Optics: measuring and testing – By alignment in lateral direction
Reexamination Certificate
1995-09-28
2002-03-26
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By alignment in lateral direction
C356S400000, C356S401000, C250S548000
Reexamination Certificate
active
06362883
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of electronic displays, and, more particularly, flat panel displays, and even more particularly, field emission display (“FED”) devices.
As technology for producing small, portable electronic devices progresses, so does the need for electronic displays which are small, provide good resolution, and consume small amounts of power in order to provide extended battery operation. Past displays have been constructed based upon cathode ray tube (“CRT”) or liquid crystal display (“LCD”) technology. However, neither of these technologies is perfectly suited to the demands of current electronic devices.
CRT's have excellent display characteristics, such as, color, brightness, contrast and resolution. However, they are also large, bulky and consume power at rates which are incompatible with extended battery operation of current portable computers.
LCD displays consume relatively little power and are thin in size. However, by comparison with CRT technology, they provide poor contrast, and only limited ranges of viewing angles are possible. Further, color versions of LCDs also tend to consume power at a rate which is incompatible with extended battery operation.
As a result of the above described deficiencies of CRT and LCD technology, efforts are underway to develop new types of electronic displays for the latest electronic devices. One technology currently being developed is known as “field emission display technology.” The basic construction of a field emission display, or (“FED”) is shown in FIG.
1
. As seen in the figure, a field emission display, also referred to as a “flat panel display,” comprises a faceplate
100
with a transparent conductor
102
formed thereon. Phosphor dots
112
are then formed on the transparent conductor
102
. The faceplate
100
of the FED is separated from a baseplate
114
by a spacer
104
. The plates
100
and
104
are also referred to as substrates. The spacers serve to prevent the baseplate from being pushed into contact with the faceplate by atmospheric pressure when the space between the baseplate and the faceplate is evacuated. A plurality of emitters
106
are formed on the baseplate. The emitters
106
are constructed by thin film processes common to the semi-conductor industry. Numerous emitters
106
are formed on the baseplate
114
to provide a spatially uniform source of electrons.
During manufacturing, a seal is formed around the outer boundaries of the faceplate
100
and the baseplate
114
to contain the evacuated space between them. Before this seal can be formed, it is important that the faceplate
100
is accurately aligned with the baseplate
114
in order to produce an acceptable flat panel display. In order to obtain the necessary alignment, corresponding alignment marks are often placed on the faceplate
100
and the baseplate
114
. Optical equipment for detecting these alignment marks is then used to ensure that the plates are properly aligned.
FIG. 1B
shows an example of such alignment marks. As shown, substrate
100
is patterned with alignment marks
102
. Substrate
100
may be either a faceplate or a baseplate. Substrate
104
is provided with alignment marks
106
which correspond to alignment marks
102
on substrate
100
. As the substrates are assembled, optical equipment is used to simultaneously observe alignment marks
106
and
102
to ensure proper alignment of the substrates.
However, this technique is not completely satisfactory. In order for the optical equipment to ensure that the substrates are properly aligned, the equipment must be able to accurately focus on the edges of alignment marks
102
and
106
. Further, the optical equipment must be able to focus on alignment marks
102
and
106
simultaneously as the substrates are being aligned. Such accurate focusing of the optical equipment is difficult due to the relatively large spacing between the substrates in a flat panel display. Moreover, the problem is compounded because, as the magnifying power of the optics is increased to provide an accurate image of the alignment marks, the depth of focus is correspondingly decreased thus making it even more difficult to focus on both substrates simultaneously. For example, for a flat panel display having a 500 micron gap between substrates
100
and
106
, there are no optics presently available which would provide a micron (order of magnitude) accuracy. Further still, optics capable of producing an acceptable alignment are expensive and add to the overall cost of the manufacture of the flat panel display.
Accordingly, there is a need in the art for a method and apparatus of aligning flat panel displays which will overcome the above-mentioned problems.
SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided a method of aligning substrates in an apparatus for aligning a flat panel display having a plurality of substrates. Although the following discussion often focuses on field emissions displays, it is to be understood that the present invention also has application with other flat panel displays such as LCDs and plasma displays. In one embodiment, the method for aligning the substrates comprises providing an optical path through each substrate, wherein alignment of the optical paths corresponds a desired alignment of the substrates. In another aspect, the invention comprises directing a light into the optical path of a first substrate, detecting the light exiting the optical path of a second substrate and positioning the substrates relative to each other such that the amount of detected light is optimized.
According to another embodiment of the invention, there is provided an apparatus for aligning a plurality of substrates in a field emission display, each substrate having a path allowing for the passage of light, the paths being disposed such that alignment of the paths corresponds to a desired alignment of the substrates. In one version, the apparatus has a source which directs a light into the optical path of a first substrate, a detector of the light exiting the optical path of a second substrate, and a positioner which determines the amount of light detected and positions the substrates relative to each other such that the amount of detected light is optimized.
REFERENCES:
patent: 4904087 (1990-02-01), Harvey et al.
patent: 5337151 (1994-08-01), Baxter et al.
Font Frank G.
Hale and Dorr LLP
Lauchman Layla
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