Research On The Design,Fabrication And Performance Of Capacitive Humidity Sensor Based On SnO₂/MoS₂

Humidity sensors,as an important branch of the sensor field,play an important role in various fields.It can be divided into six categories according to the measurement principle.Thereinto,capacitive humidity sensors have the most widely application due to high sensitivity.Capacitive humidity sensors have been developing for many years.Although many problems have been solved,there is still a drawback that its sensitivity at low humidity range is much lower than at high humidity range.The main reason,reported in papers,is that the capacitance of the sensor increases exponentially as humidity augment.Nowadays,scholars try to solve this problem by developing materials which have better properties.They attempt to improve the sensitivity at low humidity range by increasing it in entire humidity test interval,but this method does not solve the problem fundamentally.Therefore,this paper focuses on research of capacitive sensors.We probe the sensor performance with effect of electrode structure and seek a method to improve the sensitivity of sensors at low humidity range.In this paper,we chose to use SnO₂ to modify MoS₂ as the sensing materials to improve the performance of humidity detection.This composite is first used in capacitive humidity sensors.It was synthesized by hydrothermal method,morphology and crystal form were characterized by scanning electron microscopy and X-ray diffraction.In order to study the effects of humidity sensitivity in different doping ratios of composites,we synthesized three different doping ratios（10:1,5:1 and2:1）of SnO₂/MoS₂.For testing electrode,the interdigital electrode was fabricated by MEMS（Micro-Electro-Mechanical System）process.In order to explore the relationship between the response of sensor’s humidity and the gap size of interdigital electrode,the electrode gap is designed to be discrete variable and the minimum gap size is 5μm while the maximum size is 300μm.According to our research,the size of interdigitated electrode gap has an important influence on humidity-sensitive response behavior because of the difference in surface conduction mechanism.As for sensors with small electrodes gap,the capacitance descends exponentially with the increase of humidity which result in ultra-high sensitivity in low humidity range.Inversely,the sensors with large electrode gap have an ultra-high sensitivity in high humidity range because the capacitance value increases exponentially when the humidity augment.Moreover,different sensing materials have different segmentation thresholds in large or small electrode gap.The experimental results show that the composite with a mass doping ratio of2:1 has a small gap threshold of 20μm and a large gap threshold of 100μm.It has the maximum response both at the small and large electrodes gap and many other excellent properties such as short response time and recovery time,small hysteresis and excellent repeatability.As for the SnO₂/MoS₂ humidity sensor based on doping ratios of 10:1 and 5:1,the small gap and large gap segmentation thresholds are both larger than 300μm.Moreover,the sensor with 10:1 doping ratio has the highest sensitivity at low humidity range.