Silicon-Based Device to Harness Waste Heat into DC Power


Tiny silicon solid-state devices can catch and convert the waste heat into the electrical power without directly touching the heat source

Researchers have developed the tiny silicon-based device that can control and make use of waste heat and turns it into the electrical power. The team calls its device an infrared rectenna which is a solid-state device with no moving parts to jam, bend or break, and doesn’t directly touch the heat source.

Silicon device to catch infrared radiation

The device is about 1/8 inch by 1/8 inch, half as thick as a dime and is metallically shiny. The top is aluminium that is etched with stripes roughly 20 times smaller than the width of a human hair. This pattern is too small to be seen by the naked eye but serves as an antenna to catch the infrared radiation.

Between the aluminium top and the silicon bottom is a thin layer of silicon dioxide. This layer is about 20 silicon atoms thick or 16,000 times thinner than a human hair. The patterned and etched aluminium antenna channels the infrared radiation into this thin layer.

The infrared radiation trapped in the silicon dioxide creates fast electrical oscillations, about 50 trillion times a second. This pushes electrons back and forth between the aluminium and the silicon in an asymmetric manner and the process is called rectification which ultimately generates net DC electrical current.

Production is same as of ICs industry

The team makes the infrared rectenna with the same processes used by the integrated circuit industry and is scalable. The fabrication challenge which the researchers found was to insert small amounts of other elements into the silicon, or doping it so that it would reflect infrared light like a metal.

This rectenna produces 8 nanowatts of power per square centimetre from a specialised heat lamp at 840 degrees.

Improvements required for enhancing efficiency

The ideas include making the rectenna’s top pattern 2D x’s instead of 1D stripes to absorb infrared light over all polarisations. Redesigning its rectifying layer to make it a full-wave rectifier instead of the current half-wave rectifier and also making it on a thinner silicon wafer to minimise the power loss due to resistance.

By making such improvements it is expected that the power output per unit area will increase hence, can be an alternative to RTGs for compact power supplies. Well, the team has been issued a patent for the infrared rectenna and have filed several additional patents.