Daniela Andrijasevic

Hybrid integration of GaAs quantum cascade lasers with Si substrates by thermocompression bonding

A hybrid GaAs quantum cascade laser system obtained by Au–Au thermocompression bonding epilayer down onto gold coated silicon substrates is presented in this paper. The performance of the hybrid laser in low-duty-cycle pulsed operation in comparison to an unbonded one was not deteriorated. The lasers run with a threshold of 4.6kA∕cm2, emit around 12μm, and with a maximum optical output power of 550mW at cryogenic temperatures. The key advantage of such hybrid chips is the possibility of integrating III-V cascade lasers with established silicon photonics technology, such as silicon-on-insulator waveguides, V-groove fiber coupling and microfluidics.

Low Temperature non-viscous adhesive bonding in MEMS

This paper discusses various aspects of the design, the realisation and the testing of an bonding technique for assembly of micro(optoelectronic) systems. The proposed concept of non-viscous adhesives micro bonding overcomes the main disadvantages of the traditional MEMS bonding processes like requirements for high voltage, high temperature, high quality of surfaces, etc. Experiments were performed with different solid adhesives with low softening point (65degC and 72degC), while process parameters: softening time, softening temperature and working distance were varied. Suitable process parameters were finally identified and established. In parallel, adequate numerical simulations in programme package ANSYStrade were done in order to accelerate the procedure of process parameter optimisation. Obtained experimental results are in good agreement with those gained by simulations. The main advantages of this technique are: low processing temperature, applicability for different material combinations, partial reversibility, and partial biocompatibility. Additionally, this technological system is very compact, it can be easily integrated into existing production lines, and it seems to be cost efficient solution.

A Novel Protective Cover in Assembling of Micro Components in a SEM Chamber

This paper presents a novel approach to assembly of micro components in a scanning electron microscope (SEM) chamber. A new set, called protective cover for micro components, allows their quick positioning on the platform inside the SEM chamber without gluing. It is well known that the vacuum pumps, especially turbo one, which evacuated a SEM chamber, are highly sensitive to foreign object damage. This is the reason why the micro components are glued on the specimen holder in the SEM chamber. On the other hand, the grippers that have to pick, lift and place the micro components in a desired system (position, orientation) are very fragile. They can not overcome the adhesive force of the glue and remove the particle from the specimen holder. The presented system is standardized and can be mounted without additional time, modification or expenses into the SEM chamber. It enables, on the one hand, easier manipulation of the micro components that do not need to be glued on the specimen holder and, on the other hand, introduces further automation in the manipulation process in the SEM chamber since it creates thus a necessary basis for modular assembling system. Furthermore, it is very important for the automated assembly process that the micro components are exactly positioned. The standardisation in the micro world becomes more and more essential. The uniformity of parts, operations and tools strongly supports an automatic assembly system

Photonic crystal band edge and defect states in the spectral response of intersubband detectors

We fabricated photonic crystal intersubband detectors and measured the spectral photocurrent upon angle and polarization resolved illumination. Light is coupled into the cavity whenever phase matching occurs between a cavity mode and the incident wave. The method allows us to map out the photonic band structure including its polarization dependence, which is shown to be highly correlated with the symmetry properties. Furthermore we discuss our investigations of non‐bandgap defect states concerning dispersion, linewidth and geometrical tunability.

Grating‐Induced Beam‐Tuning in Quantum Cascade Ring Lasers

We describe the fabrication and operation of quantum cascade ring lasers providing grating‐coupled surface emission. The devices exhibit tunable far fields, ranging from spot‐ to ring‐shaped symmetric beam cross sections, depending on the grating period. This—along with threshold current densities as low as for comparable Fabry‐Perot lasers ‐ demonstrates the compatibility of reduced beam divergence and two‐dimensional integrability, resulting in an attractive light source for spectroscopic applications.

Thermal Characterization of the Micro Bonding Process Using a Hot Air Stream

The possible solution for bonding two different materials with intermediate layer of adhesive at relatively low temperatures in the micro domain is proposed in this paper. A stream of hot gas has been used for melting and softening different kinds of adhesives. After cooling down at room temperature, adhesives harden forming a stable and strong bond. The gas is heated as it passes through the tube with the heater developed on it. The parameters which induce the heat transfer and the process performance generally are considered through various experiments and by numerical simulations. Some advantages of this process are applicability for different material combinations, cost and time efficiency, compact size of equipment etc

Hot gas stream application in micro-bonding technique

This paper presents a new concept for bonding micro-parts with dimensions in the range of 50 μm to 300 μm. Two different kinds of adhesives - polyurethane adhesive foil and hot melt glue - were applied to a basic substrate by different techniques. The focused and concentrated hot gas stream softened glue which had been applied in a solid state. Micro-parts were then embossed in the softened glue, or covered and shielded by it. In this way, a rigid and compact bond was obtained after cooling. For the positioning of micro-parts (optical fibers), it has been necessary to manufacture adequate V-grooves. Finite element analyses using the ANSYSTM program package were performed in order to evaluate parameters which govern the heat transfer to the adhesive and substrate respectively. Experimental results are in good agreement with results obtained by the numerical simulations. The advantages of this new approach are small system size, low capital costs, simple usage, applicability to many material combinations, easy integration into existing production lines, etc.

A novel protective cover for microcomponents

Abstract This paper presents a novel tool for assembly of micro particles in a SEM chamber. A new mechanismus, called Protective Cover for Microcomponents, which allows the positioning of the micro parts on the platform inside the chamber without gluing them on the platform is proposed. It is well known the vacuum pump, especially turbo pump, that makes a vacuum in the SEM chamber, has higher sensitivity to foreign object damage. That is the reason why the micro parts are glued on the disks in the platform of the SEM chamber. Otherwise, the grippers that have to pick, to lift and place the particle in a desired system (position, orientation) are very fragile and can not overcome the adhesive force of glue and separating the particle from the disk. Besides, for the automated assembly process it is very important that the particles stay on the exactly defined location and position. The showed system is standard and can be mounted without additional time, modification or expenses into the SEM chamber. It enables, on the one hand, easier manipulation of the micro parts, that need not to glue on the base and, on the other hand, opens the door for introduction more automation in the manipulation process in the SEM chamber by making a basis for modular assembly system. Therefore the future constructing of a modular holder which can correspond to different requirements of the assembly of numerous microsystems will also be reported. Need for standardisation in micro world becomes more and more articulate. With a higher level of standardisation, the degree of automation grows up, too. The uniformity of parts, operations and tools is a strong support to an automation assembly system.