Integrated micromachined quantum barrier mixers for high harmonic number millimeter wave receivers

This thesis presents the results of my endeavours at Leeds on research into subharmonic mixing employing double barrier resonant tunneling device (Quantum Barrier Device) at microwave and millimeter wave frequencies and an enabling technology for future improvement of the Quantum Barrier mixer. The research commenced with an empirical study of the electrical characteristics of a typical Quantum Barrier Device, and a model was developed to accurately simulate the discontinuities in the current-voltage characteristic as well as the capacitance-voltage behavior in the dc and the frequency domain. With a detailed analytical model, a general theory of subharmonic mixing was derived to demonstrate, with experimental proof, factors which favor the use of a Quantum Barrier Device as a mixing device at microwave frequencies, and to reveal any shortcomings. Measurements of a mixer at microwave frequencies and a harmonic multiplier at millimeter wave frequencies were also carried out, and presented with suggestions for possible improvements on the existing Quantum Barrier Device structure. In addition, several novel polymer-based micromachining technologies were developed for integration of these high frequency devices in the future, and presented in this thesis with S-parameter measurements. Particular reference was given to a handful of membrane-based micromachining technologies that enable a planar membrane-based printed circuit to be fabricated on a 5 micron thick polymer membrane in the absence of any steps involving thermal oxidation and low pressure chemical vapor deposition (LPCVD). The relatively low-cost low-temperature process uses a photosensitive resin (SU-8) to form a self-supporting membrane to which active devices can be mounted. Measured losses of transmission lines in these technologies are typically no more than 0.5 dB/cm at W-band, and this performance is comparable to the existing GaAs (or Silicon) membrane technologies.