Deep beneath our feet is a nearly unlimited supply of renewable energy originating in the super-dense core of Earth. At up to 7,000 degrees Celsius (12,600 F), the heat from the planet’s interior could be a key part of our energy future, but first we need the technology to dig deep enough to reliably take advantage of it. Temperatures can reach several hundred degrees at a depth of four to six kilometers (2.5 to 3.7 miles) — more than enough to provide oodles of geothermal power. However, the electronics that power the drilling and construction equipment have trouble surviving these hellish extremes.

A new type of microchip developed at the Fraunhofer Institute for Microelectronic Circuits and Systems (IMS) could change that. The new, smaller chip can withstand temperatures in excess of 300 degrees Celsius without loss of performance.

Implementing geothermal power is more complicated than just drilling a bore hole straight down. The Earth’s crust doesn’t heat up uniformly as you get deeper, so a range of sensors and control mechanisms are needed to find the best places to tap into this wellspring of renewable energy. Conventional semiconductor chips designed for the heat begin to hit their thermal limits at around 200 degrees Celsius, but before that they begin to experience performance degradation. By 250 degrees, they’re toast.

Past efforts have involved elaborate active cooling system to keep probes from malfunctioning as temperatures rise, but the new Fraunhofer chip was designed from the ground up to be able to survive high temperatures without elaborate cooling. This chip uses a manufacturing process of 0.35 µm (350 nm), which is more than ten times larger than the consumer chips we’ve been seeing in recent years. However, a modern Intel chip is only capable of running at 100 degrees Celsius. Other heat-tolerant chips use inefficient manufacturing processes upwards of 1 µm (1000nm), so 350nm isn’t bad. Then, how did they do it?

Engineers used a silicon-on-insulator (SOI) CMOS design to allow circuits stand up to higher temperatures. The SOI design is intended to combat an effect of heat known as current leakage. Each transistor in the IMS chip is essentially insulated from its neighbors by an additional non-conductive layer, thus preventing electrical currents from flowing outside the intended path (current leakage). Uncontrolled, current leakage causes errors and poor performance long before the chip itself melts into a pile of slag. In addition to the insulation protecting transistors, IMS opted to use tungsten in the chips rather than aluminum to reduce long-term damage from heat.

While they were designed for geothermal research, the team see these advanced heat-tolerant processors as having applications in a number of important areas. For example, avionics sensors could be placed closer to turbine engines on planes for more accurate readings. They might also find use in industrial settings where long-term exposure to heat can fry lesser chips. The Fraunhofer Institute has been pleased with early tests of this fabrication process and plans to offer it as a service later this year.