We have investigated the effect of electron effective mass (me*) and tail acceptor-like edge traps density (NTA) on the electrical characteristics of amorphous-InGaZnO (a-IGZO) thin-film transistors (TFTs) through numerical simulation. To examine the credibility of our simulation, we found that by adjusting me* to 0.34 of the free electron mass (mo), we can preferentially derive the experimentally obtained electrical properties of conventional a-IGZO TFTs through our simulation. Our initial simulation considered the effect of me* on the electrical characteristics independent of NTA. We varied the me* value while not changing the other variables related to traps density not dependent on it. As me* was incremented to 0.44 mo, the field-effect mobility (µfe) and the on-state current (Ion) decreased due to the higher sub-gap scattering based on electron capture behavior. However, the threshold voltage (Vth) was not significantly changed due to fixed effective acceptor-like traps (NTA). In reality, since the magnitude of NTA was affected by the magnitude of me*, we controlled me* together with NTA value as a secondary simulation. As the magnitude of both me* and NTA increased, µfe and Ion deceased showing the same phenomena as the first simulation. The magnitude of Vth was higher when compared to the first simulation due to the lower conductivity in the channel. In this regard, our simulation methods showed that controlling me* and NTA simultaneously would be expected to predict and optimize the electrical characteristics of a-IGZO TFTs more precisely.
We fabricate high-performance solution-processed SnO 2 thin-film transistors (TFTs) exhibiting improved carrier transport features by exposing the ultraviolet/ozone (UV/O 3 ) on the SnO 2 film during the pre-annealing stage. The SnO 2 layer is treated with different UV/O 3 -exposure times from 0 to 60 minutes before the post-annealing step. As UV/O 3 -exposure time increases from 0 to 30 minutes, the M-O-M (M, metal; and O, oxygen) network, mass density, and oxygen vacancies of films are enhanced. In contrast, the M-O-M network and mass density decrease, while the oxygen vacancies rather increase when the UV/O 3 -exposure time reaches 60 minutes beyond 30 minutes. The SnO 2 (Sn 4+ ) phase, thickness, and surface morphology of SnO 2 films are not considerably changed regardless of UV/O 3 -exposure time. When the UV/O 3 -exposure time is 30 minutes, devices demonstrate superior field-effect mobility (10.1 cm 2 V −1 s −1 ) at approximately two times higher than the TFT without UV/O 3 -exposure. Furthermore, the SnO 2 TFT with UV/O 3 -exposure time for 30 minutes shows improved subthreshold-swing characteristics and a high on/off current ratio. These devices are adequate for use in high-resolution active-matrix LCDs or OLED displays that demand a high field-effect mobility (>10 cm 2 V −1 s −1 ) and on/off ratio (>10 6 ).
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