Optical fingerprint sensor with forgery detection and associated methods

Abstract

An optical fingerprint sensor with forgery detection and a method for detecting a forged fingerprint detected using the optical fingerprint sensor are provided. The optical fingerprint sensor includes: a plurality of lenses; an image sensor including a pixel array that includes a plurality of first photodiodes and a plurality of second photodiodes; and at least one perforated baffle layer having a plurality of aperture diaphragms, wherein each second photodiode is configured to detect light that has passed through the lens and at least one aperture diaphragm not aligned with the lens along the optical axis. The method for detecting a forged fingerprint detected using the optical fingerprint sensor includes: detecting large-angle light incident on a plurality of anti-forgery photodiodes, wherein the plurality of anti-forgery photodiodes are interleaved with a plurality of imaging photodiodes; determining at least partially an angular distribution of the light based on the large-angle light; and detecting a forged fingerprint at least partially based on the angular distribution of the light.

Description

Technical Field

[0001] The present invention relates to an optical fingerprint sensor with forgery detection and a method for detecting a forged fingerprint detected by the optical fingerprint sensor. Background Art

[0002] Fingerprint sensing is becoming an increasingly common tool for (a) authorizing access to electronic devices such as smartphones, (b) accessing confidential electronic records, and (c) electronic transactions such as financial transactions over the Internet. Fingerprint sensing meets the market demand for an authentication mechanism that eliminates the need to enter (and remember) passwords and also eliminates the need to keep track of multiple different passwords associated with different devices and / or accounts. Fingerprint sensing is a well-established form of biometric identification, and optical fingerprint sensors have been used for many years, for example, by law enforcement agencies.

[0003] Several different types of fingerprint sensors have been designed for smartphones and other mobile devices. Each of these types of fingerprint sensors images a finger to obtain a fingerprint. A camera-based fingerprint scanner uses an imaging lens and an image sensor to capture an image of the fingerprint. A collimator-based fingerprint scanner utilizes an array of lenses aligned above the image sensor to sense the fingerprint, where a collimator is added above the image sensor. The collimator helps map light from a specific area of the fingerprint sample to be detected by a corresponding area of the image sensor by forming a channel through which the light must propagate to reach the image sensor.

[0004] One problem with fingerprint image sensing is the possibility of creating a false or forged (spoof) fingerprint that deceives the fingerprint sensor in order to gain access to the device. Forged fingerprints can be created in a variety of ways, including printing a fingerprint image on paper and forming a molded object that reproduces the desired fingerprint pattern. If created with a high enough resolution and fidelity to the real fingerprint, these forgery methods can deceive the fingerprint sensor and allow unauthorized access to the device and account. Image sensor-based fingerprint sensors have difficulty distinguishing a real fingerprint from a forged fingerprint, making the fingerprint sensor a less reliable authentication method. Summary of the Invention

[0005] Collimator-based fingerprint sensors narrow the acceptable paths through which electromagnetic energy can travel between a fingerprint sample and an image sensor. In some cases, they do this by forming a channel or cone that transmits electromagnetic energy but blocks incident electromagnetic energy whose angles and positions are not within this intended path. This allows electromagnetic energy from a particular region of the fingerprint sample to reach only the region of the image sensor that is intended to image that region of the fingerprint and reduces the electromagnetic energy from any other region of the fingerprint sample from reaching that region of the image sensor. This can be achieved in several ways, including an array of perforated baffle layers located between a lens array and the image sensor. Each perforated baffle layer has holes aligned above each pixel of the image sensor, and the width of each hole is configured to transmit only a narrow cone of acceptable angles of incident electromagnetic energy. This design has been used to help improve image quality and the performance of under-screen fingerprint sensors. The terms "light" and "electromagnetic energy" are used interchangeably in this document. The electromagnetic energy in this document refers to electromagnetic energy with wavelengths between 0.4 and 2 microns.

[0006] There are techniques for overcoming fingerprint sensors and gaining unauthorized access to devices and information, including creating fake fingerprints. Fake fingerprints include printed images of fingerprints and molded objects that reproduce the three-dimensional structure of a target fingerprint sample. Current techniques for detecting fake fingerprints mainly rely on examining real and fake fingerprints and using algorithms to detect differences in the images of individual fingerprints generated by fingerprint sensors. Since fake fingerprints are made with higher resolution and fidelity, the images they produce on fingerprint sensors become difficult to distinguish from real fingerprint samples. Using only images is a limitation for forgery detection and makes fingerprint sensors vulnerable to high-quality, high-resolution fake fingerprint attacks.

[0007] When a printed or molded fake fingerprint sample is used on a fingerprint sensor, the material properties of the sample play a role in how electromagnetic energy interacts between the sample and the fingerprint sensor. This can be exploited to increase forgery detection. Electromagnetic energy scatters from the sample at a range of outgoing angles. This distribution of scattered electromagnetic energy depends on the material being sampled. A human finger, a printed image, and a molded object can produce the same image on an image sensor, but they produce different angular distributions of reflected and scattered electromagnetic energy. A fingerprint sensor that can detect this angular distribution has a stronger ability to detect forgeries than a sensor that only records the image of the sample.

[0008] By leveraging the physical design of a perforated baffle layer collimator available for an optical fingerprint sensor, it is possible to detect the angular distribution of electromagnetic energy. By design, electromagnetic energy with a small angle of incidence, that is, electromagnetic energy with a small angular divergence relative to the surface normal of the image sensor, is transmitted through the collimator to a pixel of the image sensor that corresponds to the physical location on the fingerprint sample from which the electromagnetic energy originated. Here, these pixels of the image sensor are referred to as imaging pixels. Typically, the imaging pixels are aligned with at least one hole and a given lens along a line that is generally parallel to the surface normal of the image sensor. Electromagnetic energy traveling towards the fingerprint sensor at a large enough angle of incidence can pass through the given lens and then through a hole that is not aligned with that lens, after which it can impinge on the image sensor between adjacent imaging pixels. Such light is generally not useful for imaging the fingerprint sample and is thus ignored. In the embodiments described herein, electromagnetic energy with a large angle of incidence, namely so-called large-angle light, is detected and used to measure the authenticity of the fingerprint sample. By detecting the large-angle light, the fingerprint sensor records additional information about the sample that can be used to confirm whether the sample is a real finger or a forged finger.

[0009] When an algorithm is employed to detect forged fingerprints, the additional information provided by detecting the large-angle light can also be input into the algorithm to improve the accuracy of electronic forgery detection. This is particularly valuable for the use of machine learning algorithms that can automatically compare the differences between training sets. The variations in the angular distribution caused by the material properties of the sample will be available for the machine learning algorithm, which will be able to identify forged fingerprints based on a combination of image details and angular distribution.

[0010] In one aspect, there is provided an optical fingerprint sensor with forgery detection. The optical fingerprint sensor includes: a plurality of lenses L m＝0 、L1、……L J-1 , which have a lens pitch along a horizontal direction orthogonal to the lens axis of lens L0, and each lens has a certain width; an image sensor, including a pixel array, the pixel array including a plurality of first photodiodes I m＝0 、I1、……I J-1 , the plurality of first photodiodes having a first photodiode pitch equal to the lens pitch in the horizontal direction, and the center of the photosensitive surface of each first photodiode I m and the optical center of each lens L m forming a plurality of optical axes O m＝0 、O1、……O J-1 in the optical axes O m that are perpendicular to the photosensitive surface of the pixel array; at least one perforated baffle layer located between the image sensor and the plurality of lenses, each of the at least one perforated baffle layer being at a corresponding height z kthere, and each having a corresponding plurality of aperture diaphragms A m＝0 , A1, …… A J-1 , each aperture diaphragm A m is centered with respect to the optical axis O m ; and a plurality of second photodiodes S included in the pixel array m＝0 , S1, …… S K-1 , the plurality of second photodiodes being intercalated with the plurality of first photodiodes such that the second photodiode S m is horizontally located between the first photodiode I m and the first photodiode I m+1 , wherein each second photodiode is configured to detect electromagnetic energy that has passed through the lens L m and at least one aperture diaphragm A that is not aligned with L m along the optical axis O m . x≠m

[0011] In some embodiments, between adjacent aperture diaphragms of the plurality of aperture diaphragms, each of the at least one perforated baffle layer is opaque to visible electromagnetic energy.

[0012] In some embodiments, the at least one aperture diaphragm A m is aligned along the optical axis O m , having a corresponding width such that at least one aperture diaphragm A m collectively transmits electromagnetic energy falling within an acceptance angle, the acceptance angle being measured as the angular divergence of rays incident on the center of the photosensitive surface of the first photodiode I m with respect to the optical axis O m .

[0013] In some embodiments, each aperture diaphragm of the plurality of aperture diaphragms on each of the at least one perforated baffle layer is circular in a horizontal plane.

[0014] In some embodiments, one of the at least one perforated baffle layers has a distance z equal to or less than 10 micrometers k , and has a plurality of second aperture diaphragms SA m＝0 , SA1, …… SA K-1 , each second photodiode S m having a second aperture diaphragm SA m , each second aperture diaphragm SA m being centered with respect to the center of the photosensitive surface of each second photodiode S m in a direction parallel to the optical axis O m .

[0015] In some embodiments, the at least one perforated baffle layer includes four baffle layers.

[0016] In some embodiments, the number J of the first photodiodes is equal to the number K of the second photodiodes.

[0017] In some embodiments, the plurality of second photodiodes have a second photodiode pitch equal to the lens pitch in the horizontal direction.

[0018] In another aspect, a method for detecting a forged fingerprint detected by an optical fingerprint sensor is provided. The method includes: detecting large-angle light incident on a plurality of anti-forgery photodiodes of a pixel array, the large-angle light being electromagnetic energy incident on a lens above the pixel array, and having an incident angle diverging by more than 5 degrees with respect to the optical axis of the lens; wherein the plurality of anti-forgery photodiodes are interleaved with a plurality of imaging photodiodes such that each anti-forgery photodiode among the plurality of anti-forgery photodiodes is located between adjacent imaging photodiodes among the plurality of imaging photodiodes; determining an angular distribution of the electromagnetic energy at least in part based on the detected large-angle light; and detecting a forged fingerprint at least in part based on the angular distribution of the electromagnetic energy.

[0019] In some embodiments, the plurality of anti-forgery photodiodes and the plurality of imaging photodiodes are formed in a single pixel array.

[0020] In some embodiments, the method further includes detecting small-angle light incident on the plurality of imaging photodiodes of the pixel array, the small-angle light being incident electromagnetic energy incident on a lens above the pixel array with an incident angle diverging by less than 5 degrees with respect to the optical axis of the lens.

[0021] In some embodiments, the determining step further includes determining the angular distribution of the electromagnetic energy at least in part based on the detected small-angle light.

[0022] In some embodiments, the method further includes preventing light at a larger angle from irradiating the plurality of imaging photodiodes with a plurality of perforated baffle layers.

[0023] In some embodiments, the method further includes guiding small-angle light with a plurality of lenses, each lens guiding the small-angle light to one of the plurality of imaging photodiodes.

[0024] In some embodiments, the method further includes illuminating a fingerprint sample with electromagnetic energy from a display, the plurality of anti-forgery photodiodes and the plurality of imaging photodiodes being located under the glass of the display.

[0025] In some embodiments, the method further includes illuminating the fingerprint sample with a non-uniform illumination pattern.

[0026] In some embodiments, the method further includes applying at least one matching algorithm to the detection of large-angle light.

[0027] In some embodiments, the at least one matching algorithm includes a machine learning algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1A and 1B FIG. illustrates a cross-sectional side view of an optical fingerprint sensor that utilizes a plurality of second photodiodes to detect light to identify a forged fingerprint.

[0029] Figure 2 is according to an embodiment of Figure 1A and 1B a schematic cross-sectional view of a portion of an optical fingerprint sensor.

[0030] Figure 3 is according to an embodiment of Figure 1A and 1B an optical fingerprint sensor having a fourth perforated baffle layer at a position less than 10 micrometers above the photosensitive surface of the image sensor.

[0031] Figure 4 FIG. is a flowchart illustrating a method of detecting a forged fingerprint using a plurality of anti-forgery pixels, which in an embodiment can be combined with Figure 1A , Figure 1B , Figure 2 or Figure 3 an optical fingerprint sensor for use.

[0032] Figure 5 FIG. illustrates a finger scanned by an optical fingerprint sensor according to an embodiment mounted under the screen of a mobile device Figure 1A and 1B .

[0033] Figure 6A FIG. illustrates a cross-sectional top view of a pixel array according to an embodiment, which is an example of the pixel array of Figure 3 .

[0034] Figure 6B FIG. illustrates a top view of a perforated baffle layer according to an embodiment, which is an example of the perforated baffle layer of Figure 3 .

[0035] Figure 7A FIG. illustrates a cross-sectional top view of a pixel array according to an embodiment, which is an example of the pixel array of Figure 3An example of a pixel array.

[0036] Figure 7B FIG. shows a top view of a perforated baffle layer according to an embodiment, the perforated baffle layer being Figure 3 An example of a perforated baffle layer. Detailed Description

[0037] As used herein, the phrase "an example" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present invention. Thus, the appearances of the phrases "in an example" or "in an embodiment" in various places in this specification are not necessarily all referring to the same example. Further, in one or more examples, the particular features, structures, or characteristics may be combined in any suitable manner.

[0038] For ease of description, spatially relative terms, such as "below", "beneath", "under", "lower", "above", "upper", etc., may be used herein to describe the relationship of one element or feature to another (one or more) element or feature shown in the figures. It should be understood that, in addition to the orientation depicted in the figures, the spatially relative terms are intended to encompass different orientations of the device in use or operation. For example, if the device in the figures is turned over, an element described as "below" or "beneath" or "under" another element or feature would then be oriented "above" the other element or feature. Thus, the terms "beneath" and "under" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein are to be interpreted accordingly. Further, it should be understood that when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or there can be one or more intervening layers.

[0039] The term semiconductor substrate may refer to a substrate formed using semiconductors such as silicon, silicon-germanium, germanium, gallium arsenide, and combinations thereof. The term semiconductor substrate may also refer to a substrate formed of one or more semiconductors that has undergone previous process steps for forming regions and / or junctions in the substrate. A semiconductor substrate may also include various features such as doped and undoped semiconductors, silicon epitaxial layers, and other semiconductor structures formed on the substrate.

[0040] Throughout the specification, several technical terms are used. These terms will take on their ordinary meaning in the art to which they pertain, unless specifically defined herein or the context in which they are used clearly indicates otherwise. It should be noted that in this document, element names and symbols may be used interchangeably (e.g., Si and silicon); however, both have exactly the same meaning.

[0041] Figure 1A and 1BFIG. shows a cross-sectional side view of an optical fingerprint sensor 100 that utilizes a plurality of second photodiodes 118 to detect electromagnetic energy to identify forged fingerprints. The second photodiodes 118 are also referred to herein as anti-forgery photodiodes. Figure 1A and 1B The cross-section shown is parallel to the plane formed by the orthogonal axes 198X and 198Z, hereinafter referred to as the x-z plane, and both axes 198X and 198Z are orthogonal to axis 198Y. The plane formed by the orthogonal axes 198X and 198Y (hereinafter referred to as the x-y plane), and planes parallel to the x-y plane are referred to as horizontal planes. Unless otherwise specified, the height of an object herein refers to the extent of the object along axis 198Z. In this document, references to axis x, y, or z refer to axes 198X, 198Y, and 198Z, respectively. Additionally, in this document, width refers to the extent of an object along the x-axis, depth refers to the extent of an object along the y-axis, thickness (or thinness) refers to the extent of an object along the z-axis, and vertical refers to the direction along the z-axis. Further, in this document, above refers to a relative position that is a distance away in the positive direction along axis 198Z, and below refers to a relative position that is a distance away in the negative direction along axis 198Z. Figure 1A and 1B are best viewed together.

[0042] The optical fingerprint sensor 100 includes a plurality of lenses 170, an image sensor 110, and at least one perforated baffle layer 160. The plurality of lenses 170 includes J lenses, 170(m = 0), 170(1), 170(2), …… 170(J - 1). Each lens 170 has a lens width 172, and the plurality of lenses 170 has a lens pitch 173 along the horizontal direction. In Figure 1A and Figure 1B the horizontal direction, the lens width 172 and the lens pitch 173 are equal, but the lens width 172 can be less than the lens pitch 173 without departing from the scope of the present invention. The lens 170(0) has a lens axis 174 parallel to axis 198Z. The plurality of lenses 170 are located above the photosensitive surface 116 of the image sensor 110. The image sensor 110 includes a pixel array 112, and the pixel array 112 includes a plurality of first photodiodes 114. The first photodiodes 114 include J photodiodes, 114(m = 0), 114(1), 114(2), …… 114(J - 1). The plurality of first photodiodes 114 have a first photodiode pitch 124, in Figure 1A and 1BIn the illustrated embodiment, in the horizontal direction, the first photodiode pitch 124 is equal to the lens pitch 173. A line connecting the optical center of each lens 170 to the center 122 of the photosensitive surface 117 of each first photodiode 114 forms one of the plurality of optical axes 176. In an embodiment, each of the plurality of optical axes 176 is perpendicular to the photosensitive surface 116, and each lens 170 has a lens axis 174 that is aligned with the optical axis 176 of the corresponding first photodiode 114. In an embodiment, the optical axis 176(m) of each lens 170(m) depends on the horizontal position of the lens 170(m). In a so-called "fan-out" design, the lens 170(m) aligned with the photodiode 114(m) near the center of the pixel array 112 has an optical axis 176(m) that is substantially perpendicular to the photosensitive surface 116, but the lens 170(n) aligned with the photodiode 114(n) near the edge of the pixel array 112 has an optical axis 176(n) that is angled with respect to the surface normal of the photosensitive surface 116. In Figure 1A and 1B In the illustrated embodiment, the distance between each lens 170 and the corresponding first photodiode 114 is configured together with the focal length of the lens 170 such that collimated electromagnetic energy incident on the lens 170 from the positive z direction and parallel to the optical axis 176 will be focused onto the center 122 of the first photodiode 114. The plurality of first photodiodes 114 record light reflected from a fingerprint sample, which is then used to generate a fingerprint image. In an embodiment, each first photodiode 114 is a sub-array of a pixel array 112 that includes more than one photodiode.

[0043] Each perforated baffle layer 160 is located between the plurality of lenses 170 and the image sensor 110. Each of at least one perforated baffle layer 160 is located at a corresponding height 162 above the pixel array 112. Figure 1A and 1B The illustrated embodiment includes three perforated baffle layers 160A, 160B, and 160C, which are at heights 162A, 162B, and 162C above the pixel array 112, respectively. The optical fingerprint sensor 100 may have more or fewer perforated baffle layers 160 without departing from the scope of the invention. The relative spacing and height of each perforated baffle layer 160 above the pixel array 112 are for illustrative purposes and do not imply a limitation on the possible configurations of the perforated baffle layers 160 within the optical fingerprint sensor 100.

[0044] Each perforated baffle layer 160 has a corresponding plurality of aperture diaphragms 164, which includes J aperture diaphragms, 164A(m = 0), 164A(1), 164A(2), …… 164A(J - 1). Each aperture diaphragm 164 is centered along a corresponding optical axis 176 with a given first photodiode 114. For example, the aperture diaphragms 164A(0), 164A(1), and 164A(2) of the perforated baffle layer 160A are centered with the corresponding optical axes 176(0), 176(1), and 176(2). For clarity of illustration, some of the optical axes are not shown. In Figure 1A and 1B In the illustrated embodiment, the aperture diaphragms 164A(1), 164B(1), and 164C(1) are centered with the optical axis 176(1) (not shown for clarity of illustration).

[0045] The pixel array 112 includes a plurality of second photodiodes 118, which includes k photodiodes, 118(k = 0), 118(1), 118(2), …… 118(k - 1). The plurality of second photodiodes 118 are interleaved with the plurality of first photodiodes 114 such that the second photodiode 118(k) is horizontally located between the first photodiode 114(m) and the first photodiode 114(m + 1). Each second photodiode 118 is configured to detect electromagnetic energy that has passed through the lens L m and not along the optical axis O m aligned with L m and at least one aperture diaphragm A x≠m This is illustrated in Figure 1B . The electromagnetic energy ray 190 passes through the lens 170(m = 0) and passes through the aperture diaphragm 164C(m = 1). Another electromagnetic energy ray 192 passes through the lens 170(m = 0) and passes through the aperture diaphragms 164A(m = 1), 164B(m = 1), and 164C(m = 2). Both the electromagnetic energy rays 190 and 192 are detected by the second photodiodes (118(1) and 118(2) respectively) among the plurality of second photodiodes 118. In one embodiment, each second photodiode 118 is a sub - array of the pixel array 112 that includes more than one photodiode.

[0046] The electromagnetic energy detected by the plurality of second photodiodes 118 enters the optical fingerprint sensor 100 at a large incident angle with respect to the optical axis 176. This large - angle electromagnetic energy is here quantified as the incident electromagnetic energy incident on the lens 170(m), whose incident angle diverges by more than 5 degrees with respect to the optical axis 176(m).

[0047] In one embodiment, each of the perforated baffle layers 160 is opaque to visible electromagnetic energy (e.g., light) incident on the perforated baffle layer 160 between adjacent aperture diaphragms of the plurality of aperture diaphragms 164. This reduces the number of paths that the incident electromagnetic energy can take and still be incident on the plurality of first photodiodes 114. As previously discussed, each perforated baffle layer 160 helps the optical fingerprint sensor 100 record an image of a fingerprint sample.

[0048] Figure 2 is a schematic cross-sectional view of a portion of the optical fingerprint sensor 100, which includes first photodiodes 114(m), centers 122(m) of photosensitive surfaces 117, along with lenses 170(m), optical axes 176(m), and sections of at least one perforated baffle layer 160A, 160B, and 160C respectively including aperture diaphragms 164A(m), 164B(m), and 164C(m).

[0049] Figure 2 Each of the aperture diaphragms 164A(m), 164B(m), and 164C(m) shown is centered with respect to the optical axis 176(m). The widths of each of the aperture diaphragms 164A(m), 164B(m), and 164C(m) are such that they together transmit electromagnetic energy incident on the lens 170(m) that falls within an acceptance angle 178, the acceptance angle 178 being measured as the angular divergence of rays incident on the lens 170(m) with respect to the optical axis 176(m). When an electromagnetic energy ray 194 with an incident angle greater than the acceptance angle 178 is incident on the perforated baffle layer 160C, it is prevented from illuminating the first photodiode 114(m). In an embodiment, each aperture diaphragm of the plurality of aperture diaphragms 164 on each of the at least one perforated baffle layer is circular in a horizontal plane.

[0050] Figure 3 is a schematic cross-sectional view of an optical fingerprint sensor 300, which is an example of the optical fingerprint sensor 100 of FIG. 1. In Figure 3 the embodiment shown, at least one perforated baffle layer 360 includes a fourth perforated baffle layer 360D, which is at a distance 362D less than 10 microns above the photosensitive surface 316 of the image sensor 310. The perforated baffle layer 360D has a plurality of aperture diaphragms 364, which have J aperture diaphragms 364D(0), 364D(1), …… 364D(J - 1) (not shown), similar to Figure 1A 、 Figure 1B and Figure 2Those shown in. The perforated baffle layer 360D further includes a plurality of second aperture diaphragms 368, which have K aperture diaphragms 368D(0), 368D(1),..., 368D(K - 1), and each of the plurality of second photodiodes 318 has a second aperture diaphragm 368. As Figure 3 shown, each second aperture diaphragm 368 is centered with respect to the center of the photosensitive surface (not shown) of the corresponding second photodiode 318 in a direction parallel to the optical axis 374. The plurality of second aperture diaphragms 368 on the perforated baffle layer 360D allow the plurality of second photodiodes 318 to detect electromagnetic energy while further restricting the available paths that allow the plurality of first photodiodes 314 to detect electromagnetic energy. The distance 362D can vary depending on the manufacturing processes used and the tolerances associated with those processes.

[0051] In one embodiment, the number of first photodiodes 314 is equal to the number of second photodiodes 318. Thus, the number of lenses 370, the number of aperture diaphragms on each perforated baffle layer 360, and the number of second aperture diaphragms 368 are also equal to each other and equal to the number of first photodiodes 314 and the number of second photodiodes 318. More succinctly, the above counts J and K are equal. However, this need not be the case. The relative numbers of first photodiodes 314 and second photodiodes 318 can vary without departing from the scope of the invention.

[0052] Figure 3 illustrates an embodiment in which the plurality of second photodiodes 318 have a second photodiode pitch 320 that is equal to the first photodiode pitch 324 and the lens pitch 373 in the horizontal direction. However, the first photodiode pitch 324 and the second photodiode pitch 320 need not be equal, and embodiments can have a second photodiode pitch 320 that is larger or smaller relative to the first photodiode pitch 324 without departing from the scope of the invention. In an embodiment, each second photodiode 318 is wider and / or has a greater depth than each first photodiode 314. The relative widths and depths of each first photodiode 314 and each second photodiode 318 can vary without departing from the scope of the invention.

[0053] Figure 4 is a flowchart of a method 400 for detecting a forged fingerprint using a plurality of anti - forgery pixels. The method 400 can be performed by Figure 1A , Figure 1B , Figure 2 and Figure 3implemented by any one of the optical fingerprint sensors 100 or 300. The method 400 includes blocks 410, 460, and 470. In an embodiment, the method 400 further includes at least one of blocks 402, 404, 430, 432, 434, 436, and 472.

[0054] In block 410, large-angle light incident on a plurality of anti-forgery photodiodes of a pixel array is detected. The large-angle electromagnetic energy is here quantified as incident electromagnetic energy that is incident on a lens at an incident angle diverging by more than 5 degrees with respect to the optical axis of the lens. The plurality of anti-forgery photodiodes are interleaved with a plurality of imaging photodiodes such that each anti-forgery photodiode of the plurality of anti-forgery photodiodes is located between adjacent imaging photodiodes of the plurality of imaging photodiodes. In an example of block 410, electromagnetic energy rays 190 and 192 are detected by second photodiodes (118(1) and 118(2) respectively) among the plurality of second photodiodes 118.

[0055] In block 460, an angular distribution of electromagnetic energy is determined at least in part based on the detected large-angle light. In one example of block 460, the angular distribution of electromagnetic energy is determined at least in part by electromagnetic energy rays 190 and 192 detected by the plurality of second photodiodes 118.

[0056] In block 470, a forged fingerprint is detected at least in part based on the angular distribution of electromagnetic energy.

[0057] In certain embodiments, the method 400 includes Figure 4 one or more additional blocks of the flowchart. In block 402, a fingerprint sample is illuminated with electromagnetic energy from a display, and the plurality of anti-forgery photodiodes and the plurality of imaging photodiodes are positioned under the glass of the display. An example of a device implementing block 402 is illustrated in Figure 5 as described below. In block 404, the fingerprint sample is illuminated with a non-uniform illumination pattern, which helps to determine the angular distribution of electromagnetic energy in block 460.

[0058] In block 430, small-angle light incident on a plurality of imaging photodiodes of a pixel array is detected. The small-angle electromagnetic energy is here quantified as incident electromagnetic energy that is incident on a lens at an incident angle diverging by less than 5 degrees with respect to the optical axis of the lens. In an example of block 430, the electromagnetic energy is transmitted through lens 170(0), then passes through aperture stops 164A(0), 164B(0), and 164C(0), and is then detected by first photodiode 114(0).

[0059] The block 430 may include a block 432, in which the angular distribution of the electromagnetic energy is determined at least in part based on the detected small-angle light. In one example of block 432, the angular distribution of the electromagnetic energy is at least in part based on (i) the electromagnetic energy that propagates through the lens 170(0) and then passes through the aperture stops 164A(0), 164B(0), and 164C(0) and is then detected by the first photodiode 114(0), and (ii) the Figure 1B electromagnetic energy 190 and 192 detected by the second photodiodes (118(1) and 118(2) respectively) of the plurality of second photodiodes 118.

[0060] In block 434, at least one perforated baffle layer is used to prevent large-angle light from irradiating the plurality of imaging photodiodes. In an example of block 434, the electromagnetic energy ray 194 is blocked by the perforated baffle layer 160A from reaching the first photodiode 114(m), as Figure 2 shown.

[0061] In block 436, the small-angle light is guided by a plurality of lenses, where the lenses guide the small-angle light toward one of the plurality of imaging photodiodes. In an example of block 436, the electromagnetic energy is transmitted through the lens 170(0), then passes through the aperture stops 164A(0), 164B(0), and 164C(0), and is then detected by the first photodiode 114(0), as Figure 1A shown.

[0062] In block 472, at least one matching algorithm is applied to the detected large-angle light. In an embodiment, at least one matching algorithm includes a machine learning algorithm.

[0063] Figure 5 An optical fingerprint sensor 100 installed under a display in a mobile device 502 is shown. The display includes a cover glass 504 and a light-emitting layer 506. The optical fingerprint sensor 100 is scanning a fingerprint sample 508, and the optical fingerprint sensor 100 is shown in more detail in the inset on the right. In an embodiment, the mobile device 502 may be a mobile phone, a tablet computer, or other electronic device having a display. In an embodiment, the light-emitting layer 506 illuminates the fingerprint sample 508 with a non-uniform illumination pattern that includes one or more of the following: (i) alternating bright and dark lines, (ii) square illumination spots, and (iii) illuminating only a portion of the fingerprint sample, such as only illuminating one edge of the fingerprint sample. The non-uniform illumination pattern helps to determine the angular distribution emitted by the fingerprint sample 508.

[0064] The electronic device 502 includes at least one processor 552 communicatively coupled to a display, an optical fingerprint sensor 100 / 300, and a memory 554 storing an application 556 (e.g., software / firmware), the application 556 including machine-readable instructions that, when executed by the processor 552, control the display and the optical fingerprint sensor 100 / 300 to capture an image of a finger 508 touching a cover lens 504 adjacent to the optical fingerprint sensor 100 / 300 to detect when a fingerprint sample 508 is a forged fingerprint.

[0065] Figure 6A is a cross-sectional top view of a pixel array 612, the pixel array 612 being Figure 3 an example of pixels 312 of an optical fingerprint sensor 300. Figure 6B Illustrated is a top view of a perforated baffle layer 660D, the perforated baffle layer 660D being Figure 3 an example of a perforated baffle layer 360D of an optical fingerprint scanner 300. Figure 6A The cross-section shown and Figure 6B the top view shown are parallel to the x-y plane formed by orthogonal axes 198X and 198Y. Figure 6A and 6B are best viewed together.

[0066] The pixel array 612 includes a plurality of first photodiodes 614 (shown hatched) and a plurality of second photodiodes 618 (shown dotted). The perforated baffle layer 660D includes a plurality of first aperture diaphragms 664D (circular apertures), each first photodiode 614 having one first aperture diaphragm 664D. The perforated baffle layer 660D further includes a plurality of second aperture diaphragms 668D (rectangular apertures), each second photodiode 618 having one second aperture diaphragm 668D. The perforated baffle layer 660D is designed to be located above the pixel array 612 such that (a) the center of each first aperture diaphragm 664D is centered with respect to the center of the photosensitive surface (not shown) of the corresponding first photodiode 614 in a direction parallel to the optical axis 676 of each first photodiode 614, and (b) the center of each second aperture diaphragm 668D is centered with respect to the center of the photosensitive surface (not shown) of the corresponding second photodiode 618. The plurality of first aperture diaphragms 664D on the perforated baffle layer 660D allow the plurality of first photodiodes 614 to detect light (not shown) at small angles, while the plurality of second aperture diaphragms 668D on the perforated baffle layer 660D allow the plurality of second photodiodes 618 to detect light (not shown) at large angles. Due to the relative amounts of small-angle light reaching each first photodiode 614 and large-angle light reaching each second photodiode 618, the area of each second aperture diaphragm 668D is greater than the area of each first aperture diaphragm 664D. In Figure 6AIn the illustrated embodiment, the relative areas of each first aperture stop 664D and each second aperture stop 668D are selected such that during a single exposure of a fingerprint sample (not shown), the detected light intensity of each first photodiode 614 is 20 times greater than the detected light intensity of each second photodiode 618. This corresponds to a ratio of the area of each second aperture stop 668D to the area of each first aperture stop 664D of 5:1. This ratio can be greater or smaller without departing from the scope of the invention. In Figure 6A and 6B the illustrated embodiment, the unfilled squares (shown filled white) of the pixel array 612 are unused photodiodes. This reduces the potential resolution of the pixel array 612, but advantageously reduces crosstalk between the photodiodes, which reduces noise.

[0067] The pixel array 612 is Figure 3 an example of the pixel array 312 of Figure 3 and includes only certain components from the description of Figure 3 . The pixel array 612, the plurality of first photodiodes 614, the plurality of second photodiodes 618, the perforated baffle layer 660D, the plurality of first aperture stops 664D, and the plurality of second aperture stops 668D are respectively

[0068] Figure 7A an example of the pixel array 312, the plurality of first photodiodes 314, the plurality of second photodiodes 318, the perforated baffle layer 360D, the plurality of first aperture stops 364D, and the plurality of second aperture stops 368D of Figure 3 , and the description of each corresponding element applies between the two figures. Figure 7B illustrates a top view of the perforated baffle layer 760D, which is Figure 3 an example of the perforated baffle layer 360D of the optical fingerprint scanner 300 of Figure 7A The illustrated cross-section and Figure 7B the illustrated top view are parallel to the x-y plane formed by the orthogonal axes 198X and 198Y. Figure 7A and 7B are best viewed together.

[0069] The pixel array 712 includes a plurality of first photodiodes 714 (shown filled with slashes) and a plurality of second photodiodes 718 (shown filled with dots). The perforated baffle layer 760D includes a plurality of first aperture diaphragms 764D (circular apertures), with each first photodiode 714 having one first aperture diaphragm 764D. The perforated baffle layer 760D further includes a plurality of second aperture diaphragms 768D (rectangular apertures), with each second photodiode 718 having one second aperture diaphragm 768D. The perforated baffle layer 760D is designed to be located above the pixel array 712 such that (a) the center of each first aperture diaphragm 764D is centered with respect to the center of the photosensitive surface (not shown) of the corresponding first photodiode 714 in a direction parallel to the optical axis 776 of each first photodiode 714, and (b) the center of each second aperture diaphragm 768D is centered with respect to the center of the photosensitive surface (not shown) of the corresponding second photodiode. The plurality of first aperture diaphragms 764D on the perforated baffle layer 760D allow the plurality of first photodiodes 714 to detect light at a small angle (not shown), while the plurality of second aperture diaphragms 768D on the perforated baffle layer 760D allow the plurality of second photodiodes 718 to detect light at a large angle (not shown). Due to the relative amounts of small-angle light reaching each first photodiode 714 and large-angle light reaching each second photodiode 718, the area of each second aperture diaphragm 768D is larger than the area of each first aperture diaphragm 764D. In Figure 7A the illustrated embodiment, the relative areas of each first aperture diaphragm 764D and each second aperture diaphragm 768D are selected such that during a single exposure of a fingerprint sample (not shown), the detected light intensity of each first photodiode 714 is 20 times greater than the detected light intensity of each second photodiode 718. This corresponds to a ratio of the area of each second aperture diaphragm 768D to the area of each first aperture diaphragm 764D of 5:1. This ratio can be larger or smaller without departing from the scope of the present invention. The pixel array 712 does not include unused photodiodes (such as those shown filled white in the pixel array 612 of Figure 6A ), which advantageously increases the resolution of the pixel array 712 but may disadvantageously allow crosstalk between the photodiodes, resulting in noise. Other configurations of the first photodiodes 714 and second photodiodes 718 within the pixel array 712 allow optimization between resolution and sensitivity based on the requirements of the pixel array 712 and do not depart from the scope of the present invention.

[0070] The pixel array 712 is Figure 3 an example of the pixel array 312 of Figure 3Certain components of the described. The pixel array 712, the plurality of first photodiodes 714, the plurality of second photodiodes 718, the perforated baffle layer 760D, the plurality of first aperture diaphragms 764D, and the plurality of second aperture diaphragms 768D are respectively Figure 3 Examples of the pixel array 312, the plurality of first photodiodes 314, the plurality of second photodiodes 318, the perforated baffle layer 360D, the plurality of first aperture diaphragms 364D, and the plurality of second aperture diaphragms 368D, and the description of each corresponding element applies between the two figures.

[0071] Without departing from the scope of the present invention, changes may be made to the above methods and systems. Therefore, it should be noted that the content contained in the above description or shown in the drawings should be construed as illustrative rather than restrictive. The following claims are intended to cover all general and specific features described herein, as well as all statements that may be said to fall within the scope of the present methods and systems between them in terms of language.

[0072] Feature combination

[0073] (A1) In a first aspect, an optical fingerprint sensor with forgery detection includes: a plurality of lenses L m＝0 , L1, …… L J-1 , which have a lens pitch in a horizontal direction orthogonal to the lens axis of lens L0, and each lens has a certain width; an image sensor, which includes a pixel array, and the pixel array includes a plurality of first photodiodes I m＝0 , I1, …… I J-1 , the plurality of first photodiodes have a first photodiode pitch equal to the lens pitch in the horizontal direction, and the center of the photosensitive surface of each first photodiode I m and the optical center of each lens L m form a plurality of optical axes O m＝0 , O1, …… O J-1 among which the optical axis O m ; at least one perforated baffle layer located between the image sensor and the plurality of lenses, each of the at least one perforated baffle layer is located at a corresponding height z k above the pixel array, and each has a corresponding plurality of aperture diaphragms A m＝0 , A1, …… A J-1 , each aperture diaphragm A m is centered with respect to the optical axis O m ; and a plurality of second photodiodes S m＝0 , S1, …… S K-1 included in the pixel array, the plurality of second photodiodes are interleaved with the plurality of first photodiodes such that the second photodiode S mHorizontally located between the first photodiode I m and the first photodiode I m+1 wherein each second photodiode is configured to detect electromagnetic energy that has passed through the lens L m and at least one aperture stop A m not aligned with L m along the optical axis O x≠m .

[0074] (A2) In the embodiment of A1, between adjacent aperture stops of the plurality of aperture stops, each of at least one perforated baffle layer is opaque to visible electromagnetic energy.

[0075] (A3) In the embodiment of A2, at least one aperture stop A m is aligned along the optical axis O m with a corresponding width such that at least one aperture stop A m collectively transmits electromagnetic energy falling within an acceptance angle, the acceptance angle being measured as the angular divergence of rays incident on the center of the photosensitive surface of the first photodiode I m with respect to the optical axis O m .

[0076] (A4) In the embodiment of any one of A1 to A3, each aperture stop of the plurality of aperture stops on each of at least one perforated baffle layer is circular in the horizontal plane.

[0077] (A5) In the embodiment of any one of A1 to A4, at least one of the perforated baffle layers has a distance z less than 10 micrometers k and has a plurality of second aperture stops SA m＝0 , SA1, …… SA K-1 , each second photodiode S m having a second aperture stop SA m , each second aperture stop SA m being centered with respect to the center of the photosensitive surface of each second photodiode S m in a direction parallel to the optical axis O m .

[0078] (A6) In the embodiment of any one of A1 to A5, at least one perforated baffle layer includes four baffle layers.

[0079] (A7) In the embodiment of any one of A1 to A6, the number J of the first photodiodes is equal to the number K of the second photodiodes.

[0080] (A8)In the embodiment of any one of A1 to A7, the plurality of second photodiodes have a second photodiode pitch equal to the lens pitch in the horizontal direction.

[0081] (B1)In a second aspect, a method for detecting a forged fingerprint detected using an optical fingerprint sensor includes: detecting large-angle light incident on a plurality of anti-forgery photodiodes of a pixel array, the large-angle light being incident electromagnetic energy incident on a lens above the pixel array at an incident angle diverging by more than 5 degrees with respect to the optical axis of the lens; wherein the plurality of anti-forgery photodiodes are interleaved with a plurality of imaging photodiodes such that each anti-forgery photodiode among the plurality of anti-forgery photodiodes is located between adjacent imaging photodiodes among the plurality of imaging photodiodes; determining an angular distribution of the electromagnetic energy at least in part based on the detected large-angle light; and detecting a forged fingerprint at least in part based on the angular distribution of the electromagnetic energy.

[0082] (B2)In an embodiment of B1, the plurality of anti-forgery photodiodes and the plurality of imaging photodiodes are formed in a single pixel array.

[0083] (B3)In an embodiment of B1 or B2, the method further includes detecting small-angle light incident on the plurality of imaging photodiodes of the pixel array, the small-angle light being incident electromagnetic energy incident on a lens above the pixel array at an incident angle diverging by more than 5 degrees with respect to the optical axis of the lens.

[0084] (B4)In an embodiment of B3, the determining step further includes determining an angular distribution of the electromagnetic energy at least in part based on the detected small-angle light.

[0085] (B5)In an embodiment of any one of B1 to B4, the method further includes preventing light at a larger angle from irradiating the plurality of imaging photodiodes with a plurality of perforated baffle layers.

[0086] (B6)In an embodiment of any one of B1 to B5, the method further includes guiding the small-angle light with a plurality of lenses, each lens guiding the small-angle light to one of the plurality of imaging photodiodes.

[0087] (B7)In an embodiment of any one of B1 to B6, the method further includes illuminating a fingerprint sample with electromagnetic energy from a display, the plurality of anti-forgery photodiodes and the plurality of imaging photodiodes being located under the glass of the display.

[0088] (B8)In an embodiment of B7, the method further includes illuminating the fingerprint sample with a non-uniform illumination pattern.

[0089] (B9)In an embodiment of any one of B1 to B8, the method further includes applying at least one matching algorithm to the detection of the large-angle light.

[0090] (B10) In the embodiment of B9, at least one matching algorithm includes a machine learning algorithm.

Claims

1. An optical fingerprint sensor with forgery detection, comprising: Multiple lenses L m＝0 、L1, …… L J-1 , having lens spacings in a horizontal direction orthogonal to the lens axis of lens L0, and each lens having a certain width; An image sensor, the image sensor includes a pixel array, and the pixel array includes a plurality of first photodiodes I m＝0 , I1, …… I J-1 . The plurality of first photodiodes have a first photodiode pitch equal to the lens pitch in the horizontal direction. The center of the photosensitive surface of each first photodiode I m and each lens L m form a plurality of optical axes O m＝0 , O1, …… O J-1 including the optical axis O m ; At least one perforated baffle layer located between the image sensor and the plurality of lenses, each of the at least one perforated baffle layer being at a respective height z above the pixel array k and each having a respective plurality of aperture diaphragms A m＝0 , A1, …… A J-1 , each aperture diaphragm A m being centered with respect to the optical axis O m ; and A plurality of second photodiodes S included in the pixel array m＝0 , S1, …… S K-1 , the plurality of second photodiodes are interposed with the plurality of first photodiodes, such that the second photodiode S m is located in the horizontal direction between the first photodiode I m and the first photodiode I m+1 . where each second photodiode is configured to detect electromagnetic energy that has passed through the lens L m and that has not passed along the optical axis O m and that is not aligned with at least one aperture stop m aligned with L.

2. The optical fingerprint sensor according to claim 1, wherein, Between adjacent aperture diaphragms of the plurality of aperture diaphragms, each of the at least one perforated baffle layer is opaque to visible electromagnetic energy.

3. The optical fingerprint sensor according to claim 2, wherein, At least one aperture stop A m is aligned along the optical axis O m and has a corresponding width such that the at least one aperture stop A m collectively transmits electromagnetic energy falling within an acceptance angle, which is measured as the angular divergence of rays with respect to the optical axis O m where the rays are incident on the center of the photosensitive surface of the first photodiode I m of the photosensitive surface of the first photodiode I 4. The optical fingerprint sensor according to claim 1, wherein Each aperture diaphragm of the plurality of aperture diaphragms on each of the at least one perforated baffle layer is circular in the horizontal plane.

5. The optical fingerprint sensor according to claim 1, wherein, One of the at least one perforated baffle layer has a distance z equal to or less than 10 micrometers k , and has a plurality of second aperture diaphragms SA m＝0 , SA1, …… SA K-1 , each second photodiode S m has a second aperture diaphragm SA m , each second aperture diaphragm SA m is centered with respect to the center of the photosensitive surface of each second photodiode S m in a direction parallel to the optical axis O m .

6. The optical fingerprint sensor according to claim 1, wherein, The at least one perforated baffle layer includes four baffle layers.

7. The optical fingerprint sensor according to claim 1, wherein, The number J of the first photodiodes is equal to the number K of the second photodiodes.

8. The optical fingerprint sensor according to claim 1, wherein The plurality of second photodiodes have a second photodiode pitch equal to the lens pitch in the horizontal direction.

9. A method for detecting a forged fingerprint detected by the optical fingerprint sensor according to claim 1, comprising: Detecting large-angle light incident on the plurality of second photodiodes, where the large-angle electromagnetic energy is incident electromagnetic energy incident on the lens at an incident angle diverging by more than 5 degrees with respect to the optical axis of the lens; Determining the angular distribution of the electromagnetic energy at least in part based on the detected large-angle light; And Detecting a forged fingerprint at least in part based on the angular distribution of the electromagnetic energy.

10. The method according to claim 9, wherein, The plurality of second photodiodes are anti-forgery photodiodes and the plurality of first photodiodes are imaging photodiodes formed in a single pixel array.

11. The method according to claim 9, further comprising detecting small-angle light incident on the plurality of first photodiodes of the pixel array, where the small-angle light is incident electromagnetic energy incident on the lens at an incident angle diverging by less than 5 degrees with respect to the optical axis of the lens.

12. The method according to claim 11, wherein, The step of determining the angular distribution of the electromagnetic energy at least in part based on the detected large-angle light further includes determining the angular distribution of the electromagnetic energy at least in part based on the detected small-angle light.

13. The method according to claim 9, further comprising preventing light at a larger angle from irradiating the plurality of first photodiodes with a plurality of perforated baffle layers.

14. The method according to claim 9, further comprising guiding small-angle light with a plurality of lenses, each lens guiding the small-angle light to one of the plurality of first photodiodes.

15. The method according to claim 9, further comprising illuminating a fingerprint sample with electromagnetic energy from a display, where the plurality of second photodiodes and the plurality of first photodiodes are located under the glass of the display.

16. The method according to claim 15, further comprising illuminating the fingerprint sample with a non-uniform illumination pattern.

17. The method according to claim 9, further comprising applying at least one matching algorithm to the detection of the large-angle light.

18. The method according to claim 17, wherein, One of the plurality of matching algorithms includes a machine learning algorithm.

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