Patent Application
20230267760
The invention refers to a biometric authentication system, according to claim 1, a touch screen according to claim 19 and an electronic device according to claim 20.
Today, biometric authentication systems as face recognition or fingerprint identification systems are integrated in a broad range of electronic devices like cell phones, touch pads, computers or any other input/output devices.
Capacitive systems analyzing a more or less two-dimensional surface of a three-dimensional object pressed against or being in touch with the surface of an authentication region have been in use for fingerprint sensors since long. These systems however tend to fail when contact pressure is too low and cannot be integrated directly into the surface of a touchscreen without reducing the display area of the front side. Only recently also optical fingerprint identification systems have been introduced to the markets which have been integrated into full front displays of hand-held devices. Despite of certain improvements which could be achieved also with detection reliability there are still issues with contact pressure, all the more when it comes to new detection issues like counterfeit protection by distinction of living and dead material, which could be shown recently to be feasible by analyses of two different wavelength, e.g. blue, green, yellow, or orange, within the visible light spectrum. For all of these issues however, elimination of disturbing background NIR-illumination coming from the outside or from the display illumination itself is crucial when it comes to analyze reflected signals of a certain wavelength or in a certain wavelength range. Dielectric filters for the NIR-range as used today tend to have a complicated thick multilayer design reaching several micrometers of thickness being not only expensive but may also rise adhesion problems due to layer tension. Additionally, such filters tend to have a strong dependency of the filter characteristic from the incident angle of the light, which limits analyzing regions essentially or makes additional efforts to align the optical path before it reaches the sensor. It should be mentioned that NIR according to the usual definition comprises a wavelength range from 780 nm to 3 μm including the spectral range of IR-A and IR-B. However, filters as used with biometric authentication systems, especially with fingerprint systems may or should also block visible red light in the range from 640 nm to 780 nm or at least the far red range of it, to optimize signal processing in the blue, green, yellow or orange range.
It is therefore an issue of the present invention to improve the performance of optical biometric authentication systems to analyze a more or less two-dimensional surface as mentioned above. Improvements should be realized in detection reliability, accuracy of the analyzed wavelength region and/or cost of ownership.
A biometric authentication system according to the present invention comprises at least:
The optical filter is a layered near infrared (NIR) filter consisting of
The minimum layer stack may end with an outermost blocking layer, in this case the blocking layer constitutes the layer furthermost from the substrate surface.
Alternatively, the layer stack may have a dielectric layer stack provided on the outer surface of the blocking layer.
The blocking layer may consist of at least one of TiOx, ZnOx, SnOx, CryOx and/or NiCrOx. In general, with layer-filters as described above bandwidth filters of different width can be produced in a band-range from about 400 nm to about 1650 nm. For biometric authentication like fingerprint recognition systems however a transparency bandwidth from about 400 nm to 650 nm would be most convenient. In certain cases also a smaller bandwidth e.g. from 400 nm to 600 nm might be preferably. Further embodiments to optimize certain filter parameters are described in the following. A metal interface layer consisting of a metal corresponding to a respective metal of a metal oxide layer may be provided between at least one neighbouring silver layer, which can be a preceding and/or a next silver layer, to avoid any oxidation of the sensible silver surface. The metal interface layer being in direct contact to both the neighbouring silver and the respective metal oxide layer. Metal oxide layers as mentioned above may comprise also substoichiometric regions or sublayers, at least at the silver side(s) of the metal oxide layers whereas other regions or sublayers may be stoichiometric or nearly stoichiometric. That means the metal-oxide layer side(s) directly in contact with the silver or the interface layer may be substoichiometric from about 5% to 50% of the stoichiometric value, e.g. TiO1.0-1.9, ZnO0.5-0.95, SnO1.0-1.9.
Alternatively layers can be gradient-like or graduated, e.g. from the metal interface layer at the silver contact face to a substoichiometric, a near stoichiometric, or even a stoichiometric composition, e.g. at the substrate side of the inner ZnOx or inner TiOx layer, in the middle of the further ZnOx and/or TiOx layers, or at the outer side of the outer ZnOx and/or outer TiOx layer. The same refers to other elements of the blocking layer as referred above when the blocking layer should replace the outer ZnOx or outer TiOx layer.
The at least one ZnOx layer may be an aluminum doped ZnOx:Al (AZO) layer which may have an atomic Al/Zn ratio r Zn/Al from 90 to 99%, e.g. about 5% Al. Alternatively the at least one ZnOx layer may be a galium doped ZnOx:Gal (GaZO) layer which may have an atomic Ga/Zn ratio r Zn/Ga from 90 to 99%, e.g. about 5% Ga.
In a further embodiment of the invention the NIR-filter may comprise an AR-stack consisting of alternating high and low refractive layers which is deposited on one of the outer ZnOx layer, the outer TiOx layer, or the blocking layer whereby antireflective (AR) properties of the filter can be optimized and sharp filter edges can be realized. To yield respective AR-properties the AR-stack should consist of at least four layers but may have essentially more, e.g. from 16 to 32 layers.
In a further embodiment a metallic or semi-conductive seed layer, which may consist of metals like Zn, Ti, Cr, or semiconductors like Si, may be provided at the substrate surface.
A further AR-stack which may also have ultraviolet (UV) light damping or blocking properties can be arranged as a stack of alternating high and low refractive layers between the substrate and the metallic or semi-metallic seed layer and the inner metal oxide (ZnOx or TiOx) layer. The further AR-stack may comprise at least 2 alternating layers of high and low index materials. A number between two and four layers will be usually suffice. In a further embodiment a SiO2 layer, or a stack of alternating SiO2 and Ta203 layers can be sandwiched between two ZnOx layers, or an inner TiO2 layer and an outer ZnOxlayer, whereat the ZnOx layers or the inner TiO2 layer and the outer ZnOx layer are adjacent to a silver layer with their side facing away from the sandwiched layer(s).
Respective ZnOx layers can comprise or consist of AZO or GaZO layers. Alternatively, the sandwiched stack can consist of any combination of low index material like SiO2 and high index materials, such as TiO2, Nb2O5, HfO2, ZrO2 or Si3N4. Only a substoichiometric oxide and/or a titanium, a Zn or an aluminum doped zinc (Zn:Al) layer may be provided between the respective sandwiching oxide layer and the silver layer in analogy to the layer sequence Ag/metal (Zn, Zn:Al or Ti)/substoichiometric oxide (of Zn, Zn:Al or Ti)/near or even stoichiometric oxide (of Zn, Zn:Al or Ti), or can be gradient-like or graduated as described above.
In one embodiment the light emitting source can be a planar light source arranged below the authentication region, e.g. in a vertical direction from the front face of the cover plate. The arrangement can be within the protective plate, e.g. with split cover plates, on the backside of the protective plate or in a distance from and facing the reverse side of the cover plate. The planar light source can be an OLED array or a part of an OLED array, e.g. the OLED array of a respective device, situated within or near the optical path of the biometric authentication system.
In a further embodiment the light emitting source can be a separate light source arranged below the authentication region on or in a distance from the reverse side of the cover plate. This can be in a vertical direction from the authentication region or oblique, in an angle to the authentication region.
The optical path of the system may comprise a lens or a mirror to focus the reflected light to the sensor. Alternatively, the optical path may comprise a collimator.
The invention is further directed to an electronic device comprising a touch screen and a system as described above. The device can be a cell phone, a touch pad, a computer, or any other input/output device, like geographic positioning systems (GPS), geodetic or other measurement systems and the like.
It should be mentioned that all features as shown or discussed in connection with only one of the embodiments of the present invention and not further discussed with other embodiments can be seen to be features well adapted to improve the performance of other embodiments of the present invention too, as long such a combination cannot be immediately recognized as being prima facie inexpedient for the man of art. Therefore, with the exception as mentioned all combinations of features of certain embodiments can be combined with other embodiments where such features are not mentioned explicitly.
The invention shall now be further exemplified with the help of figures. It should be mentioned that the figures are merely drawn to demonstrate the function of one or usually several embodiments of the invention without showing scaled dimensions or proper proportions of certain components to make the principals of the invention easier to see. The figures show:
It should be noted that with
Usually it would be expedient to apply filter stacks 30 deposited directly on a system component instead of using a separate filter. However such optical filters 31, due to their smaller dimension compared e.g. to the cover plate of a display, and the lack of potential sensitive electronic components as would be with a sensor, might be more efficient and cost effective to produce, especially when it comes to deposit highly sophisticated layer stacks of different materials in an expensive and volume-limited multi-chamber PVD-equipment.
In
On the right side of
With reference to the complexity of the systems due to the necessity of focusing or aligning the reflected light as shown in
This characteristic does not comprise higher transmittance and steeper and more defined filter edges only, see
Extensive experiments with pure dielectric stacks as preferably used for filters in the optics and photonics industries did not yield an essential improvement. As can be seen with
Many material combinations have been tested also with mixed di-electric and silver stacks and have been analyzed with reference to their optical performance. However, absorption curves of SiO2/Ag and Si3N4/Ag layers as shown in
However, surprisingly by use of a combination of metal oxide layers from ZnOx, AZO, GaZO and/or TiOx and silver layers tailored NIR-filter stacks having high transmission in the visible light band and good blocking properties for NIR-filters could be produced. At the same time UV-blocking properties are good enough to block harmful radiation from about 400 nm or lower wavelength. Due to the thin thickness of about one micrometer or even less, such coatings can be perfectly used with microelectronics components. Additional AR- and UV-blocking properties or higher transparency in the bandwidth gap and better edge acutance could be added by use of dielectric stacks 11 which can be also arranged directly on the substrate S or seed layer 1′ as a further dielectric stack 13, be sandwiched between further ZnOxlayer(s) and/or a further TiOX layer, e.g. stack 14, and/or be placed on top of the basic NIR blocking stack 12.
Some principles on such coating set-ups are shown in
In detail the optical filter is a layered near infrared (NIR) filter consisting of
It should be mentioned that blocking stack 12 shows two silver 2,4 and respective ZnOx layers 1,3,5 only for reasons of clearness, whereas filters from 2 to 6 silver layers, especially from 3 to 5 silver layers can be used to optimize the respective filter designs, see e.g.
With reference to the inner further or outer TiOx layers, the latter may be also a blocking layer, good optical properties could be reached when alternating TiOx/ZnOx/Ag/TiOx/ZnOx/Ag layers where used as exemplarily shown in table 5.
The minimum layer stack ends with the outermost blocking layer 6. In this case the layer furthermost from the substrate, which may consist of at least one of TiOX, ZnOx, SnOx, CryOx and/or NiCrOx. The blocking layer 6 can be used on top of outer metal oxide layer 5 as shown or may replace the outer metal oxide layer 5.
With reference to the deposition of the layer stack which can be performed e.g. by sputtering, it should be mentioned that it is important to provide as an interface a metallic layer of one or a few nanometers at each side of the silver layer 2, 4 to avoid any oxidation of the silver surface which would influence optical properties like reflexivity of the silver layer. Such metallic interface layers are illustrated in dotted lines in
In a further embodiment of the invention the NIR-filter may comprise a dielectric stack 11 consisting of alternating high and low refractive layers deposited on one of the following layers: the outer ZnOx layer, the outer TiOxlayer, or the blocking layer whereby antireflective (AR) properties of the filter can be optimized and sharp filter edges can be realized. This stack will consist of at least four layers however may have essentially more.
Further tuning or improving optical properties of the filter may comprise an embodiment of the invention having a SiO2 layer, which is a low index material layer, or a stack 14 of alternating SiO2 and at least one high index layer consisting of high index material sandwiched between two further metal oxide layers, whereat each of the two further metal oxide layers is in direct contact to a or to the SiO2 layer, and is adjacent to a respective silver layer with its side facing away from the sandwiched SiO2 layer(s). The high index material may consist of Ta2O5, TiO2, Nb2O5, HfO2, ZrO2 or Si3N4 and the sandwiched stack may be a three layer stack consisting of two SiO2 layers and a high index layer again sandwiched between the two SiO2 layers.
With
Examples of a respective NIR-filter stacks are given in tables 4 to 7 and
Both designs are relatively simple NIR-filters consisting of four alternating AZO or GaZO/Ag layers completed with an outer AZO or GaZO layer, having a physical layer thickness between 50 and 200 nm, which is thin. The only relevant difference is the physical thickness of certain AZO or GaZO layers, especially of the inner AZO or GaZO layer nearest to the substrate, which is thicker with design 2. Therewith in comparison of
As can be seen a shift of the NIR edge of smaller 30 nm which is smaller than 5% could be reached in case of both designs, whereas the shift of the UV-edge was nearly neglectable. Design 2 again yielded a better uniformity. In view of the considerable different angle of the 60° measurement this minor change seems to be quite satisfying.
All photospectrometric measurements have been taken with a PhotonRT spectrometer by Essen-Optics. Optical samples have been deposited on a 200 mm glass of the D263-type in a commercial CLN 200 BPM-equipment from Evatec AG, Switzerland. Examples of the process parameters as used can be found in table 8. The same equipment and comparable process parameters have been used to produce respective filters on various components in the optical path as described above.
Table 5 refers to coating design 3 comprising an alternating TiOx/ZnOx/Ag/TiOx/ZnOx/Ag . . . layer not shown in the figures.
Table 6 refers to design 4 to 7, all in a medium thickness range between about 200 and 1000 nm, where optical transmittance of designs 5 to 7 is shown in
Medium NIR-filters as shown in
Table 7 refers to designs 10 to 12, all in a thick thickness range between about 1000 and 2500 nm, where optical transmittance of designs 5, 10, 11 and 12 is shown in
For many biometric authentication systems, especially fingerprint identification systems, less sophisticated designs in the middle or even low thickness range will suffice to analyze the pattern produced by the object, e.g. the fingerprint, with good resolution.
Finally, it should be mentioned that a combination of features mentioned with one embodiment, examples or types of the present invention can be combined with any other embodiment, example or type of the invention unless being obviously in contradiction.
+All processes for test glasses and filters have been produced on a commercially available Evatec vacuum equipment of the type: CLN 200 BPM, MSP, Solaris and/or LLS;
++Planar cathodes with target dimensions circular 200-450 mm or rectangular 1 × b = 35 − 85 × 13 cm, were used for all experiments, rotatable cathode targets can be used as well.
| Number | Date | Country | Kind |
|---|---|---|---|
| 00887/20 | Jul 2020 | CH | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/066785 | 6/21/2021 | WO |
