Fraunhofer Institute for Silicon Technology
Fraunhofer Institute for Silicon Technology

Inertial Sensors

Micro Electro Mechanical Systems (MEMS) combine small device size with low cost in production and high reliability.

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Poly Silicon Process Platform

The PSM-X2 polysilicon technology platform uses a low-stress, 10-30µm thick polysilicon layer to create static and moving sensor structures. By using high-resolution lithography, minimum structure widths down to 0.5µm can be realized. Vertical patterning is achieved by a high precision deep etch process (DRIE). For capacitive detection of movements perpendicular to the plane, bottom counter electrodes are implemented at a distance of 1.5µm. The direction of motion of micromechanical systems is thus not limited to in-plane motions, but so-called out-of-plane motions can also be excited and detected. Additive, functional layers increase the reliability and robustness of the MEMS element (e.g. anti-stiction, shock resistance).

 

An encapsulation of the components at wafer level is integrated in the process. The firm bond between sensor and lid wafer, the so-called wafer-level packaging, is created here by a gold-silicon eutectic at around 400°C. The metallic bond frame ensures a hermetic seal so that the pressure set during the bonding process is maintained over the entire service life. The metallic bond frame ensures a hermetic seal so that the pressure set during the bonding process is maintained over the entire service life. By integrating a getter layer, an internal pressure of up to 10-6 bar can be achieved. The use of the novel Multi Pressure WLP Technology patented by ISIT allows the setting of different cavity internal pressures on wafer level (large picture). The PSM-X2 platform is currently used in the field of inertial sensors, micromirrors and electron-optical deflection units.