Performance and reliability test of MEMS optical scanners

Abstract

MEMS scanners are among the devices which have been investigated since the very beginning of MEMS development. The main concern of this paper is to report and discuss suitable measurement techniques and to compare and verify this methods on different scanners for examples. Analysis of scanner reaction based on image processing is covered in a first section. It is shown that an Electronic Speckle Interferometer (ESPI), a Scanning Laser Doppler Interferometer (SLDI) and a phase shift interferometer are suitable for measuring different motion characteristics. The SLDI is used for rapid measurement of FRF at a large number of locations at the scanner. A phase shift interferometer with stroboscopic illumination has been utilized for measuring the deformation of scanners operating them at resonant frequency. Measurement of static displacement and of thermal deformation is the main application of ESPI technique and shown on the example of a galvanometric scanner. A next section is dedicated to functional tests and to qualification of methods for wafer level test. The application of a tilt angle measuring set up containing a position sensitive semiconductor device and a laser diode and of a laser Doppler interferometer is analyzed. Measurement of resonant frequencies in an early production state is the topic of a third section. It provides information about geometry properties of the scanners suspension and about mechanical stress inside suspending torsion or bending beams. Moreover it enables selection of scanner chips with characteristics which do not meet the specification and the cost for packaging of this bad dies is saved.