Explain why iPhone 7 will cancel the entity home key: The growing Touch ID

Lei Feng network (search "Lei Feng Net" public concern) by: author of this article dragondevil, Microarray chief scientist, electronics and software designers. Relevant characters of this article are Setlak, the founder of Authentec and the main technical inventor, Touch ID designer, and the discoverer of the technical principles based on all commercial capacitive fingerprint sensors outside the CQT technology route.

It is rumored that the iPhone 7 will use the entity Home button, and the virtual home button will be used on the iPhone 7 Plus. Since Apple has not yet officially released, this article is based on the model that the author got. Speculation: If iPhone 7 Plus is on Virtual Home key, what could be the reason? What will happen to the Touch ID?


(Netscape iPhone7 and iPhone 7 plus spy photos)

Compared with the iPhone 6 Plus, the iPhone 7 Plus does not appear to be large in appearance, and the physical Home key on the iPhone 6 Plus limits the inscribed rectangle whose chip size is at most to the inner wall of the entity key. Therefore, the iPhone 7 Plus with the virtual home button is used. On the further expansion of the Touch ID area.

Compared to iPhone 6S Plus, iPhone 7 Plus did not grow, but Touch ID continues to grow:

I would like to review this article I wrote to Lei Fengnet: "Touch ID is getting bigger! What's the secret behind the iPhone 6s Home button? 》

If Apple's approach to the limit reached 90% or more, then the second-generation Touch ID will undoubtedly greatly improve security and user experience. This book deserves a lot of exaggeration, but declaring that the second-generation security upgrade is tantamount to publishing the first generation of security flaws. So Apple simply uses "faster" to make it bigger and never mentions "bigger" things. .

This is the second generation of Touch ID on Apple's consideration.

The physical Home key limits the inscribed rectangle with the largest wafer size to the inner wall of the physical key. When the wafer size cannot be enlarged, the pixel array size depends on the layout efficiency. The image on the left is the iPhone 5S Touch ID 1.0, 88 x 88 pixel array; the image on the right is the iPhone 6S Touch ID 2.0, 96 x 112 pixel array. You can see that the layout has changed a lot.

However, compared to the "Domestic Touch ID" on the same size wafer to achieve 120x120 pixel array, Apple's design is too rugged (bao) Yong (le).

Moreover, the limited increase in the layout efficiency of Touch ID 2.0 is not an independent innovation, but a reference to the patented technology of “domestic TouchID”: based on the module structure disclosed in patent CN201510230871.1, TSV packaging can be used; the TSV package passes silicon Perforation saves the front side of the wafer for wire-space (the black area on the left and right sides of Touch ID 1.0) and has an area for layout pixels.  

But the reason why Apple is Apple is that when technology competition enters the bottleneck, it can be a god. To further expand the area of ​​the fingerprint sensor, it is necessary to break through the physical limitations of physical buttons. Therefore, the iPhone 7 plus adopts the “Under Glass” scheme : Place the capacitive fingerprint sensor under the cover glass, and read the fingerprint through the cover glass to make the fingerprint sensor wafer. The size is no longer limited by the size of the keys.

The idea of ​​using a capacitive fingerprint sensor to penetrate a thick medium was first seen in a U.S. patent "method and apparatus for sensing" filed on October 8, 2010 by Apple, Inc. The Chinese patent application CN201180055850.6 was submitted on October 7, 2011. 5 discloses the exponential attenuation effect of the capacitive fingerprint sensor image response, although the medium thickness increases and the fingerprint ridge line period decreases:

Through the study of the physical laws of the electric field, Apple found that in order to penetrate a medium with a thickness of 300 μm to 400 μm, the capacitance signal would be attenuated by hundreds or thousands of times, and the finer the fingerprint, the more severe the attenuation would be. So we have never seen what Apple, one of the technology leaders, claimed to have penetrated 700um, but some people confused the capacitance value and the capacitance signal, which is inversely proportional to the size and distance. ) Laugh (zhi) big (tou) party (ding).

In order to achieve a sufficiently high sensitivity to measure a drastically attenuated capacitive signal, it is first necessary to acquire one of the most aggressive companies. As a result, Apple purchased Authentec in 2012 and obtained the exclusive rights of RF-type fingerprint sensor technology and most of the patents for capacitive fingerprint sensors in the industry.

Secondly, it is necessary to significantly improve the original level of technology. For example, the differential image synthesis technology disclosed in CN201180055850.6 is used to collect vertical differential images and horizontal differential images separately using a specially designed circuit and then software to synthesize a fingerprint image.

The inductive boost high voltage drive technology disclosed in CN201310224334.2 is used to drive the ground potential of the sensor, which is equivalent to driving the absolute ground potential including the human body in the sensor reference system, thereby exceeding the drive voltage of the external metal ring. Cap:

This was when Touch ID 1.0 was born in 2013.

The disadvantage is that the sensor area is a bit small and the safety is insufficient . So Touch ID 2.0 got a small step forward by relying on the chao (xi) design of the “domestic touch ID”. Finally Touch ID 3.0 is back in technology.

As a designer of “Domestic Touch ID”, I’m in the process of developing technology together with Touch ID designer Setlak. For example, the Touch ID 1.0 thickness is 1.2mm, the domestic Touch ID improves the structural design, reduces the thickness to 1.1mm, and the Touch ID 2.0 irrelevant structural design requires that the thickness be reduced to 1.06mm. Although slightly behind in the technology competition, this is because I started from scratch and I can't compare with Setlak's back to the tree. In fact, in 2015, I released the Under Glass engineering prototype in a small area. However, Apple's mobile phone brands are not just following Apple but are not willing to lead. From this point of view, selling Authentec to Apple from the perspective of Setlak as the designer wants new technologies to be applied first is also extremely correct.

Closer to home, capacitive fingerprint sensor technology is no matter how good the sensitivity is, how high, it can't stop the exponential attenuation effect of the signal when the medium thickness increases. On the one hand, the thicker the glass, the better the structural strength. On the other hand, the fingerprint identification requires the glass to be as thin as possible. This requires the determination of a compromise point. The apple god of the first (re) knowledge (ai) first (yan) thought (jiu) disclosed in the patent as early as 2013 that the glass can be thinned to 250um, and when it is mass-produced, it must be higher than this value, reaching 300um or more. However, it should not exceed 400um.

The Touch ID design of the iPhone 7 uses a process of locally thinning and chemically strengthening the front of the cover glass, which not only reduces the thickness of the cover media of the Touch ID, but also provides the user with tactile guiding grooves; especially important is the flatness. The bottom surface of the chip is no longer limited in size, and the sensor pixel array can be made as large as the groove to ensure fingerprint identification security.

In order to further improve the experience of using virtual keys, you can also provide vibration feedback through the introduction of Force Touch, so that feel infinitely close to the physical keys .

After doing so much work, the chip of Touch ID is finally not limited by the physical key frame, and the Sensor area can be made as large as the inscribed square of the virtual key area, and the touch of the key cannot be reduced.

However, it is not so much trouble, direct "domestic Touch ID" is not in place yet?

Whether Apple will use the virtual home button on the iPhone 7 plus isn't known, wait until the 8th morning announcement.

Lei Feng Net Note: Lei Feng network exclusive article, reproduced please contact the authorizing and retain the source and author, not to delete the content.

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