Tips for MEMS mechanical testing

January 15, 2016 // By Julien Happich
A provider of scientific instruments for the mechanical testing and robotic handling of microscopic samples, Swiss company FemtoTools AG is taking its know-how to MEMS R&D labs.

In a recent presentation, the company is considering optical and electrical testing scenarios versus the mechanical testing of MEMS for which it has developed a MEMS Probe station, the FT-MPS02.

The wafer-level MEMS testing instrument offers direct mechanical and electrical testing of the MEMS' characteristics, a more complete solution than today's most common alternatives such as electrical response measurement or optical vibration analysis, according to Femtotools.

In his brochure, the company's CEO Dr. Felix Beyeler highlights that most standard instrumentation used for testing MEMS has been designed for semiconductors and is optimized for electrical testing only, which means the mechanical properties of the MEMS are typically only measured at a late stage in the R&D process in final tests.

Yet, he explains, only true mechanical testing with a direct probe contact and concurrent electrical testing or stimulation allows researchers to precisely characterize the relationship between a MEMS' electrical signals and mechanical properties, with force-deflection-time data and without having to make any mathematical assumptions.

It also allows researchers to validate or improve their models, optimize their processes and detect problems early, at wafer level to select good dies only for further packaging. In some cases, the tool could also be used to refine material model libraries in CAD tools relying on Finite Element Analysis.

With a force resolution down to 5nN at the tip of its 50um by 50um silicon probe (optionally, the tip can be furnished by a sharp tungsten probe with a tip radius smaller than 2um), the MEMS probe station can characterize most MEMS sensors and actuators (which can create forces in the Nanonewton to Millinewton range).

On unpackaged wafers and chips, the unit can measure sensor output signal versus applied deflection/load, actuation force versus driving signal, actuation deflection versus driving signal. It can directly measure many other parameters that optical or electrical testing would miss or would have to derive from models, such as stiffness, linearity, elastic/plastic