FABRICATION OF MICRO LINE GROOVES STRUCTURE ON PLASTIC FILM BY COMBINATION OF ULTRA PRECISION MACHINING AND HOT EMBOSSING METHOD

FABRICATION OF MICRO LINE GROOVES STRUCTURE ON PLASTIC FILM BY COMBINATION OF ULTRA-PRECISION MACHINING AND HOT EMBOSSING METHOD Duc Phuc Truong 1 , Masahiko Yoshino 2 1 School of Mec

FABRICATION OF MICRO LINE GROOVES STRUCTURE ON PLASTIC FILM BY COMBINATION OF ULTRA-PRECISION

MACHINING AND HOT EMBOSSING METHOD

Duc Phuc Truong 1 , Masahiko Yoshino 2

1

School of Mechanical Engineering, Hanoi University of Science and Technology

No 1 Dai Co Viet Road, Hanoi, Vietnam

Tel & Fax: +84 3869-2440 Email: phuc.truongduc@hust.edu.vn

2

Department of Mechanical and Control Engineering, Tokyo Institute of Technology

2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan

ABSTRACT:

In this research, the authors report an efficient

method to fabricate micro line grooves structure

on a plastic film by combincation of ultra-precision

machining and hot embossing method This

process is comprised of two steps: machining of

micro line grooves structure on a Ni-P plate

(called Ni-P master mold); using the Ni-P master

mold to imprint the micro line grooves structure to

a plastic film by hot embossing The results show

that the micro line grooves structure of about 1 µm

in pitch and 0.35 µm in height was sucessfully fabricated on the plastic film with high fidelity, low cost and high throughput The Ni-P master mold can be used many times to imprint micro line grooves structure on plastic films This demonstrates a possibility for fabrication of high precision micro line grooves structure without using costly methods like photolithography

Keywords: micro lines structure, ultra-precision machining, master mold, plastic film

1 INTRODUCTION

Metallic nano/micro structures have reported a

broad applications such as in electronic devices

[1-2], bio sensors [3-6], photovoltaic devices [7-8],

display devices [9], and catalyst [10-11] These

applications generally utilize the special properties

of metallic nano/micro structures known as

localize surface plasmon resonance (LSPR)

LSPR is a collective oscillation of the electrons of

the nano/micro strutures when they are exposed

to the light at a specific wavelength Interestingly,

this LSPR property of nano/micro structures does

not only depend on the die electric constant of the

surrounding environment but it also depends on

the shape, size and arrangement of the

nano/micro structures Therefore, a lot of efforts

have been put in controlling the shape, size, and

arrangement of nano/micro structures in order to

achieve high performance of LSPR property of the

nano/micro structures Nano/micro line or wire

structures are expected to provide excellent LSPR

performance, especially for bio sensing devices [12-14] Effiective methods for fabrication of nano/micro line structures are highy desired for utilizing these structures in bio sensing applications at a low cost Generally, nano/micro line structures are fabricated by the top-down approaches such as electron beam lithography (EBL) [15-16], focus ion beam (FIB) milling [17] and soft-lithography [18-20] However, these methods generally consist of sophisticated steps, they require stringent in controlling the process conditions, and also require costly equipments which result in low throughput, high production cost On the other hand, the bottom-up approaches such as chemical synthesis or anodic aluminum oxide (AAO) mask desposition [21-22] are appropriate for fabrication of nano/micro line

or wire structures at low cost However, these methods requires complicated chemical process and using a lot of toxic chemical solutions In

order to overcome these disadvantages, in this

paper, our group developed a combination

process of ultra-precision machining and hot

embossing method This method solely utilizes

mechanical processes with low cost equipments,

simple in controlling, and without toxic chemical

The objective of this paper is to verify the

feasiblity of this method and demonstration of its

capability for fabrication of micro line grooves

structure a hard master mold and then imprinting

that micro line grooves structure on a plastic film

2 EXPERIMENTAL METHOD

Figure 1 shows the proposed process to fabricate micro line grooves strucure on a plastic film This process comprises two steps: (1) micro line grooves structure is fabricated on a hard metal substrate by ultra-precision machining; (2) the micro line grooves structure is imprinted on a plastic film by hot embossing method The lower photographs in Fig 1 illustrate the micro line grooves structure machined on the Ni-P master mold and the micro line grooves structure imprinted on a plastic film by hot embossing The experiments were conducted as follows:

Figure 1 Process for fabrication of micro line grooves structure on a plastic film

Specimen preparation:

A SS400 steel plate was used as a metal

substrate It’s surface was polished until the

surface roughness lower than Ra 8.0 nm Then

the steel substrate was plated with a hard layer of

Ni-P alloy by using non-electrolytic plating

method The chemical composition of Ni-P alloy

was Nikel (N) for 88% and phosphorus (P) for

12% Thickness of Ni-P plating layer was around

20 µm After plating, the Ni-P plating layer was

polished again to improve the surface roughness

and flatness Roughness of finished surface of the

Ni-P layer was Ra 6.3 nm, and flatness was less

than 0.2 µm in cutting distance for 10 mm

2.1 Ultra-precision machining of micro line

structure on master mold

A series of micro line grooves structure was

machined on the polished Ni-P layer by using

shows the ultra-precision cutting machine using in the experiment The machine consists of three axes i.e X, Y and Z axis The feed resolutions are

10 nm for X, Y axis and 1 nm for Z axis The stroke are 40 mm for X and Z axis, and 20 mm for

Y axis The movement of the axes was controlled

by a computer A cutting tool made of single crystal diamond was mount on Z axis The width

of the tool is 0.9 mm The tool rake angle is 0 and the clearance angle is 10 The edge angle of the tool is 90 The tool edge was ground very sharp It’s nose radius is was verify to be less than 50 nm The shape of the diamond tool is shown in figure 2 (c) The cutting force was measured by placing a load cell on Z axis, and the cutting force was recorded by a computer program The cutting length of line grooves are 5

mm, and pitch of the line grooves structure (i.e the distance between line grooves) is 1 μm

for all the line grooves Depth of machined line

grooves is around 350nm The cutting condition is

(a) Ultra-precision cutting machine

(b) Cutting process

(c) Diamond tool

Figure 2 (a) Ultra-precision cutting machine; (b) Cutting Process; (c) Diamond tool

2.2 Hot embossing of micro line grooves structure

from the master mold to a plastic film

The micro line grooves structure machined on

the Ni-P master mold was used to imprint on a

plastic film by hot embossing method The plastic

film was made of Cyclo-olefin polymer film (called

COP film, Zeon ZF14-100) The thickness of COP

film is around 100 µm

Figure 3 shows the equiment and the

specimen set up for hot embossing The COP film

was placed in contact with the Ni-P master mold

A quartz glass plate was placed on the COP film

to assure the flatness and uniform contact

between the COP film and the Ni-P master mold

The quartz glass plate, COP film and Ni-P master

mold were placed in between the heating plates of

the embossing equipment

Then both the upper and lower plate were

heated to 180C and kept constant during the

embossing process The temperture is measure

by a thermal sensor After that the load was applied to compress the Ni-P master mold in contact with the COP film The compression load was controlled to 5 MPa and the compression time is maintain for 1 minute Then, the heating plates were cooled down by feeding cool water through the channels inside the heating plates until the their temperature became lower than

40C

Finally, the compression load is released The COP film was detacted from the Ni-P master mold A negative micro line grooves structure of the Ni-P master mold was imprinted on the COP film The topology of the micro line grooves structure on the Ni-P master mold and on the COP film was analized by using an AFM (Keyence VN-8010 Hybrid Microscope)

Cutting direction

Diamond tool

Ni-P substrate Diamond tool

Z stage

X,Y stages Tilt adjustment Load cell

Figure 3 Hot embossing equipment and speciment set up

3 RESULTS AND DISCUSSIONS

Figure 4 shows AFM images and the cross

section of the micro line grooves structure

machined on the Ni-P master mold It is confirmed

that dense and uniform micro line grooves

structure was successfully fabricated on the Ni-P

master mold by ultra-precision cutting It is also verified that the pitch of the line grooves structure (i.e the distances between the line grooves) is almost 1 µm, and depths of grooves are 300 ~

450 nm The average depth of the line grooves is

Figure 4 Micro line grooves structure machined on Ni-P master mold

Figure 5 shows AFM images and the cross

section of the micro line grooves structure on the

COP film fabricated by hot embossing It is found

that a negative structure of the line grooves

structure on the master mold is successfully

imprinted onto the COP film It is also verified that

the pitch of the line grooves (i.e the distance

between the line grooves ) is almost 1 μm and the

heights of crests are from 270 ~ 440 nm and the

average heigh of the crests is about 352 nm

which is almost the same as pitch and depth of

line grooves on the master mold This implies that

the micro line grooves structure imprinted on the COP film is high fidelity Interestingly, the Ni-P master mold can be used many times to imprint micro line grooves structure on the plastic films, and later on the plastic film with the micro line grooves structure can be used as a mold for nano/micro imprinting fabrication methods Therefore, it demonstrates that the process is capable for fabrication of micro line grooves structure at high throughput and low production cost

2µm

Figure 5 Micro line grooves structure imprinted on COP film by hot embossing

4 CONCLUSION

(1) An efficient, low cost, and high throughput

fabrication process for micro line grooves

structure on a plastic film by combination of

ultra-precision machining and hot embossing method

was proposed in this paper Its feasibility was

demonstrated experimentally

(2) Micro line grooves structure with the pitch

of 1 µm and an average depth of 354 nm was

successfully fabricated on the Ni-P master mold

by ultra-precision cutting using a diamond tool

(3) A negative micro line grooves structure

was successfully inprinted on a COP film by hot

embossing method The pitch of the micro line grooves structure on COP film is 1 µm and average height of the crests is 352 nm The imprinted structure is high fidelity

ACKNOWLEDGMENT

The experiements were conducted in Department of Mechanical Engineering, Tokyo Institute of Technology, Tokyo, Japan The project was support by Hanoi University of Science and Technology (Grant research No T2017-PC-111) and research fellowship from AUN/SEED Net

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CHẾ TẠO CẤU TRÚC RÃNH THẲNG CẤP ĐỘ MICRO TRÊN TẤM MÀNG MỎNG NHỰA BẰNG PHƯƠNG PHÁP GIA CÔNG SIÊU CHÍNH

XÁC KẾT HỢP VỚI IN DẬP NÓNG

TÓM TẮT:

Trong nghiên cứu này tác giả trình bày

phương pháp hiệu quả để chế tạo cấu trúc rãnh

thẳng cấp độ micro trên tấm màng mỏng nhựa

bằng kết hợp giữa gia công siêu chính xác với

phương pháp in dập nóng Phương pháp này bao

gồm hai bước: trước hết, gia công các rãnh micro

trên tấm khuôn cái Ni-P, sau đó dùng tấm khuôn

cái Ni-P để in cấu trúc rãnh thẳng micro lên tấm

màng mỏng nhựa bằng phương pháp in dập nóng

Kết quả cho thấy cấu trúc rãnh thẳng với khoảng

cách bước khoảng 1 µm và chiều cao khoảng

0,35 µm đã được chế tạo thành công với độ chính xác, sắc nét và chi phí thấp và năng suất cao bằng phương pháp đề ra trong nghiên cứu này Tấm khuôn cái Ni-P có thể sử dụng nhiều lần để

in dập ra nhiều cấu trúc rãnh thẳng micro trên các tấm màng mỏng nhựa Kết quả nghiên cứu minh chứng cho việc chế tạo cấu trúc rãnh thẳng chính xác cao bằng phương pháp gia công truyền thống chi phí thấp và không dùng đến các phương pháp đắt đỏ như quang khắc

Từ khóa: cấu trúc rãnh micro, gia công siêu chính xác, khuôn cái, màng mỏng nhựa