Fundamental LSI technology for the age of multi-core devices

NEC Corp.’s new technology is able to "visualize" the thermal distribution and reduce the power consumption of LSI, which has become an increasingly serious challenge as the miniaturization of LSI continues to advance. These latest developments have been demonstrated through NEC's SX-9 super computer.

The technology features scores of thermal sensors, 1/10 the size of previously available sensors, which are internally located throughout the LSI, and convert temperature changes into digital signals that enable the heat distribution of the LSI to be "visualized" in real-time. The miniaturization of the thermal sensors enables them to be widely distributed throughout the LSI, which increases the precision of measurements. The technology allows thermal distribution to be "visualized," hence independent local measures can be taken on specific regions of an LSI chip in order to control heat. This allows tasks to be delegated to less active areas of a chip, which reduces the total amount of electricity required for operations and lessens the environmental impact. Specifically, the widespread use of devices equipped with this latest technology and LSI multi-cores will result in greater optimization of clock-frequency, data processing and voltage levels, which will deliver a 20 to 50 percent reduction in the power consumption of LSI devices (based on calculations performed by NEC on two-core processing and power voltage control). Below are the primary features of this technology.

INCREASING THERMAL SENSORS WITHIN LSI

The thermal sensors are able to calculate temperatures by measuring leakage currents from transistors through miniature conversion circuits that convert leakage currents to digital signals. The sensors are 1/10 the size of conventional diode based sensors and they are equipped with circuits that detect and convert leakage currents to digital signals. Even if the power voltage changes while the LSI is operating, measurements remain highly accurate and errors are contained to less than 2ºC. Moreover, only a relatively small number of the previously available, larger, thermal sensors could be placed within an LSI. Scores of the new miniature sensors may now be placed within an LSI in order to provide an accurate real-time "visualization" of a device's heat distribution.

CORRECTION OF TEMPERATURE MISCALCULATIONS CAUSED BY MANUFACTURING VARIATIONS

A conversion equation has been developed in order to measure the volume of an active LSI's leakage current and to convert it into a temperature. Temperature miscalculations may be corrected through new technologies that take one measure of each thermal sensor's leakage current at room temperature, a process that formerly required multiple measurements, to improve the accuracy of results. Until now, LSI were limited to thermal sensors that delivered temperature measurements whose margin of error exceeded several tens of degrees Celsius. The latest sensors have been dramatically improved, and now provide temperature measurements that are within 3ºC of accuracy. Even though variations in the manufacturing of LSI can cause leakage current differences that are as much as 100 times different from one another, the latest sensors continue to deliver accurate readings.

Looking forward, as LSI perform more difficult procedures and chips equipped with large volume multi-core capabilities are used more often, both heat distribution and active core regions will continuously change. These conditions require the accurate calculation of high temperature areas, which is accomplished through chips outfitted with a large quantity of thermal sensors that are able to deliver temperature readings in real-time. Conventional thermal sensors were oversized and cumbersome, which prevented chips from being equipped with a large number of them, and inhibited a chip's ability to reliably manage temperature issues.

The high temperature of an LSI's internal regions has also brought on distrust in the deteriorating performance of transistors and wire connections. Leakage currents from LSI that rise more than 40ºC have increased by more than 10 times, which has caused the lifetime of transistors and wiring to decrease by approximately 50 percent. The above factors have drawn particular attention to the importance of improving the temperature management of LSI in order to reduce electric power consumption and improve reliability.

For example, data center temperatures can now be better regulated through continuous real-time monitoring of the center's temperature distribution. This enables specific sections to be intensively ventilated or certain tasks to be designated to separate servers for processing. The high temperature management technologies not only help secure greater reliability of machinery, they also improve the effectiveness of cooling systems, which results in a more dependable and ecologically friendly product. The technologies that allow an LSI's temperature distribution to be "visualized" are considered an essential part of the development of a "Data Center On Chip." This chip is reinforced with multi-core technologies that are capable of the same processing as today's data centers (based on anticipated future innovations within LSI integration and chip development) that will enable LSI of the future to perform similar functions as the data centers of today.

NEC will continue to pursue development of technologies that assist in the resolution of environmental challenges. Accordingly, these latest technologies promise to become an essential element to the improved performance of LSI, as well as the devices appearing in vehicles, digital A/Vs, networks, servers and more, which are becoming increasingly dependent on the reliability and environmentally friendly benefits of LSI.