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Title: Characterisation and application of microwave field effect transistors
Author: Luxton, Hubert Ernest George
ISNI:       0000 0001 3614 2287
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1980
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The work reported in this thesis is concerned with the determination of the microwave characteristics and possible applications of Gallium Arsenide Field Effect Transistors at frequencies from 0.1 to 12 GHz. In order to characterise these active devices with reasonable accuracy and consistency the microwave network analyser facility at Warwick has been expanded and developed to give a 2-port, computer corrected, scattering parameter measurement capability. The resulting system has been tailored to the particular needs of GaAs FET characterisation and assessment, by the inclusion of subroutines which enable gain and stability parameters to be displayed in addition to the corrected s-parameters. Various transistor package styles and corresponding test fixtures to enable the active devices to be interfaced with the network analyser have been investigated. Since the device test fixtures have used micro-strip rather than co-axial transmission lines special calibration routines and standards have been developed to enable the computer correction system to be employed for the measurements. Numerous devices have been characterised with the facility developed and the results used to establish the s—parameter characteristics of GaAs FETs at frequencies up to 12GHz. This information has been used to compare the predicted performance of different batches and types of device and in the design of circuits used to assess the actual performance of GaAs FEJTs in certain applications, such as small signal amplifiers and oscillators. Data on the effects of device processing and design changes on microwave performance have been fed back to the device manufacturer to aid optimisation of GaAs FET technology. Such measurements have shown the superior performance of aluminium versus nickel as a gate metallisation identified a weakness in electron beam fabricated devices and confirmed the advantage in using wider gate structures to lower impedances and simplify matching requirements. S-parameter data for packaged FETTs has been used to design amplifier and oscillator circuits which have been realised in order to assess the actual device performance in these applications. A comparison of predicted and measured performance at 3GHz has shown reasonable agreement. A novel tuning technique on micro-strip was used to produce amplifiers at X-Band using chip devices. Using this technique with one micron gate length FETs a high gain (>40dB) amplifier at 11.2GHz was fabricated which confirmed the suitability of GaAs FETs as amplifier devices for such applications as high gain microwave amplifiers in repeater systems. At lower frequencies the GaAs FET has been shown to give excellent noise performance and is superior in this respect to bipolar transistors. The oscillator circuits incorporating GaAs FETTs investigated exhibited two notable characteristics; good D.C. to R.F. conversion efficiency and poor noise and stability performance. The latter however, appears to result from the un-optimised nature of the circuits used. In spite of some remaining unanswered questions, the overall conclusion from this investigation is that GaAs FETs, although relatively new devices (at the time of this study 1971-74) are useful solid state devices for numerous microwave applications. The importance of the GaAs FET in microwave systems has been underlined since the completion of this early study by the tremendous increase in activity in this field to the level seen today.
Supervisor: Not available Sponsor: Science Research Council ; Plessey Company
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering