Nanometer Resolution XANES Imaging of in situ switched individual PC-RAM devices
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Nanometer Resolution XANES Imaging of in situ switched individual PC-RAM devices Jan H. Richter1,2, Alexander V. Kolobov1,2,3, Paul Fons1,2,3, Xiaomin Wang1,2, Kirill V. Mitrofanov1, Junji Tominaga1,2, Hitoshi Osawa3 and Motohiro Suzuki3 1Nanoelectronics
Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, 305-8562, Ibaraki, Japan 2Collaborative Research Team Green Nanoelectronics Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, 305-8562, Ibaraki, Japan 3SPring-8, Japan Synchrotron Radiation Institute (JASRI), Kouto 1-1-1, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan ABSTRACT We report on the study of single devices of phase-change (Ge2Sb2Te5) memory cells in line cell type devices. Devices were investigated employing an x-ray nanobeam of only about 150 nm diameter, which could be fully contained within the spatial extent of the active area within a single device cell. XANES spectra showing the device in the amorphous and crystalline state have been successfully collected after switching the device in situ at the synchrotron. By monitoring the fluorescence response of the sample constituent materials at a constant photon energy (corresponding to the Ge K-edge absorption edge) as a function of x-ray beam position on the sample 2D maps have been produced. INTRODUCTION Phase change random-access memory (PCRAM) materials have received substantial attention from the research community in recent years and in turn the endurance (write cycles) as well as the energy efficiency (lower voltages) of phase change material based memory structures have significantly improved. PCRAM utilizes a different data storage mechanism from Si technology with inherent scaling ability to a much lower ultimate scaling limit[1,2]. In PCRAM materials, information is stored in the local structure of the material as opposed Si based technology, where the method of information storage is electronic charge trapping[3]. By injecting energy into the system, be it by laser or electrical pulses, a reversible and stable transition between amorphous and crystalline states can be induced[4,5]. Originating from the atomic scale structural differences the two phases display large optical and electrical differences[6], with the crystalline phase usually possessing higher refractive index, optical absorption and electrical conductivity. For phase change memory scaling down the size of the devices, reduces the power input demand as the active volume decreases[7]. Once the phase-change has been induced, the material will reliably remain in its state for decades, which makes it suitable for long-term data storage, but is also interesting from a different perspective. This means that unlike silicon technology, where the stored electronic charge needs to be continuously replenished, PCRAM would retain information even if no power was supplied to the device, which not only leads to far reduced power consumption but also the potential of “instant on” memory. As pro
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