Accurate, precise and SI-traceable measurements of mechanical stiffness of microelectromechanical systems with forces in the range from pN to mN

• Applicant: Dr.-Ing. Valeriya Cherkasova
• Subject Area: Measurement Systems
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 550790367

Sensing MEMS have contributed greatly to advances in nanotechnology, materials science, electronics, and biomedical engineering. They differ in type of operating principle, design, purpose, but share a common property - mechanical stiffness, which, in the example of one of the simplest structure, a cantilever, can vary from 1 % to 30 % of the numerical calculated value due to manufacturing tolerances with the actual real value. This, proportionally leads to high measurement uncertainty, therefore requiring highly accurate calibration. Primary microforce calibration standards include dead weight using mass standards, electromagnetic- and electrostatic compensations, and photon momentum force methods. Each method has advantages and limitations, e.g., in dead weight method the smallest certified mass standard is 1 mg (approx. 9.8 μN). The best results for calibrating MEMS in the range of pN to mN can be achieved through a combination of methods which was originally introduced and extensively researched in ours Institute. The basis of the project is a previously developed force-displacement measurement device, combining electromagnetic and electrostatic compensation principles, making it possible to achieve unbroken chain of measurements traceable to SI units. Since the force range of the MEMS varies dependent from its type, an adaptive calibration method will be developed that uses the most optimal means of compensation depending on the characteristics of the sample. Particular attention is paid to assessing the influence of environmental conditions such as vacuum, air and dry gas on measurement accuracy. For example, experiments with changing the measurement environment are aimed at an in-depth study and construction of a theory of the behavior of the surface potential, which cannot be measured by existing electronics due to the devices’ own electric potential, and is not considered in the uncertainty budget in previous metrological studies. Objectives of the proposal include investigating the feasibility of achieving relative uncertainty of 0.1 % for forces measurements below 300 nN and 0.2 % for stiffness values calibration below 0.1 N/m, as well as the contribution of attraction and repulsion effects occurring at the moment of contact of the calibrated sample with the device. Standardized measurement protocols will be established and the comparative analyses will be carried out in the framework of cross-comparison designed and planned with the National Metrology Institute of Germany, PTB. The project strives to forge dependable and traceable methodologies for small force and stiffness measurements. This initiative advances metrology standards, fosters collaborative research efforts, and enhances the credibility of force-displacement measurements across scientific and industrial fields.

• DFG Programme: Research Grants