Mohammed Moutaouekkil

High temperature gradient nanogap-Pirani micro-sensor with maximum sensitivity around atmospheric pressure

This letter describes and discusses the design and testing of an effcient nanogap Pirani micro-sensor for pressure measurements in a wide range with a maximum sensitivity around atmospheric pressure. The structure combines a substrate-free heated wire and mechanical support using silicon oxide micro-bridges allowing both a constant nanoscale gap between the wire and the substrate and a 1 mm long and 3 µm wide wire. The high aspect ratio of wire provides a uniform heating profile along the wire and contributes to low pressure detection. At the opposite, both the nanoscale gap and the short wire length between two micro-bridges contributes to shift the high pressure limit. Tested between 10 kPa and 800 kPa, the sensor presents a wide measurement range, not fully reached by the experiments, with a maximum of sensitivity close to the atmospheric pressure and performances with up to 38 %/dec sensitivity when operation in constant temperature mode with an overheat of 20 °C.

AlN/GaN/spphire as promising structure for wireless, batteryless and packageless acoustic wave sensors for high temperature applications

Waveguiding layer acoustic waves (WLAW) technology is considered as a packageless solution for extreme miniaturization of acoustic wave devices. WLAW solution is also original and suitable for high-temperature applications. Indeed, the achievement of a stable high-temperature packaging still constitutes a technological lock, in particular regarding sealing performance. In this context, we consider AlN/GaN/Sapphire as a promising WLAW structure for high-temperature applications. Indeed, the high-temperature stability of these three materials was previously demonstrated. However, in order to develop fully operational WLAW sensors based on this layered structure, it is necessary to have a better knowledge of the behaviour of each constitutive material with respect to the temperature. Consequently, the aim of this work is to experimentally validate GaN and AlN elastic constants sets in a large temperature range, which is a prerequisite to make the design of WLAW sensors according to the targeted performance.

AlN/ZnO/LiNbO 3 packageless structure as a low-profile sensor for on-body applications

This paper describes the potential of the AlN/ZnO/LiNbO3 structure for packageless surface acoustic wave sensors. This structure, based on the waveguiding acoustic wave principle, is studied numerically and experimentally.

Theoretical study of lamb wave mode S 0 of AlN membrane bridges SiO 2

The propagation of the S0 Lamb mode in AlN membrane combined with continuous and structured SiO2 thin films is theoretically studied with respect of the materials geometrical parameters and electrical boundaries conditions. A comparison is made in terms of the phase velocity, electromechanical coupling coefficient and temperature coefficients of frequency (TCF) between the studied structures. The results show that an optimal choose of the geometrical parameters of the structure based on SiO2 ribbons can provide a better compromise between low TCF value and resonator performances. The structure also enables an optimal configuration where the SiO2 bridges can be used as a passivation layer for IDTs which consequently is very suitable for sensors applications in harsh environments.

Zero TCF resonator based on S 0 Lamb wave mode in AlN thin plate films

Resonator based S0 Lamb wave mode in AlN thin films plate has drawn great attentions thanks to its high phase velocity up to 10 km/s and large electromechanical coupling coefficient (K2). Moreover, this structure allows operation at high temperature conditions. Although several significant research efforts are ongoing to enable AlN-based piezoelectric devices for high temperature applications, an outstanding challenge in AlN-based resonators is to obtain the excellent frequency-temperature stability at operating temperatures [1]. The AlN/SiO2 composite membrane was proposed as a solution for thermal compensation but with the counterpart of degrading K2 and quality factor. In this work we propose an original structure leading to a better compromise between temperature coefficient of frequency (TCF) value and resonator performances.

SAW resonators for magnetic field sensing with (TbCo 2 /FeCo) multilayered IDTs as sensitive layer

In previous studies [1,2] we have shown the possibility to realize wireless magnetic SAW sensors with a delay line configuration using layered structures. SAW devices in resonator configuration with Ni interdigital transducers (IDT) on the substrate were also investigated by Kadota et al. [3]. The physical phenomena behind sensor behavior is still unclear and the interpretation of the results is not fully in line with the proposed theoretical models. This work aims to understand the physics and the interaction between acoustic waves and magnetostrictive layers under magnetic fields. Here, we investigate multilayer (LiNbO3/(TbCo2/FeCo)) SAW structures with different geometries and configurations.

Theoretical and experimental study of ScAlN/Sapphire structure based SAW sensor

Several SAW devices based on Sco.1Alo.9N/Sapphire bilayer structures were fabricated using various wavelengths and film thicknesses. The acoustic velocity, electromechanical coupling coefficient and temperature coefficient of frequency (TCF) of each device was then measured and the results were compared with calculations using several sets of elastic, piezoelectric and dielectric constants available in the literature. We have shown that the accuracy of available constants is not enough to permit a reliable optimization and design of SAW devices for signal processing and sensors applications.

Nanogap Pirani Sensor Operating in Constant Temperature Mode for Near Atmospheric Pressure Measurements

This paper presents a high sensitive micro-sensor designed for pressure measurements in a wide range around atmospheric pressure, for application in aerodynamics. The sensor is a temperature-resistance transducer operating with the Pirani effect, which states that below a certain pressure limit, the thermal conductivity of a gas is pressure-dependent. The sensor presents a wide measurement range between 10 kPa and about 800 kPa, in both constant current and constant temperature mode. The last mode enables high-sensitive measurements with a maximum of sensitivity around atmospheric pressure, enabling the use of the sensor for applications in aerodynamics and fluid dynamics, such as active flow control.