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Effects of Deposition Temperature on the Device Characteristics of Oxide Thin-Film Transistors Using In–Ga–Zn–O Active Channels Prepared by Atomic-Layer Deposition
journal contribution
posted on 2017-06-27, 14:55 authored by Sung-Min Yoon, Nak-Jin Seong, Kyujeong Choi, Gi-Ho Seo, Woong-Chul ShinWe demonstrated the
physical and electrical properties of the In–Ga–Zn–O
(IGZO) thin films prepared by atomic-layer deposition (ALD) method
and investigated the effects of the ALD temperature. The film composition
(atomic ratio of In:Ga:Zn) and film density were examined to be 1:1:3
and 5.9 g/cm3, respectively, for all the temperature conditions.
The optical band gaps decreased from 3.81 to 3.21 eV when the ALD
temperature increased from 130 to 170 °C. The amounts of oxygen-related
defects such as oxygen vacancies increased with increasing the ALD
temperature. It was found from the in situ temperature-dependent electrical
conductivity measurements that the electronic natures including the
defect structures and conduction mechanism of the IGZO thin films
prepared at different temperatures showed marked variations. The carrier
mobilities in the saturation regions (μsat’s)
for the fabricated thin film transistors (TFTs) using the IGZO channel
layers were estimated to be 6.1 to 14.8 cm2 V–1 s–1 with increasing the ALD temperature from 130
to 170 °C. Among the devices, when the ALD temperature was controlled
to be 150 °C, the IGZO TFTs showed the best performance, which
resulted from the fact that the amounts of oxygen vacancies and interstitial
defects could be appropriately modulated at this condition. Consequently,
the μsat, subthreshold swing, and on/off ratio for
the TFT using the IGZO channel prepared at 150 °C showed 10.4
cm2 V–1 s–1, 90 mV/dec,
and 2 × 109, respectively. The threshold voltage shifts
of this device could also be effectively reduced to be 0.6 and −3.2
V under the positive-bias and negative-bias-illumination stress conditions.
These obtained characteristics can be comparable to those for the
sputter-deposited IGZO TFTs.