MSV-400 Microscope Scanning Vibrometer - Applications

General

The MSV-400 Microscope Scanning Vibrometer series was developed especially for the vibrational analysis of MEMS (Micro-Electromechanical Systems) devices. Nowadays those devices find numerous applications in the automotive, medical, bio-chemical and aeronautic industry. As a consequence there is a huge demand for standards in MEMS-testing, both for single dies and for wafer-processing. Polytec's MSV-400 is the ideal tool for a quick and accurate motion analysis of unpackaged MEMS devices. For wafer-level testing, the MSV-400 can easily be mounted onto manual or fully automated probe-stations.

Application Areas

• Vibration measurement of MEMS
• Continuous frequency domain measurements for device performance analysis
• Microstructure failure analysis and reliability testing
• Measurements of transient behavior using time mode
• Identification of in-plane resonances through out-of-plane coupling
   

Application Examples

MEMS Mirror
Figure 1: vibration modes of micro mirror	Applied MEMS Inc. has developed a MEMS mirror device for use in optical bar code scanners. The micro-mirror is completely manufactured from single-crystal silicon. It is electrostatically actuated and offers a large rotation angle of at least ± 14°. This mirror device was extensively tested using a Polytec MSV Microscope Scanning Vibrometer. The purpose of these tests was to measure the various resonant modes and to confirm that the mirror maintains optical planarity while undergoing electrostatic actuation. Modelling analysis on the mirror has shown that the single axis mirror may be operated in a dual axis mode, which has been confirmed by the laser measurements (Figure 1): There is a primary rotational mode about the x-axis (left) and a secondary rotational mode about the y-axis (right).
MEMS Acceleration Sensor
Figure 2: MEMS acceleration sensor Figure 3: Geometry mesh on the cantilevers Figure 4: ODS animation of the cantilever	The MEMS acceleration sensor displayed in Figure 2 has been developed for frequency selective acceleration measurements. It comprises a large number of cantilever arms of different lengths. Naturally the resonance frequency for each lever will be different as well. When experiencing shock or vibration only certain levers will vibrate depending upon their resonance frequency. A Polytec MSV system was used to measure the resonance frequencies of the individual levers and for the presentation of the out-of-plane operational deflection shape. The micro sensor itself is placed under a standard microscope and is mechanically excited by a small piezo actuator. A broadband periodic chirp signal from a signal generator is applied to the actuator for excitation of all frequencies, with the same energy. The generator signal is looped back into the acquisition channel and, thus, is providing the reference phase. In Figure 3, a frame from a live video image shows the geometry mesh used to measure the ODS of the cantilevers. The analysis is performed on three example cantilevers although the sample contained more than thirty. The scanpoint grid for each lever is defined rapidly with a freehand tool on the video image. A snapshot from the 3-D ODS-animation of the a tilt mode (± 2 nm) is displayed in Figure 4.