A once-in-a-lifetime photodetector invention catalysed the story of dual-use startup ElFys

In engineering, things rarely work on the first trial. For Mikko Juntunen, the CEO of ElFys, this once-in-a-lifetime occurrence happened after he had joined the Electron Physics Group of Aalto University in Espoo, Finland, in 2013. Juntunen realised there might be a detector solution with the groundbreaking work the team was doing with black silicon and its passivation methods and with other methods of managing defects in semiconductors.

The detector invention the team made in the joint cleanroom of Aalto University and VTT laid the foundation for ElFys, the Espoo-based manufacturer of superior-quality photodetectors for light detection applications.

"In engineering, things typically don't go right on the first trial. You do things, then you fail a few times, find results, and improve. This was the only time in my engineering career that things went right on the first trial," Juntunen recalls.

Engineering has been Juntunen's lifelong ambition. Already during his engineering and physics studies, he fulfilled his dream of working at CERN, where he got to work among the world's largest and most complex scientific instruments. A career in physics followed, spanning companies and research organisations like HUT, Nokia, and Detection Technology, before joining Aalto's Electron Physics Research Group and subsequently co-founding ElFys.

"It was like the decades of dealing with semiconductors and detectors combined with the wonderful things being done in Aalto's Electron Physics Research Group then, sort of, intuitively resulted in inventing this way of doing a new type of detector."

Photodiode with sensitivity exceeding anything seen before

ElFys designs, develops and manufactures photodetectors and related services for various light detection applications with market-leading sensitivity. ElFys's light detectors achieve superior sensitivity by utilising advanced nanotechnology and atomic layer deposition technique.

"We provide a photodiode with sensitivity exceeding anything seen before, literally capturing every ray of light. It's also application-proven and fully patented. We have tens of customers who have already shown that, yes, this works," Juntunen says.

ElFys's photodiodes achieve nearly 100% light absorption and a better signal-to-noise ratio than any other comparable solution on the market. What this means for ElFys's customers in the space and defence, health monitoring, and analytical instruments sectors is, simply put, that the customers get a better measurement of whatever they are measuring.

"If you're measuring heart rate, you get a more precise result, or you can use less light for the measurement. If you are guiding missiles, you can get the lock on from further distance or use less light for the designation. If you are doing spectroscopy, you can make a better resolution and detect lower concentrations of materials," Juntunen says.

ElFys has built a global distribution network and currently has more than 100 customers in 20 countries, with an export share of about 90%. One of the customers is Thorlabs, a global optical systems provider, that has released ten products based on ElFys photodetectors.

"For a company of 11 people, our global distribution network may sound excessive. But we're building the network to support and provide for the hundreds of customers who want a small number of our detectors. We expect our business to develop to multimillions within a few years, and certain application areas are best served through the distributors."

The defence market opened up to ElFys — focus on more precise missile guidance

After Russia started its full-scale war in Ukraine in 2022, the dual-use and defence industries quickly opened to many Finnish tech companies. What had long been a no-go area for ElFys also now provided new application possibilities for their photodetector products and new growth opportunities. Once it got the green light from its investors, the company was quick to launch the defence applications for its technologies.

In the defence field, ElFys focuses on laser guidance technology for missiles. Other potential defence applications include laser warning systems, missile approach warning systems, active protection systems, and hyperspectral imaging. Currently, ElFys has more than one European missile defence prime as a customer.

On the battlefield, laser guidance works roughly in the following way. Someone, typically a soldier, illuminates the target with a laser. At the head or front part of the missile, there's a window and behind that a mechanical arrangement, a gimbal, that can move and turn as it is trying to detect the laser, like an eye looking around the battlefield for the illuminated target. When finding the laser, the missile is supposed to lock onto the target and make an accurate hit. However, amidst the possible disturbances on the battlefield, such as darkness, dust, smoke, and fire, the missile may miss the target or never find the laser to begin with.

The key element in the precision of the hit is the device that detects the light, and this is where ElFys's technology, a black silicon 4-quadrant detector, comes in. ElFys's detector enables a lock-on distance increase of up to 30%, giving the missile a longer time to find the laser, steer itself and make a more probable hit at the intended target. (The article continues below the following image.)

Advancing infrared photodetector technology as part of the European Defence Fund 2024 project

One of the milestones in the defence sector for ElFys was the company's selection for the European Defence Fund 2024's four-year, €3 million Silfrared project. The project aims to advance infrared photodetector technology using silicon and black silicon to strengthen the EU's surveillance and reconnaissance capabilities. Central to this innovation is ElFys' specialised black silicon expertise, which facilitates the creation of low-cost, high-resolution, and fast-response detectors for night vision and surveillance.

The startup is also active in the rapidly growing Defence Tech Hub network of Finnish dual-use and defence tech companies.

"The Defence Tech Hub events have been good. There's a commercial approach, and the network is collecting people together to talk. Of course, our primary interest is to gain customers, and we may also find customers within the hub."

Image: ElFys