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Is there a bright optoelectronic future for PCM?

Posted: 05 Aug 2014 ?? ?Print Version ?Bookmark and Share

Keywords:optoelectronic? phase-change memory? PCM? memory devices? optical switches?

That same experience base also suggests that having one electrode of crystallized material results in a more reliable operation. For example, in an ITO/GST/ITO structure, that would require leaving a small layer of crystallized material on the ITO surface as a nucleating site. Such an arrangement should still allow the memory cell to operate as an optical modulator. All that will be necessary is to build the additional thickness of the remnant crystallized active material into the calculation as an additional phase shift.

Pixels do not have to be as small as PCM memory devices for data storage. With a need to switch all the material between the electrodes, the problem is how big can you make a pixel before a filament will form and cause only part of the device to be crystallized.

As the ITO/GST/ITO discrete planar device characterisation work described above provides the detailed data with which to design a matrix, considerations will have to be given to providing a non-linear element to avoid any sneak path problems. In a reflective version of the PCM opto display, one possibility would be to build the optoelectronic stack on silicon. Then use the topside of the platinum as a mirror and its underside as a contact to create a Shottky diode to X-or-Y line connections of the matrix in the silicon. This would require dividing the platinum into a series of individual mirror/contacts as well as maintaining a flat surface.

Worthy of support
With the potential to spawn whole new families of optoelectronic phase-change-based switching displays and modulators, this optoelectronic venture certainly looks like a project that deserves further support and investigation. With PCM active film thickness on the order of 7 nm, new work in this area may well contribute to advancing the scaling efforts of PCM memory development where this work has its origins.

Politicians worldwide, including in the UK where this work originated, are always voicing their views on the need to support science and build from it an associated manufacturing industry. Further support for this work might provide them with an opportunity to turn their words into deeds. It is certainly deserving of that support.

1. Letter C An optoelectronic framework enabled by low- dimensional phase-change films, by Peiman Hosseini, C. David Wright & Harish Bhaskaran; Nature, Vol 511, 10 July 2014.

About the author
Ron Neale is an independent electrical/electronic manufacturing professional.

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