New dielectric tape materials for LTCC : characterisation and modelling of microwave properties
The Low Temperature Co-fired Ceramic technology (LTCC) represents a multilayer functional ceramic substrate, which due to its 3D-Integration feasibility ranks among the key technologies for future hybrid high frequency circuits. In particular the low sintering temperature of <900øC enables the application of high-conductive and low-loss metallization like silver or gold. Nevertheless, new low-sintering microwave ceramics with clearly higher dielectric constant (DK) are demanded for contemporary highly integrated HF circuits. Although many high-dielectric bulk ceramics are known for a long time, but appropriate methods must be developed for lowering the sintering temperatures and the adoption into the LTCC technology. Furthermore advanced non-destructive measuring methods are required for the accurate HF characterisation of the thin LTCC substrates. The available thesis is concerned to the development of new high-dielectric LTCC and its HF characterisation. It introduces beside the conventional glass-derived glass-ceramic approach (called passive sintering) an advanced ceramic rich concept (active sintering), with a clearly smaller portion of the particularly developed low softening B-Bi-SI-Zn glass (BBSZ). Further profound analytical investigations of the glasses and the ceramic-rich glass ceramic composite determine that not only the sinter characteristics of the glasses, but also the solubility and the mobility of the ceramic particles in the glass are significantly responsible for the low densification temperature. While the high-dielectric (DK=15) lanthanum-containing glass (LBT)- used within passive sintering - softens and densifies only between a temperature window of 720-750øC, the BBSZ glass re-amorphs and forms again glass at temperature over 700øC after a former crystallisation at ca. 450øC. Ultimately, an additional increase of the solubility of ceramics with sinter additives such as ZnO results in successfully the densification of BaNd2Ti4O12 microwave ceramics (BNT4) with 10 Vol. % BBSZ glass at 900øC. So far a DK of 64 with Q.f = 3000 GHz was achieved as well as a thermal resonance coefficient TCf of less than 5ppm. The non-destructive "split post dielectric resonator method" (SPDR) was investigated for the HF measurement of the high-dielectric LTCC substrates among other methods. After successive full-wave finite elements (FEM) modal analysis the frequently reported TE01d mode splitting was recognized as a continuously approach and/or an overhauling of TE01d mode by the EH111 hybrid, which led to a crucial improvement of the measuring accuracy. Beyond that based on the yielded experimental results the relevance of the analytical effective medium models was examined and discussed as the forecast of the dielectric behaviour of the developed LTCC Composites. In order to match the reality as accurately as possible a statistic 2D-Modell of ceramic rich composite was derived. This model shows that a thin, low dielectric glass network impacts a sufficient electromagnetic isolation the enclosed particle cluster and in contract to Bruggeman model prediction clearly lowers the effective dielectric constant DK value agreeing to the reality.
info:eu-repo/classification/ddc/620, Mikrowellenbauelement, LTCC, Glas, Dielektrische Eigenschaft, Ingenieurwissenschaften, Material Modelling, SPDR, Test Structures
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