MSA-500 Micro System Analyzer - Applications

MEMS devices such as micro-sensors and micro-actuators are found in guidance systems, automobiles, aircraft, computers, entertainment systems and medical devices. R&D and production engineers must develop new devices quickly, precisely and cost effectively. Polytec’s innovative Micro System Analyzer enables the systematic testing of the dynamic mechanical response to important electrical and physical inputs.

Successful MEMS Applications

Many MEMS devices have moving parts which may be measured with a Micro System Analyzer. Some candidate devices are accelerometers, gyroscopes, RF MEMS, optical network components (MOEMS), micro mirrors and video displays. Useful for MEMS design, development, troubleshooting and production testing, the MSA provides data for

Characterizing out-of-plane and in-plane motion of MEMS devices
Continuous frequency domain measurements for device performance analysis
Microstructure failure analysis and reliability testing
Testing and refining of simulation models
Transient behavior analysis using time-domain
Identification of in-plane resonances through out-of-plane coupling
Step response and ring down measurements to determine actuator settling times
Wafer-level MEMS motion analysis using a probe station
Bode plot graphs and analysis

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Semiautomatic, Wafer-Level Measurements of MEMS Dynamics

Wafer-level MEMS testing prior to packaging is an increasingly important measurement for achieving high yield and reliability at low production cost. Measuring the response of a MEMS device both to changing environmental conditions like pressure, light, temperature and fluids and to intrinsic parameters like resonance frequencies and displacements is crucial to the dynamic design of new sensors. Here a setup for characterizing the dynamic response of membranes using a semiautomatic probe station equipped with a scanning laser-Doppler vibrometer is described.

Step-and-Repeat MEMS Wafer Testing

Dynamic testing of a MEMS wafer covered with an array of micro-membranes is time consuming and tedious when it is done manually, one device at a time. To improve the throughput, a semiautomatic probe station, to position the wafer, and a laser-Doppler vibrometer, to perform the dynamic test on each device, were combined. The entire characterization process is controlled by software that steps the wafer and then intiates a measurement. The complete system (Figure 1A) consists of the Polytec Micro System Analyzer hardware running the Scanning Vibrometer Software, a SUSS PA200 Probe Station equipped with the Measurement Microscope Head, probe station controller hardware, and the SUSS ProberBench™ Operating System.

The first step is to align the wafer, which programs the locations of the structures on the wafer. With this information, the software generates a wafer map. The next step is to define the measurement parameters for the vibration characterization of the membrane. For the membrane array MEMS device, a grid consisting of 6 to 9 measurement points (Figure 1B, top) is fitted to a single membrane structure. After these two steps, the software is ready to initiate the step-and-repeat measurements on the MEMS device. Beginning at the first membrane, the system steps to each membrane on the wafer as originally programmed. On each membrane, a scanning vibrometer measurement is performed within 2 to 3 seconds (Figure 1C and Figure 1B, bottom) and saved together with the device ID. As a result, the full wafer map is measured and frequency spectra as well as deflection shapes of all devices are available (Figure 1D).

Download Application Note VIB-M-04 "Semiautomatic, Wafer-Level Measurements of MEMS Dynamics" (PDF) >>>

Measurements on a MEMS Comb Drive

Electrostatic comb drives are actuators where two interdigitated comb structures can be moved together or apart by applying voltage to either of the two comb electrodes. Although the drive is designed for in-plane motion, the amount of residual out-of-plane motion is easily measured
by laser vibrometry, giving a measure of the success of the design and manufacturing processes.

The comb drive shown in Figure 2A was examined first using the MSA-400’s scanning white light interferometer. The geometry data output is presented in Figure 2B. Then the out-of-plane vibration measurements were made using the laser-Doppler vibrometer mode (Figure 2C, out-of-plane vibration spectrum; Figure 2D, animated out-of-plane deflection shape). The real-time measurement capability allows any suitable broadband waveform source to drive the device. Focusing on the resonance frequency determined by laser vibrometry, in-plane measurements were made on the same comb drive using the stroboscopic system. An in-plane vibration spectrum (Bode plot) can be determined from stepped sine measurements (Figure 2E), and the motion can be visualized as a continuous video (Figure 2F).