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`LIQUIDCRYSTAL
`Fl-AT PANEL
`
`
`
`MANUFACTURING
`SCIENCE &
`TECHNOLOGY
`
`WILLIAM C. O’MARA ”
`
`-
`
`»
`
`.
`
`’ VAN NOSTRAND REINHOLD
`'
`‘
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`‘New York
`
`1
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`Gold Charm EX. 2024 .
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`Gold Charm Ex. 2024
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`1
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`

`
`
`
`Copyright © 1993 by Van Nostrand Reinhold
`
`. ‘
`
`Library of Congress Cata1og..C_[ar_d Nu”
`ISBN 0—442—01428-7
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`All rights reserved. No part of this work covered by‘ the copyright
`hereon may be reproduced or used in any form or by any means-'-
`graphic, electronic, or mechanical, including photocopying,=r_ecord‘-
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`the writtenpermissionofthepublisher,,
`,
`_
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`Thomson Publishing.
`l’I=‘P:1ogo is a trademark under license.‘
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`International Thomson Publishing
`Berkshire House
`168-173 High Holborn
`London WC1V 7AA, England
`
`Thomas Nelson Australia
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`Victoria, Australia
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`Scarborough, Ontario
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`16151413121110987654321
`
`Library of Congress Cataloging in Publication Data
`O'Mara, William C.
`Liquid crystal flat panel displays: manufacturing sciece &
`technology / William C. O'Mara,
`’
`P. Cm.
`Includes index
`ISBN 0-442-01428-7
`
`I
`
`1. Liquid crystal display. I. Title
`TK7872.L56046 1993
`621 .38--dc20
`
`1
`
`92-43119
`'
`CIP
`
`’
`
`2
`
`

`
`CHAPTER ONE: PRODUCT APPLICATIONS
`
`LIQUID CRYSTAL FLAT PANEL DISPLAYS
`
`Table 1-2 Japanese Large Flat Panel Displays
`
`Firm
`
`Size
`
`Display Type
`
`rows x columns x
`
`colors I grey scale
`(inches)
`-T.-.j.u
`640x400x8
`TF1‘ color LCD
`
`NBC
`
`9.3
`
`Matsushita
`
`Seiko Epson
`
`Sharp
`Mitsubishi
`
`Kyocera
`Stanley
`Hoshiden
`
`Toshiba
`
`Seiko
`
`Sanyo
`
`Sanyo
`Toshiba
`
`Hitachi
`
`Sharp
`Hiroshima Opto
`
`Seiko Epson
`Casio
`
`Seiko Electric
`
`Citizen
`
`Seiko Epson
`Toshiba
`
`Alps
`Hitachi
`
`9.8
`
`9.8
`9.8
`
`10
`10.1
`
`10.3
`
`10.4
`10.4
`
`10.4
`10.4
`
`10.4
`
`10.4
`
`10.4
`10.4
`
`10.5
`11
`
`7
`
`8.8
`
`9.4
`
`9.8
`10
`
`Seiko Epson
`Hoshiden
`
`13
`15
`
`STN color LCD
`MIM color LCD
`
`TFT color LCD
`TF1‘ color LCD
`
`STN color LCD
`VTN color LCD
`TF1‘ color LCD
`
`STN color LCD
`STN color LCD
`STN color LCD
`
`TFT color LCD
`
`TF1“ color LCD
`
`TF1" color LCD
`
`TET color LCD
`STN color LCD
`STN color LCD
`
`640x400x16
`
`640x480x4096
`
`640x400x4096
`640x480x4096
`
`640x480x16
`640x400x8
`640x808
`
`640x480x16
`
`640x480x64
`640x480X64
`
`640x480xfull color
`
`640X480x5l2
`640x480x4096
`
`640x480xl6nfilfion
`640x480x8
`640x430x8
`
`STN monochrome LCD
`
`640x480X1
`
`STN monochrome LCD
`
`STN monochrome LCD
`
`STN monochrome LCD
`STN monochrome LCD
`
`STN monochrome LCD
`TFT color LCD
`
`MIM monochrome LCD
`TF1" color LCD
`
`640x480x1/16
`
`640x4 80x1
`640x-480x 1/8
`
`640X400x1/ 16
`640X400X1
`
`l 12OX780x4096
`
`1280x800X1/16
`
`1280x8OOX4-O96
`
`A lot of personal computers are sold each year. In 1988, total sales of 20 million
`units were valued at $50 billion. This increased to 22 million units in 1989, and
`the share ofportahles increased from 10% to 14%. For 1990, the share of portables
`is estimated at 16%, growing to at least 25% in 1995. This represents a market of
`8 to 9 million laptops. At least 75% of these will have LCD screens, or 8 million
`LCD laptops. It’s going to be a big market
`
`3
`
`

`
`Figure 1-6 Principle of operation of a twisted nematic liquid crystal display
`
`ON
`
`.11/l///A
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`«Ir:
`
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`OFF
`
`iLiquidCrystal
`
`‘iiililiiifli
`
`I'll
`I II
`
`Imllhluw
`
`Light Source
`
`I
`! Transparent Electrode
`:
`-Polarizer (Analyzing)
`
`.
`_
`! Polarizer (Polarizing)
`I
`-Transpareni Electrode
`
`4
`
`

`
`CHAPTER ONE: PRODUCT APPLICATIONS
`
`LIQUED CRYSTAL FLAT PANEL DISPLAYS
`
`Figure 1-8 Schematic representation ofpassive and active matrix color liquid
`crystal displays.
`
`Horizontal Electrode
`
`Vertical Electrode
`
`-'uv\v\r.-wvnvn-svws-Into’
`
`S'I'N-LCD
`
`Polarizer
`
`Substrale\ Polarizer
`
`Thin Film Transistor
`
`Source Line
`
`'I'F'I'- LCD
`
`Polarizer Substrate
`
`Orientation Color
`Layer
`Filters Substrate
`
`Polarizer
`
`5
`
`

`
`The iimitations of liquid crystal switching by a multiplexing scheme can be
`
`Active Matrix Devices
`
`3
`
`overcome by placing an active device behind each pixel. The high information
`content displays for computers benefit from increased response speed, higher
`
`Contrast, and higher overall brightness. The cost of these improvements is the
`
`added fabrication sequence for thin film devices behind each pixel, a total of
`hundreds of thousands of individual devices for each display.
`
`Having a switch at each pixel greatly simplifies the electronics of the flat panel
`display. The front panel transparent electrode is not patterned at all, and acts
`
`simply as a ground electrode. Problems due to voltage nonuniformity along the
`display are reduced or eliminated. Twisted nematic liquid crystal material can be
`
`used instead of the more demanding supertwisted variety. Various kinds of
`switches have been investigated for this application,
`including diodes and
`transistors. All ofthese devices are deposited as thin films, and are patterned using
`
`technology similar to semiconductor integrated circuit methods. Current produc-
`
`tion displays employ either a metal—_insulator—metal (MIM) diode made from
`tantalum and tantalum oxide layers, or aMOS thin film transistor (TFT) made in
`
`either an amorphous silicon (a~Si) or polysilicon thin film.
`
`Polysilicon transistors have some performance advantages over a—Si devices. and
`transistor performance is good enough to allow simple integrated circuits to be
`fabricated at the outside edges of the display. These circuits act as on-board
`
`drivers, and greatly reduce the number of external connections. Processing
`requirements for polysilicon transistors currently require quartz substrates rather
`than glass. Since quartz is a much more expensive substrate, applications for
`polysilicon/quartz displays are currently limited to small displays used as
`viewfinders or projection units. One example is shown in Figure 1-11 below.
`
`Most of the development effort for flat panel displays is devoted to amorphous
`
`silicon transistor switches. The technology for depositing thin film amorphous
`silicon with stable electrical properties has been known forsome time, and is used
`
`commercially to make thin film “solar batteries” for pocket calculators[l 1].
`
`Many of these calculators have no other battery, and operate with light from room
`illumination rather than sunlight. The additional complications of transistor
`
`fabrication have so far limited production to small displays, but the difficulties are
`being overcome, and 10 inch displays are in pilot production in Japan. Full color
`
`6
`
`

`
`LIQUID CRYSTAL FLAT PANEL DISPLAYS
`
`Tsumura and coworkers at Hitachi de-
`Cstg
`TFT
`scribed a 10.3" full color display using a F‘ T
`TFT with an aluminum gate, which is
`Source (AR);
`3
`;Drain (Au)
`shown in Figure 1-16I16]. This gate
`3iNX; W0, SOUICE3 (Cr
`'
`‘
`J1 -6-Si
`design uses aluminum for low resistiv-
`I
`I
`I‘
`'
`:
`ity, and an anodized aluminum material
`forms the gate oxide of the device. Alu— C319 (/W)‘
`minum has about one tenth the electrical
`
`‘A92
`
`:
`Gate (A9)
`
`resistance of chromium. Aluminum is
`
`Figure 1-16 Aluminum gate a—Si TFT
`
`also used for the common electrode of the storage capacitor, as shown in the
`figure. The TFT is of the inverted stagger type. The storage capacitor is added to
`improve the uniformity of the displayed image.
`
`Figure 1~17 shows that stray light passing through the display structure can leak
`through, reducing display contrast. In order to eliminate this stray light, a second
`light shield was added to the structure, as shown in the lower part of the figure.
`Figure 1-18 shows the plane view of_ the active matrix device. The pixel size is
`64x192tL;n. Aperture ratio of more than 25% and contrast of 100:1 were measured.
`Using 8 level signal drivers, 512 colors were obtained for a full color dispiay.
`
`Figure 1-17 Light leakage in TFTstruczure
`
`Figure 1-18 Plan view 0fTFT
`structure with light Shield.
`
`Light Leakage
`Apenure Area
`__.4’CoEor Filter
`
`-- Drain Line
`
`I
`
`15tS_hieId
`
`I: :‘
`. 1'
`§ApertureArea§
`:<—--—>E Co[orFi|ter
`
`Drain
`Pixel=lT0
`2nd shieid
`a) Conventional Shield Structure
`b) Double Shield Structure
`
`3“bs""“e
`
`7
`
`

`
`Table 1-13 CMOS p0ly—Si TFT and a-Si:H TFT Comparison
`
`Poly-Si TFT Poly-Si TFT a-Si:I-I TFT
`HT CMOS
`LT CMOS
`NMOS
`
`fused quartz
`~l000°C
`6-8
`3
`
`hard glass
`600°C
`5‘—7
`4
`
`hard glass
`300°C
`5-6”
`2
`
`2
`
`3
`
`'
`
`40
`
`Substrate
`Maximum process temperature
`Number of mask steps
`Dielectric depositions
`(LPCVD or PECVD)
`a—Si Deposition
`(LPCVD or PECVD)
`Metal sputtering
`Ion Implantation
`Hydrogenation
`
`Threshold Voltage
`
`(Volts, n—channel)
`Mobility
`(cm2/V- s, n—channel)
`
`Shift register @ 15V; L=10}.tm
`
`i
`
`5MHz
`
`*=NMOS "=iight shield
`
`size in Figure 1-20. The cost is estimated in arbitrary units. For small displays,
`high temperature polysilicon is low in cost, even when the cost of a quartz
`substrate is included. This indicates that small displays such as video cameras and
`projection TVs will be built with this technology, to display sizes of 2—3—'inch
`diagonal. Amorphous silicon is much lower in cost for large displays. The future
`oflow temperature polysilicon lies in this large display area. As mentioned above,
`low cost relative to amorphous silicon requires a very high yield process, and
`integration of driver circuits onto the glass substrate- New manufacturing processes
`and equipment for CVD, implantation, and recrystallization will be required.
`
`A brief discussion of some of the circuit types is shown in Table 1-14. The basic
`types of integrated circuits that can be considered for driving the active matrix
`devices include D/A converters, sampled ramp, and l—of—n selector for digital
`input. On the other hand, for video input, multiplexer, sample and hold, and
`double sample and hold are available. The table shows the comparison.
`
`8
`
`

`
`LIQUID CRYSTAL FLAT PANEL DISPLAYS
`
`processing is under evalua-
`tion for some steps, as men-
`: cloned previously for ITO
`etching. Reactive etching
`; many offer advantages of
`linewidth control and repro-
`
`ducible end point detection.
`' However, for the time being,
`throughput considerations
`ensure thatmost etching steps
`
`will be performed in wet sys-
`
`I E11115.
`
`I Transistor Processes
`
`Two types of TFT structures
`are used for amorphous sili-
`con (a—Si) devices. One is the
`inverted staggered (IS) type,
`T, which can be either back
`~ channel etched (1S—BCE) or
`
`_ Iri-layered (IS—TL) . The other
`‘n called a normal staggered
`(NS) device. These three
`‘uansistors (IS-BCE,
`IS—TL,
`
`and NS) are shown in cross-
`section in Figure 2-11.
`
`i rgure 2.-11 Cr0ss—secIi0n
`=
`"new of three TFT configu-
`‘=r
`'0ns [13]
`
`MoTa(Gate)
`
`(a) Inverted Staggered (Back Channel-Etched)
`
`avSi (n+)
`
`(b) Inverted Staggered (Tri-Layered)
`
`A|(Gate)
`
`(c) Normal Staggered
`
`9