Abstract -Novel fabrication method of nanobridge array of various materials was proposed using suspended silicon nanowire array as a sacrificial template structure. Nanobridges of various materials can be simply fabricated by direct deposition with thermal evaporation on the top of prefabricated suspended silicon nanobridge arrays, which are used as a sacrificial structure. Since silicon nanowire can be easily removed by selective dry etching, nanobridge arrays of an intended material are finally obtained. In this paper, metal nanobridges of Ti/Au, around 50-200 nm in thickness and width, 5-20 μm in length were fabricated to prove the advantages of the proposed nanowire or nanobridge fabrication method. The nanobridges of Ti/Au after complete removal of sacrificial silicon nanowire template were well-established and bending of nanobridge caused by the tensile stress was observed after silicon removing. Up to 50 nm and 10 μm of silicon nanowire in diameter and length respectively was also very useful for nanowire templates

Kook-Nyung Lee

Kyounggun Lee

Min-Ho Lee

Suk-Won Jung

Woo-Kyeong Seong

CiteSeerX

Journal of Electrical Engineering & Technology Vol. 7, No. 3, pp. 396~400, 2012 
http://dx.doi.org/10.5370/JEET.2012.7.3.396 
 
396 
Fabrication of Metal Nanobridge Arrays using  
Sacrificial Silicon Nanowire  
 
 
Kook-Nyung Lee†, Kyounggun Lee*, Suk-Won Jung*, Min-Ho Lee* and Woo-Kyeong Seong*  
 
Abstract – Novel fabrication method of nanobridge array of various materials was proposed using 
suspended silicon nanowire array as a sacrificial template structure. Nanobridges of various materials 
can be simply fabricated by direct deposition with thermal evaporation on the top of prefabricated 
suspended silicon nanobridge arrays, which are used as a sacrificial structure. Since silicon nanowire 
can be easily removed by selective dry etching, nanobridge arrays of an intended material are finally 
obtained. In this paper, metal nanobridges of Ti/Au, around 50-200 nm in thickness and width, 5-20 
μm in length were fabricated to prove the advantages of the proposed nanowire or nanobridge 
fabrication method. The nanobridges of Ti/Au after complete removal of sacrificial silicon nanowire 
template were well-established and bending of nanobridge caused by the tensile stress was observed 
after silicon removing. Up to 50 nm and 10 μm of silicon nanowire in diameter and length respectively 
was also very useful for nanowire templates.   
 
Keywords: Metal nanobridge array, Suspended nanowires, Sacrificial silicon nanowires, XeF2dry 
etching, Nitride nanobridge    
 
 
 
1. Introduction 
 
Nanowires (NWs) have been researched extensively due 
to their promising electrical properties based on one-
dimensional quantum confinement effects and potential for 
nano integration. [1-3] Various kinds of technology to 
fabricate the NWs and assemble them into devices have 
been developed to realize their full potential in applications. 
[4-6] The conventional bottom-up approaches to fabricate 
NWs require complicated assembly procedures limited by 
high alignment accuracy owing to nano-scale wire size. To 
overcoming these problems, we previously proposed 
alternative approach to fabricate silicon nanowire (SiNW) 
arrays which combines top-down based micro-machining 
technology with transfer-printing of SiNWs to a device 
substrate. But the materials for NWs were limited to be 
single crystalline silicon in our previous approach. 
Recently, fabrication of metal NWs have been researched 
extensively because of its future applications such as nano-
resonator, nano-scale sensors, and field emission displays 
(FED). [7-9] Most of metal NW fabrication methods utilize 
nano template and conformal deposition of target material 
to filling on it such as a bundle of carbon-nanotube (CNT), 
anodized aluminum oxide (AAO) template, polycarbonate 
membranes, polyvinyl alcohol nanofiber and so on. Mass 
production of nanotube/nanowire shape structures are 
obtained after sacrificial template material was removed 
selectively. However, position-controlled, well-ordered, 
parallel aligned to the substrate of nanowire were hard to 
obtain, which is actually required for nanowire application 
devices such as sensors, electronics, and nano mechanical 
resonators. In this communication, we report novel method 
to fabricate well-ordered, horizontal aligned, and 
suspended metal nanobridge arrays by applying suspended 
silicon nanowire arrays for sacrificial template structure. 
Metal deposition process with evaporators was performed 
on top of the sacrificial silicon nanobridge templates. Any 
materials which can be deposited directionally to the 
nanobridge template substrate are able to be applied to this 
fabrication method. 
 
 
(b)
(d)
(a)
(c)  
Fig. 1. Fabrication process of freestanding SiNW arrays: 
(a) Si anisotropic dry etching by deep reactive ion 
etching; (b) Si anisotropic wet etching by TMAH; 
(c) Thermal oxidation for thinning nanowire; (d) 
Releasing suspended SiNW arrays by SiO2 
removing. 
†   Corresponding Author: Medical IT research center, Korea Electronics 
Technology Institute, Korea (plummyk@gmail.com) 
*  Medical IT research center, Korea Electronics Technology Institute, 
Korea 
Received: February 28, 2011; Accepted: December 8, 2011 
Kook-Nyung Lee, Kyounggun Lee, Suk-Won Jung, Min-Ho Lee and Woo-Kyeong Seong 
 
397
2. Experiment 
 
Our metal nanobridge arrays are simply fabricated by 
several steps of micromachining technology. The 
fabrication process starts with manufacturing freestanding 
SiNW arrays for a sacrificial template structure for the 
metal nanobridges. Since materials we would like to 
fabricate as a nanobridge would be deposited on top of the 
prefabricated SiNW bridge array, the inverted-triangular 
shape in cross-section of sacrificial freestanding silicon 
nanowire structure is favorable to be used for nanobridge 
templates. The fabrication process of silicon nanowire 
bridge for the template is straightforward. [10, 11]. 
Fig. 1 briefly shows the fabrication process of 
freestanding SiNW arrays which is a template for 
nanobridges of other materials. Firstly, photolithography 
and reactive-ion-etching (RIE) of silicon produce the 
silicon columns. Anisotropic wet etching of silicon 
columns using tetramethylammonium hydroxide (TMAH) 
is performed to produce hour-glass shaped silicon columns 
which are surrounded by (111) planes of silicon (Fig. 1(a), 
(b)). In order to obtain suspended silicon lines with nano 
width, the hour-glass shaped silicon columns need to be 
thermally oxidized and thinned to produce around or below 
100 nm in width or diameter of ‘nano’wire (Fig. 1(c)). 
With removal of the silicon dioxide using HF based 
solution such as buffered oxide etcher (BOE), the 
freestanding silicon nanowire bridges are finally obtained.  
Fig. 2 shows the fabrication process flow of metal 
nanobridge arrays using silicon nanowire template. 
Directional deposition of intended materials such as 
thermally evaporated metals on top of sacrificial SiNW 
array template can provide simple fabrication of metal 
nanobridge arrays. Only top side of inverted-triangular 
shape suspended silicon nanowires is deposited by target 
materials because of directional deposition of those 
materials to the SiNW arrays substrate (Fig. 2(a), (b)). The 
sacrificial SiNW arrays template is removed by isotropic 
XeF2 etching as shown in Fig. 2(c). Finally, nanobridge 
arrays of target material are obtained. In our approach to 
obtain nanobridge array of various material using 
suspended silicon nanowire template, the position, pitch, 
array density, length and width of nanobridge can be 
precisely controlled by photolithography mask. Various 
metals deposited with thermal evaporation process can be 
simply adopted to this fabrication method. 
We applied Ti/Au as nanobridge material to verify the 
proposed fabrication method. Ti was used for interlayer for 
the improvement of Au adhesion. Various width of the 
suspended silicon nanowire in range of 50 ~ 300 nm can be 
fabricated for sacrificial structure. [10] The dimension of 
Au nanobridge depends on the silicon template so that it is 
determined by the deposition thickness of metal 
evaporation and the width of sacrificial silicon nanowire. 
Fig. 3(a) and (b) show the SEM figures of fabrication 
results for the comparison of before and after Au 
evaporation on top of silicon nanowire template, 
respectively. Ti/Au was deposited around 100/600 Å in a 
thickness by thermal evaporation. Silicon nanowire around 
50 nm and 10 μm in a width and length, respectively, was 
also useful for the template. Note that the diameters (or 
width) of nanobridge gets thicker after Au deposition. We 
can see the layers boundary of deposited Ti/Au and silicon 
nanowire in the enlarged view of nanowire as shown in Fig. 
3(c). Besides, we can make sure that there are tensile stress 
caused by deposited Ti/Au layer on top of silicon 
nanobridge from the crack occurred at the both ends of 
silicon nanowire bridges as shown in Fig. 3(d), which is 
the result of that deposited Ti/Au thickness is around 
800/1200 Å. Regardless of the stress caused by Ti/Au layer, 
Ti/Au nanobridges were well fabricated just by controlling 
the deposition thickness of Ti/Au.      
Fig. 4 shows the SEM figures of the fabrication results 
of Au nanobridge after complete removal of silicon 
nanowire template. Silicon was removed in 3000 mTorr 
pressure of pure XeF2 chamber for 30 sec just after Au 
nanowire deposition. We can make sure that silicon was 
removed completely through the comparison of Fig. 3(d) 
and Fig. 4(a), which are the same specimen. In Fig. 4(b) 
and (c) Ti/Au nanobridges were well obtained by complete 
and excessive removal of silicon by XeF2 dry etching. 
Silicon under the deposited Ti/Au layer was removed by 
enough etching of silicon and observed clearly through the 
dark-colored cavity especially near the posts at the ends of 
nanobridges. Silicon sacrificial nanowire was 200 nm and 
20 μm in a diameter and length respectively. The 
deposition thickness of Ti/Au was around 10/60 nm. 
Therefore, ribbon-like Ti/Au nanobridges, which are 200 
nm, 70 nm and 20 μm in a width, thickness and length, 
respectively, were also well-established after complete 
removal of silicon templates. Bending caused by tensile 
stress from the Ti/Au deposition on top of silicon 
nanobridge was also observed.  
Fig. 4(d) shows low-stress Si3N4 deposited silicon 
 
(a)
(b)
(c)
Au nanobridge
Fig. 2. Fabrication process of metal nanobridges using
freestanding SiNWs: (a) Pre-fabricated SiNW
arrays; (b) Evaporation or deposition of target
materials (Ti/Au in this communication) on top of
suspended SiNWs; (c) Removing sacrificial silicon
nanowire to free metal nanobridges. 
Fabrication of Metal Nanobridge Arrays using Sacrificial Silicon Nanowire  
 
398 
nanobridges in a thickness of 100 nm with a low pressure 
chemical vapor deposition (LPCVD) process. Silicon 
nanowire for template was around 200 nm and 100 μm in a 
diameter and length. Note that there is no observed severe 
bending caused by thin film deposition stress as we 
expected in this conformal deposition of Si3N4 onto the 
silicon nanobridge.  
As shown in Fig. 4(a) to (c), the freestanding Au 
nanobridges are successfully fabricated. Our fabrication 
strategy using silicon nanowire sacrificial template allows 
the Au nanobridges to be well-ordered horizontally on the 
intended position of a substrate. The fabricated Au 
nanobridge arrays are horizontally-aligned to the substrate 
and both ends of the nanobridge are connected to the posts. 
This geometry of the Ti/Au nanobridges allows easy 
electrical connecting for electrical characterizations or 
other applications. With similar structure, we have already 
showed high temperature operating micro heater which has 
Ti/Pt heat resistor deposited on the insulated suspended 
silicon filaments. [12] 
 
 
3. Conclusion 
 
In conclusion, we propose novel fabrication process for 
metal nanobridge arrays and successfully fabricate Au 
      
                (a)                                                (b) 
 
     
                (c)                                                  (d) 
Fig. 3. SEM figures of Ti/Au deposited nanobridges on top of silicon nanowires: (a) SEM figure of silicon nanowire 
template before metal deposition; silicon nanowire is around 50 nm and 10 μm in diameter and length respectively;
(b) SEM figures of nanowire bridge array after Ti/Au evaporation; Ti/Au was deposited around 100/600 Å in a 
thickness with thermal evaporation; (c) Enlarged view of Ti/Au deposited nanobridge on top of silicon nanowire 
template; boxed area in Figure (b); (d) Ti/Au/silicon nanobridge array, Ti/Au was deposited 800/1200 Å on top of 
200 nm diameter silicon nanowire; note that the crack was occurred at the both ends of silicon nanobridge as arrow 
indicated. 
 
Kook-Nyung Lee, Kyounggun Lee, Suk-Won Jung, Min-Ho Lee and Woo-Kyeong Seong 
 
399
nanobridge arrays which have 50 ~ 200 nm in width and 
around 50 nm in thickness. The suspended SiNW arrays 
are employed as a sacrificial structure like nano-template. 
Any materials which are able to be deposited 
anisotropically can be applied to this fabrication method. 
The presented fabrication method has advantages of 
precise positioning and horizontal structure. Moreover, 
benefiting from conformality of material deposition 
technologies including chemical-vapor-deposition (CVD) 
and atomic layer deposition (ALD), nano-shell structure of 
various materials with a triangular silicon core would be 
easily obtained as LPCVD Si3N4 deposition shown in Fig. 
4(d). By the presented fabrication methods, the metal 
nanobridge arrays can be applied future applications such 
as nanomechanical resonator, tools for studying mechanical 
properties of materials, which is our on-going study. 
 
Acknowledgements 
 
This work was supported by the R&D program of 
MKE/KEIT (Grant No. 10035501). 
 
References 
 
[1]  Jie Xiang, Wei Lu, Yongjie Hu, Yue Wu, Hao Yan, 
and Charles M. lieber, “Ge/Si nanowire 
      
                         (a)                                             (b) 
 
      
                         (c)                                             (d) 
Fig. 4. Fabrication results of nanobridge array of various materials: (a) Ti/Au nanobirdge after removing silicon nanowire 
template; Ti/Au nanobridge is 10 μm in length and 800/1200 Å in a width. Sacrificial silicon was around 200 nm in 
diameter; (b) Suspended Ti/Au nanobridge array after removing sacrificial silicon nanowire template, Ti/Au 
nanobridges are 20 μm, around 200 nm, and 70 nm in length, width, and thickness respectively; note that Ti/Au 
nanobirdges were bended after silicon removal by tensile stress. Black colored cavity near the posts is observed by 
the silicon template removal; (c) Enlarged view of post area to make sure the removal of silicon nanowire template;
(d) LPCVD Si3N4 nanobridge with silicon nanowire core; low stress Si3N4 was deposited 1000 A thickness in 200 
nm silicon nanowire bridge in diameter. The length of nanobridge is 100 μm and 10 μm in the figure and the inset, 
respectively. 
 
Fabrication of Metal Nanobridge Arrays using Sacrificial Silicon Nanowire  
 
400 
heterostructures as high-performance field-effect 
transistors,”Nature letters, vol. 441, pp. 489-
493,2006. 
[2]  Wei Lu and Charles M. Lieber,“Nanoelectronics from 
the bottom up,”Nature materials. vol.6, pp. 841-850, 
2007. 
[3]  Nicholas A. Melosh, Akram Boukai, Frederic Diana, 
Brian Gerardot, Antonio Badolato, Pierre M. Petroff, 
and James R. Heath, “Ultrahigh-Density Nanowire 
Lattices and Circuits, ”Science, vol. 300, pp. 112-115, 
2003. 
[4]  Chuanding Cheng, Ravi Kanth Gonela, Qun Gu, and 
Donald T. Haynie,“Self-Assembly of Metallic 
Nanowires from Aqueous Solution,”Nano letters, vol. 
5(1), pp. 175-178, 2005. 
[5]  M. Calleja, M. Tello, J. Anguita, F. Garcia, and R. 
Garcia, “Fabrication of gold nanowires on insulating 
substrates by field-induced mass transport,”Applied 
Physics Letters, vol. 79, Issue 15, pp. 2471-2473, 
2001. 
[6]  Z. L. Xiao, Catherine Y. Han, U. Welp, H. H. Wang, 
W. K. Kwok, G. A. Willing, J. M. Hiller, R. E. Cook, 
D. J. Miller, and G. W. Crabtree, “Fabrication of 
Alumina Nanotubes and Nanowires by Etching 
Porous Alumina Membranes,”Nano Letters, vol. 2 
(11), pp. 1293-1297, 2002. 
[7]  Mingwei Li, Theresa S. Mayer, James A. Sioss, 
Christine D. Keating, and Rustom B. Bhiladvala, 
“Template-Grown Metal Nanowires as Resonators: 
Performance and Characterization of Dissipative and 
Elastic Properties,” Nano letters, , 7(11), pp. 3281-
3284, 2007. 
[8]  Choong-Ki Lee, Bora Lee, jisoon Ihm, and Seungwu 
Han, “Field emission of metal nanowires studied by 
first-principles methods,”Nanotechnology, , vol. 18, 
num. 47, 2007. 
[9]  A. J. Yin, J. Li, W. Jian, A. J. Bennett, and J. M. Xu, 
“Fabrication of highly ordered metallic nanowire 
arrays by electrodeposition,”Applied Physics letters, 
vol. 79, Issue 7, pp. 1039-1041, 2001. 
[10] Kook-Nyung Lee, Suk-Won Jung, Won-Hyo Kim, 
Min-Ho Lee, Kyu-Sik Shin, and Woo-Kyeong Seong, 
“Well controlled assembly of silicon nanowires by 
nanowire transfer method,”Nanotechnology, vol. 18, 
num. 44, 2007. 
[11] Kook-Nyung Lee, Suk-Won Jung, Kyu-Sik Shin, 
Won-Hyo Kim, Min-Ho Lee, and Woo-Kyeong 
Seong, “Fabrication of suspended silicon nanowire 
arrays,”Small, vol. 4, Issue 5, pp. 642-648, 2008. 
[12] Kook-Nyung Lee, Dae-Sung Lee, Suk-Won Jung, 
Yun-Ho Jang, Yong-kweon kim and Woo-kyeong 
Seong, “A high-temperature MEMS heater using 
suspended silicon structures,”Journal of 
Micromechanics and Microengineering,vol.19, num. 
11, 2009. 
 
Kook-Nyung Lee He received Ph.D 
degree in electrical engineering from 
Seoul national university. His research 
interests are NEMS/MEMS technology 
and its biosensor application. 
 
 
 
 
 
Kyounggun Lee He received B.S and 
M.S degree in electrical engineering 
from Seoul national university. He is 
now working for Hynix. His research 
interests are Nano-technology and 
DRAM. 
 
 
 
 
Suk-Won Jung He received B.S 
degree in electronics engineering from 
university of Seoul. He is currently a 
Ph. D candidate in electrical 
engineering from Seoul national 
university. His research interests are 
medical and bio devices including 
retinal prosthetic devices and nano 
biosensors.  
 
 
Min-Ho Lee He received Ph.D degree 
in Bioengineering from Rice 
University. His research interests are 
biosensing and immunoassay. 
 
 
 
 
 
 
Woo-Kyeong Seong He received Ph. 
D degree in molecular science and 
technology from Ajouuniversity. His 
research interests are biosensor, in 
vitro diagnostics, and medical-IT 
convergence technology. 
 
 
 
 
 


Fabrication of Metal Nanobridge Arrays using Sacrificial Silicon Nanowire

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=0C52FD6869F1665EB2CA9A523C79B08D?doi=10.1.1.1054.2127&rep=rep1&type=pdf

Fabrication of Metal Nanobridge Arrays using Sacrificial Silicon Nanowire

Abstract

Similar works

Full text

Available Versions

CiteSeerX