Powers of 10: 3-axis MEMS accelerometer

[Andy Resnick]

This is from a busted FitBit- one of my nieces, I think. They all know to give me their used electronics, 'cuz I love putting stuff into "The Dip" (a.k.a. Toon Acid).

This series was primarily done using epi-DIC and raised a whole new set of issues I have only partially resolved- mostly concerning camera white balance and exposure settings.

As usual, begin at 1:1 reproduction ratio:

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Then, for the sake of magnification continuity, a quick shot using the Zoom luminar:

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There are 3.5 objects here- from right to left, the MEMS device and it's cover, and the circuit that interfaces the MEMS device with the FitBit circuitry. The 0.5 object that looks like an old-timey razor blade is one of the accelerometer pieces that broke off.

Now I switch over to microscopy. Here's epi-DIC using a 4x epiplan POL:

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The three accelerometer axes are clear- the 2 smaller ones are "x" and "y" (in the plane of the device), while the larger one is "z", perpendicular to the device. The upper one (call it 'y') is broken- you may have spotted the broken piece laying off to the side on the luminar image- it somehow miraculously landed there!

Now moving to 16X epiplan POL:
The intact accelerometer:

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And the broken piece:

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The textural effect is something I can't really explain (yet). I don't think it's related to actual surface topography, as you'll see at higher magnifications. This texture is created by moving the epi-DIC prism very, very slightly off of 'extinction position'. The texture (to me) appears superficially similar to that of mica group minerals near extinction (for example, shown here: http://www.alexstrekeisen.it/immagini/d ... 020(1).jpg) but it's unclear why there should be a connection between these very dissimilar materials.

[Andy Resnick]

Proceeding to 40x epi-DIC pol:

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The texture is less prominent, and largely absent if I image at 40x epi-darkfield:

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And last is 80x epi-DIC:

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The silicon structure is nicely resolved, but the image is 'flat'. Partly this is due to poor camera exposure.

I can't go much beyond this because I am not able to perform immersion microscopy- all of the objectives I have been using are to be used without a coverslip as well. No touching! These devices are by far the most delicate things I have ever worked with, and are also the best example I know of "technology so advanced it appears as magic". I tried to convey the spatial structure of the accelerometers with the Mirau objective, here I placed the interference patter at the top and bottom surfaces:

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it's not great.... Like I said, this series introduced a whole new set of technical issues I have only partially resolved... I dunno... not my best work.

Oh well, enjoy!

[Sure Squintsalot]

That 80x epi DIC shot is really quite good! You gotta be getting close to theoretical max resolution for that lens/camera system.

[Andy Resnick]

That 80x epi DIC shot is really quite good! You gotta be getting close to theoretical max resolution for that lens/camera system.

Thanks- I took another pass with that lens, this time with improved camera control (auto white balance, manual otherwise) and got this much-improved image:

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It's clear that the texture is something real and different from surface contaminants (dust, etc)... and yeah, getting close to the diffraction limit