Researchers at the Massachusetts Institute of Technology (MIT) have developed an ultrathin infrared (IR) material that works at room temperature, which could pave the way for lightweight night vision goggles like those in the movie Predator, ArsTechnica reports.
Current military IR goggles typically use the semiconductor mercury-cadmium telluride (MCT), which requires cooling to near liquid nitrogen temperatures (–196°C) to suppress noise. This makes the cooling systems too bulky and heavy. Instead, the new MIT device uses crystalline films of magnesium-lead niobate–lead titanate (PMN-PT) just 10 nanometers thick, allowing it to capture IR radiation without cooling, according to the authors of the U.S. Air Force-funded study.
"Their cooling systems are very bulky and very heavy," explains lead author Dr. Xinyuan Zhang. "We needed a material that could operate with low noise at room temperature – and PMN-PT met this challenge."
Uncooled IR detectors have been around since World War II. They use crystals made of pyroelectric materials (such as tourmaline) that change temperature and generate an electric current when they absorb IR radiation. However, at room temperature, thermal fluctuations cause noise, which prevents the detection of weak signals.
Zhang's team determined that reducing thermal noise to the level of cooled detectors was possible by using ultrathin films. However, such films adhere strongly to the substrate, making them difficult to isolate.
The breakthrough was the discovery that PMN-PT itself has extremely weak adhesion to many substrates – a small mechanical force is enough to rapidly "peel" the film in less than a second. This "atomic disruption" does not require expensive intermediate layers or complex etching technologies.
To demonstrate the technology, the researchers created a 100-pixel IR sensor by transferring one hundred 10-nanometer PMN-PT films (each about 60 µm² in area) onto a silicon substrate. In laboratory tests, the sensor showed superior sensitivity over a wide range of wavelengths compared to the best cooled night vision devices, which respond only to a narrow spectrum.
"We were able to achieve quality comparable to or even better than MCT detectors when cooled," Zhang says.
Although the sensor is extremely thin, a complete night vision system requires optics to focus the IR radiation, power, signal processing electronics, and a carrier. The team is currently working to integrate all of these elements into a compact package suitable for head-mounted or conventional eyewear.
"I think night-vision contact lenses will be challenging to build, but I expect our technology could potentially be used to make something that looks like normal spectacles," Zhang predicts.
In addition to night vision goggles, the ultra-thin IR sensors could find applications in autonomous vehicles for navigating in fog, wearables, flexible electronics, and even ultra-small computers. The team is also exploring the possibility of transferring the new approach to other materials by moving the lead into the substrate instead of the film, which could open up even more possibilities.
"If we can generalize this method to other materials, we can use it in many other applications," Zhang concludes.