switch therefore has also been called a synthetic synapse where memory is
represented by conduction state.
The next step in creating a ‘brain inspired’ device is the fabrication of networks of
synthetic synapses (Atomic Switches). Taking the neocortex as a biologically
inspiration, self-assembly was used to incorporate atomic switches into a dense
dendritic tangle of silver nanowires resulting in a density of ~10
8 connections/cm
2 .
In response to electrical inputs which inject energy into the network, these networks
exhibit self-organization, critical power law dynamics and spatio-temporal
non-linear outputs at a multiple electrodes. The device is called an Atomic Switch
Network (ASN) and is described in detail in the next section.
4.1 Network Fabrication
Several routes to fabricate functionally complex recurrent networks have been
experimentally explored, including: seed free networks, random seed networks,
and patterned seed networks. The seeds are small areas of deposited copper that
react in solution to generate silver wires through electroless deposition. The patterned seed networks proved the most versatile, and utilized a combination of
top-down with bottom-up fabrication, a powerful general fabrication approach
known as nanoarchitectonics. Initial approaches on implementing atomic switches
into a network topology consisted of pipetting 150 μL of an isopropanol suspension
(149.8 mg Ag/L) of monodisperse silver nanowires (120–150 nm  20–50 μm,
Aldrich) onto a substrate and allowing to air dry. These devices were then activated
using the technique described in Sect. 4.2 and non-linear IV curves were subsequently observed. However, the non-uniformity in the dispersion of nanowires
initially caused concern in the area of spatially distributed activity.
With a density controlled network in mind, electrochemistry was used to grow a
recurrent silver network via copper seeds. Following the galvanic reaction below,
network growth occurs through an electroless deposition (ELD) reaction via individual atom displacement reactions between Ag
+ and Cu
0 based on respective
electric potentials. A spontaneous ELD reaction is preferred over an electrically
induced reaction to minimize artifacts and maintain the delicate nature of the
electrochemical reactions. Here, silver atoms are oxidized while copper is reduced
during the galvanic displacement reaction.
Cu s
ð Þ þ 2 Ag
þ
aq
ð Þ ! 2 Ag s
ð Þ þ Cu
2þ
s
ð Þ ΔE ¼ À1:26 V
Using this ELD reaction, a random seed network was fabricated by pipetting a
1 mL aliquot of copper microspheres 1–10 μm (99.995% purity, Alfa-Aesar) which
was then air dried. Silver nitrate (50 mM) was pipetted (20 μL) onto the center of the
device. Following the ELD described above, silver dendritic structures
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R. Aguilera et al.
represented by conduction state.
The next step in creating a ‘brain inspired’ device is the fabrication of networks of
synthetic synapses (Atomic Switches). Taking the neocortex as a biologically
inspiration, self-assembly was used to incorporate atomic switches into a dense
dendritic tangle of silver nanowires resulting in a density of ~10
8 connections/cm
2 .
In response to electrical inputs which inject energy into the network, these networks
exhibit self-organization, critical power law dynamics and spatio-temporal
non-linear outputs at a multiple electrodes. The device is called an Atomic Switch
Network (ASN) and is described in detail in the next section.
4.1 Network Fabrication
Several routes to fabricate functionally complex recurrent networks have been
experimentally explored, including: seed free networks, random seed networks,
and patterned seed networks. The seeds are small areas of deposited copper that
react in solution to generate silver wires through electroless deposition. The patterned seed networks proved the most versatile, and utilized a combination of
top-down with bottom-up fabrication, a powerful general fabrication approach
known as nanoarchitectonics. Initial approaches on implementing atomic switches
into a network topology consisted of pipetting 150 μL of an isopropanol suspension
(149.8 mg Ag/L) of monodisperse silver nanowires (120–150 nm  20–50 μm,
Aldrich) onto a substrate and allowing to air dry. These devices were then activated
using the technique described in Sect. 4.2 and non-linear IV curves were subsequently observed. However, the non-uniformity in the dispersion of nanowires
initially caused concern in the area of spatially distributed activity.
With a density controlled network in mind, electrochemistry was used to grow a
recurrent silver network via copper seeds. Following the galvanic reaction below,
network growth occurs through an electroless deposition (ELD) reaction via individual atom displacement reactions between Ag
+ and Cu
0 based on respective
electric potentials. A spontaneous ELD reaction is preferred over an electrically
induced reaction to minimize artifacts and maintain the delicate nature of the
electrochemical reactions. Here, silver atoms are oxidized while copper is reduced
during the galvanic displacement reaction.
Cu s
ð Þ þ 2 Ag
þ
aq
ð Þ ! 2 Ag s
ð Þ þ Cu
2þ
s
ð Þ ΔE ¼ À1:26 V
Using this ELD reaction, a random seed network was fabricated by pipetting a
1 mL aliquot of copper microspheres 1–10 μm (99.995% purity, Alfa-Aesar) which
was then air dried. Silver nitrate (50 mM) was pipetted (20 μL) onto the center of the
device. Following the ELD described above, silver dendritic structures
216
R. Aguilera et al.