Genome Analyzer II Internal Pics

A while back I was lucky enough to encounter a disassembled Genome Analyzer 2. I’ve played with the data from these instruments a lot, having written an image analysis and basecalling platform for this instrument so it was fun to see one on the inside.

The instrument is effectively a TIRF microscope, stage and fluidics system stuffed in a case. As is typical of early versions of scientific lab equipment, it mostly uses off-the-shelf parts stuffed in a case.

For my reference, I took a huge number of pictures. Check them out below:
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Another iPhone MEMS Mic (different configuration+layers)

iphone6smemsToday 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:

 

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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.
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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:

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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…

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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.

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The iPhone MEMS Mic in a SEM

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iPhone MEMS Mic SEM Image

SAfter playing with the BME280 I have this new fetish for all things MEMS. So today I decided to stick the iPhone 6s MEMS mic in the SEM. According to the always wonderful chipworks this is the Knowles KSM1.

The chipworks optical die image is shown below and it clearly looks very similar to the SEM image to the right.

The die seems to contain few sub-diffection limit features. The smallest features seem to be on the order of a few microns, and I assume you could make this with a 1 micron process.

 

 

 

 

 

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iPhone MEMS Mic optical image (from chipworks)

20161022_161205-bmpI was really interested in the patterning on the diaphragm. The patterning of these circles differs slightly between my SEM images and the chipworks optical image above. In fact on the SEM image they look a lot more like holes. Some Knowles patents refer to holes’ purpose as allowing a void to be etched under the diaphragm:

The perforated member contains a number of openings 21 through which a sacrificial layer (not shown) between the diaphragm and perforated member is etched during fabrication to form the air gap

Makes sense to me!

20161022_162738-bmpThe “holes” are about 10micron in diameter, pretty huge really! On another device I’d poked tweezers through one of the diaphragms. My hope was I’d either get some notion of the layer thickness or revel the structure below the diaphragm (if any). No such luck really. Other than it’s probably super-thin!

20161022_162919-bmp Below are a couple more images for your viewing pleasure. The bits sticking out below, I assume are anchor points. It’s interesting that in the image above, the diaphragm breaks right up until these anchors. So it seems it does extend all the way to this point.

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The overall construction seems straightforward (well, as awe inspiring as MEMS always is). But there are a few questions I still have… like why are there 2 diaphragms ? Is that a yield issue or a signal issue? What are the larger circles at the edge of the diaphragm? What’s the bit that sticks out to make the diaphragm Q shaped? And why is the bonding to the diaphragm seeming different on the left than the right… many questions which perhaps I’ll investigate if I find time (update: see below).

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mems_more_infoSo… this MEMS journal post has a bunch of useful information. In the image to the right you can see they’ve labeled most of the features.

This is great, but the second cross-sectional view helped even more (see below).The microphone is a capacitor whose capacitance varies, initially I was thinking that the diaphragm and the bottom of the cavity formed the capacitor. That’s not the case.

There are actually two thin layers fabricated on top of each over above the main cavity, that’s why on the SEM images you see two connection points, the bit that looks like part of an inverted ‘Q’ is going to the top plate. The central connection to the bottom. One final question I have then is how is the main cavity formed? And why is it needed? The bottom plate doesn’t look like it has release holes in it, and could it not be fixed?mems_more_chipworks

Throwing the BME280 Combined Pressure/Humidity Sensor in a SEM

20161018_140331-bmpYesterday I decided to throw a BME280 in a SEM. We purchased the hackerfarm SEM a while back, but recently I’ve been getting a bit more use out of it.

I’ve also recently been getting interested in the BME280 combined pressure/temperature humidity sensor, and plan to make a board for my espusb design based around it. This seems to be one of the few MEMS humidity sensors on the market, and seems to perform very well.

However it’s unclear exactly how the humidity sensing functions. So in the SEM it goes! The tiny can seems to contain 3 discrete dies. In the image to the right you can see the large lower die, and a much smaller upper die. Under the lower die it looks like there’s another die, I assume that’s the ADC/SPI/I2C interface controller. I’d guess that the sensors require some novel process, and are therefore fabricated separately.

20161018_140608-bmpSo… my gut feeling is that the lower die is a pressure sensor. Most MEMS pressure sensors appear to be based on a diaphragm with a piezo coating. I didn’t have time yesterday but I might try and investigate this die further in the future.

So I focused on the upper die, shown to the left, and found the construction to be surprisingly interesting.

It looks like there are 2 large pads with some kind of (I assume thin-film) placed over them.

This film was really interesting.

 

 

Moving up to 300x we can start to see structure in this film:20161018_140824-bmp

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Zooming in further and approaching the diffraction limit we can see this really interesting almost fractal like, structure.

These cracks are really interesting, and I assume not just a manufacturing defect but a functional part of the surface. I’d kind of guess that these small pores allow water to be absorbed into the surface and change the resistivity or capacitance of the layer.

The fractures range from ~1 micron to <100nm wide. The image below shows a fracture at x100000.

 

 

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I was curious to find out a bit more, while nothing is easily available online a patent search yielded some useful information. This patent from Bosch shows a very similar layout to the BME280:

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While that patent doesn’t cover the humidity measurement in detail it does contain the following paragraph:

Humidity sensors are widely used in various fields to measure the amount of water vapor present in the air of a particular environment. Humidity sensors typically include a pair of electrodes separated by a dielectric material. The dielectric layer is formed of a material, such as polymer that is configured to absorb and retain water molecules at concentrations that are proportional to the ambient humidity. The water molecules alter the dielectric constant of the polymer resulting in a change in capacitance between the two electrodes. Humidity can therefore be determined by measuring the capacitance between the two electrodes and correlating the measured capacitance to a corresponding humidity value.”

So, it looks like we might be looking at capacitive sensing across this fractured dielectric material. The text also indicates that the device labeled 16 in the figure above is the humidity sensor.

It’s possible these are so called “mudcracks” that occur when depositing thick films, like the example below from this paper on reducing cracking in spin coated films:

mudcracks_nanofabBut none of the “mudcracks” I’ve seen appear to show the disconnected, fractured structure shown in this sample.

Overall, I’m still not very clear on what exactly the material used is, of if there are trenches/other features under this fractured layer. If you have any thoughts please comment below! I’m also planning to pick up a BMP280 and see is it essentially the same device, without the top die.