Christoph Glacer

Modeling Methods of MEMS Micro-Speaker with Electrostatic Working Principle

The market for mobile devices like tablets, laptops or mobile phones is increasing rapidly. Device housings get thinner and energy efficiency is more and more important. Micro-Electro-Mechanical-System (MEMS) loudspeakers, fabricated in complementary metal oxide semiconductor (CMOS) compatible technology merge energy efficient driving technology with cost economical fabrication processes. In most cases, the fabrication of such devices within the design process is a lengthy and costly task. Therefore, the need for computer modeling tools capable of precisely simulating the multi-field interactions is increasing. The accurate modeling of such MEMS devices results in a system of coupled partial differential equations (PDEs) describing the interaction between the electric, mechanical and acoustic field. For the efficient and accurate solution we apply the Finite Element (FE) method. Thereby, we fully take the nonlinear effects into account: electrostatic force, charged moving body (loaded membrane) in an electric field, geometric nonlinearities and mechanical contact during the snap-in case between loaded membrane and stator. To efficiently handle the coupling between the mechanical and acoustic fields, we apply Mortar FE techniques, which allow different grid sizes along the coupling interface. Furthermore, we present a recently developed PML (Perfectly Matched Layer) technique, which allows limiting the acoustic computational domain even in the near field without getting spurious reflections. For computations towards the acoustic far field we us a Kirchhoff Helmholtz integral (e.g, to compute the directivity pattern). We will present simulations of a MEMS speaker system based on a single sided driving mechanism as well as an outlook on MEMS speakers using double stator systems (pull-pull-system), and discuss their efficiency (SPL) and quality (THD) towards the generated acoustic sound.

Silicon microspeaker with out-of-plane displacement

In this paper a new way of increasing the enclosed air volume between the stator and the membrane of an electrostatic loudspeaker is introduced. Instead of using a thicker sacrificial layer, a stress-induced self-raising of the stator is utilized. Corrugation grooves in combination with highly tensile silicon nitride rings are causing a deflection of the stator after the release etch. For a stator diameter of 1 mm an out of plane deflection of up to 59 μm could be measured. On the electrical side, a pull-in voltage between 4 V and 16 V for the membrane and 27 V to 67 V for different stator variants was detected. In the free-field, a sound pressure level of 50 dB SPL at 10 kHz in 10 cm distance was measured for a small array. Variations of design and layout as well as technology parameters were varied to determine the ideal system with regard to maximum deflection, displaced volume and mechanical stability.

New ways of measuring the pull-in voltage and transient behavior of parallel-plate capacitive MEMS transducers

In this paper we introduce two new ways of measuring the pull-in voltage and the transient behavior of parallel-plate capacitive microelectromechanical systems (MEMS) transducers. The advantages in the measurement speed and resolution of the so-called fast MEMS test will be discussed. Also an enhanced method, the time-resolved dynamic measurement, will be shown. With the second method, we can visualize the integral displacement of a membrane while measuring the voltage drop of a high-frequency signal over a shunt resistor/capacitor. With a more advanced charge amplifier circuit, also a force-free resonance measurement of the membrane and electrode is possible in one step. All this offers a robust and cheap option for tracing moving structures without the need of an optical line of sight.

Modeling of an electrostatically actuated microelectromechanical (MEMS) speaker system

The market for tablets, laptops and mobile devices is increasing rapidly. Device housings get thinner and energy efficiency plays a major role for battery-powered devices. Microelectromechanical (MEMS) loudspeakers, fabricated in complementary metal oxide semiconductor (CMOS) compatible technology merge energy efficient driving technology with cost economical fabrication processes. Fabricating these devices is a elaborating and expensively task. Therefore, the need of computer models, capable of precisely simulating the multi-field interactions is strongly increasing. We use a system of coupled partial differential equations (PDEs) describing the interaction between the electrostatic, mechanical and acoustical field and apply finite element method FEM to solve them. Additionally, we fully take nonlinear effects like large deformations or stress stiffening effects into account. Mortar FEM is used, to efficiently handle the coupling between mechanical and acoustical field. In combination with special boundary conditions, like perfectly matched layers (PML) truncated propagation regions can be applied in the model. We will present simulations of a MEMS speaker system based on a single sided driving mechanism starting at the electric potential applied on the two electrodes and resulting in the generated sound pressure level (SPL).