Micromechanical tunneling probes and actuators on a silicon chip

With the promotion of SPM technology, scientific interest has expanded from visual observation of static nanometric structures to in-situ investigation of mesoscopic phenomena, such as quantized electrical conductance of atom bridges. Bringing two probes or more into a tunneling distance is needed to determine the transfer function of the nanometric specimen. Technical difficulties lie in reducing the tip radius and the total size of the tip-positioning mechanism. For this reason we have previously proposed lateral tunneling unit that is a tunneling probe integrated with an electrostatic actuator produced by silicon micromachining technique. Size reduction of the whole SPM systems was found to work in favor of improving the control accuracy of tip-positioning as well as suppressing the effects of thermal drift and external vibration. Based upon these results we have recently developed such one-chip STM (scanning tunneling microscope) which is small enough to be loaded in the chamber of the transmission electron microscope. A pair of pre-aligned sharp tunneling tips has been successfully fabricated by the combination of deep dry etching and stress induced oxidation of silicon. The mutual distance of the tips is controlled by using the integrated electrostatic microactuators. The device enables us to in-situ observe atom scale phenomena in the tunneling gap.