Integrated optical systems, that allow on-chip realization of complex passive optical components and active photon detection, can have a tremendous impact in enabling new applications in sensing, imaging, spectroscopy and beyond. We demonstrate, for the first time, complex optical field manipulation and signal processing inside CMOS by exploiting light interaction with sub-wavelength metal nanostructures. Realized in the electrical interconnect layers, these optical nanostructures are co-designed and closely integrated with CMOS integrated circuits, allowing seamless integration of optics and electronics in standard digital CMOS process using standard “fabless” approach.
We present the theory, design and measurement of three prototype chips. Firstly, we demonstrate the first fully integrated CMOS fluorescence biosensor array capable of detecting tiny amount of nucleic acids and proteins without any external optical component. We present the key enabler that is a high-performance, ultra-robust nano-plasmonic filter realized with the metal interconnects. The mm-sized CMOS chip integrating the filter and high-performance photon detection circuits achieves comparable performance to commercial bench-top fluorescence readers. Secondly, we present the first fully integrated optical spectrometer without any external passive optics such as lenses, gratings, or mirrors. The architecture utilizes the metal interconnect layers to couple, disperse, guide and deflect light, integrated photon detection circuitry for read-out, and back-end signal processing for robust spectral estimation. Thirdly, we present a robust optical physically unclonable functions (PUF), where the lower-level metal interconnects are exploited to realize photonic crystals on an array of photodetectors. The passive lithographic variations of the metal layers are exploited to improve the the robustness of the PUF by a factor of 3.5X. The ability to integrate multi-functional nano-optical structures in commercial CMOS processes, along with all the complex electronics, can have a transformative impact and enables a new class of miniaturized and scalable optical system-on-chips.
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