Resistive RAM speeds past flash
Crossbar has been developing a non-volatile RAM technology based on the anti-fuse behavior of amorphous silicon that it calls resistive RAM (RRAM). That development is now paying off, according to company vice president Sylvain Dubois, with the technology reaching commercialization. Dubois told EE Times that the company has signed its first manufacturing partnership for its technology in a 40nm process and they are now licensing their technology to chip developers.
Crossbar's resistor RAM creates a conductive filament when programming its memory cell, changing the resistance between pads. (Source: Crossbar)
The RRAM cell is a vertical resistive layer of amorphous silicon between two metal pads. The device stores data by imposing a voltage across that layer to create controlled growth of a conductive "filament" through it. The filament does not fully short between the metal layers, however, which allows the process to be reversed to eliminate the filament. The difference between programmed and unprogrammed states is a 100:1 increase in current through the cell, making it easy to sense the cell's state. As this is a physical change in the cell, it remains intact when power is absent, making the memory non-volatile, and Dubois estimates that the technology will be able to achieve wear tolerance up to 1M cycles.
The RRAM's read/write circuit design allows an array to access a cell in around 20 nsec, and to write in 1-2 µsec with byte-level access, Dubois said. This speed provides a considerable advantage over traditional Flash in terms of access times as well as providing energy savings by eliminating the need to block erase in order to alter a memory location. The cell's structure allows it to fit entirely between metal layers, which provides a density advantage, including an ability to create 3D arrays.
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