Micro-Electro-Mechanical Systems are usually devices with both electrical and mechanical components. For the reliable testing of MEMS, not only the electrical but also the mechanical properties require quantitative characterization. This is especially important during the R&D phase and the MEMS manufacturing process development.
In this application microfabricated flexure-arrays are mechanically tested on wafer level using the FT-MPS02 MEMS Probestation. The flexure consists of a square-shaped pad suspended by four springs. The springs are designed such that the pads can deflect both vertically (perpendicular to the wafer plane) and horizontally (inside the wafer plane).
The vertical stiffness is measured using a FT-S1000 Microforce Sensing Probe mounted in the FT-MPS02. For the horizontal stiffness measurement a FT-S1000-LAT Lateral Microforce Sensing Probe is used. Besides the stiffness value, the linearity can be extracted from the force-deflection data shown in the graph.
During the micro-manufacturing process development, a large number of process parameters influence the mechanical properties of the MEMS structures. By defining an upper and a lower limit for the target stiffness, a chip map is created to identify the working flexures (green) and flexures that are outside the desired specifications (red). Flexures that have not been successfully released from the wafer (very high stiffness) or flexures with cracks (low stiffness) are identified. The yield rate can easily be detected by the ratio of green and red marks.