Using LCLS-based hard X-ray scattering and THz excitation to study switching dynamics of Phase-Change Memory materials
by
Peter Zalden(Stanford Institute for Materials and Energy Sciences, SLAC, Menlo Park, CA)
→
Europe/Berlin
3.11 (AER 19)
3.11
AER 19
Description
Phase-Change Materials (PCMs) are employed in optical and electronic data storage due to their ability to form a stable glass under ambient conditions, but also to crystallize with an overall growth rate of 1 m/s above 550 K. This behavior enables rapid and reversible switching at elevated temperatures. All major semiconductor companies presently work on optimizing such electronic memories by down-scaling to the lowest volume of about 2 nm still stable in a glassy state. However, the scaling laws of the time limiting crystallization process are not yet known, because its elementary processes nucleation and growth scale differently with the active volume. It is therefore essential to decouple both mechanisms in order to design the fastest possible memory device. We use optical pulses at 800 nm to pump the phase transition and probe with hard X-ray pulses from LCLS to take single Debye-Scherrer patterns that resolve the number (nucleation) and size (growth) of grains as a function of time delay. At the same time, we monitor the temperature on the ns-timescale by comparing the Debye-Waller factors of gold on the sample. Based on the promising results we expect to derive the nucleation and growth rates as a function of temperature and by applying their well-known scaling laws individually, derive design rules for such memory devices. In a separate lab-based experiment we investigate the application of THz single cycle electrical pulses instead of optical or DC electrical pulses to trigger field-driven phase transitions in these materials. THz pulses are beneficial over electrical pulses in that their electric field can be applied without the need for electrodes and cables and can be of significantly shorter duration of sub-ps. Although our field strength exceeds the DC switching field by a factor of two, we still observe Joule heating linear in intensity. This indicates that field driven processes observed earlier require a higher electric field or also rely on Joule heating. New approaches will be demonstrated to reach THz field strengths up to ~50 MV/cm.
