Ultra-Sensitive Magnetic Sensors Don't Need Ultra Cold

New SQUID arrays take advantage of strength in numbers

2 min read
Ultra-Sensitive Magnetic Sensors Don't Need Ultra Cold
This image shows a section of a 484-series SQUID array. Each SQUID consists of two Josephson junctions connected in parallel. The Josephson junctions (represented as red crosses) can be seen as 3-micron-wide narrow bridges crossing the bicrystal boundary shown with a dotted line.
Illustration: Boris Chesca / Loughborough University

Newly developed magnetic sensors not only perform better than most standard commercial devices, but also can operate at temperatures well above absolute zero, say UK researchers.

Superconducting quantum interference devices, or SQUIDs, can detect minute magnetic fields, making them useful for applications such as analyzing brain activity, medical imaging, and oil prospecting. SQUIDs work by converting magnetic flux—a measure of magnetic intensity—into a voltage.

The most sensitive commercial magnetic sensors are single SQUIDs that need to be kept at 4.2 Kelvin. Such incredibly cold temperatures, within a hair’s breadth of absolute zero, require expensive and difficult to handle liquid helium.

Now physicists at Loughborough University and Nottingham University, both in the United Kingdom, have developed a multi-SQUID magnetic sensor that can operate at 77 K, the boiling temperature of liquid nitrogen, a much cheaper refrigerant. And this array of squids they created outperforms most standard 4.2 K single SQUID magnetometersThey detailed their findings in the 20 October online edition of the journal Applied Physics Letters.

Their device incorporates anywhere from 480 to 770 SQUIDS. Engineers were aware that large arrays outperform a single low-temperature SQUID because with greater numbers comes increased sensitivity and  less noise.

But these SQUID arrays work only if all the SQUIDs experience the same magnetic flux—a state known as flux coherency—and the interactions between individual SQUIDs are minimized. These are both difficult requirements that limited previous arrays to roughly 30 SQUIDs.

This recent advance was accomplished using flux focusers, which are large patches of superconductor that can improve flux coherency and reduce interactions between SQUIDs. Previous SQUID arrays either did not have flux focusers or had ones so large that they left little room for additional SQUIDs to be integrated together on a single chip. The new design uses long, narrow flux focusers to string together an arbitrarily long series of SQUIDs.

The scientists are now working on optimizing the shape and design of their SQUID arrays to maximize their sensitivity. 

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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