2D transistors rapidly printed from the crystalline oxide skin of molten indium

Abstract

Ultrathin single-nm channels of transparent metal oxides offer unparalleled opportunities for boosting the performance of low power, multifunctional thin-film electronics. Here we report a scalable and low-temperature liquid metal printing (LMP) process for unlocking the ultrahigh mobility of 2-dimensional (2D) InOx. These continuous nanosheets are rapidly (60 cm s−1) printed over large areas (30 cm2) directly from the native oxide skin spontaneously formed on molten indium. These nanocrystalline LMP InOx films exhibit unique 2D grain morphologies leading to exceptional conductivity as deposited. Quantum confinement and low-temperature oxidative postannealing control the band structure and electronic density of states of the 2D InOx channels, yielding thin-film transistors with ultrahigh mobility (μ0 = 67 cm2 V−1s−1), excellent current saturation, and low hysteresis at temperatures down to 165 °C. This work establishes LMP 2D InOx as an ideal low-temperature transistor technology for high-performance, large area electronics such as flexible displays, active interposers, and thin-film sensors.

Continuous Liquid Metal Printed 2D Transparent Conductive Oxide Superlattices

“…Indeed, our previous XPS analysis showed significantly higher C and N content in sol‐gel InO x films which was likely related to the limited sol‐gel precursor decomposition at low‐temperatures. [ 25 ]…”

“…The intensity of the (222) and (400) peaks grows monotonically at higher deposition temperatures, which agrees with our past observations of increases in crystallinity with post‐annealing of liquid metal printed InO x films formed at 165 °C. [ 25 ]…”

“…This can be understood by considering that GaO x is, itself, substantially less conductive than InO x , with a conductivity of ≈0.01 S cm –1 (Figure S3, Supporting Information), which could limit interlayer transport across the vertically overlapping grains. Our past studies of electronic transport in 2D InO x have shown that this overlap can produce higher electron mobility, [ 25 ] which explains the clear trend that stacking InO x layers can improve transport. To further understand the mechanism of the modulation doping, we also utilized the CLMP to fabricate films capped by CLMP AlO x , SbO x , and SnO x for comparison ( Figure a) with the conductivity of pure InO x and films capped by GaO x .…”

“…This result is also consistent with our recent report of liquid metal printed 2D InO x transistors with field effect mobility as high as 67 cm 2 V –1 s –1 . [ 25 ] The films with the highest carrier concentration in the range of 8 × 10 19 –2 × 10 20 have slightly lower Hall mobility in the range of 10–15 cm 2 V –1 s –1 , which may indicate that these heterostructures induce additional trapped carrier scattering. [ 36 ] These observations correspond well with the trend that films with multiple layers of InO x are more conductive (Figure 2b).…”

“…Indeed, our previous XPS analysis showed significantly higher C and N content in sol-gel InO x films which was likely related to the limited sol-gel precursor decomposition at low-temperatures. [25] Selected area electron diffraction (SAED) analysis from the superlattice films (Figure 3a) shows peaks that can be indexed to the cubic phase of In 2 O 3 , with the strongest peak being the typical (222) orientation of InO x . X-ray diffraction (XRD) characterization confirms that 2D InO x films formed by CLMP are crystalline in their as deposited state but the GaO x films printed by this method have been observed to be amorphous across the entire range of deposition temperatures.…”