Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified... – With charge transferring layer of specified composition
Reexamination Certificate
2001-05-09
2004-06-01
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
With charge transferring layer of specified composition
C428S697000, C428S212000
Reexamination Certificate
active
06743488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the field of transparent electrical conductive coatings made of indium tin oxide which are applied to transparent substrates, especially flexible transparent polymeric film substrates. The invention also pertains to the method of making the coated substrates and the use of the coated substrates in electronic devices which require transparent conductive oxide (TCO) films having excellent electrical conductivity, mechanical durability and high transparency. Such electronic devices include liquid crystal displays (LCD), touch panels (TP) and pen entry devices, electroluminescent lamps (EL), personal digital assistants (PDA), organic light emitting devices (OLED), etc.
2. Background Information
Substrates such as flexible transparent polymeric films having a TCO coating thereon are widely used in the above noted devices because these coatings possess high optical transparency, high electrical conductivity and good mechanical stability. Indium oxide-tin oxide (indium-tin oxide commonly referred to as ITO) is often used as the TCO coating.
The indium-tin oxide coating used in this field of technology and in the present invention is a non-stoichiometric n-type semiconductor which exhibits high visible transmittance, low resistance and high infrared reflectance. For this reason, thin films of ITO are commonly used as the TCO coating in the above noted devices. Conventional reactive sputtering from a InSn alloy in an oxygen containing atmosphere (e.g., argon-oxygen atmosphere) is used to apply the ITO film or coating onto the substrate. A conductive ITO film is a partially oxidized mixture of indium and tin and thus the optoelectronic properties of such films are greatly affected by the level of oxygen admitted into the plasma during the deposition. The amount of oxygen in the ITO films used in this field of technology is well known to those skilled in the art.
On one hand, films with too little oxygen exhibit high sheet resistance and low visible transmittance. On the other hand, at a fully reacted state (complete oxidation), one achieves a transparent oxide with very high sheet resistance and high visible light transmittance. The manner of proceeding from a metallic layer to a fully oxidized layer depends on the feedback and control mechanisms employed during reactive deposition processes which are well known to those skilled in the art.
In the production of ITO coatings from an InSn target on a polymeric web (i.e., sheet), the in-situ measurement and control of the oxidation level is of pivotal importance. The traditional constant pressure controlled reactive sputtering of ITO works well and produces films with adequate properties. However, the use of such traditional constant pressure controlled reactive sputtering of ITO does not meet the demands of more stringent and sophisticated applications. This is because reactive sputter deposition of indium-tin oxide (ITO) from an alloy target is an extremely sensitive process. The quality of the deposited ITO is dependent on the ability to maintain a certain constant partial pressure of oxygen in the sputtering zone during the deposition process. Minor changes in the substrate outgassing, pumping speed, target condition or arcing can result in significant changes in the oxidation level of the deposited layer, thus producing an inferior conducting film. When producing sputtered ITO on continuous flexible substrates, on-line monitoring and feedback control in real time is essential for high quality products.
There are various methods in use today which provide for the monitoring and control of the reactant species in the glow discharge. These methods include direct or indirect partial pressure measurements and optical emissions spectroscopy. In particular, such methods include the use of a residual gas analyzer (RGA), an optical gas controller (OGC) or a plasma emission monitor (PEM). Each of the above devices provide a means for monitoring and controlling the amount of oxygen during deposition of the metal. It is well know to those skilled in the art that the amount of oxygen must be kept at a level to produce the aforementioned non-stoichiometric ITO coating which is not completely oxidized. Thus the oxygen atmosphere during deposition must be maintained at an oxygen deficiency to produce the required non-stoichiometric oxide coating.
ITO coated films are conventionally used in a wide range of applications which include touch panel devices. Touch panel devices have two opposing surfaces of the ITO films separated by spacers. Contact is made between the two opposing surfaces when the front surface is depressed by a finger or touch pen. Depending on the type of device, the location of the input is decoded by the electronic interface according to known technology. LCD devices typically include an array of transparent ITO electrodes which define the display segment or pixels to be activated. In EL displays electrical energy is converted to light energy (luminescence). EL displays use a thin film of phosphor sandwiched between dielectric layers that is sandwiched between two electrodes, one of which is ITO. When an AC voltage is applied to any of the electrodes, the phosphor will be excited so that it emits light.
Reliability during continuous operation is a problem associated with these devices. In the touch panel device it has been observed that the electrical resistance increases after continuous cycling. The ITO surfaces crack or fracture at the touch location and these fractures propagate over time to totally disrupt the operation of the device. Countermeasures have been employed in these devices to help prevent the aforementioned cracking problem. In particular, it is known to deposit a thin layer of palladium, platinum, gold or oxides of these metals onto the ITO film to protect the ITO and/or increase the surface adhesion properties of the ITO layer for subsequent processing. Methods to promote crystallization of the ITO surface after deposition have also been used to grow a hard surface. Problems have also been observed during the fabrication of EL lamps. It has been observed that the ITO film in EL lamps becomes delaminated from the polymeric substrate during processing of the phosphor layer. Pretreatment methods have been utilized to increase the surface energy of the substrates during deposition, but with limited success. Other techniques such as applying a thin metallic or oxide layer on top of the ITO has also been tried with good results.
As active metric liquid crystal displays (AMLCD) become the dominant display for portable systems such as pagers, phones and personal digital assistants, ruggedness and impact resistants become highly desirable for handling considerations as well as for flexibility during their fabrication.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide an improved sputtered TCO coating of ITO on a transparent substrate, especially a transparent polymeric film substrate, for use in applications where TCO films are conventionally employed.
It is also an objective of the present invention to improve conventional electronic devices which include a TCO as a component thereof by using the ITO of the present invention as the TCO.
It is also an objective of the present invention to provide a method for making an improved transparent conductive coating of ITO on a transparent substrate.
These and other objectives are obtained by forming a multilayered transparent conductive film or coating of ITO on a transparent substrate wherein the ITO film or coating includes distinct layers of transparent conductive ITO. The term “transparent conductive coating of ITO” as used herein refers to transparent conductive ITO coatings which are conventionally employed in well known electronic devices which require a TCO. Such devices include conventional liquid displays (LCD), touch panels (TP), electroluminescent lamps (EL), personal digital assistants (PDA), organic light emitting devices (OLED), etc. Henceforth su
Memarian Hassan
Patel Hitesh
Bacon & Thomas PLLC
CPFilms Inc.
Hon Sow-Fun
LandOfFree
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