JPWO2016031870A1 - Sensor cover plate for fingerprint authentication and fingerprint authentication unit and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the sensitivity of a fingerprint authentication sensor and to prevent the appearance of a device equipped with the fingerprint authentication sensor from being impaired, and to provide a fingerprint authentication unit and fingerprint authentication unit including the same. An electronic device including the above is provided. The sensor cover plate for fingerprint authentication of the present invention is made of ceramics, has a thickness index of 0.05 mm or less, and has a lightness index L * of 7 or less in a CIE 1976 L * a * b * color space by diffuse reflection light treatment, The chromaticness index a * is −2 or more and 2 or less, and the chromaticness index b * is −1 or more and 1 or less. [Selection figure] None

Description

  The present invention relates to a sensor cover plate for fingerprint authentication, a fingerprint authentication unit including the same, and an electronic device including the fingerprint authentication unit.

  In recent years, fingerprint authentication has been widely used as a method for identifying an individual using a physical feature unique to the individual in order to enhance security such as management of various devices and entrance / exit management of various gates. Such fingerprint authentication uses a capacitive sensor with low power consumption, particularly in a device that is miniaturized. This capacitance type sensor is for recognizing a fingerprint shape by measuring the capacitance between the unevenness of a finger as a detection object and an electrode formed on a detection body.

  In such a capacitive sensor, a cover plate is provided with a material such as an acrylic resin such as polymethacrylic acid (PPMA) resin, polycarbonate (PC) resin, or glass in order to protect the electrodes and the like. Yes. However, these materials cannot be reduced in thickness from the viewpoint of mechanical properties, and the relative dielectric constant of the material itself is low, so that there is a problem that the change in capacitance is small and the sensor sensitivity is low.

  Such a problem is common to the cover plate of the touch panel, and Patent Document 1 proposes a transparent ceramic made of zirconium oxide or aluminum oxide as the cover plate.

JP 2012-174053 A

  If transparent ceramics made of zirconium oxide or aluminum oxide described in Patent Document 1 are used for the sensor cover plate for fingerprint authentication, the dielectric constant is higher than PPMA, PC, glass, etc. and the mechanical properties are excellent. Since it is a thing, since thickness reduction can be achieved, the sensitivity of the sensor for fingerprint authentication can be raised. However, when transparent ceramics is used for the fingerprint authentication sensor cover plate, the inside of the electrode or the like is visually recognized from the outside, and there is a problem that the appearance of the device on which the fingerprint authentication sensor is mounted is impaired.

  In addition, for the problem that the appearance is impaired by the inside being visually recognized, a protective film may be formed on the front or back surface of the transparent ceramic so that the inside is not visually recognized, but the manufacturing cost increases. In addition, there is a problem in that the sensitivity of the fingerprint authentication sensor is lowered by having the protective film.

  For this reason, the sensor cover plate for fingerprint authentication is required to improve the sensitivity of the sensor for fingerprint authentication and reduce the appearance.

  The present invention has been devised to satisfy the above requirements, and can improve the sensitivity of the fingerprint authentication sensor and can reduce the appearance of the device on which the fingerprint authentication sensor is mounted. An object is to provide a plate, a fingerprint authentication unit including the plate, and an electronic device including the fingerprint authentication unit.

  The sensor cover plate for fingerprint authentication of the present invention is made of ceramics, and has a lightness index L * in the CIE 1976 L * a * b * color space of 7 mm or less (excluding zero) by diffuse reflected light treatment. The chromaticness index a * is −2 or more and 2 or less, and the chromaticness index b * is −1 or more and 1 or less.

  The fingerprint authentication unit of the present invention includes the fingerprint authentication sensor cover plate and the fingerprint authentication sensor configured as described above.

  An electronic apparatus according to the present invention includes the fingerprint authentication unit having the above configuration.

  Since the sensor cover plate for fingerprint authentication of the present invention is made of ceramics, the dielectric constant is high and the mechanical properties are high, so that the thickness can be reduced, so that the sensitivity of the fingerprint authentication sensor can be increased, and Since the inside is not visually recognized from the outside, the appearance is hardly impaired.

  The fingerprint authentication unit of the present invention has a high security function.

  The electronic device of the present invention has a high security function and an excellent aesthetic appearance.

  Hereinafter, an example of the embodiment of the sensor cover plate for fingerprint authentication of the present embodiment will be described.

  The sensor cover plate for fingerprint authentication of the present embodiment is made of ceramics, and has a lightness index L * in the CIE 1976 L * a * b * color space by diffuse reflection processing at a thickness of 0.05 mm or less (excluding zero). 7 or less, the chromaticness index a * is −2 or more and 2 or less, and the chromaticness index b * is −1 or more and 1 or less.

  The sensor cover plate for fingerprint authentication according to the present embodiment satisfying such a configuration is made of ceramics, so that the dielectric constant is high and the mechanical properties are high, so that the thickness can be reduced. Can be improved.

  When the thickness is 0.05 mm or less (excluding zero), the lightness index L * in the CIE 1976 L * a * b * color space by diffuse reflection processing is 7 or less, and the chromaticness index a * is −2 or more. When the chromaticness index b * is −1 or more and 1 or less, the inside of the electrode or the like is not visually recognized from the outside, and the appearance of the device on which the fingerprint authentication sensor is mounted is less likely to be impaired.

Here, examples of the ceramic that serves as the sensor cover plate for fingerprint authentication according to the present embodiment include a silicon nitride sintered body, an alumina sintered body, a zirconia sintered body, and the like that include the above-described coloring component having the color tone. It is done. Here, taking a zirconia sintered body as an example, the zirconia sintered body means that zirconia (ZrO ₂ ) occupies 70% by mass or more out of 100% by mass of all components constituting the zirconia sintered body. The same applies to the silicon nitride sintered body and the alumina sintered body.

  Confirmation of the material of the ceramic is carried out by measuring using an X-ray diffractometer (XRD) and identifying using a JCPDS card from the obtained 2θ (2θ is the diffraction angle) value. Can do. When the ceramic is a zirconia sintered body, the peak of zirconia appears highest in the chart obtained by measurement by XRD.

For example, the content of zirconia was identified by XRD by measuring the content of Zr using an ICP (Inductively Coupled Plasma) emission spectroscopic analyzer (ICP) or an X-ray fluorescence analyzer (XRF). The content can be calculated by converting to ZrO ₂ which is a compound. When the peak of alumina (Al ₂ O ₃ ) is the highest, the Al content may be measured and converted to Al ₂ O ₃ . In addition, when the peak of silicon nitride (Si ₃ N ₄ ) is the highest, the Si content is measured and converted to Si ₃ N ₄ , or the presence of other nitrides is not confirmed, measuring the content of nitrogen may be converted into _Si 3 _{N 4.}

  Next, the lightness index L *, chromaticness index a * and b * in the CIE 1976 L * a * b * color space by the diffuse reflected light processing are, for example, a color difference meter (former Minolta CR-221 or its successor model). It can be measured in accordance with the geometrical condition a of JIS Z 8722-2009 irradiation and light reception, with the light source being the CIE standard light source D65 and the measurement diameter being 3 mm. In addition, about a measuring object, when the surface processed into the mirror surface whose arithmetic mean roughness Ra is 0.03 micrometer or less is made into a measuring surface, and the thickness of a measuring object exceeds 0.05 mm, it will be 0.05 mm. The sample to be measured can be obtained by grinding to a mirror and mirror finishing.

  In addition, when the thickness of the measurement object is less than 0.05 mm, the surface as it is if it is mirror-finished is used as the measurement surface, and if it is not mirror-finished, the surface that is mirror-finished is used as the measurement surface. do it. When the thickness is less than 0.05 mm, the lightness index L * in the CIE 1976 L * a * b * color space by diffuse reflection processing is 7 or less, the chromaticness index a * is −2 or more and 2 or less, and the chromaticness index b * is If it is −1 or more and 1 or less, even if the thickness is 0.05 mm, the lightness index L * in the color space CIE1976L * a * b * color space is 7 or less, and the chromaticness index a * is − It is 2 or more and 2 or less, and satisfies the requirement that the chromaticness index b * is −1 or more and 1 or less.

  Here, the lightness index L * is an index indicating the lightness and darkness of the color tone. If the value of the lightness index L * is large, it is a bright color tone, and if the value of the lightness index L * is small, it is a dark color tone. is there.

  The chromaticness index a * is an index indicating the degree of color tone from red to green. If the chromaticness index a * is a large value on the plus side, the chromaticness index a * is a red color tone, and the chromaticness index a If * is a large value on the minus side, it means a greenish tone.

  The chromaticness index b * is an index indicating the degree of yellow to blue of the color tone. If the chromaticness index b * is a large value on the plus side, it is a yellowish tone, and the chromaticness index b If * is a large value on the minus side, it means a blue color tone.

  Furthermore, since the absolute values of the chromaticness index a * and b * are also indices indicating the vividness of the color tone, when the chromaticness index a * and b * absolute value is small, it means that the vivid color is suppressed. is there. In the sensor cover plate for fingerprint authentication of the present embodiment, the lightness index L * in the CIE 1976 L * a * b * color space by diffuse reflection processing is 7 or less, the chromaticness index a * is −2 or more and 2 or less, Since the chromaticness index b * is not less than −1 and not more than 1, it has a color tone close to black.

  Note that the sensor cover plate for fingerprint authentication of the present embodiment has a lightness index L * in the CIE 1976 L * a * b * color space of 7 or less and a chromaticness index a * even when the thickness is 0.1 mm. Is −2 or more and 2 or less, and the chromaticness index b * is −1 or more and 1 or less.

  And in the ceramic used as the sensor cover plate for fingerprint authentication of this embodiment, it is suitable to consist of a zirconia sintered body. This is because the zirconia sintered body has a mechanical property equivalent to that of the silicon nitride sintered body, specifically, a three-point bending strength by a test piece based on JIS R 1601-2008 is about 1000 MPa, and is nitrided. This is because it has a relative dielectric constant three times that of a silicon-based sintered body or an alumina-based sintered body. When the sensor cover plate for fingerprint authentication of the present embodiment is made of a zirconia sintered body, it can have a thickness that was not possible with PPMA, PC, glass, etc. due to excellent mechanical properties, and has a high relative dielectric constant. Therefore, the sensitivity of the fingerprint authentication sensor can be improved.

  Next, the sensor cover plate for fingerprint authentication of the present embodiment has a thickness index of 0.05 mm, the lightness index L * in the CIE 1976 L * a * b * color space by the total transmittance process is 10 or less, and the chromaticness index a *. Is preferably −2 or more and 2 or less, and the chromaticness index b * is preferably 4 or more and 8 or less.

  The sensor cover plate for fingerprint authentication satisfying such a configuration hardly transmits light, so that the inside of the electrode or the like is not visually recognized from the outside, and the device for mounting the fingerprint authentication sensor is not provided. The risk of damaging the appearance is further reduced.

  At a thickness of 0.05 mm, the lightness index L * in the CIE 1976 L * a * b * color space by the total transmittance treatment is 10 or less, the chromaticness index a * is −2 or more and 2 or less, and the chromaticness index b The sensor cover plate for fingerprint authentication whose * is 4 or more and 8 or less has a lightness index L * in the CIE 1976 L * a * b * color space of 3 or less and a chromaticness index when the thickness is 0.1 mm. a * is from −1 to 1, and the chromaticness index b * is from −1 to 1.

  Thus, when looking at each index when the thickness is 0.1 mm, by setting the thickness to 0.05 mm, the value of the brightness index L * and the value of the chromaticness index b * are increased, but the thickness is 0 If the above-mentioned range is satisfied at 0.05 mm, the inside is not visually recognized.

  Furthermore, at a thickness of 0.05 mm, the lightness index L * in the CIE 1976 L * a * b * color space by total transmitted light processing is 8 or less, the chromaticness index a * is −1 or more and 1 or less, and the chromaticness index It is preferable that b * is 5 or more and 7 or less. This is because, by satisfying such a configuration, the light can be substantially blocked, so that the inside of the electrode or the like is not visually recognized from the outside, and the appearance of the device on which the fingerprint authentication sensor is mounted is Not only is it not damaged, but even if it has a light source inside, it can block light to the extent that the light source cannot be confirmed.

  Here, the lightness index L *, the chromaticness index a * and b * in the CIE 1976 L * a * b * color space by the total transmitted light processing are, for example, a JIS Z using a spectrocolorimeter (CM-3700A manufactured by Minolta). Measurement can be performed under the conditions of the light source CIE standard light source D65, the viewing angle 10 °, the irradiation diameter φ28 mm, and the measurement diameter φ25.4 mm. In the measurement, a mask may be used as necessary.

  Moreover, it is preferable that an alumina film is provided on the surface of the ceramic. When an alumina film is provided on the surface of the ceramic, it has high scratch resistance. In addition, when the thickness of the alumina film is 0.1 μm or more and 2 μm or less, it has high scratch resistance while maintaining high sensor sensitivity.

  Next, the fingerprint authentication unit of the present embodiment includes the sensor cover plate for fingerprint authentication and the fingerprint authentication sensor of the present embodiment. As described above, the sensor cover plate for fingerprint authentication of the present embodiment has a high relative dielectric constant and high mechanical characteristics, so that it can be thinned and the sensitivity of the fingerprint authentication sensor can be increased. The fingerprint authentication unit provided with has a high security function.

  Next, since the electronic device of the present embodiment includes the fingerprint authentication unit of the present embodiment, it has a high security function and an excellent aesthetic appearance. As the electronic device of the present embodiment, for example, a built-in type mounted on an information terminal such as a mobile phone or a personal computer, a door of a building or a passenger car, an automatic teller machine (ATM), or a USB is used. There is an external type.

  Next, an example of a method for manufacturing a fingerprint authentication sensor cover plate will be described.

  First, for silicon nitride-based sintered bodies, silicon nitride powder, sintering aid powder (for example, calcium oxide, aluminum oxide, rare earth element oxide) and colored component powder (for example, iron oxide powder, tungsten oxide) Powder) is weighed in a predetermined amount and put into a barrel mill, rotary mill, vibration mill, bead mill or attritor together with a solvent, and wet-mixed and pulverized to form a slurry.

  When the sintering aid powder is calcium oxide powder, aluminum oxide powder, and rare earth element oxide powder, the sintering aid powder is a total of 100 of silicon nitride powder and sintering aid powder. Weigh out 3% by mass or more and 18.2% by mass or less. Further, in each sintering aid powder, among the total 100 mass% of the calcium oxide powder, the aluminum oxide powder and the rare earth element oxide powder, the calcium oxide powder is 0.3 mass% or more and 1.5 mass% or less, The aluminum oxide powder may be 14.2 mass% or more and 48.8 mass% or less, and the remainder may be rare earth element oxide powder.

  Further, when the coloring component powder is an iron oxide powder and a tungsten oxide powder, these powders are 0.6 mass of iron oxide powder with respect to 100 mass% in total of silicon nitride powder and sintering aid powder. % To 8.5% by mass, and the tungsten oxide powder is weighed to be 0.13% by mass to 3.7% by mass.

  Next, a desired amount of a binder is added and mixed, and then the slurry is spray-dried using a spray dryer to obtain granules. And using the obtained granule, it is set as the molded object of desired shape by the powder press method. Next, the resulting molded body is degreased at a temperature of 500 ° C. or higher and 800 ° C. or lower in a nitrogen atmosphere or a vacuum atmosphere to obtain a degreased body.

  Next, a degreased body is placed in a firing furnace in which a graphite resistance heating element is installed, and sintered at a temperature of 1700 ° C. or higher and lower than 1800 ° C. to obtain a sintered body.

  Next, for the alumina sintered body, aluminum oxide powder, colored component powder (eg, manganese carbonate powder, iron oxide powder, chromium oxide powder), and sintering aid powder (eg, calcium carbonate powder, hydroxide) A predetermined amount of magnesium powder and silicon oxide powder) is weighed to obtain a primary raw material powder.

  In addition, the sintering aid powder is weighed so as to be 0.6% by mass or more and 2% by mass or less, out of 100% by mass of all components constituting the sintered body. Further, the colored component powder is weighed so as to be 8% by mass or more and 14.4% by mass or less of 100% by mass of all components constituting the sintered body.

  Next, a desired amount of a binder, a solvent, and a dispersant are weighed and prepared, put into a stirrer together with the primary raw material powder, and mixed and stirred to obtain a slurry. Thereafter, the slurry is spray-dried using a spray dryer to obtain granules. And using the obtained granule, it is set as the molded object of desired shape by the powder press method.

  Next, a sintered body is obtained by firing at a temperature of 1450 ° C. or higher and 1600 ° C. or lower using a firing furnace in an air (oxidation) atmosphere.

  Next, for the zirconia sintered body, first, zirconia powder stabilized with yttria is prepared. In addition, an aluminum oxide powder is prepared as a sintering aid powder, and iron oxide powder, chromium oxide powder, and cobalt oxide powder are prepared as colored component powders. Of the total 100% by mass of the zirconia powder, the sintering aid powder and the coloring component powder, the aluminum oxide powder is 0.1% by mass to 1.5% by mass, and the iron oxide powder is 0.2% by mass or more. 1.5% by mass or less, chromium oxide powder is 0.5% by mass to 3% by mass, cobalt oxide powder is 0.5% by mass to 3% by mass, and the balance is zirconia powder. A primary raw material powder is used.

  Next, a desired amount of a binder, a solvent, and a dispersant are weighed and prepared, put into a stirrer together with the primary raw material powder, and mixed and stirred to obtain a slurry. Thereafter, the slurry is spray-dried using a spray dryer to obtain granules. And using the obtained granule, it is set as the molded object of desired shape by the powder press method.

  Next, after degreasing the obtained molded body, the sintered body is obtained by firing at a temperature of 1300 ° C. or higher and 1550 ° C. or lower using a firing furnace in an air atmosphere.

  And the sensor cover plate for fingerprint authentication of this embodiment can be obtained by grinding and processing the surface of the obtained sintered compact which consists of each material into desired thickness. Moreover, you may perform a mirror surface process after a grinding process.

  Further, in order to provide an alumina film on the surface of the ceramic, the film may be formed using a sputtering apparatus with an alumina ceramic as a target.

At a thickness of 0.05 mm, the lightness index L * in the CIE 1976 L * a * b * color space by total transmitted light processing is 10 or less, the chromaticness index a * is −2 or more and 2 or less, and the chromaticness index b In order to obtain the sensor cover plate for fingerprint authentication of this embodiment in which * is 4 or more and 8 or less, the equivalent circle diameter is 0.8 μm or more at the surface area of 9.074 × 10 ⁵ μm ^{2 on} the surface of the zirconia sintered body. When the pores are viewed, the porosity is 0.7 area% or more and 1.2 area% or less, and the number of pores may be 1400 or more and 2400 or less.

  In order to make the pores as described above exist, a pore forming agent having an average diameter of 1.8 μm or more and 2 μm or less and 0.1% by mass or more and less than 1.0% by mass, and a dispersant for dispersing the pore forming agent, May be added to the slurry. The pore-forming agent and the dispersant are burned away by firing, and pores having an average diameter of 1.8 μm or more and 2 μm or less are formed by the burning of the pore-forming agent.

And when the surface area of the surface of the zirconia sintered body is 9.074 × 10 ⁵ μm ² and the pores having an equivalent circle diameter of 0.8 μm or more are viewed, the porosity is 0.7 area% or more and 1.2 area. The sensor cover plate for fingerprint authentication made of a zirconia sintered body having 1400 or more and 2400 or less pores is incident due to the presence of pores and the difference in refractive index between the zirconia crystal and other crystals. Since the incident light is easily reflected and the incident light hardly transmits, the inside of the electrode or the like is less likely to be visually recognized from the outside, and the possibility of impairing the appearance of the device on which the fingerprint authentication sensor is mounted is reduced.

In addition, at a thickness of 0.05 mm, the lightness index L * in the CIE 1976 L * a * b * color space by total transmitted light processing is 8 or less, the chromaticness index a * is −1 or more and 1 or less, and the chromaticness index b In order to obtain the sensor cover plate for fingerprint authentication of this embodiment in which * is 5 or more and 7 or less, the equivalent circle diameter is 0.8 μm or more at the surface area of 9.074 × 10 ⁵ μm ^{2 on} the surface of the zirconia sintered body. When the pores are viewed, the porosity is 0.7 area% or more and 0.9 area% or less, and the number of pores may be 1400 or more and 1700 or less.

When the pores having a circle-equivalent diameter of 0.8 μm or more are observed on the surface area of 9.074 × 10 ⁵ μm ^{2 on} the surface of the zirconia sintered body, the porosity is 0.7 area% or more and 0.9 area. The sensor cover plate for fingerprint authentication made of a zirconia sintered body having 1400 or more and less than 1700 pores is incident due to the presence of pores and the refractive index difference between the zirconia crystal and other crystals. Therefore, the inside of the electrode or the like is not visually recognized from the outside, and the appearance of the device on which the fingerprint authentication sensor is mounted is not impaired.

  In addition, at a thickness of 0.05 mm, the lightness index L * in the CIE 1976 L * a * b * color space by total transmitted light processing is 8 or less, the chromaticness index a * is −1 or more and 1 or less, and the chromaticness index b The sensor cover plate for fingerprint authentication according to the present embodiment in which * is 5 or more and 7 or less has a thickness of 0.05 mm even in a structure having a light source on the lower side as well as the incident light on the upper side. However, the light can be blocked so that the light source cannot be confirmed.

  The surface of the ceramic can be blackened by carbon vapor deposition, but as described above, the ceramic blackened by carbon vapor deposition is CIE 1976 L * a * b * by the total transmittance treatment when the thickness is 0.1 mm. The lightness index L * in the color space is 15 or more. As is apparent from this value, the sensor cover for fingerprint authentication of the present embodiment in which the lightness index L * in the CIE 1976 L * a * b * color space by the total transmitted light processing is 10 or less at a half thickness of 0.05 mm It can be seen whether the plate has a low light transmittance.

Finally, the present invention is not limited to the above-described embodiments, and various changes and improvements can be made without departing from the spirit of the present invention.

The present invention relates to a capacitive fingerprint authentication sensor cover plate (hereinafter simply referred to as a pattern authentication sensor cover plate), a fingerprint authentication unit including the same, and an electronic device including the fingerprint authentication unit.

Capacitive fingerprint sensor cover plate of the present invention is a cover of capacitive type fingerprint sensor, a capacitance type fingerprint sensor cover plate ing from ceramics, the thickness of the sample At 0.05 mm or less (excluding zero), the lightness index L * in the CIE 1976 L * a * b * color space by diffuse reflection processing is 7 or less, and the chromaticness index a * is −2 or more and 2 or less. The chromaticness index b * is -1 or more and 1 or less.

Next, the sensor cover plate for fingerprint authentication of the present embodiment has a thickness index of 0.05 mm, a lightness index L * in the CIE 1976 L * a * b * color space by total transmitted light processing is 10 or less, and a chromaticness index a *. Is preferably −2 or more and 2 or less, and the chromaticness index b * is preferably 4 or more and 8 or less.

At a thickness of 0.05 mm, the lightness index L * in the CIE 1976 L * a * b * color space by total transmitted light processing is 10 or less, the chromaticness index a * is −2 or more and 2 or less, and the chromaticness index b * fingerprint authentication sensor cover plate is 4 to 8, in the thickness 0.1 mm, CIE 1976 L * a * b * is a lightness index in the color space L * is 3 or less due to total transmitted light process, chromaticness indices a * is from −1 to 1, and the chromaticness index b * is from −1 to 1.

The surface of the ceramic can be blackened by carbon vapor deposition, but as described above, the ceramic blackened by carbon vapor deposition is CIE 1976 L * a * b * by total transmitted light treatment when the thickness is 0.1 mm. The lightness index L * in the color space is 15 or more. As is apparent from this value, the sensor cover for fingerprint authentication of the present embodiment in which the lightness index L * in the CIE 1976 L * a * b * color space by the total transmitted light processing is 10 or less at a half thickness of 0.05 mm It can be seen whether the plate has a low light transmittance.

Claims (7)

  Made of ceramics and having a thickness of 0.05 mm or less, the lightness index L * in the color space CIE1976L * a * b * color space is 7 or less, the chromaticness index a * is −2 or more and 2 or less, and the chromaticity A sensor cover plate for fingerprint authentication, wherein the Kness index b * is -1 or more and 1 or less.   The sensor cover plate for fingerprint authentication according to claim 1, wherein the ceramic is made of a zirconia sintered body.   When the ceramic has a thickness of 0.05 mm, the lightness index L * in the CIE 1976 L * a * b * color space by total transmitted light processing is 10 or less, the chromaticness index a * is −2 or more and 2 or less, and the chromaticness The sensor cover plate for fingerprint authentication according to claim 2, wherein the index b * is 4 or more and 8 or less.   When the ceramic has a thickness of 0.05 mm, the lightness index L * in the CIE1976L * a * b * color space by total transmitted light treatment is 8 or less, the chromaticness index a * is −1 or more and 1 or less, and the chromaticness The sensor cover plate for fingerprint authentication according to claim 2, wherein the index b * is 5 or more and 7 or less.   The sensor cover plate for fingerprint authentication according to any one of claims 1 to 4, wherein an alumina film is provided on a surface of the ceramic.   A fingerprint authentication unit comprising the sensor cover plate for fingerprint authentication according to any one of claims 1 to 5. An electronic apparatus comprising the fingerprint authentication unit according to claim 6.