Nano Archive

Surface energy approach and AFM verification of the (CF) n treated surface effect and its correlation with adhesion reduction in microvalves

Han, Jeahyeong and Yeom, Junghoon and Mensing, Glennys and Joe, Daniel and Masel, Richard I and Shannon, Mark A (2009) Surface energy approach and AFM verification of the (CF) n treated surface effect and its correlation with adhesion reduction in microvalves. Journal of Micromechanics and Microengineering, 19 (8). 085017.

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The purpose of this paper is to outline an approach that will determine the optimal surface pairs to use in a MEMS device with demonstrated stiction problems. The approach uses the contact angle and atomic force microscopy (AFM) pull-off measurements to predict adhesion at the solid–solid interface. The results are compared to microvalves that have been fabricated with different surfaces at the seat/membrane interface. For microfabricated mechanical devices with surfaces that touch or have a small gap distance, stiction can occur during fabrication or during use. Fabricating multiple devices with different surfaces to determine the lowest stiction can be costly and time consuming. Identifying the surface pair with the least amount of surface adhesion before fabrication can lead to a reduction in device failure due to stiction, and/or time it takes to find the lowest energy surfaces via trial and error. Surface energies are obtained using the van Oss equation based on the contact angle measurements, and surface energy can be used to show the relative adhesions between two surface pairs. An AFM pull-off test is performed using nano- and micro-sized tips to quantify the effect of the different surfaces on adhesion between the solid–solid surface pairs, including SiO 2 /PI, CF n /PI, CF n /SiO 2 and CF n /CF n . The work of adhesion of the surface pairs is obtained using the Derjaguin–Muller–Toporotov (DMT) and Johnson–Kendall–Roberts (JKR) theories. The surfaces treated with a C 4 F 8 /Ar plasma to form a CF n coating showed the least amount of surface adhesion. The CF n surface treatment effects on adhesion are quantified and correlated with the reduction in the opening pressure of the microvalve whose interfaces are coated with a CF n film. The AFM pull-off test was more closely related to adhesive forces between the surfaces of the valves as seen in the opening pressure data. The adhesion calculation based on the contact angle measurements predicts the adhesion force with a similar trend but does not take into account the meniscus forces.

Item Type:Article
ID Code:11336
Deposited By:Prof. Alexey Ivanov
Deposited On:02 Nov 2011 00:24
Last Modified:02 Nov 2011 00:24

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