Two-parameter Memory Device And Study Of Synaptic Plasticity With Memristance And Memcapacitance Based On Donor-Acceptor Copolymers

With the advent of the information age,big data put forward higher requirements for the capacity of storage devices.It is urgent to find a new type of electronic components because Moore's law is facing severe challenges.Memory resistance emerges as the times require.Recently,memory elements(memory resistance and memory capacitance)represented by memory resistance have been widely investigated for the nonvolatile storage,artificial intelligence computer,analog circuit and artificial neural network areas due to the specific nonlinear electrical properties,especially in nonvolatile storage and artificial neural network.In this paper,the memory device of Al/copolymer/ITO structure is fabricated and the two-parameter memory characteristics based on the memory resistance and the memory capacitance has been achieved.The synaptic plasticity of devices based on the memory capacitance is studied.The main results are summarized as follows:1.A new copolymer with the D-A structure is designed and synthesized for achieving two-parameter memory characteristics.The molecular structure of the copolymer is analyzed and identified by FT-IR and ~1H NMR spectra.Film-forming properties of copolymer are characterized by SEM images.2.The memory device of Al/copolymer/ITO structure is fabricated.The memory resistance characteristic is tested and the memory capacitance behavior under the single resistance state is also studied.It is found that there are two resistance states and four capacitance states.The two-parameter and multi-state memory characteristics are realized.In addition,the memory capacitance behavior is regulated by controlling the voltage amplitude.In addition,we designed the voltage pulse signal to write and read the resistance and capacitance states.The two-parameter and multi-state memory characteristic of the device provides an effective approach for the realization of nonvolatile multi-level storage.3.In order to study the memory mechanism of the device,we studied the relationship between resistance and temperature.It is found that the resistance decreases with the increase of temperature,which indicates that the device has the obvious semiconductor properties.Furthermore,the fitting results of I-V data show that the mechanism of resistance switching is in good agreement with the classical trap-controlled space charge limited current theory(SCLC).Then,the capacitance switch mechanism of the device is analyzed by combining the D-A properties of the copolymer film and the phase diagram of the polarization force microscope(PFM).The capacitance switching is closely related to the polarization characteristics of D-A structure in the copolymer film.Based on these results,the correlation between memory resistance and memory capacitance is established by introducing a polarization operator of molecules,and the matrix model describing the two-parameter and multi-state memory characteristics is given.4.An artificial synaptic device with Al/copolymer/ITO structure is fabricated.The device exhibits the bidirectional gradual modulation of the capacitance state,which make it possible to simulate synaptic plasticity.The device demonstrates the excellent synaptic functions,including the paired pulse facilitation and paired pulse depression,potentiation and depression,learning-forgetting-relearning behavior.And the transition from short-term plasticity to long-term plasticity can be achieved by adjusting the number of pulses,which demonstrates that memory capacitance can be used to simulate synaptic plasticity.In addition,the device can respond to temperature stimuli in a highly neuron-like fashion,which bridges the gap between the neuromorphic chips and the temperature sensing in real world.These results provide a powerful reference for the study of artificial synapses based on memory capacitance.