Integrating MEMS and ICs

The majority of microelectromechanical system(MEMS)devices must be combined with integrated circuits(ICs)for operation in larger electronic systems.While MEMS transducers sense or control physical,optical or chemical quantities,ICs typically provide functionalities related to the signals of these transducers,such as analog-to-digital conversion,amplification,filtering and information processing as well as communication between the MEMS transducer and the outside world.Thus,the vast majority of commercial MEMS products,such as accelerometers,gyroscopes and micro-mirror arrays,are integrated and packaged together with ICs.There are a variety of possible methods of integrating and packaging MEMS and IC components,and the technology of choice strongly depends on the device,the field of application and the commercial requirements.In this review paper,traditional as well as innovative and emerging approaches to MEMS and IC integration are reviewed.These include approaches based on the hybrid integration of multiple chips(multi-chip solutions)as well as system-on-chip solutions based on wafer-level monolithic integration and heterogeneous integration techniques.These are important technological building blocks for the‘More-Than-Moore’paradigm described in the International Technology Roadmap for Semiconductors.In this paper,the various approaches are categorized in a coherent manner,their merits are discussed,and suitable application areas and implementations are critically investigated.The implications of the different MEMS and IC integration approaches for packaging,testing and final system costs are reviewed.

Micro 3D printing of a functional MEMS accelerometer

Microelectromechanical system(MEMS)devices,such as accelerometers,are widely used across industries,including the automotive,consumer electronics,and medical industries.MEMS are efficiently produced at very high volumes using large-scale semiconductor manufacturing techniques.However,these techniques are not viable for the costefficient manufacturing of specialized MEMS devices at low-and medium-scale volumes.Thus,applications that require custom-designed MEMS devices for markets with low-and medium-scale volumes of below 5000–10,000 components per year are extremely difficult to address efficiently.The 3D printing of MEMS devices could enable the efficient realization and production of MEMS devices at these low-and medium-scale volumes.However,current micro-3D printing technologies have limited capabilities for printing functional MEMS.Herein,we demonstrate a functional 3D-printed MEMS accelerometer using 3D printing by two-photon polymerization in combination with the deposition of a strain gauge transducer by metal evaporation.We characterized the responsivity,resonance frequency,and stability over time of the MEMS accelerometer.Our results demonstrate that the 3D printing of functional MEMS is a viable approach that could enable the efficient realization of a variety of custom-designed MEMS devices,addressing new application areas that are difficult or impossible to address using conventional MEMS manufacturing.

Design and fabrication of crack-junctions

Nanogap electrodes consist of pairs of electrically conducting tips that exhibit nanoscale gaps.They are building blocks for a variety of applications in quantum electronics,nanophotonics,plasmonics,nanopore sequencing,molecular electronics,and molecular sensing.Crack-junctions(CJs)constitute a new class of nanogap electrodes that are formed by controlled fracture of suspended bridge structures fabricated in an electrically conducting thin film under residual tensile stress.Key advantages of the CJ methodology over alternative technologies are that CJs can be fabricated with wafer-scale processes,and that the width of each individual nanogap can be precisely controlled in a range from o2 to 4100 nm.While the realization of CJs has been demonstrated in initial experiments,the impact of the different design parameters on the resulting CJs has not yet been studied.Here we investigate the influence of design parameters such as the dimensions and shape of the notches,the length of the electrode-bridge and the design of the anchors,on the formation and propagation of cracks and on the resulting features of the CJs.We verify that the design criteria yields accurate prediction of crack formation in electrode-bridges featuring a beam width of 280 nm and beam lengths ranging from 1 to 1.8μm.We further present design as well as experimental guidelines for the fabrication of CJs and propose an approach to initiate crack formation after release etching of the suspended electrode-bridge,thereby enabling the realization of CJs with pristine electrode surfaces.

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.