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
Sep 25, 2020
What do you think about earphone-style electroencephalography sensors that would allow your boss to monitor your brainwaves and collect your brain data while you are at work?...
Sep 25, 2020
Weird weather is one the things making 2020 memorable. As I look my home office window (WFH – yet another 2020 “thing”!), it feels like mid-summer in late September. In some places like Key West or Palm Springs, that is normal. In Pennsylvania, it is not. My...
Sep 25, 2020
[From the last episode: We looked at different ways of accessing a single bit in a memory, including the use of multiplexors.] Today we'€™re going to look more specifically at memory cells '€“ these things we'€™ve been calling bit cells. We mentioned that there are many...
Sep 25, 2020
Normally, in May, I'd have been off to Unterschleißheim, a suburb of Munich where historically we've held what used to be called CDNLive EMEA. We renamed this CadenceLIVE Europe and... [[ Click on the title to access the full blog on the Cadence Community site...

Featured Video

Texas Instruments: Pushing Power Further

Sponsored by Texas Instruments

Power is all around us. Every connection, every invention begins with power. Watch this short video to see how we are pushing the limits of power management.

Explore our power density portfolio

Featured Paper

Helping physicians achieve faster, more accurate patient diagnoses with molecular test technology

Sponsored by Texas Instruments

Point-of-care molecular diagnostics (PoC) help physicians achieve faster, more accurate patient diagnoses and treatment decisions. This article breaks down how molecular test technology works and the building blocks for a PoC molecular diagnostics analyzer sensor front end system.

Read the Article

Featured Chalk Talk

LPC5500 MCU Series

Sponsored by Mouser Electronics and NXP

Security is key in today’s edge designs, but where to start with designing-in security? Ad-hoc security strategies are recipes for disaster. In this episode of Chalk Talk, Amelia Dalton chats with Brendon Slade of NXP about the powerful new LPC5500 series of MCUs from NXP that have great performance and security designed in from the ground up.

Click here for more information about NXP Semiconductors LPC5500 Series Arm® Cortex®-M33 Microcontrollers