Diffractive Backside Structures via Nanoimprint Lithography

AbstractFor decreasing thicknesses of wafer based silicon solar cells, photon management structures to maintain high quantum efficiencies will gain importance. Diffractive gratings on the wafer back side can be designed to achieve very high path length enhancements, especially for weakly absorbed infrared radiation. This technologically demanding concept has to be realised using processes with upscaling potential. Therefore, we present a fabrication process for producing photonic structures in silicon based on interference lithography and nanoimprint lithography (NIL).We realised linear as well as crossed gratings of different depths, which were etched into the wafer back side. Polarisation dependent reflection measurements were made to get information about potential absorption enhancement as well as the occurrence of parasitic absorption in the metal reflector. This is conducted for a PECVD silicon oxide buffer layer between grating and reflector as well as a spin coated silicon oxide layer. Besides these optical characterisations, we further investigated the electrical properties of the back surface, where we applied a concept in which electrical and optical properties are decoupled. This is realised by a layer stack on the wafer back side, consisting of a thin Al2O3 passivation and a doped amorphous silicon layer

Stapelbare Funktionsschicht fuer ein modulares mikroelektronisches System

WO 2008031633 A1 UPAB: 20080604 NOVELTY - The system has a set of functional layers which includes a power supply (20), two memories (21a, 21b), logic (22), micro antenna (23) and transmitter (24), and stacked vertically. Each functional layer has a connection contact configuration, and a wiring between an electronic component and the contact configuration. The functional layers are electrically connected in a vertical manner via their respective contact configurations. The functional layers are designed with respect to the wiring and/or contact configuration for different types of vertical connection technology. USE - Modular microelectric system i.e. radio sensor, for recording environmental conditions, tracking motion of moving objects, warning before material fatigue in rotating portions, controlling virtual keyboards, determining product quality and assisting handicapped. ADVANTAGE - The functional layers are designed with respect to the wiring and/or connection contact configuration for different types of vertical connection technology, thus selecting a suitable connecting technology to make a favorable vertical connection in a cost effective manner, and hence reducing the vertical wiring complexity to minimize the space requirement for the wiring

Vorhersage von magnetischen Kopplungen in Filterschaltungen

Ziel bei der Entwicklung eines EMV-Filters ist es mit einer minimalen Anzahl von Bauteilen eine gewünschte Filterperformance zu erreichen. Dem entgegen stehen dem Designer zwei Arten von parasitären Effekten. Die erste Art beinhaltet die parasitären Elemente der Bauteile, wie z.B. die ESL und ESR der Kondensatoren oder die parasitären Windungskapazitäten der Drossel. Diese Effekte sind bekannt und leicht durch eine Impedanzmessung der Bauteile handhabbar. Trotzdem ist diese Art der Nachbildung zu ungenau, wie die starke Abweichung des gemessenen vom erwarteten Ergebnis zeigt. Diese Abweichung hat ihre Ursache in der zweiten Art der parasitären Effekte, der induktiven Verkopplung der Bauteile untereinander und ist abhängig von der Anordnung der Bauteile auf dem Schaltungsträger. So können sich Filterschaltungen mit den gleichen Topologien und verwendeten Bauteilen unterschiedlich verhalten, wenn das Filterlayout unterschiedlich ist. Zur Berücksichtigung müssten die elektromagnetischen Felder berechnet und in die Filtersimulation eingebunden werden, diese Vorgehensweise scheiterte jedoch bisher an der Komplexität des Problems. In dieser Abhandlung wird gezeigt, wie durch den Einsatz der PEEC-Methode die Komplexität der Berechnung elektromagnetischer Felder stark reduziert und für den Anwender zur Filtersimulation einsetzbar wird. Die PEEC-Methode überführt hierbei die elektromagnetischen Eigenschaften der leitenden Strukturen des Aufbaus in ein elektrisches Ersatzschaltbild aus Eigen- und Gegenparametern, welche das bisherige Filtermodell erweitern. Problematisch ist bei dieser Methode die Nachbildung permeabler Materialien, da dieses prinzipbedingt ausgeschlossen ist. Es wird dazu eine Lösung vorgestellt, welche die einfache Nachbildung von inhomogenen Permeabilitäten ermöglicht. So wird es mit dieser Methode möglich auch ferritbehaftete Bauelemente nachzubilden. Es werden die PEEC-Modelle der Bauteile passiver Filter vorgestellt und anhand von Feldmessungen verifiziert. Anhand eines Netzfilters wird die Vorgehensweise der Berechnung sowie die Einbindung der induktiven Verkopplungen in das bisherige Filtermodell demonstriert und die sehr gute Übereinstimmung von Simulation und Messung präsentiert. Dabei wird der Einfluss auch sehr geringer Verkopplungen eindringlich dargestellt. Aus den Ergebnissen werden Hinweise für den Filterdesigner abgeleitet, wie die induktiven Verkopplungen minimiert und so die gewünschte Filterperformance sichergestellt werden kann. So können im Vorfeld der Entwicklung Aussagen über die optimale Bauteilanordnung getroffen und dadurch das zeitaufwendige 'trial and error'-Verfahren des Filterentwurfs überwunden werden

Electrical modeling of the power delivery to an LED array packaged in a textile

Recent technologies enable large arrays of LEDs to be integrated into textiles, which has applications in the lighting industry. Two analytical modeling techniques are proposed that calculate the supply power at a source necessary to provide the LED drivers with a minimum voltage. The modeling techniques show a correlation with numerical simulations to within 10% but can be implemented for very large LED arrays where, for time constraints, numerical simulations become impractical. The modeling allows a designer to optimize the location of the supply voltage, which can reduce the increase in voltage over the ideal voltage by 40%

Preparation of periodically arranged metallic nanostructures using nanoimprint lithography

We present a process chain to generate periodically arranged metallic nanostructures supporting plasmons for the use in solar cells. As proof-of-concept, platinum and silver nanoparticles with a period of 1 m and a diameter of 600 nm were fabricated. For the platinum particles, an absorption enhancement for light with a wavelength of 3.6 m was observed in silicon. By decreasing structure sizes the active spectral region can be shifted to wavelength relevant for solar cell applications. Therefore, in a second step a silver grating with a smaller period and also smaller diameter of approximately 200 nm was realized

Photon Management Structures for Solar Cells - From Modeling to Fabrication

Photon Management strucutres are of increasing importance for solar cells. A coupled wave-optical and electrical simulation approach is introduced. Furthermore fabrication technologies based on interference and nanoimprint lithography are presented. Simulation and experimental results are shown for an exemplary system

Impact of process tolerances on the performance of bond wire antennas at RF/microwave frequencies

Due to the multitude of advantages bond wire antennas have over conventional planar antennas (especially onchip planar antennas), they have received much research attention within the last four years. The focus of the contributions made so far has been on exploiting different configurations of single-element and array bond wire antennas for short-range applications at RF/microwave frequencies. However, the effects of process tolerances of bond wires on the radiation characteristics of bond wire antennas have not been studied in published literature. Therefore in this paper, we investigate the impact of up to 20% fluctuations in the parameters of bond wires on the performance of 42 GHz and 60 GHz bond wire antennas. Our results reveal that the length and radius of bond wires are the most and least sensitive parameters, respectively. Furthermore, the severity of the impact of process tolerances depends on the impedance bandwidth of the original antenna, before considering the tolerances. For example, a 10% change in the length of a bond wire causes the resonance frequency of a 42 GHz antenna to be shifted out of the specified 3GHz bandwidth (40.5 GHz-43.5 GHz) required for point-to-point communication. However, although a 10% change in length of a bond wire yields a 2.5 GHz shift in the resonance frequency of a 60 GHz bond wire antenna, it doesn't completely detune the antenna because of the original 6 GHz bandwidth available, prior to the fluctuation. Therefore, to prevent the impact of process tolerances from severely degrading the performance bond wire antennas, these antennas should be designed to have larger bandwidths than specified. For experimental verification, a bond wire antenna was designed, fabricated and measured. Very good correlation was obtained between measurement and simulation

Honeycomb textured multicrystalline silicon via nanoimprint lithography

A new approach for realizing a defined texture on multicrystalline silicon for solar cells was investigated. The necessary etching mask is structured via UV-Nanoimprint Lithography as a potential substitute for photolithography. This emerging technology offers new possibilities in terms of resolution, shape of the structured patterns and requirements to the substrate´s surface quality. After the UV sensitive resist is structured and cross-linked, it serves as etching mask within a reactive ion etching process. To evaluate the quality of the textured surfaces, optical as well as electrical characterisation was conducted

Photon Management Structures Based on Interference Lithography and Nanoimprint Processes

Since micro- and nanostructures for photon management are of increasing importance in novel highefficiency solar cell concepts, structuring techniques with up-scaling potential play a key role in their realization. Interference lithography and Nanoimprint processes are presented as technologies for origination and replication of fine-tailored photonic structures on large areas. With the interference pattern of two or more coherent waves, a wide variety of structures can be generated on areas of up to 1.2 x 1.2 m². In combination with subsequent nanoimprint steps, the industrially feasible production of elaborate structures is possible. After the description of the basic technologies, four application examples are presented: (1) honeycomb structures for the front side texturization, (2) diffractive back side gratings for absorption enhancement in the spectral region near the band gap of silicon, (3) periodic and aperiodic imprinted structures as substrates for TCO deposition, and (4) plasmonic metal nanoparticle arrays manufactured by combined imprint and lift off processes