Photoactivated high-k lanthanum oxide-aluminum oxide (La2O3–Al2O3) alloy-type gate dielectrics for low-voltage-operating flexible transistors

Abstract

Low-temperature-processable gate dielectrics with high dielectric constants, low leakage current, and good electrical/mechanical stabilities are largely pursued in diverse electronics including flexible transistors, wearable sensors, integrated logic circuits, and various optoelectronic devices. Here, we report low-temperature photochemically activated gate dielectrics based on a lanthanum oxide-aluminum oxide (La2O3–Al2O3 or LAO) alloy system for a utilization in flexible metal-oxide thin-film transistors (TFTs). With proper alloying of La2O3 and Al2O3 at an optimal ratio, synergetic effects could be achieved from both gate dielectric materials, high dielectric constant and excellent insulating properties. With a La:Al ratio of 2:8, LAO gate dielectrics with high dielectric constant (k = 10.72), low surface roughness (0.517 nm), low leakage current density (1.7 × 10−10 A cm−2 @2 MV cm−1), and high breakdown field (∼4.8 MV cm−1) were achieved. By utilizing the photo-annealed LAO as a gate dielectric, low operating voltage (≤5 V) solution-processed indium-gallium-zinc-oxide (IGZO) TFTs having saturation mobility of 8.5 ± 3.25 cm2 V−1s−1, linear mobility of 10.8 ± 2.03 cm2 V−1s−1, subthreshold slope of 0.228 V dec−1, and on/off ratio of ∼105 are demonstrated. Furthermore, the fabricated IGZO TFTs exhibited negligible hysteresis characteristics (<0.1 V) and good bias stabilities (threshold voltage shift < ±0.1 V). Using an ultrathin (∼2 μm) polyimide film as a substrate, flexible IGZO TFTs successfully operating at a bending radius of 2 mm were realized.