OUM moves one step closer
Paul Bickerdyke, Electronics News
ST Microelectronics has taken one step closer to releasing ovonic unified memory (OUM) devices that could replace other forms of non-volatile memories. The Europe-based firm announced details of a research program into the switching effects of chalcogenide phase change materials, on which OUM technology is based, at the IEDM conference held in San Francisco last month (December 2002).
The chalcogenide material is an alloy of germanium, selenium and tellurium, and thin-films of it can be used to store information economically and without degradation. The material’s structure can be switched between crystalline and amorphous states (representing binary 1s and 0s) using electrical currents controlled by transistors.
Until now, this switching behaviour has been poorly understood. But starting from a band-gap model of both crystalline and amorphous chalcogenide, ST researchers at the firm’s Agrate site in Italy developed a numerical model that accounts for both the DC and transient I-V device characteristics.
ST now says that memories based on OUM technology are the best candidate to improve on Flash memory by offering superior performance and scalability. Others in the industry believe that OUM could eventually replace Flash, because even though it shows relatively high power consumption and heat generation, these are not the most important issues for solid state hard disk applications.
The technology is fully random accessible for memory addressing, and any given bit can be uniquely addressed and then written to or read from. OUM has also been shown to survive more than 10 trillion write cycles, making it useful for storing programs as well as general purpose data storage.
Cell performance has been shown to improve with shrinking size, and the technology avoids many of the scaling barriers arising in conventional charge-based technologies. For example, DRAM-based memories need a minimum amount of surface area to store the necessary amount of charge, which results in complicated structures that look like skyscrapers on the substrate. These are not only difficult to build, but add to the cost of manufacturing significantly.
14 January 2003
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