Analysis and control of the intermediate memory states of RRAM devices by means of admittance parameters

Abstract

A thorough study of the admittance of TiN/Ti/HfO 2 /W bipolar resistive memories [resistance random access memory (RRAM)] was carried out under different bias conditions and in a wide range of ac signal frequencies. We demonstrate that a continuum of intermediate states can be obtained by applying appropriate dc bias waveforms. Cumulative writing and erasing admittance cycles were performed by applying triangular voltage waveform of increasing amplitude. The influence of the initial conditions on the variation of the real (conductance) and imaginary (susceptance) components of the admittance is described. An accurate control of the memory state is achieved both in terms of the conductance and the susceptance by means of an adequate selection of the voltage values previously applied. A method to obtain three-dimensional voltage-conductance-susceptance state-plots is described in detail. Memory maps of admittance parameters as a function of the programming voltage are made by sensing the memory state at 0 V, without static power consumption. The multilevel nature of RRAM devices and their suitability for neuromorphic computation are demonstrated.

Memristive State Equation for Bipolar Resistive Switching Devices Based on a Dynamic Balance Model and its Equivalent Circuit Representation

“…As showed in [31], major (maximum voltage excursion) and minor (bounded voltage excursions) memory loops exhibit selfsimilar properties. The positive ridge function for the major loop  is obtained from (5) considering  0 =0:…”

Current Pulses to Control the Conductance in RRAM Devices

“…These devices consist of an insulating layer interposed between two metal electrodes, and exhibit memory when operating as a two terminal variable resistor, due to a conductive filament (CF) between both electrodes, which can be formed (set operation) obtaining a low resistance state (LRS), and dissolved (reset operation) obtaining a high resistance state (HRS). As the thickness of the conductive filament can be controlled in different ways, these devices actually show continuously variable conductance values [4].…”

Fundamentals and SPICE Implementation of the Dynamic Memdiode Model for Bipolar Resistive Switching Devices

“…5a, the sinusoidal input voltage, the memory state and the current flowing through the structure are plotted as a function of time, Fig. 5b illustrates the current evolution and the memory map (hysteron) of the device as a function of the applied voltage [41]. More in detail, the SB effect is recognized by the sudden current increase in the SET region (red line in Fig.…”