Abstract-The design, fabrication, and measurement results for a diaphragm-based single crystal silicon sensor element of size 820 µm × 820 µm × 500 µm are presented. The sensor element is designed for in vivo applications with respect to size and measurement range. Moreover, it is optimized for longtime operation in the human body through a built-in protection preventing biofouling on the piezoresistors. The sensitivity is about 20 mV/V for a change from 500 to 1500 mbar absolute pressure. This result is comparable to conventional sized micromachined pressure sensors. The output signal is not found to be influenced by exposure to 60 °C for three hours, a normal temperature load for a typical sterilization process for medical devices (Ethylene Oxide Sterilization). The hysteresis is low; < 0.25% of full scale output signal. The sensor element withstands an overload pressure of 3000 mbar absolute pressure. Observed decrease in the output signal with temperatures and observed nonlinearity can easily be handled by traditional electronic compensation techniques.
High-density through-wafer interconnects are of great interest for fabricating real 3D microsystems. A complete solution for realizing through-wafer interconnects is presented. The proposed solution is believed to be cost effective and easy to integrate in a device process flow. A deep reactive ion etch process was developed to etch 20 × 20 µm2 via holes through 300 µm thick silicon wafers. Thermal oxide is used to insulate the vias from the bulk silicon and heavily doped polysilicon is used as the conductor. Aluminum metallization is provided on both sides of the wafer. The electrical resistance of a single through-wafer via is close to 30 Ω.
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