MEMS Microphone Teardown

Somehow I knocked the cap off one of my MEMS microphones, so I figured we'd take a quick look at it up close.  I also have some Infineon microphones around, so we'll look at those as well.

Knowles SPH0644

This microphone itself is pretty small, 3.5 x 2.65 x 1.0mm

Close up, it’s clearly visible that there are 2 major parts to this microphone: the microphone ‘capsule’ itself on the right, and the PDM modulation chip on the left. The microphone capsule is actually two capsules in parallel. My suspicion is that this does a couple things: first, it might fit a little better than one larger diaphragm, and also, it keeps the self-resonance of the each diaphragm high, while improving the sensitivity of the system.

Here you can see the diaphragm and back plate. The back plate is a mesh material that is conducting and forms one side of the capacitor (condensor) microphone. The diaphragm is *just* below the grid and is the vibrating piece. Also, Look very closely at the dead center of each diaphragm. The actual diaphragm has a tiny hole drilled dead center, which serves as a low-frequency rolloff (high-pass filter). This helps with low frequency hvac noise and also with wind bluster. Not to mention atmospheric changes.

I popped off the diaphragm holder here, but they went flying and were not anywhere to be seen. But, here you see the bottom port itself.

Infineon IM69D120V01XTSA1

This microphone was misplaced at the board house. They should have caught this and fixed it themselves. But.. it provides us an opportunity for teardown.

Well, the microphone came off the board more easily than the metal cap comes off the microphone. I wonder if I can disassemble this…

This one was much tougher to get into than the Knowles. Clearly, it has a very different design. A couple things are notable: First, there is only 1 large diaphragm as opposed to two. The other thing is that there are 4 wires going to the sensor, as opposed to only 2 in the Knowles. I’m not entirely sure why this is. Could be for bias. Could be for balanced signaling. Could be both.

Here’s a closeup of the Infineon diaphragm. Again, it’s 2 layers, but the grid on the back plate isn’t immediately obvious. Perhaps it’s an extraordinarily fine mesh.