Atomic layer deposition (ALD) has attracted much attention, particularly for applications in nanoelectronics because of its atomic-level controllability and high-quality products. In this study, we developed a plasma-enhanced atomic layer deposition (PEALD) process to fabricate a homogeneous indium aluminum oxide (IAO) semiconductor film. Trimethylaluminum (TMA) and dimethylaluminum isopropoxide (DMAI) were used as Al precursors, which yielded different compositions. Density functional theory (DFT) calculations on the surface reactions between indium and aluminum precursors showed that while highly reactive TMA would etch In, DMAI with lower reactivity would allow indium to persist in the films, resulting in a more controlled doping of Al. The In/Al composition ratio could be further precisely controlled by adjusting the indium precursor dose time to sub-saturation. IAO based on DMAI was applied to fabricate thin-film transistors (TFTs), showing that Al can be a carrier suppressor of indium oxide. TFTs with PEALD IAO containing 3.8 atomic % Al showed a turn-on voltage of −0.4 ± 0.3 V, a subthreshold slope of 0.09 V/decade, and a field effect mobility of 18.9 cm 2 /(V s).

The ultra-high resolution display is in demand as virtual reality (VA) and augmented reality (AR) displays, and hologram display become much more important. We present vertical TFTs for the application to the driving TFT of ultra-high resolution display. The IGZO deposited by sputtering and InO x deposited by means of plasma-enhanced atomic layer deposition (PEALD) have been adopted as the channel layers. While the IGZO vertical TFT shows on-current of 0.23 mA at V g = 5 V and V ds = 2.1 V, that of InO x TFT shows 1.26 mA at the same driving condition. Author KeywordsVertical oxide TFT; Ultra high resolution display; PEALD InO x Objective and BackgroundThe recent trend in display may be listed as large SHV TV, AMOLED TV, high resolution mobile display, and new display with novel design or function such as flexible transparent display. Very recently high resolution displays become one of the big concerns 1 as virtual reality or augmented reality displays began to penetrate into the real market and hologram display is being developed. The display with resolution higher than 2000 ppi is considered to be achieved as ultra-high resolution displays. The most important factor in the ultra-high resolution display is the pixel area and the smallest TFT size would be the first criteria in the TFT point of view. The back channel etch (BCE) TFT 2 and self-aligned (SA) TFT 3 have been used for driving high resolution LCD and OLED, respectively. The comparison of foot print of TFT in Figure 1, however, shows that vertical TFT has the smallest pixel pitch value. In addition, vertical TFT can have precisely controlled short channel length defined by not the lithography instrument but the thin film thickness of spacer, resulting in high and uniform oncurrent. The paradoxical advantage of vertical TFT would be increasing channel length longer than the sub-pixel length. This would be the most important advantage of vertical TFT for the application to the high resolution display since properly designed vertical TFT allows high current gain at proper driving voltage which be decided from the threshold voltage of LCD or OLED device. Among the TFTs, oxide TFTs have been intensively researched due to the stellar performances of mobility and stability, large area uniformity, and use of existing facility 4-5 . Furthermore, architecture, materials, and process for the oxide TFT can be carefully selected depending on the device application. One of the most beautiful advantages of oxide TFT would be that it does not show short channel effect even with the channel length shorter than sub-micrometer 6-7 . This makes oxide semiconductors very suitable for the channel material of vertical TFT. Furthermore, considering the main issue in the vertical TFT, step coverage of active layer, oxide TFT would be the best selection since oxide semiconductor and gate insulator of alumina 8 or SiO 2 9 used for the oxide TFT can be deposited by means of plasma-enhanced atomic layer deposition (PEALD). PEALD provides excellent step coverage of films wi...

We adopted SiO2 film by means of plasma enhanced atomic layer deposition (PEALD) as the first gate insulator of top gate IGZO TFT. TFT post-annealed at 300oC shows mobility, Vth, and S.S of 39.9 cm2/V.s, -1V, and 0.32 V/dec., respectively. We investigated the effect of H in the gate insulator during the annealing with the comparison of bottom gate coplanar TFT with ALD grown alumina film as the gate insulator.

We investigated the effect of back channel material which plays as a channel defining layer in vertical TFT for the application to the TFT of ultra-high resolution display. Although the IGZO vertical TFT with polyimide back channel has low mobility, itshows good on/off ratio higher than 10 7 , low gate leakage current, and hard saturation behavior with channel length of 1 um.