Toward a Self-Sensing Piezoresistive Pressure Sensor for All-SiC Monolithic Integration

Abstract

This work focusses on the design and fabrication of surface micromachined pressure sensors, designed in a modular way for the integration with analog front-end read-out electronics. Polycrystalline 3C silicon carbide (SiC) was used to fabricate free-standing high topography cavities exploiting surface micromaching. The poly-SiC was in-situ doped and the membrane itself is used as piezoresistive element, thereby forming a so-called self-sensing membrane, easing fabrication. After sacrificial release, the cavity is sealed by conformal deposition of poly-SiC whereby the reference pressure of the absolute pressure sensor is determined. Aluminum and titanium metallizations were used and ohmic contacts were confirmed by wafer-scale measurements. Measurements were carried out on different devices ranging from 100 kPa down to 10 Pa at room temperature. The Wheatstone bridge yields a logarithmic response of 1.1 mVbar $^{-}1\text{V}^{-}1$ . A square 300 $\mu \text{m}$ device exhibits a logarithmic impedance behavior yielding a response of $\Delta {R} / {R}$ of $1.6\times 10^{-3}$ bar $^{-1}$ . The realized pressure devices are a first step toward a SiC ASIC + MEMS platform for intended operation in harsh environments, such as industrial process monitoring, combustion control or structural health monitoring. The future outlook of the integration concept implies extended functionality by front-end transducer read-out, signal amplification and communication.