Nikkei Electronics Asia -- July 2009
Cover Story - Part 1: Slashing Power Consumption: The Trump Card
Zero-Standby-Power ICs to Enter Practical Use

Imagine a chip that waits in Off mode for an input, that instantly turns on the power for processing when an input is detected, and then turns itself off again. An integrated circuit (IC) technology that might make possible this type of "normally-off" equipment will enter practical use in 2009: zero-standby-dissipation chips, achieved by making the entire chip, including logic, nonvolatile. As environment-friendly equipment becomes ever more important, this may be the trump card in slashing power consumption.

The industry is switching into high gear in pursuit of zero-standby-dissipation IC technology (Fig 1). Rohm Co Ltd of Japan, at the forefront of developments, prototyped a microprocessor in 2008 and is now designing custom chips for a number of equipment manufacturers. With its volume production line in Kyoto completed in May/June 2009, Rohm will begin shipping custom ICs in the second half of the year. "Equipment using the new chips may appear before the end 2009," according to a source at the company.

NEC Corp of Japan, hot on Rohm's heels, has developed a technology that runs chips even faster, and completed verification of a test chip in 2008. The firm plans to prototype a system-on-chip (SoC) within a few years in preparation for commercialization (see Part 2 of this report for details).

The zero-standby-dissipation ICs discussed here are chips made with nonvolatile logic and merged memory. A large number of chips using nonvolatile merged memory exist, such as microcontrollers with Flash memory, but the new designs use nonvolatile logic as well. The flip-flops (registers) that temporarily store computational results are made nonvolatile, so that logic circuits can continue normal operation even after the power is shut off and restored. Analog circuits, power supply circuits and the like also on the chip do not need data retention, meaning that the power to the entire chip can be cut in standby: a zero-standby-dissipation IC.

Rohm, NEC and others believe this technology will deliver significant savings in power consumption without sacrificing equipment convenience. According to Tadahiko Sugibayashi, who is with the Devices Platform Research Laboratories at NEC, "We'll be able to cut dissipation for digital consumer electronics in the standby mode to just a few percent of what it is now." In terms of annual electricity cost, he adds, "That could add up to hundreds of millions of yen in savings in Japan alone." And of course the equipment would be able to return from standby to normal operating mode instantaneously.

In the future, says a source at Rohm, "Normally-off equipment will become possible, turning itself on only when power is needed." In 2008 Rohm demonstrated its microprocessor prototype in normally-off operation, slashing dissipation by 70% from conventional designs. Rohm explains: "This technology has enormous potential in applications such as games, where the system is usually sitting and waiting for player input."

Leakage 50% Dissipation

When equipment power is turned on, ICs consume two types of power: dynamic power from transistor charging, and leakage power from transistor leakage current (Fig 2). Lower chip dissipation requires that both types are reduced, but leakage is the more pressing need. Dynamic power can be resolved to some extent through measures such as reduced clock from circuit parallelization or other techniques, and lower voltage made possible by smaller transistor geometry, but leakage is a bit harder to deal with.

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