EXECUTIVE SUMMARYtest certification document forTemperature SensorFabricated inSilicon Carbidesubmitted to:Professor Joseph PiconeECE 4512: Senior Design IDepartment of Electrical and Computer EngineeringMississippi State UniversityMississippi State, Mississippi 39762December 5, 2000Submitted by:Team Leader: Chris RiceTeam Members: Michael Jackson, Jason Wallace, Jovan BjelobrkFaculty Advisor: Dr. Steve SaddowDepartment of Electrical and Computer EngineeringMississippi State Universityemail: {cdr1, mbj1, jdw2, jb2}@ece.msstate.eduSiC TEMPERATURE SENSOR Page 2 of 16EXECUTIVE SUMMARYThere is no reliable way, using the conventional semiconductor material (silicon), todetect temperature in extreme environments. Silicon is well suited for a broad range ofapplications when operating below 250°C. To keep silicon based microelectromechanicalsystems (MEMS) within their operating limits while allowing operation in hightemperature environments can be space and cost intensive, leading to impracticality formany applications [8]. In the area of remote temperature sensing, most silicon basedtemperature 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 detectingtemperatures up to 500° C and physically withstanding temperatures in excess of thesensing range. To ensure accurate measurements, the tolerance of the device should bewithin ± .5° C at 25° C. For implementation into both new and legacy systems the sensormodule will operate over a voltage supply range of +5V to +25V.As an alternative to silicon we will incorporate silicon carbide (SiC), a newsemiconductor technology being used in harsh environments. Research has shown thatfor a fixed maximal junction temperature a SiC device can sustain about twice the powerthan a Si device [9]. High temperature operation, wide bandgap, and high electric fieldbreakdown are some of the desirable attributes that SiC possess [2]. First we willdiscover 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 datavia a RS-232 interface to a personal computer utilizing a graphical user interface systemfor the temperature display.By using silicon carbide, temperatures can be accurately sensed up to 500° C. This is adramatic increase of 333% above common rated silicon devices. Even though the sensormay not be able to acquire exceptional temperature magnitudes in excess of 500° C, thedevice will physically withstand these environments without breakdown. In addition, thedesign of this sensor will integrate analog to digital conversion in the microcontrollerused for the serial interface thereby removing the need for additional chips to performthis operation. This will reduce the cost and size of the overall package, which will makeit well suited for integration into applications requiring multiple testing points. There will be an opportunity for further developments involving integration of thisproduct with various other silicon carbide based sensors for other various applications.For example, other devices are being developed in conjunction this project that will sensevibration and pressure. The final goal of the entire project will be to usemicroelectromechanical systems (MEMS) technology to incorporate all three sensingdevices onto the same silicon carbide chip. This presents the opportunity to test theserelated stresses from a single point source. An integrated multiplexing device wouldallow for a single line acquisition of sensor data. This will provide the opportunity forECE 4512 December 5, 2000SiC TEMPERATURE SENSOR Page 3 of 16monitoring of these stresses in harsh environments where sensor data can be used totrigger compensation systems in order to allow early prevention of possible problems.1. INTRODUCTIONSilicon is well suited for many commercial applications, yet it has been shown throughresearch that this material cannot withstand the severe conditions of variousenvironments. The objective of this project is to produce a temperature-sensing devicethat will operate in harsh environments, specifically high temperature. This particularsensor is being produced for NASA to be attached to spacecraft for information gatheringpurposes. The use of silicon carbide is essential for this device to operate within the hightemperature range that propulsion systems and re-entry produce.The design constraints for this sensor are as follows:1. Temperature Sensing Range: Our device will have the ability to operate in ambienttemperatures ranging from 25° C to 500° C.2. Ambient Operating Temperature: The sensor must be able to withstand temperaturesin excess of 500° C.3. Tolerance: The device must read temperature within ± .5° C at 25° C.4. Self-heating: The unit must not generate more than 0.5° C of internal heat caused bytransistor current.5. Transient Response: The device will have a thermal time constant of less than 25 instill air and less than 5 in still liquid.6. Reliability: Our device will have the capability of making temperature readingsaccurately without frequent calibration.7. Physical Packaging: The unit must be small and lightweight, having a bolt-on design. 8. Operating Requirement: The device must operate within a voltage range of +4 to +25Volts.9. Cost: Costs involved with the device have yet to be determined.Using these guidelines, we should be able to produce a temperature sensor that will fit theapplications needed for the space program. In order to assure proper operation, the circuit design will be subjected to several pre-fabrication and post-fabrication tests. Testing performed will show that the output signalof the device will be capable of providing a voltage value with a distinguishabledifferential throughout the temperature range specified in the design constraints. Theanalog voltage value will be
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