Nano Superlattice-like Materials as Thermal Insulators for Phase-Change Random Access Memory
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Nano Superlattice-like Materials as Thermal Insulators for Phase-Change Random Access Memory D. Loke,1,2 L. P. Shi,2,† W. J. Wang,2 R. Zhao,2 L. T. Ng,2 K. G. Lim,2 H. X. Yang,2 T. C. Chong,3 and Y. C. Yeo.4 1
NUS Graduate School for Integrative Sciences & Engineering, 28 Medical Drive, Centre for Life Sciences #05-01, Singapore 117456. 2 Data Storage Institute, DSI Building, 5 Engineering Drive 1, Singapore 117608. 3 Singapore University of Technology & Design, 287 Ghim Moh Road, Singapore 279623. 4 Department of Electrical & Computer Engineering, National University of Singapore, 1 Engineering Drive 3, Singapore 117576. † To whom correspondence should be addressed. Email: [email protected]
ABSTRACT Nanoscale superlattice-like (SLL) dielectric was employed to reduce the power consumption of the Phase-change random access memory (PCRAM) cells. In this study, we have simulated and found that the cells with the SLL dielectric have a higher peak temperature compared to that of the cells with the SiO2 dielectric after constant pulse activation, due to the interface scattering mechanism. Scaling of the SLL dielectric has resulted in higher peak temperatures, which can be even higher after material/structural modifications. Furthermore, the SLL dielectric has good material properties that enable the cells to have high endurance. This shows the effectiveness of the SLL dielectric for advanced memory applications. INTRODUCTION Phase-change random access memory (PCRAM) is one of the leading candidates for next generation nonvolatile memory. Its operation is based on the reversible switching of a phasechange (PC) material between the amorphous and crystalline states by short electrical pulses and localized joule heating. PCRAM has low power consumption, fast write/erase time and high endurance, making it one of the contenders for a so-called universal memory [1-3]. Despite its excellent memory qualities, it is highly challenging for PCRAM to achieve low power due to the high temperature needed to melt and quench the PC material during amorphization. This makes it very difficult to integrate PCRAM with small Si transistors. Resolving this limitation is of great importance. It would enable the commercialization of PCRAM technology. Superlattice-like (SLL) structures have excellent thermal confinement properties due to their interface phonon scattering effects. There have been studies on PC material with SLL structures, such as GeTe/Sb2Te3 [4], Ge2Sb2Te5 (GST)/Sb2Te3 [5] or GST/GeTe [6], to reduce the power consumption and increase the speed of PCRAM. More recently, we have proposed and demonstrated the use of a SLL dielectric [7] comprising of periodic layers of GST/SiO2 not only to improve the power and speed, but also to improve the cycle endurance of PCRAM. In this work, we reveal the thermal confinement property of the SLL dielectric and its impact on the energy required for the amorphization of PCRAM cells using finite element simulations. The cells with the SLL dielectric were found to have better thermal con
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