Embedded NVM Comparison
In the embedded NVM space, there are several technologies available in the market:
- Via or diffusion ROM create “1”s and “0”s through a double metal via or a change in Vt behavior from the implant in the diffusion;
- Electrical fuse solutions blow the silicide on the poly line creating a change in resistance is; these eFuses are typically provided by the foundry;
- Embedded Flash solutions either use a split-gate architecture or a float-gate architecture depending on area, power, and performance requirements;
- Antifuse solutions create “1”s from a hard oxide breakdown of the gate causing a resistive change.
| ROM | “Fuse” | Embedded Flash | Kilopass XPM | Kilopass Gusto | |
|---|---|---|---|---|---|
| Technology | One unique mask | Silicide or Poly | Floating gate |
Oxide breakdown | Oxide breakdown |
| Additional Step | 0 | 0 – 5 | 0 – 15, UV, Bake |
0 | 0 |
| Bit Cell Size | 0.3 | 30 – 100 | 5 – 10 | 1 | 1 |
| 8Kb Macro Area | 0.2 | 2 | N/A | 1 | N/A |
| 1Mb Macro Area | 0.5 | 64 | 24 | N/A | 1 |
| Endurance (MTP) | 1 | 1 | Many | <5 | <1000 |
| Scalability | Yes | Yes | 90nm | Yes | Yes |
| Design Flexibility | None | Some | Most | More | More+ |
ROM is the smallest and fastest NVM, but it is the most inflexible. If the code changes, re-spins are required resulting in added cost and a delay to time to market. As process technology scales, the cost as well as the delay to time to market increases. A typical 65nm VIA mask respin is $200K.
Modern fuses are great for small capacity NVM needs. They are prevalent at the foundry and are often at the right price point, free. For small capacity solutions not requiring field updates or security, it is a viable solution. For capacities greater than 8Kb, it is not very viable because the bit cell is large so it cannot scale economical.
Flash technology is the most flexible as well the most costly due to additional mask layers, typically up to 15 in 90nm. The problem is it does not scale with the process technology. Below 90nm a solution is not viable.
Kilopass XPM, Gusto and Itera are based on oxide breakdown to create the NVM element. XPM plays in the better than fuse market. It is smaller, faster, lower power, and more secure the foundry fuse solution. Gusto expands Kilopass’ available market to include code storage. Its area is small enough where it is economical to tradeoff area of a ROM with the faster time to market. Given Gusto scales with process, it is a viable alternative to low endurance embedded Flash requirement and replacements of external serial Flash and EEPROM. Itera multi-time programmable non-volatile memory brings embedded MTP NVM to the advanced process geometries used to manufacture today’s SoC designs for high-volume consumer and industrial products. With up to 1 megabit (Mb) of storage capacity and 1000 cycles of re-programmability, Itera provides more than enough endurance for over 50% of mobile and consumer application.