Application Of Laser-scribed Graphene Oxide In The Humidity Sensor

Humidity sensors play an important role in the daily life,such as medical treatment,indoor humidity detection,and industrial and agricultural environment monitoring.Humidity sensors should meet the requirements of fast response to humidity change,low cost and good flexibility.Among many kinds of humidity sensors,capacitive humidity sensors have been extensively used in the commercial field as a result of their fast response and low cost.The material and manufacturing method of the capacitive humidity sensors determine their performance.However,the commercial capacitive humidity sensors usually have low sensitivity due to the properties of electrode and sensing materials and their manufacturing methods.In this paper,we made a new type of capacitive humidity sensor by using laser-scribed graphene oxide(LSG) as electrodes and graphene oxide(GO) and tin dioxide as sensing materials.This device has the advantages of high sensitivity,good stability and small volume.The main research content of the paper are:(1)DVD laser scribing of a layer of graphene oxide(GO) selectively reduced the GO in one step to make interdigital sensing electrodes while the un-scribed GO between the interdigital electrodes serves as sensing layer.The interdigital electrodes(IDEs)are laser-reduced graphene oxide(rGO or LSG)and the sensing layer are the un-scribed GO.This is an all-graphene capacitive humidity sensor(LSG humidity sensor)with an rGO/GO/rGO interdigital structure.The capacitance and AC impedance responses of the LSG humidity sensor with a change of RH between 11% and 97% were analyzed.And the humidity sensor has shown good stability and sensitivity during a 40 days-test.(2)Based on the design of the above LSG humidity sensor,a highly sensitive and low-cost LSG-GO humidity sensors were prepared by coating the(IDEs)and the GO sensing layer with additional GO layer with different GO content.The different LSG-GO sensors were tested in a range of 19.0%?97.4% RH.It was found that the LSG-GO humidity sensor made with additional GO coating of 150ml GO(4 mg/ml)had the highest sensitivity.This LSG-GO₁₅₀ humidity sensor was continuously monitored for 32 days and showed good stability.The humidity sensing mechanism was discussed.Results indicate that LSG-GO₁₅₀ is a high performance humidity sensor.(3)We directly used a DVD laser to scribe GO/SnO₂ layer(containing GO and SnO₂ semiconductor nano-particles)to obtain a new LSG-GS humidity sensor.The laser-reduced graphene oxide(rGO or LSG) with good conductivity was formed in the place where the laser was irradiated,which can be used as the electrode of the sensor.The laser un-scribed areas were still in the GO/SnO₂ state,which can be used as the sensing layer of the humidity sensor.The sensor fabrication is a one-step process which is facile and cost-efficient.When a mass ratio of GO:SnO₂ in the composite reaches 1:1,the humidity sensor(named as LSG-GS₁)has the best properties which exhibits high sensitivity and very quick response/recovery time(20s for adsorption and 18s for desorption)in the range of 11%?97% relative humidity(RH).In addition,the LSG-GS₁ also has very good stability after monitoring for 41 days.Such excellent performances of the humidity sensor can be attributed to synergistic effect of SnO₂ and GO within the composite layer.Therefore,LSG-GS₁ humidity sensor has high practical value and application prospect.