Table 1: OTP and MTP applications
Flash is not the only nonvolatile memory (NVM) mechanism available to embedded developers. Kilopass Technologies offers a range of one time programmable (OTP) and multiple time programmable (MTP) memory products. I spoke with Linh Hong, Vice President of Marketing, about Kilopass' technology and offerings.
Wong: What is the difference between OTP and MTP storage technologies?
Hong: OTP is one time programmable. Once it is programmed, it cannot be altered. MTP is multi-time programmable. This term can be used loosely to include less than 100 cycles of re-programmability or 10K to 100K cycles of re-programmability. OTP technologies include ROM, floating gate, electrical fuse, and antifuse. MTP technologies include EEPROM, Flash, SONOS, FRAM, and RRAM.
Wong: Which OTP and MTP technologies are manufacturable and mainstream? Mainstream OTP technologies include ROM, floating gate, electrical fuse, and antifuse. All these solutions are embedded and are implemented in standard CMOS without any additional mask or process steps. Foundries offer ROM and electrical fuse solutions. Kilopass licenses antifuse technology. eMemory licenses an OTP using floating gate technology but implemented in standard CMOS. Mainstream MTP technologies include EEPROM, Flash (NOR and NAND), and SONOS. These MTP technologies are available readily in discrete form. Flavors available for embedded solution in pure play foundries are in older technologies including 0.18nm and 0.13nm. Microchip (acquired SST) licenses an embedded NOR flash technology called SuperFlash. Synopsys (acquired Virage) licenses an embedded floating gate technology call AEON.
All the technologies above are manufacturable and are in mass production today.
Wong: What are key benchmarks between the OTP and MTP?
Hong: Key benchmarks between OTP and MTP include cell structure, logic process compatibility, bit cell and macro areas, endurance, security, scalability, standby and active current, random access time, manufacturing backend turnaround time (TAT) and voltage/temperature tolerance. In the table below, different OTP and MTP technologies are benchmarked.
Wong: What are key applications of OTP and MTP?
Hong: Key applications of OTP and MTP are described in the Table 1.
Wong: Which technology is the most reliable and scalable with process technology?
Hong: For OTP, the technology that is most reliable and scalable with process technology is antifuse. Reliability is measured by high temperature operating life (HTOL) and storage life (HTSL) tests to guarantee 10 years of continuous operation. HTOL and HTSL are done with 3 lots each. HTOL is at an elevated temperature of 125oC and elevated supply of nominal + 40%. The OTP memory is continuously read with various check points during the 1000 hours. During the check points, the critical peripheral circuits, such as the charge pump, are exercised to ensure it continues to operate within specifications. HTSL is at an elevated temperature of 150oC, unbiased baked since it is mimicking the shelf life of the product. To date, Kilopass OTP products have completed and passed qualification for processes from 0.18nm to 40nm. After 1000 hours, “0”s do not flip to “1”s and “1”s do not flip to “0”s. Antifuse is also the most scalable OTP technology. Given the memory bit cell consists of core NMOS devices, they scale in area with process technology and can be implemented in the most advanced process nodes. Kilopass has silicon for 28nm HKMG already.
For MTP, there isn’t a technology that is scalable with process technology. It is usually only available two or three process generations behind the common process used for SoC designs, which today is 40nm.
Wong: Which technology is the most cost effective for SOC design?
Hong: The most cost effective NVM technology for SoC designs should not require additional mask or process steps.
Wong: What is the future for OTP and MTP?
Hong: The future of OTP and MTP is bright. Antifuse OTP technology will continue to scale and be available in the most advanced nodes available. There will be greater usage because the demand for non-volatile storage is critical in today’s SoCs to offer personality to the SoC to differentiate in price or performance. We will see a continued growth in requiring higher capacity OTP for code storage because it is an inexpensive alternative to the costly external and embedded Flash solution.
Kilopass’ high capacity OTP solution Gusto has gained adoption in the consumer and mobile markets since its release mid last year as a cost reduction path to the system BOM. In the MTP space, alternatives to Flash are being developed. There are several compelling technologies in development or deployment. Some, including STT MRAM and RRAM, are many years away but if they can come to market with a stable and cost effective solution, it could create a paradigm shift in the way non-volatile memory is used.