NEC has demonstrated a low-power programmable cell array employing a NanoBridge rewritable and nonvolatile solid-electrolyte switch integrated into 90nm CMOS. The NanoBridge consists of a solid electrolyte sandwiched between Cu and Ru electrodes. Applying a positive voltage to the Cu electrode forms a Cu bridge in the solid electrolyte via electrochemical reaction, which turns the switch on.
In addition, resistance from the NanoBridge resistive switch changes between On and Off states when precipitating or dissolving a nanometer-scale Cu bridge into the solid electrolyte. When placed between the two Cu interconnects of LSI, the NanoBridge is able to connect or disconnect the two interconnects by applying a bias voltage. Therefore, circuitry can be configured after manufacturing to implement logic functions. Each NanoBridge state is nonvolatile and maintains its resistive state without power dissipation.
When applying negative voltage, the Cu atoms in the bridge return to the Cu electrode, which causes the switch to turn off. The NanoBridge can connect or disconnect the two interconnects by applying a bias voltage. Again, each NanoBridge state is nonvolatile and can retain its resistive state without power dissipation.
The uniform formation of a nanometer-scale Cu bridge results in a more narrow distribution of turn-on voltage. This leads to the successful programming of a 32x32 crossbar switch without select transistors in the logic plane. As a result, there’s no need for additional area due to NanoBridges in the logic plane.
According to NEC, the NanoBridge-equipped programmable switch is monolithically stacked on programmable logic circuits composed of transistors. The electrical properties of NanoBridge, such as the distribution of turn-on voltage, were enhanced by introducing a newly developed polymer solid electrolyte (PSE). These technologies reduced chip size and cut reduced dynamic power consumption by 25% in comparison to a reference programmable array using SRAM-based switches.
NEC believes that use of cloud computing is spreading dramatically, with computer and communications tools processing a larger number of transactions. Thus, power management of these instruments has become a serious challenge—quality of computing must be preserved while decreasing the power consumed by silicon chips.
Transactions processed by a CPU require more power and computing time than transactions processed by hardware such as an accelerator chip, which is specialized for processing specific transactions. The company says that this low-power programmable array processes different kinds of transactions through the reconfiguration of circuits, which lowers the power consumption of instruments and allows for shorter computing times.
Programmable cell array: Integrated circuit composed of configurable interconnects and a configurable logic array formed by programmable switches. A suitable logic function can be implemented by the customer or designer after manufacturing.
NanoBridge: NanoBridge is a registered trademark of NEC Corp. NanoBridge consists of a solid electrolyte sandwiched between Cu and Ru electrodes.
Polymer solid electrolyte (PSE): Solid electrolyte is a solid body in which ions can move about freely. PSE is a polymer with a free volume. The high free volume in the polymer electrolyte, in contrast, allows for the smooth formation of the Cu bridge without destroying the electrolyte.
Crossbar switch: In this structure, which consists of two-layer (input layer and output layer) wiring, electrical connections are made at certain points where wires cross over. So long as the output wires aren’t in conflict with each other, it’s possible to connect any input wire to any output wire. A 32x32 crossbar consists of 32 wires and 32 other wires that intersect them.