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.