<title>Diagnosis of microcrack initiation and estimation fracture toughness for micromachined silicon comb device with prenotch actuated by electrostatic force</title>

As the size of a mechanical structure used in microelectromechanical systems (MEMS) such as sensors and actuators becomes susceptible to defect, the effect of defects on mechanical reliability has a vital importance. So, new theoretical and experimental techniques need to be developed to estimate the micromechanical properties in MEMS. Experimental tools for macroscale testing are not necessarily applicable to MEMS structures. The electrostatically actuated test device is presented to evaluate force and frequency for microcrack initiation near sharp notch of micromachined silicon device. The designed test device consists of comb drives for loading and a suspending beam for testing. The sharp notch is introduced to the suspending beam in the test device. The notched microbeams are fully integrated with a simultaneously microfabricated electrostatic actuator, which allows microfracture and fatique test without the need of an external loading instruments and without any possible influences from external sources. On the basis of the proposed test structure and linear elastic fracture mechanics, a theoretical model to quantify the notch radius effect on fracture toughness can be obtained without pre-crack formation and critical notch radius is discussed. The test device is in its lateral resonance frequency by modifying the Rayleigh method. The microcrack initiation can be quantified from the shift in the resonance frequency that is related to the stiffness change. Diagnosis of microcrack developed in the suspending beams can be expected from the decrease in the resonance frequency. Furthermore, the microcrack growth rate may be analyzed from a decrease in resonance frequency withe time.