Amorphous InGaZnO Thin-Film Transistors—Part II: Modeling and Simulation of Negative Bias Illumination Stress-Induced Instability

Bae

IEEE Trans. Electron Devices

et al. 2012

Self Cite

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).

Section: Discussionmentioning

confidence: 99%

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

Bae

IEEE Trans. Electron Devices

et al. 2012

Self Cite

“…According to several researchers [4]- [9], the reliability of the IGZO-TFTs is related to defect states below the CBM in the a-IGZO thin films. In particular, during the lightillumination and negative-bias temperature stress (LNBTS), it is considered that the defect-like states are formed, which causes the change of the threshold voltage (V th ) of the TFTs.…”

Section: Introductionmentioning

confidence: 99%

In-line Process Monitoring for Amorphous Oxide Semiconductor TFT Fabrication using Microwave-detected Photoconductivity Decay Technique

Okuno

Tao

Morita

et al. 2014

IEICE Trans. Electron.

SUMMARYWe have investigated the microwave-detected photoconductivity responses from the amorphous In-Ga-Zn-O (a-IGZO) thin films. The time constant extracted by the slope of the slow part of the reflectivity signals are correlated with TFT performances. We have evaluated the influences of the sputtering conditions on the quality of a-IGZO thin film, as well as the influences of gate insulation films and annealing conditions, by comparing the TFT characteristics with the microwave photoconductivity decay (µ-PCD). It is concluded that the µ-PCD is a promising method for in-line process monitoring for the IGZO-TFTs fabrication. key words: oxide semiconductor, thin film transistor, microwave-detected photoconductivity decay, in-line process monitoring

“…However, there is still a lack of direct electronic structure evidence to support the variation electrical properties. It is well known that semiconductor properties strongly depend on the electronic structure, including defect states within sub-gap states [10][11][12]. Kamiya et al [11] reported that atomic and electronic structures were calculated for oxygen deficient in a-IGZO using density functional theory.…”

Section: Introductionmentioning

confidence: 99%

The origin of evolutionary device performance for GeGaInOx thin film transistor as a function of process pressure

2014

This paper addresses changes in device performance for GeGaInOx (GGIO) thin film transistors deposited as a function of process pressures, and the mechanisms responsible for electronic band structure and defect states within sub-gap states. As the process pressure decreased from 5 to 1 mTorr during sputtering of the GGIO active layer, the saturation mobility increased from 6.51 to 11.18 cm 2 /Vs and the sub-threshold swing value decreased from 0.64 to 0.21 V/ decade. Conduction band areas measured by x-ray absorption spectroscopy in GGIO films increased as the total process pressure decreased from 5 to 1 mTorr, which can help charge transport in GGIO semiconductors. In addition, the ΔVth shift during positive bias temperature stability for 3 h was also enhanced from 17.5 to 6.2 V. This improvement can be attributed to the reduction of relative near conduction band edge defect states, which was found in not only at the GGIO films level by spectral ellipsometry, but also at the device level by the Meyer-Neldel rule.