10/19/2005 - IMEC and Infineon Technologies developed a novel profiling technique for the accurate extraction of charge profiles in nitride-based memory, which allowed for the optimization of write/erase voltages using a novel operating mode. This result may overcome the major reliability problems of nitride-based memory, which hampered their competitiveness on the non-volatile Flash market.
Recently, nitride memory has regained a lot of interest because of its process simplicity and the highly localized charge trapping mechanism in nanoscale material defects. The latter could turn out to be more scalable than the conventional floating gate approach that's widely used in Flash memories today. However, this dual bit storage requires hot holes for erasing resulting in accumulation of residual charges with increasing number of write/erase cycles. This leads to new reliability issues - memory window walk-out (unstable threshold voltage) and degradation of the retention after cycling (RAC) - which delay the further dissemination of nitride technology into the wide variety of Flash application areas. As a consequence, the local charge storage concept is only competitive within a small segment of the Flash market today.
IMEC and Infineon have now realized a new profiling technique that will enable companies to fully exploit their nitride technologies. The breakthrough will allow nitride technology to compete with (conventional) Flash in its full application area of both stand-alone code and data storage Flash, as well as in the embedded arena (incl. automotive applications).
The new profiling technique allows - for the first time - the accurate and independent extraction of both electron and hole distributions. Based on this technique, write and erase operations have been optimized and a new operating mode has been found which leads to 100% matching of the carrier profiles. In case of complete matching after one write/erase cycle (i.e. the injected holes exactly compensate for the first injected electrons), the window walk-out effect disappears completely resulting in a stable threshold voltage. Also retention after cycling remains identical to the retention of a fresh device.
These results open perspectives for both high cycle applications (1,000,000 cycles have been demonstrated without verify) as well as for high retention applications (such as stand-alone code storage and automotive micro-controllers). Additional benefits of the technique are the smaller periphery (because verify may be skipped and erase voltage is lower) and the sharper distributions, which allow for further channel length scaling.
IMEC is a world-leading independent research center in nanoelectronics and nanotechnology. Its research focuses on the next generations of chips and systems, and on the enabling technologies for ambient intelligence. IMEC's research bridges the gap between fundamental research at universities and technology development in industry. Its unique balance of processing and system know-how, intellectual property portfolio, state-of-the-art infrastructure and its strong network of companies, universities and research institutes worldwide position IMEC as a key partner for shaping technologies for future systems. As an expansion of its wireless research, IMEC has created a legal entity in the Netherlands. Stichting IMEC Nederland runs activities at the Holst Centre, an independent R&D institute that develops generic technologies and technology platforms for autonomous wireless transducer solutions and systems-in-foil.
IMEC is headquartered in Leuven, Belgium, and has representatives in the US, China and Japan. Its staff of about 1400 people includes close to 500 industrial residents and guest researchers. In 2005, its revenues are estimated to be close to EUR 200 million.
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