Studies on measuring surface adhesion between sidewalls in boron doped ultrananocrystalline diamond based microelectromechanical devices

• We fabricate sidewall adhesion MEMS sensors fully made with boron doped UNCD.
• We carry out a full mechanical characterization through FE analysis.
• Loading forces are calculated observing the spring deformation with 4 nm accuracy.
• Adhesion tests are performed in humid, dry atmosphere and after oxygen cleaning.
• Seldom observations of carbon based capillary neck are recorded at a higher load force.

In this study, we have investigated the adhesion phenomena between two sidewalls in boron-doped ultrananocrystalline diamond (B-UNCD) micro-electro mechanical systems (MEMS) in a humid and dry environment. We have developed and built B-UNCD MEMS test devices, in order to assess the tribological properties of diamond micro devices in-situ. Using these devices, we have been able to measure the adhesion force with approximately 15 ]-->nN resolution, by monitoring the displacement optically with a precision of 4 nm. In the case of testing in a dry atmosphere, virtually no adhesion (< 18 nN) was observed between the sidewalls. After testing in humid air over 55,000 cycles, increased adhesion force up to 128 nN was measured. A rare observation of capillary neck formation between sidewalls at high contact force, in humid air is observed which is most probably caused by the precipitation of carbon contamination. This contamination layer can be easily removed by oxygen plasma exposure but thereafter highest adhesion force of 260 nN adhesive force was measured. Our studies demonstrate that micromechanical devices fabricated based on diamond represent a great alternative over polysilicon based devices in terms of reduced adhesion and thus long term reliability, which is a significant step forward in developing diamond based MEMS.