Abstract
Graphene oxide (GO) is a promising candidate for humidity sensing, and the uniformity and thickness of GO films are important for the reproducibility and test signal strength of humidity sensors. In this paper, uniform and thickness-controllable GO films are first formed by the surface tension of different concentrations of GO solution and then transferred to surface acoustic wave (SAW) humidity sensors. This GO film formation and transfer process has very good repeatability and stability, as evidenced by the humidity response of the sensors. With the help of the uniform and highly oxidized GO film, the humidity sensors show a significantly high sensitivity (absolute sensitivity of 25.3 kHz/%RH and relative sensitivity of 111.7 p.p.m./%RH) in a wide test range from 10%RH to 90%RH with very little hysteresis (<1%RH). The sensors achieve good reversibility, excellent short-term repeatability and stability. Moreover, the humidity sensors also show a fast response and recovery time of <10 s.
Highlights
In recent years, applications of humidity sensors have expanded from traditional industry and agriculture to medical, consumer electronics, and smart homes[1,2]
Inspired by a fabrication process of free-standing inorganic sheets[33], we propose a simple and convenient Graphene oxide (GO) film-forming method based on the surface tension of GO
After 1 μm aluminum nitride (AlN) was deposited over the Si wafer by reactive sputtering, a 200 nm gold layer was patterned on the surface of the AlN layer to form the interdigitated transducers (IDTs) and reflectors through a lift-off process
Summary
Applications of humidity sensors have expanded from traditional industry and agriculture to medical, consumer electronics, and smart homes[1,2]. Humidity sensors are required to have high sensitivity, a wide test range, small hysteresis, and fast response and recovery and need to have low cost, low energy consumption, and easy integrability[3]. Research on humidity sensors is mainly based on optical[4], resistive[5,6], capacitive[7,8], and acoustic resonant devices[9,10]. The capacitive and resistive devices are small, simple, and low cost, but they have the disadvantage of poor test accuracy. The optical devices have high test accuracy, they consume too much energy and are difficult to integrate
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