Crossbar's ReRAM technology is based on non-conductive amorphous silicon (a-Si) as the host material for a metallic filament formation. A top electrode is made of silver which provides the metallic ions for the filament. The principle of operation is that a writing voltage causes silver ions to migrate through the silicon to form a filament that eventually can connect the top and bottom electrodes. A reverse voltage causes the ions to move and break the connection. Lower voltages can be used to "read" the connection as a 1 or 0.
There are some similarities to the programmable metallization cell technology of Adesto Technologies Corp. and others and being brought to market under the term conductive bridging RAM or CBRAM.
Dubois stated that Crossbar ReRAM is performing well and licensees are receiving samples from SMIC to enable them to develop SoCs containing the standard hard macro which is an 8Mbit memory, or to develop their own hard macro NVMs for inclusion in their SoCs. Typical application include memory for energy-efficient microcontrollers used in IoT, smart sensors or wearables.
"Some applications need 16Mbit and more and some don't need that. We are working on larger macros but we also let customers develop ReRAM macros," said Dubois.
The ReRAM is already showing considerable advantages over flash memory including read latencies 20ns and write latencies of 12ns, which compare with millisecond latencies for flash memory, Dubois said. "We don't have block erase so a single byte can be rewritten," he added. As to endurance Dubois said Crossbar guarantees 100k read-write cycles. "For these applications 100k is the target although we are pushing for higher endurance," said Dubois.
Crossbar is pursuing a twin-track business strategy working on both ReRAM for embedded non-volatile and also as a technology developer of high capacity stand-alone memories. The embedded NVM is about a year ahead in terms of maturity although at the 2016 Flash Memory Summit and at 2017's Consumer Electronics Show Crossbar has been demonstrating its ability to do cross-point arrays with a select element.
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