Manufacturing Bits: July 31
Research firm devises phase-change transistor
Japan’s Riken Advanced Science Institute has created a new phase-change transistor type using vanadium dioxide materials. Demonstrated at about 1 volt in room temperature, the technology could provide a building block for low power devices, non-volatile memory and optical switches, according to Riken. The mission of Riken is to conduct comprehensive research in science and technology.
Riken has devised what it calls a metal–insulator–semiconductor field-effect transistor. The device uses the electrostatic accumulation of electrical charge on the surface of a strongly-correlated material. Riken made use of a fast phase-change material called vanadium dioxide. Vanadium dioxide transforms the material from a metal to an insulator. The phase change takes place at about 68 degrees Celsius.
Vanadium-dioxide double-layer transistor in off and on states. Source: Riken.
Riken discovered that electrostatic charging at a surface drives all the previously localized charge carriers in the bulk material into motion. This leads to the emergence of a three-dimensional metallic ground state, according to researchers.
This non-local switching of the electronic state is achieved by applying a voltage of only about 1 Volt. The results were reported in Nature.
Panasonic devises artificial photosynthesis system
Japan’s Panasonic has developed an artificial photosynthesis system that converts carbon dioxide to organic materials by illuminating it with sunlight at an efficiency of 0.2%.
The key enabler to this system is a nitride semiconductor technology. The development could be a foundation for a system capturing and converting wasted carbon dioxide from incinerators, power plants and industrial activities.
Carbon dioxide is one of the substances responsible for the greenhouse effect. Current artificial photosynthesis systems use structures such as organic complexes or plural photo-electrodes.
Panasonic’s artificial photosynthesis system has a simple structure. The company discovered that nitride semiconductor has the capability to excite the electrons with enough high energy for the carbon dioxide reduction reaction. In this case, nitride semiconductors can be used as a photo-electrode for carbon dioxide reduction.
The reduction process itself takes place on a metal catalyst at the opposite side of a nitride semiconductor photo-electrode. The metal catalyst plays a role in selecting and accelerating the reaction. The system with a nitride semiconductor and a metal catalyst generates mainly formic acid from carbon dioxide and water with light at a world’s top efficiency of 0.2%.
This development was presented at the 19th International Conference on the Conversion and Storage of Solar Energy held in Pasadena, California on July 30, 2012.
—Mark LaPedus
Tags: nitride semiconductor, Panasonic, phase-change transistor, Riken Advanced Science Institute, vanadium dioxide