M.Sc Thesis

M.Sc StudentGitelman Leonid
SubjectStudy of Micromachined Transistors as Uncooled Sensors for
IR Imaging
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Yael Nemirovsky


Methods for detecting electromagnetic radiation fall into three categories, photon detection, thermal detection and wave interaction detection.

The importance and enormous potential of Infra Red (IR) imaging for the military and homeland security is by now well established. However, the need to cool the conventional photonic sensors to cryogenic temperatures is a major draw back, in terms of cost, size and logistics. As a result, in recent years an intensive R&D effort has emerged to develop uncooled infrared imaging systems based on thermal sense mechanism.

Thermal detection mechanisms are defined as mechanisms that change some measurable property of a material due to the temperature rise caused by the absorption of electromagnetic radiation. Silicon micromachining technology caused a revolution for providing miniaturized thermally isolated structures with high thermal resistance toward the ambient and low thermal capacitance. However, the current uncooled IR imagers are based mainly on microbolometers, fabricated with use of unique temperature-sensitive materials (such as Vanadium Oxide), which are difficult to process and to integrate with the readout circuits.

In this work we present a new type of uncooled IR sensor based on micromachined thermally isolated MOS transistor - TMOS. The enabling technology for suspending the miniature structure is the well established CMOS-SOI technology, where the oxide provides natural etch stop for the backside removal of the silicon substrate by DRIE. In addition, a suspended MOS transistor senses the temperature changes and provides signal multiplexing and the ability of simple integration in readout circuits.

Modeling and measurements of actual devices show temperature coefficient of current of more than 4%/K, better than state-of-the-art microbolometer temperature coefficient of resistance. Different operation regions have been analyzed and subthreshold region is chosen for best performance (NETD better than 10mK) with an advantages of low self-heating, low power consumption and possibility for snapshot operation.