M.Sc Thesis


M.Sc StudentShor Roy
SubjectStudy of CMOS Direct Sensing for Radon and High Energy
Alpha Radiation
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Yael Nemirovsky
Full Thesis textFull thesis text - English Version


Abstract

This study focuses on CMOS sensors of ionizing radiation, which are integrated monolithically on a single chip with the Readout Circuitry. Thus, allowing fabrication of low power, low cost sensing systems for a wide range of applications. The sensors are based on a new mosaic design of an array of Floating Gate non-volatile memory like transistors, which are implemented in a standard CMOS technology, with a single polysilicon layer.

The focus of this study is mainly on detecting ionizing radiation emitted from radon gas decay. Radon is a natural, inert, invisible, odorless, chemically inactive and radioactive gas emitted from the earth. Because inhaling radon and its radioactive-decay products causes irradiation of lung tissue, prolonged exposure to a high concentration of radon significantly increases the risk of developing cancer. When radon decays, it releases alpha particles with energy of 5.5 Mega-electro-volts (MeV). When radon’s progenies decay, they release alpha particles within energy of 6MeV and 7.7MeV. Accordingly, by detecting these alpha particles, radon may be detected.

Commercially available radon sensors are either one-time use, designed to measure average concentration in a very specific period, or continues monitors, mostly based on silicon diode or ionization chamber, which are expensive.

The study describes novel solid-state radiation sensor, which was designed, modeled, fabricated and characterized.

The main parts of the research are:

1.      Technology: Design of CMOS Direct Sensing System for High Energy Alpha Radiation, using single poly.

2.      Solid State Device: Modeling the performance of the CMOS Floating Gate Transistor as a direct radiation sensor.

3.      Sensor Circuit: Modeling the performance of a mosaic array.

4.      Sensor Analog Readout: Design, Performance and Noise Modeling, layout and implementation.

5.      Sensing System: Measurements, characterization and analysis in order to show feasibility of a practical alpha and radon gas sensor based on a CMOS sensor.