Key features of SONOS-based NVM and suitability for rad-hard applications.
The demand for embedded flash memory has grown steeply over the years as many new applications emerged in consumer electronics (touchscreens, smart cards, bank cards, mobile payment, e-passport, etc.) in addition to the industrial system-on-chip (SOC) designs. The memory content of these applications has been increasing steadily due to greater requirements on system performance and code/data storage. Initially, embedded floating-gate flash memory was widely used despite the large number of mask adder required (which translates to manufacturing cost) and the challenges in preserving the baseline CMOS device models (which affects compatibility with existing IPs).
Since then, SONOS (Silicon-Oxide-Nitride-Oxide-Silicon) emerged as a compelling alternative for embedded flash memory at a significantly lower cost. SONOS has been known as an NVM technology since the 1980s. In the early days, however, it was not very successful in competing against the floating-gate technology due to higher programming voltage and less competitive data retention at high temperatures. These obstacles were solved through charge-trap engineering in the SONOS non-volatile memory stack and demonstrated 10-year retention at up to 125°C (ambient temperature) with robust margins.
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