Synaptic Emulation Based On Solution-Processed Organic Memristors

In the era of information explosion,traditional computing systems based on von Neumann construction are meeting its intrinsic limitation with heavy load,such as excessive power consumption,difficulty in speed improvement and integration on small scales.Neuromorphic structures can break bottlenecks of traditional integration circuits with the integration of memory and processing units.Depending on the reasonable construction of neurons and synapses,neuromorphic systems could realize complex learning and consideration like human brains.The synapse acting as the connection point of neurons is critical for information transmission.Thus researches of synaptic devices play an important role in application of neural network integration.Currently,memristors are widely utilized as synaptic simulators due to similarity between electrical properties and synaptic behaviors.Since the concept of TiO2 memristors was proposed in 2008,inorganic memristors with binary oxides have been developing rapidly and maturely,but explorations of organic ones are still insufficient on account of unclear mechanism and poor performance.However,merits of organic memristive devices are attracting much attention,such as biocompatibility,low cost and flexibility.Therefore,the objectives of this paper are to design novel organic memristors through solution processing method and simulate a variety of synaptic functions.The main contents of research include following three parts:Firstly:Polymer memristors are prepared by spin coating and composed of polymer electrode layers,ion-doped polymer films and metal electrodes.Conductivity of the memristive devices have close relation with movement of hole carriers.Electrical test results demonstrate apparent bipolar hysteresis effects with application of symmetrical voltages and output current changes continuously with repeated unipolar voltage scans,which are consistent with electrical features of theoretical memristors.Working mechanism model of the polymer memristors can be built reliably based on electrochromic phenomenon of polymer films.Additionally,the difference in doped ion concentration which leads to a change of hysteresis window confirms the reliability of the mechanism analysis further.Secondly:According to the physical model above,small molecule conjugate materials are chose in preparation of organic memristors instead of polymers.Since the properties of small molecule organic materials are similar to those of polymers,for example,they all belong to p-type semiconductors,the measured electrical results are also consistent.Consequently,electrochemical principle of ion-regulating resistance can be widely applied in memristive realization of other organic semiconductor materials.Thirdly:Because human brains can deal with complex behaviors and emotions with low power consumption and high speed,neuromorphic simulations are attracting more interest of researchers.Here,polymer memristors are put into synaptic simulations.Through comparison with biological synaptic activities and functions,voltage pulses are imported to mimic facilitation and depression behaviors,coexistence of short-term and long-term plasticity and frequency-dependent plasticity in synapse transition.Additionally,ion motions inside memristors during simulation have similarity with molecular mechanisms of chemical synapses,which provides a potential approach for neuromorphic bionic applications.