THESIS
2017
xi, 71 pages : illustrations ; 30 cm
Abstract
With the increasing opportunities offered by the consumer market, the microphone
industry is more important than ever. In this work, the design parameters of capacitive MEMS
microphone was analyzed based on a general one-dimensional (1D) model. The theoretical
sensitivity of the capacitive microphone is shown to be a nonlinear function of diaphragm
radius (a), thickness (h), back chamber length (L), the residual stress (σ
rs) and some other
parameters. Based on the general 1D model, a critical diaphragm radius was found located at
the inflection point of the sensitivity - radius scaling analysis curve, which reflects the
minimal equivalent spring constant of the microphone. We then modified this 1D model by
revising the diaphragm as a composited layer that is fitted to the PolyMU...[
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With the increasing opportunities offered by the consumer market, the microphone
industry is more important than ever. In this work, the design parameters of capacitive MEMS
microphone was analyzed based on a general one-dimensional (1D) model. The theoretical
sensitivity of the capacitive microphone is shown to be a nonlinear function of diaphragm
radius (a), thickness (h), back chamber length (L), the residual stress (σ
rs) and some other
parameters. Based on the general 1D model, a critical diaphragm radius was found located at
the inflection point of the sensitivity - radius scaling analysis curve, which reflects the
minimal equivalent spring constant of the microphone. We then modified this 1D model by
revising the diaphragm as a composited layer that is fitted to the PolyMUMPs process. The
modified 1D model was applied to predict the critical design parameters of the capacitive MEMS microphone to be fabricated by the PolyMUMPs process, and the critical diaphragm
radius of 300 μm is obtained. The agreement between experimental result and theoretical
prediction verifies our general 1D model, and proves the critical value can be used to guide
the design of capacitive microphone.
As parylene can be utilized in the MEMS microphone field such as the movable
diaphragm and packaging material for its great dielectric properties and high coating
uniformity, the properties of parylene should be further studied. In this work, a comparative
study of the viscoelasticity of parylene C was presented by using Nanoindentation technology
and Molecular Dynamics (MD) simulations. By applying different types of loadings on
parylene C films at different temperatures and frequencies, the complex modulus, relaxation
modulus and glass transition temperature (T
g) of the parylene C were obtained. The predicted
T
g determined from the temperature-dependent density change in the MD model is consistent
with the results in the measurements and previous works. Furthermore, with
Time-Temperature Superposition Principle (TTSP), the master curve of parylene C were
successfully determined on its creep and relaxation behaviour, for the first time, which is
critical for the parylene reliability study of bio-MEMS devices.
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