Development of a Monolithic Fiber-Based Electric Field Sensor

This project has been done on the development of a monolithic fiber-based electric field sensor, with a focus on establishing a reliable, cost-effective, and scalable production cycle to be implemented initially at a pilot and consequently at an industrial scale. The small scale and the low cost of these electrically passive sensors would enable their application where applying an external electric current is either forbidden (e.g. by the ATEX directive), or would distort the electric field and thus limit the possibility of monitoring sensitive assets. This electric field sensor works on the principles of electrostatic induction and translates the electric field to the displacement of an array of mirrors and holes suspended over a second array of mirrors. By shining the rays of light onto the suspended array, it would be possible to monitor the variations of the reflected light due to the displacement of the suspended array over the second array which is deposited on a transparent substrate. At the first phase of the project, by utilizing the COMSOL Multiphysics simulation software, the optimal parameters of the electric sensor were simulated. Based on the results of the simulations, a general process flow was drafted and received the approval from the experts at the EPFL Center of Micro/Nano Technology (CMi). Based on the finite element simulations, in order to maximize the displacement of the sensor along the electric field, it has been shown that reducing the thickness of the sensor would significantly increase the longitudinal displacement of the sensor. Additionally, in order to further decrease the stiffness of the springs connecting the suspended mass to the frames, the structural material of the sensor was selected to be Copper, which also has a high electrical permittivity and low fabrication cost. Next, the micro fabrications based on the optimized design and the process flow were carried out at the CMi ISO 5 cleanroom facilities. In order to adapt the process flows to the capabilities and the availability of the machines, several process flows have been tested and the result of which have all been documented in this report. Moreover, regarding the limited range of the available choices for having a process flow which is compatible with the CMi facilities, the recommendations for further simplifying the process and decreasing the final production costs are mentioned in this report.