A Silicon Based 4.5-GHz Near-field Capacitive Sensing Imaging Array

This paper presents a two-dimensional capacitive sensor array implemented in a 0.13-μm silicon technology for material characterization. The circuit is based on an oscillator operating at 4.5 GHz with a single inductor and a distributed capacitor. The 6×6 sensor array can be individually selected. When a dielectric material is in the near field of a pixel, it results in a shift of the oscillator frequency. A mixer is used to down-convert the the high-frequency component to an intermediate frequency. A digital core is used to acquire and process the data. The array is capable of detecting capacitance shift with a sensitivity down to 1.25 aF and a spatial resolution of 6 μm.