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nano tech | 2019
Low-Power FPGA Integrates NanoBridge Switch Device
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t the nano tech 2019, NEC Corporation showcased a new principle-based LSI, low-power field-programmable gate array (FPGA) that incorporates NanoBridge. The company has developed the NanoBridge-FPGA using the nanoelectronics platform by TIA, an open innovation hub operated by five institutions in Japan.

nano tech 2019 International Nanotechnology Exhibition & Conference was held at Tokyo Big Sight in Tokyo, Japan from Jan. 30 to Feb. 1.

The NanoBridge-FPGA employs NanoBridge, an ultrasmall non-volatile switch device, as a wiring for wiring switching, which is used for circuit reconfiguration of programmable logic devices, such as FPGAs. It features low power consumption, low voltage, and high performance. NEC plans to apply the NanoBridge-FPGA for artificial satellites and communication devices in the future.

NanoBridge Technology

Improvement of energy efficiency
With a circuit configuration that uses an atom switch, NanoBridge-FPGA achieves power savings. As shown in Fig. 1, it achieves significant power reduction through hardware configuration without depending on software processing, thereby bringing FPGA’s energy efficiency close to that of application specific integrated circuits (ASICs).

Fig. 1: Circuit reconfiguration using atom switch achieves power saving (NEC’s material)

Fig. 1: Circuit reconfiguration using atom switch achieves power saving (NEC’s material)

Basic concept of “Switch Over Logic”
Conventional FPGAs have a large switch area, and therefore, have large chip area and power consumption. As shown in Fig. 2, NanoBridge-FPGA has a small switch (NanoBridge) arranged on the logic, and reduces chip area and power consumption. As shown in the figure, an atom migration-type reconfigurable LSI (3D) can achieve an area of 1/20, wiring resistance of 1/10, switch capacity of 1/10, and area of 1/4 those of conventional static RAM switches and reconfigurable LSIs (2D).

Fig. 2: Basic concept of “Switch Over Logic” (NEC’s material)

Fig. 2: Basic concept of “Switch Over Logic” (NEC’s material)

Atom switch
Atom switch (NanoBridge) is a resistive change switch that uses ionic conduction and an electrochemical reaction of copper (Cu) ions (Fig. 3). Atom switch has a structure in which polymer solid electrolyte (PSE) is sandwiched by a chemically active Cu electrode and an inactive ruthenium (Ru) alloy electrode.

Atom switch is non-volatile, can be rewritten repeatedly, and has low capacitance (~0.2fF) and high Off/On resistance ratio (0.2GΩ to 1kΩ). Hence, when it is applied to FPGA, it can achieve 30 percent reduction of power consumption and 60 percent reduction of critical path delay compared with commercially available low-power SRAM-FPGAs.

Fig. 3: Atom switch (NEC’s material)

Fig. 3: Atom switch (NEC’s material)

Comparison of circuit area, performance
Figure 4 shows a comparison of circuit area, signal delay, and power consumption between conventional (SRAM-based) FPGA and NanoBridge-FPGA. Comparison was made at 65nm node. Logic cell area was reduced to 46.46×62.45μm, one-fourth that of conventional FPGA, and signal delay of 65 percent at the maximum and operating power consumption of 61 percent were achieved. As a result, it was confirmed that NanoBridge-FPGA is superior to conventional FPGA in all items.

Fig. 4: Logic cell (unit circuit) architecture (NEC’s material)

Fig. 4: Logic cell (unit circuit) architecture (NEC’s material)

NanoBridge-FPGA sample
An FPGA is a reconfigurable circuit that allows users to reconfigure it in accordance with application. At present, mainstream FPGA uses SRAM to hold circuit information. NEC manufactures samples in a specialty 300mm wafer fabrication line of a specialized semiconductor production company. Sample has logic capacity equivalent to 100K-ASIC gate, internal operation voltage of 1.1V, input/output voltage of 1.8V, and maximum internal clock of 256MHz, and incorporates block RAM and phase-locked loop (PLL) (Fig. 5).

Fig. 5: NanoBridge-FPGA sample (NEC’s material)

Fig. 5: NanoBridge-FPGA sample (NEC’s material)

Future Development
Figure 6 shows the NB-FPGA technology roadmap. Thus far, implementation in robot and the development of 40nm sample have been completed. NEC plans to develop a 28nm NanoBridge-FPGA by the end of FY2018, and incorporate NB-FPGA in Innovative Satellite Technology Demonstration-1 to verify practicability and reliability. In addition, the company will also apply it to communication equipment and demonstrate its low power property and advance deployment to internet of things (IoT) devices.

Fig. 6: Future development (NEC’s material)

Fig. 6: Future development (NEC’s material)

Conclusions
In the mid-1980s, Japan’s semiconductor industry was dubbed “rice of industry” and secured more than 50 percent share of the global market. However, it has been mired with challenges over the years. Much hope is put to NanoBridge technology to open up new markets.

About This Article:

The author, Yasuhiro Ukai, Ph.D., is from Ukai Display Device Institute (UDDI).