Constant-stress accelerated life test of white organic light-emitting diode based on least square method under Weibull distribution

Size: px

Start display at page:

Download "Constant-stress accelerated life test of white organic light-emitting diode based on least square method under Weibull distribution"

Mary Wilkerson
6 years ago
Views:

1 Edh Cowan Unversy Research Onlne ECU Publcaons Pos 4 Consan-sress acceleraed lfe es of whe organc lgh-eng dode based on leas square ehod under Webull dsrbuon J Zhang C Lu G Cheng X Chen J Wu See nex page for addonal auhors.8/ Ths arcle was orgnally publshed as: Zhang J., Lu C., Cheng G., Chen X., Wu J., Zhu Q., Zhang L. (4). Consan-sress acceleraed lfe es of whe organc lgh-eng dode based on leas square ehod under Webull dsrbuon. Journal of Inforaon Dsplay, 5(), Orgnal arcle avalable here Ths Journal Arcle s posed a Research Onlne. hp://ro.ecu.edu.au/ecuworkspos/479

2 Auhors J Zhang, C Lu, G Cheng, X Chen, J Wu, Q Zhu, and Lachang Zhang Ths journal arcle s avalable a Research Onlne: hp://ro.ecu.edu.au/ecuworkspos/479

3 Consan Sress Acceleraed Lfe Tes of Whe OLED Based on Leas Square Mehod under Webull Dsrbuon Janpng Zhang a *, Chao Lu b, Guolang Cheng c, Xao Chen c, Jongle Wu a, Qunzh Zhu a and La-Chang Zhang d a College of Energy and Mechancal Engneerng, Shangha Unversy of Elecrc Power, Shangha 9, Chna; b Deparen of Auoaon Scence and Technology, X an Jaoong Unversy, X an 749, Chna; c Shangha Tany Elecrc CO., LTD, Shangha, 6, Chna; d School of Engneerng, Edh Cowan Unversy, 7 Joondalup Drve, Joondalup, Perh WA 67, Ausrala Currenly, s hard o esae he relably paraeers of organc lgh eng dode (OLED) when conducng lfe es a noral sress, due o he rearkably proved lfe of OLED o housands hours. Ths work adoped hree consan sress acceleraed lfe ess (CSALT) o predc he lfe of whe OLED n a shor e. Webull funcon was appled o descrbe he lfe dsrbuon, and shape paraeers and scale paraeers were esaed by leas square ehod (LSM). Experenal es daa were sascally analyzed by usng self-developed sofware. The lfe of whe OLED predced va hs sofware s well agreeen wh hose repored fro cusoers. Nuercal resuls ndcaed ha he assupons of CSALT are correc and he CSALT s feasble o predc he lfe of whe OLED. Our work confrs ha he lfe of whe OLED ees Webull dsrbuon and ha he acceleraed lfe equaon confors o nverse power law. Furherore, he precse acceleraed paraeers are shown o be parcularly useful o enable a rapd esaon of he whe OLED lfe. Keywords: Acceleraed lfe es; whe OLED; leas square ehod (LSM); Webull dsrbuon; consan sress. Inroducon In recen years, fla panel dsplay (FPD) echnology has ade a grea progress wh he eergng of color oble phone, fla panel elevson and copuer. FPD ncludes lqud crysal dsplay (LCD), plasa dsplay panel (PDP), lgh eng dode (LED), organc lgh eng dode (OLED), and so on. Copared wh oher FPD echnologes, OLED s an nave lghng devce whch does no need backlgh or envronenal lgh. Owng o s advanages such as self-eng, fas response e, wde vewng angle, good low eperaure propery and hgh lunance, OLED dsplay echnology s becong a hospo n he feld of curren dsplay, whch aracs consderable research aenon [-]. Lfee s one of he os poran properes of OLED, whch drecly nfluence s busness prospec []. Durng he pas decade, he lfe propery and relably esaon ehods for OLED have been sgnfcanly nvesgaed by researchers worldwde. JANKOVIC e al. [4] proposed a sple acve-arx organc lgh-eng dode (AMOLED) pxel wh convenonal volage drvng and ably o copensae for he V h shf of hn-fl ranssors Correspondng auhor. Eal: jpzhanglzu@6.co

4 (TFTs), where a sable pxel operaon was acheved by he eployen of dual-gae TFT for OLED drvng. CHANG e al. [5] pu forward a whe organc lgh-eng dode (WOLED) wh color fler ebeddng n a dual-plae OLED dsplay (DOD) srucure proeced by SN x passvaon fl. Tess deonsraed ha hs srucure sgnfcanly proved he lfe of whe OLED. Copared he effcency, hea ressvy and relably of OLEDs wh ITO and IZO as anode, PINATO e al. [6] consdered he aeral selecon of OLED anode and carred ou acceleraed lfe es. Resuls showed ha OLED wh IZO as anode has a hgher relably. SHI e al. [7] revealed he facor affecng he lfee of OLED lghng odule by researchng on he relaonshp beween he eperaure dsrbuon and phooelecrc degradaon characerscs. Wh he nnovaon of he aeral desgn feld, he relably and he lfe of OLED have been proved rearkably. The lfe of os OLED dsplay devces n assve coercal applcaon has greaer han housand hours. For such long lfee, s hard o esae he relably paraeers of OLED when carryng ou lfe es a noral sress, because he lfe es ay las very long e bu only few saples fal [8]. The an lfe es ehods nclude acceleraed degradaon es (ADT) [9-] and acceleraed lfe es (ALT). ALT s a ore coonly used ehod, whch s eployed o reduce es e by ncreasng es sress levels whle keepng falure echans unchanged. ALT can be classfed no several caegores []: consan sress acceleraed lfe es (CSALT), sep sress acceleraed lfe es (SSALT), and progressve sress acceleraed lfe es (PSALT). Aong hese hree caegores of ALTs, CSALT s he os accurae and s also a beer opon f he aouns of he es saples and sresses are que sall. LIU e al. [] presened a desgn approach for sequenal consan-sress acceleraed lfe es (CSALT) wh an auxlary acceleraon facor (AAF), whch can furher aplfy he falure probably of hghly relably esng es a low sress levels whle ananng an accepable degree of exrapolaon for relably nference. LIU e al. [4] seleced he acceleraed ode and acceleraed sress level n pneuac solenod valve ALT by analyzng he sensve sress n hree knds of falure echanss such as wear, fague and agng, carred ou he ALT, and concluded ha he echancal perforance of he solenod valve s ore sable han s elecrcal perforance. In hs sudy, CSALT was perfored o oban he falure e and cuulave falure probables of whe OLED saples, and leas square ehod (LSM) was used o f curves a each sress level. Aferwards, Kologorov-Sov ess were eployed o esfy wheher OLED lfe follows Webull dsrbuon or no. OLED curve of lfe characersc paern can be obaned by LSM, and can verfy ha he OLED lfe characersc paern ees he nverse power law. In addon, whe OLED lfe nforaon can be acqured.. OLED CSALT Plan.. Selecon of Acceleraed Sress OLED s a curren-drvng devce, and curren s he os poran facor nfluencng OLED lfe [8]. Therefore, he curren was seleced as he acceleraed sress of ALT n hs work... Levels and Nubers of Acceleraed Sress The levels and nubers of acceleraed sress are wo ajor facors. Boh ensure ha he es resuls scenfcally reflec OLED lfe. The dfference beween he hghes sress and he lowes sress should be enlarged under he acceleraed sress condon n order o guaranee ha boh precson and effcency of he ess. In order o avod he

5 presen of a new falure echans, he hghes sress should be lower han he ulae level deerned by he aeral srucure and echnques of he produc. Accordng o he prncple of relably, he nu nuber of acceleraed sress n lfe es should be no less han hree. The M7 whe OLED xed wh red, green, and blue colors were used n hs work. The hree sress levels were seleced as follows: I = 9.64 A, I = 7.9 A, I =.58 A. In addon, he noral workng curren of es saples s I =.A... Falure Creron and Tes End Te The lfe of OLED devce can be defned as he duraon when he OLED lunance decreases o below 5% of nal lunance. Accordng o he creron, he falure e of each es saple was recorded. When all he saples a he hree sress levels faled, he ess were ernaed.. OLED CSALT Theory Model.. Basc Assupons Assupon : For each sress level I ( =,,,), whe OLED lfe follows Webull dsrbuon, and he dsrbuon funcon can be expressed as F( ) exp[ ( ) = - - ], > () h here s he shape paraeer whch affecs he geoerc shape of he Webull probably densy curve; η s he scale paraeer whch drecly deernes he curve s soohness. Assupon : The OLED falure echans reans unchanged whle he sress ranges fro I o I. Snce he echans of whe OLED s refleced by he shape paraeer of Webull dsrbuon, he shape paraeer a each sress level I should be unchanged, whch eans = = () = Assupon : Inverse power law can be used o esae he workng lfe characerscs of elecrcal coponens. Whe OLED acceleraed odel sasfes he nverse power law. Naely, he relaonshp beween scale paraeer η and curren sress level I s wren as lnη = α + βln I () Where α and β are acceleraed paraeers... Esaon of Webull Paraeers Equaon () can be ransfored as If ln ln[ F ( )] = ln lnη (4) y = ln ln[ F ( )] x= ln (5) a = b = lnη Equaon (4) can be splfed as he lnear relaonshp for y = ax + b (6) Afer he falure e k, a I ( =,, ) s sequenced, he correspondng cuulave falure probably F ( k, ) can be calculaed by usng he followng edan rank forula k. F ( k, ) =, k=,,, n (7) n +.4 where n = n =, n = 9. Therefore, he es daa can be wren as (, F ( )), k=,, n (8) k, k, Accordng o Equaon (5) and (8), one can oban (ln,ln ln[ F ( )] ) = ( x, y ) (9) k, k, k, k,

6 By applyng LSM o Equaon (9), he coeffcens expressed as a and b ( =,,) can be n n n a = n n b = yk, / n a xk, / n k= k= x y ( x y )/ n k, k, k, k, k= k= k= n n xk, ( xk, ) / n k= k= () Cobned Equaon (5) wh (), he shape paraeer and he scale paraeer are respecvely expressed as η a = a, h = exp( - b / a ) () The deernaon coeffcens of x k, and y are wren as k, n n n [ x y ( )/ ] k, k, x k, y n k, k= k= k= = n n n n x k, x n k, y y n k, k, k= k= k= k= I.. Lfe Esaon If OLED lfe confors o Webull dsrbuon, he calculaon forula of OLED average lfe µ and edan lfe.5 are respecvely expressed as = hg ( + ),.5 = h (ln ) ().5 where Γ () s gaa funcon; η s he scale paraeer esaed a I. Accordng o Assupon (Secon.), he shape paraeer s obaned as he weghed average of, ha s = = n / n (4) = 4. Tes Daa For he M7 whe OLED xed wh red, green and blue colors, OLED CSALTs were carred ou accordng o he acceleraed es heory R () and plan. The falure e daa of all whe OLED [ ( ) / ][ ( ) / ] saples a I ( =,, ) are lsed n Table. Table. The falure e of he esed saple under consan-sress a dfferen currens. Curren Sress/A 4 Falure Te/h 5 I = I = I = OLED Lfe Predcon Due o he calculaon coplexy n aspec of lfe esaon, a whe OLED lfe es sofware developed by he auhors was used o process and analyze he es daa. The sofware has a seres of advanages such as splcy, speedy, accuracy and generaly. 5.. Daa Processng for CSALT The consan-sress es daa lsed n Table are processed by self-developed sofware, and he sascs curves fed by LSM are ploed n Fgure. The shape paraeer, scale paraeerη, and he deernaon coeffcen

7 R of fng curve a each curren sress level can be obaned by he Equaons ()-(). These resuls are presened n Table. I s found ha R calculaed a each curren sress I ( =,,) approaches o, whch deonsraes ha he degree of lnear fng s hgh. values of he K-S es a hree acceleraed sresses are calculaed by he self-developed sofware as follows: a =.4 < D =., a =.86 < D.,., =., a =.6 < D =.9..,9 Hence, s verfed ha he K-S ess a each sress I ( =,, ) pass. 5.. Acceleraed lfe equaon Daa pons (ln I, ln η ) ( =,,) can be ploed and fed no a lnear curve by LSM, as shown n Fgure. The acceleraed paraeers obaned by LSM are α =.684, β = As such, he acceleraed lfe equaon s expressed as lnη =.684 ln I (5) Fgure. Sascal curves of consan-sress daa Table., η and R a dfferen curren sress levels Curren I = 9.64 I = 7.9 I =.58 Sress/A η R Kologorov-Srnov Tes Accordng o K-S heory [5], greaer sgnfcance level ( a =. ) was seleced due o led saples. K-S es was eployed o verfy wheher he OLED lfe follows Webull dsrbuon a each curren sress level I ( =,, ) or no. The Fgure. Curve of OLED lfe characersc paern The deernaon coeffcen R n Fgure s.999 ha s very close o, whch shows ha he degree of lnear fng s hgh. The resul also confrs ha he acceleraed odel fully obeys he nverse power law OLED Lfe Predcon a he Noral Workng Sress Afer subsung I =.A no Equaon (5), OLED scale paraeer a noral workng sress can be obaned as: h = h. Cobnng ( =,,) n Table wh Equaon (4), one can ge OLED shape paraeer

8 a noral workng sress = Therefore, accordng o Equaon (), he average lfe µ and he edan lfe.5 of whe OLED can be calculaed as follows: µ =5.h,.5 = 597h. The arke perforance deonsraes ha he lfe of whe OLED, whch was seleced as saples n he acceleraed es, s abou 6 housand hours. Therefore, whe OLED lfe esaed by consan sress acceleraed lfe ess (CSALT) n hs work s very close o he clen feedback daa wh he dfference n srucure, aeral and echnques beween OLED saples and producs excluded. 6. Conclusons Fro hree CSALTs and sascal analyss for OLED, he followng an conclusons can be drawn. ) The resuls of es sasc analyss verfy ha whe OLED lfe sasfes Webull dsrbuon and he acceleraed lfe odel follows nverse power law. ) The self-developed sofware could be used o splfy sascal analyss of OLED acceleraed lfe es and predc whe OLED lfe precsely. ) The acqured lfe nforaon can provde engneers wh poran gudelnes o prove relably and qualy of OLED producs. Acknowledgen Ths sudy was fnancally sponsored by he Progra of Shangha Subjec Chef Scens (B ype) (XD45); he Foundaon of Shangha Coee of Scence and Technology, Chna (656, dz87, 9DJ44); he Innovaon Progra of Shangha Muncpal Educaon Cosson (4ZZ54, ZZ); he Key Fund of Shangha Scence Technology Coee (65); he Naonal Naural Scence Foundaon of Chna (5765, 597). References [] Y. Y. Lu, W. D. Geng, and Y. P. Da, Journal of Cenral Souh Unversy, 9, 76 (). [] J. I. Ha, H. O. Kyong, L. Inhwan, H. R. Do, M. C. Sang, N. K. Keu, D. K. Hye, and K. K. OH, IEEE Trans. Elecron. Dev., 57, (). 请统一文献格式, 有的杂志名缩写, 有的用全名具体参考缩头杂志的文献格式 [] T. H. Chang, and S. Q. Peng, Vacuu & Cryogencs, 4, 5 (8). [4] N. D. Jankovc, and V. Brajovc, Elecroncs Le., 47, 456 (). [5] W. H. Chang, K. K. Hwa, S. P. Hee, H. P. Sung, J. S. Chang, S. C. Hong, and C. K. Woo, Journal of Dsplay Technology, 5, 54 (9). [6] A. Pnao, M. Meneghne, A. Ceser, N. Wrachen, A Tazzol, E. Zanon, and G. Meneghesso, IEEE CFP9RPS-CDR 47h Annual Inernaonal Relably Physcs Syposu, Monreal, 5 (9). [7] Y. F. Sh, J. X. Yang, W. Q. Zhu, S. Z. L, K. J Ma, F. Wang, and M. L. Zhung, Chna Illunang Engneerng Journal,, 7 (). [8] J. P. Zhang, F. Lu, Y. Lu, W. Helen, W. L. Wu, and A. X. Zhou, IEEE Trans. Elecron. Dev., 59, 4 (). [9] I. P. Jong, and J. B. Suk, IEEE Trans. Relably, 59, 74 (). [] F. K. Wang, and T. P. Chu, Mcroelecroncs Relably, 5, (). [] X. Lu, and L. C. Tang, Qualy and Relably Engneerng Inernaonal, 6, 86 (). [] J. P. Zhang, and R. T. Wang, Journal of Tesng and Evaluaon, 7, 6 (9). [] X. Lu, and L. C. Tang, Journal of Sascal Plannng and Inference, 4,968 (). [4] D. F. Lu, Z. Y. Tang, Z. C. Pe, and J. Peng, Machne Tool & Hydraulcs, 8, 6 ().

9 [5] Y. Kang, H. J. Ca, and S. B. Song, Journal of hydroelecrc engneerng,, 5 ()

THEORETICAL AUTOCORRELATIONS. ) if often denoted by γ. Note that

THEORETICAL AUTOCORRELATIONS. ) if often denoted by γ. Note that THEORETICAL AUTOCORRELATIONS Cov( y, y ) E( y E( y))( y E( y)) ρ = = Var( y) E( y E( y)) =,, L ρ = and Cov( y, y ) s ofen denoed by whle Var( y ) f ofen denoed by γ. Noe ha γ = γ and ρ = ρ and because