Realisation of very high voltage electrode-nozzle systems for MEMS

Paine, M.D., Gabriel, S., Schabmueller, C.G.J. and Evans, A.G.R. (2004) Realisation of very high voltage electrode-nozzle systems for MEMS. Sensors and Actuators A: Physical, 114 (1), 112-117. (doi:10.1016/j.sna.2004.02.013).

Abstract

A number of applications would benefit from MEMS devices that can produce very strong electrical fields with high potential differences; in particular the production and acceleration of ions or charged droplets for spacecraft or biomedical applications. We have carried out investigations into the use of silicon dioxide as an insulator in MEMS devices designed for such applications. The work focuses on axisymmetric electrode configurations that produce 10⁸ V/m electrical fields close to the axis, in vacuum. To accelerate ions to high velocities (>100 m/s) potentials of over 1 kV are required. MOS devices, consisting of aluminium insulated from the silicon substrate by SiO₂, were produced with a number of different geometries. Thermal oxides of 2 µm thickness and thermal oxides augmented by 2 µm of CVD oxide were tested for the maximum voltage held before permanent destruction. The insulator surface between two electrodes placed 50 µm apart, successfully held voltages of over 3 kV without surface flashover. We have shown that breakdown occurred through the oxide with a mean hold-off voltage of 1340 V for 2 µm oxides and 2960 V for 4 µm oxides. In the course of the experiments, we have found the importance of chip cleanliness, voltage polarity and the external measuring circuit.

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