Dynamic characterization of MEMS devices to measure and visualize mechanical response is important for product development, trouble shooting and FE model validation. The MSA Micro System Analyzers from Polytec provide fast, accurate optical measurements of out-of-plane (OOP) and in-plane motion (IP). Until now, this has been limited to unpacked devices that are optically accessible. Now, the Polytec MSA-650 IRIS Micro System Anlayzer allows even measuring through intact silicon caps on encapsulated microstructres like e.g. intertial sensors, MEMS microphones, pressure sensors and more.
The MSA-650 IRIS turn-key measurement solution comprises a controller, function generator with additional reference channels, powerful optical scanning software suite and optical sensor head with a sophisticated IR-optical design. With its dedicated IR camera and a low-coherence SLD source it is the premier full-field vibration measurement system to capture entire sample layers through silicon caps under operating conditions. This patented interferometer technology delivers excellent data quality due to superior separation of the individual device layers.
As silicon is transparent in the near infrared spectrum above wavelengths of 1050 nm, the underlying technology of infrared-interferometer-based vibration measurement opens up the possibility for inspecting of encapsulated MEMS for authentic and most representative analysis results. Polytec‘s brand new, patented state-of-the-art interferometer technology now delivers supreme data quality due to superior separation of individual device layers in the si-capped MEMS devices. With a dedicated SWIR camera and a low-coherence SLD source the MSA-650 IRIS is the worldwide first measurement system with this patented technology to visualize the si-encapsulated devices, measure in-plane vibration with down to 30 nm resolution and real-time out-of-plane vibrations up to 25 MHz with picometer resolution and below.
In order to use Laser Doppler vibrometry (LDV) for a look into encapsulated MEMS, it is necessary to study the optical properties of silicon. While silicon is opaque for visible light, it shows a good transmission in the near- infrared range starting at around 1050 nm. A limitation for transmission however, is the high refractive index of around 3.4 at 1550 nm leading to considerable Fresnel reflections at boundary interfaces.
The Polytec patented approach uses short coherent light to improve accuracy. In contrast to laser light, low coherent light from a superluminescence diode only interferes if the light paths in the interferometer are balanced within the coherence length of the source. Thereby excluding light from outside the focus. This principle is utilized in white- light interferometers or for optical coherence tomography and now for the first time in the Laser Doppler Vibrometry (LDV). Enabling scanning LDV measurements with 25 MHz bandwidth and with an amplitude resolution of 100 fm/√Hz on encapsulated MEMS.