Nonvolatile logic technology Retain data without a power supply Zero startup processing time Zero standby power consumption
ROHM successfully pioneered an IC with nonvolatile logic circuits in the register*1, an internal data storage area. ROHM was the first to start full-scale production of FeRAM (Ferroelectric Random Access Memory*2), which led to the development of nonvolatile logic technology and devices that retain the status of arithmetic processing, even when power is not supplied.
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Roadblocks to higher performance
As devices becomes more sophisticated and faster they generally require more power. In response to this ROHM has implemented a number of power-saving measures, for example, by cutting off power in PCs during CPU standby. Implementing multiple energy-saving functions and technologies can have a tremendous cumulative effect.
Data retention in ICs normally requires power supply to the registers
Logic ICs (i.e. CPUs) contain circuits known as "registers," which temporarily retain the status of various processes, background information, and the operational status of other ICs and peripheral equipment. Conventional logic ICs are volatile*3, meaning shutting off power to the IC will cause information in the register to be lost. Therefore, power must constantly be supplied to the IC.
Developing nonvolatile registers
ROHM began developing the technology for nonvolatile logic circuits by integrating ferroelectric elements in the register section. Ferroelectric elements can retain data even when there is no power supplied. Ferroelectric elements, although previously known, were seldom used due to inherent problems such as greater power loads and signal delays. ROHM solved these problems simultaneously by developing a new ferroelectric structure that enables nonvolatile operation without harming the logic performance or reliability of the IC. This technology ensures data retention, even when power is shut off. |
 Photo1 Photo of a nonvolatile CPU chip (magnified)  Photo2 Nonvolatile CPU Prototype |
New power saving methods
There are a number of conventional methods for decreasing power consumption. These include "clock gating," in which the circuit clock is stopped when arithmetic processing is not being performed, and "power gating," in which power is shut down to circuits not performing operational processing. However, with clock gating, it is not possible to stop leakage current in the circuit, reducing the power-saving effects, and with power gating, although most of the leakage current can be stopped by shutting off power, it cannot be completely eliminated due to the need for power to be supplied to the register. In contrast, with nonvolatile logic technology power can but shut off to the circuit, including for the register, making it possible to reduce power consumption to zero.
CPU gaming console power consumption reduced 70%
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Applying nonvolatile logic technology to the rapidly expanding gaming sector results in a 70% reduction in CPU power consumption by decreasing consumption to zero during standby (Fig. 1). Reductions of 85% are possible by implementing design changes to shut off power to blocks not reading or writing, even during CPU operation, while micromanaging ON/OFF power to the status register and processing circuit level within the block can bring this value to 95% or more (Fig. 2). |
Fig. 1 Example of Nonvolatile CPU Operation |
Fig. 2 Block diagram of basic CPU processing (left) and example of nonvolatile CPU power control (right)
Technology that lets you use your computer like a TV
Utilizing this technology in computers can greatly reduce startup time, which normally takes several tens of seconds, to the almost instantaneous level of TVs. With household appliances, it is common to leave them plugged in at all times, even when powered off, in order to retain data. This results in continuous power consumption (standby). ROHM estimates that in Japan alone, approximately 15 billion kWh are wasted annually (from the "Survey on Standby Power Consumption" by the Energy Conservation Center, Japan). We anticipate that by applying nonvolatile logic technology to the logic ICs used in the countless electronic products, it will be possible to promote energy savings throughout the entire electronics market. |
 Application Examples of Nonvolatile Logic Technology |
*1 Register
In digital processing (logic) circuits the storage area used to temporarily retain mid-calculation data, arithmetic processing, or operational status is called a register. Generally, registers are dispersed within the logic circuit.
*2 Ferroelectric material
A type of dielectric material wherein the information contained can be changed by applying an electrical field. Electric polarization makes changes possible at high speeds and low voltage.
*3 Volatile, Nonvolatile
These are terms that describe the characteristics of circuits and elements used to store mid-calculation data from operational processing. Storage circuits and elements that do not retain data when power is shut off are referred to as "volatile," while those that retain data even when power is shut off are called "nonvolatile."
The Index of This Issue
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vol. 4 / 2009.01 |
Cover Story 1
Retain data without a power supply
Nonvolatile Logic Technology
Cover Story 2
Breaking away from silicon
Full SiC power modules
