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Technical University of Munich

Reliable Damping Simulation of Highly Perforated MEMS by Physical Compact Modelling

Figure 1: Out-of-plane Acceleration Sensor with multiple layers, perforations and cut-outs
Fig.2: System-level damping model of a perforated MEMS with compact models accounting for the gap and fluidic resistances for perforations and boundary. Each model contains geometry parameters as well as variables accounting for environmental aspects, like surrounding gas or pressure.

Accurate and fast modeling of damping effects in high-end MEMS devices, like acceleration sensors (Fig 1) is a major challenge due to

  • small feature sizes and large aspect ratios,
  • complex device geometries & a generally very high number of perforations,
  • multiple energy domains involved, e.g. Squeeze Film Damping (SQFD),
  • low pressure packaging, leading to Knudsen Numbers Kn > 0.1.

In order to accurately predict damping in MEMS it is necessary to have models that

  • scale with shape and size of the designed device,
  • include external parameters, like surrounding gas or ambient pressure,
  • account for transition regions between differently perforated areas.

We approach this challenge by designing compact models and implement them in a finite Kirchhoffian Network, thus enabling cross-domain simulation (i.e. fluidic damping decreasing mechanical movement). This allows us to run the simulation in standard circuit simulators, speeding up the simulation process significantly.

Figure 3: Motion of the acceleration sensor in Figure 1 under mechanical acceleration captured by Laser-Doppler-Vibrometry.
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