M.Sc Thesis

M.Sc StudentWeinstein Moshe
SubjectStudy of Micromachined Microbolometers as Uncooled Sensors
for IR Imaging
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Yael Nemirovsky


    The VLSI revolution enabled the integration of millions of transistors on the same silicon chip and mass production of integrated circuits at very low cost and high reliability. The MEMS revolution takes the next step into the future by pursuing the integration of whole systems at multi- and micro- scale. Micromachining of 3-D structures in dies containing all electronic devices enables the implementation of smart microsystems able of sensing and affecting the physical environment.

    One of the promising applications that emerged in the last decade is uncooled thermal imaging. The well known method for IR imaging is to use cooled photonic sensors. Such sensors are very sensitive and have a short response time, but they suffer from a major disadvantage, they require cooling to cryogenic temperatures of 77°K. This demand dramatically increases the cost of thermal imagers based on such sensors, increases the dimensions and power consumption of the imagers.

    The innovative MEMS technology enables to implement thermally isolated resistors (microbolometers) that can sense IR radiation without cooling, and the combination with well-established silicon CMOS technology enables to integrate them in VLSI chips to perform on-line signal processing.

    In this work integrated IR sensors based on microbolometers are studied. In this approach microbolometers are used to sense temperature changes, resulting in its resistance fluctuations. Such devices are implemented using standard CMOS or CMOS-SOI technology, followed by Bulk and Surface micromachining.

    In this research different kinds of microbolometers have been studied and designed. Polysilicon microbolometers based on standard CMOS technology have been studied and Active Silicon microbolometers based on CMOS-SOI technology have been studied, designed and tested. These microbolometers have very low temperature sensitivity, but they should be implemented in low end sensors. Cadmium Sulfide microbolometers, that should be implemented in high-end sensors, have been studied and designed, as well.

    Sensors, based on microbolometers, require readout circuit, which should have very small dimensions and low noise. Readout circuit, designed for Polysilicon microbolometers readout, had been studied and tested in this research.

    The theory of the IR uncooled sensors was also studied in this research. The emphasis was on radiometric properties of thermal image system performance and microbolometers noise.

   Measured performance of Active Silicon microbolometers shows promise and potential for low cost novel sensors and it is a very challenging issue for future researches.