High-resolution micro-magnetometer based on novel nano-junction oxide SQUIDs

This Phase I SBIR project will evaluate the feasibility of developing ultra low noise micron scale magnetometers based on the novel high transition temperature high Tc superconducting quantum interference devices SQUIDs the UCSD group has developed During the past few years a group at J lich Germany has succeeded in reducing the noise of a magnetometer based on a high Tc SQUID operating at Kelvin by about an order of magnitude to a level fT Hz comparable to the noise level of low Tc SQUIDs operating at liquid helium temperature K Although this is an important breakthrough the SQUID junction is very difficult to fabricate with a very low yield greatly limiting the availability of a large number of such SQUIDs for magnetometry Recently one of us Cybart at UCSD has shown that high Tc SQUIDs can be constructed with a junction noise matching that of the J lich SQUIDs using a radically different approach that greatly eases the fabrication process with a very high yield In this approach very small nanometer scale Josephson junctions are made in a YBCO high Tc superconductor with a focused helium ion beam with a precision of nm It enables mass fabrication of highly reliable low noise SQUIDs with a very high yield unlike any other previous approaches This nano junction oxide technology is useful in numerous areas of science and technology In Phase I of this project we will focus on developing the best design for ultra low noise micron scale magnetometers with applications in biology and neuroscience We will evaluate three magnetometer designs new washer coupled SQUID sensor Transformer injected SQUID sensor and Serially connected direct injection SQUID sensor Design uses an improved type of washer to collect the magnetic flux more effectively than our previous versions Design uses inductive coupling to concentrate the magnetic flux efficiently into the SQUID Design uses a large number of direct injection SQUIDs connected in series to increase the signal to noise ratio SNR of the sensor The focused helium beam technique will provide the precision needed for producing nano junction oxide SQUIDs and the other components connected to the Josephson junctions We will select the best design in terms of SQUID junction noise and slope of the voltage vs magnetic flux transfer function The sensitivity of an array of such sensors will be evaluated in a SQUID microscope that Tristan and Moment have previously built The design of the microscope enables us to adjust the operating temperature of the sensors between K and K Since the sensitivity of the high Tc SQUIDs depends on temperature its operating temperature will be varied to determine the best temperature This will provide the benchmark for going to the Phase II portion of this project to develop a magnetic microscope As the deliverable we will provide the best sensor design and its noise and sensitivity characteristics Narrative We will use a focused helium ion beam technology with nanometer resolution to fabricate three types of micron scale magnetometers in a high Tc oxide YBCO superconductor and experimentally select the design with the best magnetic field noise and sensitivity This Phase I testing will serve as the foundation for developing micro magnetometers for diverse applications in science including applications in neuroscience Once the best magnetometer design is determined we will develop a magnetic microscope with ultra high sensitivity and bandwidth during Phase II taking advantage of this new technology in neuroscience