I. Introduction
Mems-Based micromachined pressure sensors have been used extensively for a variety of applications, where the common mechanism of operation is linked to the deflection of a thin diaphragm. Clearly, silicon is the dominant material used in micromachined pressure sensors and its perfectly elastic behavior at low temperatures and the development of adequate fabrication methods have made it very suitable for pressure sensing applications. Details of MEMS fabrication processes [1] are not the focus of this paper. Applications are numerous after initial applications were limited to the biomedical and aerospace industry [2]–[4], and further evolution into high volume low-cost use in other industries [5]–[7]. Excellent reviews on micromachined pressure sensors summarizing fabrication techniques, design and applications using silicon and other materials and the variety of uses for such sensors are available [8], [9]. This almost exclusive use of silicon in MEMS-based pressure-sensing applications has resulted in a careful scrutiny of the deformation behavior of this material under various pressure states [10]–[12]. Most of the research in this direction deals with quasi-static pressures applied on the silicon diaphragms and measuring the resulting deformation [13]. While silicon is generally expected to show brittle behavior [14], a number of other studies have also demonstrated that silicon is not brittle as generally assumed but shows localized plasticity at higher loading rates [12], [15]. Dislocation motion has been observed in the normal slip directions corresponding to the diamond cubic crystal structure of silicon as the loading rates were increased. This overall plasticity has been attributed to the phase transformation of silicon to the tin like bcc -phase which is deemed to exhibit greater plasticity [12], [15]–[18]. Such phase transformation enhanced plasticity has been observed at the microstructural scale through micro- and nano-indentation studies through creative methods by increasing the loading rates (12, 15–18). The use of micro-machined silicon-based pressure sensors has been proposed in a number of applications. In particular, injury resulting from sports arenas and defense theaters and the consequent gamut of disabling effects has propelled the study of the deformation behavior of silicon sensor diaphragms. While the response of MEMS-based silicon sensors under static pressure conditions have been researched, at the present time, there is a dearth of information regarding the deformation behavior of silicon diaphragms under conditions of dynamic applied pressure. The goal of this study is to understand the manner in which silicon-based pressure diaphragms respond in terms of maximum deflection when subjected to both applied static and dynamic pressures using experimental and FEA methods.