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iPhone 5s Touch ID – Technology Perspective

Looks Like AuthenTec Descendants

Contributed by Dick James

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It’s a matter of history now. The widely expected fingerprint sensor did show up in the iPhone, to generally good reviews, so of course we had to take a look at it.

Earlier this month, we analyzed the Touch ID sensor with a patent and market perspective.

Today, we take a technology perspective and dive into what looks like an AuthenTec descendant.

They were very efficient at taking out the sensor and separating it from the connector, so I’ve borrowed the iFixit images so that we can see the assembly.

TouchID 1+2

The top image shows the sapphire disc and the stainless steel ring that has to be contacted to make it work. In the bottom image, we can see an NXP interface chip on the flextape.

Looking closer at our black-on-black sample (our phone was a black model), we can hardly see anything since both the sapphire touch-disc and the bezel are jet black, but if we separate the sapphire disc off the bezel, then it becomes more clear, and if we flip the disc, then it becomes even more so – we can see the outline of the actual sensor chip.

New Picture

We can see from the scale in the background (in mm) that the sapphire disc is ~9.5 mm in diameter, so the chip is relatively huge, my tentative measurements had it coming in  at ~6.6 mm x 6.1 mm, not quite square. At the top edge are the remnants of the gold bond wires connecting the chip to the outside world.

New Picture (4)

This confirms what we saw during the launch of the iPhone 5s; that the TouchID was a square touch sensor (capable of reading a fingerprint using a touch action, rather than swiping across a strip, as we’re used to in other sensors) – more costly, but a lot more convenient.

The Apple video describing the sensor also showed that. Here’s a screen shot which is a relatively accurate schematic of the assembly stack (the annotations are ours):

New Picture (3)

After taking the chip off the sapphire, we can finally get a look at the layout of the die.

 

iPhone 5s Touch ID Sensor die photo

 

The capacitors are arranged in an 88 x 88 array for a total of 7744 pixels, and are ~0.051 mm (~0.002”) square, which agrees with the 500 ppi shown above.

An unusual feature of the die is the dark areas at the top and bottom edges. It appears that the silicon has been partially etched away to provide a recessed shelf within the die area for the wire bonds. That allows the top surface of the chip to be bonded straight onto the sapphire disc, minimizing the finger-to-chip distance. Other styles of packaging could have been used, similar to image sensors, but they are likely more expensive than good old fashioned wire bonds.

The title states that we think that this sensor is a descendant of the AuthenTec sensors that we found in earlier phones; why would we think that?

First, Apple bought AuthenTec back in July last year. Second, if we look at the die markings on the Apple sensor, they look similar to those on the last AuthenTec sensor that we looked at.

Here’s the Apple sensor die marking:

ME296CA_Fingerprint-Sensor_TMDR92_148163_diemrk3-c_branded

And this is the one from an AuthenTec sensor in a Motorola Atrix phone from 2011:

AES1750_TMX908_diemrk_branded

No AuthenTec (or Apple) logo on the new chip, but the style and fonts are very similar. You could also say the same for the chip layout, looking at the Atrix sensor (even though it’s clearly a swipe, not a touch sensor); again the style of layout is very similar.

AES1750_TMX908_branded

Have we made the case? I believe so! We’ll be taking a look at the way the sensor is put together in an upcoming blog.

 

Other Articles on the iPhone 5s

Inside the iPhone 5s

Inside the Apple A7 from the iPhone 5s – Updated

iPhone 5s Touch ID – Patent and Market Perspective

iPhone 5s Update – Different RF Front Ends Revealed