Overcoming the Mobility–Stability Trade-Off Using an Ultra-Thin Oxide Capping Layer via N2O Plasma Treatment

Abstract

In this work, we first employed an ultra-thin capping layer and nitrous oxide (N2O) plasma treatment to fabricate 3.2 nm indium oxide (In2O3) bottom-gate FETs via atomic layer deposition (ALD). The capped layer provided hydrogen-related defects, enabling the N2O plasma treatment to maintain high on-current (Ion). With a 30 s N2O plasma treatment on capped In2O3, the device exhibited a subthreshold swing (S.S.) of 94 mV/dec, mobility of 61 cm2/V $\cdot $ s, enhancement-mode operation, and improved immunity to stress-induced degradation. The low-frequency noise (LFN) is attributed to mobility fluctuations ( $\Delta \mu $ ) originating from the channel region. The device exhibits a normalized drain current noise power spectral density (SID/I ${_{\text {D}}} {^{{2}}}$ ) of $5.43\times 10^{-12}$ Hz ${}^{\text {$\mathord {-}$1}}$ , a benchmark value among oxide semiconductor field-effect transistors (FETs). X-ray photoelectron spectroscopy (XPS) analysis reveals that N2O plasma treatment induces oxidation and the formation of interstitial oxygen, which consequently shifts the threshold voltage (VT). This approach effectively addresses the trade-off between mobility and positive VT, offering a promising solution for high-performance 3D integration applications.