A micromachined Kelvin probe with integrated actuator for microfluidic and solid-state applications

This paper reports on a micromachined Kelvin probe structure with an integrated scanning tip and an integrated electrothermal actuator that provides axial dithering motion. The device is fabricated from metal foil by a modified microelectrodischarge machining process that allows electrical isolation within the device. In particular, it permits the incorporation of a wide epoxy plug that creates an insulating gap with low parasitic capacitance between the probe and the actuator. The epoxy structures are found to withstand the thermal and mechanical conditions encountered during device operation. The device is used to measure changes in the external surface potential of a parylene microfluidic channel as a function of varying pH of liquid inside the channel. A contact potential difference of [approximately equal to] 6V is measured for a change in pH from 4 to 8 within the channel. The device is also used to map embedded charge in a thin Si[O.sub.2] layer on a Si substrate, showing it to be suitable for monitoring microelectronics manufacturing processes. [1072] Index Terms--Contact potential, oxide charge, pH, surface potential.