Fabrication And Performance Of Graphene Oxide-based Synaptic Devices

In the field of artificial intelligence technology,artificial neural networks based on von Neumann architecture face many application barriers because of their physical limitations.To break the shackles of this architecture,it is an appropriate solution to construct neuromorphic computing systems by using electronic devices to simulate the synapses and neurons in biological system.Artificial synaptic devices are one of the core components of building neuromorphic computing systems,and their main function is simulating various types of synaptic plasticity of biological synapses,such as short-term depression(STD)and short-term facilitation(STF).The synaptic plasticity can be simulated by using memristors,transistors and other electronic devices,and their performances are often related to the material systems they used.Because of the simple preparation process and rich and adjustable electrical properties e.g.proton conductivity,graphene oxide(GO)is a promising material for artificial synaptic devices.In this thesis,we focus on the preparation and the properties of the artificial synaptic devices.We used GO as the functional layer to prepare two-terminal all-carbon synaptic devices and optoelectronic synaptic devices.In addition,an improvement scheme was proposed to the graphene electrode used in the two-terminal all-carbon synaptic device.The main results are described as follows:(1)Graphene-GO-Graphene two-terminal all-carbon synaptic device was prepared by filtration and wet-transfer process.The device showed the STD synaptic plasticity,and the minimum power consumption of a single synaptic behavior was as low as 20 a J.Capacitor-frequency characteristics and other tests indicated that the mechanism of STD characteristics of the device was the accumulation and diffusion of protons at the functional layer-electrode interface.(2)An improvement scheme for graphene electrodes in two-terminal all-carbon synaptic device was proposed.Using PET-silicone two-layer polymer material as the transfer medium,the monolayer graphene prepared by chemical vapor deposition was transferred to the target substrate.A shadow mask was used to pattern the monolayer graphene.The graphene showed an Ohmic conductivity,with a resistivity of about1.15×10~5Ω.The patterned graphene can be used as the replacement of filtered graphene electrodes.(3)High quality GO film was prepared by filtration and used as functional layers to construct the optoelectronic artificial synaptic devices.The device showed the STD synaptic plasticity.Moreover,STF as well as STD can be obtained by applying optical signals.Electrochemical impedance spectroscopy and other tests showed that the mechanism for the device’s STD synaptic plasticity was also the accumulation of protons at the functional layer-electrode interface,while the STF characteristics came from the photo-induced photochemical reaction to GO,which increased the proton concentration.