editor's blog
Subscribe Now

Yet Another Way to Sense Magnetic Fields

Seems we have so many ways of detecting the magnetic fields around us! And now we have yet another.

Some years back we covered a small company called Crocus, a maker of MRAM technology. Their MRAM cell consisted of two magnetic layers: a “pinned” reference layer and a programmable layer. The idea was that, when the layers are aligned, the tunneling resistance through the combined layers and a thin layer of dielectric between them was different from when they were anti-aligned.

So by programming the top layer to be either aligned or anti-aligned, you could store data and read it back by measuring the tunneling current through the cell (hence the resistance).

The “pinning” comes by placing the magnetic layer just over a material that, in bulk, wasn’t magnetic, but at a nano-structural level, consisted of alternating layers of atoms magnetized in opposite directions. Because they were alternating, they neutralized each other overall, but for something sitting right atop the material, it felt only the top layer, so it seemed to be magnetized. And this stabilized the magnetic layer to align and stay there.

The free layer also had a pinning material like this that stabilized it during use, but the write circuitry was able to overcome that (with the help of some heat) to allow that layer to be flipped.

So that was how it formed a memory.

Then they figured out how to do logic with it: by making both layers programmable, they could effectively implement XOR logic. Sounded interesting, although I haven’t seen any actual product come of this idea.

Now they’ve morphed things yet one more time. In this case, they’ve removed the pinning layer from the top and they’ve taken away all the write circuitry (a huge savings). Now that top layer can simply spin away according to whichever magnetic fields it happens to be in. Its direction can still be measured by checking the tunneling current.

These three configurations are illustrated in the following conceptual, super-simplified figure.

Crocus_cell_dwg.png 

In the memory application, the current had two values – one for 1, the other for 0. In the magnetic field detector implementation, the current can take on a continuous range of values between the 1 and 0 values.

The benefits they tout include low-power sensing, linearity good enough not to need compensation, and the ability to operate as high as 250 °C.

This actually isn’t a new thing – they’ve apparently been quietly selling this stuff for a couple years, and just completed a new round of funding. But it seemed worth talking about as an example of technology being repurposed for new markets.

You can find out more on their site

Leave a Reply

featured blogs
Jan 17, 2022
Today's interview features Dajana Danilovic, an application engineer based near Munich, Germany. In this video, Dajana shares about her pathway to becoming an engineer, as well as the importance of... [[ Click on the title to access the full blog on the Cadence Community sit...
Jan 13, 2022
See what's behind the boom in AI applications and explore the advanced AI chip design tools and strategies enabling AI SoCs for HPC, healthcare, and more. The post The Ins and Outs of AI Chip Design appeared first on From Silicon To Software....
Jan 12, 2022
In addition to sporting a powerful processor and supporting Bluetooth wireless communications, Seeed's XIAO BLE Sense also boasts a microphone and a 6DOF IMU....

featured video

Synopsys & Samtec: Successful 112G PAM-4 System Interoperability

Sponsored by Synopsys

This Supercomputing Conference demo shows a seamless interoperability between Synopsys' DesignWare 112G Ethernet PHY IP and Samtec's NovaRay IO and cable assembly. The demo shows excellent performance, BER at 1e-08 and total insertion loss of 37dB. Synopsys and Samtec are enabling the industry with a complete 112G PAM-4 system, which is essential for high-performance computing.

Click here for more information about DesignWare Ethernet IP Solutions

featured paper

How to Fast-Charge Your Supercapacitor

Sponsored by Analog Devices

Supercapacitors (or ultracapacitors) are suited for short charge and discharge cycles. They require high currents for fast charge as well as a high voltage with a high number in series as shown in two usage cases: an automatic pallet shuttle and a fail-safe backup system. In these and many other cases, the fast charge is provided by a flexible, high-efficiency, high-voltage, and high-current charger based on a synchronous, step-down, supercapacitor charger controller.

Click to read more

featured chalk talk

Silicon Lifecycle Management (SLM)

Sponsored by Synopsys

Wouldn’t it be great if we could keep on analyzing our IC designs once they are in the field? After all, simulation and lab measurements can never tell the whole story of how devices will behave in real-world use. In this episode of Chalk Talk, Amelia Dalton chats with Randy Fish of Synopsys about gaining better insight into IC designs through the use of embedded monitors and sensors, and how we can enable a range of new optimizations throughout the lifecycle of our designs.

Click here for more information about Silicon Lifecycle Management Platform