Device Physics Laboratory
We have developed nanotools for measuring the electrical properties of nanomaterials. The conventional probe used in scanning probe microscopy (SPM) has only one tip on the single cantilever. If we can integrate a functional device on a SPM cantilever, it will be a powerful and useful nanoelectromechanical system or nanotool for evaluating the properties of nanomaterials. However, it is very difficult to integrate the fabrication process of the functional device and that of the SPM cantilever. The recent advancement in ion optics of focused ion beam (FIB) technology has enabled us to fabricate micro- and nano-order structures. Measurement systems are integrated on a Si cantilever of SPM using newly developed fabrication methods based on nanopatterning technology. In this section, we introduce two kinds of nano-probe systems.
Measurement of electrical resistivity using a four-point-probe is a fundamental technology of electronic devices. However, the distance between the probes of an existing four-point-probe is a few micrometers. It is too large for evaluation of nano-order electrical properties of nanomaterials, such as CNT and DNA. We try to fabricate nano-four point probes for SPM using FIB technology. Fig. 1 shows a micrograph of the nano-four-point probes fabricated by FIB milling . The thin Pt film deposited on the tip of the lever is divided into 4 parts using ion beam milling. The pitch of the probes is about 500 nm. The width is about 200 nm. To miniaturize the probes, nano-four-point probes are fabricated by electron beam nanolithography. Fig. 2(a) shows Si nanoprobes with 60-nm-pitch and 20-nm-width on a silicon-on-insulator substrate. This nanodevice is cut out from the substrate by FIB milling and is transferred to the tip of a Si cantilever with four Al electrodes. W interconnections deposited by FIB deposition (FIB-W) are formed between the Si electrodes and the Al electrodes. As a result, a nanodevice system is realized on an SPM microcantilever as shown in Fig. 2(b) . FIB technology brings us a new solution for assembling nanodevices. The abilities of FIB, milling and handling of micro-scale structures and direct wiring of metal electrodes are very useful for nano- and micro-electromechanical systems.
With further miniaturization of the nanoprobe, the SPM cantilever system fabricated by FIB technology will become a useful evaluation tool for nanodevices and molecular science.
 M. Nagase et. al., Jpn. J. Appl. Phys. 42 (2003) 4856.
 M. Nagase and H. Namatsu, Jpn. J. Appl. Phys. 43 (2004), to be published.
Fig. 1. Nano-four-point-probe fabricated by FIB milling.
Fig. 2. Nano-four-point-probe assembled by FIB technology.
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