DC current induced magnetization reversal and magnetization oscillation was observed in 500 nm large size Co 90 Fe 10 /Cu/Ni 80 Fe 20 pillars. A perpendicular external field enhanced the coercive field separation between the reference layer (Co 90 Fe 10 ) and free layer (Ni 80 Fe 20 ) in the pseudo spin valve, allowing a large window of external magnetic field for exploring the free-layer reversal. The magnetization precession was manifested in terms of the multiple peaks on the differential resistance curves. Depending on the bias current and applied field, the regions of magnetic switching and magnetization precession on a dynamical stability diagram has been discussed in details. Micromagnetic simulations are shown to be in good agreement with experimental results and provide insight for synchronization of inhomogenieties in large sized device. The ability to manipulate spin-dynamics on large size devices could prove useful for increasing the output power of the spin-transfer nano-oscillators (STNOs).Spin-polarized currents can be harnessed to manipulate magnetization and excite oscillation via the spin transfer torque (STT) effect, and are utilized in the application of MRAM [1,2] and spin-transfer nano-oscillators (STNOs) [3,4] . STNOs have the advantages that their frequencies are highly tunable by current and magnetic field over a range from 2 a few GHz to 40 GHz. [3,5] Furthermore, the nanometer sized devices are among the smallest microwave oscillators yet developed [6] and their compatibility with standard silicon processing opens the possibility for on-chip applications. [7,8] However, the bottlenecks for the widespread application of STNOs lies in the enhancement of the output power above the current limit of ~ 0.5µW. [9] It has been suggested that two nano-contact STNOs in close proximity could mutually phase-lock and increase the output power; however phase-locking of more than two STNOs remains technologically challenge. [10][11][12][13][14] Instead of putting an array of STNOs nano-magnets together, we propose to make use of larger sized magnets in the hope that synchronization of multiple domains could lead to higher output power, and firstly we demonstrated that spin-transfer torque can be used to efficiently induce magnetization switching and oscillation in 500 nm large size devices. For large size device, our simulation results have shown that the non-uniform oscillations tend to synchronize with each other and generate coherent oscillation. In addition, large sized nano-magnets can be fabricated more cost-effectively through photolithography rather than using electron beam lithography. 3The magnetic multilayer was synthesized by sputtering in a Biased Target Ion Beam Deposition system (BTIBD). The deposition details can be found elsewhere. [15] The complete structure of the multilayer is SiO 2 (substrate)/20nm Ru/2.2nm Co 90 Fe 10 (reference layer)/5nm Cu/6.5nm Ni 80 Fe 20 (free layer)/5nm Ru/Ti 5nm/Au 25nm. A magnetoresistance (MR) of ~1.2% was measured in the pseudo spin-valve continuous f...

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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.

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First reported by our research group in 2007, AlN tunnel barriers grown by ICP nitridation of thin Al overlayers offer a promising alternative to Al oxide barriers for high current density SIS junctions used in quantum limited THz heterodyne receivers [1]. However, the growth rate of AlN is heavily dependent on ICP operating conditions and as new uncharacterized nitridation processes are investigated, knowledge of the barrier thickness is integral to realizing SIS junctions of desired current density, which is exponentially dependent upon barrier thickness. An in situ method for real time monitoring of ICP AlN growth on thin Al overlayers through the use of spectroscopic ellipsometry and a correlation of the determined AlN thickness to the normal resistance area product (RNA) of the resulting trilayer is reported.

High quality, low-leakage superconductorinsulatorsuperconductor (SIS) junctions with Nb electrodes and aluminum oxide barriers are widely reported in the literature, and have become integral in the design and fabrication of various superconducting circuits. However, as current densities are increased, aluminum oxide based tunnel barriers show excess leakage currents due to defects and pinholes in the barrier layer. First reported by our group in 2007, AlN tunnel barriers grown via inductively coupled plasma (ICP) nitridation of Al overlayers are a promising alternative, producing low-leakage Nb/Al-AlN/Nb SIS junctions, with current densities in excess of 30 kA/cm 2 . A correlation between junction quality and plasma dissociation has been reported for Nb/Al-AlN/Nb junctions produced via an electron cyclotron resonance (ECR) plasma. In this work, a quantitative measure of the relative dissociation (RD) of an ICP is determined through the use of a commercially available Ocean Optics USB4000 Optical Spectrometer. The effects of various ICP parameters on the RD, and a correlation between the RD and quality of the resulting Nb/Al-AlN/Nb junctions are reported.Index Terms-Aluminum nitride, inductively coupled plasma, superconductorinsulatorsuperconductor (SIS), spectroscopy. 1051-8223

Increasing the operating frequency of SIS receivers requires a shift from Nb Al AlO X Nb junctions to new material systems. Two major limiting factors of higher frequency operation are the increase in subgap leakage that occurs in AlO X barriers as current densities approach and exceed 10 kA cm 2 and the increased loss in Nb electrodes above 700 GHz. A promising alternative structure is the hybrid Nb/Al-AlN/NbTiN junction. Realization of these devices has been difficult due to the challenge of fabricating devices with repeatable current densities and electrical characteristics.We present on the fabrication and dc testing of Nb/AlN/NbTiN junctions. The AlN barrier is formed using our inductively coupled plasma (ICP) technique which allows for independent control of both ion energy and current density. This improved control enables the repeatable synthesis of high quality and high Jc barriers. Nb and NbTiN electrodes are deposited by unbalanced dc magnetron. A new fabrication process was developed to enable fabrication of junctions with area as small as 0.28 m 2 . The relationship between barrier thickness and plasma conditions is determined by in-situ discrete ellipsometry. Ellipsometry results were verified by comparison with measured current-voltage characteristics. I(V) curves for a range of junction sizes are presented. Plans for in-situ Faraday monitoring of the energy and current density of the ICP nitridation plasma will also be discussed.Index Terms-Aluminum nitride, inductively couple plasma, niobium titanium nitride, SIS.

High quality Nb-based superconductor-insulatorsuperconductor (SIS) junctions with Al oxide (AlOx) tunnel barriers grown from Al overlayers are widely reported in the literature. However, the thin barriers required for high critical current density (Jc) junctions exhibit defects that result in significant subgap leakage current that is detrimental for many applications. High quality, high-Jc junctions can be realized with AlNx barriers, but control of Jc is more difficult than with AlOx. It is therefore of interest to study the growth of thin AlOx barriers with the ultimate goal of achieving high quality, high-Jc AlOx junctions. In this work, 100% O2 and 2% O2 in Ar gas mixtures are used both statically and dynamically to grow AlOx tunnel barriers over a large range of oxygen exposures. In situ ellipsometry is used for the first time to extensively measure AlOx tunnel barrier growth in real time, revealing a number of unexpected patterns. Finally, a set of test junction wafers was fabricated that exhibited the well-known dependence of Jc on oxygen exposure (E) in order to further validate the experimental setup.