  Chaotic systems, presenting complex and non-reproducible dynamics, may be
found in nature from the interaction between planets to the evolution of the
weather, but can also be tailored using current technologies for advanced
signal processing. However, the realization of chaotic signal generators
remains challenging, due to the involved dynamics of the underlying physics. In
this paper, we experimentally and numerically present a disruptive approach to
generate a chaotic signal from a micromechanical resonator. This technique
overcomes the long-established complexity of controlling the buckling in
micro/nano-mechanical structures by modulating either the amplitude or the
frequency of the driving force applied to the resonator in the nonlinear
regime. The experimental characteristic parameters of the chaotic regime,
namely the Poincar\'e sections and Lyapunov exponents, are directly comparable
to simulations for different configurations. These results confirm that this
dynamical approach is transposable to any kind of micro/nano-mechanical
resonators, from accelerometers to microphones. We demonstrate a direct
application exploiting the mixing properties of the chaotic regime by
transforming an off-the-shelf microdiaphragm into a true random number
generator conformed to the National Institute of Standards and Technology
specifications. The versatility of this original method opens new paths to
combine chaos' unique properties with microstructures' exceptional sensitivity
leading to emergent microsystems.
