Macromodeling a phase change memory (PCM) cell by HSPICE

Abstract

This paper presents a HSPICE macromodel of a phase change memory (PCM) cell. The model simulates not only the resistance change by phase (as corresponding to the two states, amorphous and crystalline), but also the temperature profile, the crystalline fraction during the programming and the drift behavior in resistance and threshold voltage. The proposed macromodel (consisting of two models) generates the I-V and R-I plots of a PCM cell at a very small error compared with experimental data. The electrical-based modeling by HSPICE allows to fully characterize the holding voltage and the continuous behavior of the PCM resistance, while assessing the impact of the programming time. Furthermore, the proposed model takes into account the drift behavior of few parameters when the PCM is not been programmed or read, making the model more realistic. Selection of the parameters is based on operational features, so the electrical characterization of the PCM is simple, easy to simulate and intuitive.

Design and modeling of nonvolatile memories by resistive switching elements

“…Next, the proposed PCM macromodel is compared with the macromodel of [98] by the same authors. The macromodel presented in this manuscript is very different from [98].…”

“…The macromodel presented in this manuscript is very different from [98]. The first difference is its circuit simplicity; this feature is evident when considering the multiplier circuits (such as for the computation of 0.1 ) required to simulate the drift behavior of the PCM cell.…”

“…The first difference is its circuit simplicity; this feature is evident when considering the multiplier circuits (such as for the computation of 0.1 ) required to simulate the drift behavior of the PCM cell. In [98] this important computational step is also dependent on the simulation time, making the PCM macromodel of [100] more complicated. In the proposed macromodel, a single voltage controlled voltage source (VCVS) is used to generate the drift behavior.…”

“…In the proposed macromodel, a single voltage controlled voltage source (VCVS) is used to generate the drift behavior. The complexity of macromodelling is also reflected in the accuracy, because the additional circuits utilized in [98] generate a larger percentage of error in the simulation process [100]. So for example, the error between simulated and experimental data for the resistance drift grows exponentially as function of T off (at values of T off greater than 500ns the error exceeds 4%).…”

“…As for the drift behaviors of the resistance and threshold voltage, the model of [98] assumes that when the PCM cell is not been programmed, the reset (amorphous) resistance (R a ) increases with time, while the crystalline fraction of the PCM cell (C x ) remains constant [100]. However this is a simplifying assumption used in the macromodel of [98], thus further contributing to the previously described error.…”