1. Field of the Invention
The present invention relates to a method of manufacturing an optical filter for a semiconductor illuminance sensor which uses a photodetection element such as a photodiode. This kind of semiconductor illuminance sensor is used for detecting the illuminance of a periphery thereof in fields of, for example, automatic lighting control and dimming for an illumination device, backlight control for a liquid crystal display device, backlight control for a keypad of a mobile phone, night-vision switching control for a security camera, and the like. Further, the semiconductor illuminance sensor is combined with a light emitting element to be used as a proximity sensor for detecting presence/absence of an object and measuring the distance of the object.
2. Description of the Related Art
The visible light for human beings lies between 380 to 780 nm, and of this range, a range between about 440 to 700 nm is the main sensitive wavelength range. However, depending on the light color (wavelength), the human eye senses high or low brightness even among the light having the same power. Relative luminosity characteristics represent relative brightness for each color, which is sensed high by the human eye, and have a peak in the vicinity of a green color having a wavelength of 500 to 600 nm.
An illuminance sensor for backlight control of a display device and the like are desired to have spectral sensitivity characteristics close to the human luminosity characteristics.
A photodiode is used in an illuminance sensor for detecting the visible light intensity, but the spectral sensitivity characteristics of the photodiode differ from the human luminosity characteristics. Therefore, in order to bring the spectral sensitivity characteristics close to the human luminosity characteristics, as described in Japanese Utility Model Application Laid-open No. Sho 61-82230 and Japanese Patent Application Laid-open No. 2007-48795, an optical filter or a multilayer reflective film is provided on the surface of the photodiode, or as described in Japanese Patent Application Laid-open Nos. 2006-148014 and 2009-238944, photodiodes having different sensitivity characteristics are used to perform correction based on results computed from a difference of currents flowing therethrough. Further, in order to enhance the correction accuracy, in Japanese Patent Application Laid-open Nos. 2007-48795 and 2007-536728, a window for regulating the incident light is provided.
However, in a method described in Japanese Patent Application Laid-open Nos. 2006-148014 and 2009-238944, which uses a plurality of photodiodes, there are problems of cost increase due to the use of the plurality of photodiodes, and insufficient correction accuracy.
In a method described in Japanese Utility Model Application Laid-open No. Sho 61-82230, which uses the optical filter, an interference filter formed of a dielectric multilayer is used as the optical filter, and hence the cost is higher. Further, the filter characteristics vary depending on the light incident angle, and hence the detection accuracy is still insufficient.
As a countermeasure, Japanese Patent Application Laid-open Nos. 2007-48795 and 2007-536728 propose a method of providing a window for regulating the incident light, but increase in cost for forming the window cannot be avoided.
The present invention has been made to solve the problems described above, and has an object to provide a method of manufacturing an optical filter for an illuminance sensor, which has spectral characteristics close to human luminosity characteristics, has high detection accuracy, and can be manufactured at low cost.
In order to achieve the above-mentioned object, a method of manufacturing an optical filter for an illuminance sensor according to an exemplary embodiment of the present invention includes: a first step of opening a hole in a glass plate; a second step of arranging, in the hole of the glass plate, a small piece of glass having an optical filter effect and having a glass softening point lower than a glass softening point of the glass base; a third step of softening the small piece of glass under high temperature; and a fourth step of abrading both surfaces of the glass base to planarize the glass base.
Further, the hole may be a through hole.
Further, the first step may be carried out by molding.
Alternatively, the first step may be carried out by sandblasting.
Alternatively, the first step may be carried out by glass etching.
Further, the small piece of glass may have a bead shape.
Further, the third step of softening the small piece of glass under high temperature may include sandwiching the glass base with plate members and applying a pressure to the glass base.
Further, after the third step of softening the small piece of glass under high temperature, a step of sandwiching the glass base with flat molds and applying a pressure to the glass base under high temperature may be added.
Further, the hole of the glass base may have a frustum shape with a step.
Alternatively, the hole of the glass base may have a hand-drum shape in which a diameter is small at a center portion thereof.
Further, the glass plate may be a glass plate having light blocking characteristics.
Further, the glass plate may be a black glass plate.
Further, the black glass plate may contain 3 to 20% of a black pigment.
The method of manufacturing an optical filter for an illuminance sensor according to the exemplary embodiment of the present invention includes the steps of punching the glass, arranging the small piece of glass, softening the small piece of glass, and abrading. All of the manufacturing steps are simple steps, and hence the manufacturing cost can be greatly reduced as compared to a conventional method. Further, through selection of glass having a filter effect close to color correction characteristics as the small piece of glass, excellent correction characteristics can be obtained. Thus, unlike the case of using the interference filter, filter characteristics do not vary depending on the light incident angle, and further, a window for regulating the incident light is provided, and hence a cost-effective illuminance sensor having very high accuracy can be provided.
In the accompanying drawings:
A method of manufacturing an optical filter for an illuminance sensor according to the present invention includes opening a hole in a glass plate at a predetermined position and size in conformity to a sensor element, and then heating and embedding a small piece of glass having an optical filter effect, thereby manufacturing the optical filter. The used small piece of glass having the optical filter effect is selected depending on the characteristics of the sensor element and the intended use of the illuminance sensor. Further, in a step of abrading a glass base having the small piece of glass embedded therein, the thickness of the glass base is controlled, and thus an optical filter having a desired optical filter effect can be manufactured.
Specifically, the method of manufacturing an optical filter for an illuminance sensor includes a punching step, an arranging step, an embedding step, and an abrading step. In the punching step, a mold having a protrusion on a surface thereof is heated and pressed against the glass plate at a temperature equal to or higher than a softening point of the glass, to thereby form a hole. Alternatively, the hole is formed by sandblasting or glass etching. In the arranging step, the small piece of glass having the optical filter effect is arranged in the hole of the glass base. In the embedding step, the small piece of glass is heated to a temperature between a softening point of the small piece of glass and the softening point of the glass base, and the small piece of glass is softened to be embedded in the hole. In the abrading step, the projected small piece of glass after the softening is abraded and planarized. In a case where the hole is a bottomed hole, a rear surface of the glass base is abraded to expose the small piece of glass. Further, the thickness of the glass base is adjusted to have a predetermined value.
Hereinafter, a method of manufacturing an optical filter for an illuminance sensor of the present invention is described in detail with reference to the drawings.
<Punching Step>
As another method, there may be employed a method of blasting an abrasive such as alumina to the glass plate 10 to open a hole, that is, so-called sandblasting. Also in this case, the glass base 14 having a hole can be formed.
Alternatively, a resist may be printed onto the surface of the glass plate 10 except for a hole portion, a resist may also be applied over the entire glass rear surface, then the glass plate 10 may be immersed into a glass etchant such as hydrofluoric acid to open a hole, and finally the resist may be removed. Even in this case, the glass base 14 having a hole can be similarly formed.
<Arranging Step>
It is ideal that the optical filter effect necessary for the illuminance sensor conforms to a color correction curve, but in this case, the filter transmittance decreases. In a case where the sensitivity is valued, a filter for blocking only the infrared ray is used. In the latter case, phosphate glass is used, and in the former case, glass obtained by adding metal oxide such as CuO to phosphate glass is used. Phosphate glass tends to have weak moisture resistance, and hence in a case where weather resistance is demanded, adjustment may be made by adding an inorganic pigment to silicate glass. In all of the above-mentioned cases, the glass composition is adjusted so that the glass material for the small piece of glass 7 has a lower softening point than that for the glass base 14.
The glass having the optical filter effect is obtained by forming a glass rod having a diameter corresponding to the hole of the glass base 14, and cutting the glass rod to have a volume corresponding to the embedding amount. Thus, the columnar small piece of glass 7 is obtained.
Note that, a rectangular parallelepiped or cubic small piece of glass 7 is also usable, and in this case, glass in an ingot state may be sliced by a slicer or a wire cutting machine, and then may be cut to have a predetermined volume.
The small piece of glass 7 can be easily fed into the hole of the glass base by spreading the small piece of glass 7 on the glass base 14 and vibrating the glass base 14.
<Embedding Step>
The glass base 14 and the small piece of glass 7, which are obtained after finishing the arranging step illustrated in
When a coefficient of thermal expansion of the glass base 14 is larger than that of the small piece of glass 7, cracks are liable to be generated in the small piece of glass, and when the coefficient of thermal expansion of the small piece of glass 7 is larger than that of the glass base 14, the small piece of glass may be easily slipped out. Therefore, the difference therebetween is desired to be within 30×10−7/° C.
<Abrading Step>
The glass base 14 and the small piece of glass 7, which are obtained after finishing the softening and embedding of the small piece of glass 7, are abraded so that a front surface thereof is planarized, the small piece of glass 7 is exposed on a rear surface thereof, and the small piece of glass 7 has a predetermined thickness. Thus, an optical filter substrate 6 of
For reference,
<Punching Step>
<Arranging Step>
<Embedding Step>
The glass base 26 and the small piece of glass 7, which are obtained after finishing the arranging step illustrated in
<Abrading Step>
Next, abrading is performed to planarize the surface and adjust the thickness. Thus, the optical filter substrate 6 of
In this embodiment, the small piece of glass is also exposed at the rear surface in the embedding step, and hence as compared to the first embodiment, the abrading amount in the abrading step can be reduced, and the abrading cost can be reduced.
<Embedding Step>
<Planarization Step>
Next, abrading is performed to planarize the surface and adjust the thickness. Thus, the optical filter substrate 6 of FIG. 5C can be obtained.
In this embodiment, the projection of the small piece of glass after the embedding step is small and flat, and hence the glass can be prevented from being broken in the abrading step. Further, as compared to the first and second embodiments, the rate of failure during the abrading can be greatly reduced.
<Embedding Step>
In order to eliminate the above-mentioned defects, the embedding step of this embodiment is carried out by performing, after the embedding step of the second embodiment (first embedding step), the embedding step of the third embodiment (second embedding step).
<Abrading Step>
Next, abrading is performed to planarize the surface and adjust the thickness. Thus, the optical filter substrate 6 of
When the first and second embedding steps are performed as described above, regardless of the arrangement fluctuations in the arranging step or the viscosity of the softened small piece of glass, the small piece of glass can be embedded into the through hole without a gap, and hence stable production is possible.
<Arranging Step>
Note that, the bead shape may be a sphere or an ellipse, but a sphere can provide better performance in feeding into the hole.
<Embedding Step>
<Abrading Step>
Next, abrading is performed to planarize the surface and adjust the thickness. Thus, the optical filter substrate 6 of
When the bead-shaped small piece of glass 30 is used, unlike the case where a columnar or rectangular parallelepiped small piece of glass is used, the small piece of glass 30 is not arranged in a tilted manner in the arranging step. Therefore, the first embedding step of the fourth step is unnecessary, and stable production is possible with reduced steps.
<Punching Step>
<Arranging Step>
<Embedding Step>
<Abrading Step>
Next, abrading is performed to planarize the surface and adjust the thickness. Thus, the optical filter substrate 6 of
In this embodiment, in addition to the effect that the number of steps can be reduced as described above, the contact area between the small piece of glass 30 and the glass base 35 increases, and hence reliability and durability in a temperature shock test and the like are enhanced.
<Punching Step>
<Arranging Step>
<Embedding Step>
<Abrading Step>
Next, abrading is performed to planarize the surface and adjust the thickness. Thus, the optical filter substrate 6 of
Further, in this embodiment, similarly to the sixth embodiment, the contact area between the small piece of glass 30 and the glass base 40 increases, and hence reliability and durability in a temperature shock test and the like are enhanced.
In the first embodiment, glass having light blocking characteristics is used for the glass plate 10. The light blocking characteristics of the glass can be obtained by dispersing, in glass, a material having a refractive index different from that of the glass, such as Al2O3, TiO2, and ZrO2. For example, when 20% or more of ZrO2 is added to soda glass, glass having a transmittance of 5% or less at a thickness of 0.5 mm is obtained.
With use of the glass having the light blocking characteristics, incident light entering into the illuminance sensor element 4 illustrated in
As the glass having the light blocking characteristics of the eighth embodiment, black glass is used. The black glass is obtained by adding a pigment such as iron oxide to glass. For example, when 3% of black pigment mainly containing iron oxide is added to soda glass, glass having a transmittance of 5% or less at a thickness of 0.5 mm is obtained. Thus, with a lower concentration additive amount than the case of Al2O3 or TiO2, the necessary light blocking rate can be obtained. Further, when 20% of the black pigment is added, a transmittance of 5% or less can be obtained even when the thickness of the optical filter substrate 6 is 0.2 mm, and hence a thin illuminance sensor can be provided.
In the above, by means of the first to ninth embodiments, the method of manufacturing a single optical filter substrate 6 has been described, but multiple optical filter substrates 6 can be formed at once. Further, the hole into which the small piece of glass is embedded is described to have a circular shape, but depending on the sensor element, the package specification, and the intended use, the hole may have a multangular shape such as a triangular shape, a square shape, and a hexagonal shape, or a shape having a circular-arc or hyperbolic inclination surface.
A reliable optical filter for an illuminance sensor, which has spectral characteristics close to human luminosity characteristics, can be easily manufactured at low cost, and hence the present invention can contribute to supply of an illuminance sensor usable for many uses.
Number | Date | Country | Kind |
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2011-145894 | Jun 2011 | JP | national |