Tensile-strained micromechanical resonators made from crystalline InGaP with low mechanical dissipation and high optical reflectivity

Fia Hellman, MPNAT Nanotechnology, presents her master thesis with the title Tensile-strained micromechanical resonators made from crystalline InGaP with low mechanical dissipation and high optical reflectivity​.

Examiner: Witlef Wieczorek​


The interest in micro- and nanomechanical resonators has grown rapidly during the last decade due to their broad applicability within metrology and fundamental science. They have, for instance, been brought to the quantum regime and have also been demonstrated to be incredibly precise detectors of small masses, forces, or displacements. The motion of the resonator can be detected via optical means, where tremendous progress has been made with so called cavity optomechnical systems. The coupling between light and the micromechanical resonator can be increased using high-reflectivity micromechanical resonators. This can thereby be achieved by alternating the in-plane dielectric constant of the resonator with structures called photonic crystals. A precise read-out of the resonator’s displacement requires low mechanical dissipation in order that the measurement signal can exceed the thermal noise floor.

Dissipation can be minimized by carefully selecting the appropriate material, design, and operating environment for the resonator.

Mechanical dissipation can even be diluted by introducing tensile strain to the material, which acts as additional storage of energy. Mechanical dissipation is commonly quantified by the quality factor, which is the ratio between the total energy stored in the system and energy lost during one cycle.


This thesis presentation uses highly tensile-strained crystalline InGaP to realize micromechanical resonators with low mechanical dissipation.

Crystalline materials are promising candidates for highly sensitive micromechanical resonators due to their potentially low intrinsic mechanical dissipation, high intrinsic strain, and yield strength. The first part of this thesis investigates some of these properties for InGaP by comparing fabricated doubly-clamped strings with analytical models. Thereby it was inferred that the stress depends on the crystal direction with values in the range of 200-500 MPa. Further, the fabricated InGaP material shows an intrinsic quality factor between 5700 ± 1000 up to 7900 ± 1700. The second part of this thesis focuses on optimizing the geometry of trampoline-shaped  micromechanical resonators to enhance their mechanical quality factor and their optical reflectivity. A large optical reflectivity could be observed for fabricated devices patterned with a photonic crystal. FEM-based simulations were made to find dimensions of the trampoline that considerably reduce mechanical clamping loss to the surrounding supporting structure. By implementing these designs to trampoline-shaped micromechanical resonators, a quality factor of 7*10^6 at low temperatures was demonstrated, which was not limited by clamping loss.

It was instead shown that the quality factor was limited by gas damping.

The mechanical and optical properties of micromechanical resonators fabricated from crystalline InGaP demonstrated in this thesis have shown promising results and provide all requirements for the resonators to be used in optomechanical systems in the near future.​

Zoom ​https://chalmers.zoom.us/j/67300502320,  Password: 826116​
Category Student project presentation
Location: Kollektorn, lecture room, Kemivägen 9, MC2-huset
Starts: 16 August, 2022, 15:15
Ends: 16 August, 2022, 16:00

Page manager Published: Mon 08 Aug 2022.