1 Controlled and Localized Electrochemical Microfabrication …
3
replicated by applying tool cathode, which is prepared with contours that is complementary to the fabricated microstructures to EMM [16]. In addition, the machining
accuracy could be further improved by decreasing pulse duration [17]. Even spatial
resolutions below 100 nm could be available while decreasing pulse duration to the
picosecond range [15]. However, the pulse generator with the capacity of producing
picosecond pulse voltage is rarely applied to EMM, due to the limit of pulse power.
It also improves the cost of EMM. Moreover, EMM is a multi-disciplinary process
containing electromagnetic, flow field, and thermal effects. To improve the controllability and precision of EMM has become an urgent issue. Few studies attempted
to apply the sub-micron spherical tip to the EMM process.
This paper has applied a moving sub-micro spherical stylus as the tool electrode
in EMM. Both the mechanisms and advantages of EMM using a sub-micron spherical tip were analyzed. The EMM processed profiles considering various parameters,
including applied voltage, inter-electrode gap, and spherical tip diameter, has been
studied by simulation and experiments. The influences of various controlled parameters on the side gap and depth were experimentally studied with the developed setup.
Furthermore, layer-by-layer EMM has also been adopted to fabricate high aspect
ratio microfluidic channels.
1.2 Method and Materials
1.2.1 Method
In EMM, the workpiece serves as the anode, and the tool electrode serves as the
cathode. When a spherical tip and workpiece are separated at a distance in the
electrolyte environment, electrochemical reactions occur at the electrode/electrolyte
interface, while applying a voltage source between the two counter polarities. The
principle of electrochemistry-based micromachining relies on the faradic processes
occurring at the tip and the workpiece surface. The conducting workpiece materials
(M) are dissolved by anodic dissolution, i.e., M
− ne
−
→ Mn
+ . And hydrogens are
generated on the surface of the spherical end with the electrochemical reaction of
2H
+
+ 2e
−
→ H 2 (g), that is, the cathode surface, as illustrated in Fig. 1.1. Thus,
the anodic workpiece materials are removed. Based on Faraday’s law, the processed
contour is mainly concerned with the distribution of the electric current density on
the workpiece surface, which could be expressed by Eq. (1.1) [18]:
j (r ) =
U
D
1 +
r
R + D
2
−
3
2
· κ
(1.1)
where U is the tip-workpiece pulsed voltage, D is the inter-electrode gap, r is the
distance between a point on the workpiece surface, and the point under the rounded
3
replicated by applying tool cathode, which is prepared with contours that is complementary to the fabricated microstructures to EMM [16]. In addition, the machining
accuracy could be further improved by decreasing pulse duration [17]. Even spatial
resolutions below 100 nm could be available while decreasing pulse duration to the
picosecond range [15]. However, the pulse generator with the capacity of producing
picosecond pulse voltage is rarely applied to EMM, due to the limit of pulse power.
It also improves the cost of EMM. Moreover, EMM is a multi-disciplinary process
containing electromagnetic, flow field, and thermal effects. To improve the controllability and precision of EMM has become an urgent issue. Few studies attempted
to apply the sub-micron spherical tip to the EMM process.
This paper has applied a moving sub-micro spherical stylus as the tool electrode
in EMM. Both the mechanisms and advantages of EMM using a sub-micron spherical tip were analyzed. The EMM processed profiles considering various parameters,
including applied voltage, inter-electrode gap, and spherical tip diameter, has been
studied by simulation and experiments. The influences of various controlled parameters on the side gap and depth were experimentally studied with the developed setup.
Furthermore, layer-by-layer EMM has also been adopted to fabricate high aspect
ratio microfluidic channels.
1.2 Method and Materials
1.2.1 Method
In EMM, the workpiece serves as the anode, and the tool electrode serves as the
cathode. When a spherical tip and workpiece are separated at a distance in the
electrolyte environment, electrochemical reactions occur at the electrode/electrolyte
interface, while applying a voltage source between the two counter polarities. The
principle of electrochemistry-based micromachining relies on the faradic processes
occurring at the tip and the workpiece surface. The conducting workpiece materials
(M) are dissolved by anodic dissolution, i.e., M
− ne
−
→ Mn
+ . And hydrogens are
generated on the surface of the spherical end with the electrochemical reaction of
2H
+
+ 2e
−
→ H 2 (g), that is, the cathode surface, as illustrated in Fig. 1.1. Thus,
the anodic workpiece materials are removed. Based on Faraday’s law, the processed
contour is mainly concerned with the distribution of the electric current density on
the workpiece surface, which could be expressed by Eq. (1.1) [18]:
j (r ) =
U
D
1 +
r
R + D
2
−
3
2
· κ
(1.1)
where U is the tip-workpiece pulsed voltage, D is the inter-electrode gap, r is the
distance between a point on the workpiece surface, and the point under the rounded