Outstanding High Field‐Effect Mobility of 299 cm² V⁻¹ s⁻¹ by Nitrogen‐Doped SnO₂ Nanosheet Thin‐Film Transistor

Abstract

Record high field‐effect mobility (µFE) thin film transistors (TFTs) based on 5 and 7 nm thickness SnON channel layer is reported. The SnON TFT device with 7.6% nitrogen content achieves a record high µFE of 299 cm2 V−1 s−1 at 7 nm thickness and 277 cm2 V−1 s−1 at 5 nm thickness, compared to SnO2 with µFE of 211 cm2 V−1 s−1. At the same 5 nm quasi‐2D channel thickness, this µFE of nanocrystalline SnON transistor is comparable to single crystalline Si and InGaAs metal oxide semiconductor field‐effect transistor (MOSFET) and also higher than the phonon‐scattering‐limited 2D MoS2 FET. From the principle of quantum‐mechanical calculation, the high µFE of nanosheet SnON TFT is due to lower effective mass of electrons, 0.29 m0 in the conduction band in contrast to 0.41 m0 of SnO2. SnON can reduce the defect trap densities by introducing non‐oxide anions where the valence band can be controlled to remove or passivate the oxygen vacancy levels by substitutional alloying with nitrogen anions to circumvent instability, increase on‐current (ION) and improve the µFE. It is highly expected that the high performance quasi‐2D nanosheet SnON TFTs will be utilized in embedded DRAM and monolithic 3D integrated circuits (ICs).

Superior High Transistor’s Effective Mobility of 325 cm2/V-s by 5-nm Quasi-Two-Dimensional SnON nFET

“…The N states in the valence band, principally N 2p character, are the main cause of the bandgap reduction in SnON. SnO2 and N2-doped SnO2 have effective electron masses (me*) of 0.41 mo and 0.29 mo, respectively, where mo is the free electron mass which is reported in our previous work [14]. The me* for SnON is evidently smaller than SnO2, which could result in a larger µeff.…”

Superior High Transistor’s Effective Mobility of 325 cm2/V-s by 5 nm Quasi-Two-Dimensional SnON nFET

“…The N states in the valence band, principally N 2p character, are the main cause of the bandgap reduction in SnON. SnO 2 and N 2 -doped SnO 2 have effective electron masses (m e *) of 0.41 m o and 0.29 m o , respectively, where m o is the free electron mass which is reported in our previous work [ 14 ]. The m e * for SnON is evidently smaller than SnO 2 , which could result in a larger µ eff .…”

“…In this report, we measure the transistor output current over a wide range of V G , equivalent to a Q e close to 1 × 10 13 cm −2 , to analyze the device-scaling mechanism. The major findings beyond our previous published paper [ 14 ] are the much lower µ eff decay rate at high E eff than SiO 2 /Si, high-κ/InGaAs, high-κ/2D MoS 2 nFETs, etc. This is the new discovery that was never reported in any FET device.…”

“…The larger s-orbitals and the stronger overlapping of electron clouds lead to high mobility. We have earlier reported that in SnON, the localized states just above the valence band maximum (VBM) have a predominant N 2p character and the lower conduction states near the conduction band minimum (CBM) were mostly derived from Sn 5s orbitals, which results in high electron mobility in SnON [ 14 ]. This explains why the mobility of SnON nFET is significantly larger than that of ZnO.…”

“…Yet the poor µ eff for a transistor made on the backend dielectric of an IC is the basic challenge. Previously, we reported on the high field-effect mobility (µ FE ) of SnO 2 [ 9 , 12 , 13 ] and SnON FET [ 14 ], but the µ eff is the required important data for transistors. The µ eff can give crucial information on electron-scattering mechanisms over the wide range of inversion charge (Q e ).…”