Influence Of Thickness Of Semiconductor Towards Gas Sensors Based On Organic Thin Film Transistors

Organic thin film transistor?OTFT?is a kind of electronic transistor device,which is composed of organic semiconductor based on field effect.It has been receiving intriguing attention because of their inherent merits,such as lightweight,low fabrication costs,and compatibility with a wide range of flexible substrates.OTFT has widely prospect in applications including radio frequency identification tags,display backplanes,and sensor devices.Recently,gas sensor based on OTFT has become one of the hottest research points on the field of organic electronic.Nowadays,there has been a lot of work focused on the strategies and methods to improve the sensitive response of OTFT.However,most of them have the bottleneck problem of high cost or low repetition rate.Therefore,in this work,we focus on the influence of the film thickness of semiconductor on the property of OTFT gas sensors to exploit a simple but efficient way to enhance the performance of OTFT gas sensors.In this work,four kinds of organic thin film transistors with various thicknesses of organic semiconductor were fabricated.All the devices were in“bottom-gate”and“top-contact”configuration,using CuPc,PMMA,and Au as semiconductor,dielectric and electrode,respectively.The function layers were deposited onto an ITO glass substrate.This paper is constituted by the following parts:1.The dependence of electrical characteristics on organic semiconductor thickness modulation has been studied in detail.Through the property measurement under pure N₂,we identify that device with thinner CuPc film exhibited larger charge carrier mobility and current on/off ratio,meanwhile lower turn-on voltage.Through detailed analysis,the reason was concluded to the introduction of located states and the difference of grain size.2.The dependence of sensing properties on organic semiconductor thickness modulation has been discussed.Better performances were obtained in thinner devices under NO₂ exposure.When 1 ppm NO₂ was introduced,the response of 10 nm CuPc OTFT exhibited¹60 folds higher than that of 40 nm CuPc OTFT.When increase NO₂concentration to 30 ppm,the response of 10 nm CuPc OTFT reached 241.1%,which remained³5 folds higher than that of 40 nm CuPc OTFT.We consider that the enhancement of sensing properties in thinner devices was mainly attributed to the advanced NO₂ diffusion efficiency and smaller CuPc grain formation.3.The dependence of selectivity on organic semiconductor thickness modulation has been investigated.SO₂,NH₃,and H₂S,except NO₂ were introduced in the test,respectively.OTFTs with various CuPc thickness showed distinct response to different gases,and the larger variation of responses were got in devices with thinner CuPc film.Therefore,we can easily realize a gas sensor array with different thicknesses of one organic semiconductor to distinguish noxious gases from each other.In summary,this work enriches the fabrication method of the research field of OTFT,and paves a promising way on the development of high performance OTFT sensors at room temperature in the aspect of processing method and functional material.