＊1 New Business Development Center, Display Device Development Division＊2 Sharp Yonago

12

1．�Introduction

Digital Micro Shutter (DMS) Display based on MEMS

design can provide a lot of unique characteristics(1)(2).

However, because MEMS shutter is driven digitally with

either open or close state, it is necessary to set both color

and gray scale by digital field sequential driving. That

requires high frequency driving in comparison with LCD

and OLED. For example, in the case of 24 bit color, it is

necessary to refresh the MEMS panel at 1440Hz (24 * 60)

as minimum frequency. Sharp has been developed and

produced InGaZnO LCD Display(3)(4).

Oxide TFT can achieve higher mobility, such as approx.

10cm2/Vs, in comparison with a-Si TFT, and can be

manufactured on larger size mother glass with smaller

mask numbers in comparison with LTPS.

Therefore, we have focused on above merits of oxide

TFT backplane technology, and we have successfully

developed a prototype of 7” WXGA MEMS display as

shown in Fig.�1 .

Digital Micro Shutter (DMS) Display based on MEMS design and process technologies provides wide color gamut, wide operating temperature range and low power consumption, compared with LCD and OLED which are widely used at the present time.

Conventionally, DMS display was driven by LTPS TFT because of its high frequency operation.Oxide TFT as represented by InGaZnO has higher performance and reliability than a-Si TFT, as well as

better productivity for large display than LTPS TFT. The InGaZnO oxide TFT can be applied to drive DMS display with good performance. It means that uniquely high performance and large size DMS displays can be produced without significant investment.

In this paper, technologies and performance of 7 inch diagonal DMS display are explored.

MEMS技術に基づくデジタルマイクロシャッターディスプレイは，広色再現性，かつ，低消費電力の実現を可能とする。従来は，デジタルマイクロシャッターディスプレイは，高移動度を特徴とするLTPS TFTで駆動されていた。一方，InGaZnO TFTは，a-Si TFTと比較し，高い性能と信頼性を有し，かつ，LTPS TFTと比較するとより大型の基板で製造できるため，将来の大型化においても有利である。本稿では，7＂のInGaZnO MEMSディスプレイを紹介する。

7�inch�Digital�Micro�Shutter�Display�Driven�by�InGaZnO�Oxide�TFTInGaZnO MEMSディスプレイ開発

Akinori Kubota＊1 Taketoshi Nakano＊1 Hirohiko Nishiki＊1 Takeshi Hara＊1 Hidehito Kitakado＊1

Toshihiro Yamashita＊1 Yoji Taniguchi＊2 Yoshinori Tanaka＊2

Fig.1　Prototype of 7＂ WXGA MEMS display.

13シャープ技報 第108号・2015年3月

7 inch Digital Micro Shutter Display Driven by InGaZnO Oxide TFT

2．�Outline�of�7＂�MEMS�Display

Fig.�2 shows the block diagram of the 7” MEMS dis-

play prototype.

The configuration is similar to other displays.

A Control IC receives image data and commands from

host side. The control IC needs to rearrange image data to

match it with a field sequential driving of MEMS display.

Therefore, the IC needs to have a frame memory. Thus, as

a module I/F, it will be adequate to select a standard I/F

that supports an option of display modules contains a

frame memory internally.

A power management IC (PMIC) needs to generate

power supplies for both RGB LEDs and MEMS panel.

A driver IC sends binary voltages to a MEMS panel for

controlling shutter either open or close state. Therefore, the

chip does not need to have circuits for controlling analog

voltages of each output, and can be designed quite simply.

3．�Results

The outline specification of the prototype is as follows:

Table 1　A summary of CR and NTSC ratio.

Size 7.0”

Resolution 1280 x 800 (217ppi)

Contrast 3000

NTSC Ratio 120%

Regarding a brightness and power consumption, it has

been targeted to achieve a half of power consumption of

LCD. As of today, a MEMS panel is driven with FPGA

board, and a chip set is needed to realize the target.

Fig.�3 shows characteristics of color coordinate includ-

ing data measured from slanted angle. Theoretically,

MEMS display does not show any color shift on all axis.

Therefore, there is a potential to utilize MEMS display

for a professional use.

Fig.�4 shows characteristics of contrast vs viewing

angle. Contrast above 10 at +/- 80 deg can be achieved.

Especially, the Y direction, parallel with long side of a

shutter slot can achieve extremely wider viewing angle

compared to LCD display.

Regarding a response time, Fig.�5 provides a compari-

son of waveform detected by photo diode when a display

switching from black to white. In the case of MEMS dis-

play, one frame is consisted by several sub-frames and

many pulses can be observed. That means a change of lu-

minance can be different depending on start and end point

of gray scale level (Patterns of Shutter Open/Close) in the

case of MEMS display.

Although MEMS display is a field sequential color

display, response time adopting MRPT (Moving Picture

Response Time) has been evaluated and the result is shown

Fig.2　 Block Diagram of Prototype of 7＂WXGA MEMS display.

Fig.3　Color Coordinate from slanted angle.

PMIC Control IC

Fra me Me mor yCon t ro l

Log i c

Po wer Supp l i es

to MEMS Pa ne l

Po wer Supp l i es

to RG B L EDs

MEMS Panel

RGB Back Light

Driver ICs

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

y

x

MEMS

NTSC0°

X +45°

Y +45°

= 0º

= -90º= 90º

= 90º

= -90º

Panel

ƟX

ƟX

ƟV

ƟY ƟY

14

7 inch Digital Micro Shutter Display Driven by InGaZnO Oxide TFT

in Fig.�6 . MEMS display can surely switch within one

frame period. On the other hand, as well known, LCD

shows longer response time than one frame on some areas

depending on start and end of gray scale.

Also, MEMS display has a potential to secure good

image quality in the very low temperature range such as

-20C. As shown in Fig.�7 , MEMS display demonstrates

stable characteristic over a wide range of temperature.

Lastly, as shown in Fig.�8 , in comparison with a LCD

panel, a MEMS panel is flipped and placed on a backlight

module to have a light recycling effect.

Therefore, it is important to reduce unexpected reflectance

from metal patterns of TFT layers.

Fig.�9 and 10 show the optical performance under

20,000lux lighting. Fig.�9 shows module brightness versus

contrast, while Fig.�10 shows NTSC ratio versus module

brightness.

It is confirmed that equivalent optical performance can

(a) MEMS Display

(b) LCD

Fig.5　Waveforms detected by photo diode.

Fig.6　 Response time of MEMS Display between gray levels (MPRT).

0 50 100 150 200

Time [mS]

Brig

htne

ss(O

utpu

t fro

m P

hoto

Dio

de)

0 50 100 150 200

Time [mS]

Brig

htne

ss(O

utpu

t fro

m P

hoto

Dio

de)

Start

End

Res

pons

e tim

e (m

s)

255

191

128

64

0

0.00

5.00

10.00

15.00

20.00

25.00

30.00

064

128191

255

255

191

128

64

0

0.00

5.00

10.00

15.00

20.00

25.00

30.00

064

128191

255

Start

End

Res

pons

e tim

e (m

s)

(a) MEMS Display

(b) LCD Display

Fig.4　 Contrast from slanted angle.

[MEMS] View angle characteristic

0

500

1000

1500

2000

2500

3000

3500

-80 -60 -40 -20 0 20 40 60 80

Cont

rast

angle (°)

X

X

Y

Y

0

40

80

120

160

-80 -78 -76 -74 -72 -70

Cont

rast

angle (°)

X

Y

0

40

80

120

160

70 72 74 76 78 80

Cont

rast

angle (°)

X

Y

15シャープ技報 第108号・2015年3月

7 inch Digital Micro Shutter Display Driven by InGaZnO Oxide TFT

be achieved without attaching polarizer at the same

brightness setting with LCD.

Moreover, if the half power consumption of LCD can

be successfully achieved, it will be possible to make the

brightness higher utilizing the power difference under

normal usage, and to enjoy better viewability at outside.

Also, in the case of MEMS display, it can be proposed

to reduce bit plane numbers for outside usage because it is

difficult for human eyes to recognize full color gray scale

levels when the display surface was illuminated with strong

light and contrast of the display becomes lower. By doing

so, higher brightness can be realized with lower power

consumption .

4．�Summary

7” MEMS display we have developed can achieve ultra

low power consumption with high optical efficiency,

exceptional image quality with ultra wide color gamut,

agility to further reduce the power based upon bit planes

required, and good operation under wide range of

environmental temperature

By using oxide TFT as backplane technology for MEMS

display, it will be possible to widen not only the choice of

MEMS display size, but also the range of applications.

(a) MEMS Display

(b) LCD Display

Fig.8　 Cross Section of MEMS Display.

Fig.9　Contrast under 20 ,000 lux.

0102030405060708090

MEMS

-30 -20 -10 0 10 20 30

rise (V0→V255)

fall (V255→V0)

Res

pons

e tim

e (m

s)

Temperature (℃)

0102030405060708090

-30 -20 -10 0 10 20 30

LCD

rise (V0→V255)

fall (V255→V0)

Res

pons

e tim

e (m

s)

Temperature (℃)

Fig.7　 Response time of MEMS Display over the temperature (MPRT).

Backlight

Aperture Plate

Backplane

LED

MEMS Shutters

0

1

2

3

4

5

6

0 500 1000 1500 2000 2500

Cont

rast

Luminance (cd/m2)

20,000 lx Ambient Contrast

LCD MEMS

0

2

4

6

8

10

12

14

0 500 1000 1500 2000 2500

NTS

C ratio

(%

)

Luminance (cd/m2)

20,000 lx Ambient Chromaticity

LCD MEMS

Fig.10　NTSC Ratio under 20 ,000 lux.

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7 inch Digital Micro Shutter Display Driven by InGaZnO Oxide TFT

The authors would like to thank help of all Pixtronix

team and Sharp members related to a joint development

project by Pixtronix and Sharp.

Reference:[1 ] N. W. Hagood et al, “MEMS-Based Direct View Displays

Using Digital Micro Shutters”, 15th International Display Workshop, (2008)

[ 2] J. Gandhi et al, “High Image Quality of Ultra-Low Power Digital Micro Shutterbased Display Technology”, SID 37.4, 532-535 (2009)

[ 3 ] S. Yamazaki et al, ” Research, Development, and Application of Crystalline Oxide Semiconductor”, SID 15.1, 183-186 (2012)

[4 ] Kataoka et al, “Development of InGaZnO-TFT and Creation of New Devices Using InGaZnO-TFT”, SID 56.1, 771-774 (2013)