Materials for Encapsulating Micro-System-Based Electric-Field Sensors

There is a fundamental challenge in the development of all sensors in that they need access to the quantity to be measured, but they also must be protected from harmful influences from the environment. In the case of DC electric field sensors this task is especially difficult. In principle, there are two large groups of solid materials that can be used for housing and encapsulation, namely, conductors and insulators. Both entail special restrictions and benefits. Conductors can guide the field and allow the design of a field concentrator but can also reduce or even shield the electric field if the geometry is unfavorable. Insulators are needed to separate different functional parts, e.g., electrodes, but exhibit polarization and charging effects that influence the electric field. These effects can be mitigated often by calibration. However, insulators are also prone to charging effects and the charges involved are source of strong electric fields, which can interfere with the measurement to a great extent. Compared to their macroscopic sensor versions, microsystem based electric field sensors offer great advantages but they are extremely vulnerable to mechanical damage. Even the smallest dust particle scan hamper the movement of the fragile mechanical structures. Furthermore, charged particles can reach the sensor's surface along the electric field. This is especially problematic in everyday applications where these charges can accumulate on surfaces. In this work, the influence of different insulators on the static electric field is presented. The insulators are tested on their own and as part of a rudimentary encapsulation together with conductive elements. In a custom-made set-up, the stability of the electric field inside the encapsulation, made of stainless steel, was studied with a commercial electric field mill. Above this encapsulation were fields ranging from ~200 V/m up to ~4200 V/m applied by a parallel plate capacitor.