Author
Dhrubo, Md Nabil Shehtab
Other Contributors
Hella, Mona, M.; Karlicek, Robert, F.; Lu, James;
Date Issued
2023-08
Subject
Electrical engineering
Degree
MS;
Terms of Use
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute (RPI), Troy, NY. Copyright of original work retained by author.;
Abstract
Circadian rhythm irregularity is a widespread condition affecting people from all age groups.Excessive exposure to blue light is a primary factor that disrupts circadian rhythm. There-
fore, developing a spectral sensor that can detect, filter and measure blue radiation from
surroundings is quite essential. Existing literature have demonstrated progress on blue
wavelength detectors at component level but a fully integrated system architecture with
high resolution spectroscopic application has not been explored yet. Therefore, this thesis
presents a fully integrated design approach using a standardized silicon photonic technology
to detect, filter and measure blue exposure and present it as readable voltage outputs. The
work discusses in-depth about each component of the sensor and validates their theoretical
background through different simulation techniques. All of these components can be fab-
ricated using GlobalFoundries 45 nm monolithic technology, shortly known as 45SPCLO.
A silicon nitride based photonic front end is demonstrated with grating couplers showing
coupling efficiency of around 27%, tapered waveguides and optical power combining networks
with negligible loss (1%∼10%) and an optimized multimodal interference (MMI) coupler
demonstrating 80% coupling efficiency. The thesis strongly focuses on three different junc-
tion architectures for a silicon based photodiode and their comparative performances. These
architectures are referred to as single, zigzag and interweaved junctions. For the interweaved
junction architecture, a maximum simulated responsivity of 135 A/W is demonstrated under
breakdown conditions and it outperforms the other two junction architectures in linear region
as well. All the photodiode designs exhibit low junction capacitances in femtofarad range.
The small junction capacitance helps the photodetectors to interface smoothly to a low noise
trans-impedance amplifier (TIA). The TIA architecture shown in this work demonstrates an
input referred noise current of 1.4 nA, a trans-impedance gain of 140 dB and a bandwidth of
75 MHz when coupled to an output buffer amplifier. The noise current is significantly lower
than simulated photocurrent values and the bandwidth is sufficient for a spectral biosensor
which performs mostly under DC conditions effectively.;
Description
August2023; School of Engineering
Department
Dept. of Electrical, Computer, and Systems Engineering;
Publisher
Rensselaer Polytechnic Institute, Troy, NY
Relationships
Rensselaer Theses and Dissertations Online Collection;
Access
Users may download and share copies with attribution in accordance with a Creative Commons
Attribution-Noncommercial-No Derivative Works 3.0 license. No commercial use or derivatives
are permitted without the explicit approval of the author.;