Masao Nagase
Physical Science Laboratory
Multi-probe systems based on scanning probe technology
are expected to become a powerful tool for measuring electrical properties
in high resolution. We have demonstrated a feasibility of a new multi-probe
system. Four carbon probes with nano-springs have been integrated on a silicon
cantilever with aluminum electrodes by using focused-ion-beam chemical-vapor-deposition
(FIB-CVD) technique. Diamond like carbon (DLC) deposited by FIB-CVD is known
to be stiff and conductive. These properties are suitable for electrical probes.
Recently, Matsui et al. have demonstrated the fabrication of the coil spring
structure using FIB-CVD technique. [1] The nano-springs are expected to compensate
for the height difference between the probes which are not adjustable in conventional
probe systems. [2]
Figure 1 is a schematic and microphotographs of four carbon probes on a Si
cantilever. The three-dimensional FIB-CVD structures are fabricated by SMI2050
(SII-NT) in Univ. of Hyogo. [1] The height of the probe with nano-spring is
about 10μm. The diameter of the probe is 110 nm. The coil diameter of the
nano-spring is 380 nm. Figure 2 shows the electrical contact characteristics
between the conductive sample and one of the probes. The origin of the displacement
axis is the set point for AFM imaging in contact mode. The triangle mark (contact
height) indicates that this probe establishes electrical contact with the
sample at 580 nm. Since the displacement of the Si cantilever is about 200
nm at the set point, the nanospring is shortened by about 400 nm. Every probe
contacts the sample surface even if the heights of probes are different, because
the probe can shorten freely. Therefore, the nano-springs compensate for any
height differences. The mechanical characteristics are also confirmed in a
tensile test of the nano-spring grown on a conventional Si cantilever. The
shear modulus of the nanospring is estimated to be almost the same as that
of the conventional steel spring. Since no deformation of the FIB-CVD probes
is observed after imaging by atomic force microscopy (AFM) in contact mode,
the stiffness of the probes is sufficiently high.
Combining scanning probe technology and focused ion beam technology will
open a new area of micro- and nano-electromechanical systems.
[1] S. Matsui et al., J. Vac. Sci. & Technol. B 18 (2000)
3181.
[2] M. Nagase et al., Jpn. J. Appl. Phys. 42 (2003) 4856.
 |
 |
|
| Fig. 1. (a) Schematic
of four-point -probe on Si cantilever. (b) SEM micrograph of integrated
FIB-CVD multi-probe. (c) Magnified image of carbon probe with nano-spring
on Al electrode. |
Fig. 2. Displacement dependence of probe
current. Voltage of the sample (Au film) is 1V. |