We stabilize resistance of melt-quenched amorphous Ge2Sb2Te5 (a-GST) phase change memory (PCM) line cells by substantially accelerating resistance drift and bringing it to a stop within a few minutes with application of high electric field stresses. The acceleration of drift is clearly observable at electric fields > 26 MV/m at all temperatures (85 K - 300 K) and is independent of the current forced through the device, which is a strong function of temperature. The low-field (< 21 MV/m) I-V characteristics of the stabilized cells measured in 85 K - 300 K range fit well to a 2D thermally-activated hopping transport model, yielding hopping distances in the direction of the field and activation energies ranging from 2 nm and 0.2 eV at 85 K to 6 nm and 0.4 eV at 300 K. Hopping transport appears to be better aligned with the field direction at higher temperatures. The high-field current response to voltage is significantly stronger and displays a distinctly different characteristic: the differential resistances at different temperatures extrapolate to a single point (8.9x10-8 this http URL), comparable to the resistivity of copper at 60 K, at 65.6 +/- 0.4 MV/m. The physical mechanisms that give rise to the substantial increase in current in the high-field regime also accelerate resistance drift. We constructed field and temperature dependent conduction models based on the experimental results and integrated it with our electro-thermal finite element device simulation framework to analyze reset, set and read operations of PCM devices.
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Modeling Reset, Set, and Read Operations in Nanoscale Ge 2 Sb 2 Te 5 Phase‐Change Memory Devices Using Electric Field‐ and Temperature‐Dependent Material Properties
Herein, a finite element simulation framework for phase‐change memory devices that simultaneously solves for current continuity, electrothermal heating, and crystallization–amorphization dynamics using electrothermal models and dynamic material parameters that are functions of electric field and temperature is described. In this latest model, an electric field‐ and temperature‐dependent electrical conductivity model of stable amorphous Ge2Sb2Te5(GST) obtained from experiments performed on GST line cells to study Read, Reset, and Set operations of mushroom cells is incorporated. The effects of current polarity, heater height, Reset pulse rise and fall times, access device configuration, and ambient temperature are analyzed. The simulation results predict a 2x change in Reset current requirements with different current polarity due to thermoelectric effects. Heater height plays a significant role in thermal losses; ≈16% decrease in Reset current for 4x increase in the heater height is obtained. Increase in the ambient temperature results in a linear decrease in the Reset power required to achieve the same Reset/Set resistance contrast.
- Award ID(s):
- 1711626
- NSF-PAR ID:
- 10396583
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- physica status solidi (RRL) – Rapid Research Letters
- Volume:
- 17
- Issue:
- 8
- ISSN:
- 1862-6254
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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