Semiconductor device manufacturing: process – Forming bipolar transistor by formation or alteration of... – Including diode
Reexamination Certificate
2000-11-14
2004-02-03
Resan, Steven A. (Department: 1773)
Semiconductor device manufacturing: process
Forming bipolar transistor by formation or alteration of...
Including diode
C428S469000, C428S472000, C428S497000, C428S403000, C428S546000, C252S514000, C072S055000
Reexamination Certificate
active
06686249
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transparent conductive layered structure having a transparent substrate and a transparent 2-layer film consisting of a transparent conductive layer and a transparent coating layer formed in succession on this substrate, which is used, for instance, as the front panel for displays, such as Braun tubes (CRTs), etc., and in particular, relates to a transparent conductive layered structure wherein the visible light transmittance of the transparent 2-layer film has been adjusted to a prescribed range less than 100%, a display in which this transparent conductive layered structure is used, and a coating liquid for forming a transparent conductive layer that is used in the production of transparent conductive layered structures.
2. Description of the Related Art
As a result of office automation in recent years, many OA machines have been introduced to offices and an environment where work must be done all day long facing a display of an OA machine is not uncommon today.
Taking a cathode ray tube (also referred to as the above-mentioned Braun tube; CRT) of a computer as an example of an OA machine, it has been required for the use of such CRTs that, in addition to being able to easily see the display screen in order to prevent a feeling of visual fatigue, adhesion of dust and electric shock attributed to electrification of the CRT screen, etc can be avoided. Furthermore, there recently has been concerned of the detrimental effects on the human body from the low-frequency magnetic waves generated from CRTs and it is desirable that the CRT not leak such electromagnetic waves to the outside.
In addition, the above-mentioned electromagnetic waves are generated from a deflecting coil or a flyback transformer and there is a tendency toward leakage of increasingly large amounts of electromagnetic waves to the surroundings with the development of larger televisions.
Leakage of a magnetic field can be prevented for the most part by precautions such as changing the shape of the deflection coil, etc. On the other hand, it is also possible to prevent leakage of an electric field by forming a transparent conductive layer on the front glass surface of the CRT.
Such methods of preventing leakage of electric field are theoretically the same as measures recently taken to prevent electrification. However, the above-mentioned transparent conductive layer must have a much higher conductivity than conductive layers that have been formed for preventing electrification. That is, although surface resistance of 10
8
&OHgr;/□ (ohm per square) is sufficient for preventing electrification, it is necessary to form a transparent conductive layer with a low resistance of at least 10
6
&OHgr;/□ or below, preferably 5×10
3
&OHgr;/□ or below, further preferably 10
3
&OHgr;/□ or below, to prevent leakage of an electric field (electric field shielding).
Thereupon, several proposals have been made in the past in response to the above-mentioned demands, and of these, the method whereby a coating liquid for forming a transparent conductive layer of conductive microparticles and inorganic binder, such as alkyl silicate, etc., dispersed in a solvent is applied and dried on the front glass of a CRT and then baked at a temperature of about 200° C. is known as a method by which low surface resistance can be realized at a low cost.
Moreover, this method that uses a coating liquid for forming a transparent conductive layer is much more simple compared to other methods of forming transparent conductive layers, such as vacuum evaporation and sputtering, production cost is also low, and it is very useful for electric field shielding by which CRTs can be treated.
A coating liquid that uses indium tin oxide (ITO) for conductive microparticles is known as the coating liquid for the above-mentioned transparent conductive layer used in this method. However, since surface resistance of the film that is obtained is high at 10
4
to 10
6
&OHgr;/□, a corrective circuit for canceling the electric field is necessary in order to adequately block electric field leakage and therefore, there was a problem in that production cost rises accordingly. On the other hand, transmittance of film from a coating liquid for forming a transparent conductive layer using metal powder as the above-mentioned conductive microparticles is somewhat lower than that from coating liquid that uses ITO, but a film with low resistance of 10
2
to 10
3
&OHgr;/□ is obtained. Consequently, there is an advantage in terms of cost because the above-mentioned corrective circuit is not necessary and this will probably become mainstream in the future.
Moreover, the metal microparticles that are used for the above-mentioned coating liquid for forming a transparent conductive layer are limited to noble metals, such as silver, gold, platinum, rhodium, palladium, etc., which rarely oxidize in air, as shown in Japanese Laid-Open Patent Application No. Hei 8-77832 and Japanese Laid-Open Patent Application No. Hei 9-55175. This is because when metal microparticles other than a noble metal, such as iron, nickel, cobalt, etc., are used, an oxide film always forms on the surface of these metal microparticles in an air ambient atmosphere and good conductivity as a transparent conductive layer is not obtained.
On the other hand, anti-glare treatment is performed on the face panel surface in order to control reflection on the screen and thereby make the display screen easy to see. This anti-glare treatment is done by the method whereby diffused reflection at the surface is increased by making fine irregularities in the surface. However, this method cannot be said to be very desirable because image quality drops due to a reduction in resolution when it is used. Consequently, it is preferred that, instead, anti-glare treatment by the interference method be performed whereby the index of refraction of the transparent film and film thickness are controlled so that there is destructive interference of reflected light on incident light. In order to obtain low-reflection results by this type of interference method, a 2-layered film is generally used wherein optical film thickness of a film with a high index of refraction and a film with a low index of refraction is set at 1/4&lgr; and 1/4&lgr; (&lgr; is wavelength), respectively, or 1/2&lgr; and 1/4&lgr;, respectively. Film consisting of the above-mentioned indium tin oxide (ITO) microparticles is also used as this type of film with a high index of refraction.
Furthermore, of the optical constant of metals (n−ik, n: index of refraction, i
2
=−1, k: extinction coefficient), the value of n is small, but the value of k is very high when compared to ITO, etc., and therefore, even if a transparent conductive layer consisting of metal microparticles is used, the same anti-reflection results as with ITO are obtained by interference with light by film with a 2-layer structure.
The metal microparticles that are used in conventional coating liquids for forming transparent conductive layers are limited to noble metals, such as silver, gold, platinum, rhodium, palladium, etc., as previously mentioned, but when their electrical resistance is compared, specific resistance of platinum, rhodium, and palladium is 10.6, 5.1, and 10.8 &mgr;&OHgr;·cm, respectively, which is high in comparison to the 1.62 and 2.2 &mgr;&OHgr;·cm of silver and gold. Therefore, there was an advantage to using silver microparticles and gold microparticles for forming a transparent conductive layer with low surface resistance.
Nevertheless, when silver microparticles were used, there were problems with weather resistance in that there was extreme sulfidation and oxidation and degradation by brine, ultraviolet rays, etc., while when gold microparticles were used, there were none of the above-mentioned problems with weather resistance, but there were the same problems with cost as when platinum microparticles, rhodium microparticles,
Fujisaki Midori
Kato Kenji
Ohtsuka Yoshihiro
Suekane Yukiko
Yukinobu Masaya
Resan Steven A.
Sumitomo Metal & Mining Co., Ltd.
Westerman, Hattori, Daniels & Adrain, LLP
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