Abstract
In the last decades, microelectromechanical systems have been increasing their number of degrees of freedom and their structural complexity. Hence, most recently designed MEMSs have required higher mobility than in the past and higher structural strength and stability. In some applications, device thickness increased up to the order of tens (or hundred) of microns, which nowadays can be easily obtained by means of DRIE Bosch process. Unfortunately, scalloping introduces stress concentration regions in some parts of the structure. Stress concentration is a dangerous source of strength loss for the whole structure and for comb-drives actuators which may suffer from side pull-in. This paper presents an analytical approach to characterize stress concentrations in DRIE micro-machined MEMS. The method is based on the linear elasticity equations, the de Saint-Venant Principle, and the boundary value problem for the case of a torsional state of the beam. The results obtained by means of this theoretical method are then compared with those obtained by using two other methods: one based on finite difference discretization of the equations, and one based on finite element analysis (FEA). Finally, the new theoretical approach yields results which are in accordance with the known value of the stress concentration factor for asymptotically null radius notches.
Highlights
The wide range of applications has made MEMS more complicated. Their mechanical structure and internal stress state become more complex. In many of those applications, MEMS are called to interact with the environment and so they need high aspect ratios, which can be achieved by manufacturing them via Deep-Reactive Ion Etching (DRIE) process
Since this stress concentration gives rise to evident loss of structural strength for silicon, it is important to take into account the effects of scalloping on stress concentration in this kind of structures
Three different methods are proposed for stress concentration characterization of silicon DRIE micromachined structures
Summary
Interest in microelectromechanical systems devices has steadily increased in the last years.Micro-scale technologies have proven to be very effective, playing a prominent role in a wide variety of applications from different fields, such as drug delivery [1,2,3,4,5], aerospace [6,7], medical diagnosis [8,9], surgical applications [10,11,12], and cell manipulation [13,14,15].Since 2013 [16,17], a new class of MEMS, equipped with Conjugate Surface Flexure Hinges (CSFH) has been developed [18,19] and fabricated [20]. These systems consist essentially of micro compliant mechanisms where the flexure hinges are manufactured as CSFHs. These systems consist essentially of micro compliant mechanisms where the flexure hinges are manufactured as CSFHs According to the CSFH design, the center of each arc is coincident with the center of the elastic weights of the curved beam [21]
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