Monolithic microwave/millimetrewave integrated circuit resonant tunnelling diode dources with around a milliwatt output power

Resonant tunnelling diode (RTD) oscillators are considered to be one of the most promising solid-state terahertz sources which can operate at room temperature. The main limitation of RTD oscillators up to now is their low output power. For the published terahertz (THz) RTD oscillators, the output power is in the range of micro-Watts. This thesis describes systematic work on RTD device modelling, and on the design, fabrication and measurement of high power monolithic microwave integrated circuit (MMIC) RTD oscillators. The RTD device consists of a narrow bandgap layer (quantum well) sandwiched between two thin wide bandgap layers (barriers). When the device is biased, electrons with kinetic energy lower than the barriers may tunnel through the double barrier-quantum well (DBQW) structure, and the device exhibits a negative differential resistance (NDR) in this case. To investigate this phenomenon, a new numerical model based on quantum mechanics was developed. The model involves self-consistent solving of the Schrodinger equation until the quasi-eigen energy state converges. This model is expected to serve to optimize the RTD device structure for millimetre-wave and terahertz applications. Besides RTD device modelling, the fabrication process for single devices and for MMIC RTD oscillator circuits was developed and optimized on this project. Optical lithography, wet/dry etching and metallization were the main fabrication techniques utilized. For device sizes of a few square microns, the fabrication process required the development of new steps, i.e, via opening through polyimide. The fabrication process was optimized and high yield was obtained. On this project, one of the challenges was to realize RTD oscillators in the form of MMICs, aiming at about 100 GHz with milli-Watts output power, in accordance with a recently proposed power combining circuit topology. To accomplish such an oscillator, proper design of passive components was essential. On this project, these components included 50 coplanar waveguides (CPW), shorted CPW stubs, metal-insulator-metal (MIM) capacitors and thin _lm resistors. The design procedure for these components is described, and their performance characterized by DC or scattering parameter measurements as appropriate. Two types of MMIC RTD oscillator layouts were designed, fabricated and characterized. Details are described in this thesis. Measurement results showed that for the fabricated 75 GHz oscillator, the output power obtained was -0.2 dBm (0.96 mW), and for the 86 GHz oscillator, the measured output power was -4.6 dBm (0.35 mW), both of which, to the author's knowledge, were the highest power for published indium phosphide (InP)-based RTD oscillators operating in the W-band frequency range