nano 2007-01-22 07:11
Microfabrication of self-assembling elements for 3D negative-index materials
[size=3][color=DarkGreen]M. Saif Islam and V. J. Logeeswaran
bi [9j%`}
g f1C!I-qv
[b]A planar microfabrication process creates arrays of self-assembling nonplanar elements suitable for three-dimensional negative-index materials (3D-NIMs).[/b]
"O K)feHC&l
e.K+pq@.F dW5oS3_)D
[img]http://newsroom.spie.org/images/Imported/515/515big.jpg[/img] QZV8t k
Z\E:~G2] L%^5}7G6\7~
Negative-index materials (NIM) are a new class of materials (metamaterials) with simultaneous negative permittivity, ε, and negative magnetic permeability, μ, as analyzed by Victor Veselago.[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B1][color=#0000ff]1[/color][/url] This unconventional electromagnetic property allows unique and exotic applications, such as new designs in airborne radar, “perfect” thin-slab lenses with sharper images than conventional diffraction limits allow,[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B2][color=#0000ff]2,3[/color][/url] higher-resolution magnetic-resonance imaging, miniature antennas, and high-power communication-signal modulation.P7f&u"R r I{'r
.|7f&t
]!by TTd
One key strategy for engineering NIMs is constructing a periodic array of composite elements. These elements comprise both resonant negative-μ; ‘particles’, which couple to the magnetic fields, and conducting negative-ε particles, which couple to the electric fields.[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B4][color=#0000ff]4–6[/color][/url]
,[)f%g t/EjM(ee
&iQ(J$H0j#T
The dimensions of the elements should be much smaller than the wavelength of interest, by a factor of 20–100, so that the incident electromagnetic radiation “sees” a homogeneous material. Microwave realizations of NIM have been successful, but at higher terahertz, IR, and visible frequencies, the required particle size decreases. Therefore, innovative structures and precision fabrication processes are a pressing need.[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B7][color=#0000ff]7[/color][/url]+P'|+s d$o*Z+T5N.B
?Y]t!n
hB U
The large elements that comprise microwave NIMs have been limited in another way as well, because the particles used generate a field in only a single direction. In principle, the electromagnetic response can be extended from one dimension to 2D or 3D by incorporating additional particles with different orientations. Published work to date centers on 1D- and 2D-NIMs, however, because they are relatively easy to make using well-known printed-circuit-board lithography-macroassembly technology[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B4][color=#0000ff]4,8–13[/color][/url] and microlithography-macroassembly techniques.[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B7][color=#0000ff]7,14,15[/color][/url]0`O jgYJ
~"T-qu_
The above-mentioned applications, however, would ideally employ 3D, homogeneous, isotropic NIMs (3D-NIMs).[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B5][color=#0000ff]5[/color][/url] As the size of individual NIM particles shrinks, however, fabrication and assembly grow more complex. Established technologies are not amenable to realizing 3D-NIM and do not support sub-millimeter (<200μm) feature sizes reliably. Coarse macro-assembly of individual NIM particles or 2D substrate-gluing methods will not be advantageous for the high-quality, low-cost 3D-NIM media that are envisioned as building blocks for many future applications.[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B6][color=#0000ff]6,16–18[/color][/url]
J n2l5j$v Q]%l7i#z
ip9| G{sX`4m]9I
Recently, true isotropic 3D-NIM implementations have been proposed theoretically by Costas Soukoulis[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B18][color=#0000ff]18[/color][/url] and He Sailing[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B19][color=#0000ff]19[/color][/url] via integrated split-ring-array-wire arrays and by George Eleftheriades[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B20][color=#0000ff]20[/color][/url] and Christophe Caloz[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B21][color=#0000ff]21[/color][/url] via transmission-line inductor-capacitor (LC) elements. To date, however, 3D microfabrication has only been demonstrated for a single unit cell of 3D-μ; by Niels Quack et. al.[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B22][color=#0000ff]22[/color][/url]1e-Y3m#D&Q?D
,F.V"aF.[
To enable 3D-NIM topology, we developed a fabrication method using a low-cost and massively parallel microfabrication and self-assembly technique.[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B23][color=#0000ff]23[/color][/url] First, an array of elements was created through planar microfabrication techniques. The construction exploits the as-deposited residual stress imbalance in a bi-layer consisting an electron-beam-evaporated chromium metal layer and a structural layer of low-stress silicon nitride deposited on a silicon substrate. The thin chromium-and-silicon-nitride bi-layer is formed as hinges, and functions as the negative-∑ material. The strain mismatch between the two layers curls the structural layer (a flap) containing the split-ring resonators (SRR) upwards. The self-assembled out-of-plane angular position depends on the thickness and materials comprising the bi-layer.
,H2m@
G.`s^
qmW+`1G`v5s
A periodic continuation of a single, rectangular unit cell consisting of SRRs and wires were then fabricated. The individual unit cells can be designed to be isotropic and arrays of the unit cells can be stacked to achieve larger 3D structures. ~-p9~ s jSuR
6csNI-no4g1_ [
This built-in stress-actuated assembly method is suitable for applications requiring a thin dielectric layer for the SRR. The SRR and other structures are created on the membrane, which then self-assembles into the nonplanar configuration required for 3D electromagnetic response. The theoretical relationship for the metal-dielectric bi-layer has been derived[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B24][color=#0000ff]24,25[/color][/url] and successfully implemented for a single-cell portable 3D power source, nanophotonics, and 3D photonic crystals.[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B26][color=#0000ff]26[/color][/url]
@
h"Q%q` w?nW(H Q2lK
$znwB*u7G4{+A*e)O!\
Since the bi-layer hinge acts as the negative-ε element and the SRR acts as the negative-ε element, the SRR metal must be judiciously chosen to have a small interaction with the dielectric layer to avoid introducing secondary beam curvature. We used gold for the SRR particle and chromium for the hinge particle. The hinge length is chosen through the beam-curvature equation[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B24][color=#0000ff]24[/color][/url] so that the angle of the flap containing the SRR results in a negative μ. The hinge size depends also on the requirement for the negative ε values.[url=http://newsroom.spie.org/x5386.xml?highlight=x525#B14][color=#0000ff]14[/color][/url] Hence the mechanical design, microfabrication design rules and electromagnetic properties must be optimized together.v T?)],i(^'T
m#z"i%z+Dn
[url=http://newsroom.spie.org/x5386.xml?highlight=x525#fig1][color=#0000ff]Figure 1[/color][/url] shows a scanning-electron micrograph of a unit cell of the fabricated SRR and hinge. The self-assembled angle is ∼25°, as shown in [url=http://newsroom.spie.org/x5386.xml?highlight=x525#fig2][color=#0000ff]Figure 2[/color][/url]. Overall, the feasibility of the configuration is supported by the array that faithfully reproduces the unit cell, shown in [url=http://newsroom.spie.org/x5386.xml?highlight=x525#fig3][color=#0000ff]Figure 3[/color][/url].*YDmF}6Kl \+G
[img]http://newsroom.spie.org/Images/Imported/515/515_fig1.jpg[/img]S S(H WK7o G~0G
[b]Figure 1.[/b] In the self-assembled element, strain within a patterned bilayer film raises coils off of the substrate in two directions, providing the three axes of electromagnet response needed for a three-dimensional negative-index material (3D-NIM).
2x@4n
` BJ
6G
s)C:Q5H
[img]http://newsroom.spie.org/Images/Imported/515/515_fig2.jpg[/img]uD5j4h d ZU
0I!T2GxS)|Q
[b]Figure 2.[/b] The angle of curvature for the self-assembled NIM unit cell is about 25.
:Qo%m6k6t2o3K q
y A`
)x6s'qE p
Ino~'X
[img]http://newsroom.spie.org/Images/Imported/515/515_fig3.jpg[/img]Re3b?)CQ^1jO
^
Q3K cB)Fa!z`j
[b]Figure 3.[/b] Standard lithography yields an array of virtually identical self-assembled nonplanar elements suitable for 3D-NIM. ]w+y m6I
X7U(j[
$Ss4|#H
A
Our preliminary results have shown that mass manufacture of 3D-NIMs is feasible using a metal-dielectric-bilayer stress-actuated self-assembly. This fabrication method is scalable from microwave (10GHz) to optical frequencies (300THz) by appropriate choice of material, thickness, and release-etching chemistry. Efforts are currently underway to develop a parallel microfabrication and self-assembly process using a thicker released holding plate (∼5 to 10 microns) with deformable hinges for the SRR and wires. Unlike the research-based approach of fabricating a single structure for characterizing the unique properties of NIMs, our mass-manufacturable process may offer opportunities for reproducible fabrication of 3D-NIM materials with frequencies from the microwave to optical domain.
!{,A Td-M5R$o
f[gu7Y V+Q2x4]
*c
ca]b7BUX4u
[i]The authors would like to thank Dr. Jay Provine (UC Davis/BSAC), Chad Johns, Chris Edgar, Dr. Ibrahim Kimukin, the staff of Northern California Nanofabrication Center (NC2) in UC Davis and the HP-OptoNIM team of UC Berkeley, UIUC, and Duke University for helpful discussions. This work was supported by UC Davis research grant and a CITRIS grant sponsored byHewlett-Packard Company.[/i] A`_i[9p M1s
.m!A[ F_f? Zd
&Yd(r4a5f3z
Wx
`3g|
HOlHd v0r$yuk
[b]Authors [/b]8t:u%jI(v%y
M. Saif Islam, V.J. Logeeswaran "W&}B8T q
Dept. of Electrical & Computer Engineering, Univ. of California
U-wX8SI6_L
Davis, CA
t,w0M3C/A.]^T
M. Saif Islam received his PhD in Electrical Engineering from the University of California-Los Angeles (UCLA) in 2001. Before joining UC Davis in 2004 as an assistant professor, Islam worked at Hewlett-Packard Laboratories, Gazillion Bits Inc. and SDL Inc./JDS Uniphase Corporation. His honors and awards include Outstanding Junior Faculty Award, NSF Faculty Early Career Development Award (CAREER 2006) and Professor of the Year 2005. In addition, Islam has been the conference co-chair for Nanosensing: Materials and Devices (Optics East 2004-5), Nanomaterial Synthesis, Interfacing and Integration for Sensing, Electronics, Photonics, and Electro-Optics (2006), Nanophotonics for Communication: Materials, Devices and Systems (2006)..Z$l6A | EA7io?
lg1l5D s#R o+b8B
[b]References [/b]A#i8}Z[
`
G_Bvk
1. V. G. Veselago, The electrodynamics of substances with simultaneously negative values of ε and μ,
6m X"e |jt,|d
Sov. Phys. Usp. 10,#R1{f G0[h K+`
pp. 509, 1968.
t!VRG)]-P
2. J. B. Pendry, Negative refraction makes a perfect lens,\8M*dr7k.L&u
Physical Review Letter 85,
6R-TR+D&A%NX
pp. 3966, 2000.b
XL'|wz1w4a
3. N. Fang, H. Lee, C. Sun, X. Zhang, Sub-diffraction-limited optical imaging with a silver superlens,
jm l)V K$G H b$R
Science 308,
]S1Y By_%n+C5Q
pp. 534, 2005.
b4OW6m7VC
4. R. A. Shelby, D. R. Smith, S. Schultz, Experimental verification of negative index of refraction,xW3MG-cM
Science 292,
Pl8MO1{3n3d
pp. 77, 2001.8H"Q'E q7wz
5. J. B. Pendry, A. J. Holden, D. J. Robbins, W. J. Stewart, Magnetism from Conductors and Enhanced Nonlinear Phenomena,2WQO"JC2d{R#|
IEEE Trans. Microwave Theory Tech. 47,
] cL)? `"Dn:V
pp. 2057, 1999. e P5o0O5W _
6. J. B. Pendry, A. J. Holden, W. J. Stewart, I. Youngs, Extremely Low Frequency Plasmons in Metallic Mesostructures,
2]?+nKh7y5}L
Physical Review Letter 76,
p;F%x,J
~
pp. 4773, 1996.
vc:S4i*L'a
7. C. Enkrich, M. Wegener, S. Linden, S. Burger, L. Zschiedrich, F. Schmidt, J. Zhou, Th. Koschny, C. M. Soukoulis, Magnetic metamaterials at telecommunication and visible frequencies,3S(}q)}T:x$B
Physical Review Letters 95, h F^%S9U a
no. 20pp. 203901, 2005. e4G$Muka4V t
8. G. V. Eleftheriades, A. K. Iyer, P. C. Kremer, Planar negative refractive index media using periodically L-C loaded transmission lines,
CT G.g,hgar
IEEE Trans. Microwave Theory Tech. 50,n |#S Q5m)I8s7tf
pp. 2702, 2002. J | Bk;C!W
9. A. Caloz, H. Okabe, T. Awai, T. Itoh, Transmission line approach of left-handed materials,
L,jo;|5Uh)a
z7}6{
RSI Digest, IEEE AP-S/URSI Internat. Symp.,c4^b YHN W w)R
San Antonio, TX, 2002. G2zB*[Ju \y
10. R. W. Ziolkowski, Design, Fabrication & Testing of Double negative metamaterials,y+~ I8?$Iy d1XB5J"t
IEEE Trans. Antennas Propagation 51,#[ K*lz"Y
G\ @4?
no. 7pp. 1516-1529, 2003.
@j kS0o8P X
11. D. R. Smith, W. J. Padilla, D. C. Vier, S. C. Nemat-Nasser, S. S. Schultz, Composite medium with simultaneously negative permeability and permittivity,
)W @C-f#Ork
Physical Review Letters 84,DB:p+|gR
pp. 4184, 2000.r"{0q!M}!Q[+_ [
12. M. Bayindir, K. Aydin, E. Ozbay, P. Markoš;, C. M. Soukoulis, Transmission properties of composite metamaterials in free space,!lh!R%X/i:e*k Q
Applied Physics Letter 81,
K Fc1IK/i
pp. 120, 2002. iqL(k1{i-j D[5|
13. C. G. Parazzoli, R. Gregor, K. Li, B. E. C. Koltenbach, M. Tanielian, Experimental Verification and Simulation of Negative Index of Refraction Using Snell's Law,
a%f*A*W9i)B"mgz
Physical Review Letter 90,
0h
d5{_8i}N
pp. 107401, 2003.
%A F/z L:s x"D~#rW
14. H. O. Moser, B. D. F. Casse, O. Wilhelmi, B. T. Saw, Terahertz Response of a Microfabricated Rod-Split-Ring-Resonator Electromagnetic Metamaterial,"z'x*[$V c;c+w:N
Physical Review Letters 94,
z6qw+W8k dB K5@
pp. 063901, 2005.*E7@b$oT {jo
15. S. Linden, C. Enkrich, M. Wegener, J. Zhou, T. Koschny, C. M. Soukoulis, Magnetic Response of Metamaterials at 100 Terahertz,
R VR ` ue4] W
Science 306,hf[5Xd'RhS!j
pp. 1351, 2004.
!Z ^`,H y;ju
Vk
16. S. A. Ramakrishna, Physics of negative refractive index materials,
2w(@X*C
p;s
Rep. Prog. Phys. 68,
GD ^ym6Q.Z
pp. 449, 2005.
)Y-{
L cU!N(]
17. N. Engheta, R. W. Ziolkowski, A Positive Future for Double-Negative Metamaterials,oEM PN4|(D
IEEE Trans. Microwave Theory Tech. 53,
-Kl)O:F;B;Z
w*b C n
no. 4pp. 1535, 2005.
,w `^.sQd%h
18. Th. Koschny, L. Zhang, C. M. Soukoulis, Isotropic Three-Dimensional Left-Handed Metamaterials,
LeQ*pJ
Physical Review B 71,diY8g'rj
pp. 121103, 2005.$x,x9{G @a \ }
19. Simovski CR, He Sailing, Frequency range and explicit expressions for negative permittivity and permeability for an isotropic medium formed by a lattice of perfectly conducting omega particles,
;H4gf.m E k
Physics Letters A 311,5[*lOF d eY4k
no. 2–3pp. 254-263, 2003. e$Mx,Z:y `
F
20. A. Grbica, G. V. Eleftheriades, An Isotropic Three-Dimensional Negative-Refractive-Index Transmission-Line Metamaterial,9^
Hg,Y+C
Journal of Applied Physics 98,;o;U)T g
PI
pp. 043106, 2005.
_3S7v1@Yw R9Z7cI
21. C. Caloz, T. Itoh,
'P'ow(? iFQ
K6~6{
Electromagnetic Metamaterials, Transmission Line Theory and Microwave Applications,
I4_A$l6}S2X cs
Wiley and IEEE Press, 2005.T7d!dMUX tEn g'fg(uI
22. N. Quack, P. Linderholm, A. Bertsch, Ph. Renaud, Towards High Frequency 3D Magnetic Resonators Exploring Microfabricated Bimorph Cantilever Structures,
/v_ |t)`_)Go
EPFL Latsis NIM Symposium,
m%g5t @ {g
2005.
k)u:N1N]*N3?4s2A
23. Hyun Jin In, W. Arora, T. Buchner, S. M. Jurga, H. I. Smith, G. Barbastathis, The Nanostructured OrigamiTM 3D Fabrication and Assembly Process for Nanomanufacturing,
Q B(F&j:A?,F
Proc. 4th IEEE Conf. on Nanotechnology,d
S {zQ Eo/g
k,S
pp. 358-360, 2004.#}va d{"\
24. VJ Logeeswaran, M. Saif Islam, Mei-Lin Chan, David A. Horsley Wu, Shih-Yuan Wang, Self-Assembled Microfabrication Technology for 3D Isotropic Negative Index Material,
4A-g_7oDJ
Proc SPIE 6373-15,
(z!P'B }~R'C-J:H"F
2006.O Bu}/V!wJ
25. G. P. Nikishkov, Curvature estimation for multilayer hinged structures with initial strains,
A)M7`u%Y[ }a
Journal of Applied Physics 94,
w fD [iT
pp. 5333-5336, 2003.
{"k t8U ny
26. P. O. Vaccaro, K. Kubota, T. Aida, Strain-driven self-positioning of micromachined structures,
3LNP4aN;s/g'm
Applied Physics Letters 78,/R'|'V&u,b i$x4H
pp. 2852-2854, 2001.;{Gn CS5i&q*t
U2w3cXn6p?q-OY
DOI: 10.1117/2.1200612.0515
7[K5P/\ H:q1EM
DOI: 10.1117/2.1200612.0515[/color][/size]