Precision micro-mechanical components in single crystal diamond by deep reactive ion etching

The outstanding material properties of single crystal diamond have been at the origin of the long-standing interest in its exploitation for engineering of high-performance micro-and nanosystems.In particular,the extreme mechanical hardness,the highest elastic modulus of any bulk material,low density,and the promise for low friction have spurred interest most notably for micro-mechanical and MEMS applications.While reactive ion etching of diamond has been reported previously,precision structuring of freestanding micro-mechanical components in single crystal diamond by deep reactive ion etching has hitherto remained elusive,related to limitations in the etch processes,such as the need of thick hard masks,micromasking effects,and limited etch rates.In this work,we report on an optimized reactive ion etching process of single crystal diamond overcoming several of these shortcomings at the same time,and present a robust and reliable method to produce fully released micro-mechanical components in single crystal diamond.Using an optimized Al/SiO_(2) hard mask and a high-intensity oxygen plasma etch process,we obtain etch rates exceeding 30μm/h and hard mask selectivity better than 1:50.We demonstrate fully freestanding micro-mechanical components for mechanical watches made of pure single crystal diamond.The components with a thickness of 150μm are defined by lithography and deep reactive ion etching,and exhibit sidewall angles of 82°–93°with surface roughness better than 200 nm rms,demonstrating the potential of this powerful technique for precision microstructuring of single crystal diamond.

Wafer-level hermetically sealed silicon photonic MEMS

The emerging fields of silicon(Si) photonic micro–electromechanical systems(MEMS) and optomechanics enable a wide range of novel high-performance photonic devices with ultra-low power consumption, such as integrated optical MEMS phase shifters, tunable couplers, switches, and optomechanical resonators. In contrast to conventional SiO;-clad Si photonics, photonic MEMS and optomechanics have suspended and movable parts that need to be protected from environmental influence and contamination during operation. Wafer-level hermetic sealing can be a cost-efficient solution, but Si photonic MEMS that are hermetically sealed inside cavities with optical and electrical feedthroughs have not been demonstrated to date, to our knowledge. Here, we demonstrate wafer-level vacuum sealing of Si photonic MEMS inside cavities with ultra-thin caps featuring optical and electrical feedthroughs that connect the photonic MEMS on the inside to optical grating couplers and electrical bond pads on the outside. We used Si photonic MEMS devices built on foundry wafers from the iSiPP50G Si photonics platform of IMEC, Belgium. Vacuum confinement inside the sealed cavities was confirmed by an observed increase of the cutoff frequency of the electro-mechanical response of the encapsulated photonic MEMS phase shifters, due to reduction of air damping. The sealing caps are extremely thin, have a small footprint, and are compatible with subsequent flip-chip bonding onto interposers or printed circuit boards. Thus, our approach for sealing of integrated Si photonic MEMS clears a significant hurdle for their application in high-performance Si photonic circuits.