Ultrathin InGaO Thin Film Transistors by Atomic Layer Deposition

In this letter, we report on scaled ultrathin (~3 nm) InGaO (IGO) thin film transistors (TFTs) by atomic layer deposition (ALD) under a low thermal budget of 250 °C. The ALD-derived IGO channels are In-rich, with In/Ga atomic ratio of ~86:14, providing a high electron mobility of ~28.6 cm $^{{2}} \cdot \text{V}^{-{1}}\,\,\cdot \text{s}^{-{1}}$ under a ultrathin thickness of 3 nm. The resulting IGO TFTs exhibit excellent scaling behaviors down to sub-100 nm channel length ( $\text{L}_{\text {ch}}$ ). The IGO TFTs with a $\text{L}_{\text {ch}}$ of 80 nm show well-behaved electrical characteristics including a high on/off current ratio ( $\text{I}_{\text {on}}/\text{I}_{\text {off}}$ ) of ${1.8}\times {10} ^{{10}}$ , a low subthreshold swing (SS) of 92 mV/dec under $\text{V}_{\text {DS}}$ of 0.8 V. The negative- and positive-gate-bias-stress stability (NBS and PBS) of IGO TFTs are studied in both $\text{N}_{{2}}$ and air ambient, where a remarkably high PBS stability can be observed. The negative $\text{V}_{\text {th}}$ shifts during PBS and NBS test in $\text{N}_{{2}}$ ambient could be explained by the generation of donor-like traps originating from ionized oxygen vacancy, in addition to electron (de)trapping mechanism. This work presents the first demonstration of high-performance IGO TFTs with a miniatured device dimension, showing the potential for back-end-of-line (BEOL)-compatible monolithic 3D integration.