Battery-powered, Wireless MEMS Sensors for High-Sensitivity Chemical and Biological Sensing

Researchers at Oak Ridge National Laboratory (ORNL) are developing selectively coated cantilever arrays in a surface-micromachined MEMS process for very high sensitivities in chemical and biological sensing. Toward this end, we have developed a one-dimensional (1-D) 10-element microcantilever array that we have coated with gold for mercury sensing and palladium for hydrogen sensing. Ultimately we will coat each element with a different coating. Currently, measurements have been performed using a companion analog 1.2-μm CMOS eight channel readout chip also designed at ORNL specifically for the microcantilever arrays. In addition, we have combined our sensors with an ORNL-developed RF-telemetry chip having on-chip spread spectrum encoding and modulation circuitry to improve the robustness and security of sensor data in typical interferenceand multipath-impaired environments. We have also provided for a selection of distinct spreading codes to serve groups of sensors in a common environment by the application of code-division multiple-access techniques. Our initial system is configured for use in the 915-MHz Industrial, Scientific, and Medical (ISM) band. The entire package is powered by four AA batteries. 1: Integrated Microsensors Researchers at Oak Ridge National Laboratory and the University of Tennessee have been actively involved for years in various novel sensor developments and highly integrated custom analog integrated circuit development for large particle-physics experiments, some having over 300,000 channels of integrated CMOS electronics. More recently, we have begun to marry the two areas of research into integrated sensors and wireless telemetry. The first section describes selectively coated microcantilevers, a sensor technology that exhibits a great deal of promise for low-power sensing of environmental contaminants. The second section presents the present work to date on the wireless telemetry initiative. 2: Selectively-Coated Microcantilevers