Researchers at the Massachusetts Institute of Technology (MIT) have developed a manufacturing technique for silicon photonic chips that are both flexible and transparent. The key advantage of the technology is its compatibility with standard 300-millimeter semiconductor wafer production, which the researchers said could simplify the move from lab prototypes to mass manufacturing.
Silicon photonics uses light instead of electrical signals to transmit and process data. It is a technology already used in high-speed data communications and computing. However, existing photonic chips are typically built on rigid silicon substrates, which limits their use in wearable electronics, augmented reality devices and optical systems that require curved or irregular shapes.
How the process works
The new technique starts out the same way as standard semiconductor manufacturing. Optical waveguides, microscopic channels that carry light, are formed on a silicon wafer. The structure is then temporarily bonded to a second silicon wafer, after which the thick substrate is removed.
The remaining ultra-thin oxide layers and waveguides are transferred onto a transparent polyester film, and the temporary silicon support is also removed. The result is a photonic structure only a few micrometers thick that can transmit visible light and bend without breaking.
Bending and transparency tests
During testing, the chips withstood thousands of bending cycles around small-diameter cylinders without noticeable performance loss, according to the researchers. Significant degradation only began when the chips were bent around an object roughly the thickness of a toothpick.
The researchers also tested the material's transparency using a setup designed to mimic the human eye. According to their findings, the structure produces almost no haze or noticeable optical distortion, raising the possibility of placing photonic components directly in front of a user's eyes.
Potential applications
Among the most promising applications, the developers cited augmented reality glasses, curved car windshields with built-in optics, pilot visors, and thin medical and wearable devices that conform to the shape of the human body.
The technology was developed jointly with specialists from NY CREATES at the Albany NanoTech Complex, a semiconductor research and development facility in New York state. One of the main engineering challenges was preventing the ultra-thin structure from warping once the bulky silicon substrate was removed. To address this, the scientists limited processing temperatures to 500 degrees Celsius and combined industrial silicon thinning with selective chemical etching.
What comes next
The MIT team said it plans to further improve the material's transparency, boost waveguide efficiency, and integrate more complex photonic components into the flexible platform.
