Amorphous InGaZnO Thin-Film Transistors—Part I: Complete Extraction of Density of States Over the Full Subband-Gap Energy Range

Abstract

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).

Effect of direct current sputtering power on the behavior of amorphous indium-gallium-zinc-oxide thin-film transistors under negative bias illumination stress: A combination of experimental analyses and device simulation

“…Quantitative analyses are carried out by the combination of extracted sub-gap density of states (DOS) and device simulation. [12][13][14][15] Studies indicate that peroxide formation reflects well the observed behavior of the TFT under NBIS.…”

“…15 The electron doping concentration, N D , was extracted by fitting the measured I-V curves with the calculated ones over a wide range of V GS and V DS . 12,15 Figure 2(a) shows the representative transfer characteristics of three a-IGZO TFTs, of which the active layers were deposited at DC powers of 1 kW, 2 kW, and 3 kW, respectively. The threshold voltage (V T ) is defined as the V GS value that induces I DS ¼ 10 pA at V DS ¼ 0.1 V. The l FE was extracted from g m /[C OX (W/L)V DS ] at (V GS À V T )/V DS ¼ 5/0.1 V, where W is the channel width, L is the channel length, C OX is the gate oxide capacitance per unit area, and g m is the transconductance defined as @I DS /@V GS .…”

Comparative Analysis on Positive Bias Stress-Induced Instability under High VGS/Low VDSand Low VGS/High VDSin Amorphous InGaZnO Thin-Film Transistors

“…In addition, we conducted the TCAD device simulation in order to validate our model quantitatively. For a precise and reasonable analysis, the subgap trap model of a-IGZO TFT [14] was employed as follows:…”

Accurate Analytical Physical Modeling of Amorphous InGaZnO Thin-Film Transistors Accounting for Trapped and Free Charges

“…The amount of trapped charges strictly depends on the energy distribution of the localized states. The DOS shape is usually well approximated by a tail exponential [13][17]- [22] in the energy range 0.2-0.6 eV from the band-edge and by a Gaussian [13] [17] or an exponential [18]- [21] function at smaller (deep) energies. As reported in [13] In strong accumulation regime (large V G ), the Fermi energy level is moving towards the mobility band edge and hence all the trap states become filled.…”