Integrated carbon multi-probe with nano-spring on Si cantilever
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.  The nano-springs are expected to compensate for the height difference between the probes which are not adjustable in conventional probe systems. 
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.  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.
 S. Matsui et al., J. Vac. Sci. & Technol. B 18 (2000) 3181.
 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.
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