The majority of microelectromechanical system (MEMS) devices must be combined with integrated circuits (ICs) for operation in larger electronic systems. While MEMS transducers sense or control phys ...

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Integrating MEMS and ICs

The majority of microelectromechanical system (MEMS) devices must be combined with integrated circuits (ICs) for operation in larger electronic systems. While MEMS transducers sense or control physical, optical or chemical quantities, ICs typically provide functionalities related to the signals of these transducers, such as analog-to-digital conversion, amplification, filtering and information processing as well as communication between the MEMS transducer and the outside world. Thus, the vast majority of commercial MEMS products, such as accelerometers, gyroscopes and micro-mirror arrays, are integrated and packaged together with ICs. There are a variety of possible methods of integrating and packaging MEMS and IC components, and the technology of choice strongly depends on the device, the field of application and the commercial requirements. In this review paper, traditional as well as innovative and emerging approaches to MEMS and IC integration are reviewed. These include approaches based on the hybrid integration of multiple chips (multi-chip solutions) as well as system-on-chip solutions based on wafer-level monolithic integration and heterogeneous integration techniques. These are important technological building blocks for the More-Than-Moore paradigm described in the International Technology Roadmap for Semiconductors. In this paper, the various approaches are categorized in a coherent manner, their merits are discussed, and suitable application areas and implementations are critically investigated. The implications of the different MEMS and IC integration approaches for packaging, testing and final system costs are reviewed.

/pdf/integrating-mems-and-ics-5evxuk7ch7.pdf

An energy-autonomous, photovoltaic (PV)-driven and MRI-compatible CMOS implantable sensor is presented. On-chip P+/N-well diode arrays are used as CMOS-compatible PV cells to harvest μW's of power from the light that penetrates into the tissue. In this 2.5 mm × 2.5 mm sub-μW integrated system, the in-vivo physiological signals are first measured by using a subthreshold ring oscillator-based sensor, the acquired data is then modulated into a frequency-shift keying (FSK) signal, and finally transmitted neuromorphically to the skin surface by using a pair of polarized electrodes.

A Photovoltaic-Driven and Energy-Autonomous CMOS Implantable Sensor

An energy-autonomous and MRI-compatible CMOS implantable sensor is presented that operates by harvesting the energy of the light which penetrates into the tissue. On-chip P+/N-well diodes are used as on-chip photovoltaic cells and in-vivo physiological data is transmitted neuromorphically to the skin surface.

http://ieeexplore.ieee.org/iel5/5976946/5985982/05986080.pdf

A photovoltaic-driven and energy-autonomous CMOS implantable sensor

This work reports on studies and the fabrication process development of micromechanical silicon-on-insulator (SOI) devices. SOI is a promising starting material for fabrication of single crystal silicon micromechanical devices and basis for monolithic integration of sensors and integrated circuits. The buried oxide layer of an SOI wafer offers an excellent etch stop layer for silicon etching and sacrificial layer for fabrication of capacitive sensors. Deep silicon etching is studied and the aspect ratio dependency of the etch rate and loading effects are described and modeled. The etch rate of the deep silicon etching process is modeled with a simple flow conductance model, which takes into account only the initial etch rate and reaction probability and flow resistance of the etched feature. The used model predicts qualitatively the aspect-ratio-dependent etch rate for varying trench widths and rectangular shapes. The design related loading can be modeled and the effects of the loading can be minimized with proper etch mask design. The basic SOI micromechanics process is described and the drawbacks and limitations of the process are discussed. Improvements to the process are introduced as well as IR microscopy as a new method to inspect the sacrificial etch length of the SOI structure. A new fabrication process for SOI micromechanics has been developed that alleviates metallization problems during the wet etching of the sacrificial layer. The process is based on forming closed cavities under the structure layer of SOI with the help of a semi-permeable polysilicon film. Prototype SOI device fabrication results are presented. High Q single crystal silicon micro resonators have potential for replacing bulky quartz resonators in clock circuits. Monolithic integration of micromechanical devices and an integrated circuit has been demonstrated with the developed process using the embedded vacuum cavities.

/pdf/fabrication-of-soi-micromechanical-devices-45787o8ynn.pdf

Fabrication of SOI micromechanical devices

We report an integrated monolithic micromechanical capacitive pressure sensor circuit based on novel method for fabricating pressure detecting vacuum cavities into buried oxide of SOI-wafer. The method allows fabricating the readout circuit with standard bulk CMOS process. The readout circuit of the pressure sensor is a low-power CMOS relaxation oscillator.

M. Ylimaula

Papers

Monolithic SOI-MEMS capacitive pressure sensor with standard bulk CMOS readout circuit