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PublicationFan-out wafer level packaging of GaN components for RF applications( 2020)Driven by 5G or radar applications there is an increasing market for GaN device for RF power applications. GaN component packaging is done today mainly by wire bonding in combination with expensive ceramic based packaging solutions. Cost efficient Fan-out Wafer Level Packaging (FOWLP) is considered a promising solution for GaN devices offering short and low inductance interconnects, high miniaturization, good thermal solutions, potential lower cost and the possibility of integrating passive components and structure in the package and redistribution layer. However, GaN packaging also bears some challenges which have to be considered when developing new packaging technologies. GaN devices are typically quite thin in the range of 100 mm and have fragile air bridge structure on the active die side. Both aspects have to be taken into account for FOWLP concerning pick-and-place assembly, compression molding and debonding from thermal release tape. Also the influence of the redistribution layer (RDL) on the air bridges and RF performance have to be analyzed. Au is used as pad and component backside metallization. Here a good adhesion must be guaranteed to the interface materials involved. Access to the backside metallization of the GaN device is required for thermal dissipation and electrical connection if needed. The thermal concept is an important factor as the junction temperature should not exceed certain values. Besides the limits of the component itself the polymers involved as the dielectric material and the epoxy molding compound will degrade under long-term high temperature load and thus will cause reliability issues. In contrast to Si dies, the backside of the GaN device cannot be accessed by backgrinding because the metallization must not be damaged or removed. Here new solutions for backside connections during FOWLP packaging and compression molding are required. The paper will describe the technology development of a GaN based power amplifier in Fan-out Wafer Level Packaging technology. For the GaN backside access two different approaches have been evaluated, first the attachment of a Cu heat sink on theGaN backside before molding followed by a backgrinding step into the Cu heatsink and second the drilling of vias through the mold to the GaN backside followed by direct metallization of the vias for thermal and possible electrical connection. The thermal release tape used has been carefully selected and the process steps pick and-place assembly, compression molding and debonding have been optimized to avoid any damage of GaN die and air bridges. Influences of the packaging materials on the RF performance of the die have also been tested. Finally the different technology blocks developed have been combined to build a GaN based power amplifier in FOWLP.
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PublicationAdaptive camouflage panel in the visible spectral range( 2018)In this work an adaptive panel in the visible spectral range is presented. Principal possibilities and basic aspects of adaptive camouflage in the VIS are considered and some details are discussed. The panel consists of modular tiles, each containing several high power four-color-LEDs controlled by a microcontroller and high current power supply and each tile designed to operate autonomously. To control the color and the intensity several color sensors were integrated into the system. The purpose of the panel is to take on a uniform color to best match its appearance to a given reference color, where both the panel and the reference color are subject to the same environmental conditions. The panel was not designed, however, to produce different camouflage patterns. The tiles on the surface were covered by a dark plastic plate in order to provide dark and saturated colors and to guarantee a dark appearance in the passive state of the system. As was to be expected, extreme situations like high ambient brightness and direct solar illumination turned out to be particularly challenging. Substantial tests and some modifications were performed to achieve a satisfactorily uniform color reproduction of a given reference color. Physical measurements as well as observer tests have been performed to demonstrate the capability of the adaptive system.
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PublicationStudy on packaging and driver integration with GaN switches for fast switching( 2016)
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PublicationA compact W-band LFMCW radar module with high accuracy and integrated signal processing( 2015)In this paper, a compact W-band radar module will be presented, design aspects will be discussed and some measurement results of the finally realized module will be shown. The module features an integrated signal generation, full signal processing and power distribution. The signal generation is based on a phase-locked loop, optimized for linear frequency-modulated continuous-wave operation. A digital signal processor also works as internal controller and pro-vides the digital interfaces. Due to the integrated power distribution, a single 7 to 15V power supply is necessary. In contrast to most state-of-the-art W-band systems using waveguides, a liquid crystal polymer based printed circuit board with integrated antenna and dielectric lens is used to realize a very compact module size of 42mm x 80mm x 27mm and low weight of 160 g. The total power consumption is 5 W, the radio frequency output power is 3dBm and the linear frequency modulated contimuous-wave radar bandwidth is 14 GHz. The evaluated distance measurement repeatability of the module is 5 ppm (5µm deviation per meter target distance).
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PublicationRadar based detection and tracking of objects under poor visibility conditions( 2013)Places which have to be monitored permanently (such as security sectors, industrial areas or power plants) are facing the problem of large-area monitoring. Optical security cameras can observe such areas under good lighting and visibility conditions, but objects might get invisible when fog, darkness or smoke reduces the visibility. This problem can be solved with millimeter-wave radars with very high slew rates of the chirp signal. The radar has a detection range of above 100m and can determine the distance and speed of objects inside the observation area very precisely. For most applications, the positon of objects is more important than their color or size.
