Degradation Evaluation of αIGZO TFTs

液晶常用的场效应管英文回答：Thin-film transistors (TFTs) are a type of field-effect transistor (FET) that is commonly used in liquid crystal displays (LCDs). TFTs are used to control the flow of current through each pixel in an LCD, which in turncontrols the brightness and color of that pixel.There are two main types of TFTs used in LCDs: amorphous silicon (a-Si) TFTs and polycrystalline silicon (p-Si) TFTs. A-Si TFTs are made from a thin film of amorphous silicon, which is a non-crystalline form of silicon. P-Si TFTs are made from a thin film of polycrystalline silicon, which is a crystalline form of silicon.A-Si TFTs are less expensive to manufacture than p-Si TFTs, but they also have lower performance. P-Si TFTs have higher performance than a-Si TFTs, but they are also moreexpensive to manufacture.The choice of which type of TFT to use in an LCD depends on the desired performance and cost constraints.For low-cost applications, a-Si TFTs are typically used.For high-performance applications, p-Si TFTs are typically used.In addition to a-Si TFTs and p-Si TFTs, there are alsoa number of other types of TFTs that can be used in LCDs. These include cadmium selenide (CdSe) TFTs, zinc oxide (ZnO) TFTs, and indium gallium zinc oxide (IGZO) TFTs. Each typeof TFT has its own unique advantages and disadvantages, and the choice of which type to use depends on the specific application.中文回答：在液晶显示器（LCD）中，薄膜晶体管（TFT）是一种常用的场效应晶体管（FET）。

Light induced instabilities in amorphous indium–gallium–zinc–oxide thin-filmtransistorsMd Delwar Hossain Chowdhury, Piero Migliorato, and Jin JangCitation: Applied Physics Letters 97, 173506 (2010); doi: 10.1063/1.3503971View online: /10.1063/1.3503971View Table of Contents: /content/aip/journal/apl/97/17?ver=pdfcovPublished by the AIP PublishingArticles you may be interested inInvestigation of zinc interstitial ions as the origin of anomalous stress-induced hump in amorphous indiumgallium zinc oxide thin film transistorsAppl. Phys. Lett. 102, 173502 (2013); 10.1063/1.4803536Light/negative bias stress instabilities in indium gallium zinc oxide thin film transistors explained by creation ofa double donorAppl. Phys. Lett. 101, 123502 (2012); 10.1063/1.4752238Electrical instability of amorphous indium-gallium-zinc oxide thin film transistors under monochromatic lightilluminationAppl. Phys. Lett. 100, 243505 (2012); 10.1063/1.4729478Effect of annealing time on bias stress and light-induced instabilities in amorphous indium–gallium–zinc-oxidethin-film transistorsJ. Appl. Phys. 110, 114503 (2011); 10.1063/1.3662869Environment-dependent thermal instability of sol-gel derived amorphous indium-gallium-zinc-oxide thin filmtransistorsAppl. Phys. Lett. 98, 152109 (2011); 10.1063/1.3580614This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: /termsconditions. Downloaded to IP:Light induced instabilities in amorphous indium–gallium–zinc–oxide thin-film transistorsMd Delwar Hossain Chowdhury,1Piero Migliorato,1,2and Jin Jang 1,a ͒1Department of Information Display,Advanced Display Research Center,Kyung Hee University,Seoul 130-701,Republic of Korea 2Department of Engineering,Electrical Engineering Division,Cambridge University,Cambridge CB30F A,United Kingdom͑Received 15July 2010;accepted 28September 2010;published online 28October 2010͒The effect of exposure to ultraviolet radiation on the characteristics of amorphous indium–gallium–zinc–oxide thin-film transistors ͑TFTs ͒fabricated by sputtering is investigated.After illumination with 1.5mW cm −2of 365nm radiation,in the absence of any bias stress,a persistent negative shift in the characteristics is observed in the dark.The magnitude of the shift increases with exposure time,saturating after about 10min.Under these conditions the subthreshold exhibits a rigid shift of around 3.6V and 7.5V for TFTs with an active layer thickness of 20nm and 50nm,respectively.The shift in the dark increases ͑decreases ͒when a negative ͑positive ͒bias stress is applied under illumination.The instability behavior caused by exposure to light,in the absence of any bias stress,can be explained on the basis of ionization of neutral oxygen vacancies.©2010American Institute of Physics .͓doi:10.1063/1.3503971͔The interest in amorphous indium–gallium–zinc–oxide ͑a-IGZO ͒thin-film transistors ͑TFTs ͒for applications in ac-tive matrix displays,1has generated a large body of experi-mental and theoretical studies devoted to this material.2For applications,reliability and stability are of primary concern and,indeed,a number of investigations of reliability under bias stress have been published.3–7An important issue for devices that may operate in a bright light environment is whether exposure to light can affect reliability.While the effect of the combined bias stress and illumination has been recently investigated,8the role of light exposure itself has not been established.We report here a new instability behavior which is caused by exposure to light,in the absence of any bias stress.An explanation,based on ionization of neutral oxygen vacancies is proposed.The inverted staggered a-IGZO TFTs were fabricated on SiO 2-buffered glass substrate.A 60nm thick molybdenum gate was produced by sputtering.The gate insulator,a 200nm thick SiO 2film,was deposited by plasma enhanced chemical vapor deposition ͑PECVD ͒,at a substrate tempera-ture ͑T s ͒of 380°C.An a-IGZO active layer was direct cur-rent ͑DC ͒sputtered from the target In 2O 3:Ga 2O 3:ZnO =1:1:1mol %,in an oxygen partial pressure O 2/͑O 2+Ar ͒=0.66and at the substrate temperature of 200°C.The IGZO was coated with a 100nm PECVD SiO 2layer at T s of 200°C and patterned into islands.Source and drain contact regions were defined in the back SiO 2,followed by 150nm molybdenum contacts deposition and patterning.Finally the overall structure was passivated with a 200nm thick SiO 2layer,deposited at 200°C,and annealed at 250°C for 2h in vacuum.The TFT I–V characteristics were measured at room temperature,using Agilent 4156C semiconductor analyzer.All TFTs had the same W/L geometry as follows:55␮m /11␮m.For devices with an active layer thickness d=20nm,typical threshold voltage ͑from I D versus V GS forV DS =0.1V ͒,mobility,and subthreshold swing were as fol-lows:5.95V ,7.3cm 2V −1s −1,and 0.157V/dec.For light illumination a UV light-emitting diode ͑LED ͒,␭=365nm,and a visible LED ␭=530nm were used.Figures 1shows the effect of repeated +20and Ϫ20V bias stress in 10min interval on the transfer characteristics of a TFT,before exposure to UV light.This test is performed in order to exclude the presence of effects associated with mo-bile charge in the gate dielectric and back channel passiva-tion.The inset in the figure shows the gate voltage shift for the repeated stress,for I D =10−11A.The very small shifts observed underscore the good stability of the devices and the effectiveness of passivating the back channel region.6Figure 2͑a ͒shows the effect of exposure to 1.5mW cm −2of ␭=365nm ͑3.4eV ͒UV light,for 10min,a ͒Author to whom correspondence should be addressed.Electronic mail:jjang@khu.ac.kr.FIG.1.͑Color online ͒Transfer characteristics of a virgin TFT with active layer thickness d=20nm,for V DS =1V,upon application of 17alternate bias stresses:V G ͑stress ͒=+20V,Ϫ20V;duration of each alternate stress:10min;V D ͑stress ͒=0V.Only five of the overlapping characteristics are shown,including the initial unstressed one.Inset:Gate voltage shift for successive stress,for I D =10−11A.APPLIED PHYSICS LETTERS 97,173506͑2010͒0003-6951/2010/97͑17͒/173506/3/$30.00©2010American Institute of Physics 97,173506-1 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: /termsconditions. Downloaded to IP:for a TFT with active layer d=20nm.Similar effects,albeitreduced in magnitudes,are caused by prolonged ͑12h ͒ex-posure to the ␭=530nm radiation.The characteristic duringillumination shows a sizeable increase in the subthresholdcurrent,which is due to the optically generated free elec-trons.The off current also increases and a minimum appearsbetween the on and the off region.After light exposure,thedark characteristic relaxes quickly ͑within less than 1min ͒tothe one labeled as ͑3͒.Curve ͑3͒presents a rigid shift ⌬V G=3.4V with respect to the original ͑1͒in the subthresholdregion ͑I D =10pA ͒.The shift,hereafter referred to as thedark shift,is reduced upon approaching the threshold volt-age,so that V th =0.9V.We have characterized this lightinduced behavior in five nominally identical samples andfound subthreshold shifts of 3.6Ϯ0.6V.The magnitude ofthe shift increases with exposure time,saturating after about10min.The effect is not reversible at room temperature,asubthreshold dark shift of 3V remaining after -plete recovery is achieved by annealing at 250°C for 2h.Figure 2͑b ͒shows the effect of exposure to light under thesame condition as in Fig.2͑a ͒,for a TFT with active layerthickness d=50nm.The shift as a function of I D is shown inthe inset of Fig.2͑b ͒as follows:͑i ͒under illumination and͑ii ͒in the dark,for the two cases d=20and 50nm,indicating that the shift magnitude scales approximately with d.Figure 3shows the effect of simultaneous exposure to 365nm radiation,1.5mW cm −2,and bias stress.Transfer characteristics are shown for the following conditions:͑i ͒before exposure to light and stress;͑ii ͒after 10min exposure and V G ͑stress ͒=−20V,V D ͑stress ͒=0V,with light on;͑iii ͒60s after end of previous light exposure/stress;͑iv ͒after 10min exposure and V G ͑stress ͒=+20V,V D ͑stress ͒=0V,with light on;and ͑v ͒60s after end of previous light exposure/stress.The relaxation is monitored in the dark without bias stress.By comparing the curves under illumina-tion with those of Fig.2͑a ͒,one can see that for V G ͑stress ͒=−20V the subthreshold current is higher,the opposite being true when V G ͑stress ͒=+20V is paring the curves after relaxation,it is apparent that V G ͑stress ͒=−20V increases the subthreshold negative shift from Ϫ3.4to Ϫ5V at I D =10pA,whereas V G ͑stress ͒=+20V reduces it to 0.5V .The scaling of the light induced shift with active layer thickness rules out injection into the gate dielectric and/orgeneration of defects at the interface.Instead it is consistentwith light-induced generation of positive charge throughout the active layer.Considering the value 9of the absorption coefficient at the wavelength of excitation ␣Ϸ104cm −1,it is reasonable to expect that the charge is uniformly distributed and in similar concentrations,in 20and 50nm thick devices.Since the effect is not reversible at room temperature,the charge must be associated with metastable defects.The pres-ence of oxygen vacancies is well documented through opti-cal electron paramagnetic resonance ͑EPR ͒experiments in ZnO oxide single crystals.10,11These defects bind two elec-trons in their electrically neutral state V O 0and the ground state energy has been estimated by density functional theory in ZnO ͑Refs.12–14͒and a-IGZO,15indicating that the neu-tral vacancy V O 0is a deep donor.Ionization of V O 0,resulting in the singly ionized state V O +,with transition energy ␧͑0/+͒=E V +0.9eV,12,14and doubly ionized state V O ++,with tran-sition energy ␧͑0/++͒=E V +2.2/2.4eV,13–15is accompanied by substantial lattice relaxation.Due to the latter,the energy levels of V O ++are degenerate with the conduction band 12,15and expected to be metastable,since the free electrons oc-cupy lower lying states near the band minimum and need to be activated,thermally or otherwise,in order to re-establish the thermal equilibrium concentration of neutral oxygen vacancies.12Persistent photoconductivity ͑PPC ͒observed in ZnO has been explained on the basis of this model.12PPC has been recently reported in a-IGZO film fabricated byKrF FIG.2.͑Color online ͒͑a ͒Effect of exposure to 365nm radiation,1.5mW cm −2,in the absence of bias,for a TFT with active layer thickness d=20nm.͑b ͒Same for a TFT with d=50nm.Transfer characteristics,for V DS =1V:͑1͒before exposure to light;͑2͒after 10min exposure,with light on;and ͑3͒in the dark,60s after light was switched off.Inset:gate voltage shift ⌬V G vs I D for two TFTs with active layer thickness 20and 50nm;͑i ͒after 10min exposure,with light on,from curve ͑2͒;and ͑ii ͒in the dark from curve ͑3͒.The shift scales with the active layerthickness.FIG.3.͑Color online ͒Effect of simultaneous exposure to 365nm radiation,1.5mW cm −2,and bias stress for a TFT with active layer thicknessd=20nm.Transfer characteristics,for V DS =1V:͑i ͒before exposure to light and stress;͑ii ͒after 10min exposure and V G ͑stress ͒=−20V,V D ͑stress ͒=0V,with light on;͑iii ͒60s after end of previous lightexposure/stress;͑iv ͒after 10min exposure and V G ͑stress ͒=+20V,V D ͑stress ͒=0V,with light on;and ͑v ͒60s after end of previous lightexposure/stress. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: /termsconditions. Downloaded to IP:laser deposition.9The duration of the on transients͑over 20min͒is similar to that we observe for the saturation of ⌬V G under illumination.However,in contrast with the per-sistence of the shift in our TFTs,PPC in the above work9is reported to disappear after50min at room temperature.The singly ionized vacancy V O+in ZnO is also expected to be metastable on theoretical grounds12and on the basis of EPR experiments.11In the latter,V O+has been detected only during and after exposure to␭Ϸ500nm light,causing photoionization of neutral oxygen vacancies.A period of several minutes was required at room temperature in the dark for the concentration of V O+to decay to zero.11It is therefore conceivable that the light induced effects observed in the present work are associated with generation of ionized oxy-gen vacancies.16These can be produced,under band to band optical excitation,through competitive hole capture by neu-tral oxygen vacancies.The rapid initial relaxation of the characteristics after illumination can be explained with hole-electron recombination via other nonmetastable gap states.In the subthreshold region,assuming full depletion,we have⌬V G=qC OX−1N T+d,where q is the electron charge,C ox the gate oxide capacitance,N T+the concentration of ionized oxy-gen vacancies,and d the active layer thickness.From⌬V G for I D=10−11A in curve͑3͒of Fig.2͑a͒,wefind N T+=1.8ϫ1017cm−3.However,when theflat band condition is ap-proached,the active layer will become partially depleted and the shift would be reduced.Application of positive bias stress during illumination reduces the dark shift,since the increased free electron density favors the neutral state In other words,the reactions V0++e−→V0and V02++2e−→V0 are displaced to the right.Vice versa,negative bias stress increases the holes concentration,favoring ionized states. This can explain the behavior shown in Fig.3.On the basis of the present data,it is not possible to establish whether oxygen vacancies are native or created,as well as ionized, during exposure to light.This is an important point for future investigation in view of its relevance for the stability of these devices under operating conditions.In conclusion,we have presented evidence of light in-duced instabilities in a-IGZO TFTs,in the absence of bias stress.Application of negative bias stress during light expo-sure enhances,whereas positive bias stress reduces,the ef-fect of light.The results can be explained on the basis of light induced generation of metastable defect states associ-ated with ionized oxygen vacancies.The possibility that these defects are also involved in dark bias stress instabilities warrants further investigation.On the basis of the above re-sults,the use of a light shield appears mandatory in all ap-plications where these devices are subjected to prolonged exposure to light.This work was supported by the Industrial Strategic Technology Development Program͑Project No.10035225, Development of Core Technology for High Performance AMOLED on Plastic͒funded by MKE/KEIT.1J.K.Jeong,J.H.Jeong,J.H.Choi,J.S.Im,S.H.Kim,H.W.Yang,K. N.Kang,K.S.Kim,T.K.Ahn,H.J.Chung,M.Kim,B.S.Gu,J.S.Park, Y.G.Mo,H.D.Kim,and H.K.Chung,SID Int.Symp.Digest Tech. Papers2008,1.2T.Kamiya and H.Hosono,Asia Materials2,15͑2010͒.3T.C.Fung,K.Abe,H.Kumomi,and J.Kanicki,J.Disp.Technol.5,452͑2009͒.4K.Nomura,T.Kamiya,M.Hirano,and H.Hosono,Appl.Phys.Lett.95, 013502͑2009͒.5J.M.Lee,I.T.Cho,J.H.Lee,and H.I.Kwon,Appl.Phys.Lett.93, 093504͑2008͒.6J.K.Jeong,H.W.Yang,J.H.Jeong,Y.G.Mo,and H.D.Kim,Appl. Phys.Lett.93,123508͑2008͒.7M.E.Lopes,H.L.Gomes,M.C.R.Medeiros,P.Barquinha,L.Pereira, E.Fortunato,R.Martins,and I.Ferreira,Appl.Phys.Lett.95,063502͑2009͒.8M.K.Ryu,S.H.K.Park,S.H.Yang,C.W.Byun,O.S.Kwon,E.S. Park,K.I.Cho,and C.S.Hwang,SID Int.Symp.Digest Tech.Papers 2010,1.9D.H.Lee,K.I.Kawamura,K.Nomura,H.Yanagi,T.Kamiya,M.Hirano, and H.Hosono,Thin Solid Films518,3000͑2010͒.10L.S.Vlasenko and G.D.Watkins,Phys.Rev.B71,125210͑2005͒.iho,L.S.Vlasenko,and M.P.Vlasenko,J.Appl.Phys.103,123709͑2008͒.ny and A.Zunger,Phys.Rev.B72,035215͑2005͒.13A.Janotti and C.G.Van de Walle,Phys.Rev.B76,165202͑2007͒.14S.J.Clark,J.Robertson,ny,and A.Zunger,Phys.Rev.B81, 115311͑2010͒.15W.J.Lee,B.Ryu,and K.J.Chang,Physica B404,4794͑2009͒.16B.Ryu,H.K.Noh,E.A.Choi,and K.J.Chang,Appl.Phys.Lett.97, 022108͑2010͒.This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: /termsconditions. Downloaded to IP:。

高可靠性Cu BCE a-IGZO TFTs的制作王晓;葛世民;李珊【摘要】背沟道刻蚀型(BCE)非晶氧化铟镓锌薄膜晶体管(a-IGZO TFT)具有工艺简单、寄生电容小以及开口率高等优点,但BCE IGZO器件背沟道易受酸液和等离子体损伤,进而引起TFT均匀性和稳定性等方面问题,随着GOA技术的导入,对T FT 器件电学性能的均匀性和稳定性提升的要求也日益迫切,因此开发高信赖性BCE IGZO T FT是技术和市场的迫切要求.本文主要分析了基于IGZO的背沟道刻蚀型薄膜晶体管电学性质,通过优化钝化层材料,色阻材料以及GOA TFT结构等削弱因背沟道水汽吸附引起的器件劣化,偏压温度应力测试结果显示优化后的TFT展现了良好的稳定性——在80℃,栅极30 V负向偏压条件下,2000 s的ΔVth小于1 V.最终,利用优化的IGZO TFT制作了2159.mm(85 in)8K4K 120 Hz液晶显示器.【期刊名称】《液晶与显示》【年(卷),期】2018(033)011【总页数】6页(P925-930)【关键词】背沟道刻蚀型非晶氧化物薄膜晶体管;215.9mm(85in);8K4K;GOA 【作者】王晓;葛世民;李珊【作者单位】陕西科技大学电气与信息工程学院,陕西西安710049;深圳华星光电半导体显示技术有限公司,广东深圳518132;【正文语种】中文【中图分类】TN141.91 IntroductionWith the development of large size, high resolution and low power for Flat Panel Displays (FPD), Thin-Film Transistor (TFT) as the switching element of FPD has attracted much concerns by researchers. As a promising alternative to hydrogenated amorphous Si-based TFTs and low temperature poly-silicon (LTPS)-based TFTs in large scale liquid crystal displays (LCD) or transparent organic light emitting displays (OLED), the Indium-gallium-zinc-oxide (IGZO) TFTs have the advantages of high mobility, high transmittance, large scale uniformity, reasonable on/off ratio and large area deposition at room temperature [1-3], and have been attracting considerable attention for next generation FPD. As the PPI of AMLCD has increased, the aperture ratio and signal delay of the gate and data lines are main issues. Therefore, back-channel etched (BCE) structure TFT is widely used for its capability for small TFT size and low cost[4-6].The parasitic capacitance could be also decreased by using BCE-structure and the signal distortion will be reduced. Replacing Al with Cu can reduce the RC delay and contact resistance. However, it is very difficult to avoid the back channel damage from the source/drain wet etch process and obtain good device reliability.Nowadays,gate driver on array (GOA) technology is widely adopted for its advantages of low cost, narrow bezel and better yield rate of module. In the meantime, it brings great challenges to the electrical characteristics of TFTs and the reliability of array process. An obvious threshold voltage (VTH)shift could lead to the failure of GOA function.Thus, to achieve Cu BCE-structure, IGZO TFTs with excellent device characteristics and reliability is crucial for a high PPI 215.9 mm(85 in) 8K4K 120 Hz GOA LCD. In this work, an optimized process through modifying the passivation layer and optimizing the selection of color filter material and design of GOA TFT structure are introduced. Finally, a high performance 215.9 mm(85 in) 8K4K 120 Hz GOA LCD was demonstrated.2 ExperimentIn this paper, we fabricate the BCE-structure TFTs because of its shorter channel length and can be manufactured with a smaller number of photo masks. Figure 1 shows the schematic diagram of BCE-structure IGZO TFT with a PSVA display mode. Glass with sizes of 2 500 mm×2 200 mm×0.5 mm was used as the substrate material in Gen 8.5 system. The Mo/Cu double layer of 14 nm/500 nm thick was first deposited by sputtering to serve as the gate metal and then the gate insulator SiNx/SiOx dual-layer with the thickness of 300 nm/100 nm was deposited by plasma-enhanced chemical vapor deposition (PECVD). Then amorphous IGZO film of 50 nm thick was deposited on the top of gate insulator by AC sputtering at room temperature. After defining the active layer region, Mo/Cu was then deposited and formed as the Source/Drain(S/D) electrodes. SiOx film with the thickness of 300 nm as the passivation layer (PV1 layer) was then deposited. Next, color filter RGB was coated and patterned. Then SiNx film of 100 nm thick as the PV2 layer was then deposited. Finally, the pixel electrode using ITO was deposited followed by annealing.The channel length ofthe fabricated a-IGZO TFTs are 6 μm. I-V characteristics and reliability for the positive and negative gate bias temperature stress (PBTS and NBTS) were measured by Agilent B1505 precision semiconductor parameter analyzer or Keithley 4200. PBTS and NBTS were performed under gate voltage (Vg) of ±30 V, while drain voltage (Vd) of 0 V at 80 C using hot plate. The duration was 2 000.Fig.1 Schematic cross-section view of a BCE-structure a-IGZO TFT3 Results and DiscussionSince it is very difficult to avoid H2O molecules adsorbing on the back channel of the BCE-structure TFT, the VTH negative shift of GOA TFT is a main issue for the GOA function. To solve this problem, the passivation layers, the selection of color filter material and design of GOA TFT structure are three key factors.3.1 Modifying the passivation layerIn our previous work, BCE a-IGZO TFT with a dense passivation layer by adjusting the N2O/SiH4 ratio and reducing deposit rate during the PECVD process showed good environment stability[7]. In this work, we continued to examine the effect of the deposit rate during the PV1 PECVD process on the electrical characteristics of BCE-structure IGZO TFTs. The a-IGZO TFT prepared with identical procedure except different deposit rate of PV1 layers served by controlling the N2O/SiH4 ratio from 45 to 75. Then, the electrical characteristics of the above device were studied. Through lots of experiments, we have found that slower deposit rate could lead to lessΔVTH negative shift value of NBTS, but more ΔVTH positive shift value ofPBTS. As we know, the PV1 layer with fast deposit rate is not dense enough to avoid H2O molecules. H2O molecules adsorbing on the back channel could significantly increase free carrier concentration[8-12]. However, too slow deposit rate of PV1 layer could lead to the excess oxygen existing in IGZO layer. Since the excess oxygen are preferentially forming non-bridging oxygen or dangling oxygen bonds which could lead to the trap of electron carriers, thus obvious positive shift of VTH occurs both in initial VTH and during PBTS.Figure 2 shows the diagrammatic sketch of the water adsorption on the a-IGZO surface and electron carriers trapped by non-bridging oxygen or dangling oxygen bonds respectively. It seems that the performance of BTS is a balance between H2O molecules adsorbing on the back channel and non-bridging oxygen or dangling oxygen bonds in IGZO layer.(a) Water adsorption on the a-IGZO surface(b) Trap of electron carriersFig.2 Diagrammatic sketch of the water adsorption on the a-IGZO surface(a) and electron carriers trapped by non-bridging oxygen or dangling oxygen bonds(b), respectively.Through lots of experiments, a preferred PV1 layer was obtained. The optimized TFT with a preferred PV1 layer showed better BTS performance. The ΔVTH shift value of +/-30 V, 80 ℃, 2 000 s BTS results of the optimized-PV1 TFT device were about +1.18 V and -0.90 V. Figure 3 shows the transfer characteristics of above TFT device under PBTS and NBTS.(a) PBTS(b) NBTSFig.3 Transfer characteristics of a-IGZO TFT under PBTS(a) andNBTS(b)3.2 Optimizing the selection of color filter materialSince COA (color filter on array) process was applied, color filter would be on the top of PV1 layer of TFT. Because of the unavoidable existence of cracks inside PV2 layer, the adsorption/desorption dynamics of oxygen and water molecules through color filter onto the back-channel region of the oxide transistor might play an important role during bias stress. The a-IGZO TFT prepared with identical procedure except two different kinds of color filter material served as control. These two kinds of devices were respectively labeled as “TFT-1” and “TFT-2”.Figure 4 shows the transfer characteristics (Id-Vg) of TFT-1 and TFT-2 under NBTS at 80 ℃ using hot plate. The ΔVTH shift value of TFT-1 and TFT-2 under NBTS were about -2.4 V and +0.3 V respectively. The TFT-1 showed large ΔVTH shift. The specific reason that leads to this obvious difference is not studied in this paper and needs to be investigated further. Nevertheless, we can still deduce that optimizing the selection of color filter material is necessary to obtain a better device reliability.(a) NBTS of TFT-1(b) NBTS of TFT-2Fig.4 Transfer characteristics of TFT-1(a) and TFT-2(b)3.3 Optimizing the design of GOA TFT structureThe effect of the design of GOA TFT structure on the device reliability could not be ignored. In this work, the a-IGZO TFT prepared with identical procedure except two different TFT structures served as control. These two kind s of devices were respectively labeled as “STD” and “DSD” device.Figure 5 show the TFT structures of the above device respectively. Then,the electrical characteristics of STD device and DSD device were studied.To satisfy almost the same Ion for the need of specific GOA TFT, the W size of DSD device should be about 5 times of STD device.(a) STD device: W/L=100/6(b) DSD device: W/L=250/6+250/6Fig.5 TFT structures of STD device(a)and DSD device(b)Figure 6 show the transfer characteristics (Id-Vg) of the two devices respectively, measured in 80 C afterstorage. Four TFTs of each kind device were measured. The STD Device showed serious negative VTH shift. The above results may be directly attributed by the water adsorption on the a-IGZO surface. When the d evice works under NBTS, the ΔVTH shift wouldbe absolutely more obvious. However, for DSD Device, no obvious negative VTH shift was found. The design of DSD device could lead to low Vds in two each separated channel which could reduce the effect of DIBL (Drain Induced Barrier Lowering). When the DSD device works under NBTS, the negative VTH shift value is less.Fig.6 Transfer characteristics of STD device and DSD device.Based on the same theory, for a groups of fixed W/L ratio TFTs, the TFTs with a long channel length have better device reliability, even the W size is also increased. These two different channel length of devices were respectively labeled as “TFT-6” and “TFT-18”. The W and L of “TFT-6” is 250 μm and 6 μm, for “TFT-18” is 750 μm and 18 μm res pectively. Then, the electrical characteristics of TFT-6 and TFT-18 were studied.Figure 7 shows the NBTS results of TFT-6 and TFT-18, the final VTH value after NBTS were about 0.81 V and 1.49 V respectively. The final Vth value after NBTS of TFT-6 with a short channel length is negative than TFT-18.(a) NBTS of TFT-6(b) NBTS of TFT-18Fig.7 Transfer characteristics of TFT-6(a) and TFT-18(b) Although the two kinds of preferred devices designs need a larger layout, they could be employed in only a few key GOA TFT. It will not increase the width of boarder too much, but will significantly improve the GOA function stability.3.4 The improved Cu BCE-structure IGZO TFTs backplaneAfter modifying the passivation layer and optimizing the selection of color filter material and design of GOA TFT structure, the improved TFTs exhibited good reliability. Figure 8 shows the photograph of display image of 215.9 mm(85 in) 8K4K 120 Hz GOA LCD, which was fabricated in the Gen 8.5 line by employing the improved Cu BCE-structure IGZO TFTs backplane.Fig.8 215.9 mm(85 in) LCD fabricated by using optimizing Cu BCE-structure IGZO TFTs for backplane5 SummaryIn this work, a 215.9 mm(85 in) 8K4K 120 Hz GOA LCD panel was fabricated by employing Cu BCE-structure IGZO TFTs backplane. The characteristics and reliability of the a-IGZO TFTs can be improved by modifying the passivation layer and optimizing the selection of color filter material and design of GOA TFT structure, which made great contributionto the stable function of GOA circuit. Thus, an excellent image quality of 215.9 mm(85 in) 8K4K 120 Hz IGZO GOA LCD was obtained.参考文献：【相关文献】[1] NOMURA K, OHTA H, TAKAGI A, et al. Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors [J]. Nature, 2004, 432(7016): 488-492.[2] CHIANG H Q, WAGER J F. High mobility transparent thin-film transistors with amorphous zinc tin oxide channel layer [J]. Applied Physics Letters, 2005, 86: 013503. [3] 李欣予，王若铮，吴胜利，等. 绝缘层材料及结构对薄膜晶体管性能的影响[J]. 液晶与显示，2017，32(5)：344-351.LI X Y, WANG R Z, WU S L, et al. Effect of insulating layer material and structure on performance of thin film transistors [J]. Chinese Journal of Liquid Crystals and Displays,2017, 32(5): 344-351. (in Chinese)[4] ZHAO M J, LAN L F, XU H, et al. Wet-etch method for patterning metal electrodes directly on amorphous oxide semiconductor films [J]. ECS Solid State Letters, 2012, 1(5): P82-P84.[5] BAE J U, KIM D H, KIM K, et al. 10.2: Invited Paper: development of oxide TFT′s structures [J]. Sid Symposium Digest of Technical Papers, 2013, 44(1): 89-92.[6] YUKINORI S, HIROSHI K, SATOSHI H, et al. Channel-etched CAAC-OS FETs using multi-layer IGZO [J]. SID Symposium Digest of Technical Papers, 2015, 46(1): 1158-1161.[7] GE S M, LI S, CHEN S J, et al. Development of Cu BCE-structure IGZO TFT for a high-ppi 31-in. 8K × 4K GOA LCD [J]. SID Symposium Digest of Technical Papers, 2017, 48(1): 592-595.[8] BOYLE J F, JONES K A. The effects of CO, water vapor and surface temperature on the conductivity of a SnO2 gas sensor [J]. Journal of Electronic Materials, 1977, 6(6): 717-733.[9] YAMAZOE N, FUCHIGAMI J, KISHIKAWA M, et al. Interactions of tin oxide surface with O2, H2O and H2 [J]. Surface Science, 1979, 86: 335-344.[10] SHIMIZU Y, SHIMABUKURO M, ARAI H, et al. Humidity-sensitive characteristics ofLa3+-doped and undoped SrSnO3[J]. Journal of the Electrochemical Society,1989,136(4): 1206-1210.[11] PARK J S, JEONG J K, CHUNG H J, et al. Electronic transport properties of amorphous indium-gallium-zinc oxide semiconductor upon exposure to water [J]. Applied Physics Letters, 2008, 92(7): 072104.[12] CHUNG W F, CHANG T C, LI H W, et al. Influence of H2O dipole on subthreshold swing of amorphous indium-gallium-zinc-oxide thin film transistors [J]. Electrochemical and Solid-State Letters, 2011, 14(3): H114-H116.。

禁带半导体紫外探测器紫外探测技术在国防预警与跟踪、电力工业、环境监测及生命科学领域具有重要的应用，其核心器件是高性能的紫外光电探测器。

基于半导体材料的固态紫外探测器件具有体重小、功耗低、量子效率高、和便于集成等系列优势。

以碳化硅（SiC）和III族氮化物为代表的宽禁带半导体是近年来国内外重点研究和发展的新型第三代半导体材料，具有禁带宽度大、导热性能好、电子饱和漂移速度高以及化学稳定性优等特点，用于制备紫外波段的光探测器件具有显著的材料性能优势。

我们实验室在宽禁带半导体紫外探测器领域具有较强的实力。

率先在国内实现4H-SiC基紫外雪崩单光子探测器；分别研制成功高增益同质外延GaN基紫外雪崩光电探测器、国际上领先的高增益AlGaN基日盲雪崩光电探测器、具有极低暗电流的AlGaN基MSM日盲深紫外探测器、高量子效率AlGaN基PIN日盲深紫外探测器、以及现有芯片面积最大的AlGaN基日盲深紫外探测器，相关结果多次获得国际主流媒体的跟踪报导。

目前，我们的工作重点是研制高灵敏度宽禁带半导体紫外探测器，包括：紫外单光子探测器件结构设计和物理分析，紫外单光子探测线阵和日盲紫外探测阵列制备。

宽禁带半导体功率电子器件针对未来高效电力管理系统、电动汽车和广泛军事应用大容量化、高密度化和高频率化的要求，将宽禁带半导体材料应用于高档次功率电子器件可以有效解决当今功率电子器件发展所面临的“硅极限”（silicon limit）问题，将大幅度降低电能转换过程中的无益损耗，在各领域创造可观的节能空间。

宽禁带Ⅲ族氮化物半导体具有强击穿电场、高饱和漂移速度、高热导率和良好化学稳定性等系列材料性能优势，是制备新一代功率电子器件的理想材料。

这一研究方向近年来成为国际上继GaN基发光二极管和微波功率器件之后的新兴研究热点。

我们小组在这一研究领域具有较好的基础，已经研制成功AlGaN/GaN平面功率二极管，其击穿电压大于1100V，功率优值系数高达280MW/cm2。