Apparent high mobility ~30 cm²/Vs of amorphous In–Ga–Zn–O thin-film transistor and its origin

Abstract

Amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) annealed in ozone at 250°C exhibited a good subthreshold swing (S) of 123 mV/decade and a saturation mobility (® sat ) of ³10 cm 2 /Vs, but a bit large threshold voltage (V th ) of 11.6 V. Further oxygen annealing at 200°C resulted in high apparent ® sat of ³30 cm 2 /Vs and deteriorated characteristics such as a large S value and large hysteresis. The high apparent ® sat values were attributed to the electrical discharge between the gate and source electrodes. Reasonably actual ® sat values ³10 cm 2 /Vs were obtained using the actual capacitance calculated from the discharge characteristics.

Modeling and Mechanism of Enhanced Performance of In-Ga-Zn-O Thin-Film Transistors with Nanometer Thicknesses under Temperature Stress

“…15 Since the dielectric is SiO 2 rather than a dielectric material (such as a ferroelectric material) that may cause dielectric polarization, the loop is not due to dielectric polarization. 14 This electron capture mechanism is consistent with the hysteresis loop of the transfer curve of the sample as shown in Figure 2d. In Figure 2d, the square root of I DS 1/2 as a function of V GS is plotted.…”

“…If electrons are trapped by bulk states, a higher V GS is required to attract the same quantity of mobile carriers for the same channel current; oppositely, if they are trapped by interfacial states, these electrons shield V GS and cause a decrease in the effective V GS . 13,14 This positive shift is observed and reported for the first time under the pure temperature stress condition. 9 Typically, the behaviors under the voltage bias stress show a negative shift, which is attributed to electron trapping or the creation of oxygen vacancies.…”

“…The clockwise loop of the transfer curve is due to dielectric polarization or electron capture . Since the dielectric is SiO 2 rather than a dielectric material (such as a ferroelectric material) that may cause dielectric polarization, the loop is not due to dielectric polarization . This electron capture mechanism is consistent with the hysteresis loop of the transfer curve of the sample as shown in Figure d.…”

“…The negative carriers are trapped at the channel/dielectric interface or injected into the dielectric from the IGZO channel. If electrons are trapped by bulk states, a higher V GS is required to attract the same quantity of mobile carriers for the same channel current; oppositely, if they are trapped by interfacial states, these electrons shield V GS and cause a decrease in the effective V GS . , This positive shift is observed and reported for the first time under the pure temperature stress condition …”

“…Here, we identified a trend from a typical IGZO nanometer-thick TFT different from most conventional reports. − The mechanism behind this updated behavior of the transfer curve shift has been investigated by experimental evidence in five aspects, including a transfer curve loop, the exponential factor of a time-dependent shift trend, subgap density of state (DOS) measurements, X-ray photoelectron spectroscopy (XPS), and simulation. − The combination of these points can effectively explain the influence of temperature on IGZO, which will help IGZO become widely used in future markets. − …”