Investigation of Material Growth and Fabrication Processes for THz Frequency SIS Mixers

Abstract

Research and development of THz electronics seeks to comprehend and utilize one of the last uncharted regions of the electromagnetic spectrum. Sandwiched directly between the microwave and far-infrared regions, THz devices often involve a hybrid fusion of optical and small-scaled RF technologies, frequently requiring novel design, materials, and fabrication techniques. Despite the increased complexity, when compared to many well-established RF and optical technologies, THz receivers used in telescope imaging applications are of great importance to radio astronomers, with current large scale multinational radio telescope projects, such as the Atacama Large Millimeter/sub-millimeter Array (ALMA) in Chile designed to observe the universe from 31 to 950 GHz-the field of radio astronomy will be one of the immediate benefactors from the ongoing research of higher frequency THz detection.

In situ spectroscopic ellipsometry of SIS barrier formation

“…F While the oxidation of Al films is well researched and the room temperature growth is solely a function of oxygen pressure and exposure time, plasma nitridation is an inherently more complex process, with multiple nitrogen species available for AlN growth. Correlation between plasma conditions and the quality of Nb/Al-AlN/Nb junctions produced with an ECR plasma have been reported, and most recently a similar trend has been observed by our research group for AlN junctions grown via ICP [2][3][4]. As new ICP nitridation conditions are investigated during optimization of growth processes, we note the AlN growth rate is heavily dependent upon process parameters.…”

“…The resulting SE model, combined with the dispersions created as part of this work, allowed the analysis of both the AlN layer, which increases in thickness, and the underlying Al layer, which is consumed during ICP AlN growth. The specific details of the ellipsometric model are beyond the scope of this paper---the resulting dispersions, process flow for implementation in trilayer growth, and an error analysis of the full model are presented in full breadth elsewhere [4].…”

Optical Spectroscopic Analysis of ICP Nitridation for SIS Junctions With AlN Barriers

“…Our trilayer deposition system, discussed in detail elsewhere [1], [8], was equipped with an Ocean Optics USB4000 Spectrometer and a 1 inch diameter collimating lens to record optical emissions from a nitrogen ICP. A modified Copra DN-160 ICP source [9] was used to generate a plasma using 99.9999% purity N 2 gas after the system reached a base pressure less than 1.0e −7 Torr with a partial pressure of water less than 1.0e −8 Torr.…”

“…The resulting thicknesses, as determined by in-situ ellipsometry (discussed elsewhere [8], [13]), at 30 s nitridation time are plotted in Fig. 6 vs the RD of the ICP.…”

Optical Spectroscopic Study of AlN-Based SIS Devices Grown by Inductively Coupled Plasma

“…The main deposition chamber and oxidation chamber are highlighted in red and blue, respectively. determined for the UVA trilayer system that the tunnel barrier growth process is not influenced (as measurable by ellipsometer) by background oxidation of the Al overlayer once the base pressure of system and the partial pressure of H 2 O reach below 10E-8 and 3E-9 Torr, respectively [22]. The oxidation chamber is outfitted with an A. J.…”