CMOS SINGLE-PHOTON AVALANCHE DIODES AND MICROMACHINED OPTICAL FILTERS FOR INTEGRATED FLUORESCENCE SENSING

This dissertation presents a body of work that addresses the two most pressing challenges in the field of integrated fluorescence sensing, namely, the design of integrated optical sensors and the fabrication of high-rejection micro-scale optical filters. Two novel enabling technologies were introduced. They are: the perimeter-gated single-photon avalanche diode (PGSPAD), for on-chip photon counting, and the benzotriazole (BTA)-doped thin-film polymer filter, for on-chip ultraviolet light rejection. Experimental results revealed that the PGSPAD front-end, fabricated in a 0.5 μm standard mixed-signal CMOS process, had the capability of counting photons in the MHz regime. In addition, it was found that a perimeter gate, a structural feature used to suppress edge breakdown in the diode, also maximized the signal-to-noise-ratio in the high-count rate regime whereas it maximized sensitivity at low count rates. On the other hand, BTA-doped filters were demonstrated utilizing three commonly used polymers as hosts. The filters were patternable, utilizing the same procedures traditionally used to pattern the undoped polymer hosts, a key advantage for integration into microsystems. Filter performance was analyzed using a set of metrics developed for optoelectronic characterization of integrated fluorescence sensors; high rejection levels (nearing -40 dB) of UV light were observed in films of only 5 μm in thickness. Ultimately, BTA-doped filters were integrated into a portable sensor, and their use was demonstrated in two types of bioassays

Towards Integrated Fluorescence Sensing

This thesis is an account of ongoing efforts in the Integrated Biomorphic Information Systems Laboratory and the Laboratory for MicroTechnologies towards the implementation of integrated microfabricated biosensing platforms with on-chip fluorescence detection capability. The first chapter is a published, exhaustive, and critical review of state-of-the-art microfluorometers, and it offers a set of performance metrics for evaluating sensors of different architectures. The second chapter consists of material from two journal papers, currently in preparation, in which the development of a polymeric optical filter material for UV fluorescence spectroscopy is presented and its integration with a CMOS active pixel sensor (APS) discussed. The third chapter, which is also an archival publication, presents initial efforts towards achieving high-sensitivity CMOS photodetectors for photon counting-based fluorescence assays in integrated platforms