A ring oscillator circuit using a new type of transistors, silicon tunnel FETs, that are in principle operable at low voltage has been fabricated, and operating speed has been measured for the first time.

An optical micrograph, schematic diagram, and output characteristics of the newly fabricated tunnel FET ring oscillator

Up until now, the fabrication of a ring oscillator circuit using tunnel FETs necessary for operating speed measurement of the FETs has not been achievable. Several tens of transistors having little variation in characteristics have been integrated to fabricate a ring oscillator circuit using the advanced silicon device process technology of AIST, and operating speed measurement has been achieved for the first time in the world. In addition, a technique for increasing the drive current of a tunnel FET has been developed to improve operation speed by a factor of two.

In recent years, IoT-related research has been actively carried out, and LSIs operable with minute electric power have been required. So far, field effect transistors have been used for LSIs. However, reductions in drive voltage are about to reach their limits at present, and therefore as next-generation transistors replacing the field effect transistors, tunnel FETs are the focus, and are expected to be driven at an extremely low voltage of 0.2 to 0.3 V. While it has been confirmed that the tunnel FET operates as a transistor, it has not been confirmed whether or not the tunnel FET is actually high-performance because operating speed has not been measured.

The operating voltage of the fabricated tunnel FETs was higher than the expected value, and thus the researchers are aiming for lower voltage operation. In addition, for practical use, an operating speed approximately 100 times faster than that at present is required, and therefore the technique for increasing the drive current will be improved to achieve an increase in speed.