Non-Volatile Ferroelectric RAM

Created: October 27, 2017
Updated: August 18, 2024

Microcontrollers with Ferroelectric RAM ("FeRAM" or just "FRAM") have hit the market and we're hoping to see some interesting new devices enabled by the technology.

Ferroelectric memory chips store information using the hysteresis curve of the electrical field across special materials. Bits are written by applying enough voltage to change the polarization of the material, and read out by writing a known value and measuring the current released in doing so: if no current was generated while writing a "0", that implies the material already had a "0" polarization, while if a current is detected then the material must have changed orientation and been in a "1" polarization (the read process is destructive, so the original value must be rewritten after a read).

What's different about this technology compared to the currently popular, cheap, and very fastDRAM ("dynamic RAM") is that the ferroelectric material maintains state without constant updates, which means FeRAM consumes dramatically less power and robustly persists data after power has been removed. Of course, some times you don't /want/ sensitive data to persist in memory; this can be a problem even with volatile DRAM, which is susceptible to "Cold Boot attacks".

Compared to non-volatile flash memory, FeRAM can execute significantly faster writes, does not require high voltages to execute writes (so power consumption is lower), and can be rewritten to an almost unlimited number of times before wearing out (most flash memory experiences wear-out and corruption, which must be compensated for by extra circuity and provisioning in, for example, solid state disk drives).

Compared to DRAM and Flash technologies, FeRAM is less mature, more expensive, and is only available in single chip sizes up to a few megabytes. At this point it's slower than high-performance DRAM, though in most cases much faster than Flash or EEPROM. A side advantage is that FeRAM is much less susceptible to corruption in the presence of ionizing radiation, which might make it popular with aerospace and industrial engineers, or anybody trying to preserve data or instructions for decades without corruption.

Kristian Birkeland simulating the Earth's magnetosphere with a Terrella in 1895 (via wikipedia.org)

I think integrating FeRAM into existing electronic devices could greatly improve their performance and usability... What can we do with large amounts of robust low-power non-volatile memory that we couldn't do before? Consumer electronics and mobile devices could power up and down instantly while preserving state, and also recover much more elegantly from battery run down. With changes to operating systems, devices could even be built to never fully reboot or power down; at a minimum, non-sensitive device and network configuration could be stored by the BIOS without worrying about excessive hard disk reads and writes. Because the memory can be written to continuously in a round-robin style, it's appropriate for general sensing and data logging, and in particular "black box" crash logs (indeed, FeRAM is already being deployed in the auto industry). The speed and low power consumption lets engineers squeeze more functionality out of devices passively powered by rectennas (RFID chips, smart cards), thermoelectrics (engine sensors), and radioactive decay sources (satellites).

While stand-alone ferroelectric memory chips have been available for some time (from Ramtron orFujitsu for example), Texas Instruments produces a line of MSP430 microcontrollers with FeRAM built right in. These chips still have a small chunk of regular SRAM, and all the internal registers of the processor itself are SRAM, so it's not the case that all state is preserved after power loss, but they are a big step in that direction. It seems like there would be a market for small capacity SD/microSD memory cards (given their popularity in data collection devices and development kits) but I couldn't find any on the market.

Have you built or seen built anything using non-volatile RAM in an interesting way? Do you prefer an alternative technology like Phase-change memory (PRAM) or Magnetoresistive memory (MRAM)? Let us know in the comments!