Active matrix liquid crystal display with identification mark in the lower opaque conductive film

An active matrix type liquid display device with a display pattern unit formed on a glass substrate comprises an opaque thin film portion with an identification mark formed on a blank portion of and not in the display and terminal thereof. The opaque thin film portion with an identification mark is not coated with another opaque thin film thereon and is coated with a transparent film thereon so that the identification mark can be visually observed from the surface of the device.

BACKGROUND OF THE INVENTION 
The present invention relates to a liquid crystal display device, and in 
particular to a liquid crystal display device in which an identification 
mark is provided on a glass substrate. 
Related Art 
Conventional liquid crystal display devices have been provided with a 
predetermined model number representative of the model number of the 
product together with a fixed display pattern of the product. On the other 
hand, a lot of liquid crystal devices ranging from a conventional segment 
type and simple dot matrix type to an active matrix type have been sold on 
the open market. Since the active matrix type devices have a large display 
capacity which meet various needs, a lot of devices which have the same 
product model number are put on the market and have begun to be used for 
various application products having the display devices. This implies that 
the active matrix type liquid display devices are more favorable as 
ready-made products than custom-made-products. 
Therefore, tracing products by relying on only on the convention model 
numbers of the products is difficult, after the products have been put on 
the market. Although the active matrix type devices have been put on the 
market, the productivity of them is low. It is difficult to provide the 
products of the same model number with a uniform reliability specification 
as well as uniform performance specification. There is a need for an 
increase in tracability in the market for responding to product claims and 
for enhancing the product control in the course of production in order to 
improve the industrial yield. 
One approach to solving such problems is to provide an identification mark 
in the course of a production process, the mark to be effectively used for 
production control. One example of such a mark will be described with 
reference to FIGS. 1, 2 and 3. 
FIG. 1 is a schematic plan view showing the reverse side of an active 
device's substrate, which is in the course of a conventional production 
process for active matrix type liquid crystal display devices. Various 
patterned thin films are provided on the surface of a glass substrate 1 to 
provide an active device. The pattern on the surface is visually observed 
from the reverse side of the device. Various thin films are multi-layered 
on the glass substrate and a thin film laminated area 2, which is not used 
because the device does not appear in the periphery of the substrate. 
The thin film laminated area 2 corresponds to an area in which a 
photo-resist remains as an unexposed portion when the device pattern 3 is 
patterned. Therefore, most of the used thin films remain under a condition 
that they are laminated in the as-formed order. A numeral 20 shows a 
standard corner. 
The product identification mark may be provided by using the thin film 
laminated area 2. FIG. 2 is a partial enlarged plan view of an 
identification mark 5. In FIG. 2, numerals and character "9B12" is not a 
product model number, but is a production lot number. When a lowermost 
opaque film is patterned by means of a handy spot exposing device by using 
a photo-resist and a light transmitting film bearing such a character 
array, an exposure is performed as an additional step by using the 
character array as negative original. The identification mark portion 4 is 
then etched simultaneously with the etching of the device pattern portion 
3 so that each glass substrate for active device can be numbered. The 
character array 6 can be visually observed when a spot exposing portion 5 
on the reverse side of the glass substrate 1 is observed. The character 
array 6 can be used as the identification mark. 
The structure of the identification mark portion 4 in the above-mentioned 
prior art liquid crystal display device has various disadvantages as 
follows; 
FIG. 3 is a schematic sectional view showing a glass substrate 1 of the 
marking-character portion of the spot exposed portion 5. The lower metal 
film 7 which provides a gate wiring for thin film transistors formed on 
the surface of the glass substrate 1 is provided with a character array 
pattern shown in FIG. 2. However, a lower insulating layer 8, a 
semiconductor layer 9, an upper metal layer 10 and an upper insulating 
layer 11 which are successively formed to provide a thin film transistor 
array remain on the lower metal film 7 as they are laminated. Therefore, 
it is disadvantage that the character array 6 of the identification mark 
portion 4 should be always viewed from the reverse side 12 of the glass 
substrate. Frequent turning of the glass substrate upside down causes a 
poor productivity and may lower the yield due to dust. 
Since the semiconductor layer 9 can be seen, the contrast between the spot 
exposed portion 9 and the lower metal layer 7 is bad, and use of a sensor 
device is difficult although the spot exposed portion 5 can be seen by 
eyes of human being. 
The critical disadvantage is that the device pattern portion 3 cannot be 
provided with the identification mark portion 4 due to problems of 
dimension, precision and dusts since a manual spot exposure is performed. 
If the glass substrate 1 manufactured with a plurality of device pattern 
portions 3 is individually cut into discrete devices and since unnecessary 
thin film laminated portion 2 is cut out, no identification mark exists on 
the device. Manual control of correspondence between the identification 
mark and the cut away product is difficult. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a liquid crystal 
display device in which an identification mark can be readily viewed from 
the surface thereof so that control of product such as process control and 
reliability control can be sufficiently achieved. 
In order to accomplish the above-mentioned object, the present invention 
provides an active matrix type liquid display device including a display 
pattern unit formed on a glass substrate, comprising an identification 
mark portion formed on a blank portion of said display pattern unit 
excepting display and terminal areas thereof, said identification mark 
portion including an opaque thin film provided with identification mark 
and formed on said glass substrate, said opaque thin film with 
identification mark being coated with a transparent thin film thereon. 
The identification mark portion is formed inside of a cutting line for 
separating individual devices provided on the glass substrate. 
The opaque thin film provided with the identification mark is a lower metal 
film formed immediately upper side of the glass substrate. 
The identification mark includes a bar code in addition to the 
identification characters. 
The identification mark portion is formed of the opaque thin film provided 
with the indentification mark by using, for example, a lot of the lower 
metal wires formed immediately below the glass substrate in the blank 
portion excepting the display area and the terminal area of the display 
pattern portion. Only the transparent thin film is formed on the opaque 
thin film area with the identification mark. 
Accordingly, the identification mark can be confirmed from the surface of 
the device so that the control of the device is facilitated. Each discrete 
device can be added with the identification mark by forming the 
identification mark portion inside of the cutting line of the device to 
facilitate the control of the reliability of the devices. 
Control of the devices can be further facilitated by marking a bar code as 
the identification mark in combination with the character pattern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, the embodiments of the present invention will be described with 
reference to drawings. 
FIG. 4 is a schematic plan view showing the surface of a glass substrate 
for an active matrix which is in the course of a the manufacturing of 
liquid crystal display device which is a first embodiment of the present 
invention. The surface of the glass substrate 1 has with various patterned 
thin films for providing active devices, as is similar to prior art. The 
pattern can be, of course, viewed as shown in FIG. 4 if the display is 
observed from the direct observing side 15 which is opposite to the 
conventional direct observing side 12. A thin film laminated area 2 
similarly exists on the periphery of the substrate on the glass substrate 
1. This laminated portion 2 is not provided with any product 
identification mark. An area on which photo-resist working is performed in 
the course of usual manufacturing process of a device pattern portion 3 is 
used to provide a blank portion excepting a display area (matrix array 
area) and a terminal area with an identification marking portion 4. 
FIG. 5 is a partial enlarged plan view of the identification marking 
portion 4. A character pad 13 is formed of a first laminated opaque thin 
film in the blank portion of the device pattern portion 3. An additional 
pattern is thus provided in a first opaque thin film pattern forming 
exposure mask. The character pad 13 is rectangular in shape in FIG. 5. The 
shape of the pad 13 is optional, provided that the pad 3 has an area 
necessary for the identification mark. The character pad 13 is a lower 
metal film 7 made of a chromium metal film for wiring the gates of thin 
film transistors. The metal film 7 is a first opaque thin film. The blank 
portion is formed around the character pad 13. The thin film laminated 
portion 2 and the other opaque film are not formed therearound. 
The marking of characters which will become the identification mark like 
character array 6 on the character pad 13 may be performed before and 
after the patterning of the first opaque thin film. It is preferable to 
mark the characters on predetermined positions immediately after forming 
the film which is an upstream step in the manufacturing process control. 
Marking is performed by means of laser marking apparatus. Blanked marking 
characters 14 are formed by sputtering the chromium film by impinging a 
laser thereon to make a character array 6. The laser marking apparatus 
comprises a stage system for determining marking positions and a beam 
scanning system for determining the kind of marks. Both systems are 
operated under control of a computer. The accuracy of the size, kind and 
position of the identification marks is thus high. Since the chromium 
which is sputtered by the laser becomes gaseous, dusts which cannot be 
removed by washing the glass substrate 1 will not be deposited. 
Alternatively, an exposing device having a numbering capability may be 
used in lieu of the laser marking apparatus and a numbering plate which is 
overlapped on the first opaque thin film pattern mask may be used to 
perform a simultaneous patterning of the characters. 
FIG. 6 is a schematic partial sectional view of the marking characters 14 
of FIG. 5. The character pad 13 made of the lower metal film 7 to be 
marked is marked with marking characters by being bored. No opaque thin 
film is laminated on the character pad 13 excepting the lower metal film 
17 which is the first opaque thin film with mirror surface. Only lower and 
upper insulating films 8 and 11 are laminated on the pad 13. The lower and 
upper insulating films 8 and 11 generally often serve as a field 
insulating layer and a passivation film of the entire of the element and 
remain as the pattern blank portion. However, since these insulating films 
are made of a transparent film such as silicon oxide layer, silicon 
nitride layer, the face side can be made the direct viewing side 15 which 
has the mirror surface of the character pad 13 as well as the reverse side 
which is conventional direct viewing side 12. 
A feature of the present invention resides in an active matrix type liquid 
display device including a display pattern unit 3 formed on a glass 
substrate, comprising an indentification mark portion 4 formed on a blank 
portion of said display pattern unit excepting display and terminal areas 
thereof, said identification mark portion including a lower metal film 7 
which is an opaque thin film provided with an identification mark and 
formed on said glass substrate, said opaque thin film with identification 
marks being coated with only the lower and upper insulating layers 8 and 
11, as a transparent thin film as shown in FIGS. 4, 5 and 6. 
In the first embodiment, by providing such a light transmitting 
identification mark, contrast of the mark can be enhanced so that the mark 
can be visually viewed by a human being and by sensor devices. Many of the 
sensor devices use lights visual red light and near-infrared lights in the 
range of about 600 nm to about 1000 nm. The glass substrate 1 is made of 
borosilicate glass. The light transmission factor of the silicon oxide or 
silicon nitride film is about 90% for lights having wave length not less 
than 350 nm. On the other hand, the film of chromium used for gate wiring 
is about 1500 .ANG. in thickness and hardly transmits these lights. The 
transmission factor of polysilicon and amorphous silicon used as a 
semiconductor film is low. Therefore, the mark can be read at high 
contrast from both the face and reverse sides using a reflection or 
transmission detection method if an optical sensor is used. 
Referring now to FIG. 7, there is a schematic plan view showing an enlarged 
character pad portion, a second embodiment of the present invention. The 
second embodiment is substantially identical with the first embodiment 
except that identification marks are not blanked, but are left and bar 
code 16 is provided. In the second embodiment, the laser marking device 
may be used and the bar code 16 which is a feature of the present 
invention is provided in addition to visual reading character array 6 so 
that a bar code reader may be used as a sensor device. 
The bar code 16 in FIG. 7 is marked in accordance with "code 39". The 
character array 6 is an abbreviation of a start and stop mark * 
(asterisk). The bar code may be marked in accordance with the other bar 
code system. The bar code is not limited to the positive leaving pattern 
and may be read by a signal-processing. If the size of the characters of 
the character array 6 is enlarged in such a manner, a considerable width 
of the character pad is necessary. If the characters are considered as a 
subsidiary of the bar code in addition to a fact that the characters are 
read by OCR. The height of the characters may be made smaller to 2 mm so 
that it becomes convenient to provide the character array in the blank 
portion of the device pattern unit 3. 
Although the lower metal film 7 is made of chromium for gate wiring and 
constitutes the character pad 13, the character pad 13 is not limited to 
chromium for gate wiring depending upon the type of thin film transistors 
and the kind of active switching elements. The character pad 13 may be 
formed of a single opaque thin film (two laminated opaque thin films which 
are continuous are considered as functionally single film) independently 
of any type transistors and switching elements. 
Referring now to FIG. 8, there is shown a schematic plan view showing a 
third embodiment of the present invention. In this embodiment, the 
character pad 13 is formed on a blank portion of the device pattern unit 3 
excepting a display area 17 and a terminal area 18, inside of a cutting 
line passing through cutting marks 19 which is one of the features of the 
present invention. The character pad 13 is formed by laser marking in a 
blanking mode so that the OCR characters are 2 mm in height. If the use of 
a sensor device in case of OCR as well as case of bar code is considered, 
the number of digits of the marks can be made larger than the digits of a 
manual control which is relying upon a visual observation. Accordingly, 
each of all products can be provided with an identification number. Even a 
combination of a product model number and a product serial number can be 
provided. 
Providing the character pad 13 inside of the cutting mark 19 makes 
anumbered identification mark to be left on each product even if the 
device is cut along the cutting line to provide individual products. Field 
tracing is possible based upon the identification mark after the products 
have been shipped on the market. An uniform control of the products is 
possible inside and outside of a factory by using the identification 
marks. 
As mentioned above, in accordance with the present invention, a character 
pad bearing an identification mark is formed of a lower opaque thin film 
used for forming the device in a device pattern unit and the 
identification mark is marked on the pad and the other opaque thin film is 
not provided in the character pad. It is thus possible to identify the 
mark even from the side of a glass substrate so that a reversing of the 
substrate is eliminated. As a result of this, a complicated and labor 
intensive work is eliminated and lowering of yield due to a generation of 
dust is not introduced. Further, contrast of for a reading sensor as well 
as visual observation can be enhanced so that there is an advantage that a 
process control using sensor devices becomes possible. Since the character 
pad is provided inside (on the element side) the cutting marks for 
individually separating a multiplicity of display devices provided on the 
same glass substrate, an identification mark can be left on the product. 
Control of a product lot, production serial and product model can be 
easily achieved so that the tracability of products inside and outside of 
factory is enhanced. 
Since the character pad is made of a thin film which is made in the course 
of device manufacturing process and patterning of the character pad can be 
performed simultaneously with that of the thin film, no additional step is 
advantageously required. Numbering using a laser marking apparatus or a 
numbering blade of a device pattern exposing apparatus may reduce or not 
increase the number of steps, in contrast with the prior art numbering 
step using spot exposure. The position of the identification mark is more 
preferable for automatic manufacturing process than manual manufacturing 
process, resulting in a high productivity.