October 19, 2005 – European R&D consortium IMEC and chipmaker Infineon Technologies AG have developed a new profiling technique for extracting charge profiles in nitride-based nonvolatile flash memory (NVM), which will allow the technology to compete broadly against traditional flash memory for standalone code and data storage, as well as in embedded applications.
Process simplicity and highly localized charge-trapping mechanism in nanoscale material defects have drawn interest in nitride-based NVM, which is seen to be potentially more scalable than the conventional floating gate approach used in current flash memories. However, nitride-based NVM requires hot holes for erasing, which causes accumulation of residual charges during write/erase cycles, and results in reliability problems including a “window walkout effect” (i.e., unstable threshold voltage) and degradation of retention after cycling. IMEC and Infineon say they’ve developed a new profiling technique that allows for independent extraction of both electron and hole distributions, optimizing write and erase voltages and resulting in 100% matching of carrier profiles — after one write/erase cycle, the “window walkout effect” disappears completely, and retention after cycling remains identical to retention of a fresh device.
The technique also offers a smaller periphery (verify may be skipped, and erase voltage is lower), and further channel length scaling is possible through sharper distributions. IMEC and Infineon said the nitride-based NVM process opens inroads into high-cycle (1 million cycles have been demonstrated without verification) and high-retention applications (e.g., standalone code storage and automotive microcontrollers).