| This thesis describes the design and measurement of two fluorescence-based active CMOS biosensors fabricated in a TSMC 0.25 mum CMOS technology. The first biosensor consists of a 16 x 16 pixel array and utilizes long photon integration times to detect fluorescence. A process compatible unsilicided polysilicon filter is used to block the excitation source signal while allowing the fluorescent signal to pass to the nwell/psub photodiode detector. Unfortunately, the rejection of the polysilicon filter is not great enough to allow surface detection of biomolecules. To achieve sensitivities on the order of realistic biomoleculer surface densities, another active CMOS biosensor array is fabricated. The second biosensor consists of a 4 x 8 pixel array of photodiodes and enables time-gated, time-resolved fluorescence spectroscopy to achieve higher sensitivity without the need for an optical filter. The array is sensitive to photon densities as low as 1.15 x 108/cm2, has a dynamic range of over 74 dB, and can measure sub-nanosecond lifetimes with a timing resolution of better than 230 ps. Sensitivity and enhanced bandwidth are achieved through sub-sampling and averaging. |
