Перевод текста про микролинзы

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ЦЕНЫ НА РАБОТЫ ДЕМПИНГОВЫЕ (НИЖЕ РЫНОЧНЫХ)
РАССМОТРЮ ВАШИ ВАРИАНТЫ ПО СТОИМОСТИ РАБОТЫ
ЕСЛИ РАБОТА ЗАИНТЕРЕСОВАЛА, ПИШИТЕ В ЛИЧКУ, ДАВ ССЫЛКУ НА НЕЁ.


Fabrication of polymer microlens arrays using
capillary forming with a soft mold of micro-holes  array and UV-curable polymer
Chih-Yuan Chang and Sen-Yeu Yang*
Department of Mechanical Engineering, National Taiwan University
D90522016@ntu.edu.tw  Syyang@ntu.edu.tw
Long-Sun Huang
Institute of Applied Mechanics, National Taiwan University
lshuang@mems.iam.ntu.edu.tw
Kuo-Huang Hsieh
Department of Chemical Engineering, National Taiwan University, 1, Sec. 4, Roosevelt Road Taipei 106, Taiwan,
Republic of China
khhsieh@ntu.edu.tw

Abstract: This paper reports a simple and effective method to fabricate  microlens arrays with the ultraviolet-curable resins, and a soft mold of micro-holes array. During capillary forming operation, the surface of the soft mold of micro-holes array is being pressed against the ultraviolet-curable resin layer coated on the plastic substrate. An array of convex lense can be formed in the circular holes of the soft mold due to the capillary filling and surface tension. The microlens arrays have smooth surface and
uniform focusing function. The shape and height of micolens can be controlled with a proper combination of pressing pressure, pressing duration and UV curing dose. This technique shows great potential for fabricating polymer microlens arrays with high productivity and low cost.  ©2006 Optical Society of America     OCIS codes: (220.0220) Optical design and fabrication. (220.4000) Microstructure fabrication.  
(230.0230) Optical devices. (230.3990) Microstructure devices.

References and links
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2.  M. Fritze, M. B. Stern and P. W. Wyatt, “Laser-fabricated glass microlens arrays,” Opt. Lett. 23, 141-143
(1998).
3.  W. X. Yu and X.-C. Yuan, “UV induced controllable volume growth in hybrid sol-gel glass for fabrication
of a refractive microlens by use of a grayscale mask,” Opt. Express 11, 2253-2258 (2003).  
4.  D. L. MacFarlane, V. Narayan, J. A. Tatum, W. R. Cox, T. Chen and D. J. Hayes, “Microjet fabrication of
microlens arrays ,” IEEE Photon. Technol. Lett. 6, 1112-1114 (1994).
5.  S.-I. Chang and J.-B. Yoon, “Shape-controlled, high fill-factor microlens arrays fabricated by a 3D diffuser
lithography and plastic replication method,” Opt. Express 12, 6366-6371 (2004).  
6.  W. Pan, X. Shen and L. Lin, “Micro-plastic lens array fabricated by a hot intrusion process, ” J. Micromech.
Microeng. 13, 1063-1071 (2004).
7.  C. Y. Chang, S. Y. Yang, L. S. Huang and C. H. Chang, “Fabrication of plastic microlens array using gas-
assisted micro hot –embossing with a silicon mold,” Infrared phys. Technol. 48, 163-173 (2006).

1. Introduction
In recent years, microlens arrays have been widely used in many fields such as flat panel
display, micro-scanning system, fiber coupling and optical communication etc. Many methods
of fabricating microlens array have been reported. Some examples are thermal reflow method
#70566 - $15.00 USD Received 3 May 2006; revised 13 June 2006; accepted 15 June 2006
(C) 2006 OSA 26 June 2006 / Vol. 14,  No. 13 / OPTICS EXPRESS  6253
[1], laser writing [2], gray scale mask photolithography [3] and microjet fabrication .........
cycles. It is a simple, inexpensive and reproducible method for rapid fabrication micro- and
nanostructure.  
In this study, the soft mold with micro-holes array is made by casting a pre-polymer of
PDMS against a silicon master of micro-cylinders array. The silicon master of cylinders array
is prepared using photolithography and deep reactive ion etching. During capillary forming
operation, the surface of the soft mold of micro-holes array is pressing against the ultraviolet-
curable resin layer coated on the plastic substrate. Under proper pressing pressure and
pressing duration, the resin will partially fill the circular holes, and due to surface tension
form a convex surface. The resin is then cured by UV-irradiation at room temperature. After
the soft mold is removed, the plastic substrate with microlens array patterns on the surface can
be obtained. The total cycle time is less than 10 seconds. This method has many advantages
over the conventional techniques. In addition to low cost and high productivity, the shape and
height of microlens can be adjusted by changing the processing conditions.
In the experiment, a capillary forming system with UV exposure capacity has been
designed, constructed and tested. The effects of processing conditions on the shape and
quality of formed micolens are investigated. The optical property and surface roughness of
fabricated microlens array are also measured and analyzed.  
2. Experimental setup
2.1 Fabrication of soft mold with micro-holes array
First of all, the silicon wafer with a SiO2 layer is cleaned and coated with a 1.5μm thick
positive photoresist (S1813) using a spin coater. The wafer is then exposed through a mask
with 150×150 circle array features for 8 seconds using a UV mask aligner (EVG620). After
dipping in the developer for 1 min, circular photoresist columns array are obtained. The
second step is silicon dioxide layer etching by reactive ion etching in a CF4 /O2 plasma to
make the etching mask. The deep reactive ion etching process then follows so as to define the shape of the micro-cylinders into the silicon wafer. The etching rate is about 1.5μm/min, and the total processing time is about 70 minutes. A silicon master with micro-cylinders array is obtained. The Polydimethylsiloxane (PDMS) pre-polymer solution (Dow Corning SYLGARD
184), a mixture of 9:1 silicon elastomer and the curing agent is then poured on the silicon
master and cured at 80oC for 2 hours. After the PDMS replica remove fr om the master, the soft mold with micro-holes array is obtained. Figure 1 shows a SEM image and cross-
sectional view of the soft PDMS mold with micro-holes array. The micro-holes array has a
diameter of 100μm, a depth of 105μm and a pitch of 200μm.  
#70566 - $15.00 USD Received 3 May 2006; revised 13 June 2006; accepted 15 June 2006
(C) 2006 OSA 26 June 2006 / Vol. 14,  No. 13 / OPTICS EXPRESS  6254
2.2 The capillary forming facility and process
Figure 2 shows the capillary forming system with UV exposure capacity used in our
experiments. The system consists of UV-transparent top and bottom plates, a charged coupled device (CCD) camera, an UV-lamp, a shutter and a micrometer scale resolution Z-stage with hydraulic unit. The Z-stage allows the control of the distance between the mold and substrate and thus the pressing pressure. The maximum pressing pressure is 500kPa. The wavelength of the UV-lamp is between 365–410nm. The UV intensity at 365nm is 100mJ/cm2
. The UV-curing dose, which is the intensity of UV-light times the curing time, can be controlled by the shutter. An UV-curable epoxy ........
#70566 - $15.00 USD Received 3 May 2006; revised 13 June 2006; accepted 15 June 2006
(C) 2006 OSA 26 June 2006 / Vol. 14,  No. 13 / OPTICS EXPRESS  6255
investigated. The pressing pressure, pressing duration and UV curing dose used in the
experiments are between 20kPa to 140kPa, 2 to 10 seconds and 250 to 1250mJ/cm2
respectively. The qualities of formed microlens arrays are visually inspected using a charged coupled device (CCD) camera. The microlens should be of spherical shape and free of defect.
The results show that the proper pressing pressure is between 50 and 80kPa. Too high
pressure causes distortion of the pattern on the PDMS mold, resulting in sagging and collapse of microlens. The proper pressing duration is between 2 and 8 seconds. Array of microlens with spherical shape can be successfully formed. If pressing duration is too short, the liquid photopolymer will not fill the holes at all and fail to form any shape. On the other hand, if the
pressing duration is above 8 seconds, the photopolymer completely fills the holes cavity, forming flat cylinders. The amount of UV curing dose has little effect on the forming of the microlens. The UV curing dose can be between 500 and 1000mJ/cm2
Figure 3 shows a SEM image of the formed microlens array on polycarbonate (PC)
substrate and the surface profile of a single microlens. The processing condition are 50kPa of pressing pressure, 4 seconds of pressing duration and 750mJ/cm2 of UV dose for curing. The 150×150 array of microlens has been successfully fabricated over the epoxy coating on the plastic substrate. The microlens array has a diameter of 100μm, a sag height of 17.83μm and a pitch of 200μm.  
Based on geometry and optical theory, the radius of curvature (R), focal length (f) and
numerical aperture (NA) can be determined using the following equations:  
wh ere D, h and n are the diameter, the sag height and the refractive index of epoxy material,
respectively. Based on the calculation, the radius of curvature is 79μm, focal length is .........
3.2 The optical property of microlens array
The optical property of the fabricated microlens array is further measured using a beam ........
microlens array, (b) intensity profiles at the focal plane of a microlens array
3.3 The surface quality of formed microlens
Figure 5 shows the surface roughness property measured by an atomic force microscope (DI-
3100, Veeco Inc.) in a 5μm  × 5μm area on top surface of the fabricated microlens. The
specimen is randomly sel ected from a single microlens array. The average surface roughness
(Ra) is 3.586nm. Thus the resultant microlens surface shows good optical smoothness.
Fig. 5. Surface roughness measured in a 5μm × 5μm area on the top surface of the fabricated
microlens. (The average surface roughness is 3.586nm)
3.4 Influences of pressing duration on the shape of microlens
Figure 6 shows the effect of pressing duration on the shape of microlens. With the pressing
pressure of 50kPa and UV curing dose of 750mJ/cm2 , the pressing duration increases fr om 2
........
Fig. 6. Shape of microlens under various pressing duration in the UV-capillary forming process
4. Conclusion
This paper reports an effective method for rapid fabrication of microlens arrays using
ultraviolet-curable resins and soft mold with micro-holes array. By pressing the PDMS mold
of micro-holes array against the ultraviolet-curable epoxy on PC substrates with a proper
combination of processing conditions, the polymer microlens array can be fabricated. An
array of 150×150 microlens has been successfully produced with 50kPa of pressing pressure, 2~8 seconds of pressing duration and 750mJ/cm2
of UV curing dose. The pitch of the
.......
microlens arrays with versatile shape is demonstrated in this study.
Acknowledgments
This work has been supported by the National Science Council (series no NSC94-2212-E-
002-035) of Taiwan. The experimental work is mainly carried out at the MEMS Laboratory in
the Nano-Electro-Machanical-Systems Research Center at NTU. The financial and technique
supports are gratefully acknowledged.
.....
#70566 - $15.00 USD Received 3 May 2006; revised 13 June 2006; accepted 15 June 2006
(C) 2006 OSA 26 June 2006 / Vol. 14,  No. 13 / OPTICS EXPRESS  6258