

perceive at multiple scales from concept to product in

coherent fashion tackling Scaling, 3D-Model Building,

Architecture, Finite Element Meshing, Fabrication, Model

Extraction and Validation unlike VLSI Engineers who are

only concerned with the Electronics Design Automation

(EDA) software of a largely planar device. The analog and

digital interface circuits and microcontrollers designed using

mixed signal hardware description languages, VHDL or

Verilog, may form part of the MEMS design or are designed

separately.

The incumbent LCD Technology has served well the needs

of display devices for many years; however, with the massive

proliferation of display-intensive mobile multimedia devices,

there are pressing demands for new innovating technologies.

Since late seventies, Texas Instruments has led the market

with marvelous MEMS-based Digital Light Processing (DLP)

products [1] and has made available excellent documentation

[2]. In recent years, Qualcomm MEMS Technologies

launched display devices with Interferometric Modulation

(IMOD) known as Mirasol [3] and Pixtronix has

demonstrated its Digital Micro Shutter (DMS) technology

with encouraging success for mobile multimedia applications

[4]. Japanese Chimei Innolux Corporation and Hitachi

Display Ltd. have recently signed technical collaborations

with Pixtronix Inc.

In the following Section fundamentals of LCD technology

are reviewed. Section III deals with the details of working

principle, architecture and layout of the DLP 1700 MEMS

chip of Texas Instruments for typical application. The salient

features of DMS technology are discussed in Section IV. The

IMOD Mirasol Technology is overviewed in Section V. The

roadmap for the Brazilian National Research efforts for

display technology is proposed in Section VI.

II. REVIEW OF LCD TECHNOLOGY

A. Structural details of LCD

A Liquid Crystal Display (LCD) is a thin, flat display

device made up of any number of color or monochrome

pixels arrayed in front of a light source or reflector. Each

pixel of a LCD consists of a layer of liquid crystal molecules

MEMS-based Technologies for Mobile Multimedia Displays

and High Definition Television

Narpat S. GEHLOT

Faculdade de Ciências e Tecnologia – FACITECH

Campina Grande, Paraíba, Brasil 58410-858

suspended between two transparent electrodes, and two

polarizing filters, the axes of polarity of which are

perpendicular to each other. Without the liquid crystals

between them, light passing through one would be blocked

by the other. Fig. 1A shows the structural details of a

passive LCD panel.

Fig. 1A. Structural Details of a Passive LCD Panel

showing the physical layout of Back light, Polarizer, LCD

Layer, Color Filter, Glass Plates, Polarizer & Display

Surface.

B. Working Principle of LCD

Before applying an electrical charge, the liquid crystal

molecules are in relaxed state. Charges on the molecules

cause them to align themselves with microscopic grooves on

the electrodes. The grooves on the two electrodes are

perpendicular, so the molecules arrange themselves in a

helical or twisted pattern. Light passing through one filter is

rotated as it passes through the liquid crystal, allowing it to

pass through the second polarizer. Half of the light is

absorbed by the first polarizer, but otherwise the entire

assembly is transparent.

When an electric charge is applied to the electrodes, the

molecules of the liquid crystals are pulled parallel to the

electric field, thus reducing the rotation of the entering

light. If the liquid crystals are completely untwisted, light

passing through them will be polarized perpendicular to the

second polarizer, and thus be completely blocked. The pixel

will appear dark. Hence, by controlling the twist of the

liquid crystals in each pixel, light can be allowed to pass

through in varying amounts, accordingly, illuminating the

pixel. The polarizer aligned such that pixels are transparent

when relaxed and become opaque when electric field is

applied.

LCDs are designed with multiplexed control; electrodes

on one side of the display are grouped and wired together

(say, in columns), & each group gets its own voltage source.

On the other side, the electrodes are also grouped (say, in

rows), with each group getting a voltage sink. The groups

are designed so that each pixel has a unique unshared

combination of source and sink. The hardware or software

driving the controls then turns on sinks in sequence, and

drives sources for the pixels of each sink, as in [5].

C. Transmissive and Reflective Displays

LCDs can be either transmissive or reflective, depending

on the location of the light source. A transmissive LCD is

illuminated from the back by a backlight and viewed from

the opposite side. This type of LCD is used in applications

requiring high luminance levels such as computer displays,

televisions, mobile phones, and media tablets. Reflective

LCDs, often found in digital watches and calculators are

illuminated by external light reflected by a diffusing

reflector behind the display, producing darker (blacks) than

the transmissive type since the light must pass through the

LCD twice and thus attenuated twice and the display is

poorer. Transflective LCDs work as either transmissive or

reflective LCDs, depending on the ambient light. These

LCDs work reflectively when external light levels are high,

and trans-

massively in darker environments via a backlight source.

D. Color LCD Displays

In color LCDs each individual pixel is divided into three

subpixels, which are colored red, green & blue, respectively

by additional filters. Each subpixel can be controlled

independently to yield millions of possible colors for each

pixel. Color components may be arrayed in various pixel

geometries, depending on the application and the picture

color quality can be controlled by hardware or software[5].

E. Active LCD Matrix

High-resolution color displays for LCD computer

monitors and televisions use an active matrix LCD matrix.

A matrix of Thin-Film-Transistors (TFT) is added to the

polarizing and color filters, as shown in Fig. 1B. Each pixel

has its own dedicated transistor allowing each column line

to access one pixel. When a row line is activated, all of the

column lines are connected to a row of pixels and the

correct voltage is driven onto all of the column lines. The

row line is then deactivated and the next row line is

activated. All of the row lines are activated in sequence

during a refresh operation. Active-matrix displays are much

brighter and sharper than passive-matrix displays of the

same size, and have faster response and better image quality

[5].

Fig. 1B. Structural details of active matrix

LCD display showing TFT panel besides the other elements.

III. TEXAS INSTRUMENT DISPLAY TECHNOLOGY

A. Digital Light Processing (DLP) Technology

The TI DLP chip or Digital Micromirror Device (DMD)

contains a 2D-array of 480X320 (153.600) or 1024X768

(786.432) or 1.920X1.080 (2.073.600) hinge-mounted

micro-mirrors; each of these micromirrors measures less

than one-fifth of a human hair. When integrated with a

light source, projection optics, and electronics, the mirrors

on the DLP chip reflect a binary data pattern or video

image with extraordinary speed, precision and efficiency.

The DLP MEMS´s micromirrors are mounted on tiny

hinges that enable them to tilt either towards the light

source in a projection system or away from it, creating a

light or dark pixel on a projection surface. The spatial light

modulation is achieved when the bit-streamed binary data

entering CMOS circuits located under the appropriate

micromirror direct each mirror to switch on & off up to

several thousand times per second. When a mirror is

switched on more frequently than off, it reflects a light gray

pixel; a mirror that is switched off more frequently reflects

a darker gray pixel.

Fig. 2. Shows Block Diagram of projection system using

DLP 1700 MEMS chip, providing designers a pixel-level

control of the Digital Micromirror Device [6].

B. Structure and Operation of the DMD Array

The DMD mirror (pixel) is both an electro-mechanical

element having two stable positions (+12 ° and -12° for

DLP1700) actuated by electrostatics and an opto-mechanical

element in that these two positions determine the direction of

light deflected. Fig. 3. Shows Active mirror array, pitch and

hinge–axis orientation of DMD. Details of dual CMOS

memory, memory state versus mirror state, transfer of

memory state to mirror state, power up and power down,

operation of DMD array and resets are given in TI application

notes [2]. Fig. 4. Shows landed positions of micromirrors and

light paths.

C. DMD Structural and Assembly Features

The primary features of TI Series-450 DMD are described

below and illustrated in Figure 5.

● DMD active array: the 2-dimensional array of active

micromirrors that reflect light.

● WLP chip: Wafer Level Package (WLP) DMD chip that

contains the DMD active array and window glass.

● Window glass: the clear glass cover which protects the

DMD active area of micromirrors.

● Ceramic Carrier: the structure which forms the

mechanical, optical, thermal, and electrical interfaces

between the WLP DMD chip and the end-application optical

assembly.

● Window aperture: the dark coating on the inside surface

of the window around the active array.

● Encapsulation: the material used to mechanically and

environmentally protect the wire bond wires.

● Bond wires: the wires which electrically connect the

WLP DMD chip to the ceramic carrier.

● Electrical pins: the electrical interface between the

ceramic carrier and the end-application electronics.

● Thermal interface area: the area on the ceramic carrier

which allows direct contact of a heat sink or other thermal

cooling device.

● Corner chamfer: visual keying and orientation aid

located on the ceramic carrier. Also identifies the incoming

illumination direction.

(Courtesy of Texas Instruments)

(Courtesy of Texas Instruments)

(Courtesy of Texas Instruments)

Fig. 5. Series -450 DMD Features –Window Side

(Courtesy of Texas Instruments)

IV. PIXTRONIX DISPLAY TECHNOLOGY

A. Digital Micro Shutter (DMS) Technology

The DMS technology is a transmissive, Field Sequential

Color (FSC) display; utilizing R-G-B tri-color LED backlight

and having a DMS MEMS structure on the top of the TFT-

backplane, resulting in the following salient features [4]:

● Consumes only 25% of the power of TFT-LCD display due

to unique optical design which utilizes light recycling to

achieve more than 60% optical transmission efficiency.

● Unique MEMS-based DMS architecture with shutter

geometry of three slits of 105µmX13µm; eliminates the

need for the color filters, polarizers and LCD panel, by fast

switching of micro shutter at 100 µsecond for each pixel

actuating under electrostatic force controlled by TFT resulting

in wide variation of gray scale for each pixel.

● A digital controller chip along with the R-G-B LED Driver

logic controls TFT backplane by synchronously modulating

mirromirror arrays based on FSC strategy; producing full

speed video with 24 bit color depth, high contrast ratio, wide

viewing angles and color gamut of 105%.

● The DMS display works in three modes: Transparent mode,

Reflectance mode and Transmissive mode – a combination of

the transparent & the reflectance mode depending upon the

environmental conditions, thus, DMS produces excellent

images even in direct sunlight [5].

Fig. 6. Shows overall optical architecture and the structural

details of the MEMS and TFTs. Fig. 7 illustrates color gamut

comparison between Pixtronix color gamut and LCD color

gamut.

Fig. 6. Shows optical architecture and structural details of the

Micro Shutter MEMS and TFT (Courtesy of Pixtronix)

Fig. 7. Shows Gamut Comparison (Courtesy of Pixtronix)

V. QUALCOMM DISPLAY TECHNOLOGY

A. Interferometric Modulator (IMOD) Technology

A direct-view MEMS display for mobile applications

demands better solutions than deformable mirrors and

mechanical shutters. Developed to address these

shortcomings, mirasol displays are based on the principle of

interference, which is used to determine the color of the

reflected light. The IMOD pixels are switched at speeds

around 10 µseconds and have reflectivities of more than

60%, contrast ratios more than 15:1 and drive voltages as low

as 5V. The simple MEMS structure of IMOD pixel elements

provide the functions of light modulation, color selection and

memory while eliminating active TFT matrices, color filters

and polarizers; resulting in high-performance display capable

of active-matrix type functionality at passive-matrix cost [3],

[7].

B. Working Principle of IMOD (Mirasol) Display

Basically, a mirasol display is an optically resonant cavity

similar to a Fabry-Perot etalon. The device consists of a self-

supporting deformable reflective membrane and a thin-film

stack (each of which acts as one mirror of an optically

resonant cavity), both residing on a transparent substrate.

When ambient light hits the structure, it is reflected both off

the top of the thin-film stack and off the reflective membrane.

Depending on the height of the optical cavity, light of certain

wavelengths reflecting off the membrane will be slightly out

of phase with the light reflecting off the thin-film structure.

Based on the phase difference, some wavelengths will

constructively interfere, while others will destructively

interfere as shown in Fig. 8. Color generation by interference

is much more efficient in its use of light compared to

traditional filters & polarizers, which work absorption &

waste much of light entering display.

Fig. 8. IMOD structure showing light reflecting off the

thin-film stack and mirror interfering to produce color

(Courtesy of Qualcomm MEMS Technologies)

The image on a mirasol display can switch between color

& black by changing the membrane state; achieved by

applying a voltage to the thin-film stack, which is electrically

conducting & protected by an insulating layer. When a

voltage is applied, electrostatic forces cause the membrane to

collapse. The change in optical cavity results in constructive

interference at ultraviolet wavelengths, which is not visible to

human eye, so the image on the screen appears black. A full-

color display is assembled by spatially ordering IMOD

elements reflecting in the Red, Green & Blue wavelengths as

shown in Figure 8.

At the most basic level, the IMOD pixel element is a 1 bit

device which can be driven to either a dark (black) or bright

(color) state. In order to be able to show grayscale images,

spatial or temporal dithering can be used. Spatial dithering

divides a given subpixel into many smaller addressable

elements, & drives the individual elements separately in order

to obtain the gray scale. Such scheme requires an additional

row driver per element. Alternatively, temporal dithering can

be used to obtain additional gray shades. Temporal dithering

offers a lower cost display since fewer IMOD elements are

addressed & provides a higher fill factor. A combination of

both temporal & spatial dithering can be used to increase the

gray levels; such that a balance of optical efficiency/power

tradeoff is achieved [8].

VI. ROADMAP FOR RESEARCH IN DISPLAYS

To catch up with advanced countries in mobile multimedia

display technologies, it is suggested that the Brazilian federal

& private universities must first offer rigorous design oriented

courses at the senior undergraduate & graduate level in the

following areas, rest will follow with focused planning:

● Electronics Design Automation for VLSI Circuit Design

● Design of Analog and Digital Circuits by HDL

Languages

● Process and Fabrication Technologies of

Microelectronics

● Process and Fabrication Technologies for MEMS

● Theory and Simulation of MEMS Sensors & Actuators

● Design of RF-MEMS and MOEMS by Industry Software

● Optical Engineering

● Quantum Electronics and LASER Engineering

● Nanotechnology and Nanoelectronics

● Display Technologies for Mobile Multimedia & HDTV

REFERENCES

[1] L. J. Hornbeck, “Digital Light Processing for High-Brightness, High-

Resolution Applications”, (Invited Paper), Electronics Imaging EI97 &

Projection Display III, Sponsored by SPIE, San Jose, CA,1997, pp. 1-14.

[2] Available On-Line, www.ti.com, DLP Documentation, 2010.

[3] How MIRASOL Display Works: MEMS Drive IMOD Reflective

Technology, Available On-Line, www.mirasoldisplays.com,

[4] Nesbitt Hagood, et. al, “A Direct-View MEMS Display for Mobile

Applications”, Pixtronix, Inc, Andover, MA, 2007, pp. 1-4.

[5] D. Armitage, I. Underwood, & S. T. Wu. Introduction to Microdisplays.

ISBN 0-0470-85281-X, Wiley, November 2006.

[6] L. J. Hornbeck, “Digital Light Processing: A New MEMS-based Display

Technology” (Keynote Address), IEEJ 14th Sensor Symposium, Kawasaki,

Japan, June 1996, pp. 297-304.

[7] B. E. Saleh and M. C. Teich, Fundamentals of Photonics, Wiley, 2007.

[8] I. Pitas, Digital Image Processing Algorithms, Prentice Hall, 1993.