editor's blog
Subscribe Now

A Move Towards a Magnetic MEMS Relay

Relays might seem amongst the most mundane of components, and yet even they are getting a miniaturization upgrade with the help of MEMS technology. Of course, you might reasonably ask, since reed relays are already mechanical devices, why not simply make them smaller? And there’s a very specific reason: The reed is encased in glass, and that glass is fused onto the leads, which have rhodium or ruthenium or iridium on the contacts. That fusing process is hot, and if you shrink the relay too much, that heat gets too near the contacts and the metal melts.

So you’re stuck with something bigger than you might want. Which suggests a MEMS alternative. And the obvious first approach would be electrostatic. Which, being the obvious first approach, has been tried. And, according to Coto, it was beset with issues, most notably stiction. In case you haven’t run into stiction, it’s a situation where, in this case, some sort of cantilever or see-saw structure gets stuck in a closed position due to low-level forces at the tip. An always-closed relay isn’t of much value. Evidently, a couple of companies have already gone out of business trying this.

So Coto is working its way towards a magnetically-actuated relay. Only they’re taking it one step at a time, starting with the switch only, which they call their Redrock switch. It’s a magnetically-actuated switch, so you essentially supply the magnet separately.

Where, you might wonder, might this be useful? They listed a few examples where you would not want an integrated actuator:

  • A brake fluid level sensor in a car: you float the magnet in the fluid and put several sensors along the fluid reservoir column so that, as the magnet floats down, you can get advance warning that the level is dropping. With a non-MEMS approach, the sensors in this “ladder” need to be far apart so they respond independently – meaning you need a deeper reservoir. By using MEMS, the whole assembly can be made smaller.
  • A switch inside some assembly where gases or liquids are flowing; you can actuate the switch from outside with a magnet.
  • A “capsule endoscope” is a small diagnostic “pill” that tours your insides, but it might be 18 months or so between the time it’s shipped from the factory until it’s actually used – you don’t want the battery to die during that time. So a magnet can be put in the enclosing box, keeping a switch open. Only when the box is opened and the magnet is no longer present will the unit turn on.

The unit is a surface-mount device formed by etching a ceramic substrate using X-ray lithography, seeding with a titanium seed layer, and then plating with nickel/iron. On a separate wafer, copper walls are grown; this “housing” is placed over the switch in a vacuum with a gold/gold seal that results in a perfectly hermetic enclosure.

The actual switch consists of two metal blocks and a cantilever that is attached to one and lies over the other. The two blocks are of opposite magnetic polarity and concentrate the magnetic flux in the gap between the cantilever tip and the block below it, bringing the cantilever tip into contact when actuated. The result is directional: you have to approach from the right angle with the magnet for it to work (or, at the very least, sensitivity is greatest from certain angles).

Why might directionality help? Well, consider the case of an insulin pump where there was a switch in the electronics and a magnet in the disposable insulin reservoir. Apparently there was a case where a stray magnetic field from an electric drill caused insulin to be injected at the wrong time. So the directionality provides a measure of selectivity, helping to make sure that the switch isn’t necessarily moved from any old magnetic field.

The next step is to integrate a magnet into a full-on relay. But apparently this isn’t trivial: you have to print a big enough magnet. They’re looking at proof-of-concept for this by the end of the year, with production a couple years out (assuming it works, of course).

You can find out more on their website.

Leave a Reply

featured blogs
Nov 15, 2019
As we seek to go faster and faster in our systems, heat grows as does the noise from the cooling fans. It is because of this heat and noise, many companies are investigating or switching to submersible cooling (liquid immersion cooling) options. Over the last few years, subme...
Nov 15, 2019
Electronic design is ever-changing to adapt with demand. The industry is currently shifting to incorporate more rigid-flex circuits as the preferred interconnect technology for items that would otherwise be off-board, or require a smaller form factor. Industries like IoT, wea...
Nov 15, 2019
"Ey up" is a cheery multi-purpose greeting that basically means "Hello" and "Hi there" and "How are you?" and "How's things?" all rolled into one....
Nov 15, 2019
[From the last episode: we looked at how intellectual property helps designers reuse circuits.] Last week we saw that, instead of creating a new CPU, most chip designers will buy a CPU design '€“ like a blueprint of the CPU '€“ and then use that in a chip that they'€™re...
Nov 15, 2019
Last week , I visited the Cadathlon@ICCAD event at the 2019 International Conference on Computer Aided Design . It was my first CADathlon and I was quite intrigued , since the organizers webpage... [[ Click on the title to access the full blog on the Cadence Community site. ...