NIRT: Chemically Directed Surface Alignment and Wiring of Self-Assembled Nanoelectrical Circuits, CBET0708347
J. Liu‡, K. A. Nelson‡, E. Bird‡, J. Ashton‡, B. Mangold‡, E. Nelsen‡, H. Conley§, T. Pearson§, B. Davis§, D. Jones§, R. Ochoa§, F. Rivera§,
E. Pound†, Y. Geng†, B. Cragun†, T. Wickard†, R. C. Davis§, A. T. Woolley†, M. R. Linford†, D. R. Wheeler‡, and J. N. Harb‡
of Chemical Engineering, § Department of Physics and Astronomy, † Department of Chemistry and Biochemistry,
Brigham Young University, Provo, Utah 84602
Abstract
High-resolution chemical surface patterning
This poster describes nanofabrication efforts underway at BYU by an interdisciplinary research
group, ASCENT (ASsembled nanoCircuit Elements by Nucleic acid Templating) under NIRT
funding (2007). This group seeks to combine the complementary advantages of bottom-up selfassembly with top-down patterning, with the goal of providing a process for fabrication of
nanoelectronic circuits. Efforts are focused on the development and refinement of four key
technologies: (1) solution-phase assembly of structures and templates, (2) high-resolution
chemical surface patterning, (3) high-precision metallization of molecular templates, and
(4) chemically directed assembly and integration of nanostructures on surfaces. Molecular circuits
are self-assembled in solution using customized DNA templates (“test-tube circuits”). DNA selfassembly is particularly powerful because of the large number of possible nucleic-acid sequences
that enable highly selective bonding of DNA strands to each other and to other molecules.
Chemical patterning will provide anchor points to attach and align the molecular circuits on the
surface, as well as provide a means for local wiring to the anchored circuit, all with a resolution <
10 nm. Several patterning methods are being explored including polymer nanografting,
chemomechanical patterning and self assembled layers. Metallization of both the exposed DNA
and chemically templated lines is used to electrically connect active circuit elements to each other
and to the larger-scale architecture. The net result will be DNA-templated molecular circuits that
have been aligned and wired locally on an oxide surface. Interconnect technology similar to that
used currently in the semiconductor industry can then be applied to create the larger global wiring
needed for practical devices based on the molecular circuits under development.
Metallization
• Highly-selective metallization on DNA templates
• Continuous deposition for metallization of interconnects between
circuit elements
Nanografting
1)
2)
3)
4)
5)
Enables creation of direct, strong attachment to surfaces
Able to pattern in a liquid environment
Flexible for use with a range of surfaces and surface chemistries
Low cost
< 20 nm features
Silane
Glass
Poly-L-lysine
Electroless plating
Vapor phase deposition
CY3-tagged Poly-L-lysine
Scribing away
Poly-L-Lysine
with AFM tip
Replacing holes with
fluorescently tagged
Poly-L-Lysine
•
•
Selective metallization of DNA with Ag
(process modified from Yan et al., 2003)
•
Overview
Selective Ni deposition on DNA templates via
vapor phase deposition of Ni(acac)2
50min-Ni(acac)2 equilibration at 180 ºC,
followed by 5min wafer exposure at 180 ºC
Height of particles deposited on DNA: 10nm
•
Height of metallized DNA:14nm
•
Tasks
1.3K
MPS
COUNTS
• Molecular circuit assembly
• High-resolution chemical surface patterning
• Chemically directed assembly and
integration of MC’s on surfaces
• High-selectivity, high-precision metallization
1.2K
1.1K
1K
900
COUNTS
800
200
195
190
185
180
175
170
165
160
155
150
145
140
135
130
125
120
115
110
105
100
700
PDS
348
347
346
345
344
343
342
341
COUNTS
‡ Department
340
339
338
337
BINDING ENERGY - EV
600
500
Pd
peaks
400
300
200
100
950
8.5K
900
850
800
750
700
650
600
550 500
450 400
BINDING ENERGY - EV
350
300
250
200
150
100
50
0
Pd
peaks
7.5K
7K
6.5K
6K
COUNTS
COUNTS
5.5K
5K
4.5K
4K
3.5K
A
3K
B
2.5K
2K
1.5K
1K
500
950
Solution based
assembly
molecular
Chemical
surface
patterning
including
local wiring template
circuit
MC
AFM (top) shows holes after
scribing and optical
fluorescence (bottom) verifies
chemical functionality after
grafting
AFM of patterned lines and
spaces with 12 nm half pitch
created by scribing with a ~50 nm
radius tip.
D
C
MC
Molecular Circuits
50 nm
1)
2)
Contact hole for
global wiring
Chemically directed
assembly
•
Micelle Self Assembly
Local Wiring
Rapid, high resolution patterning
Can be combined with other
patterning techniques for precise
positioning and functionalization
of gold particles
< 10 nm features
surface
Metallization of wiring templates
3)
•
•
•
•
•
•
•
•
•
•
Poly(styrene-b- 2-vinylpyridine)
block copolymer forms micelles in
toluene
Gold salts enter micelle center
Micelles deposited on silicon oxide
surface
Oxygen plasma etching leaving
gold pattern on surface
Gold particle diameter: 10-15nm
Spacing: 60-70nm
(process modified from Möller et al., 2000)
Molecular circuit assembly
Source Drain Current on a bundle of
(7,6) carbon nanotubes
Designing DNA origami rectangular motif
1). Build a model
Source Drain current on a (7,6) nanotube bundle
One turn is ~3.6 nm.
2). Fold DNA scaffold strand through model
1 10
-6
5 10
-7
Current (Amps)
DNA is ~ 2 nm wide.
There is ~1 nm
between strands.
1.5 10
-6
Scaffold
strand
0
-5 10
-7
-1 10
-6
-1.5 10
-6
-1
Origami from bead-separated scaffold
3). Design complementary staple strands that cross every 1.5
turns
-0.5
0
0.5
1
1.5
2
VSD
Chemically directed assembly
and integration of MCs
A high yield of individual properly aligned
MCs at each site is desired. The assembly
can be tuned using several molecular
parameters including molecule flexibility,
ligand length, induced steric constraints,
and partial attachment binding affinity
differences. Temperature cycling, selective
ligation, and the use of multiple attach/rinse
cycles will be explored to achieve the
desired yield.
Silicon dioxide surface modified with APTES
PSS put on APTES layer
Lines created by AFM tip scribing
Lines then seeded with Pd
Electroless plating with copper
1.
2.
3.
4.
5.
e'
9.
DNA-templated PMOS circuit
Rectangle size: approx. 11 by 65 nm
Carbon nanotubes placed between
electrodes by dielectrophoresis
f'
750
700
650
600
550 500
450 400
BINDING ENERGY - EV
350
300
250
200
150
100
50
0
340
330
320
310
300
290
280
270
260
250
240
230
220
210
200
190
180
170
160
150
140
333
900
332
331
850
330
800
329
750
700
650
600
550 500
450 400
BINDING ENERGY - EV
350
300
250
200
150
100
50
0
330
329
SA
Pd
peaks
348
347
346
345
344
343
342
341
340
339
338
337
BINDING ENERGY - EV
336
335
334
333
332
331
Application of additives in electroless Pd plating to
enhance continuity and selectivity
XPS results show additives facilitate Pd plating
Sulfanilic acid showing best results
References
8.
g'
800
334
• Education of graduate students in a truly
multidisciplinary environment.
• Education of undergraduate students in a positive
mentoring environment.
• Involvement of local minority students in an outreach
program focused on science and engineering.
• Development of a method for producing wiring and
metallization at a density unmatched by any present
or near-future process.
• Development, demonstration and dissemination of
novel and transferable processes and enabling tools
for nanotechnology.
6.
7.
h'
•
•
850
335
Broader Impacts Summary
Staple
strands
A program was developed to minimize the crossover strain and
determine the DNA sequence needed for each of the staple strands
•
900
PDS
950
SA
8K
4.2K
4K
3.8K
3.6K
3.4K
3.2K
3K
2.8K
2.6K
2.4K
336
2.2K
2K
1.8K
1.6K
1.4K
1.2K
1K
800
600
400
200
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