Matthias Schmelz

Sub-micrometer-sized, cross-type Nb―AlOx―Nb tunnel junctions with low parasitic capacitance

We report on a technology for the fabrication of sub-micrometer sized cross-type Josephson tunnel junctions in niobium technology. We present the fabrication scheme and properties of cross-type junctions with linear dimensions from 10 down to 0.6??m. Sidewall passivation of the junctions is achieved by anodization as well as by planarizing the junctions with SiO in a self-aligned deposition step. The measured ratio of the sub-gap resistance to the normal resistance is about 35. Because of their low sub-gap current and low parasitic capacitance such junctions are well suited for applications like high resolution SQUIDs.

Low temperature SQUID magnetometer systems for geophysical exploration with transient electromagnetics

Geophysical exploration is getting more and more difficult—many of the easily explorable ore-bodies have been discovered and are already being exploited. Finding new mines requires new technologies and tools. Transient electromagnetics (TEM) is widely used in mineral exploration, but conventional sensors (especially induction coils) cannot fulfil the needs anymore: deep targets, very conductive targets or targets under conductive overburden are more easily (or sometimes only) detected using SQUIDs. In this paper we will focus on low temperature SQUID magnetometers. As the systems are applied worldwide it is necessary to strengthen them for all conceivable application scenarios. Here, we report on the latest development of these systems which are now routinely used in South Africa, Australia, Finland and Canada. This paper highlights the main features of the system and describes one example from mineral exploration.

Investigation of all niobium nano-SQUIDs based on sub-micrometer cross-type Josephson junctions

We report on the development of highly sensitive SQUIDs featuring sub-micrometer loop dimensions. The integration of high quality and low capacitance SIS Nb/AlOx/Nb cross-type Josephson tunnel junctions results in white flux noise levels as low as 66 n

Noise characterization of highly sensitive SQUID magnetometer systems in unshielded environments

\Phi_0

SQUIDs based on submicrometer-sized Josephson tunnel junctions fabricated in a cross-type technology

/Hz

SQUID-based setup for the absolute measurement of the Earth?s magnetic field

^{ 1/2}

Nearly quantum limited nanoSQUIDs based on cross-type Nb/AlO x /Nb junctions

, well below state-of-the-art values of their Nb-based counterparts based on constriction type junctions. Estimation of the spin sensitivity of the best SQUIDs yield

Detection of Weak Microwave Fields with an Underdamped Josephson Junction

S_\mu^{ 1/2} < 7 \mu_B

Bi-SQUIDs with submicron cross-type Josephson tunnel junctions

/Hz

Planar SQUID magnetometer integrated with bootstrap circuitry under different bias modes

^{ 1/2}