Oxide-Based Thin-Film Transistors Using Chitosan/Graphene Oxide Composite Solid Electrolytes As Gate Dielectrics

Recently,oxide thin film transistors have attracted wide attention and made considerable development because of their high motilities(>10 cm~2/Vs),low-temperature process,low costs,transparency and large-area production.Among various oxide semiconductors,InGaZnO4(IGZO)and In-Zn-O(IZO)oxide semiconductor films are widely used in the areas of thin-film solar cell,flat panel display,flexible display etc.because they can keep high electron mobility,high transparency as well as good flexibility.Meanwhile,traditional TFTs require large gate voltages to drive because of the weak capacitive coupling between the semiconductor channel and the gate electrode,which increases the power consumption and reduces the portability of the devices,and limits the area of its application greatly.In this paper,we combine graphene oxide aqueous solution with chitosan solution and fabricate low-voltage thin-film transistors using this composite electrolyte as gate dielectric at room temperature successfully.A bottom-gate structure is used:Firstly,an indium-tin-oxide(ITO)film with a thickness of 150 nm was deposited on glass substrate as the common gate electrode by radio-frequency magnetron sputtering.Secondly,a 10 ?m-thick graphene oxide/chitosan composite gate dielectric layer was deposited onto the ITO by spin coating at room temperature.Thirdly,a 50-nm-thick IZO semiconductor layer was deposited at room temperature by radio-frequency magnetron sputtering.Finally,the 200-nm-thick IZO source/drain electrodes were deposited by radio-frequency magnetron sputtering.The entire fabrication process was performed at room temperature.The source/drain electrodes and the semiconductor channel were patterned using nickel shadow masks.The channel length and width of the transistor are 80 ?m 1000 ?m respectively.The electrical characteristics of the devices were measured at room temperature in the dark with a Keithley 2636B semiconductor parameter analyzer.The dielectric capacitance of the GO/chitosan composite electrolyte film was measured with an Agilent 4294A precision impedance analyzer,and using an ITO/composite electrolyte film/ITO sandwich test structure.The experimental results show that the GO/chitosan composite electrolyte film is a good proton conductor with an unit-area capacitance of 3.16 ?F/cm~2.IZO TFTs gated by the GO/chitosan composite electrolyte film exhibits a small subthreshold swing of 100 mV/decade,a high field-effect mobility of 15.2 cm~2V-1s-1,and a large drain current In/off ration of 2×107.The positive and negative bias stability of the devices are significantly improved compared to the devices gated by pure chitosan films.We implemented an inverter with our TFT devices.The voltage transfer characteristics of the inverter were investigated and a maximal voltage gain of 4.8 was realized.The AC performance of the invert was investigated and the inverter responded well to input signals with a maximum frequency of 100 Hz.Meanwhile,we fabricated flexible TFTs on PET substrates,and such devices exhibits good flexibility and a high-performance AND logic operation.Furthermore,two-terminal operation and transistors operated as a two-terminal artificial synapse with good performances were realized.Room-temperature processed low-voltage oxide-based thin-film t:ransistors using graphene oxide/chitosan composite electrolytes as gate dielectrics are very promising for the next-generation low power consumption,wearable,portable,flexible electronics.