Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2003-11-18
2004-10-26
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S147000, C428S621000
Reexamination Certificate
active
06810181
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a substrate and an electrode structure and more specifically to an electrode structure of a substrate for an optical waveguide device to which electronic parts or the like are attached.
BACKGROUND ART
As the recent wide spread of personal computers and internet communication, the demand for the transmission of information has rapidly been increased. For this reason, there has been desired for the spread of the optical transmission means whose transmission speed is quite high even to the terminal information processing devices such as personal computers. It is thus necessary that a high quality optical waveguide for the optical interconnection should be produced in a large scale at a low price.
As materials for forming optical waveguides, there have been known inorganic materials such as glass and semiconductor materials and resins. An optical waveguide of an inorganic material is in general produced according to a method, which comprises the steps of forming a film of an inorganic material using a film-forming system such as a vacuum vapor deposition system or a sputtering device and then etching the inorganic film thus formed into an optical waveguide having a desired shape. However, the vacuum vapor deposition system or the sputtering device requires the use of an evacuation system and therefore, a large-sized and expensive apparatus should be used. Moreover, this method requires the use of an evacuation step and this makes the process more complicated. On the other hand, when preparing an optical waveguide using a resin, the film-forming process or coating and heating steps can be conducted under the atmospheric pressure and therefore, the method, which makes use of a resin, is advantageous in that quite simple system and process can be used.
Although, there have been known various kinds of resins, which can be used for forming core and clad layers of an optical waveguide, those particularly expected are polyimides each having a high glass transition point (Tg) and excellent in the heat resistance among others. When forming the core and clad layers of an optical waveguide from a polyimide, the resulting optical waveguide is expected to have long-term reliability and an ability of withstanding soldering. Among these polyimides, fluorine-containing polyimides have in general been used because of their excellent characteristic properties concerning refractive indices.
The optical waveguide device should electrically be connected to an optical part such as a laser diode or a photodiode or an electronic part. As a means for realizing such an electrical connection, the wire-bonding technique has in general been used, in which the foregoing elements are connected through a gold wire bonded thereto by the application of ultrasonics. As an electrode for the wire bonding connection, there has conventionally been used, for instance, an electrode lead-out portion as shown in
FIG. 6
, which is obtained by forming a platinum (Pt) layer
16
on a titanium (Ti) layer
15
and then forming a gold (Au) layer
14
as the upper most layer. Alternatively, an electrode lead-out portion as shown in
FIG. 7
has also been used, which is obtained by forming a chromium (Cr) layer
13
and then forming a gold (Au) layer
14
as the upper most layer.
DISCLOSURE OF THE INVENTION
In this connection, when forming a deposited (or laminate) film of, for instance, Ti, Pt or Au as an electrode and/or a deposited film of, for instance, Cr or Au on the optical waveguide prepared using a fluorine-containing polyimide, however, a problem arises such that the electrode film is peeled off from the optical waveguide during the formation of an electrode pattern since the adhesion of the fluorine-containing polyimide to the electrode is quite low.
Moreover, when processing a metal such as Ti, Pt or Au into a desired pattern in case of a deposited film of such a metal, a problem arises such that it is difficult to etch the metal film according to the wet etching technique using an etching liquid since the metals such as Ti, Pt and Au have high resistance to chemicals and that the resulting pattern is inaccurate. For this reason, such a pattern is formed by a method such as the reactive dry etching using chlorine-containing gases or the ion milling technique, but these techniques require a high cost of equipment and they require the use of large-scale equipments in order to ensure safety. Under such circumstances, there has been used an electrode lead-out portion as shown in
FIG. 7
, which is obtained by forming a chromium (Cr) layer
13
on a silicon substrate and then forming a gold (Au) layer
14
as the upper most layer. These metals may easily be etched by the wet etching technique using an etching liquid and the resulting pattern is excellent in accuracy. However, a problem arises, that is, when the electrode lead-out portion is subjected to wire bonding, the boundary between the Cr layer and the substrate is destroyed by the energy of the ultrasonics applied thereto for the wire bonding and it has thus been impossible to ensure sufficient strength in the foregoing electrical connection.
Accordingly, it is an object of the present invention to provide an electrode in which the foregoing conventional problem never arises such that the electrode is peeled off from a substrate or a polymer optical waveguide device due to the insufficient adhesion between the electrode and the substrate or the device and which is excellent in the accuracy of the resulting electrode pattern. In addition, it is another object of the present invention to provide an electrode structure, which can ensure sufficient strength at the boundary between a substrate and an electrode formed thereon to thus prevent any breakage of the boundary by the energy of ultrasonics applied thereto for wire bonding.
According to the present invention, there are thus provided electrode structures detailed below:
[1] An electrode structure, which comprises a substrate provided with an electrode formed thereon, wherein the substrate comprises a layer of a fluorine-containing polyimide and a layer of a fluorine-free resin is interposed between the polyimide layer and the electrode. The interposition of the fluorine-free resin layer permits the improvement of the adhesion between the fluorine-containing polyimide layer and the electrode.
[2] The electrode structure as set forth in the foregoing item [1], wherein the fluorine-free resin is fluorine-free polyimide. The interposition of the fluorine-free polyimide layer permits the further improvement of the adhesion between the fluorine-containing polyimide layer and the electrode.
[3] The electrode structure as set forth in the foregoing item [1] or [2], wherein the substrate is a silicon wafer on which a fluorine-containing polyimide resin layer and a fluorine-free resin layer are laminated in this order.
[4] The electrode structure as set forth in any one of the foregoing items [1] to [3], wherein the substrate is a silicon wafer on which a silicon oxide film, a fluorine-containing polyimide resin layer and a fluorine-free resin layer are laminated in this order.
[5] The electrode structure as set forth in any one of the foregoing items [1] to [4], wherein the substrate is an optical waveguide substrate.
[6] The electrode structure as set forth in any one of the foregoing items [1] to [5], wherein the electrode comprises a gold layer as the outermost or surface layer and an aluminum layer interposed between the substrate and the gold layer.
[7] The electrode structure as set forth in the foregoing item [6], wherein the electrode comprises a gold layer as the outermost or surface layer, an aluminum layer interposed between the substrate and the gold layer and further a layer of a high melting point material arranged between the gold and aluminum layers.
[8] The electrode structure as s
Matsuura Hiroyuki
Miyadera Nobuo
Yamaguchi Masatoshi
Yamanoi Kiyoshi
Hitachi Chemical Co. Ltd.
Lee John D.
Westerman Hattori Daniels & Adrian LLP
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