The Woodruff School

SUMMARY

Numerous applications in the present day ranging from testing humidity in air to detecting miniscule quantities of potentially hazardous chemical and biological agents in the air or water supplies require the development of chemical sensors that are able to perform such functions at high sensitivity and selectively. Further it has become desirable to create lab-on-chip systems that can detect multiple chemical agents and allow for sampling and testing of environments and liquids far from conventional laboratory detections system with enhanced detection capabilities. Current challenges in this area include design and characterization of low detection limit sensors, positive identification of analytes and, identification and reduction of the effect of various noise sources - both intrinsic and extrinsic to the sensor. The current work examines the performance limits of a 10-cantilever piezoresistive microcantilever array (P�CA) sensor. The microcantilevers measure analyte concentration in terms of the surface stress associated with analyte binding to the functionalized cantilever surface. The design, modeling, fabrication and characterization of this measurement platform is presented. A novel aspect of the sensors developed is the use of n-type doping which increases the sensitivity of the device by one order of magnitude. In addition, design rules for surface stress-based chemical sensors have been developed. Thermal characterization of the P�CA has been performed to allow for a more complete understanding of thermal issues in chemical sensing with piezoresistive cantilever sensors and sensor arrays. Further, a method of low-noise measurement of cantilever resistance,based on phase-sensitive detection techniques, has been developed and this has been integrated with a multiplexing circuit to measure resistance change in multiple cantilevers. Finally two novel schemes of chemical sensing- double-sided sensing and thermal array based sensing are presented as a means of extending the applicability and functionality of the P�CA.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Arnab Choudhury

TIME:	Monday, November 5, 2007, 11:00 a.m.

PLACE:	Love Building, 311

TITLE:	A Piezoresistive Microcantilever Array

COMMITTEE:	Dr. Peter J. Hesketh, Chair (ME) Dr. Levent Degertekin (ME) Dr. Zhoumin Zhang (ME) Dr. Jiri Janata (CHEM) Dr. Lawrence Bottomley (CHEM) Dr. Zhiyu Hu (ORNL)

SUMMARY Numerous applications in the present day ranging from testing humidity in air to detecting miniscule quantities of potentially hazardous chemical and biological agents in the air or water supplies require the development of chemical sensors that are able to perform such functions at high sensitivity and selectively. Further it has become desirable to create lab-on-chip systems that can detect multiple chemical agents and allow for sampling and testing of environments and liquids far from conventional laboratory detections system with enhanced detection capabilities. Current challenges in this area include design and characterization of low detection limit sensors, positive identification of analytes and, identification and reduction of the effect of various noise sources - both intrinsic and extrinsic to the sensor. The current work examines the performance limits of a 10-cantilever piezoresistive microcantilever array (P�CA) sensor. The microcantilevers measure analyte concentration in terms of the surface stress associated with analyte binding to the functionalized cantilever surface. The design, modeling, fabrication and characterization of this measurement platform is presented. A novel aspect of the sensors developed is the use of n-type doping which increases the sensitivity of the device by one order of magnitude. In addition, design rules for surface stress-based chemical sensors have been developed. Thermal characterization of the P�CA has been performed to allow for a more complete understanding of thermal issues in chemical sensing with piezoresistive cantilever sensors and sensor arrays. Further, a method of low-noise measurement of cantilever resistance,based on phase-sensitive detection techniques, has been developed and this has been integrated with a multiplexing circuit to measure resistance change in multiple cantilevers. Finally two novel schemes of chemical sensing- double-sided sensing and thermal array based sensing are presented as a means of extending the applicability and functionality of the P�CA.