Improvement in negative bias illumination stress stability of In–Ga–Zn–O thin film transistors using HfO₂gate insulators by controlling atomic-layer-deposition conditions

Abstract

The effects of atomic layer deposition (ALD) conditions for the HfO2 gate insulators (GI) on the device characteristics of the InGaZnO (IGZO) thin film transistors (TFTs) were investigated when the ALD temperature and Hf precursor purge time were varied to 200, 225, and 250 °C, and 15 and 30 s, respectively. The HfO2 thin films showed low leakage current density of 10−8 A cm−2, high dielectric constant of over 20, and smooth surface roughness at all ALD conditions. The IGZO TFTs using the HfO2 GIs showed good device characteristics such as a saturation mobility as high as 11 cm2 V−1 s−1, a subthreshold swing as low as 0.10 V/dec, and all the devices could be operated at a gate voltage as low as ±3 V. While there were no marked differences in transfer characteristics and PBS stabilities among the fabricated devices, the NBIS instabilities could be improved by increasing the ALD temperature for the formation of HfO2 GIs by reducing the oxygen vacancies within the IGZO channel.

Electron effective mass and electronic structure in nonstoichiometric amorphous Indium Gallium Zinc Oxide films

“…Since the the report on transparent and flexible thinfilm transistors (TFTs) using amorphous In-Ga-Zn oxide (a-IGZO) as active channel material [1], extensive investigations have been carried out on this material both in device fabrications [2][3][4][5][6][7] and fundamental research [7][8][9][10][11][12][13][14]. The electronic mobility in a-IGZO based TFT is far larger than that in amorphous Si:H based device [1,7].…”

Impacts of HfO2/ZnO Stack-Structured Charge-Trap Layers Controlled by Atomic Layer Deposition on Nonvolatile Memory Characteristics of In-Ga-Zn-O Channel Charge-Trap Memory Thin-Film Transistors

“…The devices showed slight dispersion of capacitance values due to the differences in dielectric constants depending on the ALD temperatures. The capacitance at an accumulation region increased as increases in ALD temperature owing to the increment of dielectric constant of the HfO 2 film [22]. Thickness variations might also influence on the capacitance dispersions, even though we calibrated the film thickness considering the deposition rate depending on the ALD temperature.…”

Amorphous InGaZnO and metal oxide semiconductor devices: an overview and current status

“…For the dielectric layer this is achieved by optimising the deposition process. For example, it has been shown that higher temperature (250 C) ALD deposited dielectric produced more stable devices than identically fabricated devices with lower temperature (200 C) ALD dielectric 269 .…”