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The characteristics of piezoelectric micro-resonators based on vibrating beams essentially depend on two basic physical coefficients, an effective Young's modulus (Y e) and a piezoelectric coupling factor (e 31e). An improved analytic model is proposed with newly derived expressions of Y e and e 31e that account for the anisotropic properties of the III-nitride materials and beam width, W. The analytic model applicable to the only axial stress is completed by finite element (FE) simulations that allow any spatial patterns of pre-stress in wafers to be studied. The value of e 31e for wider beams is analytically demonstrated to be much higher than the usual e 31, and a strong dependence of e 31e on W is also confirmed by FE simulations. Resonance frequency (f r) and actuation efficiency (η) are numerically studied for several pre-stress patterns and beam dimensions. The f r is found to be sensitive to the beam width only for resonators under 2D pre-stress while the η to the stress magnitude regardless of stress pattern. Compared with measurements published for some fabricated resonators, both analytic and FE approaches agree well quantitatively for the resonance frequency and qualitatively for the dynamic amplitude. The results of this study can help design optimization, such as appropriate electrode length and suitable beam width, to gain better performance for this type of resonators.

International audience; We present the first results about microelectromechanical (MEMS) resonators fabricated on epitaxial nitride semiconductors with thin buffers engineered for MEMS and NEMS applications. These results assess the use of thin buffers for GaN MEMS fabrication. On a 700 nm thick AlGaN/GaN epilayer, a high tensile stress is observed to increase the resonant frequency. The electromechanical coupling efficiencies of integrated transducers are assessed and compared with previously obtained results on commercially available 2-µm thick epilayers used for power transistor applications. A 28 nm/V actuation efficiency is measured on the 700-nm thick structure which is slightly better than the one measured on the 2-µm buffer. The electrical response of a gate-less detector designed as a piezoresistance was carried out and a gauge factor of 60 was estimated. These results show that material issues can be unlocked to exploit the potentialities of III-nitrides for NEMS applications.

In the present work, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown with very thin buffer layers on silicon substrates in view of developing nano electromechanical systems (NEMS) for sensors applications. To ensure transducer operation in the MHz range together with low mechanical stiffness, epitaxial structures with thickness below 1 ?m have to be developed. We report on the evolution of the material and electrical properties of AlGaN/GaN HEMTs with thicknesses varying from 2 ?m to 0.5 ?m. The set of parameters obtained includes in-plane Young modulus of 250 GPa in association with carrier density of 6???1012 cm?2 and mobility above 1000 cm2?V?1?s?1. The resulting behavior of demonstration transistors validates these epilayers for electromechanical resonators operation.

We present a method to characterize sub-10 nm capacitors and tunnel junctions by interferometric scanning microwave microscopy (iSMM) at 7.8 GHz. At such device scaling, the small water meniscus surrounding the iSMM tip should be reduced by proper tip tuning. Quantitative impedance characterization of attofarad range capacitors is achieved using an 'on-chip' calibration kit facing thousands of nanodevices. Nanoscale capacitors and tunnel barriers were detected through variations in the amplitude and phase of the reflected microwave signal, respectively. This study promises quantitative impedance characterization of a wide range of emerging functional nanoscale devices.