WO2017127995A1 - Article with high capacity per area and use of such article in finger-print sensors - Google Patents

Article with high capacity per area and use of such article in finger-print sensors Download PDF

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Publication number
WO2017127995A1
WO2017127995A1 PCT/CN2016/072045 CN2016072045W WO2017127995A1 WO 2017127995 A1 WO2017127995 A1 WO 2017127995A1 CN 2016072045 W CN2016072045 W CN 2016072045W WO 2017127995 A1 WO2017127995 A1 WO 2017127995A1
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WIPO (PCT)
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cat
article
cations
glass
preferable
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PCT/CN2016/072045
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French (fr)
Inventor
Martin Letz
Ruediger Sprengard
Michael Kluge
Ute Woelfel
Feng He
Jigang YIN
Original Assignee
Schott Glass Technologies (Suzhou) Co. Ltd.
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Application filed by Schott Glass Technologies (Suzhou) Co. Ltd. filed Critical Schott Glass Technologies (Suzhou) Co. Ltd.
Priority to PCT/CN2016/072045 priority Critical patent/WO2017127995A1/en
Publication of WO2017127995A1 publication Critical patent/WO2017127995A1/en

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
    • G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
    • G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
    • G06V40/12—Fingerprints or palmprints
    • G06V40/13—Sensors therefor
    • G06V40/1329—Protecting the fingerprint sensor against damage caused by the finger

Definitions

  • Each individual has a unique fingerprint that is defined as the pattern of valleys and ridges at the fingertip. Therefore, for a long time the fingerprint has been used as means for identification of individuals. Most commonly known is the use of fingerprints for identification of criminals that has been used in Europe since the 19th century. However, use of fingerprints for identification is much older. For example, in China fingerprints have been used for signing of contracts since more than a thousand years.
  • digital authorization might be achieved by fingerprint sensing in order to overcome the described problems caused by password-based identification.
  • digital fingerprint sensors have been developed. These sensors can be differentiated with regard to the method, by which the fingerprint is sensed. There are capacitive, optical, acoustical, thermal and pressure-sensitive fingerprint sensors. Capacitive and optical fingerprint sensors are most common.
  • Standard display glasses are used in current capacitive fingerprint sensors.
  • the glass is a die-lectric and covers a fine conducting structure on one site.
  • the conducting structure forms multi-ple tiny capacitances with parts of the finger tip that is placed on the outer site and forms the second contact of the capacitor.
  • the detected signal is a tiny voltage difference ⁇ U, which oc-curs when a small current flows through the different skin parts of the fingertip.
  • the voltage dif-ference is caused by different impedances of ridges (low impedance of water) and valleys (high impedance of air) .
  • the voltage difference can be described by the circuit shown in Figure 1, which results in the following formula (I) :
  • Fig. 1 shall not only refer to the zero of the electric potential but can also refer to an arbitrary but defined poten-tial, which can e.g. be provided by a conducting rim around the sensitive area of the fingerprint sensor.
  • Z G occurs in the denominator of the equation above, reducing Z G is a powerful tool for enhancing the resolution and sensitivity of the fingerprint sensor.
  • Z G is inversely proportional to the capacity per unit area of the cover material of the sensor. Consequently, the sensitivity and resolution of the sensor is dependent on the capacity per unit area of the cover material of the sensor.
  • the capacity per unit area depends on dielectric constant ⁇ ’ a nd on the thickness of the cover material. The higher the dielectric constant ⁇ ’ and the lower the thickness, the higher is the capacity per unit area.
  • the model assumptions behind Fig. 1 and behind Eq. (I) are valid in the limit of very thin glass substrates. At larger substrate thicknesses horizontal contributions of the capacity will further reduce the capacity contrast of the fingerprint sensor. This will give an upper limit for the thickness of the cover material.
  • ⁇ ’ 11.5 parallel to the c-axis of the crystal
  • ⁇ ’ 9.3 perpendicular to the c-axis.
  • sapphire is very expensive. Both, currently used glasses and sapphire crystals can be obtained with a thickness as low as 0.5 mm.
  • US 6,114,862 A describes a capacitive distance sensor but does not give any specifications to the dielectric, which is used as a cover.
  • US 6,762,470 B2 describes a very thin scratch resistant layer using fluorocarbon polymers. However, the dielectric constant is very low.
  • US 8,803,258 B2 describes a finger sensing device including a protective plate having a dielec-tric constant greater than 5 and a thickness greater than 40 ⁇ m.
  • the protective plate may be a glass plate.
  • a dielectric constant of up to 20 is described as being desirable.
  • suitable glasses have dielectric constants of only up to 14.5.
  • glasses with such high dielectric constants have not been available in a thickness as low as 40 ⁇ m directly from a hot forming process so far.
  • materials with high dielectric constant and low thickness are desirable, such ma-terials are not made available.
  • the problem is particularly solved by an article having a capacity per unit area of at least 0.15 pF/mm 2 , wherein the article is a glass sheet or a glass ceramic sheet.
  • the article is a glass.
  • the article has a capacity per unit area of at least 0.2 pF/mm 2 , more preferably of at least 0.3 pF/mm 2 , more preferably of at least 0.5 pF/mm 2 , more preferably of at least 0.7 pF/mm 2 , more preferably of at least 1.0 pF/mm 2 , more preferably of at least 1.2 pF/mm 2 , more preferably of at least 1.5 pF/mm 2 , more preferably of at least 1.9 pF/mm 2 , more preferably at least 2.0 pF/mm 2 , more preferably at least 2.5 pF/mm 2 , more preferably at least 3.5 pF/mm 2 , more preferably at least 4.5 pF/mm 2 , more preferably at least 5.0 pF/mm 2 , more preferably at least 10 pF/mm 2 , more preferably at least 20 pF/mm 2 , more preferably at least 50 pF/mm 2 , es
  • the high capacity per unit area can be achieved by a high dielectric constant and/or a low thickness of the article.
  • the article has a dielectric constant of at least 5, more preferably at least 5.5, more preferably at least 6, more preferably at least 6.5 more preferably at least 7, more preferably at least 8, more preferably at least 10, more preferably, at least 12, more preferably at least 15, more preferably at least 20, more preferably at least 50, more preferably at least 100, more preferably at least 200, more preferably at least 500.
  • the dielectric constant can be measured according to DIN EN 62631-1: 2012-03.
  • the article has a thickness of at most 1000 ⁇ m, more preferably at most 700 ⁇ m, more preferably at most 500 ⁇ m, more preferably at most 300 ⁇ m, more preferably at most 200 ⁇ m, more preferably at most 100 ⁇ m, more preferably at most 50 ⁇ m, more preferably at most 30 ⁇ m, more preferably at most 20 ⁇ m, more preferably at most 10 ⁇ m.
  • the thickness should not be too low because the article might break. Therefore, the thickness is preferably at least 1 ⁇ m, more preferably at least 2 ⁇ m, more preferably at most 5 ⁇ m.
  • the loss tangent (tan ⁇ ) of the article at a frequency of 1 MHz is at most 25 ⁇ 10 -3 , more preferably at most 10 ⁇ 1 0 -3 , more preferably at most 5 ⁇ 10 -3 , more preferably at most 2 ⁇ 10 -3 , more preferably at most 1 ⁇ 10 -3 , more preferably at most 0.9 ⁇ 10 -3 , more preferably at most 0.8 ⁇ 10 -3 , more preferably at most 0.7 ⁇ 10 -3 , more preferably at most 0.5 ⁇ 10 -3 .
  • a too high loss tangent will average out the voltage differences and will reduce the resolution of a fingerprint sensor.
  • the loss tangent can be measured by standard dielectric spectroscopy together with the dielectric constant.
  • the article is transparent.
  • Transparent means according to the pre-sent invention that the transmission in the visible range is at least 80%at a thickness of 500 ⁇ m.
  • transparent articles When transparent articles are used as cover for fingerprint sensors, they enable combination of fingerprint sensing function with variable visual cues provided in the fingerprinting area of a de-vice. Furthermore, also visual information from the user may be detected in order to verify user’s identity by an additional independent method.
  • the article has a refractive index of at least 1.47, more preferably at least 1.52, more preferably at least 1.55, more preferably at least 1.59, more preferably at least 1.65, more pref-erably at least 1.69, more preferably at least 1.74, more preferably at least 1.79, more prefera-bly at least 1.84, more preferably at least 1.89, more preferably at least 1.94, more preferably at least 1.99, more preferably at least 2.04.
  • the article has an Abbe number of at least 20, more preferably at least 25, more preferably at least 25, more preferably at least 30, more preferably at least 40, more preferably at least 50, more preferably at least 55.
  • the article has Knoop hardness (HK 01/20 ) of at least 400, more preferably at least 500, more preferably at least 550, more preferably at least 600, more preferably at least 650, more preferably at least 700, more preferably at least 800.
  • a high Knoop hardness is advantageous because the article is more resistant to mechanical stress and more scratch resistant.
  • the indentation depth of a rhombus-shaped diamond pressed with a defined force and time on the material is measured.
  • the diamond surfaces have defined inter-section angles of 172.5° and 130.0°.
  • the size of the permanent indentation depends on the hardness of the material, which is given by the chemical composition.
  • the Knoop hardness can be calculated from the diagonal size d of the indentation using the following formulae:
  • the standard ISO 9385: 1990 describes the measurement procedure for glasses.
  • the values for Knoop hardness HK are given for a test force of 0.9807 N (cor-responds to 0.1 kp) and an effective test period of 20 s.
  • the test was performed on polished glass surfaces at room temperature.
  • the data for hardness values are rounded to 10 HK 0.1/20 .
  • the microhardness is a function of the magnitude of the test force and decreases with increas-ing test force.
  • the article has an elastic modulus of at least 60 ⁇ 10 3 N/mm 2 , more preferably at least 70 ⁇ 10 3 N/mm 2 , more preferably at least 80 ⁇ 10 3 N/mm 2 , more preferably at least 90 ⁇ 10 3 N/mm 2 .
  • the elastic modulus should not be too high. Therefore, the article preferably has an elastic modulus of 200 ⁇ 10 3 N/mm 2 , more preferably at most 165 ⁇ 10 3 N/mm 2 , more preferably at most 150 ⁇ 10 3 N/mm 2 , more preferably at most 120 ⁇ 10 3 N/mm 2 , more preferably at most 110 ⁇ 10 3 N/mm 2 .
  • the article has a Poisson ratio ⁇ of at least 0.25, more preferably at least 0.26, more preferably at least 0.27, more preferably at least 0.28, more preferably at least 0.29, more pref-erably at least 0.30.
  • the article has at least one surface with a roughness Ra of less than 60 ⁇ m, more preferably less than10 ⁇ m, more preferably less than 1 ⁇ m, more preferably less than 100 nm, more preferably less than 10 nm, more preferably less than 5 nm, even more preferably less than 2 nm.
  • the roughness can be measured by atomic force microscopy.
  • the article has a coefficient of thermal expansion (CTE) of at most 11 ⁇ 10 -6 /K, more preferably at most 8 ⁇ 10 -6 /K, more preferably at most 7 ⁇ 10 -6 /K, more preferably at most 6 ⁇ 10 -6 /K, more preferably at most 5 ⁇ 10 -6 /K.
  • the article has a coefficient of thermal expansion (CTE) of at least 2 ⁇ 10 -6 /K, more preferably at least 2.5 ⁇ 10 -6 /K, more preferably at least 2.8 ⁇ 10 - 6 /K.
  • CTE coefficient of thermal expansion
  • the glass has a thickness variation of at most ⁇ 20 ⁇ m, more preferably at most ⁇ 15 ⁇ m,more preferably at most ⁇ 10 ⁇ m.
  • the article of this invention may be used in a number of devices or as component or part of components therefore, including but not limited to smart phones, portable computers, computer watches, tablet computers, gaming devices, TV sets, personal computers, intercommunication systems, home automation systems, automotive security systems, 3D imaging systems, gesture control systems, touch sensors, fingerprint sensors, diagnostic systems, gaming devices, inter-active displays, 3D sensing systems, home appliances, display devices, iris recognition systems and others.
  • Components therefore may include, but are not limited thereto: optical or electrical interposers, thin film batteries, illumination devices, particularly OLED or backlight units, PCBs or other electronic wiring device, electronic passive component (particularly capacitors) , cover lenses, protective layers and/or MEMS/MOEMS.
  • the article is used as a cover member in fingerprint sensors.
  • a fingerprint sensor comprising an article according to the present invention.
  • the article has a good mechanical stability, thermal shock resistance and/or scratch resistance, particularly when the article is used as a cover member of a fingerprint sen-sor device. Therefore, the article is preferably chemically and/or thermally toughenable or toughened. More preferably, the article is chemically toughenable or toughened.
  • the ion exchange layer has a thickness of at least 1 ⁇ m, more preferably at least 2 ⁇ m, more pref-erably at least 5 ⁇ m, more preferably at least 10 ⁇ m, more preferably at least 20 ⁇ m, more pref-erably at least 30 ⁇ m, more preferably at least 50 ⁇ m, when the article is chemically toughened in 100%KNO 3 .
  • the central tensile stress is at most 600 MPa, more preferably at most 500 MPa, more preferably at most 400 MPa, more preferably at most 300 MPa, more preferably at most 200 MPa, more preferably at most 150 MPa, more preferably at most 120 MPa, more preferably at most 100 MPa, more preferably at most 50 MPa, more preferably at most 20 MPa, more preferably at most 10 MPa, when the article is chemically toughened in 100%KNO 3 .
  • the central tensile stress can be measured with FSM 6000.
  • an article of the present invention can be obtained from compositions belonging to different glass families.
  • the article of the present invention is a boron-silicate glass article or an alumino-silicate glass article.
  • Glasses used in this invention are characterized by certain compositional ranges. In this de-scription we refer to the cationic compositions of the glasses. In these compositions-if nothing else is indicated- “silicon” refers to Si 4+ , “boron” refers to B 3+ , “aluminum” refers to Al 3+ , “phos-phorus” refers to P 5+ , “lithium” refers to Li + , “sodium” refers to Na + , “potassium” refers to K + , “magnesium” refers to Mg 2+ , “calcium” refers to Ca 2+ , “strontium” refers to Sr 2+ , “barium” refers to Ba 2+ , “zinc” refers to Zn 2+ , “titanium” refers to Ti 4+ , “zirconium” refers to Zr 4+ , “hafnium” refers to “Hf 4+ ” , “lanthanum” refers
  • network formers refer to cations se-lected from the group consisting of silicon, boron, aluminum and phosphorus
  • R + refers to cati-ons selected from the group consisting of lithium, sodium and potassium
  • R 2+ refers to cations selected from the group consisting of magnesium, calcium, strontium, barium and zinc
  • highly dielectric components refers to cations selected from the group consisting of titani-um, zirconium, hafnium, lanthanum, gadolinium, yttrium, tantalum, niobium and tungsten.
  • compositions of the articles of the present invention will be outlined below.
  • the arti-cles generally comprise cationic and anionic components.
  • the composition of cations in the article will be given in cationic percentages (cat. -%) , i.e. indicating the molar proportion of the respective cation relative to the total molar amount of cations in the composition.
  • the articles comprise the following components, in cat. -%, based on the total molar amount of cati-ons in the article: network formers 25 to 90 cat. -%, lithium 0 to 25 cat. -%, sodium 0 to 30 cat. -%, potassium 0 to 15 cat. -%, magnesium 0 to 10 cat.
  • the cations in the article consist of the cations mentioned in the before-mentioned list to an extent of at least 95%, more preferably at least 97%, most preferably at least 99%.
  • the cationic components of the article essentially consist of the men-tioned cations.
  • the article preferably comprises at least one anion selected from fluo-rine (F - ) , oxygen (O 2- ) , chloride (Cl - ) .
  • the anions present in the article consist of oxygen to an extent of at least 95%, more preferably at least 97%, most preferably at least 99%.
  • the anionic component of the article essentially consists of ox-ygen.
  • X-free “and , , free of component X “, respectively, as used herein, preferably refer to an article, which essentially does not comprise said component X, i.e. such component may be present in the article at most as an impurity or contamination, however, is not added to the glass composition as an individual component. This means that the component X is not added in es-sential amounts.
  • Non-essential amounts according to the present invention are amounts of less than 100 ppm, preferably less than 50 ppm and more preferably less than 10 ppm.
  • the glass- es described herein do essentially not contain any components that are not mentioned in this description.
  • network formers are selected from the group consisting of silicon, boron, aluminum and phosphorus according to the present invention.
  • net-work formers are selected from the group consisting of silicon, boron and aluminum.
  • Even more preferred network formers are selected from the group consisting of silicon and boron.
  • the network former is phosphorus.
  • the article comprises silicon in proportions of 2 to 70 cat. -%.
  • Silicon is an important network former in the glass matrix which is very important for the glass properties.
  • silicon cations are important for the chemical resistance, hardness and scratch resistance of the article.
  • the articles comprise at least 5 cat. -%of silicon, more prefer-ably at least 12 cat. -%of silicon, more preferably at least 20 cat. -%of silicon, still more prefera-bly at least 25 cat. -%of silicon, and most preferably at least 30 cat. -%of silicon.
  • con-tents of silicon cations which are too high may result in an increase of the glass transition tem-perature, making glass production uneconomical. Therefore, it is particularly preferable that the content of silicon cations is at most 65 cat. -%, further preferable at most 55 cat. -%, still more preferable at most 45 cat. -%, and most preferable at most 40 cat. -%.
  • the articles contain boron cations as a network former in addition to silicon cations.
  • the content of boron is in the range of from 0 to 55 cat. -%.
  • boron cations essentially support the stability of the article. In the case of contents of boron cations which are too low the required stability in the glass system cannot be guaranteed.
  • the articles comprise at least 0.1 cat. -%of boron, more preferably at least 10 cat. -%of boron, still more preferably at least 15 cat. -%of boron, and most preferably at least 20 cat. -%of boron.
  • the content of boron cations is at most 50 cat. -%, further preferable at most 40 cat. -%, still more preferable at most 35 cat. -%, and most preferable at most 30 cat. -%.
  • the sum of silicon and boron cations is from 25 to 90 cat. -%.
  • the sum of silicon and boron cations in the articles is at least 30 cat. -%, more preferably at least 35 cat. -%, still more preferably at least 40, and most preferably at least 50 cat. -%. It is particularly preferable that the sum of silicon and boron cations in the articles is at most 85 cat. -%, further preferable at most 80 cat. -%, still more preferable at most 75 cat. -%, and most preferable at most 72 cat. -%.
  • the glasses show a ratio of the sum of aluminum and boron relative to the amount of silicon in cationic percentages of from 0 to 16.
  • this ratio is from >0 to 5, more preferably from >0.25 to 2, most preferably from 0.3 to 1.
  • the glasses comprise at least 0.1 cat. -%of aluminum, more preferably at least 1 cat. -%of aluminum, still more prefer-ably at least 2 cat. -%of aluminum, and most preferably at least 3 cat. -%of aluminum.
  • contents of aluminum cations which are too high result in an increased tendency to crystalliza-tion. Therefore, it is particularly preferable that the content of aluminum cations is at most 20 cat. -%, further preferable at most 18 cat. -%, further preferable at most 15 cat. -%, still more pref-erable at most 10 cat. -%, and most preferable at most 8 cat. -%.
  • the main network former is phosphorus.
  • the articles may comprise other network formers, particularly silicon, boron and/or aluminium in amounts of up to 10 cat. -%.
  • phosphorus is the only network former.
  • the articles comprise phosphorus in an amount of from 25 to 45 cat. -%.
  • the amount of phosphorus in the articles is at least 27 cat. -%, more preferably at least 30 cat. -%.
  • the content of phosphorus cations should also not be too high.
  • the content of phospho-rus is at most 40 cat. -%, more preferably at most 35 cat. -%.
  • the glasses preferably contain fluxing agents to improve melting properties, particularly com-prising alkali metal cations and/or alkaline earth metal cations.
  • the sum of the amounts of the fluxing agents in the glasses is at least 5 cat. -%, more preferably at least 7 cat. -%, still more preferably at least 12 cat. -%, and most pref-erably at least 15 cat. -%.
  • the sum of the fluxing agents in the glasses is at most 40 cat. -%, further preferable at most 35 cat. -%, still more preferable at most 30 cat. -%, and most preferable at most 25 cat. -%.
  • Alkali metal cations improve the meltability of the glass and thus allow an economic production. Also, they may are necessary for allowing chemical strengthening of the glass by ion exchange treatment.
  • the alkali metal cations serve as fluxing agents.
  • the sum of the amounts of the alkali metal cations lithium, sodium and potassium in the glasses preferably is 0 to 45 cat. -%. In preferable embodiments the sum of the alkali metal cations is at least 5 cat. -%, more preferably at least 7 cat. -%, still more preferably at least 10 cat. -%, and most preferably at least 15 cat. -%.
  • the sum of the alkali metal cations is at most 40 cat. -%, further preferable at most 35 cat. -%, still more preferable at most 30 cat. -%, and most preferable at most 25 cat. -%.
  • lithium cations are contained in proportions of 0 to 25 cat. -%.
  • Lithium serves as a fluxing agent and has excellent properties for ion exchange strengthening.
  • the articles comprise preferably at least 1 cat. -%, more preferably at least 5 cat. -%.
  • lithium affects chemical stability of the glasses to a great extent so that its content should be limited. It is particularly preferable that the content of lithium cations is at most 20 cat. -%, further preferable at most 15 cat. -%, still more preferable at most 10 cat. -%.
  • lithium is replaced by other alkali metal cations so that the arti-cles comprise at most 1 cat. -%lithium, more preferably are even free of lithium cations.
  • sodium cations are contained in proportions of 0 to 30 cat. -%.
  • Sodium is a good component for ion exchange treatment. But -as with all alkali metal ions -the amount of this component should not be too high because it decreases chemical stability.
  • the glasses comprise at least 1 cat. -%of sodium, more preferably at least 3 cat. -%of sodium, still more preferably at least 5 cat. -%of sodium, and most preferably at least 8 cat. -%of sodium. It is particularly preferable that the content of sodium cations is at most 25 cat. -%, further preferable at most 22 cat. -%, still more preferable at most 20 cat. -%, and most preferable at most 15 cat. -%.
  • potassium cations are contained in proportions of 0 to 15 cat. -%.
  • the negative impact of potassium on chemical stability is less strong compared to the other alkali metal ions.
  • potassium is not suitable for ion exchange treatment.
  • the content of potassium is preferably limited because it contains isotopes that emit beta rays.
  • the articles comprise at least 1 cat. -%of potassium, more preferably at least 2 cat. -%of potassium, still more preferably at least 3 cat. -%of potassium, and most preferably at least 5.5 cat. -%of potassium. It is particularly preferable that the content of potassium cations is at most 15 cat. -%, further preferable at most 13 cat. -%, still more preferable at most 12 cat. -%.
  • the leaching tendency of the glass can be reduced by using both sodium and potassium in the glass and keeping the ratio of sodium to potassium in cat. -%in a range of up to 10, more preferably up to 5, more preferably up to 4, preferably up to 3 and most prefera-bly at less than 2. Keeping this ratio low, i.e. the sodium does not exceed a certain amount rela-tive to the amount of potassium, provides for glasses having good meltability and excellent chemical and hydrolytical resistance. Specifically, such glasses will have an HGB1 according to ISO 719: 1989. However, in order to adjust the viscosity in the melt to a desirable value, the ratio of sodium to potassium should be more than 0.5, preferably more than 0.8 and most preferably at least 1.0.
  • R 2+ cations improve the meltability of the glass and thus allow for an economic production. Dur-ing the production of the article they serve as fluxing agents.
  • the sum of the R 2+ cations mag-nesium, calcium, strontium, barium and zinc in the articles preferably is of 0 to 35 cat. -%.
  • the sum of R 2+ ions in the articles is preferably at most 30 cat. -%, further preferable at most 25 cat. -%, still more preferable at most 20 cat. -%, and most preferable at most 18 cat. -%.
  • R 2+ cations may be used to adjust the viscosity of the glasses, particularly the fine tuning of the viscosity-temperature profile.
  • R 2+ cations -as alkali metal cations- may be used as fluxing agents. Therefore, the articles preferably com-prise R 2+ cations in an amount of at least 1 cat. -%, more preferably at least 2 cat. -%, more pref-erably at least 5 cat. -%, more preferably at least 10 cat. -%.
  • magnesium cations are contained in proportions of 0 to 10 cat. -%. It is particularly preferable that the content of magnesium cations is at most 8 cat. -%, more prefera-bly at most 6 cat. -%. In preferable embodiments the glasses are free of magnesium.
  • calcium cations are contained in proportions of 0 to 15 cat. -%. It is particularly preferable that the content of calcium cations is at most 8 cat. -%, further preferable at most 5 cat. -%, further preferable at most 3 cat. -%. In preferable embodiments the glasses are free of calcium.
  • strontium cations are contained in proportions of 0 to 10 cat. -%. It is particularly preferable that the content of strontium cations is at most 8 cat. -%, further preferable at most 5 cat. -%, further preferable at most 3 cat. -%. In preferable embodiments the glasses are free of strontium.
  • barium cations are contained in proportions of 0 to 23 cat. -%.
  • Barium is preferably used for adjusting the temperature dependence of viscosity and for increasing the refractive index as well as the dielectric constant.
  • the content of barium in the arti-cles is at least 0.1 cat. -%, more preferably at least 1 cat. -%, more preferably at least 5 cat. -%.
  • the content of barium should not be too high.
  • the content of barium cati-ons is at most 22 cat. -%, more preferably at most 20 cat. -%, more preferably at most 15 cat. -%, further preferable at most 10 cat. -%.
  • the articles contain at most 1 cat. -%barium cations, more preferable are even free of barium.
  • zinc cations are contained in proportions of 0 to 17 cat. -%.
  • Zinc cati-ons may be contained in the glass as an additional fluxing agent as well as for adjusting the melting point in a targeted manner.
  • the melting point of glass may be reduced.
  • the glasses comprise at least 1 cat. -%of zinc, more preferably at least 2 cat. -%of zinc, still more preferably at least 5 cat. -%of zinc.
  • contents of zinc cations which are too high may result in a reduction of the melting point of the glasses. It is particularly preferable that the content of zinc cations is at most 15 cat. -%, further preferable at most 10 cat. -%.
  • titanium cations are contained in proportions of 0 to 50 cat. -%. Titani-um cations are added to the glasses for improving their optical properties.
  • the refractive index of the glasses can be adjusted in a targeted manner. So the refractive index increases with an increasing content of titanium cations of the glass.
  • the articles comprise at least 1 cat. -%of titanium, more pref-erably at least 2 cat. -%of titanium, still more preferably at least 5 cat. -%of titanium, and most preferably at least 10 cat. -%of titanium.
  • contents of titanium cations which are too high may result in undesirable crystallization of the glass. Therefore, it is particularly preferable that the content of titanium is at most 46 cat. -%, more preferably at most 30 cat. -%, more pref-erably at most 25 cat. -%, further preferable at most 20 cat. -%.
  • zirconium cations are contained in proportions of 0 to 8 cat. -%.
  • Zirconi-um cations may be used to adjust the refractory index of the glasses.
  • a content of zirconium cations which is too high, may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of zirconium is at most 7 cat. -%, more preferably at most 5 cat. -%, further preferable at most 2 cat. -%, still more preferable at most 1 cat. -%.
  • the glasses are free of zirconium.
  • hafnium cations are contained in proportions of 0 to 2 cat. -%.
  • Hafnium cations may be used to adjust the refractory index of the glasses.
  • a content of hafni-um cations which is too high, may decrease the meltability and particularly may lead to stronger crystallization of the glasses.
  • the content of hafnium is at most 1.5 cat. -%, further preferable at most 1 cat. -%, still more preferable at most 0.5 cat. -%.
  • the glasses are free of hafnium.
  • lanthanum cations are contained in proportions of 0 to 35 cat. -%.
  • Lan-thanum cations may be used for increasing the dielectric constants of the articles.
  • a content of lanthanum cations which is too high, may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of lanthanum is at most 20 cat. -%, further preferable at most 10 cat. -%, still more preferable at most 5 cat. -%, still more preferable at most 1 cat. -%.
  • the glasses are free of lanthanum.
  • gadolinium cations are contained in proportions of 0 to 6 cat. -%. Gado-linium cations may be used for increasing the dielectric constants of the articles. However, a content of gadolinium cations, which is too high, may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of gadolinium is at most 2 cat. -%, further preferable at most 1 cat. -%, still more preferable at most 0.1 cat. -%. In preferable embodiments the glasses are free of gadolinium.
  • yttrium cations are contained in proportions of 0 to 6 cat. -%.
  • Yttrium cations may be used for increasing the dielectric constants of the articles.
  • a content of yttrium cations which is too high, may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of yttrium is at most 5 cat. -%, further preferable at most 2 cat. -%, still more preferable at most 1 cat. -%.
  • the glasses are free of yttrium.
  • tantalum cations are contained in proportions of 0 to 5 cat. -%. Tanta-lum cations may be used for increasing the dielectric constants of the articles. However, a con-tent of tantalum cations, which is too high, may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of tan-talum is at most 4 cat. -%, further preferable at most 2 cat. -%, still more preferable at most 1 cat. -%. In preferable embodiments the glasses are free of tantalum.
  • niobium cations are contained in proportions of 0 to 42 cat. -%.
  • Niobium cations may be used for increasing the dielectric constants of the articles.
  • a content of niobium cations which is too high, may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of niobium is at most 15 cat. -%, further preferable at most 10 cat. -%, still more preferable at most 5 cat. -%.
  • the glasses are free of niobium.
  • tungsten cations are contained in proportions of 0 to 3 cat. -%. Tung-sten cations may be used for increasing the dielectric constants of the articles. However, a con-tent of tungsten cations, which is too high, may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of tungsten is at most 2 cat. -%, further preferable at most 1 cat. -%, still more preferable at most 0.1 cat. -%. In preferable embodiments the glasses are free of tungsten.
  • the glasses may comprise refining agents in an amount of up to 1 cat. -%, more preferably up to 0.5 cat. -%, more preferably up to 0.1 cat. -%.
  • refining agents are comprised in the articles in an amount of at least 0.005 cat. -%, more preferably at least 0.01 cat. -%.
  • the refining agents are selected from the group consisting of antimony, arsenic and tin. More preferably, the refining agents are selected from the group consisting of antimony and tin.
  • the articles may comprise cerium in amount of up to 0.5 cat. %, more preferably up to 0.3 cat. -%,more preferably up to 0.2 cat. -%, more preferably up to 0.1 cat. -%, more preferably up to 0.005 cat. -%.
  • Cerium may be used for increasing the radiation stability of the articles. However, in preferred embodiments, the articles are free of cerium.
  • highly dielectric components may be used for increasing the dielectric constant of the articles.
  • Highly dielectric components are cations selected from the group consisting of titanium, zirconium, hafnium, lanthanum, gadolinium, yttrium, tantalum, nio-bium and tungsten.
  • highly dielectric components decrease the meltability and particu-larly may lead to stronger crystallization of the glasses. Therefore, in preferred embodiments, the articles comprise at most 5 cat. -%, more preferably at most 3 cat. -%, more preferably less than 1 cat. -%of highly dielectric components.
  • the high capacity per unit area is preferably achieved by a very low thickness of the articles.
  • the articles comprise the following components, in cat. -%, based on the total molar amount of cations in the article: network formers 25 to 75 cat. -%, R + 0 to 45 cat. -%, R 2+ 0 to 35 cat. -%, highly dielectric components 9 to 75 cat. -%.
  • a particularly pre-ferred alternative article composition comprises the following components, in cat. -%, based on the total molar amount of cations in the article: network formers 30 to 70 cat. -%, R + 5 to 35 cat. -%,R 2+ 5 to 30 cat. -%, highly dielectric components 15 to 60 cat. -%.
  • the cations in the articles consist of the cations mentioned in the before-mentioned lists to an extent of at least 95%, more preferably at least 97%, most preferably at least 99%.
  • the cationic components of the articles essentially consist of the mentioned cations.
  • highly dielectric components may be present in the articles in amount of at least 9 cat. -%, more preferably at least 15 cat. -%, more preferably at least 20 cat. -%, more preferably at least 30 cat. -%.
  • the amount of highly dielectric components should not be too high.
  • the content of highly dielectric components in the articles is at most 75 cat. -%, more preferably at most 60 cat. -%, more preferably at most 50 cat. -%, more prefera-bly at most 40 cat. -%.
  • the ratio of dielectric components (in cat. -%) to network formers (in cat. -%) is at most 2.5, more preferably at most 2.0, more preferably at most 1.5, more preferably at most 1.0, more preferably at most 0.8, more preferably at most 0.6.
  • high grade raw materials are used for very little color absorption, which is good for exact color printing.
  • the method may comprise further steps. Further steps may be for example chemically or ther-mally toughen the glass and/or converting the glass to a glass ceramic.
  • the present invention it is advantageous according to the present invention to obtain glass arti-cles with low thickness.
  • Thin glass can in principle be obtained by grinding a thicker glass to the desired thickness.
  • sheet thicknesses as low as desired for the articles of the present invention are difficult to obtain by grinding and polishing of thicker glass sheets.
  • very thin glasses can be obtained by flat glass processes. Therefore, it is an advantage of the arti-cles of the present invention that they can be obtained by a flat glass process.
  • Flat glass pro-cesses are well known to the skilled person.
  • the flat glass processes are preferably selected from the group consisting of pressing, down-draw, re-draw, overflow fusion, floating and rolling.
  • the articles have preferably at least one, in particular two fire-polished surfaces.
  • Fire-polished surfaces are extremely smooth, i.e. they show only low rough-ness.
  • mechanical polishing in the case of fire-polishing a surface is not ground, but the material to be polished is heated to such a high temperature so that it flows, which re-sults in a smooth surface condition. Therefore, the costs for the production of a smooth surface by fire-polishing are substantially lower than the costs for the production of a very smooth me-chanically polished surface.
  • an article of the present invention is also the use of an article of the present invention as a cov-er member of a fingerprint sensor device.
  • non-substantial amounts are amounts on a weight basis of less than 1000 ppm, preferably less than 500 ppm and even more preferably less than 100 ppm.
  • values for the dielectric constant depict the dielectric constant at a frequency of 1 MHz.
  • Articles 8 to 10 showed very high dielectric constants but were not chemically toughenable.
  • Ar-ticles 1 to 7 were chemically toughenable.
  • Table 2 shows compositions with low content of highly dielectric components. Glass composi-tions are given in cat. -%. The compositions above are the final compositions measured in the glass. The skilled person knows how to obtain these glasses by melting the necessary raw ma-terials. The glasses shown in table 2 contained only oxides as the anionic component, i.e. the glasses were oxidic.
  • Figure 1 shows a scheme of the electronic circuit underlying capacitive fingerprint sensors.
  • U 0 is the voltage of a voltage source
  • Z I the inner impedance of the electronic parts
  • Z G the imped-ance of the cover material
  • Z R the impedance of ridges
  • Z V the impedance of valleys
  • ⁇ U is the voltage difference that is detected as the signal.

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Abstract

A glass or glass ceramic article with a high capacity per unit and a method for producing such article are provided. Further, the use of the article as a cover member of a fingerprint sensor device and a corresponding fingerprint sensor are provided.

Description

Article with high capacity per area and use of such article in finger-print sensors
Each individual has a unique fingerprint that is defined as the pattern of valleys and ridges at the fingertip. Therefore， for a long time the fingerprint has been used as means for identification of individuals. Most commonly known is the use of fingerprints for identification of criminals that has been used in Europe since the 19th century. However， use of fingerprints for identification is much older. For example， in China fingerprints have been used for signing of contracts since more than a thousand years.
Recently， more and more focus has been drawn to fingerprint sensing due to the progressing digitalization in the last twenty years. Individual identification is required in the digital world in order to prevent access of unauthorized individuals to data or websites. Furthermore， also for access to computers， smart phones or other digital devices generally an authorization step is required. Previously and still most commonly， individuals proved their authorization by entering a password. However， there are several draw backs related to such authorization. First， there is a security issue as passwords are frequently spied out and misused by criminals. Therefore， it is suggested that different passwords are used for each application in order to minimize possible damage. Passwords should also not be kept in written form and should be complex combina-tions of letters and other characters because this makes a spy out more difficult. However， this causes problems in the applicability because each individual should remember dozens of com-plex passwords， which is uncomfortable or even impossible in some cases.
In this regard it has been suggested that digital authorization might be achieved by fingerprint sensing in order to overcome the described problems caused by password-based identification. For this purpose， a variety of digital fingerprint sensors have been developed. These sensors can be differentiated with regard to the method， by which the fingerprint is sensed. There are capacitive， optical， acoustical， thermal and pressure-sensitive fingerprint sensors. Capacitive and optical fingerprint sensors are most common.
Standard display glasses are used in current capacitive fingerprint sensors. The glass is a die-lectric and covers a fine conducting structure on one site. The conducting structure forms multi-ple tiny capacitances with parts of the finger tip that is placed on the outer site and forms the second contact of the capacitor. The detected signal is a tiny voltage difference ΔU， which oc-curs when a small current flows through the different skin parts of the fingertip. The voltage dif-ference is caused by different impedances of ridges (low impedance of water) and valleys (high  impedance of air) . The voltage difference can be described by the circuit shown in Figure 1， which results in the following formula (I) ：
ΔU＝ (ZI/ (ZI+ZG+ZR) ) - (ZI/ (ZI+ZG+ZV) ) ＝ (ZI× (ZV-ZR) ) / ( (ZI+ZG+ZV) × (ZI+ZG+ZR) ) ，
with ZI＝inner impedance of the electronic parts， ZG＝impedance of cover material， ZR＝im-pedance of ridges， and ZV＝impedance of valleys. Where the “ground” symbol in Fig. 1 shall not only refer to the zero of the electric potential but can also refer to an arbitrary but defined poten-tial， which can e.g. be provided by a conducting rim around the sensitive area of the fingerprint sensor.
Since ZG occurs in the denominator of the equation above， reducing ZG is a powerful tool for enhancing the resolution and sensitivity of the fingerprint sensor. ZG is inversely proportional to the capacity per unit area of the cover material of the sensor. Consequently， the sensitivity and resolution of the sensor is dependent on the capacity per unit area of the cover material of the sensor. The capacity per unit area depends on dielectric constant ε’ a nd on the thickness of the cover material. The higher the dielectric constant ε’ and the lower the thickness， the higher is the capacity per unit area. The model assumptions behind Fig. 1 and behind Eq. (I) are valid in the limit of very thin glass substrates. At larger substrate thicknesses horizontal contributions of the capacity will further reduce the capacity contrast of the fingerprint sensor. This will give an upper limit for the thickness of the cover material.
In order to increase the sensitivity of the fingerprint sensors sometimes also sapphire is used， as described in US 2013/0307818 A1. Sapphire is a single crystal material， which has a dielec-tric constant of ε’ ＝11.5 parallel to the c-axis of the crystal and of ε’ ＝9.3 perpendicular to the c-axis. However， sapphire is very expensive. Both， currently used glasses and sapphire crystals can be obtained with a thickness as low as 0.5 mm.
US 6,114,862 A describes a capacitive distance sensor but does not give any specifications to the dielectric， which is used as a cover. US 6,762,470 B2 describes a very thin scratch resistant layer using fluorocarbon polymers. However， the dielectric constant is very low.
US 8,803,258 B2 describes a finger sensing device including a protective plate having a dielec-tric constant greater than 5 and a thickness greater than 40 μm. The protective plate may be a glass plate. A dielectric constant of up to 20 is described as being desirable. However， it is dis-closed that suitable glasses have dielectric constants of only up to 14.5. Moreover， it should be noted that glasses with such high dielectric constants have not been available in a thickness as low as 40 μm directly from a hot forming process so far. Thus， even though it is clear from the  disclosure that materials with high dielectric constant and low thickness are desirable， such ma-terials are not made available.
Consequently， due the absence of suitable cover materials current fingerprint sensors have a limited resolution and sensitivity， which leads to failures and misreading of the pattern of the fingertip. It is therefore an object of the present invention to overcome the problems of the prior art. This is achieved by the subject-matter of the claims.
The problem is particularly solved by an article having a capacity per unit area of at least 0.15 pF/mm2， wherein the article is a glass sheet or a glass ceramic sheet. Preferably， the article is a glass.
Preferably， the article has a capacity per unit area of at least 0.2 pF/mm2， more preferably of at least 0.3 pF/mm2， more preferably of at least 0.5 pF/mm2， more preferably of at least 0.7 pF/mm2， more preferably of at least 1.0 pF/mm2， more preferably of at least 1.2 pF/mm2， more preferably of at least 1.5 pF/mm2， more preferably of at least 1.9 pF/mm2， more preferably at least 2.0 pF/mm2， more preferably at least 2.5 pF/mm2， more preferably at least 3.5 pF/mm2， more preferably at least 4.5 pF/mm2， more preferably at least 5.0 pF/mm2， more preferably at least 10 pF/mm2， more preferably at least 20 pF/mm2， more preferably at least 50 pF/mm2， es-pecially preferably at least 100 pF/mm2. However， the capacity per unit area should also not be too high. Therefore， the capacity per unit area of the article is preferably at most 200 pF/mm2.
The high capacity per unit area can be achieved by a high dielectric constant and/or a low thickness of the article.
Preferably， the article has a dielectric constant of at least 5， more preferably at least 5.5， more preferably at least 6， more preferably at least 6.5 more preferably at least 7， more preferably at least 8， more preferably at least 10， more preferably， at least 12， more preferably at least 15， more preferably at least 20， more preferably at least 50， more preferably at least 100， more preferably at least 200， more preferably at least 500. The dielectric constant can be measured according to DIN EN 62631-1： 2012-03.
Preferably， the article has a thickness of at most 1000 μm， more preferably at most 700 μm， more preferably at most 500 μm， more preferably at most 300 μm， more preferably at most 200 μm， more preferably at most 100 μm， more preferably at most 50 μm， more preferably at most 30 μm， more preferably at most 20 μm， more preferably at most 10 μm. However， the thickness should not be too low because the article might break. Therefore， the thickness is preferably at least 1 μm， more preferably at least 2 μm， more preferably at most 5 μm.
Preferably， the loss tangent (tan δ) of the article at a frequency of 1 MHz is at most 25×10-3， more preferably at most 10×1 0-3， more preferably at most 5×10-3， more preferably at most 2×10-3， more preferably at most 1×10-3， more preferably at most 0.9×10-3， more preferably at most 0.8×10-3， more preferably at most 0.7×10-3， more preferably at most 0.5×10-3. A too high loss tangent will average out the voltage differences and will reduce the resolution of a fingerprint sensor. The loss tangent can be measured by standard dielectric spectroscopy together with the dielectric constant.
In preferred embodiments， the article is transparent. Transparent means according to the pre-sent invention that the transmission in the visible range is at least 80％at a thickness of 500 μm. When transparent articles are used as cover for fingerprint sensors， they enable combination of fingerprint sensing function with variable visual cues provided in the fingerprinting area of a de-vice. Furthermore， also visual information from the user may be detected in order to verify user’s identity by an additional independent method.
Preferably， the article has a refractive index of at least 1.47， more preferably at least 1.52， more preferably at least 1.55， more preferably at least 1.59， more preferably at least 1.65， more pref-erably at least 1.69， more preferably at least 1.74， more preferably at least 1.79， more prefera-bly at least 1.84， more preferably at least 1.89， more preferably at least 1.94， more preferably at least 1.99， more preferably at least 2.04.
Preferably， the article has an Abbe number of at least 20， more preferably at least 25， more preferably at least 25， more preferably at least 30， more preferably at least 40， more preferably at least 50， more preferably at least 55.
Preferably， the article has Knoop hardness (HK01/20) of at least 400， more preferably at least 500， more preferably at least 550， more preferably at least 600， more preferably at least 650， more preferably at least 700， more preferably at least 800. A high Knoop hardness is advantageous because the article is more resistant to mechanical stress and more scratch resistant.
In the Knoop hardness test the indentation depth of a rhombus-shaped diamond pressed with a defined force and time on the material is measured. The diamond surfaces have defined inter-section angles of 172.5° and 130.0°. During pressing of the diamond into the glass plate an elastic and plastic deformation occurs. The size of the permanent indentation depends on the hardness of the material， which is given by the chemical composition. The Knoop hardness can be calculated from the diagonal size d of the indentation using the following formulae：
HK＝1.4233×F/d2
The standard ISO 9385： 1990 describes the measurement procedure for glasses. In accordance with this standard， the values for Knoop hardness HK are given for a test force of 0.9807 N (cor-responds to 0.1 kp) and an effective test period of 20 s. The test was performed on polished glass surfaces at room temperature. The data for hardness values are rounded to 10 HK0.1/20. The microhardness is a function of the magnitude of the test force and decreases with increas-ing test force.
Preferably， the article has an elastic modulus of at least 60×103 N/mm2， more preferably at least 70×103 N/mm2， more preferably at least 80×103 N/mm2， more preferably at least 90×103 N/mm2. However， the elastic modulus should not be too high. Therefore， the article preferably has an elastic modulus of 200×103 N/mm2， more preferably at most 165×103 N/mm2， more preferably at most 150×103 N/mm2， more preferably at most 120×103 N/mm2， more preferably at most 110×103 N/mm2.
Preferably， the article has a Poisson ratio μ of at least 0.25， more preferably at least 0.26， more preferably at least 0.27， more preferably at least 0.28， more preferably at least 0.29， more pref-erably at least 0.30.
Preferably， the article has at least one surface with a roughness Ra of less than 60 μm， more preferably less than10 μm， more preferably less than 1 μm， more preferably less than 100 nm， more preferably less than 10 nm， more preferably less than 5 nm， even more preferably less than 2 nm. The roughness can be measured by atomic force microscopy.
Preferably， the article has a coefficient of thermal expansion (CTE) of at most 11×10-6/K， more preferably at most 8×10-6/K， more preferably at most 7×10-6/K， more preferably at most 6×10-6/K， more preferably at most 5×10-6/K. Preferably， the article has a coefficient of thermal expansion (CTE) of at least 2×10-6/K， more preferably at least 2.5×10-6/K， more preferably at least 2.8×10- 6/K. The above values are advantageous for adjusting the CTE to the CTE of the underlying structure when the article is for example used as a cover member in finger print sensors.
Preferably， the glass has a thickness variation of at most±20 μm， more preferably at most±15 μm，more preferably at most±10 μm.
The article of this invention may be used in a number of devices or as component or part of components therefore， including but not limited to smart phones， portable computers， computer watches， tablet computers， gaming devices， TV sets， personal computers， intercommunication systems， home automation systems， automotive security systems， 3D imaging systems， gesture control systems， touch sensors， fingerprint sensors， diagnostic systems， gaming devices， inter-active displays， 3D sensing systems， home appliances， display devices， iris recognition systems  and others. Components therefore may include， but are not limited thereto： optical or electrical interposers， thin film batteries， illumination devices， particularly OLED or backlight units， PCBs or other electronic wiring device， electronic passive component (particularly capacitors) ， cover lenses， protective layers and/or MEMS/MOEMS.
Particularly preferably， the article is used as a cover member in fingerprint sensors.
According to the present invention is also a fingerprint sensor comprising an article according to the present invention.
Advantageously， the article has a good mechanical stability， thermal shock resistance and/or scratch resistance， particularly when the article is used as a cover member of a fingerprint sen-sor device. Therefore， the article is preferably chemically and/or thermally toughenable or toughened. More preferably， the article is chemically toughenable or toughened. Preferably， the ion exchange layer has a thickness of at least 1 μm， more preferably at least 2 μm， more pref-erably at least 5 μm， more preferably at least 10 μm， more preferably at least 20 μm， more pref-erably at least 30 μm， more preferably at least 50 μm， when the article is chemically toughened in 100％KNO3. Preferably， the central tensile stress is at most 600 MPa， more preferably at most 500 MPa， more preferably at most 400 MPa， more preferably at most 300 MPa， more preferably at most 200 MPa， more preferably at most 150 MPa， more preferably at most 120 MPa， more preferably at most 100 MPa， more preferably at most 50 MPa， more preferably at most 20 MPa， more preferably at most 10 MPa， when the article is chemically toughened in 100％KNO3. The central tensile stress can be measured with FSM 6000.
In principle， an article of the present invention can be obtained from compositions belonging to different glass families. However， in some embodiments， the article of the present invention is a boron-silicate glass article or an alumino-silicate glass article.
Glasses used in this invention are characterized by certain compositional ranges. In this de-scription we refer to the cationic compositions of the glasses. In these compositions-if nothing else is indicated- “silicon” refers to Si4+， “boron” refers to B3+， “aluminum” refers to Al3+， “phos-phorus” refers to P5+， “lithium” refers to Li+， “sodium” refers to Na+， “potassium” refers to K+， “magnesium” refers to Mg2+， “calcium” refers to Ca2+， “strontium” refers to Sr2+， “barium” refers to Ba2+， “zinc” refers to Zn2+， “titanium” refers to Ti4+， “zirconium” refers to Zr4+， “hafnium” refers to “Hf4+” ， “lanthanum” refers to La3+， “gadolinium” refers to Gd3+， “yttrium” refers to y3+， “tantalum” refers to Ta5+， “niobium” refers to Nb5+， “tungsten “refers to W6+， “arsenic” refers to the sum of As3+ and As5+， “antimony” refers to the sum of Sb3+ and Sb5+， “iron” refers to the sum of Fe3+ and  Fe4+， “cerium” refers to the sum of Ce3+ and Ce4+， “tin” refers to the sum of Sn2+ and Sn4+， and “sulfur” relates to the total amount of sulfur in all its valence states and oxidation levels.
Unless indicated otherwise， within the present description， network formers refer to cations se-lected from the group consisting of silicon， boron， aluminum and phosphorus， R+ refers to cati-ons selected from the group consisting of lithium， sodium and potassium， R2+ refers to cations selected from the group consisting of magnesium， calcium， strontium， barium and zinc and the term “highly dielectric components” refers to cations selected from the group consisting of titani-um， zirconium， hafnium， lanthanum， gadolinium， yttrium， tantalum， niobium and tungsten.
Preferred compositions of the articles of the present invention will be outlined below. The arti-cles generally comprise cationic and anionic components. The composition of cations in the article will be given in cationic percentages (cat. -％) ， i.e. indicating the molar proportion of the respective cation relative to the total molar amount of cations in the composition. Preferably， the articles comprise the following components， in cat. -％， based on the total molar amount of cati-ons in the article： network formers 25 to 90 cat. -％， lithium 0 to 25 cat. -％， sodium 0 to 30 cat. -％， potassium 0 to 15 cat. -％， magnesium 0 to 10 cat. -％， calcium 0 to 15 cat. -％， strontium 0 to 10 cat. -％， barium 0 to 20 cat. -％， zinc 0 to 17 cat. -％， titanium 0 to 30 cat. -％， zirconium 0 to 7 cat. -％，hafnium 0 to 2 cat. -％， lanthanum 0 to 35 cat. -％， gadolinium 0 to 6 cat. -％， yttrium 0 to 6 cat. -％，tantalum 0 to 5 cat. -％， niobium 0 to 42 cat. -％， tungsten 0 to 3 cat. -％. In preferred embodi-ments， the cations in the article consist of the cations mentioned in the before-mentioned list to an extent of at least 95％， more preferably at least 97％， most preferably at least 99％. In most preferred embodiments， the cationic components of the article essentially consist of the men-tioned cations.
As anionic components the article preferably comprises at least one anion selected from fluo-rine (F-) ， oxygen (O2-) ， chloride (Cl-) . Most preferably， the anions present in the article consist of oxygen to an extent of at least 95％， more preferably at least 97％， most preferably at least 99％. In most preferred embodiments， the anionic component of the article essentially consists of ox-ygen.
The terms ， ， X-free “and ， ， free of component X “， respectively， as used herein， preferably refer to an article， which essentially does not comprise said component X， i.e. such component may be present in the article at most as an impurity or contamination， however， is not added to the glass composition as an individual component. This means that the component X is not added in es-sential amounts. Non-essential amounts according to the present invention are amounts of less than 100 ppm， preferably less than 50 ppm and more preferably less than 10 ppm. Thereby “X “may refer to any component， such as lead cations or arsenic cations. Preferably， the glass- es described herein do essentially not contain any components that are not mentioned in this description.
As described above， network formers are selected from the group consisting of silicon， boron， aluminum and phosphorus according to the present invention. In preferred embodiments， net-work formers are selected from the group consisting of silicon， boron and aluminum. Even more preferred network formers are selected from the group consisting of silicon and boron. In alter-native embodiments， the network former is phosphorus.
Preferably， the article comprises silicon in proportions of 2 to 70 cat. -％. Silicon is an important network former in the glass matrix which is very important for the glass properties. In particular， silicon cations are important for the chemical resistance， hardness and scratch resistance of the article. In preferable embodiments the articles comprise at least 5 cat. -％of silicon， more prefer-ably at least 12 cat. -％of silicon， more preferably at least 20 cat. -％of silicon， still more prefera-bly at least 25 cat. -％of silicon， and most preferably at least 30 cat. -％of silicon. However， con-tents of silicon cations which are too high may result in an increase of the glass transition tem-perature， making glass production uneconomical. Therefore， it is particularly preferable that the content of silicon cations is at most 65 cat. -％， further preferable at most 55 cat. -％， still more preferable at most 45 cat. -％， and most preferable at most 40 cat. -％.
In preferred embodiments， the articles contain boron cations as a network former in addition to silicon cations. Preferably， the content of boron is in the range of from 0 to 55 cat. -％. Through its network forming properties boron cations essentially support the stability of the article. In the case of contents of boron cations which are too low the required stability in the glass system cannot be guaranteed. In preferable embodiments the articles comprise at least 0.1 cat. -％of boron， more preferably at least 10 cat. -％of boron， still more preferably at least 15 cat. -％of boron， and most preferably at least 20 cat. -％of boron. Nevertheless， in the case of contents of boron cations in the glass which are too high the viscosity may be reduced strongly so that a reduction of the crystallization stability has to be accepted. Therefore， it is particularly preferable that the content of boron cations is at most 50 cat. -％， further preferable at most 40 cat. -％， still more preferable at most 35 cat. -％， and most preferable at most 30 cat. -％.
In the articles preferably the sum of silicon and boron cations is from 25 to 90 cat. -％. In prefer-able embodiments the sum of silicon and boron cations in the articles is at least 30 cat. -％， more preferably at least 35 cat. -％， still more preferably at least 40， and most preferably at least 50 cat. -％. It is particularly preferable that the sum of silicon and boron cations in the articles is at most 85 cat. -％， further preferable at most 80 cat. -％， still more preferable at most 75 cat. -％， and most preferable at most 72 cat. -％.
It has been found that the temperature dependence of refractive index is influenced by the net-work formers aluminum， silicon and boron in the glass. Therefore， the glasses show a ratio of the sum of aluminum and boron relative to the amount of silicon in cationic percentages of from 0 to 16. Preferably， this ratio is from ＞0 to 5， more preferably from ＞0.25 to 2， most preferably from 0.3 to 1.
In the articles preferably aluminum cations are contained in proportions of 0 to 20 cat. -％. The addition of aluminum cations results in improved glass forming properties and generally sup-ports the improvement of chemical resistance. In preferable embodiments the glasses comprise at least 0.1 cat. -％of aluminum， more preferably at least 1 cat. -％of aluminum， still more prefer-ably at least 2 cat. -％of aluminum， and most preferably at least 3 cat. -％of aluminum. However， contents of aluminum cations which are too high result in an increased tendency to crystalliza-tion. Therefore， it is particularly preferable that the content of aluminum cations is at most 20 cat. -％， further preferable at most 18 cat. -％， further preferable at most 15 cat. -％， still more pref-erable at most 10 cat. -％， and most preferable at most 8 cat. -％.
In alternative embodiments， the main network former is phosphorus. In such embodiments， the articles may comprise other network formers， particularly silicon， boron and/or aluminium in amounts of up to 10 cat. -％. However， preferably， in such embodiments， phosphorus is the only network former. Preferably， in such embodiments， the articles comprise phosphorus in an amount of from 25 to 45 cat. -％. Preferably， the amount of phosphorus in the articles is at least 27 cat. -％， more preferably at least 30 cat. -％. In the case of contents of phosphorus cations which are too low the required stability in the glass system cannot be guaranteed. However， the content of phosphorus cations should also not be too high. Preferably， the content of phospho-rus is at most 40 cat. -％， more preferably at most 35 cat. -％.
The glasses preferably contain fluxing agents to improve melting properties， particularly com-prising alkali metal cations and/or alkaline earth metal cations. Preferably， the sum of fluxing agents ∑ {∑R2+ (R＝Mg， Ca， Sr， Ba， Zn) + ∑R+ (R’ ＝Li， Na， K) } preferably is 5 to 45 cat. -％. In preferable embodiments the sum of the amounts of the fluxing agents in the glasses is at least 5 cat. -％， more preferably at least 7 cat. -％， still more preferably at least 12 cat. -％， and most pref-erably at least 15 cat. -％. If the amount of fluxing agents in the glass is too high， chemical re-sistance will decrease. It is particularly preferable that the sum of the fluxing agents in the glasses is at most 40 cat. -％， further preferable at most 35 cat. -％， still more preferable at most 30 cat. -％， and most preferable at most 25 cat. -％.
Alkali metal cations improve the meltability of the glass and thus allow an economic production. Also， they may are necessary for allowing chemical strengthening of the glass by ion exchange  treatment. During the production of the article the alkali metal cations serve as fluxing agents. The sum of the amounts of the alkali metal cations lithium， sodium and potassium in the glasses preferably is 0 to 45 cat. -％. In preferable embodiments the sum of the alkali metal cations is at least 5 cat. -％， more preferably at least 7 cat. -％， still more preferably at least 10 cat. -％， and most preferably at least 15 cat. -％. However， if contents of alkali metal cations are too high the weathering resistance of the glass may be compromised and thus the range of applications thereof may strongly be limited. Therefore， it is particularly preferable that the sum of the alkali metal cations is at most 40 cat. -％， further preferable at most 35 cat. -％， still more preferable at most 30 cat. -％， and most preferable at most 25 cat. -％.
In the articles preferably lithium cations are contained in proportions of 0 to 25 cat. -％. Lithium serves as a fluxing agent and has excellent properties for ion exchange strengthening. There-fore， the articles comprise preferably at least 1 cat. -％， more preferably at least 5 cat. -％. How-ever， lithium affects chemical stability of the glasses to a great extent so that its content should be limited. It is particularly preferable that the content of lithium cations is at most 20 cat. -％， further preferable at most 15 cat. -％， still more preferable at most 10 cat. -％. Moreover， in pref-erable alternative embodiments， lithium is replaced by other alkali metal cations so that the arti-cles comprise at most 1 cat. -％lithium， more preferably are even free of lithium cations.
In the glasses preferably sodium cations are contained in proportions of 0 to 30 cat. -％. Sodium is a good component for ion exchange treatment. But -as with all alkali metal ions -the amount of this component should not be too high because it decreases chemical stability. In preferable embodiments the glasses comprise at least 1 cat. -％of sodium， more preferably at least 3 cat. -％of sodium， still more preferably at least 5 cat. -％of sodium， and most preferably at least 8 cat. -％of sodium. It is particularly preferable that the content of sodium cations is at most 25 cat. -％， further preferable at most 22 cat. -％， still more preferable at most 20 cat. -％， and most preferable at most 15 cat. -％.
In the glasses preferably potassium cations are contained in proportions of 0 to 15 cat. -％. The negative impact of potassium on chemical stability is less strong compared to the other alkali metal ions. However， potassium is not suitable for ion exchange treatment. Also， the content of potassium is preferably limited because it contains isotopes that emit beta rays. In preferable embodiments the articles comprise at least 1 cat. -％of potassium， more preferably at least 2 cat. -％of potassium， still more preferably at least 3 cat. -％of potassium， and most preferably at least 5.5 cat. -％of potassium. It is particularly preferable that the content of potassium cations is at most 15 cat. -％， further preferable at most 13 cat. -％， still more preferable at most 12 cat. -％.
It has been found that the leaching tendency of the glass can be reduced by using both sodium and potassium in the glass and keeping the ratio of sodium to potassium in cat. -％in a range of up to 10， more preferably up to 5， more preferably up to 4， preferably up to 3 and most prefera-bly at less than 2. Keeping this ratio low， i.e. the sodium does not exceed a certain amount rela-tive to the amount of potassium， provides for glasses having good meltability and excellent chemical and hydrolytical resistance. Specifically， such glasses will have an HGB1 according to ISO 719： 1989. However， in order to adjust the viscosity in the melt to a desirable value， the ratio of sodium to potassium should be more than 0.5， preferably more than 0.8 and most preferably at least 1.0.
R2+ cations improve the meltability of the glass and thus allow for an economic production. Dur-ing the production of the article they serve as fluxing agents. The sum of the R2+ cations mag-nesium， calcium， strontium， barium and zinc in the articles preferably is of 0 to 35 cat. -％. When the amount of R2+ ions in the articles is too high， the chemical resistance of the articles is affect-ed. Hence， according to this invention the sum of R2+ ions in the articles is preferably at most 30 cat. -％， further preferable at most 25 cat. -％， still more preferable at most 20 cat. -％， and most preferable at most 18 cat. -％. However， R2+ cations may be used to adjust the viscosity of the glasses， particularly the fine tuning of the viscosity-temperature profile. Moreover， R2+ cations -as alkali metal cations-may be used as fluxing agents. Therefore， the articles preferably com-prise R2+ cations in an amount of at least 1 cat. -％， more preferably at least 2 cat. -％， more pref-erably at least 5 cat. -％， more preferably at least 10 cat. -％.
In the glasses preferably magnesium cations are contained in proportions of 0 to 10 cat. -％. It is particularly preferable that the content of magnesium cations is at most 8 cat. -％， more prefera-bly at most 6 cat. -％. In preferable embodiments the glasses are free of magnesium.
In the glasses preferably calcium cations are contained in proportions of 0 to 15 cat. -％. It is particularly preferable that the content of calcium cations is at most 8 cat. -％， further preferable at most 5 cat. -％， further preferable at most 3 cat. -％. In preferable embodiments the glasses are free of calcium.
In the glasses preferably strontium cations are contained in proportions of 0 to 10 cat. -％. It is particularly preferable that the content of strontium cations is at most 8 cat. -％， further preferable at most 5 cat. -％， further preferable at most 3 cat. -％. In preferable embodiments the glasses are free of strontium.
In the glasses preferably barium cations are contained in proportions of 0 to 23 cat. -％. Barium is preferably used for adjusting the temperature dependence of viscosity and for increasing the  refractive index as well as the dielectric constant. Preferably， the content of barium in the arti-cles is at least 0.1 cat. -％， more preferably at least 1 cat. -％， more preferably at least 5 cat. -％. However， the content of barium should not be too high. Preferably， the content of barium cati-ons is at most 22 cat. -％， more preferably at most 20 cat. -％， more preferably at most 15 cat. -％， further preferable at most 10 cat. -％. In preferable alternative embodiments， the articles contain at most 1 cat. -％barium cations， more preferable are even free of barium.
In the glasses preferably zinc cations are contained in proportions of 0 to 17 cat. -％. Zinc cati-ons may be contained in the glass as an additional fluxing agent as well as for adjusting the melting point in a targeted manner. By the addition of the network modifier zinc the melting point of glass may be reduced. In preferable embodiments the glasses comprise at least 1 cat. -％of zinc， more preferably at least 2 cat. -％of zinc， still more preferably at least 5 cat. -％of zinc. However， contents of zinc cations which are too high may result in a reduction of the melting point of the glasses. It is particularly preferable that the content of zinc cations is at most 15 cat. -％， further preferable at most 10 cat. -％.
In the glasses preferably titanium cations are contained in proportions of 0 to 50 cat. -％. Titani-um cations are added to the glasses for improving their optical properties. In particular， with the help of additions of titanium the refractive index of the glasses can be adjusted in a targeted manner. So the refractive index increases with an increasing content of titanium cations of the glass. In preferable embodiments the articles comprise at least 1 cat. -％of titanium， more pref-erably at least 2 cat. -％of titanium， still more preferably at least 5 cat. -％of titanium， and most preferably at least 10 cat. -％of titanium. However， contents of titanium cations which are too high may result in undesirable crystallization of the glass. Therefore， it is particularly preferable that the content of titanium is at most 46 cat. -％， more preferably at most 30 cat. -％， more pref-erably at most 25 cat. -％， further preferable at most 20 cat. -％.
In the articles preferably zirconium cations are contained in proportions of 0 to 8 cat. -％. Zirconi-um cations may be used to adjust the refractory index of the glasses. However， a content of zirconium cations， which is too high， may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of zirconium is at most 7 cat. -％， more preferably at most 5 cat. -％， further preferable at most 2 cat. -％， still more preferable at most 1 cat. -％. In preferable embodiments the glasses are free of zirconium.
In the articles preferably hafnium cations are contained in proportions of 0 to 2 cat. -％. Hafnium cations may be used to adjust the refractory index of the glasses. However， a content of hafni-um cations， which is too high， may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of hafnium is at most  1.5 cat. -％， further preferable at most 1 cat. -％， still more preferable at most 0.5 cat. -％. In pref-erable embodiments the glasses are free of hafnium.
In the articles preferably lanthanum cations are contained in proportions of 0 to 35 cat. -％. Lan-thanum cations may be used for increasing the dielectric constants of the articles. However， a content of lanthanum cations， which is too high， may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of lanthanum is at most 20 cat. -％， further preferable at most 10 cat. -％， still more preferable at most 5 cat. -％， still more preferable at most 1 cat. -％. In preferable embodiments the glasses are free of lanthanum.
In the articles preferably gadolinium cations are contained in proportions of 0 to 6 cat. -％. Gado-linium cations may be used for increasing the dielectric constants of the articles. However， a content of gadolinium cations， which is too high， may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of gadolinium is at most 2 cat. -％， further preferable at most 1 cat. -％， still more preferable at most 0.1 cat. -％. In preferable embodiments the glasses are free of gadolinium.
In the articles preferably yttrium cations are contained in proportions of 0 to 6 cat. -％. Yttrium cations may be used for increasing the dielectric constants of the articles. However， a content of yttrium cations， which is too high， may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of yttrium is at most 5 cat. -％， further preferable at most 2 cat. -％， still more preferable at most 1 cat. -％. In preferable embodiments the glasses are free of yttrium.
In the articles preferably tantalum cations are contained in proportions of 0 to 5 cat. -％. Tanta-lum cations may be used for increasing the dielectric constants of the articles. However， a con-tent of tantalum cations， which is too high， may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of tan-talum is at most 4 cat. -％， further preferable at most 2 cat. -％， still more preferable at most 1 cat. -％. In preferable embodiments the glasses are free of tantalum.
In the articles preferably niobium cations are contained in proportions of 0 to 42 cat. -％. Niobium cations may be used for increasing the dielectric constants of the articles. However， a content of niobium cations， which is too high， may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of niobium is at most 15 cat. -％， further preferable at most 10 cat. -％， still more preferable at most 5 cat. -％. In preferable embodiments the glasses are free of niobium.
In the articles preferably tungsten cations are contained in proportions of 0 to 3 cat. -％. Tung-sten cations may be used for increasing the dielectric constants of the articles. However， a con-tent of tungsten cations， which is too high， may decrease the meltability and particularly may lead to stronger crystallization of the glasses. It is particularly preferable that the content of tungsten is at most 2 cat. -％， further preferable at most 1 cat. -％， still more preferable at most 0.1 cat. -％. In preferable embodiments the glasses are free of tungsten.
The glasses may comprise refining agents in an amount of up to 1 cat. -％， more preferably up to 0.5 cat. -％， more preferably up to 0.1 cat. -％. Preferably refining agents are comprised in the articles in an amount of at least 0.005 cat. -％， more preferably at least 0.01 cat. -％. Preferably， the refining agents are selected from the group consisting of antimony， arsenic and tin. More preferably， the refining agents are selected from the group consisting of antimony and tin.
The articles may comprise cerium in amount of up to 0.5 cat. ％， more preferably up to 0.3 cat. -％，more preferably up to 0.2 cat. -％， more preferably up to 0.1 cat. -％， more preferably up to 0.005 cat. -％. Cerium may be used for increasing the radiation stability of the articles. However， in preferred embodiments， the articles are free of cerium.
According to the present invention， highly dielectric components may be used for increasing the dielectric constant of the articles. Highly dielectric components are cations selected from the group consisting of titanium， zirconium， hafnium， lanthanum， gadolinium， yttrium， tantalum， nio-bium and tungsten. However， highly dielectric components decrease the meltability and particu-larly may lead to stronger crystallization of the glasses. Therefore， in preferred embodiments， the articles comprise at most 5 cat. -％， more preferably at most 3 cat. -％， more preferably less than 1 cat. -％of highly dielectric components. In such embodiments， the high capacity per unit area is preferably achieved by a very low thickness of the articles.
However， in alternative embodiments， the articles comprise the following components， in cat. -％， based on the total molar amount of cations in the article： network formers 25 to 75 cat. -％， R+ 0 to 45 cat. -％， R2+ 0 to 35 cat. -％， highly dielectric components 9 to 75 cat. -％. A particularly pre-ferred alternative article composition comprises the following components， in cat. -％， based on the total molar amount of cations in the article： network formers 30 to 70 cat. -％， R+ 5 to 35 cat. -％，R2+ 5 to 30 cat. -％， highly dielectric components 15 to 60 cat. -％. In preferred alternative em-bodiments， the cations in the articles consist of the cations mentioned in the before-mentioned lists to an extent of at least 95％， more preferably at least 97％， most preferably at least 99％. In most preferred embodiments， the cationic components of the articles essentially consist of the mentioned cations.
In order to increase the dielectric constant of the articles， highly dielectric components may be present in the articles in amount of at least 9 cat. -％， more preferably at least 15 cat. -％， more preferably at least 20 cat. -％， more preferably at least 30 cat. -％. However， due the decrease in meltability and the stronger crystallization， the amount of highly dielectric components should not be too high. Preferably， the content of highly dielectric components in the articles is at most 75 cat. -％， more preferably at most 60 cat. -％， more preferably at most 50 cat. -％， more prefera-bly at most 40 cat. -％.
It has been found by the present inventors that such high amounts of highly dielectric compo-nents may be tolerated if an advantageous ratio of dielectric components to network formers is chosen. Preferably the ratio of dielectric components (in cat. -％) to network formers (in cat. -％) is at most 2.5， more preferably at most 2.0， more preferably at most 1.5， more preferably at most 1.0， more preferably at most 0.8， more preferably at most 0.6.
Preferably， high grade raw materials are used for very little color absorption， which is good for exact color printing.
According to the present invention is also a method for producing an article according to the present invention comprising the steps of
a) Providing a composition，
b) Melting the composition，
c) Producing a glass in a flat glass process.
The method may comprise further steps. Further steps may be for example chemically or ther-mally toughen the glass and/or converting the glass to a glass ceramic.
As explained above， it is advantageous according to the present invention to obtain glass arti-cles with low thickness. Thin glass can in principle be obtained by grinding a thicker glass to the desired thickness. However， sheet thicknesses as low as desired for the articles of the present invention are difficult to obtain by grinding and polishing of thicker glass sheets. In contrast， very thin glasses can be obtained by flat glass processes. Therefore， it is an advantage of the arti-cles of the present invention that they can be obtained by a flat glass process. Flat glass pro-cesses are well known to the skilled person. According to the present invention， the flat glass processes are preferably selected from the group consisting of pressing， down-draw， re-draw， overflow fusion， floating and rolling.
Another advantage is that due to the manufacturing methods with which the articles of the pre-sent invention can be obtained， the articles have preferably at least one， in particular two fire-polished surfaces. Fire-polished surfaces are extremely smooth， i.e. they show only low rough-ness. In contrast to mechanical polishing， in the case of fire-polishing a surface is not ground， but the material to be polished is heated to such a high temperature so that it flows， which re-sults in a smooth surface condition. Therefore， the costs for the production of a smooth surface by fire-polishing are substantially lower than the costs for the production of a very smooth me-chanically polished surface.
According to the present invention is also the use of an article of the present invention as a cov-er member of a fingerprint sensor device.
When it is stated in the present description that the articles are free of a certain component or do not contain a certain component， this means that this component is present at most as impu-rity. Thus， this means that the component has not been added on purpose and is present at most in non-substantial amounts. According to the present invention， non-substantial amounts are amounts on a weight basis of less than 1000 ppm， preferably less than 500 ppm and even more preferably less than 100 ppm.
Unless otherwise stated， in the present application values for the dielectric constant depict the dielectric constant at a frequency of 1 MHz.
Examples
Articles have been prepared by a flat glass process. Ultra-thin articles with high dielectric con-stants and low loss tangent (tan δ) were obtained. Table 1 provides an overview of different articles according to the present invention. Glass compositions are given in cat. -％. The compo-sitions above are the final compositions measured in the glass. The skilled person knows how to obtain these glasses by melting the necessary raw materials. The glasses shown in table 1 contained only oxides as the anionic component， i.e. the glasses were oxidic.
Table 1
Figure PCTCN2016072045-appb-000001
Figure PCTCN2016072045-appb-000002
Figure PCTCN2016072045-appb-000003
Articles 8 to 10 showed very high dielectric constants but were not chemically toughenable. Ar-ticles 1 to 7 were chemically toughenable.
Table 2 shows compositions with low content of highly dielectric components. Glass composi-tions are given in cat. -％. The compositions above are the final compositions measured in the glass. The skilled person knows how to obtain these glasses by melting the necessary raw ma-terials. The glasses shown in table 2 contained only oxides as the anionic component， i.e. the glasses were oxidic.
Table 2
Article No. 1 2 3 4 5 6 7 8 9 10 11 12
silicon 55 52 65 65 57 50 48 70 60 56 54 49
boron 16       13 14 1 20 15     3
aluminum 19 17     4 6 17 2 6 14 13 13
lithium             16         ＜1
sodium   21 19 15 11 10 14 7 16 22 18 24
potassium   5 6 10 8 11 ＜1 ＜1   2 7 5
magnesium 4 5               5 8 3
calcium 5   8 7     ＜1   3 ＜1 ＜1 2
barium 1   ＜1 1                
zinc     2 3 4 5     ＜1      
titanium     ＜1 ＜1 3 3            
zirconium   ＜1         2     ＜1 ＜1 ＜2
arsenic ＜1                      
antimony ＜1   ＜1 ＜1 ＜1       ＜1     ＜1 
cerium   ＜1         ＜1          
iron             ＜1 ＜1   ＜1 ＜1  
Article No. 1 2 3 4 5 6 7 8 9 10 11 12
sulfur             ＜0.6          
tin                   ＜1   ＜1
Na/K - ＞4 ＞3 ＞1 ＞1 ＜1 ＞14 ＞7 - ＞11 ＞2 ＞4
(Al+B) /si 0.6 0.3 0 0 0.3 0.4 0.4 0.3 0.35 0.25 0.25 0.3
Even though the articles shown in table 2 have lower dielectric constants in the range of from 5 to 8， the high capacity per unit area was still achieved due to the low thickness of the articles of less than 30 μm.
Description of figures
Figure 1 shows a scheme of the electronic circuit underlying capacitive fingerprint sensors. U0 is the voltage of a voltage source， ZI the inner impedance of the electronic parts， ZG the imped-ance of the cover material， ZR the impedance of ridges， ZV the impedance of valleys， and ΔU is the voltage difference that is detected as the signal.

Claims (14)

  1. Article having a capacity per unit area of at least 0.15 pF/mm2， wherein the article is a glass sheet or a glass ceramic sheet.
  2. Article according to claim 1， wherein the article is a glass.
  3. Article according to claim 1 or 2， wherein the article has a dielectric constant of at least 5.
  4. Article according to at least one of the preceding claims， wherein the article has a thickness of at most 500 μm.
  5. Article according to at least one of the preceding claims， wherein the article is transparent.
  6. Article according to at least one of the preceding claims， wherein the article has a refractive index of at least 1.47.
  7. Article according to at least one of the preceding claims， wherein the article has a coeffi-cient of thermal expansion (CTE) of at most 11x10-6/K.
  8. Article according to at least one of the preceding claims， wherein the article is chemically toughenable or toughened.
  9. Article according to at least one of the preceding claims， wherein the article is used as a cover member in fingerprint sensors.
  10. Fingerprint sensor comprising an article according to at least one of the preceding claims.
  11. Method for producing an article according to at least one of claims 1 to 9， the method com-prising the steps of
    a) Providing a composition，
    b) Melting the composition， and
    c) Producing a glass in a flat glass process.
  12. Method according to claim 11， wherein the method further comprises the step of chemically or thermally toughen the glass.
  13. Method according to claim 11 or 12， wherein the fiat glass process is selected from the group consisting of pressing， down-draw， re-draw， overflow fusion， floating and rolling.
  14. Use of an article according to at least one of claims 1 to 9 as a cover member of a finger-print sensor device.
PCT/CN2016/072045 2016-01-25 2016-01-25 Article with high capacity per area and use of such article in finger-print sensors WO2017127995A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
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JP2003188166A (en) * 2001-11-30 2003-07-04 Stmicroelectronics Inc Protection of exposed semiconductor chip using thin polymer coating
US20040188838A1 (en) * 2003-03-31 2004-09-30 Fujitsu Limited Semiconductor device for fingerprint recognition
CN1637973A (en) * 2003-12-30 2005-07-13 E.I.内穆尔杜邦公司 Thin film capacitors on ceramic
CN1826424A (en) * 2003-05-23 2006-08-30 希莫菲克斯公司 Energy conversion and storage films and devices by physical vapor deposition of titanium and titanium oxides and sub-oxides
CN102053749A (en) * 2009-10-30 2011-05-11 苹果公司 Touch sensitive device with dielectric layer
CN104024173A (en) * 2011-12-27 2014-09-03 旭硝子株式会社 Surface glass for capacitive touch sensors
CN104194271A (en) * 2014-08-29 2014-12-10 天津德高化成新材料股份有限公司 Dielectric composite material for fingerprint sensor induction layer and preparation method thereof

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003188166A (en) * 2001-11-30 2003-07-04 Stmicroelectronics Inc Protection of exposed semiconductor chip using thin polymer coating
US20040188838A1 (en) * 2003-03-31 2004-09-30 Fujitsu Limited Semiconductor device for fingerprint recognition
CN1826424A (en) * 2003-05-23 2006-08-30 希莫菲克斯公司 Energy conversion and storage films and devices by physical vapor deposition of titanium and titanium oxides and sub-oxides
CN1637973A (en) * 2003-12-30 2005-07-13 E.I.内穆尔杜邦公司 Thin film capacitors on ceramic
CN102053749A (en) * 2009-10-30 2011-05-11 苹果公司 Touch sensitive device with dielectric layer
CN104024173A (en) * 2011-12-27 2014-09-03 旭硝子株式会社 Surface glass for capacitive touch sensors
CN104194271A (en) * 2014-08-29 2014-12-10 天津德高化成新材料股份有限公司 Dielectric composite material for fingerprint sensor induction layer and preparation method thereof

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