Stamper for use in forming planar micro-lens array and method for forming thereof

For providing a stamper for forming a planar micro-lens array, a stamper is prepared by forming plural concave portions 2 for forming lens portion upon a stamping surface thereof, and a trap portion 3 is provided surrounding said plural concave portions and continuing until an outer edge thereof. Then, onto the stamping surface, on which a release agent 4 is applied, there is applied a high refractive index resin 5, and a glass substrate 6 is pressed onto the high refractive index resin 5 to exude it. With this operation, the high refractive index resin 5 is filled into each of the plural concave portions 2, and any excess is received or accommodated in the trap portion 3, thereby preventing excess resin from being forced outside.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a stamper for use in forming a large 
number of convex lens comprising resin having a high refractive index upon 
a surface of glass substrate, and also to a method for producing a 
plate-like micro-lens array by use of the stamper. 
2. Description of Related Art 
A flat-type or plate-like (planar) micro-lens array is installed into, for 
example, a part of a liquid crystal display element. Explaining a 
structure of such a liquid crystal display element by referring to FIG. 7, 
a gap is formed between glass substrates 101 and 102 by a spacer 103, into 
which liquid crystal 104 is poured. On a surface of the glass substrate 
101 there are formed opposing electrodes 101a at the side of the liquid 
crystal 104, and on a surface of the other glass substrate 102 there are 
formed transparent pixel electrodes 102a at the side of the liquid crystal 
104. Further, additional portions other than the transparent pixel 
electrodes 102a are formed which are not transparent, such as wiring, TFTs 
(thin film transistors), etc. 
Next, upon an exterior surface of the glass substrate 101 there is bonded a 
planar micro-lens array 105, serving to focus irradiated light through the 
lens portion 106 thereof into pixel electrodes (i.e., openings for the 
pixels) 102a, so as to increase the brightness of an image projected upon 
the screen. Not that the pixels and lenses (lens elements) are provided in 
plural numbers. 
An example of the method for producing such a planar micro-lens array 105 
will be explained by referring to FIG. 8 attached. 
First, recessed portions 111 are formed on the surface of the glass 
substrate 110 through an etching process, and then a resin of high 
refractive index 112 is applied thereupon and is spread over the surface 
of the glass substrate 110 by a stamper 113 so as to fill in plural 
recessed portions 111. Next, the high refractive index resin 112 is cured 
under light, thereby obtaining the lens portion 106 mentioned above. 
However, in the case of producing or forming the planar micro-lens array 
with the method mentioned above, any of the high refractive index resin 
that is excess is pushed or forced out from the edge of the glass 
substrate and is cured during the curing process. As a result, the planar 
micro-lens array itself becomes larger in dimension thereof, such that it 
cannot be bonded or attached on the other element(s) and its size does not 
fit with the other portions for installation therewith. This is a 
disadvantage. Further, if the high refractive index resin exudes to the 
reverse of the substrate, the planar micro-lens array will experience 
degraded performance. 
Furthermore, when a plurality of planar micro-lens arrays are cut out from 
a large-sized glass substrate on which multiple surfaces are formed, since 
the high refractive index resin forms a layer applied over the entire 
surface of the glass substrate, the layer of the high refractive index 
resin might be easily separated or exfoliated therefrom, or the surface of 
the micro-lens array may be damaged during a subsequent cutting procedure. 
Therefore, the applicant of the present application already proposed a 
structure, disclosed in Japanese Patent Application No. Hei-7244288 
(1995), in which a gutter portion 113 is formed surrounding the outside of 
the recessed portions 111 so as to receive or accommodate any high 
refractive index resin that exudes in excess therefrom, as shown in FIG. 
9. 
However, a problem lying in the method shown in Japanese Patent Application 
No. Hei-7244288 (1995) is that since the etching is performed on the glass 
substrate itself forming the planar micro-lens array, the etching must be 
performed on the glass substrate every time before applying the high 
refractive index resin thereon. 
Further, as shown in FIG. 9, the gutter portion 113 is formed at the same 
time that the recessed portions 111 are formed by the etching, and 
therefore the depth of it comes to be same to those of the recessed 
portions 111. As a result, there is a possibility that the gutter portion 
113 will have insufficient volume, though it may still be partially 
adequate. Nonetheless, any excess high refractive index resin cannot be 
accommodated or received therein with certainty. 
SUMMARY OF THE INVENTION 
To resolve the problems described above, according to the present 
invention, there is provided a stamper for use in forming a planar 
micro-lens array, comprising a plurality of convex high refractive resin 
portions for forming lenses, which is applied onto a planar surface of a 
glass substrate, in which, after the high refractive resin material is 
applied to plural concave portions of said stamper, the planar glass 
substrate is contacted thereon to exude the resin in between the concave 
portions and the glass plate, and is cured and separated therefrom, 
characterized in that the plurality of concave portions for forming lenses 
of said micro-lens array are formed on a stamping surface of said stamper 
by transcription or etching, and in that a trap portion is formed at an 
outer periphery of the lens of said stamping surface of said stamper by 
transcription or etching, with a depth substantially equal to that of said 
concave portions, continuing at least until an outside edge of a region 
where said glass substrate is to be contacted therewith. 
With the construction according to the present invention, the trap portion 
can be formed large enough to effectively prevent any excess high 
refractive index material from being pushed or forced out. 
Here, also according to the present invention, said stamper is formed with 
laminated layers of nickel, which are formed by performing an 
electro-forming process upon a surface of a master plate of said 
micro-lens array (transcription), or alternatively, after forming a 
plurality of small concave portions upon a surface of a glass plate as a 
model for said stamper by wet etching, a reverse mold is formed with 
laminated layers of nickel, which are formed by performing the 
electro-forming process upon the surface of the glass substrate having the 
plural concave portions, and then said stamper is formed with laminated 
layers of nickel by performing the electro-forming process upon the 
surface of the reverse mold having the plural convex portions thereon, or 
said stamper is formed with a glass substrate, upon a surface of which 
there are directly formed a large number of concave portions by a wet 
etching process. 
Further, according to the present invention, in the stamper, wherein in the 
stamping surface of said stamper there are formed plural groups of concave 
portions, corresponding to plural planar micro-lens arrays, each being 
separate, said trap portion is formed at each outside periphery of each 
group of the concave portions for each planar micro-lens array, with the 
depth substantially equal to that of said concave portions. 
Moreover, according to the present invention, there is provided a method 
for forming a planar micro-lens array by use of the stamper as defined 
above, comprising the steps of: 
turning a stamping surface of said stamper upward, upon which surface is 
applied a release agent; 
applying high refractive resin material upon the stamping surface of said 
stamper; 
pressing a glass substrate upon the high refractive resin material to exude 
the high refractive resin material into the concave portions and then 
curing the high refractive resin material to form the lens portions and 
thereafter; 
releasing the stamper to leave the planar micro-lens array formed on said 
glass surface; and 
again applying the release agent upon a molding surface of said stamper 
after the release thereof, in preparation for a subsequent process. 
With the steps mentioned above, since the etching must be performed only 
when the stamper is produced, it is possible to greatly reduce the scale 
or the number of production processes, as well as to prevent any excess 
high refractive index resin from being forced out. 
Here, as the glass substrate for forming the planar micro-lens array, there 
can be listed soda-lime glass, alkaline aluminosilicate glass, alkaline 
borosilicate glass, non-alkaline glass, crystallized glass, quartz glass, 
etc. In addition, those glass materials can be used as the material of the 
stamper. 
Further, as the high refractive index material, there can be listed 
polyester resin, epoxy resin, silicon resin, phosphazene resin, phenol 
resin, polyimide resin, acryl resin, urethane resin, etc. 
Further, the release agent to be applied upon the stamping surface of the 
stamper is appropriately a compound of fluorine group or a compound 
containing silicon group. Also, as an organic compound of the silicon 
group, preferably a resolvable one, which mainly contains polysiloxane, 
chlorsilane compound, alkoxysilane compound, disiloxane compound, and is 
resolvable into water soluble organic solvent, such as water or alcohol, 
or resolvable into hydrocarbon organic solvent or fluorine organic 
solvent, is used. 
Further, those which contain fluorine in the organic compound of the 
silicon group are very low in surface tension at the release surface of 
the mold, and therefore, they exhibit good release qualities. Those can 
also be used in a mixture thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, detailed explanation of the embodiments according to the 
present invention will be given by referring to the attached drawings. 
Here, as shown in FIGS. 1 (a) through (f) explaining the forming method by 
use of a stamper according to the present invention, the stamper 1 is 
manufactured by means of an electro-forming or wet etching process, as 
shown in FIG. 1 (a). Upon a molding or stamping surface of this stamper 1 
there is formed plural concave portions 2 for forming lens elements, and a 
trap portion 3 is formed all around the plural concave portions, 
continuing until an outer edge thereof. The depth of this trap portion 3 
is substantially equal to those of the plural concave portions 2. 
Here, an example of the method for preparing the stamper 1 will be 
explained on the basis of FIGS. 2 (a) to (d) and FIGS. 3 (a) to (e). 
First, in the method shown in FIGS. 2 (a) to (d), a layer of 
photo-sensitive film 31 is formed on a surface of a substrate 30, as show 
in FIG. 2 (a), and then, as shown in FIG. 2 (b), upon the photo-sensitive 
film 31 there is irradiated an electron beam to manufacture a master 
micro-lens array, in which convex portions 32a are formed for subsequently 
forming the lens elements 32 and the trap portion 3. 
Next, as shown in FIG. 2 (c), a nickel layer 33 is laminated upon the 
surface of the master micro-lens array by means of an electro-forming 
method, and further, as shown in FIG. 2 (d), the laminated layer is later 
separated from the master micro-lens array thus obtaining a stamper 1. 
Also, in another method shown in FIGS. 3 (a) to (e), upon the surface of a 
glass substrate 40 serving as a model, as shown in FIG. 3 (a), a wet 
etching is performed through a mask 41, and as shown in FIG. 3 (b), plural 
minute concave portions 42 are formed having a spherical or cylindrical 
surface shape, together with a trap portion 43. Further, as shown in FIG. 
3 (c), the wet etching is again performed without the mask so as to form 
plural small concave portions closely arrayed next to each other and 
aligned with one another. Then, as shown in FIG. 3 (d), a nickel layer is 
laminated onto the surface, on which the plural concave portions are 
formed closely arrayed and aligned, by means of an electro-forming method, 
to form a reverse mold 44. Further, by again laminating the nickel layer 
upon the surface of this reverse mold 44 by means of the electro-forming 
method, the stamper 1 can be obtained. 
However, the stamper 1 also can be manufactured with a glass substrate by 
the process shown in FIGS. 3 (a) to (c). 
When the stamper 1 is prepared in the manner mentioned above, a release 
agent 4 is applied onto the molding or stamping surface of the stamper 1, 
as shown in FIG. 1 (b). On the stamping surface, onto which the release 
agent 4 is applied, as shown in FIG. 1 (c), resin 5 having a high 
refractive index is applied. The high refractive index resin 5 can be of 
the light-curable type, which is cured by irradiation of UV (ultra violet) 
light, or of the heat-curable type, which is cured by applying heat 
thereto. Further, as shown in FIG. 1 (d), the glass substrate 6 is pressed 
onto the above-mentioned high refractive index resin 5 so as to exude it. 
However, it is preferable that a coupling agent be applied upon the 
surface of the glass substrate 6, which contacts with the high refractive 
index resin 5, in advance. As the coupling agent, there can be considered 
.gamma.-glycidpropyl-trimethoxy silane or mercapt-propy-trimethoxy silane. 
Also, the viscosity of the high refractive index resin 5 appropriately 
lies from 0.1 to 100 poise, and it is effective to apply the resin under a 
reduced pressure condition in order to prevent creating bubbles therein. 
By the operation mentioned above, the high refractive index resin 5 is 
filled into the plural concave portions 2, and at the same time, any 
excess high refractive index resin 5 is received into or accommodated by 
the trap portion 3, and is not disadvantageously forced outside. 
When the high refractive index resin 5 is filled in the plural of concave 
portions 2, UV light is irradiated in order to harden the high refractive 
index resin 5 to form the lens elements 7. 
Since, upon the stamping surface of the stamper 1 there is applied the 
release agent, while the coupling agent is applied upon the surface of the 
glass substrate 6 contacting with the high refractive index resin 5, the 
lens elements 7 are bonded onto the glass substrate 6. Accordingly, as 
shown in FIG. 1 (e), when the stamper 1 is removed or separated, a planar 
micro-lens array 10 comprising the lens elements 7 on the glass substrate 
6 can be obtained. 
Moreover, the stamping surface of the stamper 1, after finishing the 
forming process, as shown in FIG. 1 (f), is washed, and the release agent 
is applied again onto the stamping surface for a subsequent forming 
operation. In this manner, by using the stamper 1 repeatedly, the etching 
process is necessary only when the first stamper 1 is manufactured, 
thereby reducing the complexity and cost of the manufacturing processes 
greatly. 
FIGS. 4 (a) to (c) show a plane view of the planar micro-lens arrays 
obtained according to the present invention, in particular, FIG. 4 (a) 
shows lenses of a hexagonal shape, FIG. 4 (b) a square shape, and FIG. 4 
(c) a lenticular shape, respectively. All shapes shown may be easily 
attained according to the method of the present invention, and the 
invention may equally be applied to preparing lens arrays in other shapes. 
FIG. 5 is a view for explaining an embodiment in which plural planar 
micro-lens arrays are formed by means of a single stamper, wherein the 
high refractive index resin 5 is applied into each of the plural concave 
portions 2 of the stamper 1, and plural glass substrates 6 are placed onto 
the high refractive index resin 5, one by one. 
However, not shown in the figure, with the stamper shown in FIG. 5, it is 
also possible to obtain production of plural planar micro-lens arrays on a 
large-sized glass substrate, each of which is cut out therefrom afterward. 
FIG. 6 shows a liquid crystal display element, to which is applied the 
planar micro-lens array 10 obtained in the manner mentioned above. The 
liquid crystal display element 20 defines a cell by bonding the glass 
substrate 21 onto a glass substrate 22 through a spacer 23, and on the 
glass substrate 22 forming cells there is contacted a lens-forming surface 
comprising the planar micro-lens array 10 through a low refractive index 
material 24, such as a fluorine group resin, acrylic resin group or epoxy 
resin group, etc. Thereafter, liquid crystal 25 is filled inside the space 
defined between the glass substrate 21 and the glass substrate 22, so as 
to complete the liquid crystal display element 20. 
Further, on the surface of the glass substrate 21 or 22, at the side of the 
liquid crystal 25, there are previously formed opposing electrodes 26, 
while pixel electrodes 27 are formed on the surface of the glass substrate 
21 at the side of the liquid crystal 25. 
As is fully explained above, in accordance with the present invention, 
there is no necessity to treat the glass substrate to be the micro-lens 
array with an etching process during each time when forming thereof, 
thereby greatly simplifying the process of production thereof. 
Further, since the trap portion is formed all around the stamper, 
continuing until the outer edge thereof, any excess high refractive index 
resin will not be forced out during the forming process. And, since any 
excess high refractive index resin will not be disadvantageously forced 
out, the high refractive index resin coating film will not be torn or 
damaged when cutting plural lens arrays from a large glass substrate. 
Also, when forming a planar micro-lens array on a glass substrate using 
the method according to the invention, it is easy to insert a jig between 
the glass substrate and the stamper. Therefore, the manufacturing 
processes for producing the planar micro-lens array(s) becomes easy, and 
any possibility that the glass substrate and/or the stamper might be 
injured is significantly reduced.