Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Low-κ dielectric LTCC was developed, to realize successful co-firing with NiCuZn ferrite tapes. A critical high-temperature process in the production of highly integrated LTCC modules is the migration of silver from inner conductors into the LTCC glass phase. Intensive silver migration causes strong deformation of LTCC multilayers during firing in air.
Silver migration into the LTCC glass phase depends on oxygen content of the sintering atmosphere and can be minimized by sintering in nitrogen atmosphere. However, partial decomposition of NiCuZn-ferrite and formation of cuprite was observed during sintering in nitrogen and, consequently, the permeability of the ferrite decreases. As shown by a combined XRD/thermogravimetric study the co-firing of LTCC modules with silver metallization and integrated ferrite layer demands precise adjustment of oxygen partial pressure.
Rekonfigurierbare Mikrowellenkomponenten spielen in modernen Kommunikationssystemen eine wichtige Rolle, um den zunehmenden Anforderungen in Bezug auf Funktionalität und Flexibilität der Systeme gerecht zu werden. Für die Realisierung steuerbarer Mikrowellenbauteile eignen sich verschiedene Technologien, wie z. B. die Halbleitertechnik, mikroelektromechanische Systeme (MEMS) oder ferroelektrische Dünn- und Dickschichten. Prinzipiell zeichnen sich ferroelektrische Materialien durch hohe Schaltgeschwindigkeiten, einen vernachlässigbaren Leistungsverbrauch und geringe Prozesskosten aus. Insbesondere ferroelektrische Dickschichten auf Basis von Barium-Strontium-Titanat (BaxSri-xTiCb, BST) stellen aussichtsreiche Systeme für den Einsatz im Frequenzbereich bis ca. 12 GHz dar. Allerdings unterliegt die Herstellung dieser BST-Dickschichtvaraktoren einer Einschränkung: Aufgrund der erforderlichen hohen Sintertemperatur von über 1100°C ist die Anordnung der Varaktoren auf planare Strukturen begrenzt.
In diesem Beitrag wird zum einen die Entwicklung von BST-ZnO-B203 Komposit-Dickschichten zur Verringerung der Sintertemperatur auf 850-900°C präsentiert und die Material- und Bauteileigenschaften der Komposite bzw. entsprechender MIM-(metal-insulator-metal) Varaktoren mit planar strukturierten Varaktoren auf Basis von BST-Dickschichten verglichen. Zum anderen wird die Integration solcher MIM-Varaktoren auf Basis der niedrigsinternden BST-Komposite in LTCC Module aufgezeigt.
Chemical variability is a main strength of glass. Glass powders are therefore promising candidates for manufacturing a broad diversity of sintered materials like sintered ¬glass-ceramics, glass matrix composites or glass bonded ceramics with tailored mechanical, thermal, electrical and optical properties and complex shape. Its wide and precise adjustability makes this class of materials, even if it may not be obvious at first sight, a key component of advanced technologies. Manufacture and processing of initial glass powders often allow even more flexibility in materials design. At the same time, however, they can cause additional problems. The lecture illustrates possible consequences of glass powder processing upon glass crystallization and sintering as well as chances for targeted utilization. Simple kinetic models describing the effect of particle size distribution, surface crystallization and rigid inclusions on sintering as well effects of different milling and seeding on sinter crystallization are presented.
Advancements in pressure-assisted sintering technology for low temperature co-fired ceramics (LTCC)
(2016)
Steadily increasing demands on design and dimensional accuracy of ceramic multilayer modules, as well as the processing of new materials, require continuous improvements of manufacturing technology, especially thermal processes. The capabilities of pressure-assisted sintering (PAS) for the manufacturing of highly integrated low temperature co-fired ceramics (LTCC) multilayer have been considerably extended in the last years by procedural and device-related advancements. A lambda probe has been integrated in a sintering press prototype to monitor and control the process atmosphere. Thereby, the development of oxygen partial pressure during binder burnout of real modules can be observed. On the other hand, the oxygen partial pressure can be regulated during densification, for example to prevent diffusion of silver from circuit paths into the surrounding LTCC. Thin-film capable surfaces can be produced without post-processing by using setter plates made of glass-like carbon in an advanced PAS process under nitrogen. A newly developed advancement of this approach enables in-situ hot-embossing of LTCC during PAS by using structured glass-like carbon molds. The prototype press is further extended by a sensitive displacement transducer for monitoring the thickness shrinkage of real modules with an edge length of up to 8 inch.
The sintering behavior of sub-micron Ni0.30Cu0.20Zn0.52Fe1.98O3.99 ferrite with and without Bi2O3 addition was studied. Ferrites with 0.5 wt% Bi2O3 exhibit enhanced shrinkage at T < 900 °C with significant grain growth. Additive-free ferrite powders also sinter to high density at 900 °C, however, grain growth is very limited. Both ferrites exhibit a permeability of µ = 400–450. Multilayers consisting of ferrite and low-k dielectric LTCC layers were prepared by co-firing at 900–915 °C. The shrinkage and thermal expansion characteristics of ferrite and LTCC tapes are similar. However, the permeability of integrated ferrite layers, made from ferrite tapes with Bi2O3 additive, significantly drops after co-firing with LTCC layers compared to separately fired monolithic ferrite multilayers. Contrarily, the permeability of integrated, Bi2O3-free ferrite layers, co-fired with dielectric tapes, is identical to that of monolithic ferrite multilayers. This finding is an important step toward ferrite integration into complex LTCC multilayer architectures.