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Transfer technology is now becoming very attractive not only for new technologies such as flexible technology but also for solid state technologies when performances are limited by technological barriers that have to be overcome. In this last context, the transfer of high electron mobility transistors (HEMTs) on diamond substrates represents an opportunity to improve the thermal dissipation when the device operates at high radio frequency power levels. Up to now, the technological process for the transfer of these transistors is not detailed in the literature. In this article, the first demonstration of AlGaN/GaN HEMTs on diamond substrates by transfer technology obtained through sputtered aluminum nitride (AlN) layers bonding at low temperature is reported. Devices are first fabricated on AlGaN/GaN epilayers grown on silicon (Si) substrates. Afterward, AlGaN/GaN thin films with devices are released from the Si growth substrate and transferred at 160 °C onto a diamond substrate thanks to an AlN bonding layer. A full description of the transfer technology and all the technological limits and risks are presented. The transferred device provides a maximum DC drain current density IDS Max of 690 mA mm−1 at VGS = 0 V. Furthermore, a cutoff frequency fT of 85 GHz and a maximum oscillation frequency fMAX of 106 GHz are extracted from S-parameter measurements. [ABSTRACT FROM AUTHOR]

The main objective of this work is to study the solid-solid interfaces using a very high frequency (3GHz) ultrasonic method in order to deduce in a non-destructive way and quantitatively the quality contact at the interface, fundamental parameter in tribology. The very high frequencies allow prospecting the state of contact at the nanometer scale. The determination of the contact surface between two polished materials (Silicon-Silica) was carried out. From the measured echoes diagram, the reflection coefficient and the elasticity of the interface were extracted and compared to the ones determined by a numerical approach presented by Greenwood and Williamson [ABSTRACT FROM AUTHOR]

Starting from Gallium Nitride epitaxially grown on silicon, pre-stressed micro-resonators with integrated piezoelectric transducers have been designed, fabricated, and characterized. In clamped-clamped beams, it is well known that tensile stress can be used to increase the resonant frequency. Here we calculate the mode shape functions of out-of-plane flexural modes in pre-stressed beams and we derive a model to predict both the resonant frequency and the piezoelectric actuation factor. We show that a good agreement between theory and experimental results can be obtained and we derive the optimal design for the electromechanical transduction. Finally, our model predicts an increase of the quality factor due to the tensile stress, which is confirmed by experimental measurements under vacuum. This study demonstrates how to take advantage from the material quality and initial stress resulting of the epitaxial process. [ABSTRACT FROM AUTHOR]

Nowadays, millimeter scale power sources are key devices for providing autonomy to smart, connected, and miniaturized sensors. However, until now, planar solid state microbatteries do not yet exhibit a sufficient surface energy density. In that context, architectured 3D microbatteries appear therefore to be a good solution to improve the material mass loading while keeping small the footprint area. Beside the design itself of the 3D microbaterry, one important technological barrier to address is the conformal deposition of thin films (lithiated or not) on 3D structures. For that purpose, atomic layer deposition (ALD) technology is a powerful technique that enables conformal coatings of thin film on complex substrate. An original, robust, and highly efficient 3D scaffold is proposed to significantly improve the geometrical surface of miniaturized 3D microbattery. Four functional layers composing the 3D lithium ion microbattery stacking has been successfully deposited on simple and double microtubes 3D templates. In depth synchrotron X-ray nanotomography and high angle annular dark field transmission electron microscope analyses are used to study the interface between each layer. For the first time, using ALD, anatase TiO2 negative electrode is coated on 3D tubes with Li3PO4 lithium phosphate as electrolyte, opening the way to all solid-state 3D microbatteries. The surface capacity is significantly increased by the proposed topology (high area enlargement factor - 'thick' 3D layer), from 3.5 μA h cm−2 for a planar layer up to 0.37 mA h cm−2 for a 3D thin film (105 times higher). [ABSTRACT FROM AUTHOR]

An optimized scaffold based on silicon microtubes is designed to increase the surface capacity of 3D lithium-ion microbatteries. High-depth, mechanically robust microstructures are fabricated using microelectronic facilities. Conformal deposition of anatase TiO2 is achieved using atomic layer deposition, realizing the targeted improvement for microbatteries; a surface capacity of 0.2 mA h cm-2 at a charge rate of C/10 is obtained in standard liquid electrolyte. This work paves the way for the fabrication of solid-state 3D Li-ion microbatteries with an efficient 3D scaffold. [ABSTRACT FROM AUTHOR]

A fully integrated electromechanical resonator is described that is based on high mobility piezoelectric semiconductors for actuation and detection of nanoscale motion. We employ the two-dimensional electron gas present at an AlGaN/GaN interface and the piezoelectric properties of this heterostructure to demonstrate a resonant high-electron-mobility transistor enabling the detection of strain variation. In this device, we take advantage of the polarization field divergence originated by mechanical flexural modes for generating piezoelectric doping. This enables a modulation of carrier density which results in a large current flow and thus constitutes a motion detector with intrinsic amplification. [ABSTRACT FROM AUTHOR]

The piezoelectric actuation of a micro-electro-mechanical system (MEMS) resonator based on an AlGaN/GaN heterostructure is studied under various bias conditions. Using an actuator electrode that is also a transistor gate, we correlate the mechanical behaviour to the two-dimensional electron gas (2DEG) presence. The measured amplitude of the actuated resonator is maximum at moderate negative biases and drops near the pinch-off voltage in concordance with the 2DEG becoming depleted. Below the pinch-off voltage, residual actuation is still present, which is attributed to a more complex electric field pattern supported by quantitative modelling. The results confirm that epitaxial AlGaN barriers are fully adapted to the piezoelectric actuation of MEMS. [ABSTRACT FROM AUTHOR]