Promotionsvortrag Physik: On-Chip Mechanics as a Contribution to the 4H-SiC Technology Platform

Ankündigung des Promotionsvortrags von: Herrn André Hochreiter

Silicon carbide's (SiC) combination of high-quality single-crystalline 4H-SiC wafers and its excep-tional mechanical properties form an outstanding set of possible applications. To fully leverage these mechanical properties, this thesis introduces a monolithic fabrication strategy that forms the desired 3D-structures monolithically out of the single-crystal wafer. This approach diverges from traditional dry-etching methods by relying on a sophisticated electrochemical etching (ECE) pro-cess. By leveraging ion-implanted doping contrasts, the ECE selectively removes p-SiC while pre-serving n-SiC, resulting in a free-standing, essentially stress-free n-SiC layer for high-quality na-nomechanical resonators such as cantilevers, bridges, and membranes.

A central contribution of this work is the precise adjustment of 4H-SiC resonator properties achieved by applying controlled tensile stress through a chip-bending method using the squeeza-ble nanojunction (SNJ) setup. We achieve a 2.6-fold increase in the first eigenfrequency (f1: 540 kHz to 1400 kHz) and a five-fold boost in the quality factor (Q) of a 110x10 μm bridge resonator under 228 MPa of applied stress. This research validates the Euler-Bernoulli beam (EBB) model, using experimental laser Doppler vibrometer (LDV) measurements of the first eigenfrequency, against COMSOL simulations. To further validate the SNJ setup performance, chip-bending sim-ulations (COMSOL) are compared against white light interferometry measurements.

Overall, experimental and theoretical results align within 13% across all metrics: mechanical de-formation, eigenfrequency, and tensile stress - the latter calculated via the EBB model using LDV-measured f1 data. These results establish the SNJ method as a fully reversible post-fabrication degree of freedom that decouples device performance from fabrication precision. By enabling the dynamic adjustment of f1 and Q, this setup allows resonators to be tuned, effectively compen-sating for dimensional variances during manufacturing.

(Vortrag auf Englisch)

Dem Vortrag schließt sich eine Diskussion von 15 Minuten an. Vortrag und Diskussion sind öffentlich. Diesen Verfahrensteilen folgt ein nicht öffentliches Rigorosum von 45 Minuten.