"Our primary goal is to develop a novel 3D laser-writing method deep inside silicon, towards novel applications. We are motivated by the myriad of applications based on 3D micromachining of glass that peaked in the early 2000's. These successes had been achieved using lasers at wavelengths for which glass is transparent. Here, similarly, we demonstrated the necessary laser technology, for discovering a interaction regime in Si, which eventually led to a truly 3D laser-structuring capability deep inside Si. We also demonstrated the first functional “in-chip” optical elements.
Our efforts led to a unique 3D laser-writing toolbox for silicon (Tokel, et. al. Nature Photonics, 11, 639, 2017; Optics Letters, 42,15, 3028, 2017). We used home-made lasers operating at 1.5 μm, and demonstrated that by exploiting the nonlinear mechanisms, it is possible to demonstrate i) the first fully 3D subsurface modification of Si without altering the surface, ii) the first functional elements buried deep inside silicon, and iii) realise a novel 3D fabrication method akin to 3D-printing to create a plethora of microstructures with large-volume coverage.
Our first objective was to employ the appropriate laser technology. It had recently been shown that simply increasing the pulse energies would not work, since plasma shielding diffracts light, precluding modification (J. Appl. Phys., 117, 153105, 2015). There was no method to realize subsurface modification with fs pulses prior to ours. Our extensive efforts enabled (i) the first fs laser modification deep inside Si, and (ii) the first functional waveguides buried in Si ( Tokel, et. al., “Femtosecond laser written waveguides deep inside silicon”, Optics Letters, 42,15, 3028, 2017).
Our approach next is based on exploiting the inherent optical response of Si. The laser-material system could be considered as an evolving entity, where once a modification of Si takes place, it can reconfigure the laser, which in turn can continue modifying Si. In ""Tokel, Nature Photonics, 11, 639, 2017"", we take such a novel approach, and show functional elements and 3D architectures with 1-μm resolution, without damaging chip surface:
• holograms for wavefront control,
• lenses and gratings for beam steering,
• waveguides for optical interconnects,
• multilevel, dense data storage,
• microfluidic channels for cooling,
• through-Si vias for electrical interconnects,
• microstructures for MEMS,
• slicing of a wafer for photovoltaics.
We introduced a plethora of subsurface—that is, ‘in-chip’— elements, which constitute an entirely new capability and a disruptive technology. This was possible with close collaboration of Dr. O. Tokel, Dr. S. Ilday and Dr. F. Ö. Ilday, from Bilkent.
"
