Quantification of Electrostatic and Adhesive Forces Between Microwire and Microprobe Using Experimental and Numerical Approaches

Experimental and numerical approaches are used to quantify electrostatic and adhesive forces between a 250-µm long platinum microwire of 0.625-µm diameter and a tungsten microprobe of 5.0-µm diameter. The deformations of the microwire observed in the experiment are used as boundary conditions for the numerical analysis. The numerical analysis evaluates the respective elastic restoring forces required for the particular deformation. The microwire, with one end attached to a piezo-stage and another end free, is brought into the proximity of the microprobe by the piezo-stage. The microwire-free end is deflected instantly due to the electrostatic force and contacts the microprobe. Then, the microwire is pushed axially against the microprobe by the piezo-stage. It is deflected gradually in the lateral direction before sliding off the microprobe. The deflections are recorded and measured by an ultra-high accuracy optical microscope and verified by piezoelectric displacement sensors. The adhesive force is the reaction force at the microprobe contact surface during lateral deflection of the microwire since it is deflected without sliding off and maintains contact without normal contact force. The electrostatic and adhesive forces acting between the microwire and microprobe are balanced by the microwire elastic deformations and structural restoring forces. These two forces are quantified as 0.01007 µN and 0.059017 µN, respectively, using the FEA tool ANSYS Workbench to solve nonlinear contact problems. The method presented in this study could be used to measure electrostatic and adhesive forces in other microstructures, such as microrods, microbeams, diaphragms, microplates, etc., without force sensors.