Thermal damage limits in thermally actuated MEMS

6 Thermal damage limits in thermally actuated MEMS 

When silicon is in contact with a metal, a low-temperature liquid eutectic can be formed, far below the melting temperature of either silicon or the metal. For example, the eutectic temperature for silicon and gold occurs around 370°C for 30% silicon. In contrast, the melting point for pure gold is 1064°C, and the melting point for pure silicon is 1410°C [5]. Aluminum and silicon can form a eutectic around 577°C at around 12% silicon. In designing thermal actuators, such as gold/silicon thermal bimorph actuators or suspended heaters with metal wires and contacts, the metal should not be used in the proximity of any silicon that is heated unless the temperature is kept below the eutectic point. 

Assume the thickness of all the layers is 2 pm. Use the following formula for the average temperature  

At what temperature rise AT above ambient will a beam that is 100 pm long, 5 pm wide, and 2 pm thick buckle  

Gianchandani, Bent-beam strain sensors, J. Microelectromechanical Systems 5(1), pp. 52-58 (1996). 

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