Daniel Smith

Abstract

The use of MEMS (micro-electro-mechanical system) sensors in multiple applications of environmental monitoring help to fill the need of a small scale, low power monitoring and sensing applications. In this design, the use of single-die multiple MEMS sensors to monitor ambient temperature, relative humidity, and accelerative high-g shock were developed and tested. In addition to the sensors, signal conditioning circuits were developed for outputting the sensor data into a microcontroller to analyze and process the signals into useful information for human operators to analyze. The three sensors were fabricated using a bulk micro-machined process on 100mm silicon wafers developed in the RIT SMFL. This work extends previous work on a multisensor from a year earlier. Ion implantation is now used to tune doping levels. To help reduce cross-talk between sensors, p-wells were introduced to aid in substrate isolation. A parallel plate humidity sensor was developed, bringing the need to develop in-line processing of polyimide. Lastly, the one-axis shock sensor is upgraded into a three-axis shock sensor. The temperature sensor is made using a PN diode, utilizing the temperature dependence of the forward bias voltage drop from the Shockley diode equation, corresponding to -2.2mV/°C response over a range of -50°C to 150°C for the application operation range. Signal conditioning is a constant current mode operation, measuring the change in voltage drop across the diode. The relative humidity sensor is formed from one of two designs; an interdigitated comb-finger capacitor or a parallel plate capacitor. Polyimide was used as the dielectric material due to linear diffusion properties of water vapor to relative humidity. While the comb-finger sensor was coated with polyimide post-processing, a new thin film processing and integration technique was developed for the first time here at RIT for the parallel plate sensor. Due to the small levels of capacitive change in the range of 5% to 95% relative humidity, the sensor's capacitive measurement is run through an RC astable multivibrator circuit to produce an RC square wave. From the frequency of this wave, the capacitance, and thus the relative humidity can be computed by the microcontroller.

Library of Congress Subject Headings

Microelectromechanical systems--Design and construction; Multisensor data fusion; Microcontrollers--Design and construction; Sensor networks--Design and construction

Publication Date

8-14-2012

Document Type

Thesis

Department, Program, or Center

Electrical Engineering (KGCOE)

Advisor

Fuller, Lynn

Comments

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: TK7875 .S64 2012

Campus

RIT – Main Campus

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