Apr 29, 2013

Directing DSA

posted by Bryon Moyer

DSA – Directed Self Assembly – is 2/3 natural and 1/3 artificial. The “self assembly” part (two of the three words, to make the scoring clear) is a natural phenomenon governing how mutually immiscible materials will resolve their differences in staking out territory.

It’s the “directed” part that makes it a useful tool. We’ve looked before at some basics for controlling how to create lines, for instance. But actual circuit patterns will be more complex, and several SPIE Litho presentations focused on different ways of affecting the outcome of the self-assembly process.

MIT’s Professor Ross, for example, talked about using posts to direct the outcome. To help bias what goes where, they would “functionalize” the posts by “brushing” them with one or the other of the block copolymers, establishing an affinity for one and a “don’t go there” for the other. The big question then becomes, where to place these posts?

Given a set of posts, there are some formidable-sounding techniques for calculating what the impact will be and how the block copolymers will lay out: Self-Consistent Field Theory (or Mean Field Theory) and Dissipative Particle Dynamics, both of which deal with reducing complex fields to particles to simplify the modeling.

But the real question is, if you want a given pattern, how do you go backwards to figure out the positioning and functionalizing of the posts? Apparently, the results aren’t going to be intuitive. For example, if you want to create a T-shaped structure, you need to omit a post from the center. Go figure.

So at this point, it appears there isn’t a deterministic path to calculate where the posts should be; they used a Monte Carlo approach to back into the solution. Which may end up being satisfactory for a while or for small circuits, but for an entire large-scale SoC-scale design, I would assume (and, to be clear, this is conjecture on my part) that some separability would apply such that you could partition the entire thing into smaller solvable regions, but you’d need to be able to deal with the region boundaries to account for their interactions.

The bottom line here is that, as DSA develops into a viable production process, there will be new challenges for EDA folks to help turn circuits into DSA guiding patterns.

If you have the SPIE Litho proceedings, you can find more of the MIT presentation in paper 8680-1.

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Apr 25, 2013

ThreadX Gets Safety Certification

posted by Jim Turley

San Diego-based Express Logic just received IEC 61508 and IEC 62304 certification for its ThreadX operating system. These two standards cover the "functional safety of electrical, electronic, and programmable electronic safety-related systems." The nice part is, the certification is for bone-standard ThreadX; there is no special "safety-certified" version of the RTOS. Express Logic says it won't even charge more, now that it's certified.

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Apr 25, 2013

An Acid Trip

posted by Bryon Moyer

When you think of a high-acid environment, what do you think of? That can of soda? Lemon juice? Your stomach? Battery acid? Well, to review, neutral pH is 7. Your stomach will have a pH of 1.5 to 3.5, presumably depending on how much soda or lemon juice or Thai-spicy tom yum gai you just had. Coca-Cola Classic is around 2.5. Lemon juice: 2.0. Battery acid: 1. It’s hard to imagine electronics functioning in a bath of any of those tongue ticklers.

But there’s an environment that’s even worse. One within which an electronic component must operate. And you might never expect it. In fact, many folks didn’t expect it. It can have a pH of 0.5 or less. It’s car exhaust. And it’s not all gaseous. It can make mincemeat of your chip in a couple months. Who knew…

Certainly not the many folks trying to build pressure sensors for that environment. Sensata has just announced a relative pressure sensor for this application – and even they didn’t realize this when they started.

There are actually a couple things that they’ve done that others have had trouble with. One is simply getting this to work in such an environment; the other is doing it with a single element – other folks apparently use two pressure sensing elements (and measure the difference between them).

The Sensata approach is a two-port sensor, with one sealed port on each side of a piezo-resistive element. Each port exposes the pressure of one of the environments to be compared, so the element is, by definition, providing the relative pressure difference. The element, which, of course, has a backside etch so the membrane is accessible to front and back, is mounted in a ceramic carrier.

Then there’s the bit about the acid. There are lots of things that can be attacked, most of which are on the logic that makes sense out of the raw pressure measurement. In other words, CMOS. Much of it can be protected by suitable passivation, but you still have to get the signals in and out, and that takes metal. And, no matter how much you protect everything else, that metal isn’t going to like lots of acid.

So rather than having that logic on the same chip as the element or an ASIC collocated with the element, they put the ASIC away from the element, outside of the corrosive environment. That minimizes the part that has to be robust and protects the delicate bits.

You can find more in their release

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