Modulate the chamber pressure of the hermetic sealed MEMS device by varying the cavity depth of cap Si

Several kinds of micro-electro-mechanical systems are sensitive to pressure. Some need to interface to ambient condition in order to aim intended function, but others claim hermetic packages to keep the constant internal pressure over MEMS devices operation time [1][2]. This study presents the novel method to control the pressure level of different chambers fabricated using the same wafer-level-packaging (WLP) process. As indicated in Fig. 1, due to the out-gassing of CMOS and MEMS chips both, the chamber pressure of a hermetic sealed MEMS device can be modulated by varying the cavity depth of the cap Si substrate. Thus, pressure of hermetic sealed chambers can be easily specified by the etching depth of capped Si. In applications, the Si-above-CMOS (TSMC 0.18μm 1P5M CMOS process) MEMS process platform has been employed to demonstrate the present approach. The fabrication results demonstrate that the chamber pressure is modulated by the cavity depth of Si cap.