Christina Leinenbach

A new capacitive type MEMS microphone

A new capacitive type of MEMS microphone is presented. In contrast to existing technologies which are highly specialized for this particular type of application, our approach is based on a standard process and layer system which has been in use for more than a decade now for the manufacturing of inertial sensors. For signal conversion, a mixed-signal ASIC with digital sampling of the microphone capacitance is used. The MEMS microphone yields high signal-to-noise performance (58 dB) after mounting it in a standard LGA-type package. It is well-suited for a wide range of potential applications and demonstrates the universal scope of the used process technology.

A 10 μm thick poly-SiGe gyroscope processed above 0.35 μm CMOS

This paper describes a monolithically integrated omegaz-gyroscope fabricated in a surface-micromaching technology. As functional structure, a 10 mum thick Silicon-Germanium layer is processed above a standard high voltage 0.35 mum CMOS-ASIC. Drive and Sense of the in plane double wing gyroscope is fully capacitively. Measurement of movement is also done fully capacitively in continuous-time baseband sensing. For characterization, the gyroscope chip is mounted on a breadboard with auxiliary circuits. A noise floor of 0.01 degs/sqrt(Hz) for operation at 3 mBar is achieved.

SIGEM, low-temperature deposition of Poly-SiGe MEMs structures on standard CMOS circuits

Fabrication of surface-micromachined structures by a post-processing module above standard IC circuits is an efficient way to produce monolithic microsystems, allowing nearly independent optimization of the circuitry and the MEMS process. However, until now the high-temperature steps needed for deposition of poly-Si have limited its application. SiGeM explores the possibilities offered by the low-temperature (450°C) deposition and structuring of poly-SiGe layers, which is compatible with the temperature budget of fully-processed standard IC wafers. In the SiGeM project several low-temperature deposition methods (CVD, PECVD, LPCVD) were developed, and were evaluated with respect to growth rate and material quality. The interconnection technology to the underlying CMOS circuitry was also developed. The capabilities of this new integration technology will be demonstrated in a monolithic high-performance rate-of-turn sensor, currently considered the most demanding MEMs application in terms of material properties of the structural layer (thickness > 10mm, stress gradient < 0.3MPa/mm) and signal processing circuitry (capacitance resolution in the aF range, SNR > 110 dB). System partitioning will combine analog and DSP circuit techniques to maximize resolution and stability. Parasitic electrical coupling within different parts of the system has been analyzed, and countermeasures to reduce it have been incorporated in the design. The feasibility of the approach has already been proved by preliminary characterization of working prototypes containing released microstructures deposited on top of preamplifier circuits built on a 0.35mm, 5-metal, 2-poly, standard CMOS process from Philips Semiconductors. Resonance frequencies are in good agreement with predictions, and quality factors above 8000 have been obtained at pressures of 0.8 mTorr. Measured SNR confirms the capability to achieve a resolution of 0.015°/s over a bandwidth of 50 Hz.

Chapter Twenty Eight – Surface Micromachining

Publisher Summary Surface Micromachining is called so because instead of crystal silicon substrate as functioning material this new technology uses thin film layers deposited on the substrate surface as functioning material. This chapter explains the different types of surface micromachining processes. It details the polycrystalline silicon-based micromachining in a very detailed way with the help of photographs. Integrations concepts are viewed in a very effective manner. Monolithic integration is a very good choice for evaluation of capacitive surface-micromachined sensors, given their low base capacitance values and more supported by shrink tendencies aggressively targeting the size of the sensor core. Monolithic integration is a potential option to be considered not mainly for cost but for performance arguments. This lesson explains the role of metallic thin films in MEMS. It explains the different properties of metals in MEMS applications in a very effective way, which includes electrical conductivity, low temperature processing, etc. This chapter throws some light on SOI-wafer-based surface micromachining technologies, which is available as MEMS foundry technologies. The main advantage is that the moveable structures are made from a single crystalline device layer hence have excellent, well-defined mechanical properties and high reliability. The SOI-wafer-based surface micromachining technology has been developed for capacitive inertial sensors. To improve the electrical behavior of these types of device, refilled insulation trenches are processed prior to the fabrication of the mechanical structures.

Chapter 24 – Surface Micromachining

Surface Micromachining is so-called because instead of crystal silicon substrate as a functioning material this new technology uses thin film layers deposited on the substrate surface as functioning material. This chapter explains the different types of surface micromachining processes. It details the polycrystalline silicon-based micromachining in a very detailed way with the help of photographs. Integrations concepts are viewed in a very effective manner. Monolithic integration is a very good choice for evaluation of capacitive surface-micromachined sensors, given their low base capacitance values and more supported by shrink tendencies aggressively targeting the size of the sensor core. Monolithic integration is a potential option to be considered not mainly for cost but for performance arguments. This lesson explains the role of metallic thin films in MEMS. It explains the different properties of metals in MEMS applications in a very effective way, which includes electrical conductivity, low-temperature processing, etc. This chapter throws some light on silicononinsulator (SOI)-wafer-based surface micromachining technologies, which are available as MEMS foundry technologies. The main advantage is that the moveable structures are made from a single crystalline device layer hence have excellent, well-defined mechanical properties and high reliability. The SOI-wafer-based surface micromachining technology has been developed for capacitive inertial sensors. To improve the electrical behavior of these types of device, refilled insulation trenches are processed prior to the fabrication of the mechanical structures.