Three output ports support all of the power needs of a wireless sensor node: a 180-nW RF pulse detectable to 6 ft, for a beacon signal; a 40 to 100-nW low-frequency pulse for sensing and computing functions; and 1-nW continuous output for memory retention.

In the device, a thin film of the radioisotope63 Ni generates beta particles which are used to generate electricity in two ways. First, the particles strike a cantilever of the piezoelectric material AlN. Charge separation takes place, charge accumulates and electrostatic attraction pulls the cantilever toward the63 Ni film. When the two touch, charge dissipates and the cantilever returns to its original position, whereupon the process starts again and an ongoing oscillation of the cantilever begins. Because piezoelectric materials such as AlN generate voltage when they are subjected to mechanical stress, this oscillation produces a continuous, constant voltage.

Beta particles also strike a silicon collector cell. Similar to photovoltaics, where the interplay of sunlight with the p-n junctions in solar cells generates voltage, here beta particles interact with silicon p-n junctions in a betavoltaic cell. This leads to greater total energy efficiency.

The Cornell team will present their findings at the 52nd annual IEEE International Electron Devices Meeting Dec. 11-13 in San Francisco.