#WishIknew: What are accelerometers made of?


When you have a question about process automation that needs a short answer, let us know with #WishIknew and @Visaya! We’ll reply with a #WishIknew post. It’ll give a quick explanation, then some related articles, videos, or reviews if you want to know more.

I wish I knew what accelerometers are made of!

Eee, this one could get a post all its own! But we have to keep it short for a #WishIknew. (Let us know if you want a full post.) Okay, let’s just pick one, the piezoelectric type.

You start with a semiconductor layer and stick it to a wafer – not the vanilla kind, the electronic kind. And now I want a cookie. Anyway, stick the layer to the wafer with a thick oxide,then pattern it to the accelerometer’s geometry. The semiconductor layer has holes, so the stuff under it needs matching holes.

Next, you carve a cavity in the oxide to contain a small mass. This mass has a couple of arms holding it up. Directly below the geometry, another cavity lets the mass in the first cavity move at right angles to the surface.

Okay, now we have a couple of transducers stuck on either end of a hollow tube. You polarize these transducers and set them to a specific capacitance. Then you partially fill the tube with a heavy liquid and excite the accelerometer. Exciting, isn’t it?

While you have the device excited, you need to measure the total output voltage. You may also need to tweak the volume of the liquid until you get the voltage you want. Finally you check the outputs of each transducers, find the voltage difference, and note the dominant transducer.

Did you get all that? Did I miss anything? Let me know!

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