BIOMETRIC IMAGING DEVICE AND ELECTRONIC DEVICE

Abstract

A biometric imaging device characterized by comprising: an image sensor comprising a plurality of pixels forming a photodetector pixel array; a first aperture layer comprising openings in locations aligned with pixels of the pixel array; a first filter layer comprising a transparent material configured to block light within a predetermined first wavelength range; a transparent spacer layer arranged on the first filter layer, wherein the transparent spacer layer is configured to absorb light within a predetermined second wavelength range; and an array of microlenses arranged on the transparent spacer layer, wherein the microlenses are aligned with the openings in the aperture layer.

Claims

1. A biometric imaging device comprising: an image sensor comprising a plurality of pixels forming a photodetector pixel array; a first aperture layer comprising openings in locations aligned with pixels of the pixel array; a first filter layer comprising a transparent material configured to block light within a predetermined first wavelength range in the infrared wavelength range; a transparent spacer layer, wherein the transparent spacer layer is configured to absorb light within a predetermined second wavelength range in the infrared wavelength range; and an array of microlenses, wherein the microlenses are aligned with the openings in the first aperture layer, and wherein the transparent spacer layer is located between the array of microlenses and the aperture layer.

2. The biometric imaging device according to claim 1, wherein the transparent spacer layer is a tinted glass layer.

3. The biometric imaging device according to claim 1, wherein the transparent spacer layer exhibits a gradual increase of light absorption with increasing wavelength such that visible light is transmitted, and infrared light is absorbed.

4. The biometric imaging device according to claim 1, wherein the transparent spacer layer has a transmission in the range of 40% to 60% for wavelengths in the range of 600 nm to 700 nm, and wherein light having longer wavelengths is being blocked.

5. The biometric imaging device according to claim 1, further comprising a second filter layer comprising a transparent material configured to block light within the first wavelength range.

6. The biometric imaging device according to claim 5, wherein the first and second filter layers are arranged on respective sides of the transparent spacer layer.

7. The biometric imaging device according to claim 1, further comprising a second aperture layer comprising openings in locations aligned with pixels of the pixel array.

8. The biometric imaging device according to claim 7, wherein the openings in the second aperture layer are larger than openings in the first aperture layer.

9. The biometric imaging device according to claim 1, further comprising a light blocking layer located between adjacent microlenses.

10. The biometric imaging device according to claim 9, wherein the light blocking layer is arranged between adjacent microlenses such that light reaching the image sensor must pass through a microlens.

11. The biometric imaging device according to claim 1, further comprising a transparent base layer arranged between the microlenses and the light blocking layer.

12. The biometric imaging device according to claim 5, wherein the first and second filter layers are configured to block at least 50% of light having a wavelength higher than 570 nm.

13. The biometric imaging device according to claim 1, wherein the aperture layer is a top metal layer in the image sensor.

14. The biometric imaging device according to claim 1, wherein the aperture layer is arranged on the image sensor.

15. The biometric imaging device according to claim 1, wherein the microlenses are configured to have a focal point at the surface of the image sensor.

16. An electronic device characterized by comprising: a display screen; and a biometric imaging device according to claim 1 arranged underneath the display screen.

17. A biometric imaging device comprising: an image sensor comprising a plurality of pixels forming a photodetector pixel array; a first aperture layer comprising openings in locations aligned with pixels of the pixel array; a transparent spacer layer, wherein the transparent spacer layer is configured to absorb light within a predetermined wavelength range in the infrared wavelength range; and an array of microlenses, wherein the microlenses are aligned with the openings in the first aperture layer, and wherein the transparent spacer layer is located between the array of microlenses and the aperture layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

[0031] FIG. 1 schematically illustrates a biometric imaging system according to an embodiment of the invention;

[0032] FIG. 2 schematically illustrates a biometric imaging system according to an embodiment of the invention;

[0033] FIG. 3 schematically illustrates a biometric imaging system according to an embodiment of the invention; and

[0034] FIG. 4 schematically illustrates a biometric imaging system according to an embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0035] In the present detailed description, various embodiments of the biometric imaging system according to the present invention are mainly described with reference to a fingerprint imaging sensor suitable for use under a display panel of a consumer device such as a smartphone, tablet computer or the like.

[0036] FIG. 1 schematically illustrates a portion of a biometric imaging device 100. In particular, FIG. 1 illustrates a cross section of a portion of the biometric imaging device 100, and it should be understood that the imaging device extends further to form an imaging device of suitable size.

[0037] The biometric imaging device 100 comprises an image sensor 102 which in turn comprises a plurality of pixels 104 forming a photodetector pixel array; a first aperture layer 106 comprising openings 108 in locations aligned with pixels 104 of the pixel array. Each opening 108 of the aperture layer 106 is aligned with a pixel 104 of the image sensor 102. The image sensor 102 may however comprise more pixels than apertures such that some of the pixels in the image sensor are not being used.

[0038] The first aperture layer 106 may be formed from the topmost metal layer in a CMOS chip in which the image sensor 102 is formed. Thereby, the image sensor 102 and the first aperture layer 106 can be formed in the same manufacturing process.

[0039] The biometric imaging device 100 further comprises a first filter layer 110 comprising a transparent material 110 configured to block light within a predetermined first wavelength range and a transparent spacer layer 112, here arranged on the first filter layer 110, wherein the transparent spacer layer 112 is configured to absorb light within a predetermined second wavelength range. In the biometric imaging device 100 illustrated in FIG. 1, the first filter layer 110 is located underneath the transparent spacer layer 112. However, the first filter layer 110 may equally well be located on top of the transparent spacer layer 112 such that the transparent spacer layer 112 is arranged on the first aperture layer 106.

[0040] The first filter layer 110 is preferably configured to block at least 50% of light having a wavelength higher than 570 nm. The first wavelength range is thus comprised of wavelengths higher than 570 nm.

[0041] Moreover, the biometric imaging device 100 comprises an array of microlenses 114 here arranged on the transparent spacer layer 112, wherein the microlenses 114 are aligned with the openings 118 in the first aperture layer 106. In an embodiment where the first filter layer 110 is arranged on top of the transparent spacer layer 112, the microlens array will be arranged on the first filter layer 110.

[0042] In the described embodiment, the transparent spacer layer 112 is a tinted glass layer exhibiting a gradual increase of light absorption with increasing wavelength such that visible light is transmitted, and infrared light is absorbed. The purpose of the transparent spacer layer 112 is thus to reduce the amount of infrared light reaching the image sensor. The total absorption of the transparent spacer layer 112, which may also be referred to as a light absorbing layer, is dependent on the thickness of the layer. It is therefore possible to configure the thickness of the transparent spacer layer to sufficiently reduce optical crosstalk and other internal reflections. The cut-off wavelength of the transparent spacer layer 112, i.e. the wavelength where 50% of the light is absorbed, can be controlled by controlling the composition of the layer. In particular, the transmission properties of a transparent spacer layer 112 can be controlled by selecting the type and amount of additives in a glass material. For an optical fingerprint sensor, it may be desirable to have the cut-off region in the range of 590-630 nm.

[0043] The transparent spacer layer may for example have a transmission in the range of 40% to 60% for wavelengths in the range of 600 nm to 700 nm, and wherein light having longer wavelengths is being blocked. The first wavelength range can thus be described as the range of wavelengths above 600 nm. The second wavelength range may also be the same as the first wavelength range.

[0044] The difference between the transparent spacer layer 112 and the first filter layer 110 is that the transparent spacer layer 112 in form of a tinted glass layer is configured to absorb infrared light while the first filter layer 110 is configured to block infrared light. A filter layer configured to block light based on interference may have a sharp transmission profile as a function of wavelength and the transmission may also be dependent on the angle of incident light. In a light absorbing layer, the transition is smoother and there is no angular dependence. Accordingly, by combining an absorbing layer with a blocking layer, the advantageous properties of the respective layers can be utilized.

[0045] The biometric imaging device 100 may also comprise additional intermediate layers not described herein as long as the layers are sufficiently transparent to allow light to travel from the microlens to the image sensor without excessive losses.

[0046] FIG. 2 schematically illustrates a biometric imaging device 200 further comprising a second aperture layer 208 comprising openings 210 in locations aligned with pixels 104 of the pixel array. The openings 210 in the second aperture layer 208 are larger than the openings 108 in the first aperture layer so that the two aperture layers 106, 208 together act to narrow the beam of light reaching the pixel 104. A transparent layer 206, which may be an optically clear adhesive (OCA) layer, is arranged between the first and second aperture layers 106, 208 to define the distance between the layers 106, 208.

[0047] The biometric imaging device 200 of FIG. 2 further comprises a second filter layer 202 comprising a transparent material configured to block light within the first wavelength range. The properties of the second filter layer 202 are thus the same as the properties of the first filter layer 110. It may however be possible to provide a second filter layer having different optical properties compared to the first filter layer.

[0048] Moreover, the biometric imaging device 200 comprises a light blocking layer 204 located between adjacent microlenses 114. In other words, the light blocking layer 204 comprises openings at the locations of the microlenses 114. The light blocking layer 204 may be deposited on the device before or after the formation of the microlenses 114, and the light blocking layer 204 may be in principle be above the bottom plane of the lenses or in the same plane as the lenses. In either case, the openings of the light blocking layer 204 have a size which is equal to or smaller than the size of the microlens 114. The light blocking layer 204 also allows for a sparse arrangement of microlenses 114 in the microlens array such that there is a distance between adjacent microlenses 114. Thereby, light reaching the image sensor 102 must pass through a microlens 114.

[0049] FIG. 3 schematically illustrates a biometric imaging sensor 300 further comprising a transparent base layer 302 arranged between the microlenses 114 and the light blocking layer 204. The transparent base layer 302 may be made from same material as microlenses 114 and it may be formed in one piece together with the microlenses 114.

[0050] Further features of the biometric imaging devices 200, 300 of FIGS. 2 and 3 are similar to the features described above with reference to the biometric imaging device 100 of FIG. 1.

[0051] FIG. 4 schematically illustrates a biometric imaging device 400 similar to the device 100 illustrated in FIG. 1. The difference being that the biometric imaging device 400 of FIG. 4 does not comprise the first filter layer 110. Instead, the transparent spacer layer 112 fills the volume between the microlens array 114 and the first aperture layer 106. In some applications, it may be sufficient with only the light absorbing layer in the form of the transparent spacer layer to reduce the amount of infrared light reaching the image sensor. For a light absorbing layer, the amount of absorbed light is proportional to the thickness of the layer, and in some applications the distance between the aperture layer and the microlens array may be sufficiently large for the transparent spacer layer 112 to provide sufficient absorption without the filter layer 110 illustrated in FIG. 1.

[0052] Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the device may be omitted, interchanged or arranged in various ways, the device yet being able to perform the functionality of the present invention.

[0053] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.