A micro active probe device compatible with SOI-CMOS technologies

A surface-micromachined active probe device with built-in electrostatic actuator and on-chip CMOS circuits is described. The device has been fabricated on a silicon-on-insulator (SOI) substrate using a 0.6-μm CMOS-based process containing four polysilicon layers and one metal layer, and its basic functionality has been verified experimentally. A 0.135-μm-thick surface silicon layer of an SOI substrate was used to form cantilever beams. The very thin structures enable a probe to be turned on at a voltage as low as several volts. A stopper structure, used to avoid contact between a deflector electrode and its paired stator electrode, was formed with a small overlap area of approximately 0.05 μm². The small overlap area results in a small adhesion force, approximately 70 nN. An n-p-n junction was exploited as an isolator in the probe. A p-n junction in a released beam had only a 5-pA leakage current at a 9-V reverse bias. In addition, it has been found that electrostatic charging is a major source causing unrestorable postrelease stiction