Woo-Geun Lee

Effect of Channel Layer Thickness on Characteristics and Stability of Amorphous Hafnium-Indium-Zinc Oxide Thin Film Transistors

We investigated the channel layer thickness dependence of the characteristics and stability in amorphous hafnium indium zinc-oxide (HIZO) thin film transistors (TFTs). HIZO TFTs were prepared with various channel thicknesses from 400 to 700 A. In HIZO TFTs, carrier concentration is considerably high, which leads to channel layer thickness dependence. The threshold voltages of TFTs negatively shifted as the channel thickness increased. The threshold voltage shift at a high temperature is more severe in TFTs with thicker channel layers. The channel thickness dependence of the bias stability of HIZO TFTs is closely related to the back interface, rather than the bulk state.

The Effect of the Photo-Induced Carriers on the Reliability of Oxide TFTs Under Various Intensities of Light

We investigated the reliability of oxide TFTs under negative gate bias stress combined with various intensities of light having a wavelength of 400 nm. Light illumination caused a considerable Vth shift toward negative direction, as reported in previous works. However, the trapping probability of a single hole is not altered, which means that the basic mechanism of the charge trapping is not changed by light illumination. In oxide TFTs, the hole concentration at the channel and the characteristics of the gate insulator materials are the determinant factors of the reliability under light illumination.

P-28: The Effect of AC Bias Frequency on Threshold Voltage Shift of the Amorphous Oxide TFTs

We investigated AC bias stress instability of indium-gallium-zinc-oxide (IGZO) Thin-film transistors (TFTs). AC bias frequency dependence showed different aspect in IGZO TFTs and a-Si:H TFTs. Influencing factors to AC bias frequency dependence of instability is charge accumulation characteristic under negative bias stress, and detrapping characteristics of shallow trapped charges under positive bias stress.

Effect of Channel Length on the Reliability of Amorphous Indium?Gallium?Zinc Oxide Thin Film Transistors

We investigated the effect of the channel length on the reliability of amorphous indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs) under the negative and positive gate bias stress. The threshold voltage (Vth) was barely changed at the channel length of 8 µm under the negative bias stress. When the channel length was 10 and 15 µm, Vth shifted negatively about 0.7 and 2.5 V. However, Vth shift did not depend on the channel length under the positive bias stress. Under the negative gate bias stress, the holes might not be accumulated uniformly at the channel. Because the band gap of IGZO is large, the effect of negative gate bias is decreased when the back interface is fixed by source/drain electrode. When the channel length decreases, the amount of accumulated hole decreases and Vth shift decreases.

Comparison of Electrical Properties and Bias Stability of Double-Gate a-HIZO TFTs According to TFT Structure

We fabricated two types of double-gate amorphous hafnium-indium-zinc oxide thin-film transistors: a back-channel etch (BCE) type and an etch stopper (ES) type. The normalized on-current and field-effect mobility of the BCE type are larger than those of the ES type. Furthermore, when applied with a positive bias stress, stability trends compared for each single-gate device are different according to structures. We suggest that the reason for the different electrical properties and bias stability originates from the ES structure in which some regions under the source/drain electrodes block the top-gate field; thus, there is no carrier accumulation or charge trapping into the dielectric layer.

P-18: Suppression of Threshold Voltage Shift of Oxide-based TFT by Employing Thermal Pre-treatment

The stability of oxide-based TFT under bias stress was considerably improved by employing in-Situ thermal pretreatment, which suppresses hydrogen content in the oxide active layer. By suppressing the inflow of hydrogen, easily movable, back interface trapping was reduced and the VTH shift of the oxide TFT was suppressed successfully.