BE14CH06-Rogers ARI 9 April 2012 13:38
1 mm
100 μm
50 μm
70 μm
300 μm
100 μm
(111) silicon
Bottom silicon
Top silicon
a
Retrieve
Transfer: contact and release
c
5 mm
d b
0.10%
0.08%
0.06%
0.04%
0.02%
0
Tr
n
f
r
n
n
r
l
Anchors
Adhesives
Nano-
membranes
Strain
Figure 1
Materials, processing approaches, and layouts that yield stretchable forms of inorganic semiconductors such as silicon and gallium
arsenide. (a) Nanomembranes of these materials, produced from high-quality, single-crystal wafers using lithographic patterning and
etching. (Top) A set of flexible nanomembranes/ribbons (NMs) made of (111) silicon created by anisotropic undercut etching of a
silicon wafer. (Middle) (100) silicon NMs released from a silicon-on-insulator wafer by removal of the buried oxide. (Bottom) A large
collection of GaAs NMs prepared from epitaxial, multilayer stacks of GaAs/AlAs. Selectively etching the sacrificial AlAs layers releases
GaAs NMs. Reproduced with permission from Reference 40. Copyright Nature Publishing Group. (b) Schematic of the process for
transfer printing collections of NMs from their released forms on a source wafer to a target surface. (c) Automatic transfer printing tool.
Inset shows a collection of GaAs NMs printed onto a flexible sheet of polyethylene terephthalate. (d ) Scanning electron microscope
images and (insets) corresponding finite element modeling results for semiconductor NMs bonded to prestrained elastomeric substrates
in three different configurations. Upon releasing the prestrain, controlled buckling processes in the NMs lead to different layouts: (top)
two-dimensional herringbone “wavy” patterns (reproduced with permission from Reference 37, copyright American Chemical Society)
and noncoplanar bridge structures with (middle) straight and (bottom) serpentine (reproduced with permission from Reference 22,
copyright National Academy of Sciences) interconnects. In all cases, strains in the silicon structures themselves are less than ∼0.1%,
even when strains of the overall system exceed 100% in certain configurations.
wafer but tethered at strategic points (i.e., anchors), simply by the action of generalized adhesion
forces to the PDMS, typically dominated by van der Waals interactions (27, 45) (Figure 1b, top).
This transfer can be performed over large areas of uniform or segmented NMs using flat stamps
(27) or over selected areas using structured stamps (46) (Figure 1b, top). The retrieved collections
of NMs (i.e., solid “inks” in this procedure) are selectively delivered to target substrate surfaces,
at predefined locations with microscale precision (Figure 1b, bottom), by printing (39, 47). A
variety of approaches allow the switching in adhesion needed for efficient operation; these range
from rate-dependent viscoelastic effects (27, 48), to biomimetic strategies (45), to use of interfacial
bonding layers (49). Printing with automated tools that include high-resolution cameras for
overlay registration and multidimensional stages for positional control enables submicron scale
116 Kim et al.
Changes may still occur before final publication online and in print
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