Read-out calibration of a SOI capacitive transducer using the pull-in voltage

Abstract

The pull-in voltage of a parallel plate electrostatic transducer is used to determine the amount of over-etching in fabricated devices. A detailed analysis of the capacitor behaviour over the full displacement range yields a model, which is used to describe the relation between over-etching and measured pull-in voltage. SEM photos confirm the over-etching measurement based on pull-in voltage. This information is used to linearize a charge amplifying read-out circuit with an intrinsic nonlinear transfer function. The remaining nonlinearity error of the read-out is less than 1%.

Micromechanical Characterization of Polysilicon Films through On-Chip Tests

“…For some test structures (see, e.g., [ 20 , 21 , 22 ]), the pull-in voltage has been suggested as a possible feature of the overall structural response providing insights into the micromechanical details of the device, on top of all of the over-etch. Figure 5 gathers the values of the voltage corresponding to the pull-in instability in the case of either lateral or rotational actuation.…”

“…A variation of the Young’s modulus is shown to affect the pull-in voltage almost linearly, while the over-etch has a nonlinear impact. This observation is essential if one aims to characterize the device by using the pull-in voltage only, since that would require a one-to-one relation between the varying parameter and [ 21 ]. This issue is further illustrated in Figure 6 , through the whole response of the system for two different values of O leading to very similar values of the pull-in voltage.…”

“…Other methods use embedded structures for device characterization [ 11 , 18 , 19 ]. The deviation of the pull-in voltage from the expected value can be also adopted for process characterization [ 20 , 21 , 22 ]; however, the pull-in value is very sensitive to the accuracy of the model. Alternative stochastic methods are instead based on, e.g., Monte Carlo and spectral simulations and stochastic collocation; see [ 23 , 24 , 25 , 26 , 27 ].…”