Fingerprint recognition device

A fingerprint recognition device includes a light source, a light conversion layer, a light detector, and a light filter. The light source is configured to emit a first light having a first wavelength. The light conversion layer is configured to convert the first light to a second light having a second wavelength different from the first wavelength. The light detector is configured to detect the second light reflected by a fingerprint. The light filter is disposed between the light conversion layer and the light detector, and configured to substantially filter out the first light and substantially pass the second light.

This application claims the benefit of Taiwan application Serial No. 106143499, filed on Dec. 12, 2017. The entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a biometric recognition device. More particularly, the present disclosure relates to a fingerprint recognition device.

BACKGROUND

In various situations requiring confidentiality, to further enhance the security, biometric recognition may cooperate with or replace passwords and other conventional means of identification. As the development of biometric recognition, the application thereof also increases. According to a forecast by Transparency Market Research, which is a market research firm, the compounded revenue growth rate in the biometrics market even exceeds 20% from 2012 to 2019. Among others, fingerprint recognition accounts for about 30% of the overall biometrics market due to its biological uniqueness, which ensures security, and ease of use. Due to the vigorous development of the market, various improvements have been conducted for biometric recognition means and devices, such as those for fingerprint recognition.

SUMMARY

In the present disclosure, a device structure that can be used to conduct biometric recognition is provided for the improvement of the recognition performance. It can be applicable in fingerprint recognition.

According to some embodiments, a fingerprint recognition device may comprise a light source, a light conversion layer, a light detector, and a light filter. The light source is configured to emit a first light having a first wavelength. The light conversion layer is configured to convert the first light to a second light having a second wavelength different from the first wavelength. The light detector is configured to detect the second light reflected by a fingerprint. The light filter is disposed between the light conversion layer and the light detector, and configured to substantially filter out the first light and substantially pass the second light.

DETAILED DESCRIPTION

Various embodiments will be described more fully hereinafter with reference to accompanying drawings, which are provided for illustration and explanation purposes but not limitation purpose. For clarity, the components in the figures may not be drawn to scale. In addition, some elements and reference numerals may be omitted in some figures. In this disclosure, the description directed to one element allows for the situations in which one or more element are used, unless clearly otherwise specified. It is contemplated that the elements and features of one embodiment may be beneficially incorporated in another embodiment without further recitation.

Referring toFIG. 1andFIGS. 2A-2B, an exemplary fingerprint recognition device100is shown. The fingerprint recognition device100comprises a light source110, a light conversion layer120, a light detector140, and a light filter150. The light source110is configured to emit a first light L1. The first light L1has a first wavelength λ1. The light conversion layer120is configured to convert the first light L1to a second light L2. The second light L2has a second wavelength λ2different from the first wavelength λ1. The light detector140is configured to detect the second light L2reflected by the fingerprint of a user's finger200. The light filter150is disposed between the light conversion layer120and the light detector140. The light filter150is configured to substantially filter out the first light L1and substantially pass the second light L2. Herein, said substantially filter out the first light L1and substantially pass the second light L2does not require that the first light L1is completely filtered out and the second light L2is not lost at all, but merely require that most of the first light L1is filtered and most of the second light L2can pass through the filter150. All the implementations that a distinguishability of the light filter150between the first light L1and the second light L2enough to provide a fingerprint image at the light detector140without an interference caused by the first light L1are acceptable.

In the exemplary fingerprint recognition device100, the light source110is disposed under the light conversion layer120. According to some embodiments, the light source110may be a monochromatic light source. The suitable monochromatic light sources comprise, but not limited to, a light emitting diode (LED) light source, an electroluminescence (EL) cold light source, an organic light emitting diode (OLED) light source, and a cold cathode fluorescent lamp (CCFL) light source. It can be understood that, even that a monochromatic light source is used, the first light L1may not be a light of a single wavelength. The first light L1may have a light emission spectrum with a peak, and the first wavelength λ1can be the wavelength of highest emissivity in the light emission spectrum of the first light L1. Similarly, the second light L2converted by the light conversion layer120may have a light emission spectrum with a peak, and the second wavelength λ2can be the wavelength of highest emissivity in the light emission spectrum of the second light L2.

According to some embodiments, as shown inFIG. 1, the light conversion layer120may comprise a medium125and light conversion particles130dispersed in the medium125. According to some embodiments, the medium125may be formed of a thermosetting plastic or a thermoplastic, the suitable materials comprise, but not limited to, epoxy, phenolic resin, bismaleimide (BMI), nylon, polystyrene, polycarbonate, polyethylene, polypropylene, vinyl resin, and a semi-crystalline plastic or an amorphous plastic may be used. According to some embodiments, the light conversion particles130may be formed of at least one of a quantum dot material, an inorganic fluorescent material, an organic fluorescent material, and a phosphor material so as to excite the second light L2. The suitable quantum dot materials comprise, but not limited to, those with a core formed of CdSe, ZnSe, GaAs, or InP and a single shell or multi-shells formed of a material having an energy gap larger than the energy gap of the core, wherein the shell(s) encapsulate(s) the core. The suitable inorganic fluorescent materials comprise, but not limited to, YAG, InGaN, silicate, and combinations thereof. The suitable organic fluorescent materials comprise, but not limited to, naphthalene, anthracene, phenanthrene, fluoranthene, pyrene, 1,2-chrysene, 9,10-triphenylene, perylene, substituted aromatic derivatives thereof, and combinations of all the materials described above (including the derivatives). The suitable phosphor materials comprise, but not limited to, FIrpic, FIr6, UGH materials, and combinations thereof. According to some embodiments, the light conversion particles130have particle sizes smaller than the second wavelength λ2. As such, the second light L2from the finger200toward the light detector140will not be deflected by the light conversion particles130, and thereby the clarity of fingerprint imaging can be ensured. In some embodiments, the particle sizes of the light conversion particles130are smaller than 10 nm. In some embodiments, suitable light conversion particles130can be used such that λ2−λ1≥20 nm. As such, it is easier for the light filter150to distinguish the second light L2from the first light L1. The first light L1is filtered out, while at the same time, most of the second light L2that is actually used for fingerprint imaging is allowed to pass the filter150and be detected by the light detector140.

For example, in some embodiments, the light source110emits a first light L1with a wavelength in a range from 400 nm to 500 nm, and the light conversion layer120converts the first light L1to a second light L2with a wavelength in a range from 450 nm to 600 nm, such as by the light conversion particles130. Further, a light filter150allowing for the passage of the light of a wavelength equal to or larger than 480 nm is used correspondingly. In some other embodiments, the light source110emits a first light L1with a wavelength in a range from 520 nm to 530 nm, and the light conversion layer120converts the first light L1to a second light L2with a wavelength in a range from 600 nm to 700 nm, such as by the light conversion particles130. Further, a light filter150allowing for the passage of the light of a wavelength equal to or larger than 600 nm is used correspondingly. However, the collocation of the components can be further adjusted as needed without particular limitations, as long as the arrangement does not depart from the scope of the disclosure.

According to some embodiments, the light detector140may be, but not limited to, a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor.

According to some embodiments, the light filter150has a first transmittance R1at the first wavelength λ1, the light filter150has a second transmittance R2at the second wavelength λ2, and R2−R1>50%. As such, it is easier for the light filter150to distinguish the second light L2from the first light L1. The first light L1is filtered out, while at the same time, the second light L2is allowed to pass the filter150and be detected by the light detector140.

Referring toFIGS. 2A-2B, specific operation of the fingerprint recognition device as shown inFIG. 1is illustrated. As shown inFIG. 2A, the first light L1emitted by the light source110arrives at the light conversion layer120, and the first light L1is converted to the second light L2by the light conversion particles130. For fingerprinting recognition, in addition to the quality of the detector used to detect the light reflected by the finger, the uniformity of the light (light uniformity) provided to the finger may also affect the fingerprint image. When said light uniformity is not good enough, uneven brightness is found in the formed image. In the fingerprint recognition device according to embodiments, through the arrangement of the light conversion layer120, particularly the light conversion particles130therein, uniform light can be provided to the finger to be detected. The second light L2arrives at the finger200of the user, and is reflected thereby. Since the light reflected by the valleys220is stronger than the light reflected by the ridges210, a fingerprint image can be formed. As shown inFIG. 2B, the second light L2reflected by the finger200passes downward through the light conversion layer120and the light filter150, and the second light L2is detected by the light detector140. Because the particle sizes of the light conversion particles130are smaller than the second wavelength λ2, even by an order of magnitude, the reflected second light L2will not be deflected by the light conversion particles130when it passes through the light conversion layer120. This ensure the clarity for the detection and imaging of the subsequent light detector140. In contrast, micron-scale structures or scattering particles that scatter the light from the light source are the common means for increasing the light uniformity proved to the finger currently. However, these structures have sizes which even larger than the wavelengths of the light, and thereby the reflected light is also scattered, deflected, or otherwise affected. Such situations subsequently lead to the poor imaging performance.

In a fingerprint recognition device100in which the light source110is disposed under the light conversion layer120as shown inFIG. 1, the light source110and the light detector140may be manufactured together on a substrate such as, but not limited to, a wafer. Referring toFIG. 3, an exemplary arrangement of the light source110, the light detector140, and the light filter150under such situations is shown. As shown inFIG. 3, the fingerprint recognition device100may comprise a plurality of light sources110and a plurality of light detectors140, and the light sources110and the light detectors140are disposed on a substrate105of the fingerprint recognition device100. The light sources110and the light detectors140are individually arranged in columns (of a matrix), and the columns of the light sources110and the columns of the light detectors140are alternately disposed. In this arrangement, the light filter150may be disposed on the light detectors140, and do not cover the light sources110.

Referring toFIG. 4, another exemplary arrangement of the light source110, the light detector140, and the light filter150is shown. As shown inFIG. 4, the fingerprint recognition device100may comprise a plurality of light sources110and a plurality of light detectors140, and the light sources110and the light detectors140are disposed on a substrate105of the fingerprint recognition device100. The light detectors140are arranged in a matrix and define a detection area A of the substrate105, and the light sources110are arranged in columns outside the detection area A. In this arrangement, the light filter150may be disposed on the whole detection area A. However, the light filter150does not extend to the region outside the detection area A. As such, similar to the embodiment ofFIG. 3, the light sources110are not covered by the light filter150.

Referring toFIG. 5, another exemplary fingerprint recognition device102is shown. The fingerprint recognition device102differs from the fingerprint recognition device100, wherein the differences are shown in the fingerprint recognition device102where the light source112is disposed at a side of the light conversion layer120. For example, the light sources112are disposed outside the light conversion layer120and adjacent to two opposite side surfaces S1and S2of the light conversion layer120. As such, the first light L1emitted from the light source110enters the light conversion layer120from a side thereof, and the first light L1is converted to a second light L2by the light conversion particles130.

Referring toFIG. 6, another exemplary fingerprint recognition device104is shown. The fingerprint recognition device104differs from the fingerprint recognition device100, wherein the differences are shown as that the fingerprint recognition device104further comprises a lens164. The lens164is disposed between the light detector144and the light filter154. The lens164is configured to focus the reflected second light L2. Because the lens164is used to focus the reflected second light L2, the required areas and amounts of the light detectors144in the fingerprint recognition device104can be reduced, and thereby the required areas and amounts of the light filters154can be reduced.

Referring toFIGS. 7A-7B, still another exemplary fingerprint recognition device106is shown, whereinFIG. 7Aillustrates a cross sectional view of the fingerprint recognition device106, andFIG. 7Billustrates a top view of the arrangement of the light source116and the light detector140in the fingerprint recognition device106. The fingerprint recognition device106differs from the fingerprint recognition device100, wherein the differences are shown in the fingerprint recognition device106where the light source116surrounds the light detector140, the light source116defines a central opening117, and the light detector140is disposed in the central opening117. Such arrangement is beneficial for decreasing the thickness of the fingerprint recognition device. Thereby, the fingerprint recognition device106can be thinner than the fingerprint recognition device100. In some further embodiments, the light source with a thinner thickness such as an electroluminescent sheet may be used. In some embodiments, one side of the light filter150may contact the light detector140, and another side of the light filter150may contact the light conversion layer120, as shown inFIG. 7A, so as to further decrease the thickness of the fingerprint recognition device.

Specific embodiments and comparative examples are given below so as to provide a further understanding of the fingerprint recognition device according to embodiments.

The First Group of Embodiments and Comparative Examples

First Embodiment

Referring toFIG. 8, a fingerprint recognition device300of first embodiment (1stE) is shown. The fingerprint recognition device300has a configuration similar to the configuration of the fingerprint recognition device104. More specifically, the fingerprint recognition device300comprises a light source310, a light conversion layer320having light conversion particles330, a light detector340, a light filter350, and a lens360that are similar to the light source110, the light conversion layer120, the light detector140, the light filter150, and the lens164described above, respectively. In this embodiment, the light source310is a blue light source, and the light filter350is a green light filter. The fingerprint recognition device300further comprises a substrate305and a frame370. The frame370connects the light conversion layer320and the substrate305so as to define an accommodation space S, and the light source310, the light detector340, the light filter350, and the lens360are disposed in the accommodation space S. The light conversion layer320is separated from the light filter350by a gap H, of which the medium is air. The gap H can be adjusted based on the focal length of the lens360. The frame370may be bloomed so as to further decrease the interference of the external light and improve the recognition performance. The fingerprint recognition device300further comprises a fixing plate380and a fixing frame385. The fixing frame385is configured to fix the light filter350, the lens360, and the light detector340. The fixing plate380connects the fixing frame385with the frame370. The fingerprint recognition device300has a total height of about 6.5 mm.

First Comparative Example

Referring toFIG. 9, a fingerprint recognition device302of first comparative example (1stCE) is shown. The fingerprint recognition device302differs from the fingerprint recognition device300of first embodiment, wherein the differences are shown in the fingerprint recognition device302where a simple glass plate322without being processed to form particular optical structures is disposed instead of the light conversion layer320. In addition, in the fingerprint recognition device302, there is no light filter350.

Second Comparative Example

Referring toFIG. 10, a fingerprint recognition device304of second comparative example (2ndCE) is shown. The fingerprint recognition device304is similar to the fingerprint recognition device302, but further comprises a diffusion layer324formed under the glass plate322.

Third Comparative Example

Referring toFIG. 11, a fingerprint recognition device306of third comparative example (3rdCE) is shown. The fingerprint recognition device306is similar to the fingerprint recognition device302, but further comprises a multi-layered finger pressed film326disposed on the glass plate322.

Fourth Comparative Example

Referring toFIG. 12, a fingerprint recognition device308of fourth comparative example (4thCE) is shown. The fingerprint recognition device308differs from the fingerprint recognition device300of first embodiment, wherein the differences are shown in the fingerprint recognition device308where a light filter358different from the light filter350is used. The light filter358is a red light filter.FIGS. 13A-13Bshow the emission and transmission spectra of the fingerprint recognition device300of the first embodiment and the fingerprint recognition device308of the fourth comparative example, respectively. The curve C1shows the emissivity of the light source310at various wavelengths, i.e., the light emission spectrum of the first light, the peak is at about 470 nm, and it may be considered as the first wavelength. The curve C2shows the emissivity at various wavelengths of the light emitted by the light conversion particles330after receive the light from the light source310, i.e., the light emission spectrum of the second light, the peak is at about 496 nm, and it may be considered as the second wavelength. The curve C3shows the transmittance of the light filter350for the light at various wavelengths. The curve C4shows the transmittance of the light filter358for the light at various wavelengths. It can be seen fromFIG. 13A, the light filter350substantially allows for the passage of the second light (the light reflected by the finger). The transmittance at the peak of the second wavelength, i.e., 496 nm, is higher than 80%. In addition, the light filter350substantially filters out the first light (the light emitted by the light source310). The transmittance at the peak of the first wavelength, i.e., 470 nm, is only about 10%. It can be seen fromFIG. 13B, in addition to filter out most of the first light (the light emitted by the light source310), the light filter358also filters out most of the second light (the light reflected by the finger). The transmittances at both the peak of the first light and the peak of the second light are only about 10%.

Test Results and Discussion of the First Group of Embodiments and Comparative Examples

Fingerprint recognition is performed with the fingerprint recognition devices300to308of the first embodiment and the first to fourth comparative examples, and the images are observed. For ease of understanding the quality of imaging, a “Figure of Merit” (FoM) is defined herein based on the intensity of a fingerprint signal and a standard deviation (STDEV) of a light uniformity:

F⁢⁢o⁢⁢M=intensity⁢⁢⁢of⁢⁢the⁢⁢fingerprint⁢⁢signalSTDEV⁢⁢of⁢⁢the⁢⁢light⁢⁢⁢uniformity.
The intensity of a fingerprint signal is obtained from the (gray scale) image of the light detector340by measurement of the average difference between the intensities of the light reflected from the ridges and the valley in a specific distance. A larger said difference, i.e., a higher intensity of the (gray scale) image, means a clearer fingerprint. The standard deviation of a light uniformity is obtained by taking a specific area from the (gray scale) image of the light detector340and measuring the standard deviation of the (gray scale) image. Because the fingerprint recognition devices300to308have light detectors340but no light sources310in the center portions, if a light uniformity cannot be provided such as by a light conversion layer320, there will be a dark spot at the center of a fingerprint image, and thereby the recognition is affected. In addition, there may be light spots at positions corresponding to the light sources310, and thereby lead to a higher standard deviation. Therefore, FoM as defined here can reflect the quality of the fingerprint images. A higher FoM value means a better fingerprint image. The obtained intensity of the fingerprint signals and standard deviations of the light uniformity of the first group of embodiment and comparative examples are listed in Table 1 (referred to as “Intensity” and “STDEV”, respectively, for simplification), so as the FoM values calculated thereby. In addition, for the quality of the fingerprint images can be distinguished in a more intuitive manner, normalization based on first comparative example (defined as 100%) is conducted, and the normalized results are listed in Table 1. The observed appearances of the images are also provided in Table 1.

Referring to Table 1, in the fingerprint recognition device302of first comparative example, a simple glass plate322, which does not provide a light uniform function, is used. As such, a fingerprint image can be observed, but clear light spots and dark spots are also found. In the fingerprint recognition device304of second comparative example, a diffusion layer324that can improve the light uniformity is formed under the glass plate322, and thereby no light or dark spots are observed. However, the light reflected by the finger is also scattered by the diffusion layer324. As such, the light reflected by the ridges and the light reflected by the valleys are not distinguishable. No “fingerprint” image is formed. In the fingerprint recognition device306of third comparative example, rather than a diffusion layer324, a finger pressed film326is used, and a fingerprint image can be observed. However, the finger pressed film326provides only poor light uniformity, and thereby clear light spots and dark spots are found, similar to the situation of first comparative example.

As for the fingerprint recognition device308of fourth comparative example, while the light conversion layer320is provided to uniformise the light, the light filter358used therein also filters out most of the reflected light as shown inFIG. 13B, and thereby the intensity of the fingerprint signal is decreased. In addition, the light filter358fails to provide enough distinguishment between the light emitted by the light source310and the light reflected by the finger, the signal intensity of the light to be observed and that of the noise light are almost equivalent, and thereby the fingerprint image is easily interfered by the light emitted by the light source310. Such situation causes more serious light spots, which caused by the light source310, and dark spots, which caused by the position of the light detector340that leads to the lack of a light source in the center portion. As such, the standard deviation of the light uniformity increases. All these effects lead to the decrease of the FoM value.

In the fingerprint recognition device300of first embodiment, the light conversion layer320is used to uniformise the light, and a matching light filter350is the selection. The light filter350provides good distinguishment between the light emitted by the light source310and the light reflected by the finger. As such, no light spots or dark spots are generated. A clear fingerprint image can be observed.

The Second Group of Embodiments and Comparative Examples

Second Embodiment

Referring toFIG. 14, a fingerprint recognition device400of second embodiment (2ndE) is shown. The fingerprint recognition device400has a configuration similar to the configuration of the fingerprint recognition device106. More specifically, the fingerprint recognition device400comprises a light source410, a light conversion layer420having light conversion particles430, a light detector440, and a light filter450that are similar to the light source116, the light conversion layer120, the light detector140, and the light filter150described above, respectively. In this embodiment, the light source410is a blue light source, and the light filter450is a green light filter the same as the light filter350used in first embodiment. Such configuration can decrease the thickness of the fingerprint recognition device. As such, the fingerprint recognition device400has a total height of only about 1 mm.

Fifth Comparative Example

Referring toFIG. 15, a fingerprint recognition device402of fifth comparative example (5thCE) is shown. The fingerprint recognition device402differs from the fingerprint recognition device400of second embodiment, wherein the differences are shown in the fingerprint recognition device402where a simple glass plate422without being processed to form particular optical structures is disposed instead of the light conversion layer420. In addition, in the fingerprint recognition device402, there is no light filter450.

Test Results and Discussion of the Second Group of Embodiments and Comparative Examples

Fingerprint recognition is performed with the fingerprint recognition devices400to402of second embodiment and fifth comparative example, and the images are observed. Similar to the first group of embodiment and comparative examples, the quality of imaging is reflected by FoM. The obtained intensity of the fingerprint signals and standard deviations of the light uniformity of the second group of embodiment and comparative examples are listed in Table 2 (referred to as “Intensity” and “STDEV”, respectively, for simplification), so as the FoM values calculated thereby. In addition, for the quality of the fingerprint images can be distinguished in a more intuitive manner, normalization based on fifth comparative example (defined as 100%) is conducted, and the normalized results are listed in Table 2. For each observed images, the numbers of pixels corresponding to various intensities of the light are calculated so as to obtain a brightness distribution profile of the image, as shown inFIG. 16, wherein curves C5and C6show the brightness distribution profiles of second embodiment and fifth comparative example, respectively.

Referring toFIG. 16, the curve C5is more concentrated than the curve C6. It means that, in an implementation in which the light conversion layer420is used, a brightness distribution is narrower. Referring to Table 2, in the fingerprint recognition device400of second embodiment, the light conversion layer420is used to uniformise the light. As such, a higher FoM value than that of the fingerprint recognition device402of fifth comparative example, and thereby a better fingerprint image, can be obtained.