Nanoscale phase transformation in Ge2Sb2Te5 using encapsulated scanning probes and retraction force microscopy

Abstract

Encapsulated conducting probes that can sustain high currents are used to study the nanoscale properties of thin-film stacks comprising of a phase-change chalcogenide, Ge(2)Sb(2)Te(5). Scaling studies on this promising candidate for random-access memory devices had thus far required extensive lithography and nanoscale growth. This seriously hampers rapid materials characterization. This article describes the use of two key techniques, an encapsulated conductive probe and its use in retraction mode, whereby the attractive force between tip and sample is used to maintain electrical contact. The effective transformation of nanoscale dots of amorphous Ge(2)Sb(2)Te(5) into the crystalline state is achieved and the electrical conductivity of the transformed structures is probed. The use of retraction force microscopy in a robust manner is demonstrated by reading the conductivity of the crystalline dots. Both these techniques could enable rapid electrical characterization of nanoscale materials, without extensive nanopatterning, thus reducing material development cycles.

The Design of Rewritable Ultrahigh Density Scanning-Probe Phase-Change Memories

“…In the encapsulated-tip design modeled here, a small, highly conductive PtSi region (here 20nm diameter) provides the electrical contact, and is surrounded by a relatively large (40 nm) insulating SiO 2 (encapsulating) cladding. Such tips have recently been fabricated by IBM and shown to maintain excellent conduction and sustain little wear after many meters of sliding contact [23,24] as well as successfully writing crystalline bits in GST media [25]. The second major design change, elucidated in detail below, is the use of a medium specifically designed to allow for re-writing.…”

Scanning probe memories – Technology and applications

“…6 where a small, highly conducting PtSi region is 'encapsulated' by a much larger, non-conducting SiO 2 region. Such encapsulated tip designs have recently been fabricated [24] and shown to be not only capable of successful writing and reading of nanoscale bits in phase-change media, but also to possess much better wear characteristics than conventional tips [25].…”

The Route for Ultra-High Recording Density Using Probe-Based Data Storage Device

“…The thickness of GST layer used here is considered as 10 nm, which is a typical thickness for phase-change probe memory. 32,33,42 Regarding tip design, one of the most attractive features of phase-change probe memory is to allow the usage of a smoother tip than other probe techniques requiring a very sharp tip, since the current is passing through the Hertzian contact area between tip and sample. 43 Therefore, the tip does not need to be physically sharp, but merely electrically sharp (small electrical contact area).…”