Scientists at Massachusetts Institute of Technology have created scalable manufacturing technology for flexible and transparent photonic integrated circuits.
Traditional optical microchips are based on brittle silicon substrates that are highly breakable and opaque
This means that they do not allow any visible light to pass through.
In collaboration with semiconductor foundries, scientists have managed to create extremely thin optical waveguides transferred onto transparent film substrates without affecting the quality of signals.
This innovative fabrication technology makes it possible to produce optical circuits that can bend without breaking.
Developing wafer-scale fabrication technologies for transparent optical circuits
The engineering teams used the technique of employing conventional thin semiconductor manufacturing tools to design the advanced photonic structures simultaneously across the entire silicon wafers.
Normal manufacturing processes need relatively high temperatures, which will cause melting of the flexible polymer film substrate at once.
The scientists refined low-temperature deposition techniques to form optical waveguides under controlled temperature conditions.
This is the wafer fabrication process.
Control of the thermal budget made the combination of hard semiconductor materials possible with flexible substrates applied on an industrial scale.
Development of an effective workflow closes the gap between physical lab science and actual industrial practices.
The transfer of micro-scale photonic layers onto flexible polymer film substrates
To fabricate flexible optical chips, it was necessary to transfer thin waveguide circuits from their original hard silicon substrates.
Chemical etching agents were employed to remove selectively the bottom layers without damaging the thin and delicate optical layers placed above them.
These automatic systems raised the micron-thin waveguide circuits and transferred them to a flexible transparent polyester film.
The flexibility of the substrate protects the delicate components, which are made of silicon, from physical breakage.
Flexibility of the polymer gives an opportunity to make hard microchips flexible enough to bend in an irregular manner.
The demonstration of mechanical reliability in multiple bending cycles
The protocol for testing included exposing new photonic circuits to a large amount of physical strain due to the bending by automated robots.
The efficiency of the optical signal transmission was checked throughout the whole procedure during multiple bending events.
Optica reported that from the tests, it was evident that the channels through which light travels do not break or scatter light.
Resistance to bending indicates that the silicon photonic components can function efficiently even in complex moving machines.
Great resistance to mechanical pressure allows exploration of new ways for optical sensor integration into flexible materials.
The optical transparency of light-guiding channels
Light travels unhindered through the special polymer substrates and waveguide layers.
Optical transparency means that the surfaces underneath the microchip can be easily seen, as reported by MIT.
Efficient light signal transmission allows the light to travel without power loss through the whole circuit network.
Transparent optical performance means that the devices can be applied to glass panes, windshield car screens, and AR goggles.
The combination of efficient light transmission and perfect optical transparency provides unique opportunities for invisible electronics.
Wearable devices’ future usage in medicine and display technology
Biomedical scientists plan to implant flexible chips into smart health patches that will control many life signs.
AR developers want to use optical waveguides’ transparency feature to create clear images on top of the wearable correctional glasses.
Mass production will make the production of such optical elements for use in consumer electronics more efficient.
Optics for narrow purposes become commercial consumer products through mass production and mass adoption by industry and the public.
Further development of the transparent photonic technology is going to change the way humans interact with wearable digital displays, with multiple new applications on the horizon.
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