用反应溅射法沉积SiO_x绝缘层的InGaZnO-TFT的光照稳定性(英文)

制备了基于反应溅射SiOx绝缘层的InGaZnO-TFT,并系统地研究了InGaZnO-TFT在白光照射下的稳定性,主要涉及到光照、负偏压、正偏压、光照负偏压和光照正偏压5种情况。结果表明,器件在光照和负偏压光照下的阈值偏移较大,而在正偏压光照情况下的阈值偏移几乎可以忽略。采用C-V方法证明阈值电压漂移是源于绝缘层/有源层附近及界面处的缺陷。另外,采用指数模式计算了缺陷态的弛豫时间。本研究的目的就是揭示InGaZnO-TFT在白光照射和偏压下的不稳定的原因。     

Degradation characteristics and mechanism of PMOSFETs under NBT--PBT--NBT stress

Degradation characteristics of PMOSFETs under negative bias temperature--positive bias temperature--negative bias temperature (NBT--PBT--NBT) stress conditions are investigated in this paper. It is found that for all device parameters, the threshold voltage has the largest shift under the first NBT stress condition. When the polarity of gate voltage is changed to positive, the shift of device parameters can be greatly recovered. However, this recovery is unstable. The more severe degradation appears soon after reapplication of NBT stress condition. The second NBT stress causes in linear drain current to degrade greatly, which is different from that of the first NBT stress. This more severe parameter shift results from the wear out of silicon substrate and oxide interface during the first NBT and PBT stress due to carrier trapping/detrapping and hydrogen related species diffusion.     

Experimental evaluation of interface states during time-dependent dielectric breakdown of GaN-based MIS-HEMTs with LPCVD-SiN_x gate dielectric

We experimentally evaluated the interface state density of Ga N MIS-HEMTs during time-dependent dielectric breakdown(TDDB). Under a high forward gate bias stress, newly increased traps generate both at the Si Nx/Al Ga N interface and the Si Nx bulk, resulting in the voltage shift and the increase of the voltage hysteresis. When prolonging the stress duration, the defects density generated in the Si Nx dielectric becomes dominating, which drastically increases the gate leakage current and causes the catastrophic failure. After recovery by UV light illumination, the negative shift in threshold voltage(compared with the fresh one) confirms the accumulation of positive charge at the Si Nx/Al Ga N interface and/or in Si Nx bulk, which is possibly ascribed to the broken bonds after long-term stress. These results experimentally confirm the role of defects in the TDDB of Ga N-based MIS-HEMTs.     

低温透明非晶IGZO薄膜晶体管的光照稳定性

采用室温射频磁控溅射非晶铟镓锌氧化合物(a-IGZO), 在相对低的温度(<200 ℃)下成功制备底栅a-IGZO 薄膜晶体管器件, 其场效应迁移率10 cm^-2·V^-1·s^-1, 开关比大于10⁷, 亚阈值摆幅 SS为0.4 V/dec, 阈值电压为3.6 V. 栅电压正向和负向扫描未发现电滞现象. 白光发光二极管光照对器件的输出特性基本没有影响, 表明制备的器件可用于透明显示器件. 研究了器件的光照稳定性, 光照10000 s后器件阈值电压负向偏移约0.8 V, 这种漂移是由于界面电荷束缚所致. 关键词： 非晶铟镓锌氧化合物 薄膜晶体管 光照稳定性 电滞现象     

Long-term stability of InP MIS devices

Room-temperature bias stress measurements were performed on n-type InP MIS capacitors. A wide range of interface passivation processes and gate dielectrics was investigated. A generally observed behaviour under positive bias stress is a slow trapping - fast detrapping consistent with a trap distribution in the interfacial layer above the conduction band edge of InP. Large variations both in the magnitude and in the time dependence of the flat-band voltage shift ΔV_FB are observed. We discuss these drift behaviours in terms of interface traps - rather than bulk dielectric traps - in relation with the physico-chemical properties of the interface. It is shown that devices based on InP treated by annealing under arsenic pressure and controlled oxidation exhibit a very good stability. For any passivation procedure, the drift is strongly diminished if the device is stressed with AC voltage compared to DC voltage.     

超深亚微米PMOS器件的NBTI退化机理

对超深亚微米PMOS器件的负栅压温度不稳定性(NBTI)退化机理进行了研究.主要集中在对器件施加NBT和随后的PBT应力后器件阈值电压的漂移上.实验证明反型沟道中空穴在栅氧中的俘获以及氢分子在栅氧中的扩散是引起NBTI退化的主要原因.当应力条件变为PBT时，陷落的空穴可以快速退陷，但只有部分氢分子可以扩散回栅氧与衬底界面钝化硅悬挂键，这就导致了PBT条件下阈值电压只能部分恢复. 关键词： 超深亚微米PMOS器件 负偏压温度不稳定性 界面陷阱 氢气     

Degradation and its fast recovery in a-IGZO thin-film transistors under negative gate bias stress

A new type of degradation phenomena featured with increased subthreshold swing and threshold voltage after negative gate bias stress (NBS) is observed for amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs), which can recover in a short time. After comparing with the degradation phenomena under negative bias illumination stress (NBIS), positive bias stress (PBS), and positive bias illumination stress (PBIS), degradation mechanisms under NBS is proposed to be the generation of singly charged oxygen vacancies ($V_{\mathrm{o}}^{+}$) in addition to the commonly reported doubly charged oxygen vacancies ($V_{\mathrm{o}}^{2+}$). Furthermore, the NBS degradation phenomena can only be observed when the transfer curves after NBS are measured from the negative gate bias to the positive gate bias direction due to the fast recovery of $V_{\mathrm{o}}^{+}$ under positive gate bias. The proposed degradation mechanisms are verified by TCAD simulation.     

薄膜热处理对ZnO薄膜晶体管性能的提高

制备了两种以SiO2为绝缘层的底栅ZnO薄膜晶体管,分别以未退火和退火处理的ZnO薄膜作为有源层.与未退火处理的ZnO薄膜晶体管相比,退火处理的ZnO薄膜晶体管的饱和迁移率由2.3 cm2/(V·s)增大至3.12 cm2/(V·s),阈值电压由20.8V减小至9.9V,亚阈值摆幅由2.6 V/dec减小至1.9 V/...     

Bias stress effect in low-voltage organic thin-film transistors

The bias stress effect in pentacene organic thin-film transistors has been investigated. The transistors utilize a thin gate dielectric based on an organic self-assembled monolayer and thus can be operated at low voltages. The bias stress-induced threshold voltage shift has been analyzed for different drain-source voltages. By fitting the time-dependent threshold voltage shift to a stretched exponential function, both the maximum (equilibrium) threshold voltage shift and the time constant of the threshold voltage shift were determined for each drain-source voltage. It was found that both the equilibrium threshold voltage shift and the time constant decrease significantly with increasing drain-source voltage. This suggests that when a drain-source voltage is applied to the transistor during gate bias stress, the tilting of the HOMO and LUMO bands along the channel creates a pathway for the fast release of trapped carriers.     

0.25-μm PMOSFETs中热载流子的退化特性和解释

本文研究了深亚微米PMOSFETs的热载流子效应。研究发现热载流子效应包括界面态的产生和氧化层中固定正电荷的形成。通过实验证明了深亚微米PMOSFETs中这两种机制的重要性。首先，氧化层固定正电荷的产生在深亚微米PMOSFETs中起作用，使得器件的阈值电压退化，最终限制了表面沟道晶体管的使用寿命。对于先进的模拟和混合信号的应用，工艺和器件的可靠性必须按照阈值电压的漂移重新定义，而不仅仅依照跨导的退化或者栅氧化层的寿命来定义。其次，空穴注入产生的界面态也影响器件的特性。推断了热载流子效应的形成过程。     

Study of Ti addition in channel layers for In-Zn-O thin film transistors

Ti added In-Zn-O thin films and their application to thin film transistors were studied. The In-Zn-O films were deposited by pulsed plasma deposition using targets with various Ti contents added. High content of Ti in In-Zn-O films was found to induce a decrease in carrier concentration. The effect was attributed to suppression of oxygen vacancies by Ti incorporation. For thin film transistors with Ti added In-Zn-O as channel layer materials, threshold voltage showed positive shift as Ti content increases and field effect mobility was not decreased at the same time. Results of a bias stress experiment on device fabricated at room temperature are also given.     

双电层氧化锌薄膜晶体管偏压应力稳定性

以环保可降解的天然生物材料制备功能器件越来越受到关注,利用天然鸡蛋清作为栅介质层,采用射频磁控溅射法在其上沉积ZnO薄膜有源层,制备低压双电层氧化锌基薄膜晶体管（ZnO-TFT）并对其电学特性进行了表征,研究了器件在栅偏压和漏偏压应力下电性能的稳定性及其内在的物理机制。该ZnO-TFT器件呈现出良好的电特性,载流子饱和迁移率为5.99 cm²/（V·s）,阈值电压为2.18 V,亚阈值摆幅为0.57 V/dec,开关电流比为1.2×10⁵,工作电压低至3 V。研究表明,在偏压应力作用下,该ZnO-TFT器件电性能存在一定的不稳定性,我们认为栅偏压应力引起的电性能变化可能来源于栅介质附近及界面处的正电荷聚集、充放电效应和新陷阱态的复合效应;漏偏压应力引起的电性能变化可能来源于焦耳热引起的氧空位及沟道中的电子陷阱。     

绝缘体上硅金属氧化物半导体场效应晶体管中辐射导致的寄生效应研究

基于⁶⁰Co γ射线源研究了总剂量辐射对绝缘体上硅（silicon on insulator,SOI）金属氧化物半导体场效应晶体管器件的影响.通过对比不同尺寸器件的辐射响应,分析了导致辐照后器件性能退化的不同机制.实验表明：器件的性能退化来源于辐射增强的寄生效应;浅沟槽隔离（shallow trench isolation,STI）寄生晶体管的开启导致了关态漏电流随总剂量呈指数增加,直到达到饱和;STI氧化层的陷阱电荷共享导致了窄沟道器件的阈值电压漂移,而短沟道器件的阈值电压漂移则来自于背栅阈值耦合;在同一工艺下,尺寸较小的器件对总剂量效应更敏感.探讨了背栅和体区加负偏压对总剂量效应的影响,SOI器件背栅或体区的负偏压可以在一定程度上抑制辐射增强的寄生效应,从而改善辐照后器件的电学特性.     

AlGaN/GaN高电子迁移率器件外部边缘电容的物理模型

AlGaN/GaN HEMT外部边缘电容Cofd是由栅极垂直侧壁与二维电子气水平壁之间的电场构成的等效电容.本文基于保角映射法对Cofd进行物理建模,考虑沟道长度调制效应,研究外部偏置、阈值电压漂移和温度变化对Cofd的影响:随着漏源偏压从零开始增加,Cofd先保持不变再开始衰减,其衰减速率随栅源偏压的增加而减缓;AlGaN势垒层中施主杂质浓度的减小和Al组分的减小都可引起阈值电压的正向漂移,正向阈值漂移会加强沟道长度调制效应对Cofd的影响,导致Cofd呈线性衰减.在大漏极偏压工作情况下,Cofd对器件工作温度的变化更加敏感.     

NBT导致的深亚微米PMOS器件退化与物理机理

研究了深亚微米PMOS器件在负偏压温度(negative bias temperature, NBT) 应力前后的电流电压特性随应力时间的退化，重点分析了NBT应力对PMOS器件阈值电压漂移的影响，通过实验证明了在栅氧化层和衬底界面附近的电化学反应和栅氧化层内与氢相关的元素的扩散，是PMOS器件中NBT效应产生的主要原因.指出NBT导致的PMOS器件退化依赖于反应机理和扩散机理两种机理的平衡. 关键词： 深亚微米PMOS器件 负偏压温度不稳定性 界面态 氧化层固定正电荷     

Effect of overdrive voltage on PBTI trapping behavior in GaN MIS-HEMT with LPCVD SiN_x gate dielectric

The effect of high overdrive voltage on the positive bias temperature instability(PBTI)trapping behavior is investigated for GaN metal–insulator–semiconductor high electron mobility transistor(MIS-HEMT)with LPCVD-SiNx gate dielectric.A higher overdrive voltage is more effective to accelerate the electrons trapping process,resulting in a unique trapping behavior,i.e.,a larger threshold voltage shift with a weaker time dependence and a weaker temperature dependence.Combining the degradation of electrical parameters with the frequency–conductance measurements,the unique trapping behavior is ascribed to the defect energy profile inside the gate dielectric changing with stress time,new interface/border traps with a broad distribution above the channel Fermi level are introduced by high overdrive voltage.     

Photo-induced electrical instability in hydrogenated amorphous silicon based thin-film transistors and the effect of its phase transition

We investigate the origin of photo-induced electrical instability in hydrogenated amorphous silicon based thin-film transistors (a-Si:H TFTs). Photo instability alone was accompanied by a positive shift in the threshold voltage (V_TH) caused by photo irradiation, and even larger positive or negative shift further exacerbated the instability caused by photo-induced electrical bias stress. Such phenomena can occur as a result of extended charge trapping and/or the creation of defect-states at the semiconductor/dielectric interface or in the gate dielectric. The mechanism for such is difficult to describe through chemical interactions of electron-donating and -withdrawing molecules that exhibit a shift in V_TH in only one direction. We also prove that a transition from an amorphous to a protocrystalline phase improves the photo-induced electrical stability. Such results originate from a reduction in the density of the localized states in protocrystalline-Si:H films relative to that of a-Si:H. We believe that this study provides significant information on the device physics of optoelectronics, which commonly exhibit photo-induced instability and charge transport, as a result of prolonged exposure to photo irradiation.     

High-photosensitivity polymer thin-film transistors based on poly（3-hexylthiophene）

Polymer thin-film transistors(PTFTs) based on poly(3-hexylthiophene) are fabricated by the spin-coating process,and their photo-sensing characteristics are investigated under steady-state visible-light illumination.The photosensitivity of the device is strongly modulated by gate voltage under various illuminations.When the device is in the subthreshold operating mode,a significant increase in its drain current is observed with a maximum photosensitivity of 1.7×10 3 at an illumination intensity of 1200 lx,and even with a relatively high photosensitivity of 611 at a low illumination intensity of 100 lx.However,when the device is in the on-state operating mode,the photosensitivity is very low:only 1.88 at an illumination intensity of 1200 lx for a gate voltage of-20 V and a drain voltage of -20 V.The results indicate that the devices could be used as photo-detectors or sensors in the range of visible light.The modulation mechanism of the photosensitivity in the PTFT is discussed in detail.     

Effect of channel thickness on electrical performance of amorphous IGZO thin-film transistor with atomic layer deposited alumina oxide dielectric

We have investigated the electrical performance of amorphous indium–gallium–zinc oxide (α-IGZO) thin-film transistors with various channel thicknesses. It is observed that when the α-IGZO thickness increases, the threshold voltage decreases as reported at other researches. The intrinsic field-effect mobility as high as 11.1 cm²/Vs and sub threshold slope as low as ∼0.2 V/decade are independent on the thickness of α-IGZO channel, which indicate the excellent interface between α-IGZO and atomic layer deposited Al₂O₃ dielectric even for the case with α-IGZO thickness as thin as 10 nm. However, the source and drain series resistances increased with increasing of α-IGZO channel thickness, which results in the apparent field-effect mobility decreasing. The threshold voltage shift (ΔV_th) under negative bias stress (NBS) and negative bias illumination stress (NBIS) were investigated, also. The hump-effect in the sub threshold region under NBS and threshold voltage shift to negative position under NBIS were enhanced with decreasing of α-IGZO channel thickness, owing to the enhancement of vertical electrical field in channel.     

Al_2O_3薄层修饰SiN_x绝缘层的IGZO-TFTs器件的性能研究

采用原子层沉积工艺(ALD)生长均匀致密的三氧化二铝(Al2O3)薄层对氮化硅(Si Nx)绝缘层进行修饰,研究了铟镓锌氧薄膜晶体管(IGZO-TFTs)器件的性能。当Al2O3修饰层厚度为4 nm时,绝缘层-有源层界面的最大缺陷态密度相比于未修饰器件降低了17.2%,器件性能得到显著改善。场效应迁移率由1.19 cm2/(V·s)提高到7.11 cm2/(V·s),阈值电压由39.70 V降低到25.37 V,1 h正向偏压应力下的阈值电压漂移量由2.19 V减小到1.41 V。