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MEMS resonators are today widely investigated as a desirable alternative to quartz resonators in real-time clock applications, because of their low-cost, integration capability properties. Nevertheless, MEMS resonators performances are still not competitive, especially in terms of frequency stability and device equivalent resistance (and, then, power consumption). We propose a new structure for a MEMS resonator, with a vertical-like transduction mechanism, which exhibits promising features. The vertical resonator can be fabricated with the low-cost, high performance THELMA technology, and it is designed to be efficiently frequency tunable. With respect to the commonly investigated lateral resonators, it is expected to have lower equivalent resistances and improved large-scale repeatability characteristics.

In this work we present a new approach to fabricate Bulk Acoustic Wave resonators based on reflector-on-membrane structure, on which piezoelectric film and electrodes are deposited as active part. The reflector provides enhancement of the fundamental thickness mode resonance of the piezoelectric layer, and strong attenuation of additional resonances of the membrane structure. The membrane in turn avoids the presence of multiple resonances close to the fundamental one, as it happens in the case of a simple two-layers reflector SMR. Moreover a novel combination of layers is proposed for the acoustic reflector.

This chapter presents two case studies showing how the proposed approach applies to smart system design and optimization. The former is the virtual prototyping platform built for a laser pico-projector actuator, where MEMS, analog and digital components are simulated with the aim of optimizing the resulting image quality by means of firmware tuning. The latter, in the context of wearable equipment for inertial body motion reconstruction, deals with the modeling of an inertial sensor node, supporting system accuracy evaluation and sensor fusion enhancement. Finally, the Open-Source Test Case (OSTC) is described, showing a complete modeling and simulation flow on a publicly available design.

In this work we have studied the role of excitons in two different low barrier metal–semiconductor–metal (MSM) GaN-based UV photodetectors at high temperature. The active material of the two MSM devices consists of bulk GaN grown by metal organic chemical vapour deposition (MOCVD), and of an AlGaN/GaN heterostructure forming a two-dimensional electron gas (2DEG) grown by molecular beam epitaxy/magnetron sputtering epitaxy (MBE/MSE) system. The response of the devices has been characterized at the wavelength of 325 nm (He–Cd laser) as a function of the temperature in the range between room temperature and 700 K. The Arrhenius plot obtained by the decay times of the photocurrent allowed us to calculate the activation energies of some trapping mechanisms responsible of the persistent photocurrent (PPC). This shows that in both device the GaN excitonic resonances provide the most important contribution to the PPC on the millisecond time scale at low temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work we report on the high temperature characterization of two different interdigitated metal–semiconductor–metal (MSM) GaN-based photodetectors. The active material of the two MSM devices consists of bulk GaN grown by metal organic chemical vapor deposition (MOCVD), and of an AlGaN/GaN heterostructure grown by molecular beam epitaxy/magnetron sputtering epitaxy (MBE/MSE) system. Some of the trapping mechanisms which are at the origin of the persistent photocurrent (PPC) effects in GaN-based devices have been studied. The analysis of the decay time as a function of the temperature shows that in both devices the GaN excitonic resonances provide the most important contribution to the PPC on the millisecond time scale at low temperature. The densities of the trap centers involved in the PPC were obtained in both samples by measuring the photocurrent as a function of optical power sweeped in the upward and downward direction.

The high temperature. characterisation of low barrier metal-semiconductor-metal (MSM) GaN-bulk photodetectors is reported. A very high DC responsivity of 6.7 x 10(6) A/W at room temperature and of 1.4 x 10(6) A/W at 450 K was achieved at the wavelength of 325 nm. These values, which are to our knowledge the highest reported in the literature, are in good agreement with our theoretical calculations.