design document for Temperature Sensor Fabricated in Silicon Carbide submitted to: Professor Joseph Picone ECE 4522: Senior Design II Department of Electrical and Computer Engineering Mississippi State University Mississippi State, Mississippi 39762 May 1, 2001 Submitted by: Team Leader: Jason Wallace Team Members: Michael Jackson, Chris Rice, Jovan Bjelobrk Faculty Advisor: Dr. Steve Saddow Department of Electrical and Computer Engineering Mississippi State University email: {jdw2, mbj1, cdr1, jb2}@ece.msstate.eduSiC TEMPERATURE SENSOR Page 2 of 2 ECE 4512 May 1, 2001 EXECUTIVE SUMMARY There is no reliable way, using the conventional semiconductor material (silicon), to detect temperature in extreme environments. Silicon is well suited for a broad range of applications when operating below 250°C. To keep silicon based microelectromechanical systems (MEMS) within their operating limits while allowing operation in high temperature environments can be space and cost intensive, leading to impracticality for many applications [8]. In the area of remote temperature sensing, most silicon based temperature sensors are rated by their manufacturer for temperature sensing ranges of 0 -150° C. This temperature sensor must be a small bolt on package capable of detecting temperatures up to 500° C and physically withstanding temperatures in excess of the sensing range. To ensure accurate measurements, the tolerance of the device should be within ± .5° C at 25° C. For implementation into both new and legacy systems the sensor module will operate over a voltage supply range of +5V to +25V. As an alternative to silicon we will incorporate silicon carbide (SiC), a new semiconductor technology being used in harsh environments. Research has shown that for a fixed maximal junction temperature a SiC device can sustain about twice the power than a Si device [9]. High temperature operation, wide bandgap, and high electric field breakdown are some of the desirable attributes that SiC possess [2]. First we will discover through our own testing the thermal characteristics of SiC as compared to Si. After which, we will implement a design to sense temperature and transmit acquired data via a RS-232 interface to a personal computer utilizing a graphical user interface system for the temperature display. By using silicon carbide, temperatures can be accurately sensed up to 500° C. This is a dramatic increase of 333% above common rated silicon devices. Even though the sensor may not be able to acquire exceptional temperature magnitudes in excess of 500° C, the device will physically withstand these environments without breakdown. In addition, the design of this sensor will integrate analog to digital conversion in the microcontroller used for the serial interface thereby removing the need for additional chips to perform this operation. This will reduce the cost and size of the overall package, which will make it well suited for integration into applications requiring multiple testing points. There will be an opportunity for further developments involving integration of this product with various other silicon carbide based sensors for other various applications. For example, other devices are being developed in conjunction this project that will sense vibration and pressure. The final goal of the entire project will be to use microelectromechanical systems (MEMS) technology to incorporate all three sensing devices onto the same silicon carbide chip. This presents the opportunity to test these related stresses from a single point source. An integrated multiplexing device would allow for a single line acquisition of sensor data. This will provide the opportunity for monitoring of these stresses in harsh environments where sensor data can be used to trigger compensation systems in order to allow early prevention of possible problems.SiC TEMPERATURE SENSOR Page 3 of 3 ECE 4512 May 1, 2001 TABLE OF CONTENTS ABSTRACT ............................................................................................................ 5 1. INTRODUCTION..................................................................................................... 5 2. PROBLEM .............................................................................................................. 6 3. OBJECTIVES ......................................................................................................... 7 3.1 Temperature Sensing Range............................................................................. 9 3.2 Ambient Operating Temperature ...................................................................... 9 3.3 Tolerance ............................................................................................................. 9 3.4 Self-Heating ......................................................................................................... 9 3.5 Transient Response ........................................................................................... 9 3.6 Reliability .............................................................................................................. 9 3.7 Physical Packaging ............................................................................................ 10 3.8 Operating Voltage ............................................................................................... 10 3.9 Cost ....................................................................................................................... 10 4. APPROACH ............................................................................................................10 4.1 Silicon Carbide Sensor .......................................................................................11 4.1-1 Geometric Parameters ................................................................................... 11 4.1-2 Device Parameter Design .............................................................................. 12 4.1-3 Mask Layout
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