Jones, Geraint Rhys (2021) GaN-on-Si pressure, flow, and thermal conductivity sensors for harsh environments. PhD thesis, University of Warwick.
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Abstract
There is a growing number of applications that demand sensors and devices that can deal with harsh environments, which has led to new materials being used to realise these. One material that has demonstrated promise in high temperature, high radiation, chemically and mechanically harsh environments is Gallium Nitride (GaN). GaN on a silicon platform has advantages over other group III-N materials, in that a variety of Micro Electromechanical System (MEMS) fabrication techniques can be used, and Complementary Metal Oxide Semiconductor (CMOS) circuitry can be monolithically integrated on the same chip. Pressure, flow, and thermal conductivity sensors are of particular interest in harsh environments, and these have been investigated here.
A ring-HEMT pressure sensor is presented, that utilises a High-Electron Mobility Transistor (HEMT) embedded into the edge of a GaN membrane released from a silicon substrate. This device was tested in different bias conditions to find the best operating conditions for high sensitivity and low power consumption. This pressure sensor was modelled mechanically in an Finite Element Method (FEM) package, and the results fed into an analytical model to estimate the change in carrier concentration.
Two flow sensors are presented. The first is a hot-film device using gold metallisation to create a thermoresitive flow sensor. The second uses the 2DEG at an AlGaN/GaN heterojunction as the hot-wire heating element. This work proved the operation of both sensors at ow rates up to 5 SLPM.
Finally, a thermal conductivity sensor is presented based on the gold hot-film device, using gold/2DEG thermocouples as temperature sensors upstream and downstream of the heating element. Simultaneous measuring of the ow rate and thermal conductivity was achieved using an artificial neural network to discriminate between the two fluid properties. Principal Components Regression (PCR) and Partial Least Squares Regression (PLSR) linear statistical methods were also explored for this discrimination, but with limited success.
| Item Type: | Thesis [via Doctoral College] (PhD) |
|---|---|
| Subjects: | T Technology > TA Engineering (General). Civil engineering (General) T Technology > TJ Mechanical engineering and machinery T Technology > TK Electrical engineering. Electronics Nuclear engineering |
| Library of Congress Subject Headings (LCSH): | Pressure transducers, Transducers, Microelectromechanical systems, Metal oxide semiconductors, Complementary, Gallium nitride, Thermal conductivity |
| Official Date: | February 2021 |
| Dates: | Date Event February 2021 UNSPECIFIED |
| Institution: | University of Warwick |
| Theses Department: | School of Engineering |
| Thesis Type: | PhD |
| Publication Status: | Unpublished |
| Supervisor(s)/Advisor: | Gardner, J. W. (Julian W.), 1958- |
| Sponsors: | Engineering and Physical Sciences Research Council |
| Format of File: | |
| Extent: | xviii, 158 leaves : illustrations |
| Language: | eng |
| URI: | https://wrap.warwick.ac.uk/162579/ |
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