Hydrated lithium phosphate as a low temperature processable solid electrolyte for high performance printed electronics

Abstract

Ion-conducting oxide (ICO) electrolytes have contributed to the advancement of various electrochemical devices, from lithium-ion batteries to electrochemical sensors. Notably, the ICOs have also been used as solid electrolytes for printed thin film transistors (TFTs). However, the printed TFT technology typically aims for flexible electronic applications, where the high process temperature of ICOs creates a big hindrance. In this regard, in the present study, we propose and demonstrate an extremely low temperature processable (~120 °C) solid electrolyte in the form of hydrated lithium phosphate (Li₃PO₄). The fully inkjet-printed TFTs fabricated with amorphous indium gallium oxide (a-IGO) as the semiconductor material demonstrate excellent transistor performance parameters, such as high On-Off ratio, high width-normalized On-current density (I _D,ON /W), and width-normalized transconductance (g _m /W) of 3.8×10⁸, 63.2 μA/μm, 39.4 μS/μm, respectively, and a subthreshold slope close to the Boltzmann limit (61 mV/decade). The maximum and average linear field-effect mobility of the TFTs is estimated to be 42.8 and 28.9 cm²/Vs, respectively. The unipolar, depletion load type pseudo-CMOS inverters demonstrate rail-to-rail switching, for supply voltages from 0.5 to 2 V, with a signal gain up to 33.4 V/V. The present results demonstrate the emergence of a novel low temperature processed ICO-based solid electrolyte for printed TFTs to be used in various printable, wearable and portable electronic applications.