A Pull‐in Based Test Mechanism for Device Diagnostic and Process Characterization

Abstract

A test technique for capacitive MEMS accelerometers and electrostatic microactuators, based on the measurement of pull-in voltages and resonance frequency, is described. Using this combination of measurements, one can estimate process-induced variations in the device layout dimensions as well as deviations from nominal value in material properties, which can be used either for testing or device diagnostics purposes. Measurements performed on fabricated devices confirm that the 250 nm overetch observed on SEM images can be correctly estimated using the proposed technique.

Auto-calibration of capacitive MEMS accelerometers based on pull-in voltage

“…The proposed calibration method uses the first option to perform the calibration by estimating the full accelerometer details (using the test method proposed by Rocha et al (2008)) and applying ±1 g equivalent test signals (using electrostatic forces) to the actuation Table 1 Example of the test mechanism concept using simulated data…”

“…Moreover, it can be implemented using simple electronic circuits. This concept was introduced by Rocha et al (2008) and it was used to identify processinduced variations in the actual device geometry.…”

“…As already mentioned, these models can be very complex, and therefore the modelling becomes one of the critical parts of the proposed calibration method. More details about the test mechanism can be found in the work by Rocha et al (2008), where all the relevant non-idealities, including fringe-fields, are taken into consideration.…”

“…Initially, the pull-in test mechanism was used (Rocha et al 2008). It should be noted that the model proposed by Rocha et al (2008) and used in this work takes into account the non-linear behaviour of the device, including fringe-fields. The resonance frequency was determined by acquiring the devices free oscillations (in vacuum) followed by a FFT.…”

“…The new concept for auto-calibration introduced here results from previous work on process characterization based on pull-in voltage measurement techniques (Rocha et al 2004(Rocha et al , 2008. In fact, when pull-in voltage measurements are combined with the measurement of the resonance frequency (a single measurement is needed), fabrication process non-idealities, such as over-etching and process asymmetries, can be accurately estimated.…”