PHD Defense - Fabrication Methods for Environmentally Hardened Sensors

 

 

Department of Electrical Engineering

University PhD Oral Examination

Fabrication Methods for Environmentally Hardened Sensors

Anthony F. Flannery Jr.

February 3, 2011 @ 2:00 PM

Refreshments at 1:45 PM

CIS-X 101 (Auditorium)

Abstract

Micromachined sensors have continued to open exciting new doors in the field of metrology. Applications for different types of sensors and sensing systems have proven a fertile ground for cross-disciplinary research and many new sensor developments are being made in the fields of biology, pharmacology, chemistry, and genetics. The need for sensors that can function successfully in a broad range of environments is clear. Whether the task is to produce devices which can tolerate harsh chemical environments or those which will not interfere with delicate biochemical processes, developments in both materials and fabrication techniques will continue to be necessary as sensors leave the laboratory and interface with the real world.

In this work, a process for low-temperature, low-stress PECVD silicon carbide was developed. The deposition conditions were CMOS compatible. This also makes the film suitable for devices with gold and other materials with lower temperature limits. Key electrical and physical properties relevant to micromachined transducers were determined. The chemistry of the film was also investigated and an important criterion to achieve chemical resistance was discovered, adding understanding to its usefulness in fabricating environmentally hardened transducers.

Work was also done developing two main fabrication techniques. The first was an improved method for depositing and patterning high stress metals, specifically iridium. Iridium is of particular interest because of its useful electrochemical properties and its chemical resistance. Advancements were made in the areas of stress reduction and liftoff structures. The second was in the area of non-planar lithography, allowing the application of chemically resistant coatings on the sidewalls of microfluidic structures.

These techniques were applied in several different applications. An iridium microelectrode array capable of performing electrochemical analysis in hydrofluoric acid was fabricated and tested. The effect of coating a micromachined pressure sensor was explored. A gasketing process for fabricating chemically resistant microfluidic channels was proposed and fabricated.