Practical Shortwave Infrared Sensing

To enable the development of the next generation of self-driving vehicles, service robots, and more, advances are needed in the area of computer vision. Visual information provides artificially intelligent systems with a wealth of information about the world that can help them to navigate and interact with everyday objects. But despite the tremendous advancements that have been made in algorithms that process visual data in recent years, there are still many limitations in the capabilities of the sensors that collect the visual data upon which they rely.

Imagine a self-driving car using a traditional image sensor to collect information about its surroundings. Any number of common occurrences, like a flash of bright sunlight, fog, haze, or smoke can instantly render the self-driving system blind and incapable of safely continuing to operate. For this reason, engineers and researchers have been exploring the use of alternative types of sensors. One particularly promising alternative technology for computer vision applications is photodetectors that are sensitive in the shortwave-infrared (SWIR) range of the spectrum.

This type of sensor can see through bright sunlight, fog, and other similar factors that blind traditional images sensors. However, SWIR sensing technologies generally contain heavy metals like lead and mercury that make them highly undesirable. This renders them unusable in many areas due to restrictions on the use of certain hazardous materials. Moreover, producing large numbers of these types of sensors could result in serious environmental consequences, particularly as components reach the end of their useful life and wind up in landfills.

A team led by researchers at The Barcelona Institute of Science and Technology have demonstrated a new type of SWIR-sensitive photodetector that does not require the use of any hazardous materials, which offers the promise of supplying computer vision algorithms with a more reliable source of visual information. The method of production is compatible with current high-volume complementary metal-oxide-semiconductor fabrication processes. This factor could make these sensors practical for widespread use in many applications.

The novel photodetectors are based on colloidal quantum dots composed of non-toxic, phosphine-free silver telluride that is deposited on an indium tin oxide-coated glass substrate. These sensors can operate at normal room temperatures and maintain the sensitivity levels of their counterparts that contain hazardous materials. And — unprecedented for quantum dot technology — the sensors can detect radiation well into the infrared spectrum, recording signals of up to 1,600 nanometers in wavelength.

Describing the implications of their work, one of the researchers noted that “accessing the SWIR with a low-cost technology for consumer electronics will unleash the potential of this spectral range with a huge range of applications including improved vision systems for automotive industry (cars) enabling vision and driving under adverse weather conditions.”

At present, the team is exploring ways to further improve the performance of their device by changing the stack of layers that make up the sensor. They are also looking into possible modifications of the sensor’s chemistry to enhance its stability and performance.