  Optical spectrometers are widely used scientific equipment with many
applications involving material characterization, chemical analysis, disease
diagnostics, surveillance, etc. Emerging applications in biomedical and
communication fields have boosted the research in the miniaturization of
spectrometers. Recently, reconstruction-based spectrometers have gained
popularity for their compact size, easy maneuverability, and versatile
utilities. These devices exploit the superior computational capabilities of
recent computers to reconstruct hyperspectral images using detectors with
distinct responsivity to different wavelengths. In this paper, we propose a
CMOS compatible reconstruction-based on-chip spectrometer pixels capable of
spectrally resolving the visible spectrum with 1 nm spectral resolution
maintaining high accuracy (>95 %) and low footprint (8 um x 8 um), all without
the use of any additional filters. A single spectrometer pixel is formed by an
array of silicon photodiodes, each having a distinct absorption spectrum due to
their integrated nanostructures, this allows us to computationally reconstruct
the hyperspectral image. To achieve distinct responsivity, we utilize random
photon-trapping nanostructures per photodiode with different dimensions and
shapes that modify the coupling of light at different wavelengths. This also
reduces the spectrometer pixel footprint (comparable to conventional camera
pixels), thus improving spatial resolution. Moreover, deep trench isolation
(DTI) reduces the crosstalk between adjacent photodiodes. This miniaturized
spectrometer can be utilized for real-time in-situ biomedical applications such
as Fluorescence Lifetime Imaging Microscopy (FLIM), pulse oximetry, disease
diagnostics, and surgical guidance.
