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Pin-Hole Control in Thin Film Coatings, Methods for Reducing the Occurrence of Shorting with Thin Film Electrodes, and Related Technology

IP.com Disclosure Number: IPCOM000245103D
Publication Date: 2016-Feb-08
Document File: 3 page(s) / 169K

Publishing Venue

The IP.com Prior Art Database

Abstract

Thin film electrodes are used in many applications (such as semiconductor devices, photovoltaics, displays, smart windows). These thin film electrodes may be transparent, semi-transparent, or opaque. They may be made of metal like silver or copper, or metal oxides such as indium tin oxide. In some devices, there is a possibility of an electrical short circuit (or short, for short) occurring between an electrode and another conductive layer in the device. An example would be a short occurring through the liquid crystal layer between two electrodes in a display device. This short will often damage the device. One way of reducing the occurrence of shorts is to provide a nonconductive or semiconductive layer between the electrode and other layers. This layer provides a barrier to current flow between the two conductive layers, and will herein be referred to as an overcoat. This overcoat layer functions best when it completely covers the electrode. One defect that may occur in thin films, such as sputtered thin films, is a pinhole, which is a small opening in the film caused by debris, stress, chemical reaction, or some other factor. Pinholes are more common in films which have undergone a heat treatment, which some thin films electrodes may require (to achieve good electrical conductivity). A pinhole in the overcoat layer provides a low resistance path between the electrode and other layers.

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Memo: Pin-Hole Control in Thin Film Coatings, Methods for Reducing the Occurrence of Shorting with Thin Film Electrodes, and Related Technology

Thin film electrodes are used in many applications (such as semiconductor devices, photovoltaics, displays, smart windows).  These thin film electrodes may be transparent, semi-transparent, or opaque.  They may be made of metal like silver or copper, or metal oxides such as indium tin oxide.  In some devices, there is a possibility of an electrical short circuit (or short, for short) occurring between an electrode and another conductive layer in the device.  An example would be a short occurring through the liquid crystal layer between two electrodes in a display device.  This short will often damage the device.  One way of reducing the occurrence of shorts is to provide a nonconductive or semiconductive layer between the electrode and other layers.  This layer provides a barrier to current flow between the two conductive layers, and will herein be referred to as an overcoat.  This overcoat layer functions best when it completely covers the electrode.  One defect that may occur in thin films, such as sputtered thin films, is a pinhole, which is a small opening in the film caused by debris, stress, chemical reaction, or some other factor.  Pinholes are more common in films which have undergone a heat treatment, which some thin films electrodes may require (to achieve good electrical conductivity).  A pinhole in the overcoat layer provides a low resistance path between the electrode and other layers. 

Several methods to improve the performance of these overcoat layers (and reduce the occurrence of shorting further) have been developed.  The simplest option is to apply the overcoat layer after the heat treatment step.  Since the heat treatment opens up pinholes, the overcoat layer which does not undergo the heat treatment will have less pinholes.  Another method is to deposit a first overcoat layer before heat treatment and a second overcoat layer after heat treatment.  Since this second overcoat layer is not heat treated, it has a lower concentration of pinholes.  Additionally, any pinholes in this second overcoat layer will only reach the top of the first nonconductive layer (and pinholes in the first overcoat layer will only reach the bottom of the second overcoat layer).  The likelihood of there being a pinhole in the same spot in both of the overcoat layers is small, and so the chance of a short is further reduced.  

An example would be a heat treated indium tin oxide (“ITO”) coating on glass.  The ITO could be coated with an overcoat layer (such as silicon nitride) before heat treatment to reduce the likelihood of shorting.  To further reduce the likelihood of shorting, a second over-coat of silicon nitride could be applied after heat treatment. ITO and silicon nitride are just examples, there are many materials that could be used. For example, the ITO can be replaced with...