MEMS Teardown And Macroscopic Models

There is a bit of a paradox when it comes to miniaturization. When electronics replaced mechanical devices, it was often the case that the electronic version was smaller. When transistors and, later, ICs, came around, things got smaller still. However, as things shrink to microscopic scales, transistors don’t work well, and you often find — full circle — mechanical devices. [Breaking Taps] has an investigation of a MEMS chip. MEMS is short for Micro Electromechanical Systems, which operate in a decidedly mechanical way. You can see the video, which has some gorgeous electron microscopy, below. The best part, though, is the 3D-printed macroscale mechanisms that let you see how the pieces work.

Decapsulating the MPU-6050 was challenging. We usually mill a cavity on the top of an IC and use fuming nitric on a hot plate (under a fume hood) to remove the remaining epoxy. However, the construction of these chips has two pieces of silicon sandwiched together, so you need to fully expose the die to split them apart, so our usual method might not work so well. Splitting them open, though, damaged parts of the chip, so the video shows a composite of several devices.

The parts inside are microscopically small. It took a week to trace everything out and make the 3D-printed macroscale mechanisms that help explain how each piece works. Seeing a model of the accelerometer that is large enough to handle in your hands is very helpful in understanding how they work. You can build your own but be warned: the clearances are very tight, so you need a well-calibrated printer.

Like anyone who makes content, it is easy to find people to correct your mistakes, and [Breaking Taps] did have a minor misspeak you can read about in the first pinned comment. But the error is small, and we predict unless you are an expert MEMS designer, you’ll learn something new by watching this video.

Your phone isn’t the only beneficiary of these tiny mechanical devices. We’ve seen, for example, digital levels. Self-balancing robots come to mind, too.

Thanks to [smellsofbikes] for the tip!

18 thoughts on “MEMS Teardown And Macroscopic Models

    1. There are fully solid state gyros technologies, namely fiber optic gyro (fog), ring laser gyroscopes (rlg) and hemispherical resonator gyro (hrg). With no moving parts.

    1. You would be right, except you’re not. The word “decapsulation” has been used for well over a decade at this point in the reverse-engineering community. Nobody needs another pedant, there are more than enough of them around as it is.

      1. I love to try to logic out the origin and meaning of words. Before Google, you could really think about things to try to work on your logic. You wouldn’t always come to the correct conclusion but that wasn’t the point. I use Google every day like everyone else but I think something intangible but significant has been lost when we have instant access to all the correct answers.

        We see a lack of critical thinking skills and I wonder if instant access to answers isn’t part of the problem. I have no problem with pedants.

        1. Do you call a person who welds a welder or a weldor?

          But somewhere along the line, people got the wrong word into their head and began calling the person who uses a welder after the equipment they use.

          Humans who did complex math were called computors before computers existed but when complex mechanical and electronic computing devices came along they were naturally called computers. Some time before the demise of the profession of human computor they were being called computers.

          May as well call sailors sailers and directors directers, detectors detecters.

          Far as I’m concerned a person claiming to be a welder should be able to shoot flames or electric sparks from their fingers. I’d love to see that in some superhero comic. Someone asks the SH with the power of flaming/sparking fingers “Are you a welder?” “Yep, just let me finish this and I’ll be right with you.” *grabs a welding rod and proceeds to TIG weld the item with an index finger* “If you’d said you were looking for a weldor, I’d have used the arc welder over there. But since you need a welder, I’m your guy, and I won’t need to lug around a heavy machine.”

    2. Nope, big pedantry fail there. Capsulate is the root verb (but isn’t commonly used by itself in modern English). It means ‘to be in a capsule’. Adding the prefix ‘en’ to form ‘Encapsulate’ means ‘to put into a capsule’ and the inverse meaning ‘to take out of a capsule’ is formed by adding the prefix ‘de’ to the root verb.
      Your suggestion of stacking prefixes is like saying that your garden is outinside your house.

    3. I like to use an etymology “dictionary” to check this kind of thing.
      A good one is Etymology Online
      encapsulate (v.)
      1842 (implied in encapsulated), “enclose in a capsule,” from en- (1) “make, put in” + capsule + -ate (2). Figurative use by 1939. Related: Encapsulating

      So decapsulate would be correct.
      active word-forming element in English and in many verbs inherited from French and Latin, from Latin de “down, down from, from, off; concerning” (see de), also used as a prefix in Latin, usually meaning “down, off, away, from among, down from,” but also “down to the bottom, totally” hence “completely” (intensive or completive), which is its sense in many English words.

      As a Latin prefix it also had the function of undoing or reversing a verb’s action, and hence it came to be used as a pure privative — “not, do the opposite of, undo” — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

  1. “However, as things shrink to microscopic scales, transistors don’t work well, and you often find — full circle — mechanical devices. ”

    What. MEMS devices are an order of magnitude larger than transistors, and transistors are continuing to shrink to smaller process scales (with at least a 10x shrinkage demonstrated in lab samples).
    MEMS has nothing to do with transistor scaling, MEMS exists to make existing mechanical devices cheaper and more compact by manufacturing them as planar components via etching rather than as assemblies of discrete components.

    It’s as utterly nonsensical as claiming cars exist because ponies could not be bred small enough.

  2. Cool! I worked in MEMS for a number of years. Some of the images of MEMS devices he showed early in the video are from around 25 years ago which is crazy to think about. One of the things not discussed here is the fluid dynamics which are quiet complex, and one reason why macroscopic models do not behave identically to the MEMS components, in fact those are often exploited or frustrating difficult to deal with.

    Friction at this scale is also a fun one, gears for example don’t quit work like you’d expect. Same with thermodynamics, you can get comparatively large displacements with thermal actuators which isn’t something you’ll see in macroscopic devices.

    Also, while most of MEMS is indeed done in silicon, it isn’t the only material, nor is MEMS a purely subtractive processes. A company I knew did various metals in a deposition process allowing you to essentially 3D print structures at this scale.

  3. This shows why some iPhones had problems with exposure to even tiny amounts of helium. They had a MEMS accelerometer that was vented to the atmosphere and relied on the viscosity of normal air in order to work correctly. The much lower density of helium bollixed the super tiny moving parts. IIRC in cases of exposure to high concentrations of helium the MEMS device would be damaged and no longer work with the return of normal air.

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