| Due to the excellent optical and electrical properties of WO3 wide bandgap oxide semiconductor,it has attracted increasing attention in broad application prospects,such as electronic information devices,smart windows,gas sensitive devices and other fields.Control of the physical properties of WO3 has always been a hot topic in physics,chemistry and other related disciplines.It is an ideal method to regulate the electrical and optical properties of WO3 devices continuously and reversibly by electric field.The applied electric field can change the concentration of carriers in devices through electrostatic interaction,and as a consequence,change the performance of the devices.This regulation mode is volatile,which means the performance of devices will quickly return to its initial state when the external electric field is removed.Another modulation method is to use ionic migration driven by electric field,resulting in electrochemical redox reaction or doping.This regulation is non-volatile,and its regulation effect on devices physical properties will be retained after the removal of external electric field.In this thesis,we use electric field induced ion intercalation/extraction to regulate the physical properties of WO3 films.The electrochromic properties and the underlying mechanism of WO3 thin film was explored.Based on the electrical property modulation of WO3 thin film,an electrolyte-gated artificial synaptic transistor device is designed and constructed,and the rich physical mechanism behind it is discussed.The main contents are summarized as follows:(1)WO3 thin films were prepared by reactive sputtering at room temperature using magnetron sputtering technology.The microstructure and surface morphology of films were characterized by XRD and AFM,which indicate that amorphous WO3 films with high specific surface area were prepared.Subsequently;,we studied the effect of annealing on the films and found that surface roughness of films would be reduced by annealing.(2)The electrochromic properties of amorphous WO3 films were studied by using LiClO4/PC solution as the electrolyte.An electrochemical workstation was used to apply a circulating electric field to the device to control the flow of Li+into and out of WO3 film,and more than 75%of the optical modulation range was achieved.XPS measurement confirms that the valence state of tungsten ions changes during the electrochromic process and redox reaction takes place.In addition,the optical modulation range decreases to about 50%after 1000 cycles,which is mainly related to the decrease of charge transfer during the cycle.(3)An Au/WO3/Ta2O5/Li2SiO3/Ta2O5/Au all-solid three-terminal electrolyte gated transistor was prepared.The top Ta2O5 works as a protective layer,meanwhile the middle Ta2O5 plays a blocking layer.Electrical properties of WO3 thin films are controlled by electric field to drive the intercalation/extraction of Li+in WO3.Because different gating voltage amplitudes have different regulation mechanisms on the resistance state of the WO3 channel,volatile and nonvolatile channel conductance regulation can be realized to simulate the short-term plasticity and long-term plasticity in biological nerves.In addition,devices have good retention characteristics due to the Ta2O5 barrier layer.By controlling the number of pulses applied to the gate,devices can realize multi-state storage.Finally,a three layer network was built to simulate image recognition training of handwritten data set using the conductance updates of the devices,which shows a high recognition accuracy more than 95%. |
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