Comparative study of high-k metal oxide–PVP/PMMA hybrid gate dielectrics for low-temperature, all-solution-processed flexible In2O3 thin film transistors

Abstract

Flexible thin-film transistors (TFTs) require dielectric layers that simultaneously provide high capacitance, low leakage current, and mechanical robustness during processing, while being compatible with low-temperature processing on polymer substrates. Here, we report a systematic comparative study of organic–inorganic hybrid gate dielectrics obtained by blending a PVP/PMMA co-polymer with five high-k metal oxides (Al₂O₃, HfO₂, ZrO₂, Gd₂O₃ and Y₂O₃) via a low temperature sol–gel route and spin-coating, followed by ≤200 °C thermal treatment. The dielectric properties were evaluated in rigid and flexible MIM capacitors and subsequently integrated into fully solution-processed In₂O₃ TFTs fabricated on glass and flexible PEN substrates. Among the systems, ZrOx–PVP/PMMA delivers the highest dielectric constant which, in rigid TFTs, enables a saturation mobility of 1.22 cm² V⁻¹ s⁻¹, an I_ON/I_OFF ratio of 10⁶, a threshold voltage of 1 V and a subthreshold swing of 0.75 V dec⁻¹, while AlOx–PVP/PMMA shows increased hysteresis consistent with residual –OH related traps. On flexible PEN, devices using HfOx–PVP/PMMA and ZrOx–PVP/PMMA retain stable operation under bending radii down to 7.5 mm with negligible parameter variation, highlighting the mechanical resilience of the hybrid networks. This systematic comparison of five metal-oxide chemistries within the same PVP/PMMA matrix demonstrates the viability of low-temperature, all-solution processed hybrid dielectrics for next-generation flexible oxide electronics.