In high-temperature applications, such as pressure sensing in turbine engines and compressors, high-temperature materials and data retrieval methods are required. The microelectronics packaging infrastructure provides high-temperature ceramic materials, fabrication tools, and well-developed processing techniques that have the potential for applicability in high-temperature sensing. Based on this infrastructure, a completely passive ceramic pressure sensor that uses a wireless telemetry scheme has been developed. The passive nature of the telemetry removes the need for electronics, power supplies, or contacts to withstand the high-temperature environment. The sensor contains a passive LC resonator comprised of a movable diaphragm capacitor and a fixed inductor, thereby causing the sensor resonant frequency to be pressure-dependent. Data is retrieved with an external loop antenna. The sensor has been fabricated and characterized and was compared with an electromechanical model. It was operated up to 400 C in a pressure range from 0 to 7 Bar. The average sensitivity and accuracy of three typical sensors are: 141 kHz Bar 1 and 24 mbar, respectively.
The results of this paper are pertinent to micromachined integrated chemical sensors, infrared sources and hotplates, among others. We report on the operation and characterization of micromachined complementary metal-oxide semiconductor (CMOS) microstructures with integrated CMOS polysilicon heaters at temperatures up to 1200 K. The new results concern the stability of integrated CMOS polysilicon heaters under such extreme conditions. Two resistance drift phenomena appearing above the polysilicon recrystallization temperature T cr ≈ 870 K were identified. The first is a reversible resistance relaxation leading to resistance changes of several tens of per cent. Relaxation times are of the order of minutes and point to a thermally activated process. The second drift mechanism leads to slow resistance changes, for example, 3% after six hours above T cr . Temperature calibration of such devices supported by finite element simulations is proven to be feasible and reliable. Despite the large temperature gradients in the heated microstructures, natural convection in the surrounding gas was found to be ineffective in comparison with heat conduction.
This paper describes a micromachined magnetic field sensor based on magnetic resonant structures. A micromechanical resonator fabricated using surface micromachining techniques is modified so as to incorporate a magnetic material. The shift of the fundamental mechanical resonant frequency of the device, caused by the interaction of the external magnetic field and the magnetic component of the resonant system, is used to determine the amplitude or the direction of the external field. We have designed, fabricated and tested two types of micromachined magnetic field sensors relying on the proposed principle of operation. The fabrication of the sensors follows CMOS-compatible and low temperature processes based on surface micromachining. Devices have been fabricated which exhibit a minimum resolution of 45 • at 30 µT or less, at an excitation voltage of 10 V, demonstrating their utility as a magnetic compass. The power consumed to actuate the resonator is on the order of 20 nW. A theoretical model of the magnetic field sensor was developed using vibration analysis and nonlinear deflection theory. Good agreement was observed between the predicted and observed behavior of the compass.
This invited review of the merging of MEMS and IC technology includes a summary of the current technological approaches to IC MEMS, illustrations by selected IC MEMS microtransducer demonstrators, an outline of the MEMS CAD tools SOLIDIS and ICMAT, and a critical evaluation.
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