Nanostructure–property relations for phase‐change random access memory (PCRAM) line cells

Abstract

. (2012). Nanostructure-property relations for phase-change random access memory (PCRAM) line cells. Physica status solidi b-Basic solid state physics, 249(10), 1972249(10), -1977249(10), . DOI: 10.1002 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Phase-change random access memory (PCRAM) cells have been studied extensively using electrical characterization and rather limited by detailed structure characterization. The combination of these two characterization techniques has hardly been exploited and it is the focus of the present work. Particularly, for improving the reliability of PCRAM such combined studies can be considered indispensable. Here, weshow results for PCRAM line cells after series of voltage pulses with increasing magnitude are applied, leading to the first minimum sized amorphous mark, maximum amorphous resistance and over-programming, respectively. Furthermore, the crucial effect of electromigration limiting the endurance (cyclability) of the cells is demonstrated.

Correlative transmission electron microscopy and electrical properties study of switchable phase-change random access memory line cells

“…27,28 (4) The relations between amorphous mark length and resistance or threshold voltage tend to be proportional, but for detailed studies of these relations correlative research on switchable PRAM TEM samples is needed. 9,16 The present work contributes to answering questions 1 and 4.…”

“…In our previous work for the same PCM, a threshold field of 26 6 2 V/lm was determined. 9 In the seminal work by Lankhorst et al, 2 a threshold field for the same PCM of 14 V/lm was derived, but their data show that for short line cells the threshold field seems higher than for long ones (ranging between 20 and 10 V/lm). This indeed also seems to hold in our case, because in our previous work 9 the line cells examined had a length of 225 nm and in this chapter the length of the line cells is 800 nm.…”

“…In order to avoid these effects we performed in a previous work electrical characterization on real memory cells and brought these cells to certain well defined final states and then prepared (locally thinned) the cells such that they could be analyzed by TEM. 9 In this way, we were able to establish and understand nanostructure property relations for actual memory cells.…”

“…These processes are not properly observed and understood for nanoscale PCM cells. 9,16,[19][20][21][22][23][24] (3) The transformation from the crystalline to the amorphous phase is associated with a volumetric expansion of about 6%. 25,26 Since the phase-change material is completely encapsulated, this volumetric expansion will create large stresses within the PCM.…”

Distinguishing mechanisms of morphological instabilities in phase change materials during switching

“…Heating induces an increase in atomic mobility which enables rapid phase transformations, but which can also induce morphological changes adversely affecting device performance and reliability. Some studies [4][5][6] have addressed device reliability by observing changes in microstructure and nanostructure morphology during heat-induced phase switching. Morphology changes leading to void formation have been observed in electrically-switched GeTe nanowires [5].…”