Silicon double spring for the simultaneous calibration of probing forces and deflections in the micro range

Abstract

A new reference spring for the simultaneous calibration of probing force and displacement has been developed. The spring consists of two single silicon springs, which are placed at a distance of 3 μm from each other. Each single spring consists of a moveable shaft, which is suspended and guided by four double-folded silicon springs. This leads to a much higher stiffness of the spring perpendicular to the direction of movement than in the direction of movement. The area of contact of the double spring has a size of 50 μm × 60 μm. However, measurable changes in the calibration parameters could not be observed when we varied the location of the loading point within this area. Furthermore, it could be shown for measurements at different temperatures that the calibration parameters also show a very small dependence on temperature (<0.4%/K between 22 °C and 23 °C). A further outstanding property of this new reference spring is its small non-linearity of the force deflection curve of 0.1%. The spring can be used for the calibration of force and the displacement of atomic force microscopes, nanoindenters, and stylus instruments in the micro-Newton range up to 12 μN and up to 3 μm displacements.

Comparing AFM cantilever stiffness measured using the thermal vibration and the improved thermal vibration methods with that of an SI traceable method based on MEMS

“…Small temperature variations of some tenth of a degree do not influence the measured stiffness of the MEMS as a previous investigation of a MEMS spring over a time period of 60 h showed [9].…”

“…The PTB has developed two devices which allow precise stiffness calibrations. The working horse is the microforce measuring device based on a compensation balance for force measurement and on a nanopositioning device for deflection measurement which is able to achieve stiffness uncertainties of 4% [8][9][10][11]. Smaller uncertainties below 1% are aimed at with PTB's primary nanonewton force facility [12].…”

3.1.4 - Silizium-Mikro-Kraftnormal

“…für Tastschnittgeräte mit Biegebalken-Normalen aus Silizium möglich [7]. Für die Kalibrierung von Indentern für die instrumentierte Eindringprüfung sind kalibrierte mikromechanische Silizium-Federn verfügbar, die allerdings neben einer hohen Linearität einen Kalibrierpunkt in der Kraft-Auslenkungs-Charakteristik aufweisen [8][9][10]. Man erreicht dies durch eine Verbindung zweier Federkörper in einem Chip-Stapel [8,9] oder auch monolithisch integriert an der Oberfläche eines einzigen Chips [10].…”