HK1251693B - Under screen sensor assembly - Google Patents

Description

Sensor assembly under screen

Technical Field

The present invention relates to sensors for use in electronic devices such as cell phones.

Background

Electronic devices, in particular mobile electronic devices, are becoming more and more popular. The data processed in these devices is growing in both quantity and sensitivity. There is a need for an advantageous safety device to protect users from potential injury. The novel security device must be excellent in terms of precision, form factor and usability.

Conventional fingerprint sensor devices are known. See, for example, us patent 8,358,816. Such devices use a linear light sensor to capture a user's fingerprint. Access to the electronic device is granted if the captured fingerprint matches the fingerprint of the user. However, linear light sensors may be hacked, making them weak security devices. For example, a fingerprint may simply be printed on a piece of paper and passed through a sensor. The linear sensor cannot make any distinction between a fake paper copy and a real finger. Linear sensors require a sliding movement by the user. The sliding must be precise and well positioned, thus making it sometimes difficult to use. The packaging of such devices typically does not have a sufficiently small form factor and efficient device integration design. The package is typically bulky and typically requires a specially designed device cover with a window.

Disclosure of Invention

The above problems and needs are solved by a sensor assembly comprising: a silicon substrate having opposing top and bottom surfaces; a sensor integrally formed on or in the top surface of the silicon substrate; a plurality of bond pads formed at a top surface of the silicon substrate and electrically coupled to the sensor; a trench formed in the top surface of the silicon substrate and extending toward but not reaching the bottom surface; a plurality of conductive first traces, each conductive first trace extending from one of the bond pads along the top surface of the silicon substrate, along a sidewall of the trench, and along a bottom of the trench; one or more vias formed in the bottom surface of the silicon substrate and extending toward but not to the top surface, wherein the one or more vias terminate at the bottom of the trench in a manner that exposes the plurality of electrically conductive first traces; and a plurality of conductive second traces, each extending from one of the conductive first traces at the bottom of the trench along the sidewalls of the one or more holes and along the bottom surface of the silicon substrate.

A handset, comprising: a front screen; a visual display disposed below the front screen and viewable through the front screen; a sensor assembly disposed under and sensing an area of the front screen; and control electronics electrically connected to the sensor assembly and the visual display. The sensor assembly includes: a silicon substrate having opposing top and bottom surfaces; a sensor integrally formed on or in the top surface of the silicon substrate; a plurality of bond pads formed at a top surface of the silicon substrate and electrically coupled to the sensor; a trench formed in the top surface of the silicon substrate and extending toward but not reaching the bottom surface; a plurality of conductive first traces, each conductive first trace extending from one of the bond pads along the top surface of the silicon substrate, along sidewalls of the trench, and along the bottom of the trench; one or more vias formed in the bottom surface of the silicon substrate and extending toward but not to the top surface, wherein the one or more vias terminate at the bottom of the trench in a manner that exposes the plurality of electrically conductive first traces; and a plurality of conductive second traces, each extending from one of the conductive first traces at the bottom of the trench along the sidewalls of the one or more holes and along the bottom surface of the silicon substrate.

A sensor assembly, comprising: a silicon substrate having opposing top and bottom surfaces; a sensor integrally formed on or in the top surface of the silicon substrate; a plurality of first bond pads formed at a top surface of the silicon substrate and electrically coupled to the sensor; a trench extending between the top and bottom surfaces; a plurality of second bond pads extending across the trench at the bottom surface; and a plurality of wires, each wire extending from one of the first bond pads into the trench and to one of the second bond pads; and a plurality of conductive traces, each conductive trace extending from one of the second bond pads and along the bottom surface of the silicon substrate.

A method of forming a sensor assembly, comprising: providing a sensor die (the sensor die having a silicon substrate with opposing top and bottom surfaces, a sensor integrally formed on or in the top surface of the silicon substrate, and a plurality of first bond pads formed at the top surface of the silicon substrate and electrically coupled to the sensor); forming a trench in the top surface of the silicon substrate, the trench extending toward but not reaching the bottom surface; forming a second bond pad at a bottom of the trench; connecting a plurality of wires between the first bonding pad and the second bonding pad; filling the trench with an insulating material; recessing a bottom surface of the silicon substrate to expose the second bonding pad; and forming a plurality of conductive traces, each conductive trace extending from one of the second bond pads and along the bottom surface of the silicon substrate.

Other objects and features of the present invention will become apparent by a review of the specification, claims and appended figures.

Drawings

FIGS. 1A-1E are top views illustrating the steps of forming a sensor assembly of the present invention.

Fig. 2A-2M are side cross-sectional views illustrating the steps of forming a sensor assembly of the present invention.

Fig. 3A is a top view of the front screen of the handset.

Fig. 3B is a side cross-sectional front view of the handset.

Fig. 4A-4F are side cross-sectional views illustrating the steps of forming an alternative embodiment of the sensor assembly of the present invention.

Detailed Description

The present invention relates to biometric (fingerprint) sensors, packaging of fingerprint sensors and integration of such devices. The present invention uses sensory technologies such as capacitive, electromagnetic, and infrared and photon sensing, using a range of sensory devices to achieve optimal reading of fingerprints. The present invention also includes ultra-thin packaging and device integration where the sensor can be placed directly under the top screen of the handheld device for fingerprint identification and authentication.

FIGS. 1A-1E and 2A-2M illustrate steps for forming a packaged sensor assembly of the present invention. The process begins by providing the illustrated sensor assembly 10 as shown in fig. 1A (top view) and 2A (side cross-sectional view). Sensor assembly 10 includes a silicon substrate 12 as well as a sensor 14, support circuitry 16 for sensor 14, bond pads 18 and a dielectric layer 20 electrically connected to sensor 14 and/or circuitry 16 (for off-chip signals), all formed at the top surface of substrate 12 or in the top surface of substrate 12. The sensor 14 constitutes the active area of the sensor assembly 10 and may be any type of sensor, such as a capacitive sensor, an electromagnetic sensor, an ultrasonic sensor, a temperature sensor, a pressure sensor and/or a photonic sensor. The sensor 14 preferably comprises a plurality of sensors of different types, placed side by side, on top of one another, or staggered. For example, a photonic sensor may be used to detect fingerprint information from a finger passing through the sensor 14, while one or more of the other types of sensors listed above may be used to confirm that the optically sensed fingerprint originates from a real finger and not from some printed or other fake media. Other sensor(s) may also help capture and/or confirm sensed fingerprint data. It should be understood that although only one sensor assembly 10 is shown in fig. 1A and 2A, there are a plurality of such assemblies formed on a single wafer substrate 12.

In the region of the substrate 12 between the bond pads 18 of two adjacent sensor assemblies 10, a trench 22 is formed through the dielectric layer 20 and into the top surface of the substrate 12. The trench 22 may be formed using a photolithographic process and an anisotropic dry etch process to etch through the dielectric layer 20 and into the silicon substrate 12. Mechanical sawing or any other mechanical grinding process may also be used to form the trenches 22. There may be two grooves between adjacent sensor assemblies, as shown in fig. 1B and 2B, with one groove 22 on either side of a dicing line 24 along which the wafer is to be diced. Alternatively, there may be a single trench 22 extending across the cut line 24 as shown in fig. 1C and 2C. The trenches 22 may have vertical sidewalls as shown or sloped sidewalls. The grooves 22 may be formed on two opposing sides of the sensor 14 as shown or on all four sides of the sensor 14. Preferably, the length of the trench 22 is less than the respective lengths of the sensor 14 and the bond pad 18.

The insulating material 26 is randomly (or pseudo-randomly) deposited over the structure except in the area over the bond pads 18 and sensors 14. Insulating material 26 may be, for example, silicon dioxide or silicon nitride. Preferably, the insulating material 26 is silicon dioxide having a thickness of at least 0.5 μm. The insulating material 26 may be formed by Plasma Enhanced Chemical Vapor Deposition (PECVD) or any other suitable deposition method(s), followed by a photolithographic process and etching to remove portions of the insulating material over the bond pads 18 and sensors 14. A conductive material, such as an aluminum alloy, copper/titanium or any other conductive material known in the art, is formed over the structure (preferably aluminum deposited by sputtering) and then selectively removed using photolithography and etching processes in addition to the electrical traces 28 and their bond pads. Each trace 28 extends from one of the bond pads 18 along the insulating material 26 and down a sidewall of one of the trenches 22 and terminates in a bond pad 30 at the bottom of the trench 22, as shown in fig. 1D and 2D.

A dielectric (insulating) encapsulant 32 may be randomly (or pseudo-randomly) deposited over the structures including in trench 22 while leaving sensor 14 exposed, as shown in fig. 1E and 2E. Dielectric material 32 may be silicon dioxide, silicon nitride, a photoimageable polymer, epoxy, or other suitable material. Preferably, the dielectric material 32 is made of a photoimageable polymer. The photoimageable material deposition method may be spin coating and/or spray coating or any other suitable deposition method(s) and then selectively removed using a photolithography and etching process to expose the sensors 14. The encapsulation material 32 will serve as a support layer for the traces 28 and bond pads 30 at the bottom of the trenches 22.

The sensor 14 may be protected by a transparent/translucent substrate and/or by a protective film coating over the sensor 14. The protective material 34 may be randomly (or pseudo-randomly) deposited over the entire surface and selectively removed so that it covers the sensor 14, as shown in fig. 2F. The protective material 34 may be silicon dioxide or silicon nitride or any suitable polymer material. Preferably, the protective material 34 is made of at least 0.5 μm silicon dioxide and silicon nitride, deposited by Physical Vapor Deposition (PVD) or any other suitable deposition method(s). Alternatively, the sensor 14 may be protected by a translucent or transparent substrate 36, the translucent or transparent substrate 36 being bonded to the sensor active side using an adhesive epoxy material, as shown in fig. 2G. Bonding may be performed using wafer pressure bonding or spin bonding equipment. As shown in fig. 2H, sensor 14 may be protected by both protective material 34 and substrate 36.

Silicon thinning may be performed on the bottom surface of substrate 12 by mechanical grinding, chemical Mechanical Polishing (CMP), wet etching, atmospheric Downstream Plasma (ADP), dry Chemical Etching (DCE), combinations of the above processes, or any other suitable silicon thinning method(s). The preferred thickness of substrate 12 after thinning is about 150 microns. Holes (vias) 38 are then formed in the bottom surface of substrate 12, each hole extending from the bottom surface of substrate 12 to the bottom of one of trenches 22 and through insulating layer 26, leaving traces 28 and/or their bond pads 30 exposed, as shown in fig. 2I. During and after the formation of the holes 38, the encapsulation material 32 will serve as a support layer for the traces 28 and bond pads 30 at the bottom of the trenches 22. The holes 38 may be formed by a laser, a combination of lithographic and etching (plasma or chemical) processes or any other suitable method. Preferably, there is a single hole 38 for each bond pad 30. Alternatively, a single hole 38 may contain multiple bond pads 30 in a manner similar to trench 22.

An insulating material 40 is formed on the bottom surface of substrate 12, including in holes 38. Insulative material 40 can be silicon dioxide, silicon nitride, or a photoimageable polymeric material. Preferably, insulative material 40 is made of at least 0.5 μm of silicon dioxide, formed by Physical Vapor Deposition (PVD) or any other suitable deposition method(s). A photolithographic process and a dry plasma etch are used to remove portions of insulative material 40 over traces 28 or their bond pad regions 30 in holes 38. A conductive layer is formed on the bottom surface of substrate 12 and selectively removed using photolithographic etching to form conductive traces 42. Each trace 42 extends from one of the traces 28 along a sidewall of one of the holes 38 and outwardly along the layer 40 along the bottom surface of the substrate 12, as shown in fig. 2J. Traces 42 may be formed of aluminum, copper, or any other conductive material(s) known in the art. Alternatively, the traces 42 may be nickel/gold plated or nickel/palladium/gold plated (nickel/palladium/gold).

An encapsulating insulating layer 44 may be deposited over the entire bottom surface of the substrate 12 and traces 42 and selectively removed by photolithography and etching to expose the contact pad portions 42a of the traces 42. The insulating layer 44 may be silicon dioxide, silicon nitride, a photoimageable polymer or an epoxy. Preferably, the insulating layer 44 is made of a photoimageable polymer. The interconnection 46 may be formed on the contact pad portion 42 a. The interconnects 46 may be Ball Grid Arrays (BGAs), land Grid Arrays (LGAs), plated bumps, adhesive bumps, stud bumps, or any other suitable interconnection technology. Preferably, the interconnect 46 is a BGA as shown in fig. 2K.

Wafer-level dicing/separation of the components may be accomplished using a mechanical blade dicing apparatus, laser dicing, or any other suitable process to dice/separate the wafer along dicing/separation lines to produce the unitary sensor assemblies 10. The sensor assembly 10 may be connected to an external circuit 48 (flexible or rigid substrate/PCB) having contact pads 50 and traces or circuitry 52 using BGA interconnects 46, as illustrated in fig. 2L. Alternatively, in the case of the LGA, an interconnect using an Anisotropic Conductive Film (ACF) may be used.

The sensor assembly 10 may be mounted directly to the underside of a front screen for an electronic device in which the assembly 10 is used. For example, as shown in fig. 2M and 3A-3B, the sensor assembly 10 is mounted to a front screen 54 of a cell phone 55. Screen 54 is a dielectric such as plastic, glass, or any other suitable material used in the art. The optical transparency of the screen 54 is preferred, but optional. The handset 55 includes a front screen 54, a visual display 55a mounted to (and preferably viewable through) the front screen 54, a sensor display 10 mounted to the front screen 54, and control electronics 55b for providing handset functions (well known in the art) in response to signals from the sensor assembly 10. The screen 54 may also include coatings and other electronic device structure layers. Optionally, the screen 54 may include recessed (concave) areas 56 in its upper surface directly above the sensor 14 to enhance the sensitivity of the sensor and/or ink coating on its inner surface. The sensitivity increases as the distance between the external environment and the sensor 14 decreases. The recessed regions 56 may be formed by etching, mechanical grinding, or any other suitable method for the particular cover substrate 54. The depression depth may be up to 50% of the screen thickness. The sensor assembly 10 can be picked up and placed on the backside of the cover substrate 54. The adhesive layer may be activated by heat, pressure, chemical agents or any other suitable method.

The packaged sensor shown in fig. 2M and 3A-3B has many advantages. First, the sensor assembly 10 is mounted directly to the front screen 54 of the handset without requiring any special windows or protrusions in the screen 54. Second, the traces 28 carry the sensor signals away from the bond pads 18 on the top surface of the substrate with the least added thickness. The smallest structure above the top surface of substrate 12 (insulation 20, 26, and 32 and traces 28) means the distance between sensor 14 and screen 54, and thus the distance between sensor 14 and the finger that is detected at the surface of screen 54 is the smallest (for maximum sensor performance). The thickness of substrate 12 may be minimized because traces 28 and 42 extend through substrate 12. Routing the sensor signals to the bottom side of the substrate 12 provides a convenient and reliable electrical connection to an external PCB through interconnects 46.

Fig. 4A-4F illustrate the formation of an alternative embodiment using wires instead of traces to electrically connect to the bond pads 18 of the sensor assembly 10. The process begins with the structure shown in fig. 2B. Instead of forming traces 28 that extend down into trenches 22 and form contact pads 30, contact pads 30 are formed at the bottom of trenches 22 without any traces extending from trenches 22, as shown in fig. 4A. A protective material 34 is then formed over the sensor 14 as described above. A wire bonding process is then used to attach each of the wires 60 extending between (and providing an electrical connection between) one of the bond pads 18 and one of the bond pads 30, as shown in fig. 4B.

The dielectric encapsulation material 32 is then formed as discussed above, covering the conductive lines 60 but leaving the sensor 14 exposed, as shown in fig. 4C. The substrate 12 is then thinned by recessing the bottom surface of the silicon substrate 12 until the bond pads 30 are exposed from the bottom (and removing the insulating layer 26). This bottom surface recess may be accomplished by mechanical grinding, chemical Mechanical Polishing (CMP), wet etching, atmospheric Downstream Plasma (ADP), dry Chemical Etching (DCE), or a combination of the above processes or any other suitable silicon thinning method(s) applied to the bottom surface of substrate 12. A layer of insulating material 62 is deposited on the bottom surface of substrate 12. The entire bottom surface of the substrate 12 or only a portion thereof may be recessed. The insulating layer 62 may be silicon dioxide, silicon nitride or a photoimageable polymeric material. Preferably, insulating layer 62 is made of at least 0.5 μm of silicon dioxide formed by Physical Vapor Deposition (PVD) or any other suitable deposition method(s). A photolithography process and a dry plasma etch are used to remove the portion of insulating layer 62 over bond pad 30, as shown in fig. 4D.

A layer of conductive material, such as aluminum, copper or any other conductive material, is formed on the bottom surface of the substrate 12. Metallic materials such as aluminum are preferred and may be deposited by a sputtering process. The conductive material is then selectively removed using a photolithographic process and etching, leaving its traces 64 such that each trace extends from one of the bond pads 30 and along the bottom surface of the substrate 12 over the insulating layer 62. Alternatively, the traces 64 may be nickel/palladium/gold plated. A dielectric encapsulation insulating layer 66 is deposited over the bottom surface of the substrate 12, including over the traces 64. Selected portions of layer 66 are removed (e.g., by photolithography and etching) to expose portions of traces 64 that make up bond pads 64 a. Dielectric layer 66 may be silicon dioxide, silicon nitride, a photoimageable polymer, an epoxy, or the like. Preferably, the dielectric layer 66 is made of a photoimageable polymer. The photoimageable material deposition method may be spin coating and/or spray coating, any other suitable deposition method(s). As shown in fig. 4E, an interconnection 68 such as a Ball Grid Array (BGA) is formed on the bonding pad 64 a. The interconnects may instead be LGAs, plated bumps, adhesive bumps, stud bumps, or any other suitable interconnection method. Stencil printing or ball placement techniques may be used for ball grid array formation. The structure is then split and mounted to the external PCB 48 and front screen 54 as described above, resulting in the final structure shown in fig. 4F.

It is to be understood that the present invention is not limited to the embodiment(s) described above and illustrated herein, but encompasses any and all variations falling within the scope of any claim. For example, reference herein to the invention is not intended to limit the scope of any claim or claim term, but merely to one or more features that may be covered by one or more of the claims. The above-described materials, procedures, and numerical examples are illustrative only and should not be construed as limiting the claims. Moreover, as is apparent from the claims and specification, not all method steps need be performed in the exact order illustrated or claimed, but rather in any order that allows for the proper formation of a packaged sensor assembly. A single layer of material may be formed as multiple layers of such or similar materials, or vice versa. Finally, the terms "forming" and "formed" as used herein shall include material deposition, material growth, or any other technique employed to provide the disclosed or claimed materials.

It should be noted that as used herein, the terms "above … …" and "on … …" inclusively include "directly on … …" (no intermediate material, element or space disposed therebetween) and "indirectly on … …" (intermediate material, element or space disposed therebetween). Likewise, the term "adjacent" includes "directly adjacent" (no intermediate material, element or space disposed therebetween) and "indirectly adjacent" (intermediate material, element or space disposed therebetween), "mounted to" includes "directly mounted to" (no intermediate material, element or space disposed therebetween) and "indirectly mounted to" (intermediate material, element or space disposed therebetween), and "electrically coupled" includes "directly electrically coupled to" (no intermediate material or element disposed therebetween that electrically connects the elements together) and "indirectly electrically coupled to" (intermediate material or element disposed therebetween that electrically connects the elements together). For example, forming an element "over a substrate" can include forming the element directly on the substrate with no intervening materials/elements present therebetween, as well as forming the element indirectly on the substrate with one or more intervening materials/elements present therebetween.

Claims (10)

1. A sensor assembly, comprising:

a silicon substrate having opposing top and bottom surfaces;

a sensor integrally formed on or in the top surface of the silicon substrate;

a plurality of bond pads formed at a top surface of the silicon substrate and electrically coupled to the sensor;

a trench formed in the top surface of the silicon substrate and extending toward but not reaching the bottom surface;

a plurality of conductive first traces, each conductive first trace extending from one of the bond pads along the top surface of the silicon substrate, along a sidewall of the trench, and along a bottom of the trench;

a plurality of holes formed in the bottom surface of the silicon substrate and extending toward but not to the top surface, wherein the plurality of holes terminate at the bottom of the trench in a manner that exposes the plurality of conductive first traces;

a plurality of conductive second traces, each extending from one of the conductive first traces at the bottom of the trench along a sidewall of one of the holes and along the bottom surface of the silicon substrate, wherein the plurality of holes are separate holes, each of the separate holes having only one of the conductive second traces extending therein;

a layer of protective material disposed directly over the sensor and not over the first trace; and

a protective substrate disposed directly over the layer of protective material and disposed over the first trace;

wherein:

a plurality of conductive first traces insulated from the top surface of the silicon substrate and the sidewalls of the trench; and

the plurality of conductive second traces are insulated from the bottom surface of the silicon substrate and the sidewalls of the plurality of holes.

2. The sensor assembly of claim 1, further comprising:

an encapsulation material filling the trench and providing support for the conductive first trace at the bottom of the trench.

3. The sensor assembly of claim 1, further comprising:

a plurality of interconnects, each interconnect electrically connected to a portion of one of the conductive second traces disposed over the bottom surface.

4. The sensor assembly of claim 3, further comprising:

a printed circuit board having a plurality of second bond pads, wherein each of the plurality of interconnects is electrically connected to one of the second bond pads.

5. A handset, comprising:

a front screen;

a visual display disposed below the front screen and viewable through the front screen;

a sensor assembly disposed below and sensing an area of the front screen, wherein the sensor assembly comprises: a silicon substrate having opposing top and bottom surfaces,

a sensor integrally formed on or in the top surface of the silicon substrate,

a plurality of bond pads formed at the top surface of the silicon substrate and electrically coupled to the sensor,

a trench formed in the top surface of the silicon substrate and extending toward but not reaching the bottom surface,

a plurality of conductive first traces, each conductive first trace extending from one of the bond pads along the top surface of the silicon substrate, along a sidewall of the trench and along a bottom of the trench,

a plurality of holes formed in the bottom surface of the silicon substrate and extending toward but not to the top surface, wherein the plurality of holes terminate at the bottom of the trench in a manner that exposes the plurality of conductive first traces,

a plurality of conductive second traces, each extending from one of the conductive first traces at the bottom of the trench along a sidewall of one of the holes and along the bottom surface of the silicon substrate, wherein the plurality of holes are separate holes, each of the separate holes having only one of the conductive second traces extending therein;

a layer of protective material disposed directly on the sensor and not disposed over the first traces, wherein the front screen is disposed directly on the layer of protective material and over the first traces;

wherein:

a plurality of conductive first traces insulated from the top surface of the silicon substrate and the sidewalls of the trench; and

a plurality of conductive second traces insulated from the bottom surface of the silicon substrate and the sidewalls of the plurality of holes; and

control electronics electrically connected to the sensor assembly and the visual display.

6. The handset of claim 5, further comprising:

an encapsulation material filling the trench and providing support for the conductive first trace at the bottom of the trench.

7. The cell phone of claim 5, wherein the front screen includes a top surface having a recessed portion above the sensor component.

8. The cell phone of claim 5, wherein the front screen includes a bottom surface, and the visual display and the sensor assembly are mounted to the bottom surface of the front screen.

9. The handset of claim 5, wherein the sensor assembly further comprises:

a plurality of interconnects, each interconnect electrically connected to a portion of one of the conductive second traces disposed over the bottom surface.

10. The handset of claim 9, wherein the sensor assembly further comprises:

a printed circuit board having a plurality of second bond pads, wherein each of the plurality of interconnects is electrically connected to one of the second bond pads.