•The performance of AlGaInP Based Red LEDs was improved by Combination of Omnidirectional Mirror and AuZn Micro-contacts.•The low-refractive-indexed dielectric MgF2 layer acted as current blocking ...and reflection-enhancing layer.•The cylindrical alloyed AuZn micro-contacts perforated through MgF2 layer played roles in current spreading and injection.•The area ratio of AuZn micro-contacts was optimized to improve the performance of the LED.
An omnidirectional reflector (ODR) consisted of (MgF2)/Ag was employed in AlGaInP-based vertical red light-emitting diodes (LEDs) in order to increase the light extraction hence the wall-plug efficiency. In this structure, the dielectric MgF2 layer with low refractive index acted as current blocking and reflection enhancing layer. The cylindrical AuZn alloy micro-contacts perforated through the MgF2 layer and played roles in current spreading and injection. The area ratio of AuZn micro-contacts was optimized to improve the performance of the LED. The results indicated that increasing the area ratio of micro-contacts led to the improvement of current injection uniformity and reduction of forward voltage especially at higher injection current, but at the expense of light extraction by reducing reflection. After optimized, the best performance of red-light LEDs can be obtained with 3% area ratio of micro-contacts.
CNTs can have the ability to act as compliant small-scale springs or as shock resistance micro-contactors. This work investigates the performance of vertically-aligned CNTs (VA-CNTs) as ...micro-contactors in electromechanical testing applications for testing at wafer-level chip-scale-packaging (WLCSP) and wafer-level-packaging (WLP). Fabricated on ohmic substrates, 500-μm-tall CNT-metal composite contact structures are electromechanically characterized. The probe design and architecture are scalable, allowing for the assembly of thousands of probes in short manufacturing times, with easy pitch control. We discuss the effects of the metallization morphology and thickness on the compliance and electromechanical response of the metal-CNT composite contacts. Pd-metallized CNT contactors show up to 25 μm of compliance, with contact resistance as low as 460 mΩ (3.6 kΩ/μm) and network resistivity of 1.8 × 10−5 Ω cm, after 2500 touchdowns, with 50 μm of over-travel; they form reproducible and repeatable contacts, with less than 5% contact resistance degradation. Failure mechanisms are studied in-situ and after cyclic testing and show that, for top-cap-and-side metallized contacts, the CNT-metal shell provides stiffness to the probe structure in the elastic region, whilst reducing the contact resistance. The stable low resistance achieved, the high repeatability and endurance of the manufactured probes make CNT micro-contacts a viable candidate for WLP and WLCSP testing.
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The aim of this work is to propose an analysis of mechanisms inducing surface interaction by friction during high sliding speed. Specific devices including a ballistic setup were used to reproduce ...extreme sliding conditions combining high speed and high pressure. The titanium alloy/tantalum tribo-pair is chosen to investigate the frictional and material transfer mechanisms. The tangential force measurement is used to follow the evolution of the friction coefficient at a macroscopic scale. The evolution of the sliding surface was analyzed by confocal 3D microscope to evaluate material transfer and real contact surface area. Numerical modeling of micro-contact at the asperities scale is presented to illustrate the scenarii involved during friction. The energy needed to shear a junction is estimated and analyzed for several types of interaction. Different behaviors have been taken into account in order to investigate the global forces generated by the contact including strong and weak contacts. The analysis of energy is available to predict the global friction force in a large range of velocities. Correlations between experimental measurements and numerical predictions are used to validate the proposed approach. The results can be interpreted as following: (1) at lower velocity the main mechanism dominating the interaction between asperities becomes ploughing with large volume of plastic deformation (2) at higher velocity the main mechanism is shear localization requiring less energy and force for shearing the junctions.
A new class of experimental techniques is presented which allows the behavior of elementary collective excitations (quasiparticles) in solids to be studied at the mesoscopic scale. New experimental ...equipment is being constructed in the classical scheme of an atomic force microscope in which the sensor of primary information is a cantilever. The defining feature of the proposed sensor based on a cantilever is the addition of a generator and detector of quasiparticles to its design. The generator is located either on the tip of the cantilever or in close proximity to the needle on the cantilever, so that the flow of quasiparticles emitted by the generator propagates along the needle of the cantilever to the point where the needle tip touches the surface. The detector is located in a similar way. The measured quantity is the reflection coefficient of the flux of quasiparticles from the interface between the cantilever needle tip and the surface being scanned.
As the reliability of electrical microcontacts has proved to be the main limitation to a fast-growing production of ultraminiaturized switches, a thorough understanding of their failure mechanisms is ...an all-important purpose. This paper aims at showing that conducting-probe Atomic Force Microscopy (cp-AFM) is an adequate tool to actuate and study electrical contacts. By choosing relevant cantilevers and operating mode of the cp-AFM, dimensions, gap and force level representative of existing microelectromechanical switches (MEMS switches) are obtained. With two examples, the advantages of using a cp-AFM in force mode for studying physical phenomena at very low scale are highlighted. The reported investigations concern material transfer between contact parts and contact bounces. Those two undesirable phenomena induce surface damages and impinge reliability of MEMS switches. In both cases an explanatory scenario of phenomena occurring at nanoscale is proposed and preventive recommendations for improving the lifetime of such devices are suggested.
Some aspects of novel micro-contacts in Microwave Chip Carriers Arnaudov, Radosvet; Videkov, Valentin; Avdgiiski, Bojidar ...
2010 10th International Conference on Actual Problems of Electronic Instrument Engineering APEIE-2010,
2010-Sept.
Conference Proceeding
Design and development of novel type micro-contacts in Microwave Chip Carriers to Printed Circuit Board (PCB) assembly are presented in this paper. A new concept of micro-contacts for packaging ...solutions of microwave and mm-wave MMICs is depicted. Simulation and Vector Network Analyzer (VNA) measurement results for these micro-contact transitions are discussed. The results show that electrical parameters are highly dependent on the transition dimensions and substrate features. These contacts are based on male stud (bump) and female (ring) approach. When mating each other, clips effect and self-alignment features appear. Special attention is paid to the shape of the micro-contacts in order to facilitate assembly and strengthen the connection. Equivalent electrical circuit is proposed for SPICE simulation of the DC contact resistance. Finally, the article discusses technological development of the proposed new micro-contact stud/ring pair by means of low cost Ultra-violet electroplating, lithography and molding (UV-LIGA) process.
Some aspects of novel micro-contacts in Microwave Chip Carriers Arnaudov, Radosvet; Videkov, Valentin; Avdgiiski, Bojidar ...
2010 10th International Conference on Actual Problems of Electronic Instrument Engineering APEIE-2010,
2010-Sept.
Conference Proceeding
Design and development of novel type micro-contacts in Microwave Chip Carriers to Printed Circuit Board (PCB) assembly are presented in this paper. A new concept of micro-contacts for packaging ...solutions of microwave and mm-wave MMICs is depicted. Simulation and Vector Network Analyzer (VNA) measurement results for these micro-contact transitions are discussed. The results show that electrical parameters are highly dependent on the transition dimensions and substrate features. These contacts are based on male stud (bump) and female (ring) approach. When mating each other, clips effect and self-alignment features appear. Special attention is paid to the shape of the micro-contacts in order to facilitate assembly and strengthen the connection. Equivalent electrical circuit is proposed for SPICE simulation of the DC contact resistance. Finally, the article discusses technological development of the proposed new micro-contact stud/ring pair by means of low cost Ultra-violet electroplating, lithography and molding (UV-LIGA) process.
The present article describes the development and production of horizontal elements in 3D micro-contacts, implemented in IC package to PCB assembly and micro mechanical actuators. Instead of the ...standard vacuum deposition of metal films onto dielectric interfaces and lift-off stripping, an alternative method aiming at simplicity and lower-cost, relative to the technology roadmap is proposed. This method employs chemical activation and pre-treatment of the dielectric photoresist surfaces with fluid carbon content substance, thus providing also electrical conductivity for direct metal electroplating. A special regime of reverse electrochemical deposition is applied in order to enhance the adhesion of the layer, deposited onto the activated surface. This paper presents experimental results of the horizontal elements investigation, relative to the 3D micro-contacts. Thermal simulations of the proposed structures are also included. This issue is of a great importance, due to the nature of the horizontal elements - actuator type and bending features.
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