Optoelectronic Synapse Devices Based On A-Si_1-x:Ru_x Thin Films

For human beings,nearly 80%of external information is obtained through the eyes,so artificial visual system has always been an important part of artificial intelligence.Using electrical synapse devices to build artificial visual systems requires image sensing modules to sense optical signals and convert them to electrical signals,increasing the complexity,and power consumption of the artificial visual systems.Optoelectronic synapse devices can directly sense,calculate and store optical signals.Compared with electrical synapse devices,the optoelectronic ones have lower power consumption,higher bandwidth,and lower crosstalk,which are regarded to be the best choice to build artificial visual systems.So far,the external optical signals used to simulate synaptic behaviors are mostly ultraviolet or blue light,and the advantages of optoelectronic synapse devices in bandwidth have not been fully reflected.In this thesis,based on a-Si_1-x:Ru_x films,ITO/a-Si_1-x:Ru_x/ITO and ITO/SiO_y/a-Si_1-x:Ru_x/ITO optoelectronic synapse devices were successfully fabricated through magnetron sputtering.The electrical,optical,and synaptic properties as well as the working mechanisms have been investigated.The main results are as follows:（1）The a-Si_1-x:Ru_x films are near-infrared sensitive materials with low resistance and high absorption.The optoelectronic synapse device structured as ITO/a-Si_1-x:Ru_x/ITO has a certain persistent photoconductive effect in a wideband range from 450 nm to 905 nm,completely simulating the paired-pulse facilitation behaviors.However,due to the weak persistent photoconductive effect,the device could not further realize the transformation from short-term plasticity to long-term plasticity.（2）Compared with the ITO/a-Si_1-x:Ru_x/ITO device,ITO/SiO_y/a-Si_1-x:Ru_x/ITO optoelectronic synapse devices have stronger persistent photoconductive effects.The photocurrent decreases with the increase of thickness but increases with the increase of oxygen content of the SiO_y layer.The persistent photoconductive effect is enhanced with the increase of the film thickness but becomes weaker with the increase of oxygen content of the inserted SiO_y functional layer,which plays a positive role in regulating the barrier height for the persistent photoconductive effect of the optimized device.（3）Based on ITO/SiO_y/a-Si_1-x:Ru_x/ITO memristive devices,many optoelectronic synapse behaviors,including paired-pulse facilitation,short-term plasticity to long-term plasticity transition,and learning experience,have been simulated successfully under light excitation.The artificial visual functions such as gray image preprocessing and iris effect have been successfully simulated by an array composed of individual ITO/SiO_y/a-Si_1-x:Ru_x/ITO optoelectronic synapse devices.Moreover,the ITO/SiO_y/a-Si_1-x:Ru_x/ITO synapse device could also realize the continuous regulation of resistance by electric excitation,and has the potential to be used as electrical synapse.