Temperature-Dependent Instability of Bias Stress in InGaZnO Thin-Film Transistors

Abstract

Abstract-The instability of the gate bias and drain bias stresses is observed at high temperature in amorphous InGaZnO thin-film transistors (a-IGZO TFTs). The transfer characteristics of a-IGZO TFTs at different temperatures are also investigated in this paper. The transfer curve exhibits an apparent subthreshold current stretchout phenomenon at high temperature. The stretchout phenomenon becomes more serious with the increase of the temperature. In addition, thermally induced holes are accumulated by the negative gate voltage and get trapped in the gate dielectric or at the dielectric/channel interface at high temperature. The negative threshold voltage shifts with stress time and this is because the trapped holes induce more electrons. For drain bias stress at high temperature, the transfer curve exhibits an apparent shift during drain bias stress at high temperature compared with the same at room temperature. At high temperature, thermally induced holes are trapped in the gate insulator, especially near the drain region. Capacitancevoltage measurements have been used to prove the nonuniform hole-trapping phenomenon. Furthermore, the simulation of the capacitance-voltage and current-voltage curves also have been applied to confirm the hole-trapping distribution. The obtained results clarify that the instability is caused by nonuniform hole-trapping phenomenon.Index Terms-Bias stress, indium gallium zinc oxide (IGZO), technology computer-aided design (TCAD), temperature, thin-film transistors (TFTs).

Degradation of current–voltage and low frequency noise characteristics under negative bias illumination stress in InZnO thin film transistors

“…The value of τ 0 is equal to 10 −10 s for traps distributed near the interface. Equation (6) states that the probability of penetration into the gate oxide decreases exponentially with distance. The extracted density profiles of trapped charges before and after stress are shown in Fig.…”

“…As reported in Refs. [3]- [6], the electrical characteristics and the typical parameters of IZO TFTs may change in the above environments, which may further influence the performances of the image capture and display system. Moreover, IZO TFTs may be simultaneously subjected to diverse stresses.…”

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“…4) Also the negative shift in threshold voltage of the driving TFT for inactive pixels needs further investigation, but it is suspected that this behavior is a result of the thermal and photo-instability of the backplane TFTs. Indeed, InGaZnO based TFTs are known to suffer from threshold voltage instability (negative threshold voltage shift) under prolonged illumination [10]- [12] and heating [13]. Although the sub-pixels for which the light output increased were not active during the aging experiment, they were illuminated by neighboring pixels and kept at a high temperature for a long time.…”

A novel ultra large size organic light emitting diode display for premium televisions

“…9,10 From a performance point of view, there were improvements in TFT characteristic and improvement in reliability characteristics. [11][12][13] With the development of process technology, the number of masks required for TFT production has been reduced and the yield has been improved. However, the evolution of oxide TFT structure is still needed to make the progress of OLED displays for premium TV and gain a competitive edge in the display market.…”

“…Its structure has been developed into a coplanar type with small and low parasitic capacitance to increase the pixel aperture ratio 9,10 . From a performance point of view, there were improvements in TFT characteristic and improvement in reliability characteristics 11–13 . With the development of process technology, the number of masks required for TFT production has been reduced and the yield has been improved.…”