Quality-factor and frequency shifts of suspended Ge membranes

Abstract

Crack initiation and growth are key issues when it comes to the mechanical reliability of microelectronic devices and microelectromechanical systems, especially when a system is fabricated using a suspended membrane as a platform. In this study, two suspended Ge membranes on a silicon substrate were investigated by measuring their vibrational response over a frequency range of 50 kHz to 500 kHz. Key material properties were identified by measuring the frequencies and mode patterns for a set of vibrational resonant modes using a laser interferometer. The membranes were subject to thermal cycling over a temperature range of 25 °C to 97 °C. The temperature dependence of mechanical properties, including residual stress and the quality (Q-) factor of each membrane, were studied at low pressure (10−3 mbar)and at room pressure. Experimental results are compared with models. The change in biaxial stress with temperature agrees well for a perfect membrane. Unexpected behaviour was observed in one membrane which showed an increase in Q-factor with the temperature at low pressure, but the opposite behaviour at room pressure. This phenomenon was caused by cracks in the membrane caused by large amplitude vibrations of the membrane combined with thermal cycling.