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MIT Reports 400 GHz Graphene Transistor Possible With 'Negative Resistance'
An anonymous reader writes "The idea is to take a standard graphene field-effect transistor and find the circumstances in which it demonstrates negative resistance (or negative differential resistance, as they call it). They then use the dip in voltage, like a kind of switch, to perform logic. They show how several graphene field-effect transistors can be combined and manipulated in a way that produces conventional logic gates. Graphene-based circuit can match patterns and it has several important advantages over silicon-based versions. Liu and co can build elementary XOR gates out of only three graphene field-effect transistors compared to the eight or more required using silicon. That translates into a significantly smaller area on a chip. What's more, graphene transistors can operate at speeds of over 400 GHz."
Negative differential resistance just means that the current goes down when you increase voltage.
Interestingly, the entire electric grid is developing NDR, and that is a big problem for power companies. In the old days, if there was too much demand for electricity, or if transformers were overheating, the power company could reduce the voltage (a "brown-out") and the current would fall. But with more and more switching power supplies in electronics and fluorescent lights, that doesn't work as well anymore. The switching power supply in your computer and CFLs will compensate for reduced voltage by increasing the duration of the "on" phase of the switch, thus drawing additional current, the opposite of normal resistance.