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Silicon Carbide High Temperature Thermoelectric Flow Sensor

Lei, Man I
http://rave.ohiolink.edu/etdc/view?acc_num=case1283278445

Abstract Details

2011, Doctor of Philosophy, Case Western Reserve University, Materials Science and Engineering.
Current high temperature flow measurement devices are bulky, expensive and have slow response time. Therefore, there has been increasing demand for developing a flow sensor that has high temperature capability yet is small in size, fast in response time, and low in cost through mass fabrication. In this thesis, a high temperature flow sensor utilizing micromachining and microfabrication technology has been designed, simulated, fabricated, packaged and tested. This micro flow sensor is developed based on heavily-nitrogen-doped polycrystalline silicon carbide (n-SiC) thin film, a high temperature semiconductor well known for its mechanical robustness and chemical inertness in high temperatures and harsh environments. The small thermal mass and wide operating temperature range provide an excellent platform for a flow sensor operating with the thermal sensing principle. The n-SiC thermoelectric flow sensor prototype developed here is based on the calorimetric sensing mechanism. The sensor has a n-SiC heater for thermal marker creation, an upstream and a downstream n-SiC/p-Si thermopile for flow sensing, and a n-SiC thermistor for ambient temperature monitoring. This device is packaged in a stainless steel enclosure with a bypass channel. The tested flow range is between 0 to 20,000 sccm. The flow sensor has demonstrated high temperature capability and mechanical robustness up to 450 °C on a hotplate at zero flow condition, and up to 300 °C in a heated flow stream. The device has a response time of 8 ms. Maximum power consumption is 96 mW when operated at 8 mA (12 V) and 45 mW when operated at 5 mA (9V), with a sensor warm-up time less than 1 minute. In addition, the thermoelectric properties of n-SiC have been thoroughly studied through the characterization of the electrical resistivity, the Seebeck coefficient and the thermal conductivity of n-SiC thin film. The 0.93 μm-thick, n-SiC thin film utilized in the thermoelectric flow sensor has an electrical resistivity of 9.94 mΩ-cm, with a negative temperature coefficient (TCR) between 685 ppm/°C to 701 ppm/°C. The effect of film thickness on the electrical resistivity of n-SiC thin films has also been studied. The resistivity of n-SiC film decreases by a factor of ~7, from 38 mΩ-cm for the 100 nm-thick films to 5.4 mΩ-cm for the 1.78 μm-thick films. The Seebeck coefficient is measured to be -10 μVK-1 at room temperature, with a lateral thermal conductivity of 64 Wm-1K-1. The Seebeck coefficient increased to -20 μVK-1 at 300°C.
Mehran Mehregany (Advisor)
Pirouz Pirouz (Committee Member)
James McGuffin-Cawley (Committee Member)
Arthur Heuer (Committee Member)
155 p.
Electrical Engineering; Engineering; Materials Science
silicon carbide; thermoelectric; flow sensor; Seebeck coefficient; thermal conductivity; resistivity

Recommended Citations

Citations

  • Lei, M. I. (2011). Silicon Carbide High Temperature Thermoelectric Flow Sensor [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1283278445

    APA Style (7th edition)

  • Lei, Man I. Silicon Carbide High Temperature Thermoelectric Flow Sensor. 2011. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1283278445.

    MLA Style (8th edition)

  • Lei, Man I. "Silicon Carbide High Temperature Thermoelectric Flow Sensor." Doctoral dissertation, Case Western Reserve University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1283278445

    Chicago Manual of Style (17th edition)

case1283278445
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This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.