Nowadays, the MOS (Metal-Oxide-Semiconductor) transistor probes have been reported for the surface electric properties, since they have the potentials to overcome the limitations of EFM (Electrostatic Force Microscope) system [1,2]. However, they show the fabrication difficulties due to the 3-dimensional tip shape of MOS transistor. Therefore, we proposed and fabricated a novel SPM probe with planar MOS transistor and FIB (Focused Ion Beam) nano tip in the previous research [3]. This process becomes easier compared with that of 3-d tip, and the tip sharpness can be also improved.
In this paper, the V-shaped MOS transistor probe with nano tip is designed, fabricated and evaluated for surface electric properties. The V-shaped cantilever has the improved lateral stiffness in comparison to the rectangular cantilever [4], and the device has advantages in the accurate measurements and applications. The arm width, angle, and length are determined with PBA (Parallel Beam Approximation) equations [5].
The gate channel width is also determined to detect both (+) and (-) electric signals. Since usual MOS transistor has no current at less than 0 gate voltages, (-) electric signals are not detected. Our device has slightly doped gate region, and the current flows even at less than 0 gate voltages. Therefore, the device can detect (-) electric signals as well as (+) electric signals.
The semiconductor analyzer is used to measure the properties of the device. The sensitivity becomes higher with the increased drain voltages, and the result shows the 467µA/V at 6V drain voltage. The scanning properties are also investigated with patterned metal structures. The experiments are performed up to the measuring limit, and no considerable degradation is observed. From these results, we can know the fabricated device shows the possibility for the surface electric properties with high sensitivity and high working frequency.
[1] H. Park et al., App. Phys. Lett., Vol. 84, No. 10, pp. 1734-1736, 2004
[2] S. H. Lee et al., Microsyst. Technol., Vol. 13, No. 5-6, pp. 579-587, 2007
[3] S. H. Lee et al., ICN+T 2006, Switzerland, 2006
[4] T. R. Albrecht et al., J. Vac. Sci. Technol. A, Vol. 8, No. 4, pp. 3386-3396, 1990
[5] J. E. Sader, Rev. Sci. Instrum., Vol. 66, No. 9, pp.4583-4587, 1995
|