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MEMS-based micro speakers are attractive candidates as sound transducers for smart devices, particularly wearables and hearables. For such devices, high sound pressure levels, low harmonic distortion and low power consumption are required for industrial, consumer and medical applications. The ability to integrate with microelectronic circuitry, as well as scalable batch production to enable low unit costs, are the key factors benchmarking a technology. The Nanoscopic Electrostatic Drive based, novel micro speaker concept presented in this work essentially comprises in-plane, electrostatic bending actuators, and uses the chip volume rather than the its surface for sound generation. We describe the principle, design, fabrication, and first characterization results. Various design options and governing equations are given and discussed. In a standard acoustical test setup (ear simulator), a MEMS micro speaker generated a sound pressure level of 69 dB at 500 Hz with a total harmonic distortion of 4.4%, thus proving the concept. Further potential on sound pressure as well as linearity improvement is outlined. We expect that the described methods can be used to enhance and design other MEMS devices and foster modeling and simulation approaches.
Wafer level vacuum packaging of scanning micro-mirrors using glass-frit and anodic bonding methods
(2013)
In der Arbeitsgruppe integrierte Siliziumsysteme des Fraunhofer IPMS werden am Standort Cottbus innovative Anwen-dungen eines neuartigen nanoskopischen elektrostatischen Antriebs (nanoskopic electrostatic drive – NED) untersucht. Eine der vielversprechendsten Anwendungen sind Lautsprecher. Vollständig aus Silizium gefertigte MEMS-Lautsprecher auf Basis von NED-Biegeaktoren werden vor den akustischen Messungen mechanisch und elektrisch cha-rakterisiert. Beidseitig eingespannte elektrostatisch betriebene in-plane NED-Aktoren werden dabei über einen Fre-quenzbereich von 20 Hz bis 20 kHz angeregt. Dabei sind die Strukturen oft verdeckt, was ihre Charakterisierung er-schwert. Es werden zerstörungsfreie optische Methoden präsentiert, mit deren Hilfe die Bestimmung der mechanischen Schwingungseigenschaften einzelner Aktoren ermöglicht wird sowie die Beweglichkeit im verdeckten Zustand nach-gewiesen werden kann.
MEMS converter for interacting with a volume flow of a fluid and method of manufacturing the same
(2018)
Mikromechanisches System zum Durchstimmen von Lasern (Micromechanical system for tuning of lasers)
(2015)
Acoustic impedance matching structures can be used on capacitive micromachined ultrasonic transducers (CMUT) to increase acoustic energy transmission into the load medium. Our contribution contains a systematic study of the viability of the two-photon-polymerization lithography process for the fabrication of acoustic impedance matching metamaterials. For this purpose, acoustic simulations were conducted to find optimized dimensions of the matching structure. Based on the proposed dimensions, parameter sweeps were manufactured on substitute substrates, resulting in a viable parameter space for the direct fabrication on CMUT devices.
Additive manufacturing using two-photon polymerization (TPP) lithography is increasingly used in industry and research. Parameter sweeps of cuboid structures fabricated using TPP lithography were investigated across the parameters of the laser power and scan speed to find dependent mechanical material properties. The employed photoresists were examined using Raman spectroscopy to find the degree of conversion (DC) of monomer to polymer, and subsequently, micro- or nanoindentation was used to find Young’s modulus (E). For the photoresist IP-Dip, the attained DC and E ranged from 20% to 45% and 1 to 2.1 GPa, respectively. The results were compared with reports found in the literature. For IP-Q, the attained DC and E ranged from 53% to 80% and 0.5 to 1.3 GPa, respectively. The characterized properties of IP-Q manifest as the current state of knowledge of the material.
MEMS-based miniature near-infrared spectrometer for application in environmental and food monitoring
(2014)
We present two novel micro scanning mirrors with large aperture and HR dielectric coatings suitable for high power laser applications in a miniaturized laser instrument. An electrostatic driven 2D-raster scanning mirror with 5×7.1mm aperture is used for dynamic steering of the ps-laser beam of the laser cutting process. A second magnetic 2D-beam steering mirror enables a static beam correction of a hand guided laser instrument. Optimizations of a magnetic gimbal micromirror with 6 mm × 8 mm mirror plate are presented; here static deflections of 3° were reached. Both MEMS devices were successfully tested with a high power ps-laser at 532nm up to 20W CW.
Integrated optical interconnections in silicon chips have the potential to replace electrical interconnects between integrated circuits thanks to their high bandwidth and low energy communication promises. A silicon dielectric waveguide can be etched through the full thickness of a silicon substrate providing a monolithically integrated solution for 2.5D and 3D photonic architectures. The optical through-silicon waveguide design presented here is based on Finite Difference Time Domain simulations, while the fabrication takes advantage of the innovative plasma cryo-etching process that provides smooth sidewalls and tapering angle tunability. Such structures can provide effective mode size conversion, therefore favoring the coupling of external light sources to photonic integrated circuits and the stacking of multiple optically interconnected dies.
MEMS transducer for interacting with a volume flow of a fluid, and method for producing the same
(2023)
Translatory MOEMS actuator and system integration for miniaturized Fourier transform spectrometers
(2014)
For several years, Fraunhofer IPMS has been developing a new type of an electrostatic MEMS actuator, called nanoscopic electrostatic drive - NED. Since the first publication in 2015, the project group at IPMS has succeeded in providing lateral actuators, which serve as innovative drives in applications such as micro-positioners or micro-speakers. These applications require a high long-term stability of the drive in order to ensure that the system operates as desired. For this purpose, the reliability of such novel lateral electrostatic actuators was evaluated. Long-term studies of NED actuators have shown that different degradation phenomena can occur during operation. The experiments indicate that high electric fields in the range of several MV/m are one of the most important triggers of the degradations observed. On the one hand, they lead to anodic oxidation occurring at the boundary layers between the NED electrodes and neighbored insulators, which results in corrosion of the silicon electrodes. On the other hand, geometry-based field enhancement far from the insulator interfaces lead to permanent field emission, which causes dark discharges in the electrode gap. This in turn leads to cold plasma oxidation and the growth of oxide b ulges on the electrode surfaces. In the course of the experiments, it was shown that corrosion does not take place in a vacuum and can be avoided with the help of passivation layers. Non silicon oxides, e.g. Al2O3, are well suited as passivation layers. Although they bring additional flexural rigidity to the overall structure, which changes the mechanical behavior of the actuators, they increase the effective relative permittivity in the electrode gap, which in turn makes the actuators more effective. Thanks to the passivation coating,the lifespan of the NED actuators was increased and they can become even more effective by choosing a layer with suitable properties.
We present results for a microsystem inchworm motor based on Nanoscopic Electrostatic Drive (NED) actuators, fabricated by single crystalline silicon bulk micro-machining on a silicon-on-insulator (SOI) wafer. Actuator elements can easily be added to or removed from the inchworm drive allowing a high adaptability of force and contact area with the movable surface as well as an efficient use of the system’s footprint. In principle, travel ranges of several mm can be easily obtained due to very modular design of the system. The presented inchworm drive is capable of controllable motion up to 1 mm and can generate a force of 1.4 mN at 130V corresponding to a force density of 0.8 mN/mm2 with an average maximum DC power consumption of 11.8 muW in each cycle. Furthermore, the voltage-displacement characteristics of the actuator element was validated by finite element method (FEM).
Optical interconnections are a promising step for-ward to overcome the intrinsic limitations of electrical inter-connections in integrated circuits. In this work, we present a finite element method (FEM) simulation study of a dielectric waveguide etched through the full thickness of a silicon substrate. In particular, it is investigated the effect of the bridge-to-core size ratio on the first two supported modes. Then, the influence of the waveguide sidewalls tapering angle on the three-dimensional beam propagation is studied. Such optical through-silicon waveguide (OTSW), if nonadiabatically tapered can provide effective mode size conversion and favour the coupling of external light sources to photonic integrated circuits.
Structuring polymers on micro-electro-mechanical-systems (MEMS) for the manufacturing of acoustical and optical metamaterials using the two-photon polymerization process depends on reliable and controllable regulation of the intensity. Reflecting surfaces, diffracting elements and structures with poor heat dissipation can be problematic obstacles for the incident focused and pulsed laser beam. Thermal and optical simulations were performed and compared to test structures. A compensated fabrication approach was successfully applied to create optimized conditions in the polymerized volume.
A large deflection polymer bending actuator was employed in the design of an integrated micro-lens with electrically adjustable focal length. This micro-lens consisted of micro-fluidic chambers bonded together and sealed by an elastomeric lens membrane to which the polymer actuator has been attached. For focal length optimization, the chambers could be filled with fluids of different refractive indices. The multilayered actuator of radial shape and the variable micro-lens chip design were optimized using 2D FEM simulations. Fabrication steps included bonding of polymer actuator stack with the elastomeric lens membrane on a micro-machined silicon wafer. For a tunable micro-lens with 3 mm aperture, a tuning range in optical power between 0 and more than 15 dpt was achieved.
Miniaturization of a fast tunable external cavity QCL with customized gratings and MOEMS components
(2014)
In this paper, an in-plane reciprocating displacement micropump for liquids and gases which is actuated by a new class of electrostatic bending actuators is reported. The so-called “Nano Electrostatic Drive” is capable of deflecting beyond the electrode gap distance, enabling large generated forces and deflections. Depending on the requirements of the targeted system, the micropump can be modularly designed to meet the specified differential pressures and flow rates by a serial and parallel arrangement of equally working pumping base units. Two selected, medium specific micropump test structure devices for pumping air and isopropanol were designed and investigated. An analytical approach of the driving unit is presented and two-way Fluid-Structure Interaction (FSI) simulations of the micropump were carried out to determine the dynamic behavior. The simulation showed that the test structure device designed for air expected to overcome a total differential pressure of 130 kPa and deliver a flow rate of 0.11 sccm at a 265 Hz driving frequency. The isopropanol design is expected to generate 210 kPa and pump 0.01 sccm at 21 Hz. The device is monolithically fabricated by CMOS-compatible bulk micromachining processes under the use of standard materials only, such as crystalline silicon, silicon dioxide and alumina.