SAW-based capacitive sensor with hemispherical electrode for nano-precision gap measurement

Abstract

Nano-precision gap measurement in the sub-micron range presents its own unique engineering challenge. The popular capacitive sensor platform, for example, is susceptible to the erroneous effect of electrode tilting and high noise floor, both of which are exacerbated by the small form factor required of a nano-precision gap sensor. In this paper, a capacitive gap sensor with a hemispherical electrode, used in combination with a SAW filter is presented. The proposed system outperforms the existing ones on two fronts. First, the system is virtually immune to the effect of electrode tilting due to the improved capacitor geometry. Second, it benefits from the outstanding signal conditioning capability of the SAW filter. Construction and characterization of a SAW-based capacitive gap sensor having resolution as fine as 10 nm are described.