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Non-Volatile Memory (NVM)



Memory in which information is retained even when a power source is not present.

Non-volatile memory is becoming more complicated at advanced nodes, where price, speed, power and utilization are feeding into some very application-specific tradeoffs about where to place that memory. NVM’s capacity is hard to scale at smaller geometries, and it needs higher voltages to program the cells. More die area may be needed to support capacities required by the additional processing cores at finer process geometries, and additional manufacturing cost may be required to support higher voltages.1

NVM can be embedded into a chip, or it can be moved off chip with various types of interconnect technology. But that decision is more complicated than it might first appear. It depends on the process node, the voltage, the type of NVM and what’s being stored in it, as well as the overall chip or system budget. It is a balancing act between the power/performance improvements of smaller geometries and how much memory can be embedded cost-effectively.

Fundamentally, there are two types of NVM:

  • Multi-time programmable (MTP) NVM can be programmed many times.
  • One-time programmable (OTP) NVM can be programmed once.

Some MTP NVM will work with a standard CMOS process, whereby no extra steps or masks are involved. Because they can be manufactured using a standard CMOS process, these MTP NVMs can continue to be scaled, but they require a floating gate, like a flash cell. A charge is trapped on a floating gate.

Then there’s the regular gate and the transistor. When you erase it, you remove the charge from the floating gate. Also, this floating gate requires a thicker oxide, and not all processes offer that. This is why MTP scaling basically stopped at 40nm and 28nm. Beyond that, it’s difficult to do it because the oxide thickness is not there to do to make it happen.

However, if NVM could be embedded in the same logic process without having to make tweaks to the process, then the costs are more manageable, and this is exactly what Synopsys was after with its acquisition of Sidense and Kilopass, both of which developed versions of OTP NVM.

The OTP technology doesn’t require the thicker oxide that is required for the MTP, and there is no floating gate.

1 MUTSCHLER, Ann. “Non-Volatile Memory Tradeoffs Intensify,” Semiconductor Engineering, JANUARY 22ND, 2020,