Electrode plate, liquid crystal device and production thereof

Details Electrode plate, liquid crystal device and production thereof Electrode plate, liquid crystal device and production thereof

1999-11-23

2002-12-31

Gulakowski, Randy (Department: 1746)

Etching a substrate: processes

Forming or treating article containing a liquid crystal...

C216S013000, C216S095000, C216S085000, C216S105000, C216S109000

Reexamination Certificate

active

06500352

ABSTRACT:

Liquid crystal devices of TN (twisted nematic) type, STN (super twisted nematic) type, etc., have conventionally adopted electrode plates comprising ITO (indium tin oxide) films, etc., as transparent electrodes formed on glass substrates in many cases.
The above-mentioned conventional transparent electrode (ITO) has a relatively large resistivity so that it is liable to cause a problematic delay in transmission of applied voltage waveforms according to recent demands for a larger display size and a higher resolution. Particularly, in a liquid crystal device using a ferroelectric liquid crystal requiring a smaller substrate gap or liquid crystal layer thickness on the order of 1.0-2.0 &mgr;m, the transmission delay of an applied voltage waveform is liable to be noticeable. A reduced resistance may be given by use of a thicker transparent electrode, but such a transparent electrode having an increased thickness is liable to exhibit poor adhesion onto a glass substrate and require a longer time for film formation, thus resulting in an increased production cost.
In order to solve these problems, there has been proposed a liquid crystal device equipped with an electrode plate comprising a glass substrate having thereon low resistivity metal electrodes of aluminum, etc., and thereon transparent electrodes of ITO, etc., electrically contacting the metal electrodes. Further, in order to comply with demands for liquid crystal devices with a higher aperture ratio and a high speed responsiveness in recent years, it has been desired to develop a metal electrode material of even lower resistivity.
When using metal electrodes of copper having a lower resistivity than aluminum, it is possible to realize a higher aperture ratio and a higher speed responsiveness, but problems are liable to occur regarding adhesion between a glass substrate and a copper electrode layer and the corrosive nature of copper. As a solution to such problems, there has been proposed an electrode plate having a sectional structure as shown in
FIG. 17
including a glass substrate
100
having thereon an adhesion layer
101
of chromium, a principal conductor layer
102
of copper and thereon a chromium-copper alloy layer
103
formed by sintering in a reducing atmosphere. The adhesion layer
101
and the principal conductor layer
102
may be formed by forming a chromium layer and a copper layer respectively by sputtering on the glass substrate, followed by etching in a prescribed electrode pattern.
When providing ordinary print circuit boards, the etching of a copper layer may be performed using an iron chloride solution, a copper chloride solution or a liquid acid mixture principally comprising nitric acid and phosphoric acid as an etchant (or etching liquid), and dipping a substrate coated with a copper layer together with an etching pattern in a vessel of the etchant or showering the etchant onto the substrate to etch the copper layer into a desired pattern.
However, in the electrode plate structure shown in
FIG. 17
including a glass substrate
100
and a laminate film disposed thereon comprising a copper principal conductor layer
102
and a chromium adhesion layer
101
for enhancing the adhesion between the copper layer
102
and the glass substrate
100
, the chromium layer
101
and the copper layer
102
cannot be patterned in a single etching step. More specifically, when an etchant as described above having an etching effect on both the chromium and copper layers is used for etching of the laminate layer, a cell effect occurs between the chromium and copper layers via the etchant. As a result, the layer of chromium (similar to molybdenum and titanium) having a larger ionization tendency (i.e., a smaller standard electrode potential) than copper is selectively etched to result in an abnormal undercut. The undercut may remain within a tolerable limit for an electrode or wire pattern having a width on the order of mm as in ordinary print circuit boards, but provides a serious problem for providing an electrode or wire pattern having a width on the order of 10 &mgr;m. Thus, the undercut can lead to peeling of the laminate electrode pattern.
For the above reason, it is necessary to use an etchant reacting only on the adhesion layer metal and an etchant reacting only on copper and repeat the etching of the respective metal layers while changing the etchant. More specifically, in the case of providing a chromium adhesion layer, it is possible to effect selective etching of the chromium and copper layers in multiple steps using etchants selectively reacting on chromium and copper, but this requires a complicated process and a considerable processing time. Moreover, the chromium-containing etching waste liquid can provide another difficulty with respect to environmental pollution.
On the other hand, in the case of providing an adhesion layer of molybdenum or titanium, most etchants reactive with these metals are also reactive with copper and also cause the undercut problem. Incidentally, the use of a potassium ferricyanide solution allows selective etching of molybdenum, but simultaneously promotes the growth of a stable oxide film on copper. The oxide film functions as a passivation film against a copper chloride solution as a selective etchant for copper, thus preventing the copper etching. An acid solution containing nitric acid, etc., can effect etching of a copper layer coated with the oxide film, but this is also accompanied with the problem of undercut arising from the difference in ionization tendency.
On the other hand, in the dry etching process, such as the reactive etching process, etc., the above-mentioned problems arising from the difference in ionization tendency can be obviated, but the etching speed is too small for commercial application.
As another process for providing a patterned copper film without resorting to an etching process, it has been proposed to form an adhesion layer film of chromium, molybdenum, etc., by sputtering, followed by etching into an electrode pattern, and to selectively coat the patterned adhesive layer with copper by plating and also with a protective layer by plating, etc. This process obviates most of the practical problems mentioned above accompanying copper electrode production, but it is difficult to form an accurate film thickness on the order of &mgr;m as required on an electrode plate for a liquid crystal device. Further, the adhesion layer formed by sputtering on the glass substrate shows a good adhesion onto the glass substrate, but shows a rather poor adhesion with a copper plating layer, thus possibly requiring another adhesion promoting layer between the adhesion layer and the copper layer.
From the above discussion, it is still desirable to provide an electrode plate with patterned electrodes by sequentially forming an adhesive layer and a copper layer on a substrate and then etching the layers in a prescribed electrode or wire pattern. In this instance, it is desired to effect simultaneous etching of the adhesive layer and the copper layer in a single etching step.
On the other hand, the wet etching process has been frequently used as an etching process for locally removing or patterning a film formed on a substrate not only for production of semiconductor devices and ornamental articles, because of a simple structure and a low production cost.
FIG. 11
is an illustration of such a wet etching process. Referring to
FIG. 11
, in this process, a vessel
81
, such as a beaker, is charged with an etchant
82
, in which a substrate
84
having thereon a pattern of resist
83
exposing portions to be etched is dipped for a prescribed period. After the prescribed time, the substrate
84
is taken out and washed with, e.g., a large amount of flowing water to terminate the etching. In this way, a film on a substrate can be etched into various patterns through a simple step according to the wet etching process.
In the wet etching process, however, a difficulty is sometimes encountered in that the etching speed can vary locally on the substrate depending on the af

Affiliated with

Also associated with

Rating

Electrode plate, liquid crystal device and production thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Electrode plate, liquid crystal device and production thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrode plate, liquid crystal device and production thereof will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2998239