Today I pulled apart another MEMS Mic. This was from a replacement flexpcb for an iPhone 6s I bought on eBay. I expected the MEMS sensor to be identical to the one I posted yesterday. But it turns out it was quite different.
Optically it resembled the image shown on the right (from chipworks), with a single diaphragm and 4 bonding pads. Chipworks say this is a Goertek GWM2.
A couple of interesting things happened when I was playing with the 2 MEMS packages on this flex. Firstly, when I removed the package on one device the whole MEMS die came with it.
This meant I got a view of the underside of the device, this is the side that the sound hits:
What confuses me slightly is that there appear to be release holes on this side of the diaphragm too. I would have expected it to be solid as appeared to be the case in the chipworks images I posted yesterday. The release holes also seem to be a little smaller than the previous sensor. On the order of 7 microns.
The other interesting thing that happened is that I found I was able to pull the layers away from the mic using a pair to tweezers. I was amazed that the diaphragm remained largely intact. I stuck this down with some polyimide tape and it imaged quite well, this is layer furthest from the sound inlet:
I even managed to remove the diaphragm “below” this (nearest the sound), but wasn’t so successful at taping it down. Here it is sitting on the back of polyimide tape. I’m surprised how well the sample image without being grounded…
I’m not sure exactly what is happening in the following image. It looks like this diaphragm maybe more complex. While a hexagonal mesh is present, it seems like there a solid layer behind this (this would somewhat explain the fact that the “sound-side” mesh above looks like it has holes in it). It also seems to have holes of different sizes… I couldn’t acquire very good images here… I suspect the sample wasn’t very stable sitting on the polyimide tape.