Gerold Schröpfer

Lateral optical accelerometer micromachined in (100) silicon with remote readout based on coherence modulation

Abstract A novel type of optical silicon accelerometer is demonstrated. A non-conventional wet etching technique for (100) silicon allows us to make a highly symmetrical seismic mass with a pure lateral translation movement. This ensures a low sensitivity to accelerations that are not along the sensing axis. To detect the displacement of the seismic mass due to accelerations, an optical fiber can be easily and precisely implemented to form a Fabry-Perot interferometer. A detection method based on coherence modulation allows remote acceleration sensing through a fiber-optic link without any electrical link between the measurement region and the signal output. The sensitivity of the demonstrated system is 1.8 V g −1 for a measurement range of ±10 g and a resolution of less than 1mg. Moreover, the fabrication technique and the multiplexing capability of the detection method open the way to a 3D single-chip accelerometer, the measurements of which could be sent directly through a single optical link.

Novel 3D modeling methods for virtual fabrication and EDA compatible design of MEMS via parametric libraries

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.

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

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.

Collective wet etching of a 3D monolithic silicon seismic mass system

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.

VHDL–1076.1 modeling examples for microsystem simulation

Miniaturized, integrated sensors and actuators are a rapidly growing field with great future potential. To further promote their use, specialists must make them more accessible to system designers. This can be done through behavioral modeling of sensors and actuators using analog hardware description languages. The resulting models can be used in conjunction with models of the associated electronics to simulate a complete microsystem. This chapter presents VHDL 1076.1 modeling and simulation considerations applied to this field.

Global model generation for a capacitive silicon accelerometer by finite- element analysis

A method to evaluate capacitance based on parameter extraction from finite- element analysis as well as a global model for a novel silicon microfabricated accelerometer are presented. Mechanical simulations have been performed and results are coupled with the capacitance-evaluation method to compute the static and dynamic response of the accelerometer. Using both mechanical data and capacitance data, a global model for the accelerometer is generated with models written in Hardware Description Language for Analogue device (HDL- A(TM)). An improvement of the capacitive displacement detection technique is obtained

MEMS System-Level Modeling and Simulation in Smart Systems

MEMS are miniaturized sensors or actuators and are essential to enabling “smart systems” to interact with their physical environment. These devices add the “ears,” “eyes,” “noses,” and “touch” to these systems. The system-level modeling of MEMS requires considering not only the multi-physical behavior of these devices but also their electronic readout circuitry and packaging. This chapter describes a methodology for MEMS system-level design and its implementation in commercially available software. We introduce the Coventor MEMS+® environment for creating system-aware MEMS models, an approach based on a library of 3-D, high-order parametric finite elements. Model-order reduction techniques are employed to reduce the complexity of the multi degree-of-freedom models, to speed up simulation time and to provide a path for designing MEMS together with electronic hardware. The influence of the package surrounding the MEMS device can be simulated by combining traditional finite element simulations with the new methodology of MEMS+. Finally, we discuss the virtual co-development of embedded software and MEMS hardware.

Comparison between an optical and a capacitive transducer for a novel multiaxial bulk-micromachined accelerometer

Recently, we demonstrated the feasibility of a novel 3D silicon bulk-micromachined accelerometer with an optical or a capacitive read-out. In this paper we will compare both detection techniques, and also show their potentials and limitations. The mechanical elements of the accelerometers are fabricated by an unconventional wet etching process of (100) silicon, resulting in symmetrically suspended seismic masses with a high lateral sensitivity and very low transverse sensitivities. For the detection of the seismic mass displacement under the effect of an acceleration, two possibilities are investigated. Firstly, by forming a Fabry- Perot cavity between the seismic mass and the output of an optical fiber, the acceleration can be sensed by measuring the optical path change. Secondly, comb shaped electrodes have been implemented to form a capacitive transducer. Both techniques can be used to build a 3D accelerometer system. Finally, we show that the noise floors of both devices are on the same order of magnitude, leading to a potentially high sensitivity (down to 1 (mu) g/(root)Hz). The optical device shows the advantage of multiplexing capability, passive fiber alignment, distant read-out, and immunity to electromagnetic interference. The capacitive transducer has beside the general advantages of an electrostatic transducer (such as possible closed loop-operation, wide temperature range, low power operation) a linear capacitive change versus displacements.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Capacitive detection method evaluation for silicon accelerometer by physical parameter extraction from finite element simulations

A capacitance evaluation method based on the extraction of physical parameters from finite element (FE) analysis is presented. Mechanical simulations and this capacitance evaluation method were applied to a new, highly symmetrical, silicon accelerometer in view of globally modeling the sensor system. The commercial hardware description language HDLA/sup TM/ is used to develop a compact behavioral macromodels for SPICE simulators.