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A new method for fabricating microchannels for microfluidic applications on soda-lime glass has been developed. It consists of a combination of a laser direct write technique for fabricating the microchannels and a thermal treatment for reshaping and/or improving the morphological qualities of the generated microchannels. The proposed technique allows us to obtain microchannels with a minimum diameter of 8 µm and 1.5 µm of depth. A decrease of two orders of magnitude of the average roughness generated after the laser ablation, reaching values of the order of the unprocessed glass, has been obtained thanks to the thermal treatment. The use of pulsed nanosecond lasers for the laser direct write presents the benefits of using lasers commonly implemented in the industry for laser processing of materials. This fact makes the technique presented highly competitive compared with others used for glass microstructuring.
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Fabrication of microchannels on soda-lime glass substrates
with a Nd:YVO
Daniel Nieto
, Tamara Delgado, María Teresa Flores-Arias
Microoptics and GRIN Optics Group, Applied Physics Department, Faculty of Physics, University of Santiago de Compostela, Santiago de Compostela,
E15782 Spain
article info
Article history:
Received 29 November 2013
Received in revised form
28 May 2014
Accepted 4 June 2014
Laser ablation
A new method for fabricating microchannels for microuidic applications on soda-lime glass has been
developed. It consists of a combination of a laser direct write technique for fabricating the microchannels
and a thermal treatment for reshaping and/or improving the morphological qualities of the generated
microchannels. The proposed technique allows us to obtain microchannels with a minimum diameter of
8mm and 1.5 mm of depth. A decrease of two orders of magnitude of the average roughness generated
after the laser ablation, reaching values of the orderof the unprocessed glass, has been obtained thanks to
the thermal treatment. The use of pulsed nanosecond lasers for the laser direct write presents the
benets of using lasers commonly implemented in the industry for laser processing of materials. This fact
makes the technique presented highly competitive compared with others used for glass microstructuring.
&2014 Elsevier Ltd. All rights reserved.
1. Introduction
Microuidics is a quickly developing engineering science for
targeting transportation and handling a small volume of liquids in
an increasing number of applications such as biomedical diagnos-
tic, micro fuel cells and microelectronics cooling [14]. These
applications demand transparent materials that allow high resolu-
tion imaging, uorescence microscopy, and also to analyze para-
meters such as laminar ow, mass transport driven by diffusion
rather than turbulence and constant removal of waste products
[57]. Glass materials are commonly used due to the benecial
optical properties, their surface stability and solvent compatibility,
as well as due to their straightforward and well-known fabrication
techniques [8,9]. Glass also overcomes many limitations of poly-
mers because of their mechanical durability, reusability, low auto-
uorescence and smooth surface. The high cost involved in glass
processing and the material itself limit their usage as disposable
devices, so high quality devices made of glass and disposable low-
cost devices made of plastic are the two routes of challenging
demands to be solved by microuidics.
A huge variety of methods exist for the fabrication of micro-
uidic devices, the choice among them depends on the size and
shape of the required features as well as on the materials to be
treated. Embossing, injection molding, and similar thermoforming
techniques, while providing excellent throughput and cost, are
ineffective for glass [10]. Lithography techniques require advanced
facilities and numerous processing steps. A big number of
researchers have demonstrated the fabrication of channels in glass
using electron beam lithography, photolithography and, wet and
dry etching [1114]. These techniques provide high-quality micro-
uidic systems, with the inconvenience of the required sophisti-
cated equipment located in clean rooms and the production of
toxic waste, so signicant challenges still remain for fabricating
low-cost and reliable microchannels in glass. In general, in a
microuidic channel the surface roughness is mostly caused by
an inaccurate mask and its imprecise alignment in the fabrication
process. These are common problems that are difcult and
expensive to avoid. In this context, laser micromachining, because
of its non-contact nature, offers several advantages for fabricating
microchannels, including the capability to form complex shapes
with minimal mechanical and thermal deformation. Fabrication of
microchannels on glass by laser ablation techniques has been
investigated and reported using CO
, UV and ultra short pulse
lasers [1517]. Literature shows that the fabrication of microchan-
nels is more efcient with pulsed laser instead of CW laser [2,18].
Regarding the pulsed laser, although femtoseconds lasers give
better results than nanoseconds lasers, in terms of surface quality
and accuracy of the elements fabricated on glasses, debris deposi-
tion and so on [19], the advantages of using nanosecond IR lasers
comes from the difference in cost between femto and nanosecond
lasers, and therefore, the higher possibilities to industrially imple-
ment this technique.
Contents lists available at ScienceDirect
journal homepage:
Optics and Lasers in Engineering
0143-8166/&2014 Elsevier Ltd. All rights reserved.
Corresponding author.
E-mail address: (D. Nieto).
Optics and Lasers in Engineering 63 (2014) 1118
One of the main aims of this paper is to overcome the still
signicant challenges for fabricating low-cost and reliable micro-
uidic modules in transparent media using nanosecond lasers
with comparable quality of those obtained with femtosecond
lasers. In the present work, a fast, simple but reliable process is
reported for the fabrication of the microchannels using a Nd:YVO
nanosecond IR laser. The fabrication method combines a laser
direct-write technique with a thermal treatment that reduces the
damage created on the glass during the laser ablation and change
the roughness (Ra) improving the morphological quality of the
microchannels. These two steps make possible to fabricate micro-
channels with comparable characteristics and quality as those
obtained by other methods [20], preserving the advantages of the
laser direct-write technique (exibility in terms of design, fast
prototyping, low-cost, non-contaminantion of the sample, etc).
In Section 2, the experimental procedure for fabricating micro-
channels is presented. Section 3 analyzes the thermal treatment
and morphological characterization of microchannels as function
of temperature. Section 4 contains some conclusions and remarks.
2. Microchannels fabrication
We present a direct-write technique for fabricating microui-
dics microchannels based on the ablation of a soda-lime glass
substrate with a laser of circular Gaussian beam prole followed
by a thermal treatment. The thermal treatment reduces the
damage created during laser ablation, which lead to an improve-
ment of morphological quality of microchannels generated by
laser. The laser setup consists of a Q-Switch Nd:YVO
operating at 1064 nm combined with a galvanometer system for
addressing the output laser beam (Fig. 1). A at-eld lens, of effective
focal length 100 mm, provides a uniform irradiance distribution on
glass substrate over a working area of 80 80 mm
optimize the fabrication process, a previous study was made by
focusing one laser shot on the glass substrate. The mark obtained
was analyzed with a confocal microscope. This initial step let us
determine the laser parameters used for the laser direct-write
process. The morphology of the microchannels in terms of shape
and roughness was analyzed with a confocal microscope SENSO-
FAR 2300 Plm.
For fabricating the microchannels in soda-lime substrate, we
used the following laser parameters: power 8 W, repetition rate
10 kHz, wavelength 1064 nm and pulse width 20 ns. The ablation
threshold (112 J/cm
) was dened as the minimal energy required
for fabricating a homogeneous microchannel in the glass substrate
[18]. We study the inuence of pulse overlapping. It is a crucial
parameter to reach a good nal microchannel. For achieving
uniform microchannels, we analyze the pulse overlap, Od dened
as follows:
Od ¼ð1υ=2ω
is the galvo scanner speed (mm/s), 2
is the focused spot
diameter and fis the laser repetition rate.
We have analyzed experimentally the uniformity of the micro-
channels obtained at different scan speed for getting the optimal
pulses overlapping (see Fig. 2). We have used the same laser
parameters (power: 8 W, repetition rate: 10 kHz, pulse width:
20 ns and pulse energy: 0.8 mJ) for fabricating the microchannels
varying only the scan speed from 10 mm/s to 140 mm/s.
In Fig. 2 we can see that the best results were obtained for the
channels fabricated between 40 mm/s and 80 mm/s (Fig. 2dande).
Fig. 1. Laser setup for fabricating the microchannels.
Fig. 2. Confocal images of one microchannel obtained by laser ablation of glass at 10 kHz, 8 W for scan speeds values of (a) 140 mm/s, (b) 120 mm/s, (c) 100 mm/s,
(d) 80 mm/s, (e) 40 mm/s and (f) 10 mm/s.
D. Nieto et al. / Optics and Lasers in Engineering 63 (2014) 111812
At low scan speed, the high overlapping of the pulses delivers too
much energy at the surface, which leads to a distortion on the
microchannels (Fig. 2f). For scan speeds higher than 40 mm/s, it can
be appreciated the interaction of each pulse with the substrate
(Fig. 2ac), which also increases the average roughness and does
not allow the formation of the microchannels. Fig. 3 shows the pulse
overlap, obtained using Eq. (1), and the average roughness measured
at different scan speeds. In terms of pulse overlap (Fig. 3a), values in
the range of 6080% are needed for fabricating microchannels with
good qualities. For scan speed values in the interval of 4080 mm/s,
values of roughness around 55 nm are obtained (Fig. 3b).
Fig. 4 shows a microchannel fabricated using the optimal pulse
overlapping obtained from the study presented above and laser
parameters of 8 W, 10 kHz and scan speed 50 mm/s. The resulting
channel exhibits a surface roughness of 54 nm, diameter of 8 mm
and height of 3 mm.
In order to fabricate different microchannel congurations, a
study of the evolution of depth and diameter with the number of
laserpassesoverthesameplacewasdone.Fig. 5 shows the evolution
of depth and diameter versus the number of laser passes.
It is evident from Fig. 5 that the channel aspect ratio
varies with the number of passes. The diameter dreaches its
saturation value after 5 laser passes, increasing just around
200 nm per laser pass and varying only 1
m after 5 passes, above
these values it is maintained almost constant. In contrast, the
height of the channel hincreases as the number of passes
increases, reaching a saturation value after 6 passes. An increase
of 1
m per laser pass is achieved, up to a value of 12
m. This
behavior can be related with the non-evacuation of the debris
generated during laser ablation from the bottom of the channel as
well as the lack of focus as the depth of the microchannel
increases. On the other hand, the diameter of the microchannel,
which is maintained almost constant with the number of passes, is
related with the diameter of the laser beam.
The greatest challenge to be overcome using a laser direct-
write technique for fabricating microchannels is to obtain good
quality junctions, since the propelled material of the subsequent
channels is deposited on the existing microchannel, which dete-
riorates the quality of the microchannel. Since the debris gener-
ated change the Ra,crucial for obtaining good micro-optical and
micro-uidics elements, a study of debris deposition for a micro-
channel with a depth of 4.5
m was undertaken. The laser uence
(190 J/cm
) was chosen to be higher than the ablation threshold of
glass, which ensures us to have energy enough to propel the debris
far away from the ablated region. The results are shown in Fig. 6.
In Fig. 6a, we can see how the propelled material, resulting
from the ablation process, is deposited at the edge of the micro-
channel. From this image we extract a transversal prole (Fig. 6b),
which lets us analyze the debris deposition at different distances
from the center of the microchannel. In Fig. 6b, square 1 shows the
portion of the surface measured for determining the average
roughness over the glass with debris near the microchannel that
is the standard deviation of the debris lm height. The average
roughness is estimated to be 12.3 nm in the region between 7 and
12 mm from the center of the microchannel. Square 2 shows the
portion of the surface measured for determining the average
roughness over the glass with debris, far away from the micro-
channel. The average roughness is estimated to be 12.3 nm in the
region dened by a distance from 12 to 20 mm from the center of
the microchannel. Square 3 shows the portion of the surface
measured for determining the average roughness over the glass
without debris. The roughness is estimated to be 6.2 nm for a
distance greater than 20 mm. The line across the prole shows the
difference in depth of the glass surface and the area where debris
was deposited after ablation. From these data we can obtain
information about the quantity of debris removed and the deposi-
tion when we fabricate shallow and deep channels. In addition, at
high uencies, where a huge quantity of material is generated
during laser ablation, it was appreciated the need of using a
cleaning process after laser exposure, that involves a chemical
etching process using Hydrouoric acid (HF). Hydrouoric acid is
an etchant which attacks glasses at signicant high etch rate [16].
Commercial soda-lime glass used in this work is composed of SiO
(73.8%), Na
O (12.7%), CaO (8.6%), MgO (4.1%) and small amounts
of Fe
(0.14%) and Al
(0.1%). Etching soda-lime glass in a HF
solution forms insoluble products which are believed to be mainly
and MgF
The mechanism for eliminating the debris depends on the
concentration of the acid, on the etching time and on the
temperature of the process. However, HF is not only a strong
corrosive, but also highly toxic towards higher concentrations, so
the etching process was performed at 10% HF concentration, which
Scan Speed (mm/s)
56.16 54.4 62.14
Roughness (Ra) (nm)
Scan Speed (mm/s)
Pulse overlap (O
Fig. 3. (a) Evolution of pulse overlapping and (b) roughness versus scan speed in the range of 10140 mm/s.
Fig. 4. Initial microchannel fabricated by laser ablation.
D. Nieto et al. / Optics and Lasers in Engineering 63 (2014) 1118 13
in terms of security, reduces considerably percentages of toxic
vapor that contaminate the work space. Fig. 7 shows a SEM top
view image of one microchannel before (Fig. 7a) and after (Fig. 7b)
HF etching.
In Fig. 7a debris deposited at the top of the microchannels
during the laser ablation can be observed. In Fig. 7b we can see
how the debris was successfully eliminated after chemical etching.
The elimination of debris will improve the quality of the micro-
channel, while if maintained at the edge of the microchannel, they
would be mixed with the glass material during the thermal
treatment resulting in bad quality of the nal microchannel.
3. Thermal treatment
After fabricating the initial structures and eliminating debris
around the channel using HF acid. A thermal treatment was
applied in an oven for improving its morphological properties.
The samples were reowed in a Heraeus mua furnace for 2 h at
temperatures between 620 1C and 670 1C (steps of 10 1C). The
working range has been chosen to be higher than glass transition
temperature of soda-lime glass (Tg ¼564 1C). Fig. 8 shows the
initial shape of the etched glass pattern by laser ablation and the
shape obtained after the material displacement with the thermal
This displacement of material and the consequent accumula-
tion in the bottom leads to a reduction in height. The diameter is
increased due to the material reowed from the top of the edges
of the microchannels to the bottom of the crater. This effect
allows both, the thermal reow and the lling of the irregular
structure of the crater leading to an improvement on the
morphological qualities. Since the viscosity of glass material is
strongly temperature dependent, different thermal reow tem-
peratures in the range of 620670 1Cweretestedtostudythe
inuence of temperature on surface curve change. The heights
of the microchannels obtained at different temperatures are
in the range of 2002.5 mm, and the diameter in the range of
825 mm(seeFigs. 9 and 10). Fig. 9 shows the topographic
prole of the fabricated microchannels at different tested
Fig. 6. (a) Confocal image of a channel of height 4.5 μm. Enlarged pictures at the top, shows SEM images of glass (1) without debris and (2) with debris deposited at the edge
of the microchannel. (b) Half transverse prole of a channel with debris deposition at different distances from the center of the microchannel represented by different
regions using numbered squares: square 1 (from 7 to 12 mm), square 2 (from 12 mmto20mm) and square 3 (distance greater than 20 mm).
Fig. 5. (a) Evolution of depth and (b) diameter with the number of laser passes.
D. Nieto et al. / Optics and Lasers in Engineering 63 (2014) 111814
As it can be appreciated in Fig. 9, for a temperature of 620 1C,
there was almost no change in the surface shape. For a reow
temperature higher than 670 1C, the initial shape surface prole
becomes at so microchannels obtained by laser direct-write tend
to disappear. Fig. 10 shows a 3D confocal image of microuidics
microchannels fabricated at different reow temperatures.
The specicow resistance for each microchannel is strongly
dependent on the geometry and on the roughness. The surface
roughness on the wall of the channel increases by decreasing the
ow rate, since the change of hydraulic resistance is proportional
to the change of surface roughness, for determining the quality of
the microchannels fabricated at different thermal reow tempera-
tures, the roughness was determined at the bottom of the
channels. The roughness average of the glass surface before laser
ablation was 3.68 nm, after laser ablation it increases till 640 nm.
Table 1, shows the evolution of roughness for temperatures
between 620 1C and 670 1C, taken at steps of 10 1C. Since the
purpose of thermal treatment in the case of microchannels is to
reduce the roughness generated during laser ablation, it is impor-
tant to nd a compromise between shape modication and
roughness reduction. Ideally, the shape should be maintained
while the thermal reow should reduce the surface roughness.
By applying the thermal treatment at 620 1C (for 2 h) we were
able to obtain high quality microchannels maintaining the initial
shape and reducing the roughness. At 670 1C the roughness
obtained was similar to the unprocessed glass but the channel
shape changes considerably. In terms of roughness, the thermal
treatment permits us to obtain values of roughness in the range of
unprocessed glass. The roughness average (Ra) at the bottom of
the microchannels before thermal treatment was Ra¼640 nm and
after thermal treatment at 670 1C was Ra¼7.35 nm, this is in the
order of the unprocessed soda-lime glass surface (3.68 nm), which
means that the quality of surface is much better after thermal
treatment. The best result was obtained for 630 1C, at this
temperature the initial shape was maintained almost constant,
and the roughness achieved a value of 57.15 nm, good enough for
microuidics applications on glass [19,20].
After obtaining the best parameters for fabricating optimal
microchannels, in order to study the microuidic capabilities of
our technique, we focused on fabricating microchannels with
different congurations trying to solve the main problems related
with the laser ablation of glass, in particular for creating uniform
and free of debris channels. Next, attention is turned to the
analysis of the intersection of two microchannels. When the laser
passes twice over the same position, as at the intersection of two
microchannels, the excess of energy on the same point creates a
deeper structure, thus, affecting an accurate uid ow (Fig. 11a).
This is a crucial point to be overcome for obtaining a good
intersection that becomes in a nice structure for microuidic
For improving these intersections, an important parameter to
take into account is the number of laser pulses delivered at the
beginning and the end of each individual channel. Due to the
characteristic of the Q-switch Nd:YVO
laser used in this work,
when the shutter is opened for the rst time in order to liberate
the energy stored in the laser cavity, the rst emitted pulse is more
Fig. 7. (a) SEM image of the microchannel top surface before chemical etching and, (b) SEM image of the microchannel top surface after 10 min in 10% HF aqueous solution.
Fig. 8. Material displacement mechanisms for fabricating microchannels.
Fig. 9. Cross-sectional prole of the microchannels at different thermal reow
temperature. Six different results at different reow temperatures are shown:
T1¼620 1C, T2¼630 1C, T3¼640 1C, T4¼650 1C, T5¼660 1C and T6¼670 1C.
D. Nieto et al. / Optics and Lasers in Engineering 63 (2014) 1118 15
intense than the following. Usually, this can be corrected with the
software of the laser, which lets us modify and control the rst
pulses that reach the sample. In the specic software of the Ron
Powerline E this can be modied using a control named Limit.
Fig. 11 shows the intersection of two microchannels for different
values of this limit.
As it can be appreciated in Fig. 11a, selecting a high value of the
limit (200), too much energy is delivered at the beginning of the
channel, so a deeper structure is created at the intersection of two
channels. In Fig. 11c we select a low value of the limit (50) which
turns in a bad intersection where not all the material is removed
between both channels. Fig. 11bshowstheintersectionobtained
with the optimal value of the limit (100) for the laser parameter used.
Fig. 12 shows different microchannel congurations fabricated
using the optimal laser parameters obtained for soda-lime glass
substrate (limit 100, power of 8 W, rep. rate 10 kHz and scan speed
100 mm/s). Special attention has been taken on creating uniform
and free of debris channels with very good denition at intersec-
tions and curves.
4. Conclusions
A hybrid method for fabricating microuidic microchannels on
soda-lime glass has been developed. It consists of a combination of
Fig. 10. Confocal images of microchannels obtained after thermal treatment at different temperatures.
Table 1
Comparison of roughness evolution with thermal
Temperature (1C) Ra (nm)
620 125.14
630 57.14
640 39.45
650 29.40
660 16.43
670 7.35
D. Nieto et al. / Optics and Lasers in Engineering 63 (2014) 111816
the laser direct-write technique for fabricating the promoting
glass structures and a thermal treatment for reshaping and/or
improving the morphological qualities of the generated micro-
channels. The obtained microchannels have a minimum dia-
meter of 8 mmanddepthof1.5mm. A decrease of the roughness
average generated after laser ablation, of two orders of magni-
tude reaching values of the order of the unprocessed glass, has
been obtained thanks to the thermal treatment applied. The
main advantage of using pulsed nanoseconds lasers for the laser
direct write, includes the benets of using lasers commonly
implemented for laser processing of materials applications,
which makes the technique presented in this work highly
competitive compared to other techniques commonly used on
glass microstructuring.
This work has been supported by the Consellería de Cultura,
Xunta de Galicia/FEDER, under the Contract EM2012/019.
[1] Erickson D, Li D. Integrated microuidic devices. Anal Chim Acta
[2] Cheng Y, Sugioka K, Midorikawa K. Microuidic laser embedded in glass by
three-dimensional femtosecond laser microprocessing. Opt Lett 2004;29:
[3] Cattaneo F, Baldwin K, Yang S, Krupenkine T, Ramachandran S, Rogers JA.
Digitally tunable microuidic optical ber devices. J Microelectromech Syst
Fig. 11. Intersection of two microchannels obtained with different values of limit (a) 20 0, (b) 100, and (c) 50. At the bottom enlarged views of theses intersections are shown.
The laser parameters used were: power 8 W, rep. rate 10 kHz and scan speed 100 mm/s.
Fig. 12. Confocal image of some complex structures created on glass.
D. Nieto et al. / Optics and Lasers in Engineering 63 (2014) 1118 17
[4] Whitesides GM. The origins and the future of microuidics. Nature
[5] Rajabi T, Huck V, Ahrens R, Apfel MC, Kim SE, Schneider SW, et al. Develop-
ment of a novel two-channel microuidic system for biomedical applications
in cancer research. Biomed Tech 2012;57:9212.
[6] Huang CW, Lee GB. A microuidic system for automatic cell culture. J
Micromech Microeng 2007;17:1266.
[7] Andersson H, Van Den Berg A. Microfabrication and microuidics for tissue
engineering: state of the art and future opportunities. Lab Chip 2004;4:98103.
[8] Li Y, Qu S, Guo Z. Fabrication of microuidic devices in silica glass by water-
assisted ablation with femtosecond laser pulses. J Micromech Microeng
[9] Cheng JY, Yen MH, Wei CW, Chuang YC, Young TH. Crack-free direct-writing on
glass using a low-power UV laser in the manufacture of a microuidic chip.
J Micromech Microeng 2005;15:1147.
[10] Becker H, Heim U. Hot embossing as a method for the fabrication of polymer
high aspect ratio structures. Sens Actuator 2000;83:1305.
[11] Martin KD. Etching mechanism of vitreous silico dioxide in HF-based solu-
tions. J Am Chem Soc 2000;122:434551 .
[12] Clerc PA, Dellmann L, Gretillat F, Gretillat MA, Inderm PF, Jeanneret S, et al.
Advanced deep reactive ion etching: a versatile tool for microelectromecha-
nical systems. J Micromech Microeng 1998;8:2728.
[13] Kopitkovas G, Lippert T, Venturini J, David C, Wokaun A. Laser induced
backside wet etching: mechanisms and fabrication of micro-optical elements.
J Phys:Conf Ser 2007;59:52653.
[14] Wakaki M, Komachi Y, Kanai G. Microlenses and microlens arrays formed on a
glass plate by use of a CO
laser. Appl Opt 1998;37:62731.
[15] Sohn IK, Lee MS, Woo JS, Lee SM, Chung JY. Fabrication of photonic devices
directly written within glass using a femtosecond laser. Opt Express
[16] Marcinkevičius A, Juodkazis S, Watanabe M, Miwa M, Matsuo S, Misawa, et al.
Femtosecond laser-assisted three-dimensional microfabrication in silica. Opt
Lett 2001;26:2779.
[17] Wang ZK, Zheng HYR, Lim YH, Wang ZF, Lam YC. Improving surface smooth-
ness of laser-fabricated microchannels for microuidic application. J Micro-
mech Microeng 2011;21:095008.
[18] Kasaai MR, Kacham V, Theberge F, Chin SL. The interaction of femtosecond and
nanosecond laser pulses with the surface of glass. J Non-Cryst Solids
[19] Giridhar MS, Seong K, lzgen AS, Khulbe P, Peyghambarian N, Mansuripur M.
Femtosecond pulsed laser micromachining of glass substrates with application
to microuidic devices. Appl Opt 2004;43:45849.
[20] Lin CH, Lee GH, Lin YH, Chang GL. A fast prototyping process for fabrication of
microuidic systems on soda-lime glass. J Micromech Microeng 2001;11:
D. Nieto et al. / Optics and Lasers in Engineering 63 (2014) 111818
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... Further, the α fibre is only observed on the SS304L side. (4) For the nano-indentation, the hardness and modulus of copper, SS304L and bonding interface increase with the increase of rolling reduction, and it can be revealed that the dislocation will be piled up at the interfaces of copper side during deformation. For the micro hardness, the hardness of copper and SS304L increases when rolling reduction increases, due to the strain-hardening effect for copper, and accumulated dislocation and phase transformation for SS304L during the rolling, respectively. ...
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Laser machining has become a prominent tool for macro as well as micro-manufacturing because of their increasing demand in industries such as electronics , aerospace, turbine, automobile, etc. Among various laser-based machining processes, laser drilling has gained importance due to requirements of precise and high aspect ratio holes. Apart from machining capabilities , the quality of microholes in terms of shape, size and tolerance matters to a great extent. So in this paper we investigate the dimensional accuracy and quality in terms of the circularity of microholes of 100 µm diameter drilled in Cu sheet using a Nd:YAG laser. The microholes were analysed to evaluate the geometrical profile and the measured data were examined to obtain their quality characteristics. The standard deviation was 2.98 µm having a mean error of 21.75 µm. Ferret's diameter analysis revealed that the average circu-larity of the microholes was 0.95. A recast layer was observed which was generated due to resolidification of melt onto the walls of holes.
... Depending on the applications of micro channel-based devices, different types of materials are preferred. Basically, micro channels are created on polymeric, glass, silicon as well as on metallic substrates [10][11][12][13][14][15]. Among them, metallic substrates are widely used for electronics and mechanical engineering-related applications. ...
Fabrication of micro channels is an important aspect in the development of microfluidic devices, such as microreactors, micro heat exchangers, micro heat sinks and fuel cell bipolar plates. An ultra-thin metal foil rolling for the fabrication of micro composite channels was first proposed in this study, which is able to improve product function and reduce operational cost. Copper/SS304L composite foils with the thickness of 0.3 mm for copper and 0.1 mm for SS304L after annealing at 900 • C were used to form micro channels under different rolling reductions (0.10-0.25 mm) and velocities (7.07-35.35 mm/s), and the processing characteristics, material deformation behaviours and processing mechanisms of the rolling process were investigated. The results show that the ridges and channels are asymmetrical in all samples, while the ridges become more round with the increase of rolling reduction and the decrease of rolling velocity. For the samples with different rolling reductions , the difference between set rolling reductions and the forming depth first decreases and then increases. Besides, the micro features, including micro scratches, adhesion and smooth surfaces on the surfaces of micro channels become more significant with the increase of rolling reduction, and thus the roughness increase with increased rolling reduction. For the samples with different rolling velocities, a lower velocity would be conducive to fabricating the micro channels with a higher forming accuracy. As the rolling velocity increases, the micro scratches, adhesion and smooth surfaces on the surfaces of micro channels can be reduced during rolling process.
... The motivations behind choosing soda-lime glass as the alternate substrate are its cost-effectiveness and broad applicability in microfluidic and other MEMS devices. Soda-lime glass substrates are also widely implemented as they provide advantages over other materials in terms of high electrical insulation, surface stability, high resistance to mechanical stress, and compatibility with a wide range of microfabrication techniques [23][24][25]. We also report for the first-time data for the moving MCL of an evaporating water droplet to demonstrate this approach's functionality at elevated temperatures and during a dynamic and realistic heat transfer process. ...
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Knowledge of the location and speed of a moving multiphase contact line provides significant and valuable insight into the fundamental physics behind condensation- and evaporation- based processes such as occur in high heat flux thermal management solutions. From an application perspective, this information can be leveraged to ascertain and enhance device design and performance of phase change-based cooling processes. In this work, we present a capacitance-based phase interface sensing approach capable of measuring the location and speed of a moving multi-phase interface at the microscale, evaluate the impact of substrate material on its performance, and demonstrate its ability to function at elevated temperatures during water droplet evaporation. The sensing is accomplished via an array of planar interdigitated electrodes upon either a doped semiconductor or dielectric substrate. Measuring capacitance changes with time facilitates sensing of the contact line as it passes over each electrode pair. This capacitive sensing scheme is noninvasive to the system under study, allowing its implementation into many types of existing hardware and devices and does not require optical access to the phase change area of the device. Results for unconstrained water droplets are presented, and it is shown that the choice of substrate material has a marked impact on sensing behavior in terms of sensor coupling. Finally, data for the moving multiphase contact line of an evaporating water droplet is presented to demonstrate functionality at elevated temperatures and during a dynamic heat transfer process.
... The performance of a fluidic device strongly depends on the surface characteristics of the channel, therefore the ability to modify the surface is a crucial factor to optimize the overall device operation. As surface roughness can be modified in a controlled manner by post-thermal treatments [35], some of the samples have been further subjected to a heat treatment to evaluate the influence on the roughness. In addition, a comparison between channels fabricated by LIPAA and SLIPAA is also presented and analyzed. ...
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Subaquatic indirect Laser-Induced Plasma-Assisted Ablation (SLIPAA) is proposed as a laser-based technique for glass processing. In this configuration, a water layer is added between a metallic target and a soda-lime glass substrate, so the processing of the glass is due to a combination of the ablation mechanism, the shock waves, and the cavitation bubbles. Thus, this method makes it possible to produce higher depth structures than those performed up to now by other standard laser techniques based on ablation, achieving structures in glass with rectangular cross-sectional profiles. Channels of 1 mm width are fabricated, reaching an average maximal depth value of almost 1400 µm at 30 passes of the laser beam while keeping the focal position fixed. Furthermore, the difference between processing the material with and without the addition of the water layer is presented. The influence of the processing parameters on the shape and quality of the fabricated structures is studied by optical and confocal microscopy, microcomputed tomography, and scanning electron microscopy. Compositional analysis of the glass is performed by energy dispersive X-ray technique to assess the transference of material from the metallic target to the fabricated channels. Deeper and more complex structures are obtained by refocusing the laser beam on the target and adding a pulsed flowing water film.
... This is mainly because the overlap rate of the laser pulse is higher at low-speed scanning. Consequently, it is easier to produce ablation splash during processing (Nieto et al., 2014). However, the processing method with high scanning speed and multiple scanning times can easily cause slag deposition at the bottom of the microchannel due to the failure in the timely discharge of ablation splashes generated in the microchannel (Hedieh, 2018). ...
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Femtosecond laser processing is widely used in the micromachining of hard and brittle materials. Preparation of tapered microchannels with customizable cross-sections in silica glass using ultrafast lasers is of great significance in the field of microfluidic applications. In this paper, the width and depth of tapered microchannel in silica glass are predicted by combining theoretical modeling and machine learning. The functional relationship between laser processing parameters and microchannel width is obtained by theoretical modeling and introducing correction coefficients. The estimated model width is highly consistent with the experimental results. To solve the complex nonlinear mapping relationship between microchannel depth and processing parameters, a machine learning method based on a backpropagation neural network algorithm is proposed. By reasonably selecting model parameters, accurate prediction of microchannel depth is achieved with the corresponding average relative prediction error of 5.174%. Based on the proposed method, an effective parameter optimization strategy for achieving microchannels of specific sizes is developed. This method provides a new scheme for size prediction and controllable fabrication of silica glass microchannels with a femtosecond laser. Moreover, the proposed approach significantly reduces the time and cost of trial and error during actual processing and product development.
Hot embossing is an efficient technology for the fabrication of glass micro- and nanostructures. However, the long cycle time, high energy consumption, and high nitrogen emissions in traditional hot embossing approach hinders sustainable production of glass micro-optics. Therefore, this paper proposes a novel two-stage gravity-assisted hot embossing process that enables the fabrication of high-quality glass micro-pillar arrays in a rapid, green manner. In this approach, the two-stage gravity loading unit provides accurate force on glass preform through a simple control system, and the tailor-made heating module based on Si3N4 ceramic heaters requires an energy consumption of just 700 kJ per molding cycle. As a result, the proposed approach is featured by low energy consumption and high manufacturing efficiency. In this study, the effects of the embossing temperature, force, and time on the replication accuracy of a K9 glass micro-pillar array were investigated through a series of hot embossing experiments. Afterward, the form accuracy, uniformity of microstructures, and warpage of glass replicas under the optimal process parameters were evaluated separately. Finally, repeated hot embossing experiments were conducted to demonstrate the reproducibility of the hot embossing process. The experimental results show that embossing temperature had the most significant effect on the replication accuracy of glass micro-pillars. By optimizing the process parameters, the embossed glass micro-pillars could achieve transfer ratios of 99.00% and 95.14% in height and diameter, respectively. Moreover, the surface roughness of glass micro-pillars was less than 5 nm, and the warpage amplitude of glass replicas in a 3.9 × 3.9 mm area was smaller than 1 μm. The small discrepancy in geometric features of glass replica in the repeated trails reflects the satisfactory reproducibility of this hot embossing process on the micro and nano scales. The results indicate the strong industrialization potential of the proposed two-stage gravity-assisted hot embossing machine and hot embossing process for fabricating high-quality glass microstructures more cleanly and sustainably.
An overview of the significance of microchannels and transparent materials in many scientific and industrial applications is given in this chapter. The importance of laser machining of transparent materials is also presented, followed by a comprehensive discussion on laser-induced plasma-assisted ablation (LIPAA) process in terms of its types, laser process parameters and workpiece materials. The current study also presents the effective fabrication of microchannels on polycarbonate (PC) by LIPAA using a conventional millisecond Nd: YAG laser and copper as the target metal.KeywordsLaserTransparent materialLIPAAPolycarbonateMicrochannel
The high transmission of transparent polycarbonate (PC) over a range of wavelengths makes laser processing of such materials a challenging task. It is thus highly appreciated to apply an appropriate technique to process transparent materials, which can be successfully achieved by the novel technique of LIPAA. LIPAA is a high-potential machining technique that overcomes the challenge of machining transparent materials regardless of their high transparency in the visible and near-infrared spectral ranges. This paper demonstrates the successful simulation of micromachining of the transparent PC sheet. Further, the model developed has a realistic approach by simulating simultaneous ablation of both transparent PC and metal target. Extreme numerical simulations were performed by varying the laser process parameters, viz. pulse repetition rate, pulse duration and pulse power density, keeping the scanning speed at a fixed value of 4 mm/s. The width and the depth of the microchannel for each set of parameters were determined and were validated with the experimental results. The simulated solutions were found to be in sound agreement with the experimental results. Subsequently, the influence of the laser parameters on the geometric parameters was studied.
Among various detection and analysis platforms, a microfluidic chip-based electrochemical sensing detection platform is a new type of detection platform. In this study, a microfluidic electrochemical detection platform for cadmium ion detection is proposed, and the performance of the detection platform is optimized in terms of both the microchannel size and electrode modifications. The detection mixing processes of the detector with different microchannel sizes, including the concentration distribution in the channel, pressure decay variation and electrolyte current density variation in the detector, were investigated by finite element model calculations. The analysis shows that the size of the microchannel in the detector affects the fluid and thus further affects the chemical reaction. If the size of the electrode does not match the size of the microchannel, insufficient sample volume will lead to inaccurate measurements, reduced sensitivity and increased detection limits. It was found that the sensitivity of the electrochemical sensor was highest when the size of the microchannel in the chip was 400 μm. After optimization, the optimal detection limit for cadmium ions was 0.03 μg L-1 (S/N = 3). The proposed sensing platform is simple in design and stable in structure, and is suitable for field screening and rapid response to heavy metal contamination events.
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A reaction mechanism for the etching of silicon nitride layers in aqueous hydrofluoric acid solutions is proposed. The surface of Si3N4 consists of SiNH2 groups that are etched from the solid matrix via three possible routes. Depending on the pH, these SiNH2 groups are protonated (pKa = 1.4) to SiNH3+. At <pH 4, the rate-limiting step consists of an elimination of NH3 and a subsequent addition of F- or HF to the vacant surface site to form Si-F. At >pH 3, the elimination of NH2- is assisted by HF2-, followed by a transfer of one of the fluorides of HF2- to the vacant site. All subsequent reaction steps to remove the SiF unit are nucleophilic substitution reactions with low activation energies. The etch rates and mechanism of different types of silicon nitride films are compared with that of SiO2 etching. Therefore, etch selectivity between these two materials can be explained. The theory is also applicable for silicon hydrogen passivation.
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Advanced deep reactive ion etching (ADRIE) is a new tool for the fabrication of bulk micromachined devices. Different sensors and actuators which use ADRIE alone or combined with other technologies such as surface micromachining of silicon are presented here. These examples demonstrate the potential and the design freedom of this tool, allowing a large number of different shapes to be patterned and new smart devices to be realized.
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This paper describes a fast, low-cost but reliable process for the fabrication of microfluidic systems on soda-lime glass substrates. Instead of using an expensive metal or polisilicon/nitride layer as an etch mask, a thin layer of AZ 4620 positive photoresist (PR) is used for buffered oxide etching (BOE) of soda-lime glass. A novel two-step baking process prolongs the survival time of the PR mask in the etchant, which avoids serious peeling problems of the PR. A new process to remove precipitated particles generated during the etching process is also reported in which the glass substrate is dipped into a 1 M hydrochloride solution. A microfluidic channel with a depth of 35.95±0.39 µm is formed after 40 min BOE in an ultrasonic bath. The resulting channel has a smooth profile with a surface roughness of less than 45.95±7.96 Å. Glass chips with microfluidic channels are then bonded at 580 °C for 20 min to seal the channel while a slight pressure is applied. A new bonding process has been developed such that the whole process can be finished within 10 h. To our knowledge, this is the shortest processing time that has ever been reported. In the present study, an innovative microfluidic device, a `micro flow-through sampling chip', has been demonstrated using the fabrication method. Successful sampling and separation of Cy5-labelled bovine serum albumin (BSA) and anti-BSA has been achieved. This simple fabrication process is suitable for fast prototyping and mass production of microfluidic systems.
Conference Paper
This study presents a new chip capable of automating the cell culture process by using microfluidic technology. This microfluidic cell culture system comprising of microheaters, a micro temperature sensor, micropumps, microvalves, microchannels, a cell culture area and several reservoirs was fabricated by using micro-electro-mechanical-systems (MEMS) fabrication processes. Manual cell culture processes can be performed on this chip without using incubators. A typical cell culturing process for human lung cancer cells (A549) was successfully performed to demonstrate the capability of the developed microfluidic system. This automatic cell culturing system can be eventually integrated with subsequent microfluidic modules for cell purification, collection, counting and lysis to form a cell-based micro-total-analysis-system.
Polymer microfabrication methods are becoming increasingly important as low-cost alternatives to the silicon or glass-based MEMS technologies. We present in this paper the technology of hot embossing as a flexible, low-cost microfabrication method for polymer microstructures, which uses the replication of a micromachined embossing master to generate microstructures on a polymer substrate. With this fabrication technology high aspect ratio structures can be fabricated over large surface areas, which allows a commercially successful manufacturing of polymer microcomponents.
The interaction of femtosecond and nanosecond laser pulses with the surface of glass was compared. The glass was placed inside a vacuum chamber. The laser pulses were focused on the glass surface. The morphology of irradiated glass surfaces and of the materials ejected from the surfaces was examined by scanning electron and optical microscopy. During femtosecond laser irradiation, molten material was ejected from the interaction zone on the glass surface. Nanosecond laser pulses (15 mJ/pulse) induced cracks on the surface of glass, whereas the laser with an energy of 8 mJ/pulse removed a thin layer from the surface through the sputtering process. In the former case, pieces of glass were ejected from the interaction zone, whereas spherical fine powder was produced in the latter case. The femtosecond laser can significantly localize the damage zone. Interference fringes similar to liquid waves were generated on the surface. This indicates that the glass was melted locally by the femtosecond laser irradiation. Shock waves generated by the nanosecond laser (15 mJ/pulse) caused cracks in the glass. The femtosecond laser has advantages over the nanosecond laser due to the creation of a smaller and more precise hole with lower pulse energy and/or a lower repetition rate.
We have fabricated a microdiverter with a protrusion and a complicated micromixer with grid-like structures in silica glass by using water-assisted femtosecond laser ablation. When distilled water is introduced into the fabricated microchannel, the blocking and redepositing effects of ablated debris can be reduced greatly. The total length of the fabricated microfluidic devices is 6 mm without any deformation. The diameters of the fabricated microchannels can be controlled by changing the used pulse energies and the width of the laser-scanning region inside the sample. The experimental results show that it is possible to fabricate high-quality and high-aspect-ratio complicated microfluidic devices in single step without the need of using photosensitive glass or post-processing.
Inexpensive and flexible CO2 laser rapid prototyping of polymer microfluidics is facing challenges due to the rough microchannel surface typically with a roughness Ra in the µm range produced directly through laser ablation. In this study, a wet chemical etching technique was developed and used successfully to carry out smoothing of microchannel surfaces fabricated on a polymethyl methacrylate substrate using CO2 laser direct writing. The microchannel surface roughness of a few µm was significantly reduced through etching in acetone diluted with ethanol in an ultrasonic bath in a short time cycle. The surface roughness Ra of below 10 nm could be achieved through etching in the heated etchant solution while without noted deformation in a microchannel structure. The mechanism to reduce surface roughness by the tunable solubility of a polymer in a liquid through concentration and temperature control is discussed with respect to the effect of the etching parameters: acetone concentration, etching time and the temperature of the etching solution. The results would be attractive for microfluidic chip applications when using laser prototyping.