Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Patent
1997-05-23
1998-09-22
Marcheschi, Michael
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
501 66, 501 67, 501 69, C03C 3078, C03C 3087, C03C 3093, C03C 3085
Patent
active
058113614
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATION
This application is a 371 of international application No. PCT/JP96/02750, filed Sep. 25, 1996.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an alkali-free glass substrate for use as a substrate for a display such as a liquid crystal display and an EL display, a filter, a sensor, and the like.
2. Description of the Prior Art
Conventionally, a glass substrate has widely been used as a substrate for a flat panel display such as a liquid crystal display, a filter, a sensor, and the like.
On a surface of the glass substrate of the type, a transparent conductive film, an insulating film, a semiconductor film, and a metal film are deposited and various circuits or patterns are formed by photolithography etching (photo etching). In such deposition and photo etching processes, the glass substrate is subjected to various kinds of heat treatment and chemical treatment.
For example, in case of an active matrix liquid crystal display of a thin-film-transistor (TFT) type, the insulating film and the transparent conductive film are deposited on the glass substrate and a number of TFTs of amorphous silicon or polycrystalline silicon are formed by the photo etching. In these processes, the glass substrate is subjected to the heat treatment at a temperature on the order of several hundreds degrees centigrate and to the chemical treatment by various chemicals such as sulfuric acid, hydrochloric acid, alkali solution, hydrofluoric acid, and buffered hydrofluoric acid.
Among others, buffered hydrofluoric acid is widely used in etching of the insulating film. The buffered hydrofluoric acid tends to erode a glass so that its surface is clouded. During the erosion, reaction with a glass component occurs and produces a reaction product, which may clog a mesh or pores of filtration screens used in the process or adhere onto the glass substrate. On the other hand, hydrochloric acid is used in etching of an ITO film and a chromium film. The hydrochloric acid also tends to erode the glass so that its surface suffers discoloration, cloudness, and cracks. It is very important to provide buffered-hydrofluoric-acid resistance and hydrochloric-acid resistance to the glass substrate of the type.
Therefore, the glass substrate for use in the active matrix liquid crystal display of a TFT type is required to have following characteristics.
(1) To contain substantially no alkali metal oxide because, if alkali metal oxide is contained in the glass, alkali ion is diffused in a deposited semiconductor material during heat treatment to result in degradation of a film characteristic.
(2) To have chemical resistance such that no degradation is caused by chemicals including various kinds of acid and alkali used in a photo etching process.
(3) To cause no heat contraction by heat treatment in a deposition or an annealing process. For this purpose, to have a high strain point. For example, in case of a polycrystalline silicon TFT-LCD requiring a working temperature of about 600.degree. C. or more, the glass substrate for such application must have a strain point of 650.degree. C. or more.
Taking the meltability and the formability into consideration, the glass substrate of the type is further required to have following characteristics.
(4) To be excellent in meltability so that a melting defect unfavorable as the glass substrate does not occur in the glass.
(5) To be excellent in devitrification resistance so that no foreign substance is produced in the glass during melting or forming.
In recent years, an electronic device such as the active matrix liquid crystal display of a TFT type is coming into use in a field of personal application and is therefore required to be light in weight. Consequently, the glass substrate is also required to be light in weight so that reduction in thickness is pursued. On the other hand, the electronic device of the type is also increased in size. Under the circumstances, the reduction in thickness is inevitably limited, taking the strength of t
REFERENCES:
patent: 3496401 (1970-02-01), Dumbaugh, Jr.
patent: 5244847 (1993-09-01), Kushitani et al.
patent: 5489558 (1996-02-01), Moffatt et al.
Marcheschi Michael
Nippon Electric Glass Co. Ltd.
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