Optical Analysis of 3D Mechanical Motions

The importance of precise experimental dynamic characterization of micro-devices such as micro-electro-mechanical systems (MEMS) is ever increasing in research and development activities as well as in routine measurements at the wafer level.

For such measurements, Laser Doppler vibrometry has been established as the essential tool due to its ability to obtain the entire frequency spectrum in real time, non-invasively, phase-resolved and with ultra-high vibration resolution. As a result, settling characteristics, transient response, and any vibration waveform (not limited to periodic motion) can be studied easily, rapidly and accurately.

Laser Doppler Vibrometry

Laser Doppler vibrometry has emerged as a standard technique for investigating in- and out-of-plane 3D mechanical vibration components of macro-sized objects in real time. Until now, this technique was limited to just out-of-plane (OOP) vibration measurement for micro systems.

Simultaneous acquisition and analysis of three motion directions is required for micro systems and other small objects containing complex motion patterns. Previously, in-plane motion of micro systems was observed using relatively slow and inefficient techniques, which are based on high-speed image processing technology such as stroboscopic video microscopy with resolution down to the nm range. To qualify new MEMS devices, it is often necessary to have a higher in-plane resolution.

Polytec’s MSA-100-3D Micro System Analyzer

Polytec offers a new measurement system called the MSA-100-3D to fulfil the in-plane measurement needs for micro systems such as MEMS. The micro system analyzer uses a revolutionary approach to laser Doppler vibrometry. With in-plane resolution down to the sub-picometer (pm) level, the system provides genuine real-time 3D vibration data by measuring vibration from three different directions.

This capability is extremely important for MEMS research and development activities because the dominant motion components of most MEMS devices are in their plane, for example, gyroscopic sensors and accelerometers.

The new MSA-100-3D Micro System Analyzer

The MSA-100-3D can perform high spatial resolution measurements on micro-devices without any problem, due .to the laser spot size of less than 4 µm. With a large stand-off distance, the new instrument can perform measurements even on deep, structured samples.

Clear real-time images can be obtained with two integrated video cameras, which simplify and accelerate system set-up. The system also has a wide range of hardware and software options, which help it adapt to the requirements of a specific application. Addtionally, a scanning option helps it easily achieve full-field measurements of 3D deflection shapes.

Polytec offers the MSA-100-3D in different configurations with bandwidths of up to 25 MHz.

The in- and out-of-plane modes of a MEMS cantilever device are shown in Figure 1. Semi-automated or fully automated testing of MEMS can be performed at the wafer level by integrating the MSA-100-3D into a vacuum probe-station facilitated by the instrument's special shape, long working distance, and a removable compensation glass window.

Figure 1. Out-of-plane and in-plane deflection shapes of a MEMS cantilever device.

The MSA-100-3D is an innovative solution that creates potential for new opportunities to develop and test MEMS devices and other smaller precision mechanical components used in fields such as entomology as well as in the data storage industry.


This information has been sourced, reviewed and adapted from materials provided by Polytec Ltd.

For more information on this source, please visit Polytec Ltd.


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