Fabricating freely suspended structures optimized regarding mechanical and electrochemical stability for sensor applications

Highlight
• detailed analysis of the reactions of different material combinations in buffered oxide etch (BOE)
• new mechanism of hydrogen embrittlement in thin film layer systems with ITO
• prevention of corrosion and hydrogen embrittlement by galvanic isolation
• fabrication of a gas sensor that allows the measurement of gas concentration and identification of the gaseous substance in-situ

The concept of the micro-structured gas sensor discussed in this article promises the measurement of gas concentration and identification of gaseous substances in-situ. Furthermore it is fabricated exclusively using processes that are part of standard CMOS technology. In most MEMS devices a suspended structure is the main part of the sensor chip, realised using a wet etching sacrificial layer process. In this research we investigated the mechanical stability of different materials for the levitating structure and the electrochemical compatibility of the materials in the chip. A detailed analysis of the reactions of different material combinations in buffered oxide etch (BOE) revealed the occurrence of corrosion and hydrogen embrittlement in Al-ITO-LaB6 systems. From there a new mechanism of hydrogen embrittlement in thin film layer systems with ITO was proposed. Finally we showed an optimized way of fabricating the sensor chip with prevention of corrosion and hydrogen embrittlement by galvanic isolation.

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