Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-07-17
2003-11-11
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S155000, C349S153000, C349S190000
Reexamination Certificate
active
06646709
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a liquid crystal display unit and, more particularly, to a liquid crystal display unit with a spacer and a process for fabricating thereof.
DESCRIPTION OF THE RELATED ART
The liquid crystal display unit has a pair of transparent substrate structure spaced from each other, and liquid crystal is filled in the gap between the transparent substrate structures. An active matrix liquid crystal display unit is popular, and has the following structure. Pixel electrodes are arranged on one of the transparent substrate in matrix, and thin film transistors are connected between data lines and the pixel electrodes. The pixel electrodes are, by way of example, formed of indium tin oxide. A common electrode is provided in such a manner that electric field is created between each pixel electrode and the common electrode. A pair of polarizing plates is incorporated in the active matrix liquid crystal display unit. Black light passes one of the polarizing plates before entry into the liquid crystal, and images are produced through the other polarizing plate after passing the liquid crystal. The pixel electrode, the common electrode and a piece of liquid crystal form in combination a capacitive pixel. The piece of liquid crystal serves as a dielectric layer of the capacitor. The transparency of the piece of liquid crystal is varied depending upon the intensity of the electric field created in the capacitive pixel as follows.
The thin film transistors are sequentially changed to on-state, and the data lines are electrically connected through the thin film transistors to the associated pixel electrodes. Image-carrying signals are supplied to the data lines in synchronization with the selection of the pixel electrodes, and change the potential level on the pixel electrodes. Electric fields are created between the pixel electrodes and a common electrode, and pieces of liquid crystal over the pixel electrodes are selectively twisted so as to change the transparency of the pixels. Only predetermined polarized light passes the selected pixels. The matrix of pixels partially transfers the back light, and partially interrupts it. As a result, a picture is produced on the matrix of pixels. Thus, the picture is produced on the matrix of pixels through the electrooptic anisotropy.
The matrix of pixels occupies most of the major surface of the substrate structure. However, the peripheral area is not available for the image production. The area assigned to the matrix and the peripheral area are herein-below referred to as “image producing area” and “frame”, respectively. The active matrix liquid crystal display unit includes a black matrix and color filters. The black matrix is provided for enhancement of the contrast. The pixels are surrounded by the black matrix, and the black matrix prevents the pixels from leakage light. The color filters are usually provided on the transparent substrate opposite to the transparent substrate for the pixel electrodes and the thin film transistors. A red filter, a green filter and a blue filter are respectively associated with the three pixel electrodes, and colored images are produced on the matrix of pixels with the assistance of the colored filters.
The active matrix liquid crystal display units are categorized into two groups. The first category is featured by the common electrode formed on the transparent substrate opposed to the other transparent substrate where the pixel electrodes and the thin film transistors are formed. An active matrix liquid crystal display unit of the first category is referred to as “twisted nematic type liquid crystal display unit”. On the other hand, the other category is featured by the common electrode formed on the transparent substrate together with the pixel electrodes and the thin film transistors. An active matrix liquid crystal display unit of the second category is referred to as “in-plane switching type liquid crystal display unit”. The electrooptic anisotropy is used in both twisted nematic and in-plane switching type liquid crystal display units for producing images.
As described hereinbefore, the pixel electrode, the common electrode and the piece of liquid crystal form in combination the capacitive pixel, and the transparency is varied depending upon the intensity of the electric field created in the capacitive pixel. If the liquid crystal layer is changed in resistivity and/or thickness, the capacitance of the pixel is varied, and the picture on the matrix becomes less clear. On the other hand, if the liquid crystal layer is constant in resistivity and thickness over a long time period, the active matrix liquid crystal display unit continuously produces fine images on the matrix of pixels.
The thickness of liquid crystal layer is equal to the gap between the substrate structures. If the gap is constant, the liquid crystal layer does not change the thickness. On the other hand, if the gap is changed, the liquid crystal layer also changes the thickness. For this reason, a spacer is provided between the substrate structure for keeping the gap constant.
The spacer is, by way of example, implemented by micro-pearls scattered in the substrate structure at a predetermined density. Another spacer has a column shape. Photo-sensitive synthetic resin is spread over the substrate structure, and the photo-sensitive synthetic resin layer is selectively exposed to light. A latent image is produced in the photo-sensitive synthetic resin layer. When the latent image is developed, the column-shaped spacer is left at predetermined positions on the substrate structure. Yet another spacer is produced in the assembling stage of the liquid crystal display unit. Micro-pearls are mixed in sealing agent. The sealing agent is spread over the periphery of the substrate structure and predetermined area. The micro-pearls are spread together with the sealing agent. The other substrate structure is aligned with the substrate structure, and is assembled therewith. The micro-pearls keep the substrate structures spaced from each other for producing the gap.
However, the inner surfaces of the substrate structures are not flat due to the signal lines, electrodes and color filters. In other words, the substrate structures have rolled inner surfaces. If the substrate structures are assembled in such a manner as to oppose the rolled inner surfaces to each other, the gap is varied, and, accordingly, makes the liquid crystal layer varied in thickness. In order to make the inner surface flat, soft coating layers are spread over the rolled inner surfaces of the substrate structures. The signal lines, electrodes and color filters are covered with the soft coating layers, and the inner surfaces of the substrate structures become flat. This results in a constant gap.
FIGS. 1 and 2
shows a typical example of the in-plane switching type liquid crystal display unit. The prior art liquid crystal display unit is broken down into a pair of substrate structures and liquid crystal confined between the lower substrate structure and the upper substrate structure. Thin film transistors are incorporated in the lower substrate structure, and color filters are formed in the upper substrate structure.
The lower substrate structure is fabricated on the basis of a transparent substrate
100
. Gate electrodes
3
and a common electrode
4
are formed on the transparent substrate
100
, and are covered with an insulating layer
10
. Data lines
5
, a drain electrode
7
, a source electrode
6
and a pixel electrode
2
are patterned on the insulating layer
4
, and are converted with a passivation layer
8
. The gate electrodes
2
extend in perpendicular to the data lines
6
, and thin film transistors are assigned to regions where the gate electrodes
2
cross the data lines
6
. Amorphous silicon layers
1
are formed in the regions on the insulating layer
10
. The amorphous silicon layer
1
has a drain region, a source region and a channel region, and the drain electrode
7
and the source electrode
6
are held in contact with the dr
DiGrazio Jeanne
Foley & Lardner
Kim Robert H.
NEC LCD Technologies Ltd.
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