Overcoming Negative nFET V_TH by Defect-Compensated Low-Thermal Budget ITO-IGZO Hetero-Oxide Channel to Achieve Record Mobility and Enhancement-mode Operation

Abstract

We have successfully demonstrated, low-thermal budget oxide-based FETs with a record I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D,max</inf> of $790\mu\mathrm{A}/\mu\mathrm{m}$ at V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</inf> = 1V, an enhancement-mode operation (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DH</inf> >0), S.S. <90 mV/dec., and DIBL ~20mV/V at an ultra-scaled channel length LCH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf> of 50 nm. This is enabled by an optimized InSnO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> -InGaZnO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> hetero-junction channel to achieve channel defect self-compensation [1]. This approach overcomes the fundamental issue of negative VTH seen in n-type oxide FETs due to donor-type channel oxygen vacancy (Vo) and the limited tunability of gate metal work function. Through our ITO-IGZO channel and defect self-compensation approach, our transistor effective mobility $(\mu_{\text{eff}})$ is boosted to $110\mathrm{~cm}^{2}/\mathrm{V}\cdot\mathrm{s}$ with the channel thickness (TCH) scaled down to 4 nm. This unique T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CH</inf> -independent mobility behavior is not observed for IGZO or ITO mono-channel FETs. With such enhancement, our ITO-IGZO FETs exhibit the best-in-class mobility among oxide-based FETs, and are competitive to unstrained Silicon thin film and SOI FETs, while being compatible with sub- 400 °C back-end-of-line (BEOL) processes.