Optical characterization of dynamics inside Si-capped MEMS

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.

Highlights

  • IR capability to measure MEMS dynamics through different layers of Si-capped devices
  • Real-time out-of-plane response measurement up to 25 MHz (w/o post-processing)
  • Sub-picometer out-of-plane displacement resolution
  • Straighforward FE model validation of MEMS in final state
  • Superior separation of the individual device layers
  • Stroboscopic video microscope to measure in-plane motion up to 2.5 MHz
  • Automated system that integrates well for production (probe station compatibility)

Superior separation of the individual device layers

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.

Modal testing of silicon encapsulated MEMS 

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.

Use the leading technology in vibration analysis

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 Poyltec 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.

Accessories and components

Tripods, test stands, positioning stages

A-STD-TST-01 Test Stand

Test stand providing ample workspace. With motorized z-axis, travel range 200 mm.

A-STD-BAS-02 Base Stand

Rigid support for the sensor head. Includes manual focus block with 100 mm travel range with coarse and fine drive. Interfaces to commercially available optical tables.

A-STD-F50 Focus Block

Travel Range 50 mm. With coarse and fine drive for manual z-axis adjustment of the sensor head. Interfaces with commercially available wafer probe stations.

Vibration isolation, breadboards

A-TAB-AIR-01 Active Vibration Isolation Table

Air-damped vibration isolation table with active level adjustment. Compatibility: A-STD-TST-01 Test Stand, A-STD-BAS-02 Base Stand.

A-TAB-ELC-01 Active Vibration Isolation Table

Electronically controlled voice coil stabilization for highest isolation performance. Compatibility: A-STD-TST-01 Test Stand, A-STD-BAS-02 Base Stand.

A-BBO-ME02 Breadboard

Breadboard with metric hole pattern. Footprint 900 mm x 600 mm. Compatibility: A-STD-BAS-02 Base Stand.

A-AVI-MELA Active Vibration Isolation Breadboard

Electronically controlled for highest vibration isolation performance. With metric hole pattern. Footprint 600 x 800 mm. Compatibility: A-STD-BAS-02 Base Stand.

Miscellaneous

MSA-A-WPM Wafer Prober Module

Together with the A-PST-200P XY Positioning Stage, the wafer prober module forms a motorized platform for electrical contacting and high-precision measurement of wafers and substrates up to 200 mm in diameter.


Your PolyXpert in Vibrometry