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Apple's fingerprint sensor encapsulation tech could be headed for future iPhone

Fingerprint sensor surface array (16), die (14) and bezels (18). | Source: USPTO

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The U.S. Patent and Trademark Office on Thursday published an Apple filing for a unique encapsulation structure which holds both a fingerprint sensor and its conductive bezel, allowing for a smaller, more protective final component suitable for a mobile device.

Apple's patent application, filed in February and titled "Integrally molded die and bezel structure for fingerprint sensors and the like," describes a unitary encapsulation structure that protects a delicate biometric array, while still allowing for a portion of the sensor and bezel to be exposed or thinly coated with a protective seal. While the filing is for a "strip" type sensor, the technology can feasibly be applied to other fingerprinting methods.

As noted in the filing, current electrical-based sensors are formed in a package containing the die, which holds a semiconductor and said sensors along with related circuitry. Because of the small die size, secondary structures like a lead frame and wires are needed to make an electrical connection between the die and the printed circuit board on which it is situated. These structures are then encased in an encapsulation material to protect the intricate wirebonding and other internal components from damage.

Because such sensors can only operate within a certain threshold distance between a user's fingerprint and the die, many encapsulation methods leave the package uncovered.

Current circuit designs may also use a small electrical current to charge a user's finger for reading. In order to send the correct current through the finger, small contact structures are formed and disposed near the sensing die. These "bezels" are largely positioned in the same plane as the upper sensing surface of the die, thus ensuring both a charged finger and ideal positioning for the sensor.

Cutaway of assembly with finger.

Apple's patent filing looks to combine the encapsulated die with the bezel contact structures to form a single unitary package:

By encasing both the bezel and the sensor die in the encapsulation structure, those elements may be brought closer together than heretofore possible. In addition, the encapsulation structure physically protects the bezel and sensor die, and in particular maintains the spacing therebetween, in a fashion not possible by currently known device designs.

In one embodiment, the sensor assembly includes a substrate like a PCB or ceramic structure with a region specifically designed to receive a die assembly, as well as regions for holding bezels. The encapsulation structure is molded from a resin or plastic and is injected in such a way as to leave the top portion of the die and bezel parallel or nearly coplanar. These structures can be either partially exposed, or covered with a thin layer of material to protect it from the elements.

In addition to the above embodiments, the filing notes that the bezels can be provided with visual indicators and possibly a light source.

The invention would prove to be of substantial value if Apple were to deploy a fingerprint reader in a future iteration of the iPhone, as the tech would allow for a small, reasonably durable component that can withstand everyday wear and tear.

View of bezel frame according to one embodiment.

Apple is widely rumored to be incorporating fingerprint scanning technology into its next-generation iOS devices, with the forthcoming "iPhone 5" being a prime candidate. Rumors and speculation were sparked by the company's 2012 acquisition of biometrics firm Authentec.

Interestingly, Apple's filing cites multiple patents and patent applications on fingerprint biometrics owned by STMicroelectronics, one of the world's largest semiconductor companies. Besides sensors and embedded processing solutions, the firm also supplied Apple with the three-axis gyroscope found in the iPhone 5.

At least one of the inventors credited with the application, Giovanni Gozzini, is also named on the cited STMicroelectronics patents. Accompanying Gozzini in the Apple-assigned filing are Robert Henry Bond and Alan Kramer.