Many companies are working on non-volatile memory technologies with byte addressable, random access capability. They are expected to initially provide an alternative to flash memory and compete with DRAM chips in certain applications.

The flash memory in common use is non-volatile, but it must be written in blocks somewhat like disk sectors, which makes it slower. DRAM memory can be written one byte at a time, but loses its content without power. Both have drawbacks the industry would love to eliminate. New memory technologies are in various stages of development or implementation.

A DRAM Replacement?
Any RAM technology that replaces flash memory will be a huge success. However, if a non-volatile technology eventually succeeds in replacing DRAM chips, the main memory used in computers, it will dramatically change the way software is written. All operating systems and applications are designed to continuously save data to the disk. When main memory finally "remembers," many data elements would reside in memory at all times. In addition, computers would always be "instant-on" and would not waste AC or battery power when idle.

MRAM
(Magnetic RAM) A non-volatile, random access memory technology that is designed to initially replace flash memory and, potentially, DRAM memory. MRAM uses magnetic, thin film elements on a silicon substrate that can be built on the same chip with the logic circuits. DRAM, SRAM and flash memories cannot all be embedded on the CPU chip.

Although many large companies, such as IBM and Intel, are working on MRAM, NVE Corporation, Eden Prairie, MN is a small company that is a leader in this field with more than 30 patents.

Similar and Different
Writing bits in MRAM is similar to magnetic disks and early magnetic core storage. The 0s and 1s are created by different polarizations of the electrons within a ferromagnetic material. The major difference between MRAM and other magnetic technologies is in the reading. MRAM uses a tunnel junction, and the bit is read as the resistance in that junction.




A Magnetoresisive RAM Bit
This diagram shows one magnetic bit in the Magnetoresistive RAM technology from NVE Corporation. The data state (0 or 1) is determined by the polarization of the tunnel junction, and the bit is read as the resistance in that junction.

NRAM
(NanoRAM) A non-volatile, random access memory technology from Nantero, Inc., Woburn, MA that is designed to initially replace flash memory and, potentially, DRAM memory. NRAM uses carbon nanotube ribbons for the bits. The ribbons physically move within a 13 nm space, which determines their data state (0 or 1). Using standard CMOS fabrication facilities, in late 2006, Nantero stated that it developed all the solutions required to use carbon nanotubes in mass production.




Carbon Nanotube Bits
The data state (0 or 1) of an NRAM bit is determined by the physical arrangement of the carbon nanotube ribbons.

PHASE CHANGE MEMORY
A non-volatile, random access memory technology that is designed to initially replace flash memory and, potentially, DRAM memory. It employs the same phase change principle used in rewritable optical discs (CD-RWs, DVD-RWs, etc.). Also called "phase change RAM" (PRAM and PCRAM), chalcogenide RAM (C-RAM) and Ovonyx Unified Memory (OUM), Ovonyx, Inc., Rochester Hills, MI is the pioneer in this field with patents that date back to the 1960s. Via licensing agreements with Ovonyx, Samsung introduced a prototype and BAE Systems introduced its C-RAM chip in 2006.

Memory Vs. Disk
In phase change technology, the bit is switched between amorphous (unstructured) and crystalline (highly structured) states. However, in phase change memory, the bits are altered by electricity rather than by laser as in optical discs. Phase change memory bits are also denser than the bits in optical discs.

MEMRITOR
(MEMory ResISTOR) A non-volatile memory technology that can change its resistance in varying levels. It comprises a cell made of two layers of titanium dioxide, one of which is conductive because it is missing a few oxygen atoms. When a positive charge is applied to the layer with the missing atoms, the vacancies are pushed into the other layer, making it conductive as well and changing its resistance. The more the cell is charged, the lower its resistance. It can offer resistance in two states for a digital 0 or 1 or to levels in between to go beyond a binary system. Negative charges are used to reverse the effect.

Very Fast and High Density
Two distinct advantages of memristors are that moving the vacancies between the adjacent levels can be done much faster than other known switching methods, and the cell density approaches that of hard disks. Theorized by Leon Chua in the early 1970s, the first memristors were demonstrated by HP in 2008. If commercially viable, memristors may replace flash memory and dynamic RAM (DRAM) in the future.

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