A silicon key to long-life batteries

Using some of the same manufacturing techniques that produce microchips, researchers have created a porous-silicon diode that may lead to improved betavoltaics.

Such devices convert low levels of radiation into electricity and can have useful lives spanning several decades.

While producing as little as one-thousandth of the power of conventional chemical batteries, the new "BetaBattery" concept is more efficient and potentially less expensive than similar designs and should be easier to manufacture.

If the new diode proves successful when incorporated into a finished battery, it could help power such hard-to-service, long-life systems as structural sensors on bridges, climate monitoring equipment and satellites.

The battery's staying power is tied to the enduring nature of its fuel, tritium, a hydrogen isotope that releases electrons in a process called beta decay. The porous-silicon semiconductors generate electricity by absorbing the electrons, just as a solar cell generates electricity by absorbing energy from incoming photons of light.

Researchers have been attempting to convert radiation into electricity since the development of the transistor more than 50 years ago. Mastering the junctions between relatively electron-rich and electron-poor regions of semiconductor material (p-n junctions) led to many modern electronic products.

"The 3-D porous silicon configuration is excellent for absorbing essentially all the kinetic energy of the source electrons," says co-author Nazir Kherani of the University of Toronto.

"Tritium emits only low energy beta particles (electrons) that can be shielded by very thin materials, such as a sheet of paper," says Gadeken.

"The  hermetically-sealed, metallic BetaBattery  cases  will encapsulate the entire radioactive energy source, just like a normal battery contains its chemical source so it cannot escape."

The BetaBattery may prove better suited to certain tasks than chemical batteries when power needs are limited. The structures are robust--tolerant to motion and shock, and functional from -- 1480 Fahrenheit (-1000 Celsius) to 3020 F (1500C)--and may never have to be changed for the lifetime of the device.