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We present a simple two-step etching process based on anisotropic wet etching of (100) silicon. As one example a system of three seismic masses on one chip has been fabricated. All three masses are symmetrically suspended by four high aspect ratio beams. The highly symmetrical design minimizes mechanical cross-sensitivities. Moreover, the three devices exhibit almost perfect rectangular alignment due to the orientation along the directions of the silicon crystal. Besides experimental results, design rules for the photolithography-masks are presented.

In this paper, we present a silicon bulk-microfabrication method which helps to overcome simultaneously several limitations of multi-axis micro-accelerometers. The method demonstrates an orginal solution to the building of a symmetrical structure by using double-side wet etching. This is a low-cost alternative to existing techniques for the fabrication of highly-symmetrical, single crystal silicon structures. The proposed approach provides low mechanical cross-sensitivities as well as the possibility of a batch fabrication process of the whole three-dimensional device without loss of accuracy due to assembly operation. For the fabrication of thin suspended beams with vertical sidewalls, a non-conventional alignment of from the wafer flat was used. This alignment allows one to fabricate two perpendicular devices on one wafer in the same etching step. The etching was performed with a simple standard wet etching process in a KOH solution. A number of structures were fabricated to demonstrate the feasibility of this method. Aspect ratios (beam height over beam thickness) of over 35 were easily achieved. Undercut directions were determined and design rules for the mask layout were established. To describe the mechanical behaviour of the fabricated structure, an analytical model was implemented and a finite-element simulation was performed. First measurements of the seismic mass displacement were performed with an optical comparator, and they agree with theoretically obtained results. The new design offers the possibility of a two-axis accelerometer system on one wafer, consisting of two sensor elements rotated by . A three-axis monolithic accelerometer system with intrinsic perpendicular alignment due to the rectangular symmetry of the (100) planes can be realized, by including a third sensor element sensitive to vertical accelerations.

This paper provides a brief summary of the state-of-the-art of MEMS-specific modeling techniques and describes the validation of new models for a parametric component library. Two recently developed 3D modeling tools are described in more detail. The first one captures a methodology for designing MEMS devices and simulating them together with integrated electronics within a standard electronic design automation (EDA) environment. The MEMS designer can construct the MEMS model directly in a 3D view. The resulting 3D model differs from a typical feature-based 3D CAD modeling tool in that there is an underlying behavioral model and parametric layout associated with each MEMS component. The model of the complete MEMS device that is shared with the standard EDA environment can be fully parameterized with respect to manufacturing-and design-dependent variables. Another recent innovation is a process modeling tool that allows accurate and highly realistic visualization of the step-by-step creation of 3D micro-fabricated devices. The novelty of the tool lies in its use of voxels (3D pixels) rather than conventional 3D CAD techniques to represent the 3D geometry. Case studies for experimental devices are presented showing how the examination of these virtual prototypes can reveal design errors before mask tape out, support process development before actual fabrication and also enable failure analysis after manufacturing.

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