A method for manfacturing a membrane in a (111) surface of a (100) silicium wafer

The invention relates to a method for the fabrication of a membrane oriented in a (111) plane of a (100) silicon wafer. To this end the method comprises the following steps: applying a mask to both sides of the wafer, wherein portions of the sides are covered by the mask; and the at least partial removal by etching away silicon material from the portions of the two sides of the wafer that are not covered. This method is characterised in that the etching step substantially removes the silicon material forming recesses in the two surfaces of the wafer, such that the walls of the recesses are formed by (111) planes, and in that not covered portions at both sides of the wafer are aligned in relation to one another such that a (111) plane is formed and the distance d between said two planes is less than the thickness of the silicon waferApplied Science

Photolithography on bulk micromachined substrates

Photolithography on high topography substrates, such as the sidewalls or the bottom of cavities and trenches created by bulk micromachining, enables the design of complex three-dimensional structures. When a contact lithography system is used to pattern such substrates, local gaps exist between the mask and the substrate. In this paper we investigate the deformation of patterns as a result of these local gaps. We determine the position accuracy and the minimum size of features that can be patterned as a function of the gap distance. Deformations introduced by the optical system are quantified for a common exposure tool, and compared to pattern deformation due to variations in photoresist layer thickness. Finally, methods to improve the quality of patterns transferred through gaps up to 350 ?m are discussedKavli Institute of NanoscienceApplied Science

Buckling beam micromechanical memory with on-chip readout

We have used double clamped beams to implement a mechanical memory. Compressive stress is generated by resistive heating of the beams and beyond the buckling limit the bistable regime is accessed. Bits are written by applying lateral electrostatic forces. The state of the beam is read out by measuring the capacitance between beam and electrodes. Two ways to implement a mechanical memory are discussed: compensation of initial beam imperfections and snap through of the postbuckled beam. Although significant relaxation effects are observed, both methods prove reliable over thousands of write cycles.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin

Strain-dependent damping in nanomechanical resonators from thin MoS2 crystals

We investigate the effect of mechanical strain on the dynamics of thin MoS2 nanodrum resonators. Using a piezoelectric crystal, compressive and tensile biaxial strain is induced in initially flat and buckled devices. In the flat device, we observe a remarkable strain-dependence of the resonance line width, while the change in the resonance frequency is relatively small. In the buckled device, the strain-dependence of the damping is less pronounced, and a clear hysteresis is observed. The experiment suggests that geometric imperfections, such as microscopic wrinkles, could play a role in the strong dissipation observed in nanoresonators fabricated from 2-D materials.QN/Quantum NanoscienceApplied Science

Large Tunability of Strain in WO₃ Single-Crystal Microresonators Controlled by Exposure to H₂ Gas

Strain engineering is one of the most effective approaches to manipulate the physical state of materials, control their electronic properties, and enable crucial functionalities. Because of their rich phase diagrams arising from competing ground states, quantum materials are an ideal playground for on-demand material control and can be used to develop emergent technologies, such as adaptive electronics or neuromorphic computing. It was recently suggested that complex oxides could bring unprecedented functionalities to the field of nanomechanics, but the possibility of precisely controlling the stress state of materials is so far lacking. Here, we demonstrate the wide and reversible manipulation of the stress state of single-crystal WO3 by strain engineering controlled by catalytic hydrogenation. Progressive incorporation of hydrogen in freestanding ultrathin structures determines large variations of their mechanical resonance frequencies, inducing static deformation. Our results demonstrate hydrogen doping as a new paradigm to reversibly manipulate the mechanical properties of nanodevices based on materials control.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.QN/Caviglia LabQN/AfdelingsbureauQN/van der Zant La

Interactions between directly- and parametrically-driven vibration modes in a micromechanical resonator

The interactions between parametrically- and directly-driven vibration modes of a clamped-clamped beam resonator are studied. An integrated piezoelectric transducer is used for direct and parametric excitation. First, the parametric amplification and oscillation of a single mode are analyzed by the power and phase dependence below and above the threshold for parametric oscillation. Then, the motion of a parametrically-driven mode is detected by the induced change in resonance frequency in another mode of the same resonator. The resonance frequency shift is the result of the nonlinear coupling between the modes by the displacement-induced tension in the beam. These nonlinear modal interactions result in the quadratic relation between the resonance frequency of one mode and the amplitude of another mode. The amplitude of a parametrically-oscillating mode depends on the square root of the pump frequency. Combining these dependencies yields a linear relation between the resonance frequency of the directly-driven mode and the frequency of the parametrically-oscillating mode.QN/Quantum NanoscienceApplied Science

Direct and parametric synchronization of a graphene self-oscillator

QN/van der Zant LabQN/Steeneken LabQN/Quantum NanoscienceDynamics of Micro and Nano System

Size-dependent effective Young’s modulus of silicon nitride cantilevers

The effective Young’s modulus of silicon nitride cantilevers is determined for thicknesses in the range of 20–684 nm by measuring resonance frequencies from thermal noise spectra. A significant deviation from the bulk value is observed for cantilevers thinner than 150 nm. To explain the observations we have compared the thickness dependence of the effective Young’s modulus for the first and second flexural resonance mode and measured the static curvature profiles of the cantilevers. We conclude that surface stress cannot explain the observed behavior. A surface elasticity model fits the experimental data consistently.Kavli Institute of NanoscienceApplied Science

High-quality-factor tantalum oxide nanomechanical resonators by laser oxidation of TaSe2

Controlling the strain in two-dimensional (2D) materials is an interesting avenue to tailor the mechanical properties of nanoelectromechanical systems. Here, we demonstrate a technique to fabricate ultrathin tantalum oxide nanomechanical resonators with large stress by the laser oxidation of nano-drumhead resonators composed of tantalum diselenide (TaSe2), a layered 2D material belonging to the metal dichalcogenides. Before the study of their mechanical properties with a laser interferometer, we verified the oxidation and crystallinity of the freely suspended tantalum oxide using high-resolution electron microscopy. We demonstrate that the stress of tantalum oxide resonators increases by 140 MPa (with respect to pristine TaSe2 resonators), which causes an enhancement in the quality factor (14 times larger) and resonance frequency (9 times larger) of these resonators.QN/Quantum NanoscienceApplied Science