Oxide Electronic-Double-Layer Transistors & Neuromorphic Devices

During the past ten years,artificial intelligence has been developed rapidly and becomes an indispensable part of our life.However,the current artificial intelligence products are built on the Von Neumann architecture computers through a lot of algorithm.The storage unit and the data processing unit in these computers are separated and a large amount of data will be transmitted between the storage unit and the processing unit.In the big data era,this will inevitably limit the computational efficiency.Human brain is an intricate network consisting of 10¹¹neurons and each neuron is connected with other neurons though 10³-10⁴synapses.There are a large number of parallel connections in the human brain,thus our brain can process multi-dimensional information simultaneously,and this process is always selective,plastic and fault tolerant.In recent years,lots of emerging electronic devices were put foreword to simulating synapse and neuron functions.The simulation of synapse functions is widely believed as the first step to build the artificial intelligence system.Oxide electric-double-layer（EDL）transistor is a kind of field effect thin film transistor which uses electrolyte as gate insulator and oxide semiconductor as channel.Under the external electric field,ions in electrolyte will migrate and gather at the interface of electrolyte and semiconductor to induce the generation of charge carriers in semiconductor.As a result,a large EDL capacitance will be formed and the operation voltage of the transistor can be effectively reduce.Since the EDL transistor is a kind of ion/electron coupling device,the mechanism is similar to the process of information transmission in the synapse.Thus,it is possible for EDL transistors to simulate synaptic functions.In recent years,a series of results has been reported.In this thesis,we fabricated three types of oxide EDL transistors.First,we studied the electrical properties of these transistors,and then we used these devices to simulate some synaptic functions.The specific contents are as follows:（1）An IZO EDL transistor gated by PVA/GO electrolyte was fabricated by radio-frequency magnetron sputtering with a metal-shadow mask.The specific capacitance of PVG/GO film is～2.1μF/cm²and the leakage is less than 3 n A.The EDL transistor exhibits good electronic performance,such as a high current on/off ratio of～3.1×10⁵,a low subthreshold swing of～107 m V/decade,a small threshold voltage of～0.12 V.By application of various pulse voltages,some short-term synaptic functions were successfully mimicked,such as EPSC,PPF,PTP and filtering behavior.The EPSC response is adjusted by pulse amplitude and width.Moreover,by application of repeated high ampiltude pulse,the transition from short term memory to long term memory is realized.By applying different bias on a lateral gate,long term plasticity also can be tuned.（2）Chitosan solution was drop-cast onto ITO substrate and dried in ambient air to form a uniform chitosan film.The root-mean-square roughness of chitosan film is estimated to be～1.6 nm which is suitable for electronic device applications.The molecular structure of chitosan film was obtained by FT-IR spectra.A high capacitance of～2.9mF/cm²were obtained.The ITO EDL transistor with three lateral gates were fabricated with a self-assembing processing by sputtering with a metal-shadow mask.The current on/off ratios are all over 10⁵,suggesting that the device can be regulated by different gates.By application of pulse and bias on two lateral gates respectively,EPSC and filtering are tuned.At last,we investigated the spatiotemporal integration functions of dendrite,and the super-linear integration and coincidence detection are realized.（3）The IWO semiconductor was prepared on chitosan film by sputtering,then Ag electrodes were evaporated on the IWO films to fabricate the IWO EDL transistor.The capacitance and current on/off ratio are 5.7μF/cm²and 2.0×10⁶,respectively.The EPSC response are deeply investigated by changing pulse amplitude,width and reading voltage.The energy consumption can be reduced to 1.3f J by application of a pulse（0.1 V,35 ms）with a reading voltage of 10^-4V.Based on different pulse schemes,Hebbian and anti-Hebbian learning rules are achieved.Multistore memory（sensory memory,short-term memory and long-term memory）are also mimicked by application of a pulse（4 V,20 ms）with different pulse number and frequency.Finally,classical conditioning was successfully demonstrated in a single IWO EDL transistor.Our results suggest that such oxide neuromorphic transistors have potential advantages in neuromorphic applications.