Noise Characterisation of Graphene FETs
Abstract: This thesis deals with the first noise performance study of graphene field effect transistors (G-FETs) at microwave frequencies. It considers G-FETs in two different applications, as a subharmonic resistive mixer and in an amplifier. The work encompasses cleanroom fabrication, as well as characterisation by measurement and modelling. As part of the work a G-FET amplifier operating at 1 GHz with 10 dB small-signal power gain is designed, an 8 dB improvement comparing to earlier reports. The amplifier noise figure is measured to be 6.4±0.4 dB at 1 GHz. Modelling by the Pospieszalski temperature noise model predicts the minimum extrinsic and intrinsic noise figure of the G-FET itself to be Fmin,ex = 3.3 dB and Fmin,in = 1.0 dB, respectively. Furthermore, the subharmonic mixer exhibits a down-conversion loss of 20-22 dB to fIF = 100 MHz in the RF frequency interval fRF = 2-5 GHz. The mixer noise figure closely mimics the conversion loss, which suggests the noise of the mixer to be thermal in origin. Conventional FET modelling methods have proven helpful in the analysis also for G-FETs.
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