UC Santa Barbara

Microwave Kinetic Inductance Detectors (MKIDs) are a superconducting detector technology capable of measuring photon arrival times to the microsecond level with moderate energy resolution. MKIDs are essentially superconducting microresonators, and when a photon is incident on the inductor portion of the microresonator, the inductance temporarily increases and the resonant frequency decreases. An array of MKIDs can be naturally multiplexed and read out by assigning each detector a unique resonant frequency during fabrication and coupling the detectors to a single transmission line. A frequency domain multiplexing scheme can then be used to pass a microwave frequency comb through the transmission line to probe the microresonators and listen for photon events. In order to meet the demands of the next generation of astronomical instrumentation, MKIDs need improvements in three main areas: pixel yield, energy resolution, and quantum efficiency. I have investigated new fabrication techniques and materials systems to address these issues. Most notably, I have fabricated MKIDs with platinum silicide as the superconducting layer and have measured especially high resonator internal quality factors (>10^6). Platinum silicide films can also be made much more uniformly than the traditional sub-stoichiometric titanium nitride films used in the field, increasing pixel yield. In addition, platinum silicide intrinsically has a higher absorption rate for optical photons than titanium nitride. These platinum silicide detectors are used in two new MKID planet imaging instruments, the Dark-speckle Near-IR Energy-resolved Superconducting Spectrophotometer (DARKNESS) and the MKID Exoplanet Camera (MEC). Optical MKIDs have already been demonstrated on sky with the first generation MKID instrument, the Array Camera for Optical to Near-IR Spectrophotometry (ARCONS). I have used ARCONS to primarily observe compact objects, such as AM CVn systems and detached white dwarfs. In particular, I used ARCONS to observe orbital expansion in the eclipsing binary system SDSS J0926+3624, with a period rate of change of 9.68 microseconds/year.

I open my thesis with an general introduction to the field of low temperature detectors and describe the role that MKIDs have within the field. In Chapter 2, I provide a detailed description of the detection principles behind MKIDs and define important superconducting resonator parameters.

In Chapter 3, I move on to describe some of the issues that were limiting the performance of MKIDs. I examine some of the early fabrication techniques and material systems utilized to try to mitigate these issues. In Chapter 4, I describe the platinum silicide material system, which proved to be the most important recent development for advancing the detectors described in this work. The early PtSi work was done using simple one-layer test masks, but the material system was later adapted to the full-multilayer fabrication process. The fabrication of large-format MKID arrays using PtSi for the DARKNESS and MEC arrays is described in detail in Chapter 5.

I conclude my thesis with an overview of some of the astronomical applications of MKIDs. More specifically, I describe my work with compact binary systems that was done with ARCONS. Finally, I explain exciting new MKID applications that are only recently becoming possible as the technology continues to advance.