A micromachined scanning grating interferometer for the out-of-plane vibration measurement of MEMS

A micromachined scanning grating interferometer (µSGI) is presented for use in measuring the out-of-plane vibration of microelectromechanical systems (MEMS). The µSGI uses a phase sensitive deformable diffraction grating to achieve interferometric axial resolution and a microfabricated lens to improve lateral resolution of the measurement. The grating is intended to be actuated to control diffraction patterns while measuring the MEMS vibration to increase measurement sensitivity. The deformable grating and the microlens are fabricated by surface micromachining techniques on separate wafers which are then precisely aligned and assembled. The fabricated deformable grating shows an actuation range of 0.54 µm and an operating voltage of under 31 V. An assembled grating and lens chip are successfully integrated with a silicon photodiode in less than 2 cm 3 . The integrated µSGI has been demonstrated by measuring 4.4 nm, 900 kHz vibration of a MEMS device while actuating the deformable grating in the measurement.