Integrated Multifunctional Environmental Sensors

Abstract

We present the design, microfabrication, and characterization of ten sensors on one silicon die. We demonstrate simultaneous monitoring of multiple environmental parameters, including temperature, humidity, light intensity, pressure, wind speed, wind direction, magnetic field, and acceleration in three axes. Through an integrated design and fabrication process, these ten functions require only six photolithography mask steps. Temperature is measured redundantly using aluminum and doped silicon resistance thermal detectors and a bandgap temperature sensor. Humidity is transduced by the dielectric change of a polymer due to water absorption. Light intensity is measured with a p-n junction photodiode and doped silicon photoresistor. Pressure is transduced using piezoresistor strain gauges on a sealed membrane. Wind speed and direction are measured with two perpendicular hot wire anemometers. Magnetic field strength is measured with a doped Hall effect sensor. Acceleration in three axes is measured using electrostatic comb finger accelerometers, and an additional <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -axis accelerometer uses piezoresistor strain gauges. We measured the cross-sensitivity of each function to all other environmental parameters and can use the chip's multifunctional capabilities to compensate for these effects. Sensor integration can enable significant cost, size, and power savings over ten individual devices and facilitate deployment in novel applications.