LSI features high radiation tolerance for use in space

Current FPGAs (SRAM-type FPGAs), when used in space, pose the problem of changes occurring to the information written in the SRAM and malfunctions being caused due to the effects of radiation. However, this NanoBridge technology enables a tenfold improvement over the power efficiency of conventional FPGAs as well as providing them with high radiation tolerance.

NEC has conducted an operation demonstration jointly with the Japan Aerospace Exploration Agency (JAXA), using the newly developed NB-FPGA in a tough radioactive terrestrial environment. As a result, it has confirmed that the ON and OFF states of the NanoBridge remain unchanged, whether radiation is delivered or not.

"Based on the result, NEC expects that the NanoBridge will be able to reduce the frequency of errors caused by radiation to one percent or less and contribute to the creation of an LSI that offers high radiation tolerance and ultra-low power consumption simultaneously," said Yuichi Nakamura, General Manager, System Platform Research Laboratories, NEC Corporation.

This NB-FPGA was developed jointly by NEC and AIST, building on the success of NEDO's ‘Low-power Electronics Association & Project (LEAP),’ and is one of the TIA's open innovation achievements.

Going forward, NEC and JAXA will validate the usability and reliability of the NB-FPGA by incorporating it in the Innovative Satellite Technology Demonstration 1, which will be launched in FY2018.

Devices used in satellites are required to be extremely reliable. Even so, they are susceptible to circuitry failures called single event phenomena due to the effects of strong radiation in space. The occurrence of failures due to radiation poses a similar challenge in terrestrial communication devices as well. For example, if radiation is delivered to an LSI, an electrical charge occurs in the semiconductor substrate. As a result, a failure occurs to the SRAMs in FPGAs that record information based on the amount of charge, causing a change in the circuit configuration.

The NanoBridge uses the cross-link of metal atoms in a solid electrolyte to place the signals into the ON or OFF state. The ON or OFF state is maintained even after voltage is released. The cross-link created by metal atoms in the NanoBridge is free from the impact of electrical charges generated by the delivery of radiation.

Accordingly, the possibility of rewriting is extremely remote in the circuit of NB-FPGA, even in a space environment that is exposed to a large amount of radiation, thereby making the product reliable.

The NB-FPGA will be incorporated in the Innovative Satellite Technology Demonstration 1, which will be launched in FY2018, and a demonstration experiment of compressing and transmitting camera-captured images through the NB-FPGA will be carried out in a harsh environment.

Compatibility and usability have been improved by applying 4-input LUT used in conventional FPGAs to the circuit system. 8,000 LUTs are mounted on a 64x64 cell array chip. (In a demonstration experiment in space, 37,000 LUTs will be mounted on the NB-FPGA to compress images.)

The reliability of the switch that is in the OFF state has been improved by applying a three-terminal structure to the NanoBridge switch. One NB-FPGA contains up to 51 million switches, which are used for changing signals and as the memory of LUTs.

Going forward, NEC will develop NB-FPGA for application with satellite systems by utilising the evaluation results in the Innovative Satellite Technology Demonstration programme conducted by JAXA.