Investigation On Operation Methods Of Resistive Random Access Memory

Resistive random access memory(RRAM) is one of the most promising candidates for future high-density non-volatile memory(NVM) application, owning to its characteristics of simple cell structure, fast program/erase(P/E) speed, excellent scalability, low power consumption, and good compatibility with the standard complementary metal–oxide–semiconductor(CMOS) process. However, in order to meet the practical application requirements, the performance of RRAM still needs to be improved in the following aspects:(a) The controversial switching mechanism;(b) The reduction of the variations of resistive switching parameters. So far, few works have been systematically studied the detailed influence of DC and pulse operations on the performance of oxide-based RRAM. In this work, to address the above challenges, we have investigated the impact of program/erase operation on the performance of the RRAM device through comprehensive device characterization and exploring possible solutions in test and operation methods.This thesis focuses on the innovation of operation methods and improvement of the instrument function module to improve the performance of the RRAM device, mainly including the following parts:(1) A novel pulse operation method is proposed to improve the performance of RRAM device based on a Ti/Hf O2/Pt structure. In the current sweep mode, the SET process is current-controlled with the applied positive bias. In the negative voltage sweep mode for RESET process, RESET is voltage-controlled. Based on the different characteristics of the SET/RESET process under different control mode in DC sweep, we use pulse operation with the width and height can be adjusted, which can control the SET and RESET process, respectively. Our new method is different from the traditional pulse operation in which both the width and height of program/erase pulses are constant. So the SET/RESET events can be accurate achieved by the adjusting width or height of the pulse. Through the operation, the uniformity and endurance of the RRAM device have been significantly improved.(2) The functional module of the electrical characteristic measurement system was developed. Firstly, we designed a pulse measurement circuit to make the voltage dropped on the RRAM more stable and to decrease the parasitic capacitance, reducing the variation of the applied voltage and the device parameter. Secondly, a measurement method, which can gain the dependence of the program/erase speed on the voltage amplitude automatically, was proposed. At last, the endurance of RRAM was improved due to elimination of the hard-breakdown by modulating the pulse width forced on the RRAM during program process.These results have profound significance for the optimization and application of the RRAM.