In An Election Year: OTP For IoT

The arguments for choosing one-time programmable embedded memory for IoT designs.


Borrowing from this year’s hottest topic –– the Presidential Election –– let’s nominate one-time programmable (OTP) embedded memory for the Internet of Things (IoT). It’s sure to be the winner for any number of reasons, but most likely it is because of its built-in security features. As a memory-on-chip technology, antifuse OTP is paving the way for IoT designers to come up with new and innovative applications since it is able to protect sensitive information, simplifying interfaces and usability.

Embedded memory requirements for IoT devices eliminate most OTP rivals. While we concede embedded ROM provides low power and cost for fixed non-application code, it is not commercially viable for changing application firmware, another critical concern for IoT designers.

Commodity Flash is eliminated as well, even though there’s an assumption that it provides a low programmable “cost per bit.” External Flash can have a lower cost per bit, though typical IoT applications would be better served with lower cost per bit embedded non-volatile memory (eNVM). External Flash consumes higher power for Execute in Place (XIP) applications or if shadowed in on-chip SRAM, and has increased wake time because of copy and reduced security.

Adding protection at the vulnerable physical layer is relatively simple to do using OTP since the antifuse eNVM is implemented in standard logic CMOS with no additional masks or processing steps. Information programmed into an antifuse eNVM provides physical security to help make the entire system impenetrable because the bitcell can’t be hacked using passive, semi-invasive or invasive approaches.

Since the bitcell does not store a charge, there is no electrical evidence of the state of the non-volatile memory bitcell. Rather, an initial “0” or programmed “1” is read through the process of sensing current and not voltage. Passive techniques using current profiles to find word patterns are unsuccessful because the bitcell current for “0” is indistinguishable from a “1.”

Invasive techniques, such as backside attacks or scanning electron microscopy (SEM) passive voltage contrast, don’t work because the programming of the bitcell occurs underneath the gate oxide. Establishing the location of the oxide breakdown using chemical etching or mechanical polishing and by looking at a cross-section or top view does not work either because the breakdown is so small, in the order of several angstroms. Therefore, antifuse OTP technology comes out ahead as the most secure of eNVM technologies.

The campaign pledge to foil hackers is resonating with IoT designers. Close to 50-billion connected devices by 2020 will need embedded software, not hardware, as their differentiation. OTP is noted for its small silicon footprint, high-endurance, low-cost and hack-proof security features, all key differentiators for IoT designers. Once the results are in and counted within the IoT market segment, OTP will be the surefire embedded memory winner. OTP’s popular campaign platform proves it is unmistakably well suited for IoT.