Resistive random-access memory

Resistive random-access memory (RRAM or ReRAM) is a type of non-volatile (NV) random-access (RAM) computer memory that works by changing the resistance across a dielectric solid-state material often referred to as a memristor. This technology bears some similarities to conductive-bridging RAM (CBRAM), and phase-change memory (PCM).

CBRAM involves one electrode providing ions that dissolve readily in an electrolyte material, while PCM involves generating sufficient Joule heating to effect amorphous-to-crystalline or crystalline-to-amorphous phase changes. On the other hand, RRAM involves generating defects in a thin oxide layer, known as oxygen vacancies (oxide bond locations where the oxygen has been removed), which can subsequently charge and drift under an electric field. The motion of oxygen ions and vacancies in the oxide would be analogous to the motion of electrons and holes in a semiconductor.

RRAM is currently under development by a number of companies, some of which have filed patent applications claiming various implementations of this technology. RRAM has entered commercialization on an initially limited KB-capacity scale.

Although anticipated as a replacement technology for flash memory, the cost benefit and performance benefit of RRAM have not been enough for companies to proceed with the replacement. A broad range of materials apparently can potentially be used for RRAM. However, the discovery that the popular high-κ gate dielectric HfO₂ can be used as a low-voltage RRAM has greatly encouraged others to investigate many other possibilities. Among others, SiOx has been identified to offer significant benefits. Weebit-Nano Ltd is one company that is pursuing SiOx and has already demonstrated functional devices.

In February 2012 Rambus bought an RRAM company called Unity Semiconductor for $35 million.Panasonic launched an RRAM evaluation kit in May 2012, based on a tantalum oxide 1T1R (1 transistor – 1 resistor) memory cell architecture.

In 2013, Crossbar introduced an RRAM prototype as a chip about the size of a postage stamp that could store 1 TB of data. In August 2013, the company claimed that large-scale production of their RRAM chips was scheduled for 2015. The memory structure (Ag/a-Si/Si) closely resembles a silver-based CBRAM.

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