Frank Steinhäußer

A finite 3D field simulation method for permittivity gradient implementation of a novel porosification process in LTCC

High frequency substrates show a manifold variety of complex permittivities for different applications. Recent research results demonstrated the possibility of local decrease of the permittivity on LTCC by chemical etching processes, which enables the design of high quality antennas on LTCC. This paper shows a novel approach on the determination of the quantitative reduction of the effective permittivity by scanning electron microscope analyses in combination with finite 3D field simulations of the resulting inhomogeneous material. By the characterization of two different porosified LTCCs it could be shown that this process is suitable for direct antenna integration on glass-ceramic substrates with enhanced values of relative permittivities.

Electromagnetic analysis of conductor track surface roughnesses from 1 GHz to 110 GHz

Conductor tracks comprise a frequency dependent attenuation of electromagnetic waves, since with increasing frequency the current flow is displaced to the near surface region due to the skin effect. Therefore, the effective length of the conductor is increased by the surface roughness, while its effective cross-section is decreased by current displacement, both leading to higher metallization loss. In this paper, surface topographies of typical conductor materials were recorded by confocal microscopy and rebuilt as 3D CAD models. Subsequent electromagnetic simulations reveal the influence due to roughness on high frequency characteristics for physical vapor deposited, thick film and photochemically etched microstrips.

The influence by trapezoidal conductor shapes on ring-resonator based material characterization up to 110 GHz

Material characterization by ring-resonator based measurements is well established since the early 20th century. Since then, the demand on spectral complex permittivity characterizations of RF materials and dielectric covers at higher microwave frequencies rises. Nowadays, both free space applications, e.g. 77 GHz automotive radar systems, and dielectrics for microchip packages require accurate knowledge of the relative permittivity in order to optimize RF circuit designs. With increasing frequencies, the conductor shape of photochemically etched ring-resonators gets more influence on the effective ring radius, and therefore the measured resonance frequencies, which results in an error for the relative permittivity determination. This paper provides correction factors for the ring radii up to 110 GHz, compensating the altered field distribution due to trapezoidal edges.

Electromagnetic analysis of fringed microstrip lines on porosified LTCC

Recent investigations demonstrated that porosification of LTCC enables a local modification of material properties, in particular of the effective permittivity. These studies revealed that the electric field strength is highest at the lower conductor track edges on the porosified substrate. The local field strength peaks cause substantial influence on the effectiveness of permittivity reduction due near-surface material abrasions. In this paper, the influences of these randomly fringed boundaries on electromagnetic properties are investigated for different degrees of fraying. The gained results are compared to measured screen print edges by scanning electron microscope image analysis of co-fired and post-fired gold conductors, and will contribute for reliable circuit design on porous LTCC in the future.

Silver Metallization on Porosified LTCC Deposited by Pulse Plating Technique

Present microelectronic devices especially when including high frequency applications are in need of highly integrated metallization technologies. Silver is considered as a future interconnection material for such devices and systems due to its low bulk resistivity of about 1.6 μΩ·cm at 20°C. Conventional thick film metallization techniques on low temperature co-fired ceramics such as screen printing are only partly capable of meeting the requirements in terms of lateral resolution and precision. Furthermore, on advanced surfaces such as porosified composite LTCC, also thin film metallization techniques (e.g. sputtering) meet their limits due to a poor coverage and hence, a low electrical conductivity. In this study, it is shown, that bipolar pulse plating of silver is capable of bridging the pores of the surface of the porosified substrate without penetrating them. The plated metallizations feature very fine grains with an average diameter of approx. 90 nm and a maximum up to 250 nm. The film resistivity...

Porösizierte Glaskeramik-Substrate für die Radarsensorik

Fur Komfortfunktionen und aktive Sicherheitsfunktionen werden in modernen Fahrzeugen Radarsensoren im freigegebenen Frequenzband zwischen 77 GHz und 79 GHz benotigt. Um einen langzeitstabilen Betrieb bei gleichzeitig geringer Baugrose der Radarsensoren zu gewahrleisten, mussen robuste Materialsysteme mit geeigneten dielektrischen Eigenschaften im Bereich der Aufbau- und Verbindungstechnik verwendet werden. Kommerzielle LTCC (engl.: low temperature cofired ceramics) Glaskeramiksubstrate ermoglichen einen dreidimensionalen Aufbau bei hervorragenden Hochfrequenzeigenschaften. Um die Antennencharakteristik zu optimieren, wird ein Porosizier-Verfahren vorgestellt, um eine lokal reduzierte Permittivitat zu erreichen. Dabei wird nasschemisch das Glaskeramikmaterial porosiziert, um oberflachennah eine Schicht mit reduzierter dielektrischer Konstante zu erzielen. Diese wird durch den Vergleich von Hochfrequenzmessungen mit numerischen Simulationsergebnissen bestimmt.

A simplified equivalent model for microwave characteristics of porosified LTCC

High frequency materials show a manifold variety of complex permittivities for different applications. Recent research results demonstrated that porosification of Low Temperature Cofired Ceramics (LTCC) represents a new manufacturing technology, which enables local selective reduction of the relative permittivity. The permittivity gradients were measured and subsequently modeled to perform electromagnetic field simulations. The results of the generated complex CAD model can be used, to create a simplified equivalent model, which is suitable for rapid RF circuit design on porosified LTCC. Since material properties vary between circuit components on dense and porous LTCC, the permittivity-dependency on the lumped elements of the transmission line model is considered. It is shown that the introduced porosification gradient can be transferred to an equivalent circuit diagram according to the transmission line model.