Method for reducing the height of optical fingerprint recognition module

Abstract

The present invention provides a method for reducing the height of an optical fingerprint recognition module, wherein the optical fingerprint recognition module comprises a collimating device and an image sensor, and an independent infrared cutoff filter element is removed from the optical fingerprint recognition module to reduce the overall height of the optical fingerprint recognition module, shorten the optical path of incident light, improve imaging quality, and better meet the application requirements of slim portable electronic devices.

Description

Technical Field

[0001] The invention relates to a method for reducing the height of an optical fingerprint recognition module. Background Art

[0002] The current fingerprint recognition solutions include optical technology, silicon technology (capacitive / radio frequency), ultrasonic technology, etc. Among them, optical fingerprint recognition technology has been widely used in portable electronic devices.

[0003] Optical fingerprint recognition technology uses optical imaging equipment based on the principle of total reflection of light (FTIR). Light shines on the glass surface with fingerprints pressed on it, and the reflected light is captured by the image sensor. The amount of reflected light depends on the depth of the fingerprint ridges and valleys pressed on the glass surface, as well as the oil and moisture between the skin and the glass. After the light passes through the glass and hits the center of the valley, it is totally reflected at the interface between the glass and the air, and the light is reflected to the image sensor, while the light directed to the ridge is not totally reflected, but is absorbed by the contact surface between the ridge and the glass or diffusely reflected to other centers, thus forming an image of the fingerprint on the image sensor.

[0004] Figure 1 The structure of an existing optical fingerprint recognition module is shown. The optical fingerprint recognition module includes a collimator 1, an image sensor 2, and an infrared cutoff filter element 3. The reflected light with fingerprint information passes through the collimator 1 and is incident on the photosensitive unit of the image sensor 2. The image sensor 2 absorbs it and converts it into an electrical signal output, thereby forming a fingerprint image. Figure 1 In the illustrated embodiment, the infrared cutoff filter element 3 is disposed between the collimating device 1 and the image sensor 2; in other embodiments not shown, the infrared cutoff filter element 3 may also be disposed above the collimating device 1. Due to the effect of the infrared cutoff filter element 3, the infrared light in the incident light is reduced from entering the image sensor 2 to cause noise crosstalk and image distortion.

[0005] However, with the rapid development of portable electronic devices, the dimensions of portable electronic devices are becoming increasingly thinner, and the available installation space for their components is becoming increasingly limited. Due to the presence of the infrared cutoff filter element 3, it is difficult to further reduce the height of the optical fingerprint recognition module, which not only results in a longer optical path of the incident light, affecting the imaging quality, but also makes it inconvenient to apply it to slim portable electronic devices.

[0006] Therefore, how to adopt a more effective method to reduce the height of the optical fingerprint recognition module to improve the imaging quality and better meet the application requirements of slim portable electronic devices is a technical problem that needs to be solved at present. Summary of the invention

[0007] The purpose of the present invention is to provide a method for reducing the height of an optical fingerprint recognition module, thereby improving imaging quality and better meeting the application requirements of slim portable electronic devices.

[0008] Based on the above considerations, the present invention provides a method for reducing the height of an optical fingerprint recognition module, wherein the optical fingerprint recognition module includes a collimation device and an image sensor, and an independent infrared cutoff filter element is removed from the optical fingerprint recognition module to reduce the overall height of the optical fingerprint recognition module.

[0009] Preferably, the reflected light carrying the fingerprint information is incident on the photosensitive unit of the image sensor through a collimating device, and the material of the collimating device has the property of absorbing infrared light.

[0010] Preferably, the collimating device is made of silicon material with through holes.

[0011] Preferably, the depletion region depth of the PN junction of the photosensitive unit of the image sensor is less than 3 μm, so as to reduce the absorption of infrared light by the photosensitive unit.

[0012] Preferably, the image sensor adopts an N-type substrate to reduce noise crosstalk caused by infrared light.

[0013] Preferably, the surface of the image sensor has an infrared cutoff filter plating layer or an infrared cutoff filter coating.

[0014] Preferably, a planarized dielectric layer is formed on the surface of the image sensor, and an infrared cutoff filter coating layer is formed on the planarized dielectric layer.

[0015] Preferably, the dielectric layer is formed by physical vapor deposition, and the dielectric layer is planarized by chemical mechanical polishing.

[0016] Preferably, the dielectric layer is a silicon dioxide layer.

[0017] Preferably, the infrared cutoff filter coating is formed by spin spraying.

[0018] Preferably, the infrared cutoff filter coating is an organic coating.

[0019] The method of reducing the height of an optical fingerprint recognition module of the present invention comprises a collimating device and an image sensor, and an independent infrared cutoff filter element is removed from the optical fingerprint recognition module to reduce the overall height of the optical fingerprint recognition module, shorten the optical path of the incident light, improve the imaging quality, and better meet the application requirements of slim portable electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Other features, objects and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0021] Figure 1 It is a structural schematic diagram of an optical fingerprint recognition module in the prior art;

[0022] Figure 2 A schematic diagram of the structure of an optical fingerprint recognition module according to an embodiment of the present invention;

[0023] Figure 3 A partial cross-sectional view of an image sensor of an optical fingerprint recognition module according to an embodiment of the present invention;

[0024] Figure 4 is a schematic structural diagram of an optical fingerprint recognition module according to another embodiment of the present invention;

[0025] Figure 5 FIG. 4 is a partial cross-sectional view of an image sensor of an optical fingerprint recognition module according to another embodiment of the present invention.

[0026] In the drawings, the same or similar reference numerals denote the same or similar devices (modules) or steps throughout different drawings. DETAILED DESCRIPTION

[0027] In order to solve the problems in the above-mentioned prior art, the present invention provides a method for reducing the height of an optical fingerprint recognition module, wherein the optical fingerprint recognition module includes a collimation device and an image sensor, and an independent infrared cutoff filter element is removed from the optical fingerprint recognition module to reduce the overall height of the optical fingerprint recognition module, shorten the optical path of the incident light, improve the imaging quality, and better meet the application requirements of slim portable electronic devices.

[0028] In the following specific description of the preferred embodiments, reference will be made to the attached drawings which constitute a part of the present invention. The attached drawings show by way of example specific embodiments that can implement the present invention. The illustrative embodiments are not intended to be exhaustive of all embodiments according to the present invention. It will be appreciated that other embodiments may be utilized, and structural or logical modifications may also be made without departing from the scope of the present invention. Therefore, the following specific description is not restrictive, and the scope of the present invention is limited by the appended claims.

[0029] The present invention provides a method for reducing the height of an optical fingerprint recognition module, such as Figure 2As shown, the optical fingerprint recognition module of the present invention includes a collimation device 101 and an image sensor 102. Different from the prior art, the optical fingerprint recognition module of the present invention removes an independent infrared cutoff filter element, thereby effectively reducing the overall height of the optical fingerprint recognition module. Since the height of the existing infrared cutoff filter element is generally above 110μm, the overall height H' of the optical fingerprint recognition module of the present invention is at least 110μm lower than the overall height H of the optical fingerprint recognition module of the prior art, which greatly shortens the optical path of the incident light, improves the imaging quality, and can better meet the application requirements of slim portable electronic devices.

[0030] In a preferred embodiment of the optical fingerprint recognition module of the present invention, the reflected light carrying the fingerprint information is incident on the photosensitive unit of the image sensor 102 through the collimating device 101. The material of the collimating device 101 has the property of absorbing infrared light, such as a silicon material with through holes. Therefore, most of the infrared light in the incident light can be effectively filtered out, thereby reducing the infrared light in the incident light entering the image sensor 102 to cause noise crosstalk and image distortion.

[0031] like Figure 3 As shown, in this preferred embodiment, the preferred range of the depletion region depth of the PN junction 105 of the photosensitive unit of the image sensor 102 is less than 3μm. Compared with the prior art, in the optical fingerprint recognition module of the present invention, the depletion region of the PN junction 105 of the photosensitive unit of the image sensor 102 is closer to the surface of the image sensor 102 to reduce the absorption of infrared light by the photosensitive unit. Further preferably, the image sensor 102 adopts an N-type substrate 106 to reduce noise crosstalk and image distortion caused by infrared light. The N-type substrate 106 may include an N-type doped substrate and an N-type doped epitaxial layer epitaxially grown on the substrate. Of course, multiple epitaxial layers may also be formed on a P-type doped substrate, and the topmost epitaxial layer is an N-type doped epitaxial layer.

[0032] Figure 4 , Figure 5 The structure of an optical fingerprint recognition module according to another embodiment of the present invention is shown, and the optical fingerprint recognition module includes a collimating device 201 and an image sensor 202, wherein the surface of the image sensor 202 has an infrared cutoff filter plating layer or an infrared cutoff filter coating 203 to filter infrared light in the incident light, thereby reducing the infrared light in the incident light entering the image sensor 202 to cause noise crosstalk and image distortion. In addition, since the independent infrared cutoff filter element is removed from the optical fingerprint recognition module of the present invention, the overall height of the optical fingerprint recognition module is effectively reduced, the optical path of the incident light is shortened, the imaging quality is improved, and the application requirements of slim portable electronic devices are better met.

[0033] Preferably, a dielectric layer 204 is formed on the surface of the image sensor 202 by physical vapor deposition (PVD), the dielectric layer 204 is planarized by chemical mechanical polishing (CMP), and then an infrared cutoff filter coating 203 is formed on the planarized dielectric layer 204. The dielectric layer 204 may be a silicon dioxide layer.

[0034] Preferably, the infrared cut-off filter coating 203 is formed on the surface of the image sensor 202 by spin-spraying. The infrared cut-off filter coating 203 is an organic coating.

[0035] The present invention discloses a method for reducing the height of an optical fingerprint recognition module, wherein the optical fingerprint recognition module comprises a collimating device and an image sensor, and an independent infrared cutoff filter element is removed from the optical fingerprint recognition module to reduce the overall height of the optical fingerprint recognition module, shorten the optical path of incident light, improve imaging quality, and better meet the application requirements of slim portable electronic devices.

[0036] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, in any case, the embodiments should be considered exemplary and non-restrictive. Furthermore, it is apparent that the term "comprising" does not exclude other elements and steps, and the wording "a" does not exclude the plural. Multiple elements stated in a device claim may also be implemented by one element. The words first, second, etc. are used to indicate names and do not indicate any particular order.

Claims

1. A method for reducing the height of an optical fingerprint recognition module, characterized in that: The optical fingerprint recognition module includes a collimator and an image sensor. The reflected light with fingerprint information is incident on the photosensitive unit of the image sensor through the collimating device, and most of the infrared light in the incident light is filtered out by utilizing the infrared light absorption property of the material of the collimating device, thereby reducing the infrared light in the incident light from entering the image sensor; The photosensitive unit of the image sensor includes an N-type substrate and a PN junction formed in the N-type substrate, and the depletion region depth of the PN junction is less than 3 μm, so that the depletion region of the PN junction is closer to the surface of the image sensor, thereby reducing the absorption of infrared light by the photosensitive unit; The independent infrared cutoff filter element is removed from the optical fingerprint recognition module to reduce the overall height of the optical fingerprint recognition module.

2. The method for reducing the height of an optical fingerprint recognition module according to claim 1, characterized in that: The alignment device is made of silicon material with through holes.

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