Publications

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

We have developed an ambient temperature, SiO₂/Si wafer - scale process for Josephson junctions based on Nb electrodes and Ta x N barriers with tunable electronic properties. The films are fabricated by magnetron sputtering. The electronic properties of the Ta_xN barriers are controlled by adjusting the nitrogen flow during sputtering. This technology offers a scalable alternative to the more traditional junctions based on AlO_x barriers for low - power, high - performance computing.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

This work reports the utilization of a recently developed film, ScAlN, as a silicon etch mask offering significant improvements in high etch selectivity to silicon. Utilization of ScAlN as a fluorine chemistry based deep reactive ion etch mask demonstrated etch selectivity at 23 550:1, four times better than AlN, 11 times better than Al2O3, and 148 times better than silicon dioxide with significantly less resputtering at high bias voltage than either Al2O3 or AlN. Ellipsometry film thickness measurements show less than 0.3 nm/min mask erosion rates for ScAlN. Micromasking of resputtered Al for Al2O3, AlN, and ScAlN etch masks is also reported here, utilizing cross-sectional scanning electron microscope and confocal microscope roughness measurements. With lower etch bias, the reduced etch rate can be optimized to achieve a trench bottom surface roughness that is comparable to SiO2 etch masks. Etch mask selectivity enabled by ScAlN is likely to make significant improvements in microelectromechanical systems, wafer level packaging, and plasma dicing of silicon.

Abstract not provided.

Abstract not provided.

With the advent of the internet-of-things, sensors that are constantly alert yet consuming near-zero power are desired. Remote sensing applications where sensor replacement is costly or hazardous would also benefit. Piezoelectric micro-electro-mechanical systems (MEMS) convert mechanical or acoustic energy into electrical signals while consuming zero power. When coupled with low-power complementary metal-oxide-semiconductor (CMOS) circuits, a near-zero power sensing system is formed. This work describes piezoelectric MEMS microphones based on aluminum nitride (AlN). The microphones operate as passive acoustic filters by placing their resonant response within bandwidths of interest. Devices are demonstrated with operational frequencies from 430 Hz to greater than 10 kHz with quality factors as large as 3,000 and open-circuit voltages exceeding 600 mV/Pa.

Abstract not provided.

Niobium and niobium nitride thin films are transitioning from fundamental research toward wafer scale manufacturing with technology drivers that include superconducting circuits and electronics, optical single photon detectors, logic, and memory. Successful microfabrication requires precise control over the properties of sputtered superconducting films, including oxidation. Previous work has demonstrated the mechanism in oxidation of Nb and how film structure could have deleterious effects upon the superconducting properties. This study provides an examination of atmospheric oxidation of NbN films. By examination of the room temperature sheet resistance of NbN bulk oxidation was identified and confirmed by secondary ion mass spectrometry. Meissner magnetic measurements confirmed the bulk oxidation not observed with simple cryogenic resistivity measurements.

Vacuum gap λ/2 microwave resonators are demonstrated as a route toward higher integration in superconducting qubit circuits. The resonators are fabricated from pieces on two silicon chips bonded together with an In-Sb bond. Measurements of the devices yield resonant frequencies in good agreement with simulations. Creating low loss circuits in this geometry is also discussed.

Properties of NbN and TaxN thin films grown at ambient temperatures on SiO2/Si substrates by reactive-pulsed laser deposition and reactive magnetron sputtering (MS) as a function of N2 gas flow were investigated. Both techniques produced films with smooth surfaces, where the surface roughness did not depend on the N2 gas flow during growth. High crystalline quality, (111) oriented NbN films with Tc up to 11 K were produced by both techniques for N contents near 50%. The low temperature transport properties of the TaxN films depended upon both the N2 partial pressure used during growth and the film thickness. The root mean square surface roughness of TaxN films grown by MS increased as the film thickness decreased down to 10 nm.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Pyroelectric coefficients were measured for 20 nm thick crystalline hafnium zirconium oxide (Hf1-xZrxO2) thin films across a composition range of 0 ≤ x ≤ 1. Pyroelectric currents were collected near room temperature under zero applied bias and a sinusoidal oscillating temperature profile to separate the influence of non-pyroelectric currents. The pyroelectric coefficient was observed to correlate with zirconium content, increased orthorhombic/tetragonal phase content, and maximum polarization response. The largest measured absolute value was 48 μCm−2 K−1 for a composition with x = 0.64, while no pyroelectric response was measured for compositions which displayed no remanent polarization (x = 0, 0.91, and 1).

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

This study reports on selective isotropic dry etching of chemically vapor deposited (CVD) Ge thin film, release layers using a Shibaura chemical downstream etcher (CDE) with NF₃ and Ar based plasma chemistry. Relative etch rates between Ge, Si and SiN_x are described with etch rate reductions achieved by adjusting plasma chemistry with O₂. Formation of oxides reducing etch rates were measured for both Ge and Si, but nitrides or oxy-nitrides created using direct injection of NO into the process chamber were measured to increase Si and SiN_x etch rates while retarding Ge etching.

Inductive coupling and matching networks are used to increase the bandwidth of filters realized with aluminum nitride contour-mode resonators. Filter bandwidth has been doubled using a wirebonded combination of a wafer-level-packaged resonator chip and a high-Q integrated inductor chip. The three-pole filters have a center frequency near 500 MHz, an area of 9 mm × 9 mm, insertion loss of < 5 dB for a bandwidth of 0.4%, and a resonator unloaded Q of 1600.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

A method for patterning on vertical silicon surfaces in high aspect ratio silicon topography is presented. A Faraday cage is used to direct energetic reactive ions obliquely through a patterned suspended membrane positioned over the topography. The technique is capable of forming high-fidelity pattern (100 nm) features, adding an additional fabrication capability to standard top-down fabrication approaches.

Emerging nano-photonic and nano-opto-mechanical applications benefit from fabrication of complex three-dimensional structures. Creation of micrometer scale and sub-micrometer scale structures can be performed either additively, or subtractively. Additive techniques, where material is deposited, such as direct laser write, interferometric lithography, nano-origami and colloidal self-assembly have been used to create a wide array of complex sub-micrometer structures. Example of subtractive fabrication of three-dimensional structures, where material is removed, are less common.

Abstract not provided.

Superconducting qubits have made great strides in coherence time, gating, and algorithms. However, to achieve real scalability, more is required. We propose to study the problem of coupling and decoupling a transmon, a popular type of superconducting qubit, from its host resonator, which serves the dual role of a bus connecting qubits together and a readout channel. The transmon couples to its host resonator via its electric-dipole moment. We plan to use a trick of quantum mechanics to null the dipole moment and decouple the transmon. In doing so, we hope to study a variety of physics associated with multi-qubit operation, control, and readout.

Aluminum nitride (AlN) radio frequency (RF) MEMS filters utilize piezoelectric coupling for high-performance electrical filters with frequency diversity in a small form factor. Furthermore, the compatibility of AlN with CMOS fabrication makes AlN extremely attractive from a commercial standpoint. A technological hurdle has been the ability to package these suspended resonator devices at a wafer level with high yield. In this work, we describe wafer-level packaging (WLP) of AlN MEMS RF filters in an all silicon package with solder balls on nickel vanadium / gold (NiV/Au) bond pads that are subsequently ready for flip chip bonding. For this integration scheme, we utilize a 150 mm device wafer, fabricated in a CMOS foundry, and bond at the wafer level to a cavity silicon wafer, which hermetically encapsulates each device. The cavity wafer is then uniformly plasma etched back using a deep reactive ion etcher resulting in a 100 μm thick hermetic silicon lid encapsulating each die, balled with 250 μm 90/10 Pb/Sn solder balls and finally diced into individually packaged dies. Each die can be frequency-trimmed to an exact frequency by rapid temperature annealing the stress of the metallization layers of each resonator. The resulting technology yields a completely packaged wafer of 900 encapsulated die (14 mm2 by 800 μm thick) with multiple resonators and filters at various frequencies in each package.

Abstract not provided.