Thickness-Engineered Extremely-thin Channel High Performance ITO TFTs with Raised S/D Architecture: Record-Low R<sub>SD</sub>, Highest Moblity (Sub-4 nm T<sub>CH</sub> Regime), and High V<sub>TH</sub> Tunability
Yuye Kang, Kaizhen Han, Yue Chen, Xiao Gong
Abstract
Utilizing the strong thickness-dependent property of ITO film, we report high-performance ITO TFTs having extremely-thin channel (2 to 3.5 nm), a raised S/D (RSD) structure, and channel length (L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf> ) down to 50 nm. The combination of the extremely-thin channel and the RSD helps to achieve record-low S/D series resistance (R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SD</inf> ) and record-high effective mobility $\mu_{eff}(72$ cm$^{2} /\mathrm{V}\cdot \mathrm{s}$) at sub-4 nm channel thickness (T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf> ) regime among all ITO TFTs. We perform systematic investigation on the impacts of T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf> , including mobility, subthreshold swing (SS), threshold voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</inf> ), quantization effect, and temperature dependence, etc. The results highlight the T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf> engineering as a powerful knob to realize enhancement mode operation $(\mathrm{V}_{TH} \gt 0)$ while maintaining high performance and excellent control of short channel effects. The device with T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf> as small as 2 nm shows positive V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</inf> of 0.3 V, high peak $\mathrm{G}_{\mathrm {{m}}}(\mathrm{G}_{{\mathrm {m}},\max})$ of 508 (at V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</inf> of 1 V), and SS of 85 mV/decade