Antifuse NVM seeks to topple ROM

ROM is the oldest embedded non-volatile memory. First developed by IDMs in the 1970s and brought to the mass silicon market shortly after, ROM is the smallest and fastest embedded non-volatile memory in the market.

But it is also the most inflexible; it cannot be programmed post manufacture. If the content of the ROM changes, respin cost, as well as delayed time to market are incurred. In advanced process technologies, such as 40nm, a VIA ROM respin averages 30 days in fab and $150K per respin. With time to market being the cornerstone of success for a silicon chip company, this is not acceptable.

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Given ROM's major shortcomings, a betting man would have wagered that ROM would have become obsolete with the advent of other NVM technologies by now. But ROM is still going strong because other embedded NVM technologies such as fuses, Flash, and SONOS cannot match the cost performance of a ROM.

Fuses can be programmed post manufacture but fall short because they cannot scale economically above 1KB. With ROM being used to store microcode in the 64KB range, fuses are too expensive to even consider. Flash- and SONOS-based technologies are the most flexible but also the most expensive due to additional processing steps. Unless one needs 10,000 write/erase cycles, flash or SONOS are not good ROM replacement candidates due to the 25 percent to 35 percent cost increase.

It would seem that designers may have to continue using the archaic and inflexible ROM for another decade, and pay the increasingly high price of delayed time to market when faced with respins in advanced processes. Fortunately, there is hope in sight to provide relief for next generation multi- media processors and mobile baseband chipsets which are heavy on ROM content. There are emerging NVM technologies that may finally render the ROM obsolete. These technologies include the resistive RAM (RRAM) and antifuse. Both of these the potential to match, if not improve, the cost performance of a ROM in addition to being field programmable. Figure 1 benchmarks key metrics between ROM, RRAM and Antifuse.

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