The purpose of this dissertation is to study Sb-rich binary materials extended for applications in phase-change memory (PCM). Studied characteristics include thin-film properties and memory-cells performance of Ga-Sb alloys and Sb-C materials, and the crystallization behavior of ultra-thin phase-change films. Finally, we propose an alloy design method to reasonably predict the ultra-fast crystallization behavior.
The Sb-rich, Ga-Sb films (91 to 77 at% Sb) exhibit a high crystallization temperature (Tx, 183 to 261 °C), and high activation energy of crystallization (Ea, 2.3 ~ 8.3 eV), resulting in good thermal stability. The kinetic exponent is smaller than 1.5 at Sb < 86 at%, denoting that the crystallization mechanism is one-dimensional crystal-growth from nuclei. The temperature corresponding to 10-year data-retention (T10Y), is 180 °C for Ga19Sb81, and 148 °C for Ga16Sb84, respectively. A steep resistance drop during crystallization arises mainly from the sharp increase in carrier- concentration with p-type conduction. Ga16Sb84 memory cells demonstrate SET- RESET switching at pulse-width 10 ns and durability >1E5 cycles.
According to phase-diagrams, carbon and antimony are immiscible and not forming Sb-carbides. However, carbon addition is able to stabilize amorphous Sb phase. Raman and XPS spectra depict formation of C-Sb bonds in Sb-C films, which renders long-range ordering of amorphous Sb to higher crystallization temperatures. Thermal stability of amorphous Sb-C films is precipitously enhanced to show Tx of 256 and 262 °C, Ea of 3.14 and 3.52 eV, at 8 and 13 at% C, respectively. Structure of C-Sb films after full crystallization belongs to Sb phase. The T10Y of 87 at% Sb films is 168 °C. Memory test-cells made of Sb92C8 film show reversible switching at pulse-width 100 ns. It also shows the typical snapback behavior by applying I-sweep mode at the threshold voltage of 1.5 V, and full-SET at 2.1 V (snapback).
As decreasing film thickness of Ga16Sb84 films from 10 to 3 nm, the exponential increase in crystallization temperature (from 221 to 249 °C), electrical resistance ratio (1E3 to 1E5), and the stabilized Sb(Ga) phase (after annealing at 500 °C in 10nm-film) are attributed to increased specific interface-energies and inhomogeneous interfacial strain at the interfaces. This phenomenon is also observed in ultra-thin Sb films.
We propose an isothermal-heating transformation curve and a continuous-heating transformation curve, which extrapolate from Arrhenius’ and Kissinger’s plots, to predict the crystallization behavior of Sb-rich binary material under very fast ramp rate. It also provides a useful method to design suitable compositions with good thermal stability, fast crystallization speed, and good data retention ability

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