Vertical integration of microchips by magnetic assembly and edge wire bonding

The out-of-plane integration of microfabricated planar microchips into functional three-dimensional(3D)devices is a challenge in various emerging MEMS applications such as advanced biosensors and flow sensors.However,no conventional approach currently provides a versatile solution to vertically assemble sensitive or fragile microchips into a separate receiving substrate and to create electrical connections.In this study,we present a method to realize vertical magnetic-field-assisted assembly of discrete silicon microchips into a target receiving substrate and subsequent electrical contacting of the microchips by edge wire bonding,to create interconnections between the receiving substrate and the vertically oriented microchips.Vertical assembly is achieved by combining carefully designed microchip geometries for shape matching and striped patterns of the ferromagnetic material(nickel)on the backside of the microchips,enabling controlled vertical lifting directionality independently of the microchip’s aspect ratio.To form electrical connections between the receiving substrate and a vertically assembled microchip,featuring standard metallic contact electrodes only on its frontside,an edge wire bonding process was developed to realize ball bonds on the top sidewall of the vertically placed microchip.The top sidewall features silicon trenches in correspondence to the frontside electrodes,which induce deformation of the free air balls and result in both mechanical ball bond fixation and around-the-edge metallic connections.The edge wire bonds are realized at room temperature and show minimal contact resistance(<0.2Ω)and excellent mechanical robustness(>168 mN in pull tests).In our approach,the microchips and the receiving substrate are independently manufactured using standard silicon micromachining processes and materials,with a subsequent heterogeneous integration of the components.Thus,this integration technology potentially enables emerging MEMS applications that require 3D out-of-plane assembly of microchips.

Manufacture and characterization of graphene membranes with suspended silicon proof masses for MEMS and NEMS applications

Graphene’s unparalleled strength,chemical stability,ultimate surface-to-volume ratio and excellent electronic properties make it an ideal candidate as a material for membranes in micro-and nanoelectromechanical systems(MEMS and NEMS).However,the integration of graphene into MEMS or NEMS devices and suspended structures such as proof masses on graphene membranes raises several technological challenges,including collapse and rupture of the graphene.We have developed a robust route for realizing membranes made of double-layer CVD graphene and suspending large silicon proof masses on membranes with high yields.We have demonstrated the manufacture of square graphene membranes with side lengths from 7µm to 110µm,and suspended proof masses consisting of solid silicon cubes that are from 5µm×5µm×16.4µm to 100µm×100µm×16.4µm in size.Our approach is compatible with wafer-scale MEMS and semiconductor manufacturing technologies,and the manufacturing yields of the graphene membranes with suspended proof masses were>90%,with>70%of the graphene membranes having>90%graphene area without visible defects.The measured resonance frequencies of the realized structures ranged from tens to hundreds of kHz,with quality factors ranging from 63 to 148.The graphene membranes with suspended proof masses were extremely robust,and were able to withstand indentation forces from an atomic force microscope(AFM)tip of up to~7000nN.The proposed approach for the reliable and large-scale manufacture of graphene membranes with suspended proof masses will enable the development and study of innovative NEMS devices with new functionalities and improved performances.

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.

Soft metamaterial with programmable ferromagnetism

Magnetopolymers are of interest in smart material applications;however,changing their magnetic properties post synthesis is complicated.In this study,we introduce easily programmable polymer magnetic composites comprising 2D lattices of droplets of solid-liquid phase change material,with each droplet containing a single magnetic dipole particle.These composites are ferromagnetic with a Curie temperature defined by the rotational freedom of the particles above the droplet melting point.We demonstrate magnetopolymers combining high remanence characteristics with Curie temperatures below the composite degradation temperature.We easily reprogram the material between four states:(1)a superparamagnetic state above the melting point which,in the absence of an external magnetic field,spontaneously collapses to;(2)an artificial spin ice state,which after cooling forms either;(3)a spin glass state with low bulk remanence,or;(4)a ferromagnetic state with high bulk remanence when cooled in the presence of an external magnetic field.We observe the spontaneous emergence of 2D magnetic vortices in the spin ice and elucidate the correlation of these vortex structures with the external bulk remanence.We also demonstrate the easy programming of magnetically latching structures.

Integrated silicon ohotonic MEMS

Silicon photonics has emerged as a mature technology that is expected to play a key role in critical emerging applications,including very high data rate optical communications,distance sensing for autonomous vehicles,photonic-accelerated computing,and quantum information processing.The success of silicon photonics has been enabled by the unique combination of performance,high yield,and high-volume capacity that can only be achieved by standardizing manufacturing technology.Today,standardized silicon photonics technology platforms implemented by foundries provide access to optimized library components,including low-loss optical routing,fast modulation,continuous tuning,high-speed germanium photodiodes,and high-effciency optical and electrical interfaces.However,silicon's relatively weak electro-optic effects result in modulators with a significant footprint and thermo-optic tuning devices that require high power consumption,which are substantial impediments for very large-scale integration in silicon photonics.Microelectromechanical systems(MEMS)technology can enhance silicon photonics with building blocks that are compact,low-loss,broadband,fast and require very low power consumption.Here,we introduce a silicon photonic MEMS platform consisting of high-performance nano-opto-electromechanical devices fully integrated alongside standard silicon photonics foundry components,with wafer-level sealing for long-term reliability,flip-chip bonding to redistribution interposers,and fibre-array attachment for high port count optical and electrical interfacing.Our experimental demonstration of fundamental silicon photonic MEMS circuit elements,including power couplers,phase shifters and wavelength-division multiplexing devices using standardized technology lifts previous impediments to enable scaling to very large photonic integrated circuits for applications in telecommunications,neuromorphic computing,sensing,programmable photonics,and quantum computing.

Nanoelectromechanical Sensors Based on Suspended 2D Materials

The unique properties and atomic thickness of two-dimensional(2D)materials enable smaller and better nanoelectromechanical sensors with novel functionalities.During the last decade,many studies have successfully shown the feasibility of using suspended membranes of 2D materials in pressure sensors,microphones,accelerometers,and mass and gas sensors.In this review,we explain the different sensing concepts and give an overview of the relevant material properties,fabrication routes,and device operation principles.Finally,we discuss sensor readout and integration methods and provide comparisons against the state of the art to show both the challenges and promises of 2D material-based nanoelectromechanical sensing.

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.