1,720,963 research outputs found
High-Aspect-Ratio CMOS add-on modules for RF passive components
No full textCommercial wireless communication technologies stemmed mostly from the research done through and after the Second World War as outlined in Chapter 1. Earlier systems were intended for military applications, hence had very high performance and were very expensive and bulky. Later, with the dawn of commercial microwave applications, the systems began to shrink in size and cost. This was possible due to technological developments in the fabrication of integrated circuits. These developments allowed for the integration of more and more active components into one chip. However passive components could not catch up with the trend due to integration problems. Passive components were very big and, when fabricated on a substrate, suffered from parasitic effects, as well as substrate and metal loss. To overcome these issues, researchers developed several technological solutions, some of which are explained in chapter 2, to improve the integration of passive components. Some key points of these technologies are compatibility with core processes such as CMOS, and cost and complexity of fabrication. This work focuses on a technological process intended to reduce metal loss in passive devices. The process is based on the implementation of a thick top metal layer that will reduce the metal loss. However just increasing metal thickness would not be very effective in high frequencies due to skin effect, which practically renders the core of a metal useless in terms of current carrying capability. Therefore rather than just increasing the thickness the process focuses on increasing aspect ratio (height/width). In this way it is possible to utilize side walls of metal tracks for carrying current and have a much lower resistance for the same metal width. The process is tested with spiral inductors fabricated on several different substrates. The experimental results are presented in Chapter 3. Both experimental and theoretical results (simulations) verify that the idea of using side walls for carrying current is actually viable. The process helps increasing quality factors of inductors on both low-loss (HRS) and lossy (LRS) substrates. Performance improvement is more significant on LRS, since high aspect ratio process also reduces device footprint, hence substrate loss. In addition to evaluating its electromagnetic performance, thermal characteristics of the process are also investigated. This became a necessity after experimenting on suspended inductors with thin metallization under high input power. As outlined in chapter 4 under high-power conditions suspended inductors may heat up to 400 oC. This was expected due to lack of thermal dissipation paths for a suspended inductor. What was unexpected was the role of the underlying membrane, which acted as a thermal shunt and averaged the temperature between windings preventing even higher local temperatures. After modeling the structure through simulation it was seen that majority of the power was dissipated through metal leads. Hence increasing the thickness of metal with high aspect ratio processing would help in alleviating the problem. Experiments done on suspended inductors with thick metallization indeed showed that the problem was significantly reduced. Final part of the work investigates the effect of high aspect ratio process on integrated coplanar waveguides. Therefore several CPWs were fabricated on HRS and glass substrates and their performance were measured. The results given in Chapter 5 indicate lower loss due to high aspect ratio metallization. However metal loss is not the only problem that sets back transmission line integration. The chip area consumption of transmission lines is also a big issue that prevents integration. In order to reduce transmission line size another high aspect ratio process was introduced. This process uses DRIE to etch trenches in silicon and electroplating to fill them with copper. Resulting structures are high aspect ratio CPWs that are embedded in the silicon substrate. They have considerably higher effective permittivities which results in ~80% shorter transmission lines for the same electrical length. In conclusion, high aspect ratio metal processing helps in integration of passive devices such as spiral inductors and CPW lines by reducing their loss and size. Since it is a simple and cost effective process that is compatible with core processes, it is expected to be widely applicable.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Mixed-potential volume integral-equation approach for circular spiral inductors
No full textElectrical Engineering, Mathematics and Computer Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Artificial Dielectric Shields for Integrated Transmission Lines
No full textWe present a novel shielding method for on-chip transmission lines built on conductive silicon substrates. The shield consists of an artificial dielectric with a very high in-plane dielectric constant, built from two patterned metal layers isolated by a very thin dielectric film. Inserted below an integrated coplanar transmission line, the artificial dielectric layer blocks the electric field of the line from entering the silicon substrate. Shielded coplanar waveguides fabricated on a conventional silicon wafer show a two- to three-fold loss reduction compared to unshielded lines at frequencies below 30 GHz.Delft Institute of Microsystems and NanoelectronicsElectrical Engineering, Mathematics and Computer Scienc
Thermal Issues in Micromachined Spiral Inductors for High-Power Applications
No full textAn experimental study of the self-heating of micromachined spiral inductors operated under high-power conditions is presented. Typical suspended spiral coils are shown to develop highly elevated temperatures (up to several hundred degrees) under the flow of a moderate to high (> 60 mA) dc current, which often applies to inductors in radio frequency power circuits. This can lead to the degradation of quality factor and even device failure. The role of various heat dissipation mechanisms relevant for a suspended coil is discussed and analyzed by means of experiments and thermal simulations. Possible solutions to the self-heating issue are discussed and experimentally demonstrated.Electrical Engineering, Mathematics and Computer Scienc
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