AC Bias-Temperature Stability of a-InGaZnO Thin-Film Transistors With Metal Source/Drain Recessed Electrodes (original) (raw)
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IEEE Transactions on Electron Devices, 2012
A combination of the multifrequency C-V and the generation-recombination current spectroscopy is proposed for a complete extraction of density of states (DOS) in amorphous InGaZnO thin-film transistors (a-IGZO TFTs) over the full subband-gap energy range (E V ≤ E ≤ E C) including the interface trap density between the gate oxide and the a-IGZO active layer. In particular, our result on the separate extraction of acceptorand donor-like DOS is noticeable for a systematic design of amorphous oxide semiconductor TFTs because the former determines their dc characteristics and the latter does their threshold voltage (V T) instability under practical operation conditions. The proposed approach can be used to optimize the fabrication process of thin-film materials with high mobility and stability for massproduction-level amorphous oxide semiconductor TFTs. Index Terms-Amorphous InGaZnO (a-IGZO), density of states (DOS), full subband gap, thin-film transistors (TFTs). I. INTRODUCTION T HE AMORPHOUS InGaZnO thin-film transistor (a-IGZO TFT) has been recognized as one of promising candidates substituting hydrogenated amorphous silicon (a-Si:H), low-temperature polycrystalline silicon, and organic TFTs as switching/driving devices in active-matrix liquid crystal displays (AMLCDs) and/or active-matrix organic light-emitting diode displays (AMOLEDs) because of its considerable merits in flexibility, visible light transparency, large-area uniformity of a low temperature sputter-deposited amorphous material, and high carrier mobility. Moreover, very Manuscript
P-14: a-IGZO TFT Based Pixel Circuits for AM-OLED Displays
SID Symposium Digest of Technical Papers, 2012
In this paper, we analyze application of amorphous Indium-Gallium-Zinc-Oxide thin film transistors (a-InGaZnO TFTs) to voltage-driven pixel electrode circuit that could be used for 4.3in. wide video graphics array (WVGA) full color active-matrix organic light-emitting displays (AM-OLEDs). Simulation results, based on a-InGaZnO TFT and OLED experimental data, show that both device sizes and operational voltages can be reduced when compared to the same circuit using hydrogenated amorphous silicon (a-Si:H) TFTs. Moreover, the a-InGaZnO TFT pixel circuit can compensate for the threshold voltage variation (ΔV TH) of driving TFT within acceptable operating error range.
Journal of Electronic Materials, 2013
The effect of low-temperature annealing treatment for various durations on the stability of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors was investigated. By this treatment, IGZO TFTs showed enhanced electrical characteristics and better stability under positive gate bias stress with increasing annealing time up to 18,000 s. For all V G stresses at different annealing times, the experimentally measured threshold voltage shift (DV th) as a function of stress time was precisely modeled with a stretched-exponential function. DV th was generated by carrier trapping, not by defect creation. It was verified that the decrease of interface trap state density (N it) and free carriers resulted in the decrease of DV th with increasing annealing time. However, the characteristic trapping time of the carriers increased up to 5.3 9 10 3 s with increasing annealing time to 7,200 s and then decreased, implying that the interface quality between active layer/insulator was deteriorated with further annealing. In this study, successful fabrication of IGZO TFTs by post treatment with optimized duration is demonstrated for flexible display applications.
IEEE Transactions on Electron Devices, 2000
The electrical characteristics and stability of dualgate (DG) coplanar homojunction amorphous indium-galliumzinc-oxide thin-film transistors (a-IGZO TFTs) on glass substrates are described herein. In this device structure, both top gate (TG) and bottom gate are defined by lithography, allowing independent biasing when adjacent TFTs are present. The DG a-IGZO TFT demonstrates excellent electrical performance with subthreshold swing (SS) of 99 mV/dec, field-effect mobility of 15.1 cm 2 /V · s, and ON-OFF current ratio of 10 9 . By applying various bias voltages on the TG electrode, it is found that the TFT threshold voltage can be controlled without any change of the SS and off current. Under conditions of negative bias temperature stress (BTS), the transfer curves of the TFT exhibit negligible shifts after 10 000 s. Larger shifts are observed under conditions of a positive BTS. Finally, the application of this DG device to active-matrix organic light-emitting displays is suggested.
Solid-state Electronics, 2015
The electrical properties and stability of ultra-high definition (UHD) amorphous In-Ga-Zn-O (a-IGZO) thin-film transistor (TFT) arrays with short channel (width/length = 12/3 lm) were examined. A-IGZO TFT arrays have a mobility of $6 cm 2 /V s, subthreshold swing (S.S.) of 0.34 V/decade, threshold voltage of 3.32 V, and drain current (I d) on/off ratio of <10 9 with I off below 10 À13 A. Overall these devices showed slightly different electrical characteristics as compared to the long channel devices; non-saturation of output curve at high drain-to-source voltage (V ds), negative shift of threshold voltage with increasing V ds , and the mobility reduction at high gate voltage (V gs) were observed. The second derivative method adopting Tikhonov's regularization theory is suggested for the robust threshold voltage extraction. The temperature dependency of c-value was established after taking into consideration the impact of source/drain contact resistances. The AC bias-temperature stress was used to simulate the actual operation of active matrix liquid crystal displays (AM-LCDs). The threshold voltage shift had a dependency on the magnitude of drain bias stress, frequency, and duty cycle due to the impact ionization accelerated at high temperature. This study demonstrates that the short channel effects, source/drain contact resistances and impact ionization have to be taken into account during optimization of UHD AM-LCDs.
Applied Physics Letters, 2011
We have analyzed the time-temperature dependence of positive bias stress ͑PBS͒ and recovery in amorphous indium-gallium-zinc-oxide ͑a-IGZO͒ Thin-film-transistors ͑TFTs͒ incorporating SiO 2 back channel passivation. The data are fitted to stretched exponentials, yielding the time constant and stretch parameter  as fitting parameters. As-fabricated samples and samples annealed in vacuum at 250°C 200 h are compared. The time constant for room temperature stress increases fivefold with the 200 h anneal to the value = 1.3ϫ 10 6 s. The dependence of from stress temperature is well described by an Arrhenius plot, with activation E = 0.95 eV. Stress and recovery show very similar activation energies, supporting the defect formation in the bulk or at the gate insulator/a-IGZO interface as the mechanism responsible for PBS.
a-InGaZnO thin-film transistors for AMOLEDs: Electrical stability and pixel-circuit simulation
Journal of the Society for Information Display, 2009
Inverted-staggered amorphous In-Ga-Zn-O (a-InGaZnO) thin-film transistors (TFTs) were fabricated and characterized on glass substrates. The a-InGaZnO TFTs exhibit adequate field-effect mobilities, sharp subthreshold slopes, and very low off-currents. The current temperature stress (CTS) on the a-InGaZnO TFTs was performed, and the effect of stress temperature (T STR ), stress current (I STR ), and TFT biasing condition on their electrical stability was investigated. Finally, SPICE modelling for a-InGaZnO TFTs was developed based on experimental data. Several active-matrix organic light-emitting-display (AMOLED) pixel circuits were simulated, and the potential advantages of using a-InGaZnO TFTs were discussed.