[InvitedTalk ]QuantumDot LED fabricated by TransferMold Method

Transcription

1 The Institute 工二 ltute Image 工 Information 工 nformatlon Television Engineers lslon Englneers 2015 年 3 月 13 日 ( 金 ) 映像情報メディア学会技術報告 ITE Technical Report Vol.39,NQ.12 1 夏 )Y (Mar.2015 ) [ 招待講演 ] 転写モールド法による量子ドット LED の作製 中本正幸文宗鉉 静岡大学大学院工学研究科, 電子工学研究所 静岡県浜松市中区城北 E mail : m rie.shizuoka.ac.jp あらまし量子ドットデバイスは, 高色純度ディスプレイやランプ, 太陽電池など様々なデバイスに応用が期待されている. 一量子ドットを均に再現性良く配置することが重要である. 本研究では, 中本研独自の均一性 再現陸 に優れた転写モールド法を用いて作製したモールド型量子ドット発光デバイス (LED ) を作製し, 従来の平面型より 高輝度な発光を目指した. モールド型量子ドット LED の輝度は平面型と比較して,633 倍に上がった, モールドに量 子ドットを配置することで, キャリアの注入効率が上がったため, 輝度が高くなったと考えられる. 転写モールド法によるモールド型量子ドット LED は, 従来の平面型と比較して高輝度を実現する可能性を示した. キーワード量子ドット, 発光デバイス, 転写モールド法, モールド型量子ドット発光デバイス [InvitedTalk ]QuantumDot LED fabricated by Method Mayuki NAKAMOTO JonghyunMOON GraduateSchool Engineering, ResearchInstitute Electronics, ShizuokaUniversity3 Shizuoka, Japan E mail : m rie.shizuoka.acjp 5 ljoho, H atsu, Abstract Highlyuniforrn quanturndot ()lightemi 而 ng diodes ( ) have en developedby using 血 brication method to realize lyej 五 cient brightdisplaydeviceshaving good color purity.the brightness w 633 times, compare that flat.the carrier i 切 ection e 缶 ciency Tr 跚 sfer improveddue to uniforrn out 脚 icle aggregation. Transfbr Meld method is usefu1 forly efficient arid good color purity to a great extent, Keyword QuantumDots,Ligh 祀 mi 賃 ing Diodes, Transf ヒr Method, Trans 驚 r 1.In 0 UC ion Quantumdots (s) are semiconductor nanocrystai material unique optical properties, possibleto adjust b gap depending on size colloid [1 2.Many researchers companies have studied about applications for s in light emitting diodes ( ),transistor,solar cells, diode lers. Especially, quantum dot light emitting diodes ( ) are increinginterest an emerging light source, since ith advantages good color purity ee color tunability [4 ] Large area displays using organic light emitting diodes (O ),are available commercially.however,organic molecules O tend to degrade are sensitive to humidity prone to oxidation. Therefore, organic emissive material in OLED displaysisreplaced by s,causes are inorganic semiconductors more stable in presence vapor or oxygen than ir organic semiconductors. water M,Bawendi V.Bulovic firstlydeveloped, by using phe separation phenomenon organic material colloidal quantum dots, which had a multilayer thin film structure single film exhibited luminous efficiency to about O,5% [3 ]. In recent,seth Coe Sullivan et al. ( Vision, Inc, ) developed full color active matrix by using printingtechniques, LED display prototype were demonstrated resolutions 100 ppi more than loo% NTSC color gamut, announced at IDW ll (InternationalDisplay Workshops,201D [ 51.B.Choi et al. (Samsung Electronics ) demonstrated 4 inch full color by using a printing process a hafnium indium zinc oxide TFT backplane 320x240 pixel array [6 ]. C.L e et a 畳. ( Seoul National Univ. ) developed inverted structure, which have ITO a cathode Al an anode,to overcome low quantum efficient poor stable stard structure hav 正 ng a large potentialenergy barriertween HTL s.their inverted exh 正 bit much er efficlency, EQE red,green blue 21 Copyright o 2015 by ITE NII-Electronic N 工工一 Electronlc Llbrary Library Service

2 TheInstitute Institute Image Information InEoimation Television Engineeis Engineers 7.3%, 5.8%, 1.7%, respectively [7].J.Jang et al., having ETL using metal-oxide to improve efficiency, having (KyungHee Univ.) reported Cs2C03 doped AZO exhibited brightness about 60,OOO cd/m2 in deep red [8]Ṭhey reported all solution processed by using inverted structures metal oxides charge transporting layers. Theses solution processing LED fabrication is a strong advantage about large area deposition lew cest, rmal vacuum deposition,announced at IDW,14 [9]. J. Mers et al, (NanoPhotonica Inc.) developed colloidal quantum-dot solution proeessed hybrid light-emitting diodes(sq) by using crystalline ZnO nanoparticles an ETL, which exhibit power efficiencies 18, 63, 2.4 lmfw, external quantum efficiencies up to 12%, 14%, 10.7% for red, green, deep blue emitting [10]. In addition, Vision developed backlight LCDs by using a narrowb color filterarray combined 25 nm FWHM emitting red green s achieved ly enhanced color gamut ef 120% NTSC 90% Rec (UHDTV celer space), 70% NTSC 50% Rec fer conventional LCD displays,announced at IDW'14. The development ly stable luminous efficient LED is necessary to selve following problems. The forrnation layer is difficult cause particleaggregation due to surfaee s covered organic ligs. Also, a phe separation ten eccurs it is difficultto ly disperse s. In addition, conventional formation methods s layerhave en developed by soluble using process flat such spin coating, dipping, dropping spray methods [11], by using se conventional formation methods, have issuessuch particle aggregation [12]. Therefore, s should required to realize ly efficient good color purity. In field vacuum nanoelectronic devices utilizing fieldemitter arrays, emitter tip sharpening, ity, ernitter material selection, repreducibility are required. fabricatien method h en developed to obtain sharp,, low operation field emitter arrays (FEAs) for ly effieient reliable vacuum nanoelectronic r [)A ]1] (a)fabricatlen by Sianisotropic etching N (b}sputtering ernitter materia{ after rmal oxidization in Moltt TpansfoF FEAs ` Emittermaterial Si02 layer Gla$s (c) Etching Si Si02 Iayer after a"odic bonding by using glsss Fig. 1:Fabrication process FEAs devices [12-14] Ṭhe tip sharpness less than 10 nm radius, good uniformity low work function material usage, have en obtained. The fierd emitter array fabrication process is illustratedin Fig. 1. Si s were formed by anisotropic etching using 30 wt% KOH (Potsiumhydrexide) aqueous solutions to make pyramidal holes very sharp corners, i.e., in Fig. 1(a). Using Si s is ey to make lots Si FEAs ly reproducibly [12-14]. The s can used repeatedly. Thermal Si02 layer w formed in Si for intrinsictip sharpening FEAs [13]. An emitter material w sputtered in Si in Fig. 1(b). Then, w bonded on gls by anodic-bonding method. FEAs were fabricatedafter remove ef Si by using TMAH (Tetramethylammeniumhydroxide) solution in Fig. 1(c). Using this method, FEAs can obtained reproducibly ly [15-18]. Therefore, s having no aggregation, can obtained by using formatien s in. In this reproducible work, ly have en developed by using fabrication method to realize extremely brightness good color purity flat panel displays. 2. Experimental have en fabricatedby using Si s, which were prepared by fabrication method [19], Figure 2 shows energy leveldiagram. A cadmium-free indium phosphidelzinc sulfide (InPtZnS) w used a quantum dot material, -22- NII-Electronic Library Service

3 TheInstitute Institute Image Image Information InEoimation Television Engineeis Engineers rx or02cathoae{al} v (a)rrormationefcade en Si patterning Si02 layer rc (b)fortnation E!L, ETL layer in ArKrdetlTO) Fig. 2: Energy leveldiagram LED. Cathode anode materials are Al ITO, respectively, which h valence conduction b energy -7.8 ev -3.8 ev, respectively. Ti02 (titanium dioxide) w used an ETL (electron-transpert layer) well a blocking layer fbr a hole-iniectionfrom anode to cathode, The valence b level Ti02 is -7.8 ev, that InP/ZnS. Nickel oxide (NiO) w used hole-transport layer (HTL) well an electron blockinglayer,cause itslower conduction b level(-3.0 ev), that InPtZnS. Al (aluminum)layer w used a cathode, cause ef small energy barriertween Al Ti02, election injection efficiency. Lithium fluoride(lif) copper (II)phthalocyanine (CuPc) were used electron-itijection layer (EIL) hole-injectionlayer (HIL) to irnprove carrier injection efficiency, respectively. Indium tin oxide (ITO)is used an anede, cause a transparent electrede well a top emission deyice structure using a Si, Figure 3 show fabrication process ef. Si s were formed by anisotropic etching to make, The Si s were prepared size 50 pm. The were fabricated on Si having 7 layers Al(100 nm)tlif (2 nm)iti02(50 nm)/slnio(40 nm)icupc(15 nm)iito (100 nm), Al thin film a eathode w formed in Si by sputtering method. The patterned Si02 layer outside region w formed by sputtering med photolithography process infig,3(a).this patterned Si02 layer plays role blocking leakage threugh area out s tween eade anede. LiF layer an EIL w formed by rmal evaporation methods, Ti02 layer an ETL w formed on LiF layerby sputtering methocl. Then. (c)formatiom vatl,hil aneae HILFM. Fig,3: Fabrication process layer s having an average diameter 5.8 nm concentration 5.0 mglml in toluene, w formed by spin coating method, w heated at 110 ec for 30 min in Fig. 3(b).s had photoluminescence peak (PL) peak at 530 nrn fu11-widthat halfmaximum (FWHM) ef nm. Then, NiO CuPc a HTL a HIL, were formed by sputtering med rmal evaporatien method, respectively. Then, ITO having a sheet resistance 47 9fM an w formed by sputtering method, infig. 3(c). The relation tween brightness yoltage were evaluated by using TOPCON SR-ULI spectreradiometer coupled a supply. The brightness were flat, which have layerto formed on flat. 3. Results discussions Figure 4(a) shows SEM image Si. In ce (100)oriented Si s havingan etching rnk, pyramidal holes () very sharp eorners were fbrmed by anisotropic etching using 30 wt% potsium hydroxide (KOH) aqueous solutions, The size isdefined by width opening at were controlled by using e-am lithography. The average size w 48.7 pm. Stard deviation size w O.3 pm. In addition, average pitches w 97,7 pm. The stard deviations pitches w O.5 pm, It means that Si made by method exhibited ly ity. Figure 4(b) shows photoluminescence image having -23- NII-Electronic NII-Electionic Library Service

4 The Institute TheInstitute Image Image Information Infoimation TelevisionEngineeis Television Engineers A= 600.ecxVmeno=-=ua.:rc (a} 300 (b} (a) Fig. 4: SEM image Si (45etilted view), (b)photoluminescence Meld image O (top-view). Si sfti02(etl)flif(etl)tal(cathode) s that Meld. The materials This rnethod. Figure 5 having efficient LED. The brightnessat The The flat malmm2). density included anode dots. However, quantum reduced s. tween arranged have patterned Si02 tween cathode that improved, cause particle by Uniform color In ly realize this haye en fabrication unifermity shows flat, The well flat numr layers, s should to required having good uniferrn developed having by using advantage The luminance reliabmty. reproducible Motd T : : having 3 Layers,4 layers, 5 layers, 6 7 layers,were fttbricated s, ETLIs, 200 o [layer} Layer numr ETL/s/HTL, EIL/ETL/s/HTL, tween EIL/ETL/s/HTL/HIL cade The brightness increed from 155, 139, 234, 274 to flat -O- i Ftat respectively. 633 times, 800 ua layer injectionefficiency s flat tween brightness relation HIL. efficient med rc 6 efficiency carrier ly study, $. Figure, purity. ': injectien enhanced EIL, ETL, HTL adding aggregation The brightness exhibited layers for carrier improved due to flat LED from 3 layers, 4 layers, 5 layers, 6 layers, to 7 injection efficiency out LED 4. Conclusion (8.7 s 633 times, carr{er low Ieakage. The layers in would layers, cause 3.3 times, non- insulationlayer.the leakage flat ef exhibited leakage due to cathode density flat malmm2 Flat increes 15 V for 633 times that 28.8 w fiat., were + good tween brightness relatien (V) Fig. 5: Relation tween brightness fiat able, shows obtained purity. color can method 16 insicle only s 12 -O- It is found positioned are ly te apply by to HTL HIL, 8 Voltage on fore formation 4 Fig. 6: Relation tween brightness layer numr flat. -24NII-Electronic Library Service

5 TheInstitute Institute Image Image Information InEoimation Television Engineeis Engineers w 633 times that fiat. The carrier injection efflciency improved due to out particle aggregation. method isusefu! for ly efficient luminescent having good color purity to a great extent. Reference [1] J.Ritter,P,Kazl, Z. Zhou, M. Stevenson, C. Breen, Y. Niu, I, Song, J. S. Steckel, S. Coe-Sullivan, "Quantum Dots in Lighting Display: From R&D to Product Launch", Proc. IDW'09, pp (2009), [2]P. T. Kazl, J. S. Steckel, M. Cox, C. Reush, D. Ramprad, C. Breen, M. Misic, V. DiFilippe, M. Anc, J. Ritter, S. Coe-Sullivan, "Progress in Developing High Efflciency Quantum Dot Displays", SID Symposium. Digest, Vbl, 38, pp, (2007). [3]P. Kazl, Z. Zhou. M. Stevenson, Y, Niu, C, Breen, J. Perkins, S.-J. Kim, G Mahan, J. Steckel, S. Coe-Sullivan, J, Ritter, "Quantum Dot Light Emitting Diodes for Full-color Active-matrix Displays", Proc. ldw'10, pp (2010). "Full-color [4]J. Perkins, S, Coe-Sullivan, et al., Active-matrix QuantumDet Light Emitting Device Displays", Proc. IDW'11, pp.i (2011). "Realization [5]B. L. Choi et al., Full-Color Quantum Dot Display", Proc. IDW'11, pp (2011). [6]C. H. Lee et al., Light-Emitting "Quantum-Dot Diedes for Full-Color Displays", Prec. IDW'13, pp (2013), [7]J. Jang et al., Light ErnittingDiodes "Quantum-dot for Improvements Brightness Efficiency", Proc. ldw'13, pp (2013). [8]J, Jang et al., Solution Processed Quantum-dot "All Light Emitting Diodes", Proc. IDW'14, pp (2014). [9]J. R. Mers et al,, "High efficiency, patterned, solutien processed quantum dot light-emitting diodes for displays",proc. IDW'14, pp (2014). [10]S.Coe-Sullivan, J. S. Steekel,L. A, Kim, M, G Bawendi, V. Bulovic, "Method for fabricatien saturated RGB quantum dot lightemitting devices", Proceedings efspie, VOI,5739, pp, (2005). [11]S.Coe-Sullivan, W, -K. Weo, M. Bawendi, V. Bulovic, "Electroluminescence from Single Monolayers Nanocrystals in Molecular Organie Devices", Nature, Vbl. 420, pp , (2002). [12]M Ṇakamoto, T. Hegawa, T, Ono, T, Sakai, N, Sakuma, "Low operation fieldemitter arrays using low work function materials fabricated by transfer mold technique", Tech. Digest IEDM'96, pp e (1996). [13]M. Nakameto, T. Hegawa, K. Fukuda, "Uniform, stable integrated field emitter arrays for performance displays vacuum microelectronic switching devices", Tech. Digest IEDM'97, pp (1997). [14]M. Nakamoto K. Fukuda, "Field electron emission from LaB6 TiN emitter arrays fabricatedby transfer mold technique", Appl. Surf. Sci.,Vol, 202, pp , (2002). [15]M,Nakamoto, J.Moon, K, Shirateri, "Lew work function nanometer-erder centrolled transfer mold field-emitterarrays", J.Vac. Sci.Technol. B, Vol.28, pp. C2Bl-C2B4, (2010). "Suitability [16]M. Nakamoto, J. Moon, low-werk-function titanium nitride coated transfer mold field emitter arrays for harsh environment applications", J. Vac, Sci, Technol, B, Vbl. 29, pp. 02Bl12-02Bl17, (2011). [17]M. Nakamoto, J. Moon, "Extremely environment-hard Iow work function transfer-mold fieldemitter arrays", Appl. Surf. Sci,, Vbl.275, pp ,(2013). [18]M. Nakamoto, J. Moon, "Stable, ruggedized, nanometer-erder size transfer mold field emitter array in harsh oxygen radical environment", J. Vac. Sci. Technol. B, Vbl, 33, pp, 03CI CI07-8, (2014). i19]r.matsuhana, M, Nakamoto, "Highly J. Moon, Uniform QuantumDot Light Emitting Diodes", Proc. IDW'13, pp (2013), -25- NII-Electronic NII-Electionic Library Service