Memory capacitance behavior at single resistance state in memristor and multi-state characteristic

Abstract

With the advent of the information age, big data put forward higher requirements for capacity of storage devices. Compared with the method of reducing the size of the device to enhance the integration level, the high density storage of increasing the memory state of the single device will be very beneficial to solving the problem. In this work, we propose an idea of two-parameter and multi-state memory device involved in both resistance and capacitance operation levels. At first, a new donor-acceptor (D-A)-type copolymer is designed and synthesized. Then, the memory device of Al/copolymer/ITO structure is fabricated, and the current-voltage (<i>I-V</i>) and capacitance-voltage (<i>C-V</i>) curves are measured by a KEITHLEY 4200 semiconductor characterization system. The device not only displays the obvious memory resistance characteristics, but also has the memory capacitance behavior in single resistance state, which results in two resistance states and four capacitance states, so that the device has the capability of two-parameter and multi-state memory. In addition, the device shows more capacitance states after the switching behavior has been modulated by the voltage amplitude, which provides an effective method to control the memory states. In order to study the conductive mechanism of the device, we test the relationship between resistance and temperature. It is found that the resistance decreases with the increase of temperature, indicating that the device has the obvious semiconductor properties. Furthermore, the fitting results of <i>I-V</i> data show that the mechanism of resistance switching is in good consistence with the classical trap-controlled space charge limited current theory. The capacitance switching in single resistance state is closely related to the polarization characteristic of D-A structure in the copolymer film. The polarization force microscopy phase image shows that the copolymer film has obvious polarization and depolarization characteristics under the external electric field. Based on the polarization characteristics of copolymer, 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. The above results show that the multi-state memory characteristics will store more information than 2-bits mode in a single cell, which will provide a reference for improving the storage density of information.