Analysis: The Study of Drift in Phase Change Memories

In this thesis, the focus is on gaining new insights into the phenomenon of drift in phase change memories (PCMs) and identifying strategies to mitigate it. PCM devices are a type of non-volatile memory that uses a reversible phase transition in a material, typically a chalcogenide glass-like material, to store and retrieve data.

The Origin of Structural Relaxation

One of the key aspects studied in this research is the origin of structural relaxation in PCM devices. The researchers conducted drift measurements over a wide range of time scales, spanning nine orders of magnitude, to observe the onset of relaxation in a melt-quenched state. Two models, namely the Gibbs relaxation model and the collective relaxation model, were appraised based on the data obtained.

Furthermore, a refined version of the collective relaxation model was introduced, taking into account the limited number of structural defects. This analysis provides valuable insights into how structural changes occur over time in PCM devices and their impact on device performance.

Exploiting Nanoscale Effects in PCM Devices

As technology advances, the scaling of PCM devices to smaller dimensions becomes crucial for achieving higher storage densities and reducing power consumption. This study explores the potential of exploiting nanoscale effects in PCMs, particularly focusing on the use of a single element, Antimony, as a PCM material.

The researchers assessed the feasibility of using Antimony in PCM devices and characterized its power efficiency, stability against crystallization, and drift under different degrees of confinement. Understanding the behavior of PCM devices at the nanoscale is essential for optimizing their performance and reliability in future applications.

State-Dependent Drift in Projected Memory Cells

Novel device concepts are being developed to reduce drift in PCM devices by decoupling the cell resistance from the electronic properties of the amorphous phase. This research investigates the concept of incorporating a shunt resistor, scaling with the amount of amorphous material, to mitigate drift.

Simulations and drift characteristics of a projected memory cell were examined to test the effectiveness of this concept. The study identified the contact resistance between the phase change material and the shunt resistor as a crucial parameter influencing the desired device properties and mitigating drift.


This thesis provides a comprehensive analysis of drift phenomenon in PCM devices and introduces strategies to mitigate it. The studies conducted shed light on the origin of structural relaxation, nano-scale effects on device performance, and novel device concepts to minimize drift. The findings in this research have implications for the design and optimization of PCM devices, paving the way for future advancements in non-volatile memories.

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