CMOS BIOSENSORS FOR PORTABLE MOLECULAR DIAGNOSTIC SYSTEM
Open AccessIn this dissertation, two sensor designs based on low cost CMOS 0.5um n-well process were proposed for labeled molecular diagnostic applications. One of the designs is a Hall Effect magnetic sensor for magnetic bead label detection. The other design is a Single-Photon Avalanche Diode for photonic label detection. In addition, a novel CMOS & Microfluidic integration technology was proposed to achieve a lab on chip system. The proposed novel differential CMOS split-drain Hall Effect Magnetic Field-Effect Transistor (MAGFET) was fabricated employing CMOS 0.5µm process. Based on the device modeling, simulation and the signal to noise ratio analysis, I found that the optimal sensitivity can be achieved when the MAGFET channel width to length ratio is equal to 1.3. And when the MAGFET is scaled down, its SNR performance can sustain its peak and be more sensitive to the geometry variations. Future more, a novel circular CMOS MAGFET design was introduced and a novel device geometry design methodology was proposed to optimize the magnetic particle detection sensitivity. Compared to the traditional rectangular MAGFET, the circular MAGFET has compatible SNR peak performance. However, when the size of the MAGFET is scaled down in order to detect smaller magnetic particles, the circular MAGFET has more robust SNR performance, design flexibility and tolerance to processing variations. In the end, a 2.8 µm diameter magnetic beads detection and monitoring experiment was successfully performed using the proposed MAGFET design. The Single-Photon Avalanche Diode (SPAD) design was also implemented in the cost efficient CMOS process, n-well 0.5μm process. This SPAD design used the lateral diffusion of the n-wells to create a low n- doping density area as the guard ring to prevent the premature breakdown at the edge of SPAD. This design solution had to violate several foundry design rules to be implemented in CMOS 0.5μm process. Through the TCAD simulation and fabricated design characterization, the proper gap length between n-wells was found to create the guard ring that allows the SPAD to work in the Geiger Mode. The dark count rate (DCR) of the SPAD was 750/Hz at 14.85V bias voltage without cooling. The integrated active quenching circuit had 60ns FWHM output pulse. The proposed novel biosensor package method, Liquid Metal Microfluidic Package (LMMP), can enable the integration of the CMOS detector chip and microfluidics channels. In this novel package, some of the microfluidics channels were designed to deliver liquid metal or low melting point solder to realize the electrical interconnections of the CMOS chip. The other microfluidic channels were designed to deliver test liquid samples to CMOS detector. This proposed technology has several advantages. First, microfluidics channels can accurately and rapidly deliver sample to CMOS detectors. Secondly, microfluidics channels can deliver the test sample to be very close with the detector, so the sensitivity of the system can be improved while keeping the system portable. Finally, less volume of test sample is needed due to small dimension of the microfluidics channel, so the daily operation cost of such system can be reduced. Such portable biosensors can have broad applications ranging from point-of-care molecular diagnostics to environmental monitoring, food safety inspection and bioterrorism detection.
- All rights reserved
Notice to Authors
If you are the author of this work and you have any questions about the information on this page, please use the Contact form to get in touch with us.