Electrostatic Voltage Sensor Based on a High Aspect-Ratio Copper Actuator Levitating over a Small Air Gap

Inhalt:
A variable parallel-plate capacitor is fabricated in a micromechanical surface process with a high-aspect ratio actuator, reinforced by copper electroplating employing a sacrificial photo-resist layer. The device works as an RMS voltage sensor using the principle of electrostatic force. A copper layer with a coplanar waveguide below the actuator provides separated excitation and sensing electrodes. For low-loss electrical connectivity flip-chip technology is employed using solder paste. The presented design achieves a freely levitating plate area of up to 3x3 mm² and an initial gap distance of only 1.5 µm. A pull-in voltage below 1 V at frequencies from DC up to 1 GHz and sensitivities up to 1 fF/mV are demonstrated.