Phase Change Memory Materials via Non-Aqueous Electrodeposition into Nano-structured Templates

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This project is concerned with developing non-aqueous electrochemical methods and suitably tailored reagents to facilitate spatially selective electrodeposition of binary (e.g. In2(Se,Te)3, Sb2(Se,Te)3, Ge(Se,Te)) and the ternary chalcogenide materials (e.g. Ge2Sb2Te5, doped Sb2Te3) for applications in solid-state phase change memory (PCM). The key objectives are to demonstrate successful deposition of the target materials inside nano-scale (down to 2 nm) confined cell structures and to establish the effect of down-scaling pore size on the deposition process. Successful electrodeposition of well-defined compound semiconductor alloy compositions of these types will provide a significant new enabling technology which could also have a major impact on the other applications requiring semiconductor alloy deposition on a nano-scale. Using non-aqueous solvents (such as MeCN, propylene carbonate or chlorofluorocarbons) will bring several advantages over aqueous processes:(i) the use of a much wider range of reagents which can be tailored to the application;(ii) access to more reactive alloy compositions;(iii) a wider range of deposition potentials,while these solvents are more readily available, less expensive, much more easy to purify and less viscous (important for penetrating narrow. high aspect-ratio pores) than for example ionic liquids.These chalcogenide alloys are of major interest for phase change memory (PCM) materials - an emerging technology for non-volatile memory which is expected to compete with (and even replace) FLASH memory in specialist and everyday consumer electronics. Production of these alloys by electrodeposition could bring several advantages over current methods of production (mainly PVD), since it allows spatially selective deposition (since the materials are only deposited on the electrode surface), filling the pores of the templates from the bottom, hence enabling complete filling even of very narrow nanopores - leading to a very significant reduction of the dimensions of each individual cell, and hence potentially much higher cell density. In turn this will lead to faster switching between the crystalline and non-crystalline phases, leading to smaller devices and greater energy efficiency. To achieve these targets requires a multidisciplinary approach involving several key contributions: (i) to develop (and refine) new tailored molecular compounds (electrochemical reagents) with elements from the p-block (gallium, indium, germanium, antimony) in combination with groups containing the chalcogens i.e. the elements selenium and tellurium; (ii) to use these as reagents for the growth of the binary & ternary alloy materials by electrochemical deposition into nano-structured silica or alumina templates comprised of very narrow parallel pores with well-defined diameters between 1000 nm and 2 nm; (iii) characterisation of the deposited materials to determine the element ratios present (composition), their crystal structures, and phase change properties;(iv) deposition of the 'best' compositions into well-defined pores on a chip array to allow switching of the arrays memory cells in an actual device, hence demonstrating the true potential of this new approach.The team of investigators brings together a complementary and internationally unique set of skills and expertise to achieve these targets, while the input from our Project Partners, Ilika Technologies Ltd will add considerable value to the project.