Wafer-level hermetically sealed silicon photonic MEMS

Abstract

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 SiO2-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. 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 cut-off 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 (PCBs). Thus, our approach for sealing of integrated Si photonic MEMS clears a significant hurdle for their application in high-performance Si photonic circuits.

Programmable silicon photonic circuits powered by MEMS

“…The solution in the MORPHIC project is to hermetically seal the MEMS devices in a vacuum cavity using a silicon lid. [30][31][32] The wafer-scale process is schematically depicted in Fig. 5.…”

“…The process is described in detail in. 32 When performed in a vacuum or low pressure, the hermeticity of the sealing can be verified by measuring the inward deflection of the silicon lid using white-light interferometry. This shows a high yield well over 90%, 30 and even devices which are not hermetically encapsulated are still protected from most environmental effects.…”

Integrated Photonics Packaging: Challenges and Opportunities

“…Finally, the challenge is exacerbated by the diverse application-specific requirements. For instance, co-packaging of photonic and electronic chips inside a multichip module (MCM), an emerging trend for high-speed data communications, , also imposes added level of complexity and compatibility requirements; packaging of photonic sensors often demands functionalization and protection of exposed waveguide surfaces and integration with analyte-handling systems; − and specialized hermetic packages are critical to optomechanical device integration …”

“…For instance, co-packaging of photonic and electronic chips inside a multichip module (MCM), an emerging trend for highspeed data communications, 18,19 also imposes added level of complexity and compatibility requirements; packaging of photonic sensors often demands functionalization and protection of exposed waveguide surfaces and integration with analytehandling systems; 20−22 and specialized hermetic packages are critical to optomechanical device integration. 23 In this perspective, we offer our viewpoint on the "packaging bottleneck" by outlining the open questions yet to be addressed on six critical aspects of photonic packaging: on/off-chip optical coupling, packaging of laser sources, electronic−photonic copackaging, thermal management design, packaging for emerging applications such as sensing and imaging, and standardization of photonic package design rules. Table 1 summarizes the state of the art of different coupling schemes, classified into two main configurations: edge and surface-normal coupling.…”

Large scale programmable photonic circuits using silicon photonic MEMS

“…For this, we have developed a wafer level post-processing flow based on vapor-phase hydrofluoric acid (HF) etching that releases the MEMS structures. The open cavities with free-standing MEMS waveguides are then hermetically sealed in order to protect the MEMS structures from environmental influence and contamination during operation [4].…”