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Title: Introducing the hybrid unipolar bipolar field effect transistor : the HUBFET
Author: Donnellan, Benedict T.
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2013
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Modern commercial aircraft are becoming increasingly dependent on electrical power. More and more of the systems traditionally powered by hydraulics or pneumatics are being migrated to run on electricity. One consequence of the move towards electrical power is the increase in the storage capacity of the bat- teries used to supplement the power generation. The increase in battery size increases the maximum stress that a short circuit failure can put on the power distribution system. Although such failures are extremely rare, the fail safe switches in the distribution system must be capable of handling extremely high energy short circuits and turning off the power to protect the electrical systems from damage. Traditionally aircraft have used electromechanical relays in this role. However, they are large, heavy and slow to switch. As the potential power level is increased, the slow switching becomes more of a problem. The solution is a semiconductor switch. An IGBT can handle the high short circuit currents and switches fast enough to prevent short circuits damaging key systems. However, the inherent voltage drop in the forward current path significantly reduces its efficiency during nominal operation. A power MOSFET would be considerably more efficient than an IGBT during nominal operation. However, during high current surges, the ohmic behaviour of the switch leads to extremely high power loss and thermal failure. In this thesis a solution to this problem is presented. A new class of semiconductor device is proposed that has the highly efficient low current performance of the power MOSFET and the high current handling capability of the IGBT. The device has been named the Hybrid Unipolar Bipolar Field Effect Transistor or HUBFET. The HUBFET operates in unipolar mode, like a MOSFET, at low currents and in bipolar mode, like an IGBT, at high currents. The structure of the HUBFET is a merging of the MOSFET and IGBT. It is a vertical device with a traditional MOS gate structure, however the backside consists of alternating regions of both N-type and P-type doping. Through simulation the key on-state characteristics of the HUBFET have been shown. Fabricated test modules have been tested to validate the simulations and to show how the HUBFET can dynamically transistion from unipolar to bipolar mode during a short circuit event. Following the proof of concept the pattern of implants on the backside of the device that give the HUBFET its characteristic were investigated and potential improvements to the design were identified.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering ; TL Motor vehicles. Aeronautics. Astronautics