MEMS As Scientific Instruments: Precise Measurement of the Adhesion Energy with an Adhered Cantilever

Unwanted adhesion between soft elements of MEMS is a serious problem in the fabrication and operation of MEMS. Although the main reason for stiction is capillary forces, the adhesion persists even if these forces are excluded. It occurs due to omnipresent dispersion forces. In this paper, the adhesion forces in Si–Ru system are analysed using a modified measuring setup based on the adhered minicantilever. The adhesion energy is measured with a precision of 10% and the average distance between rough surfaces at contact is evaluated on the basis of the Lifshitz theory. It is shown that, due to surface roughness and large nominal area of contact, the capillary forces do not play a significant role even at very high humidity. The role of these forces increases with the decrease of the nominal area. The measured adhesion per unit area is 1.58 ± 0.12 µJ/m2. It includes both the dispersion and electrostatic forces, but the latter give a contribution smaller than 0.33 µJ/m2. The average separation distance between surfaces is estimated as 41.9 ± 1.3 nm. Deeper understanding of adhesion is important for the design of MEMS devices.