DDR, DDR2, DDR3, DDR4… Then What?

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As DDR4 SDRAM roles out into production this year, we still have a question to be answered. What will come next? DDR4 SDRAM will most likely be the last DDR SDRAM to be produced.

Newer technologies which are non-volatile (Can hold memory even when powered off) are being researched.  Phase-change Memory (PRAM or PCM) is one of these technologies, which Micron is developing.  Micron states, “PCM enables higher read and write bandwidth, lower latency, and higher endurance than existing nonvolatile memory technologies. It addresses the growing performance gap between DRAM and nonvolatile memory technologies, such as NAND Flash. ”

PRAM works by altering the state of chalcogenides between two electrodes and a resistor which heats up the chalcogenides and alters it’s state which alters it’s resistance, but when the heat is withdrawn the chalcogenides keep their state.  This is how they are non-volatile and can keep their memory after being powered off. You can visit Micron’s website to learn more on how they work.

Next, there is Magnetoresistive Ram (MRAM). MRAM works by using two ferromagnetic plates. One of these plates is a magnet with a permanent polarity, while the other can be changed to match an exterior field to store memory. Memory is then read by reading the electrical resistance of the cell. MRAM has been underdevelopment for a long time, since the 1990’s, but has never taken off into wide-scale use. In November of 2013, Buffalo Technology and Everspin announced a new industrial SATA III SSD that incorporates Everspin’s Spin-Torque MRAM as cache memory and Japan launched a satellite (Spritesat) with MRAM technology in 2008.

Last, but not least is Resistive RAM (RRAM). RRAM uses a dielectric that has been made conductive through high voltage shocks which forms a filament inside of it. After this filament has been created an appropriate voltage can either reset it (break) or set it (form).  If it is broken then there would be higher resistance and if it was formed it would have lower resistance.  RRAM is faster than PRAM with the switching time for RRAM less than 10 nanoseconds. Also, RRAM compared to MRAM has a smaller and simpler cell structure.  Crossbar is scheduled to start large scale production of RRAM in 2015 making RRAM one of the next and most likely candidates to replace SDRAM.

 

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