Fabrication of a new highly-symmetrical, in-plane accelerometer structure by anisotropic etching of (100) silicon

Abstract

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.

Micromachined High-Aspect-Ratio Parylene Spring and Its Application to Low-Frequency Accelerometers

“…1(c)]. This is followed by a parylene-C deposition with a thickness of [10][11][12][13][14][15][16][17][18][19][20] to refill the trenches [see Fig Clearly, the parylene-C deposition is conformal, and the film thickness is almost uniform even inside the deep trench. This is because the mean free path of parylene molecules is as small as a few cm, and also because the sticking coefficient, which is defined by the ratio between the number of molecules reacting with a radical chain end and the number of incident monomer molecules onto the surface, is as low as at room temperature [28].…”

“…The final goal of the present study is to develop micro-fabrication technology to be used to produce soft springs for in-plane transducers such as accelerometers [15]- [20] and energy harvesting devices [21], [22]. For these devices, sensitivity to mechanical force should vary by orders of magnitude depending on the direction.…”

Ultrasonic Transducers

“…With (100) wafer, diverse MEMS devices such as accelerometer [44][45][46][47][48], micro optical clips [49][50], acoustic transducers [51], and scanning micro mirrors [52][53] have been fabricated. The reason that (100) wafer is preferred lies in the orientations of (111) planes in it.…”

“…With (100) wafer, not only flat beams, oblique or even vertical beams are also obtainable [46][47][48]. Fig.…”

Estudio, Modelado e Implementación Paralela de Sistemas Celulares Utilizados en Microfabricación

“…Entre los dispositivos basados en tecnología MEMS destacan los sensores de presión [81], acelerómetros [82], sensores de flujo de gas [83], microactuadores [84] o microinyectores [85]. La industria basada en MEMS ha sufrido un crecimiento continuo [86].…”