Mosaic Techmology. Industriat Etectronies& :lystems DevetoptttentLaborator:y MitsubishiiilectricCorporation th'ogo,japan

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1 IDY Large Screen Using CRT Mosaic Techmology Displays 1. InroducioR Naoki SHIRAMATSU, Masaaki NAKA}gO and Shujli I}VAI\l Indusria Eecronies& :lysems DeveopenLaboraor:y MisubishiiilecricCorporaion hogo,japan Kozaburo SHIBAYAMA and Kazuya meshma NagasakiPVerks MisubishiElecricCor;poraioi Nagasaki,.lapan 2. Appl;cabiliy of he CRT o large screen mosaic displays rveeds for large screen displays have been illcreasing in recen years. Large screeii inosai,c disp.!ays,whleh consis of a marix array of many ligh-emlssive elemens, ean easily realize n large screen size and provlde common visual ijlformaion wih he sensaioik or power and realiy o many specaors. They haye been main]y lnsalled in spors sadiums for var,ious videoseryices. They are, al. presen, huporan media as in"ormaion display sysenis in public spaces such as concourses or he ransporaion ersnlnals and inelligen bulidings. In 1980, a large sereen mosalc display was firs developed uslng single-plxel CRTs. CRTs are well-suled for-a 11gh-emisslye elemen bec:ause ofl helr abilly ef eming high brighness ligh wih a Iow power consumpion. Many sudies have been examined o obain a good performanee in his decade. This paper. reviews advances in Iarge screen mosalc displays uslng CRT echnology, especially in ligh-emissiye elemens. Firs, we briefly summarize he appiicabilly of CRTs o a ligh-emlsslye elemen;. We, hen, describe CRT ligh-emissive elemens ha have been deyeioped and recen sudies for a high plcure qually, And, sye al.sq discuss some echnical subjecs for fuure sudies A large screen /anosalc display, whlgh consiss of jnany lighlemlssive elemens; has advanages sucll ha is screen slze ean be deermined lexibly and l ean be mainained parially, Kurahashi (1983)indicaed ha IIgh-emisslve devices of Iarge ScChraereaigeMrOiSsaiieesEiSPIaYS have following PIiould l) Iligh brlghness of1000 ; 2ooo cdlm2 o ensure sharp images; 2) High lumlnous efficieney for he low power consumpion; 3) Wide reproducion range of colors as he convenlonal eleylsions; 4) Fas response for 60 fleldslsec operaon; 5) Long operaing life of more hanlousands of hours. CRTs salsfy all hes,e eondilons and have aehieved much sg-perlor performanee wih respec o he brighness and he luminous efficieney. Incandescen lam]ps (ILs)and Fluorescen lampfi (FLs}are also eapable of emiing. he hlgh brighness IIgh. In case of ILs, primary co!ors are obaned using color fi}ers.their emiing ligh has he low color emperaure of K; herefore, hey haye a disadvanage ha he luminous gdficlency decreases wlh he increase of he pirly of he blue eolor. ITLs exhibi a high brighness and a good color r:eprodu,cion. Their, operalon, however, is ILable o be affeced by he ambience empera;ure, and heir lumlnous ef.flcieney is somewha lewer han ha of CRTs.

2 3. CllT Iigh-enissive elemens 3.1 Single- pixel Clllr Figure 1 shows an exerior view of a floqd-beam CRT whlch is a ligh-emssiye elemen of he firs developed large screen mosalc dlsplay for oudoor use {Kurahashi 1981). The hree kinds of CRTs, having an ouside diameer of 20, 28 and 34 mm respecvely, were developed, and are used properly according o he screen slze and he viewing disance. Figure 2 shows a basic srucure of a flood-beam CRT. Thermoelecrons emled from he cahode are spread unifqrmly by he funcion of an elecrosaic lens and are irradiaed unfermly ono he phosphor screen. The phosphor whlch is exied by he elecron beam emls he ligh. The flood-beam CRT achieved lxe luminous efflclency of almos 10 lmlw in he ayerage of R, G and B. Figure 3 shows radlason specra of a flood-beam CRT and Figure 4 shows specral ransmianceof glass bulbs. Since he glass bulb has a selecye absorpon specrum mached o he radlalun specra of phosphors, i absorbs he Incidcn ligh effeciyely. Figur.e 5 shows Vhe comparison beween he color reproducion range of he flood-beam CRT and ha of he oher display devices. This figure indlcaes he superlory of he CRT. oo sosi ooshv co2-!oor 20 o VVdve-Lengh {nm) 6507oo l.i/ Fig.3 Radiaion specra of a CRT flood-beam ico - eee Fg.1A flood-beam CRT g oog.sco8-ac PhosphorGsgrid G2 grid GigridBase Glass blub Elecronbeom nzl r Heae Cahode Flg.2Basic srucure of a flood-beam CRT o 4oo 450 Fig.4 5co 550 VSlave-Lengh600(nm)6507oo Specral ransmissions bulbs of glass Figure 6 shows he flrs large screen mosaic display for oudoor use developed in The drsplay consiss of 240(ID x 160(V) flood-beam CRTs arranged wih he plch of 45 mm in is 10.8 m(h) x 7.2 m{v) screen sze. The brighness of he display is 100o cdlm

3 The Insiue ofimageinformaion of Image Informaion andtelevision and Television Engineers O.8 O.7 O,6 O,5y O.4 O.5 O.2 o. oo.1 a2 o.3 o.4 x o.s os o.7 as phosphor plxels arranged on s 77 mm x 77 mm fla surface. Figure 8 shows an elecrode srucure of a fla marlx CRT. X-grd eiecrodes for column seleclng are prlned on an lnsulaed board. Box-shaped Y-grd elecrodes for row seleclng coyer Ilne cahodes. They have convex meshes o dlffuse elecron beams. When he elecrical po;enial of boh he X- and Y-grid elecrodes are posilve wlh respec o he lne cahode volage, he elecron beam passes hrough he convex mesh of he Y-grid elecrode. The dffused elecron beam s acceleraed by he anode yolage. I ls, hen, lrradaed ono he phosphor screen. mai/"# /./l/.or-lx, eei Fig.5 CIE chromaiciy emlssive devices dagram of ligh- Fig.7 A f!a marix CRT MsphorsereensFacegass sn 1 Anode Fig.6A large screen mosaic uslrg flood-beam CRTsdisplay 3.2 Muli-pixel CIVIr The appearanee of large screen mosaic displays opened a new marke and acivaed he echnlcal sudies on lgh-emissive elemens includlng oher dlsplay devices. As needs for a high picure qually ncrease, he developmen has shifed from he single-pixel CRT o he mull-plxel CRT, whch has plural plxels ln is vacuum envelope. Jumboron devlces (Ohkoshl 1985, IIayashi e al. 1989) and fla marix CRTs (Iwaae al. 1987, Shiramasu e al 1989) have been developed. In hls seclon, we descrbe a fla marlx CRT for odoor use (Shlramasue al. 1989). Flgure 7 shows an exerlor yiew of a fla marlx CRT for oudoor use. I consiss of 16 ergless Ygrld-elecrede IecredeNo Leed K r, SeTemgass ConvexLineC Xgrid-e meshcothede Irwiaedbourd Fig.8 Elecrode srucure of a fla marlx CRT Since he lgh emisslon of a fla marix CRT is orginally he same as ha of he flood-beam CRT, a good color reproduclqn range can be obained. The luminous effciency of a fla marlx CRT has been remarkably lmproved. Tha of a green phosphor has achleved 60 lm/w (Nlshi e al. 1989}. The brighness of a fla marlx CRT is 4ooo cd!m2, which is much iigherhan ha of a flood-beam -43-

4 CRT. Figure 9 shows an example of a large screen mosaic display using fla marlx CRTs, I consiss of 148(II) x 88(V) fla marix CRTs in is 12 mcii) x 7 m(v> screen size. While he pxel densiy of he display shown in Fgure 6 ls 494 doslm2, ha of he display shown in Figure 9 has increased o 2soo doslm2. As menioned above, ]arge screen mosalc displays have been realized using flood-beam CRTs, a high brlghness a a high luminous efficiency and a high pixel densly have been achleved by he developmen of a muli-pixel CRT. The Sudes for a high pcure qually are sil! proceedlng and he followng secion descrbes hem. Fig.9 A large screen mosaie display using fla marix CRTs 4. Sudies for a high picure qualiy 4.1 Improvemen of he pixel paerii for high brighlless Alhough h.e brighness of a CRT lncreases linearly wih he anode curren densiy, i resuls in shorer 11feime of he phosphor. To increase he brighness malnalning he anode curren densiy eonsan, he aperure ralo needs o be higher, I ls, however, desirabie ha he spacer glass ls hick so as o mainaln he srengh of he vacuum enyelope. The plxel area is, herefore, resriced because of he hickness of he spacer glass. As a mehod o en}arge he pixel area mainaining he hickness of he spacer glass, he cofivenlonal pixel paern shown in Flgure 10 (a) was modified lno he pixel paerri shown ln Figure 10 (b).in he modlfied pixel paern, sixeen color plxels are arranged so ha he space wihin each array of four plxels ceuld be narrower han he space beween he arrays. IIoweyer, he Impairmen of he picure qualiy ean be caused by unequally spaced pixels. To obain he plxel paern ln whlch he plcure qually ls no impaired, a subjecive evalualon es of overall picure qualiy was performed usng compuer slmulaed picures (Shiramasu e al 1989). As a resul, he aperure raio of 25X was improved o 42k by modlfying he pixel paern on he bass of he experimenal resuls. [I]O[]DDD oodddd od@@@[] D@@@@o Dee@@@D D@pm@siD Dooao[] DODDOD Ca),cor,yenienai. kb) rfiqdlflecs.. Flg.10.Modifieaion of he pix el p.a. erb / In case of he pxel agrangemen in whch RL, areas Qf.G and B-plxel are equal, he anode curren densiy of G-phosphor ends o be higher ehan.ha of Ri.and B- phof,phors. Ths causes rapid decllnlng of he brlghness of a G-phosphor. Ths endeney canno be disregarded, espe.clally a a high brlghness. The R-G-B-G qgadruple arrangemen can avoid his problem because he number of G-plxels ls as wice as ha of R- and B-plxels. Whlle, some invesigalons are necessary concerning oher plxel arrangemens as rio arrangemen and delpa arrangemen ec. Wih he rio arrangemen, Ohkoshl e al. (19B7) modifed he convenonal paern ino he new paern, in which he area of G-plxel is larger han ha of R- and B-pixel. 4.2 Simplificaion of clecrode srueure fvr high pixel densiy In he elecrode srucure of he fla marix CRT, bach phospl}or pixel independenly needs X-, Y-grid elecrodes and a Ilne cahode. Snce a hlgh pixel deris.iyusng such an elecrode srucue resuls ln he lncrease of he number of he elecrcal pars and he processes, -44- ]:ooo[ ]DoDa[ ]E@E@[ ]@E@@[ ]@@@@[ ]@@@@[ ]D[]DD[ ]DZ[]O[ a high manuracurlng cos

5 is caused. Therefore, a slmplfied elecrode srucure ol lmproved producivly is necessary. In ease of he shorer pixel pch, l s dlfficul Lo weld eaeh shor llne cahode so ha every conac pon can have he same elecrcal resisance. As he emperaure of one 11ne cahode differs from anoher, he amoun of he emied hermoelecrons of dirrers from anoher. This leads o an uneven 11gh emsslon. Each line cahode would be longer, if i can operae as a common elecron source o plural phosphor pixels. This also conribues for a low cos because of he decrease of elecrlcal pars. Shied eiecrede Phespher Aperure screens Facegass Anode xcontros planeelecrodeeonemyg[assbackplane eenrolelecrode LineCCahede Fig.11 Improved elecrode srucure of a fla uarix CRT ln order o solye hese problems, Ichikawa e al. (1989) proposed a new elecrode srucure of a fla marlx CRT. Fgure 11 shows he cross seconal yiew, Boh X- and Y-grid elecrodes, whlch are referred o as backplane conrol elecrodes, are The shleld prined on he boom glass. elecrode ls locaed beween he anede and he coinmon line cahode, I derei)dshe elecrlcal poenial around he line cahode from he high anode volage and diffuses he elecron beam wh is aperure. Ichikawa e al. confirmed he swiching of four plxels by he operaion of he wo X-, Y-grid elecrodes and a common lne cahode by he compuer slmulaion (Figure 12) and he rial ISghemissive elemen. The new elecrode srucure achieved he pixel plch of 7.5 mm, whlle he pixel pich of he eonvenional fla marix al. 1987) is 15 CRT for indeor use (Iwaae mm. 4.3 Color lens fller for high conras Alhough a high aperure raio ls available for a hlgh brlghness, i resuls ln a low conras. especially under he direc sunllgh. This ls because he lnclden ilgh is refleced by he phosphor plane a a hlgh reflecance; hererore, he dark brlghness increases. As a convenlonal mehod o lncrease he conras ralo of he dlsplay lmage, he sunshade had been used o obsruc he Ineiden sunligh. The dark brighness, however, does no sufficienly decrease uslng he sunshade. Alhough i is possble o decrease he reflecance of he phqsphor plane by addlng he pigmen ino he phosphor, hs resuls In a reducion of he brighness of he screen mage, Thus, i ls no approprlae for oudoor use. Fig. 13 A Color lens fller for hgh conras Fig. 12 Compuer simulaion of elecron rajecories -45- Nakano e al.(1989) developed a colqr lens fiier shown ln Figure 13, The R-, G- and B-color filers are coaed on he baekside of a marix array of he plasie condenser lenses. Each color filer has a seleclve absorpion specrum mached o he radiaiqn specrum of each color phosphor. The condenser lenses compensae he reducon of he

6 brighness by lie color filers. The concenralon or he color filer is deermlned so ha he ransmiance of he eolor filer is equal o he reclproeal of be geiin o he condenser ]ens. Figure 14 shows he comparison beween he characerisics ol he conras raio o he la marix CICT wih a color lens rller and ha of he fla marix CRT wihou a eolor lens filer. 30 -o6 20org8 io 5.2 Deyelopmen of all adyanced eleerode srucure The eleerode srucure mus be simpllfied iiiorder o achieve boh he high pixel densiy and ke good produciviy. The preeeding secion has deserlbed he new elecrode srucure, in whlch all he grid elecrodes are formed by he prining echnique and eacll line cahode ls sreched for plural pixels. Furhermore, i is necessary o lnveslgae he, elecrqn source which proyldes a uniform elecron emlssion even if he plxel densiy is yery high. Cold cahode (Spind e al. 1989) realized by he micro-fabrieaion eehnique is suiable for,a hsgh pixel densiy. I has a possibi}iy of being applled o an elecron souree for ligh emissive-devices of he nex generaion. o O 100co 200oo 5eooo llluminanceux] Fig. 14 Conras characerisics of a fla marix CRT wih a color lens filer 5. Teclmical subjecs for ruure sudies In he preceding secion, some sudies for a high picure qualiy have been revewed. The lmproyemen of he pixel paern and he developmen or he color lens fler were oucloor ligh-emlssive malnly examined for elemeiis, while he slmpllfled elecrode srucure was aeslgned for indoor lighemssive elemens. Their achlevemens are, of course, appligable Vo boh he oudoor and indoor Iigh-emissive elemens. In his secion, we descrlbe some echnical subjecs for iuure sudies:. 5.1 Reducion or he dead space in he fron surface I ls essenial o reduce he anode eurreri densly ior lie longer lifelne of a phosphor. Accordingiy, he high aperure raio needs o be hlgh, The pixel paern shown ln Fgure 10 (b)ls available for he enlargemen of he pixel area. In addion o he improyemen of he pixel paern, i should be considered o make he spacer glass lself hlmier. By applying he hln ancl ough glass inaerlal o he spacer glass o he vacuum enyeope, he area where l]e phosphor pixels canno be locaed can be reduced. NIshll e al.(lgs9) : Jupan DisplayS9, p.659- Consequenly, he aperure ralo increases. This also conribues lie shorer plxel pich Conclusions CRT ls a well-suied dlsplay devlee Ior a Ilgh-emisslve eiemen of a large screen mosaic display. Ten years ago, of large screen displays single-pixel CRTs opened a new needs for a high plcure qually deyelopmen of a ligh-emissive he appearanee for oudoor use using marke. As increase, he eiemen has shifed from he single-pixel CRT o he muli-pixei CRT, This paper lias described he eehnieal adyances ln CRT ligh-emlssive elemens ln his decade and he subjecs for fuure sudies. I is expeced ha a hlgh picure qualiy will be achleved as eehnical probiems are bejng solved, and he marke will be expanded furher. Aeknowedgemens The auhors wish o hank Prof. K. Kurahaslii a Himeji Dokkyo Univ. for his helpul advice. They would also like o hank members of Noriake Company Ld. and Ise Elecronies Corpdraion fo} heir paricipaion in echnieal discussioris, References Kurahashi e al.(19sl) : SIDSl. p,132. Kurahashl{19a3) : JaPan DlsplayS3, p.420. Lwaa e al,(198t) : Euro blsplay87. p.19g Shlramasu e al.(19b9j : 1oc.or he SID, 30. p.309 Ohkoshl(1985): Sl])a5, p 18 llayash e al,(198g) : SiD89, p.9s Ohkosh e al.(19s7) : Jap.Soc.of App.Phys.,fu,p.I517 Ichlkarva e a.{lg89) : Japan DispLayS9, p.2tg. Nakanu e al,"vs9) : he 2eC.h Jon Conf: on lmnglrig TeelLno}ogy, p.293 (19S9) Spind e al,(19s9] : IEEE rans. ED-36, p.225