Humidity Sensing Properties and Negative Differential Resistance Effects of TiO2 Nanowires

Abstract

This paper reports a humidity sensor based on TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanowires. The humidity sensor prepared with a simple and easy technology exhibits obviously high sensitivity and fast response/recovery speed. A series of analyses including scanning electron microscopy, specific surface area analysis, water contact angle, and complex impedance spectrum were used to analyze superior humidity sensing performance of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanowires. The results demonstrate that higher sensitivity of the sensor probably stems from larger specific area of nanowires, and its faster response might be attributed to the continuity of nanowires and their intricate connection network, which offer highways for water molecules diffusion and charges transport. Besides, the current-voltage characteristic of the sensor presents a negative differential resistance effect (NDR) with a very low bias voltage under certain humidity level at room temperature, which facilitates compatibility with some low voltage integrated circuit. The tip enhancement of electric field caused by TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanowire end is suggested to explain the mechanism of NDR at very low bias voltage. The high-performance humidity sensor provides a way to study the gender difference in moisture loss through skin evaporation with a non-contact manner, which can avoid the interference of contact state between the sensor and the skin.