NANO OPTICAL SYSTEMS-ON-CHIP IN THE VISIBLE RANGE: FROM BIOSENSING TO SECURITY

Abstract

Integrated optical systems, that allow on-chip realization of complex optical passive components and active optical detection systems, can have a tremendous impact in enabling new applications in sensing, imaging, spectroscopy and others through the ultra-miniaturization of complex optical instrumentation. This can not only enable sensing technologies at the edge for biomedical applications such as smart health, environmental sensing for smart cities, but also potentially open doors through new sensing modalities such as for in-vivo applications. CMOS technology has allowed single-chip integration of millions of pixels for image sensors. In this dissertation, we focus on techniques to realize complex optical field manipulation and signal processing elements inside CMOS by exploiting optical interaction with sub-wavelength metal nanostructures realized in the electrical interconnects layers. This is a new paradigm since in modern day silicon IC processes, these metal feature sizes are in the deep sub-wavelength regime (below 100 nm). In particular, we demonstrate for the first time massively parallelizable nanoplasmonic structures integrated with electronics in the same CMOS substrate. We adopt the same "fabless" approach in today’s semiconductor industry with absolutely "no change" of either fabrication or processing, and show that copper interconnects in an industry standard digital CMOS process (65 nm node) can be exploited to allow subwavelength optical field processing in a massively scalable fashion. To demonstrate this approach and range of applicability across new systems, we present three different optical system-on-chips (SoCs) in this dissertation.

Firstly, we demonstrate the first optics-free fully integrated CMOS fluorescence-based biosensor array that eliminate all external optics for a single-chip system capable of massively multiplexed biomolecular sensing capability (proteins and nucleic acids) with surface sensitivity comparable to commercial fluorescence readers. To achieve such functionality, we demonstrate integrated nanoplasmonic waveguide-based filters, relying on coupled surface-plasmon polariton modes, capable of more than 50 dB of rejection ratio across a wide range of incident angles and in the presence of scattering. We present the complete theory and design guidelines to achieve such robust filter performance. The first optics-free 96-sensor CMOS fluorescence sensing system demonstrates surface sensitivity of 5 zeptomoles of quantum dot-based labels, and volume sensitivities of 100 fM for nucleic acids and 5 pM for proteins that are comparable to, if not better, than commercial fluorescence readers.

Secondly, optical spectrometry in the visible and near-infrared range has a wide range of applications in healthcare, sensing, imaging, and diagnostics. This dissertation also presents the first fully integrated optical spectrometer in standard bulk CMOS process without custom fabrication, post-processing, or any external passive optical structure such as lenses, gratings, collimators, or mirrors. The architecture exploits metal interconnect layers available in CMOS processes with subwavelength feature sizes to guide, manipulate, control and diffract light, integrated photodetector, and read-out circuitry to detect dispersed light, and then back-end signal processing for robust spectral estimation. The chip, realized in bulk 65-nm low power-CMOS process, measures 0.64 mm 0.56 mm in active area, and achieves 1.4 nm in peak detection accuracy for continuous wave excitations between 500 and 830 nm.

Thirdly, this dissertation presents a robust optical physically unclonable functions (PUFs) realized under the same CMOS nanooptics-electronics co-design approach. The passive lithographic variations of lower level metal interconnects are exploited to realize resonant photonic crystals on an array of photodetectors to include variations that are robust to noise processes. The chip is realized in a standard 65-nm CMOS process with no additional post-processing. The addition of the structures increases the coefficient of variation by a factor of 3.5X compared to only active device variations, which creates extremely robust PUF responses. The ability to integrate multi-functional nano-optical structures in a commercial CMOS process, along with all the complex electronics, can have a transformative impact and enables a new class of miniaturized and scalable chip-sized optical system-on-chips.