Types of non-volatile RAM (NVRAM)

I thought of writing this blog on types of NVRAM (Non Volatile RAM) to share and also, enhance my knowledge on NVRAM market. In my knowledge, currently, there are three types of technologies on NVRAM are available in market.

In NVRAM, each bit has its own memory address, and can be part of the computer's addressable memory along with the volatile static and dynamic RAM (SRAM and DRAM) chips shipped with the computer.

NVRAM are devices which are able to retain information when electrical power is removed.

The first semiconductor NVRAM technology was battery-backed SRAM. It was created by the simple expedient of providing a rechargeable battery to keep power applied to the SRAM when system power was removed. This is still in use and works well for limited time periods, but the batteries take up useful space, and eventually discharge. Computer users who store their computers without power for long periods of time find that the units lose their CMOS setup information because it is typically stored in battery-backed SRAM.

Today, so-called flash memory takes the place of battery-backed SRAM in a number of applications. Most notably, flash has made possible compact "memory sticks," which are just flash memory chips packaged along with a USB interface. When plugged into a USB port, they appear as a "removable drive." They serve the same function as floppy disks. Flash memory can be (and is) used for more reliable CMOS Setup storage and virtually any other NVRAM application. Flash's main drawback is a limitation on the number of read/write cycles its cells can endure.

A second type of NVRAM that is currently gaining popularity is magneto resistive RAM (MRAM). MRAM's greatest advantage over flash is a virtually unlimited number of read/write cycles.

A third NVRAM technology currently in production is the ferroelectric RAM (FRAM). Like DRAM, FRAM stores information as voltage on a capacitor. Instead of using a linear dielectric, such as silicon dioxide (basically, glass), FRAM uses a non-linear ferroelectric dielectric, such as lead zirconate titanate (PZT). PZT is a crystalline material whose crystal unit cells have a permanent electric dipole moment. Applying an electric field (by putting a charging voltage across the capacitor) causes atomic rearrangements within the unit cells to align all the dipole moments with the impressed electric field. Removing the supply voltage leaves the dipoles still aligned, so the potential difference between the plates persists.

Other NVRAM technologies under development include phase-change RAM (PRAM), Silicon-Oxide-Nitride-Oxide-Silicon (SONOS), Resistive Random Access Memory (RRAM), Nano-RAM (NRAM), and perhaps others. All of these are under development.