Low-temperature Co-fired Ceramic Structure Research Articles

Continuous Flow Analytical Microsystems Based on Low-Temperature Co-Fired Ceramic Technology. Integrated Potentiometric Detection Based on Solvent Polymeric Ion-Selective Electrodes

In this paper, the low-temperature co-fired ceramics (LTCC) technology, which has been commonly used for electronic applications, is presented as a useful alternative to construct continuous flow analytical microsystems. This technology enables not only the fabrication of complex three-dimensional structures rapidly and at a realistic cost but also the integration of the elements needed to carry out a whole analytical process, such as pretreatment steps, mixers, and detection systems. In this work, a simple and general procedure for the integration of ion-selective electrodes based on liquid ion exchanger is proposed and illustrated by using ammonium- and nitrate-selective membranes. Additionally, a screen-printed reference electrode was easily incorporated into the microfluidic LTCC structure allowing a complete on-chip integration of the potentiometric detection. Analytical features of the proposed systems are presented.

Integration Concepts for the Fabrication of LTCC Structures

At the Keck Smart Materials Integration Laboratory at Penn State University, low‐temperature co‐fired ceramic (LTCC) material systems have been used to fabricate a number of devices for a variety of applications. This article presents an overview of the integration of the concepts and materials that we have used to achieve miniaturization and unique device function. Examples of microwave filters, metamaterial antennas, and a dielectrophoretic cell sorter will be presented, with emphasis on device modeling and design, prototype construction methods, and test results.

Influence of processing and conduction materials on properties of co-fired resistors in LTCC structures

The motivation of this study is the need for fundamental understanding of the effects of processing conditions on the electrical properties of low-temperature co-fired ceramic (LTCC) tapes, those screen printed with commercial thick-film pastes of electronic components for increased reliability. The method of the study is realized by analyzing the physical and chemical effects of mono/multilayer firing and firing temperatures on the temperature coefficient of resistance (TCR) and sheet resistance (SR) values of the positive temperature coefficient (PTC) resistors screen-printed on LTCC tapes. The results are discussed with respect to the information obtained by the scanning electron microscopy (SEM), electro dispersive X-ray analysis (EDXS), X-ray and dilatometry analysis. It is shown that the content of pastes combined with varying processing conditions result in deviation from expected TCR and SR values due to the chemical and/or mechanical reactions.

Structural and electrical properties of perovskite ruthenate-based lead-free thick film resistors on alumina and LTCC

CaRuO3 perovskite-based lead-free thick-film resistors (TFRs) were prepared on 96%-alumina and Low Temperature Co-fired Ceramic (LTCC) substrates. The microstructure evolution, possible interactions, and electrical properties of resistors were investigated. The hot and cold TCR values of all the resistors were measured in the temperature range (+20 to +120 ∘C) and (+20 to −120 ∘C), respectively. TFRs with 25% by vol. of CaRuO3 on alumina exhibit a sheet resistance Rs = 5kΩ/sq. with hot and cold TCR of 225 and 470 ppm/∘C respectively, whereas the same composition gives 1.2 kΩ/sq., 16.5 kΩ/sq. and 0.7 kΩ/sq. for co-fired, post-fired resistors on LTCC and buried resistors, respectively. The hot (HTCR) and cold (CTCR) values were evaluated; HTCR = 190 ppm/∘C and CTCR = 314 ppm/∘C were found for co-fired structures; HTCR = 216 ppm/∘C and CTCR = 205 ppm/∘C for post-fired samples and HTCR = 520 ppm/∘C and CTCR = 350 ppm/∘C for buried in LTCC structures.

Evaluation of compatibility of thick-film PTC thermistors and LTCC structures

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film thermistors with high positive temperature coefficients of resistivity, i.e. PTC 5093 (Du Pont) fired either on “green” LTCC (low temperature cofired ceramics) substrates or buried within LTCC structures, were evaluated. The active phase (ruthenium oxide) in the PTC thermistors is not present in the dried films but is formed during firing due to the decomposition of the ruthenate phase. Because of interactions between a glassy LTCC material and thermistors electrical characteristic, i.e. sheet resistivities and noise indices of thermistors fired on the surface LTCC substrates, changed from values obtained on alumina substrates. The differences in the measured electrical parameters were attributed to the interactions between the thermistor layers and the glassy LTCC substrates. The inter-diffusion of oxides, mainly PbO and Al 2O 3, was confirmed by microanalysis. In the case of buried thermistors, presumably due to the incompatibility of both materials, the structure de-laminated during firing. Cracks between the buried PTC films and the LTCC substrates as well as cracks in PTC films resulted in high sheet resistivities and high noise indices.

Canonical ridge waveguide filters in LTCC or metallic resonators

A new physical realization of an elliptic function filter response is proposed for achieving compact size, wide bandwidth, wide spurious free stopband and high-selectivity performance. The filter configuration can be implemented in conventional waveguide technology or embedded in a multilayer low-temperature co-fired ceramic structure for integration with other circuitry in a chip module. The filter is analyzed using rigorous mode matching. To validate the concept, prototypes of four- and six-cavity elliptic filters are designed following a systematic procedure. Approximate synthesis is used to obtain initial dimensions of the filter and the desired optimum response is obtained by means of a final full-wave optimization. The results are verified with other numerical methods and with the measurements of a fourth-order waveguide filter.

Microsensor based on low temperature cofired ceramics and gas-sensitive thin film

A novel design of gas sensor using low temperature cofired ceramics (LTCC) and thin film technologies is presented. The LTCC structure is composed essentially of two ceramic layers with interlayer thick film Pt heater, interdigitated electrodes on top, contact pads and metallic connections realised by vias. The thin films of both SnO 2 and In 2O 3, intentionally doped and activated, were deposited on top of the structure. With some modifications of the lamination process and heat treatment parameters, the authors obtained the upper ceramic layer with the roughness not exceeding 250 nm, what was suitable for thin film technology. The films deposited onto such LTCC structure revealed the sensing properties very similar to the reference films deposited onto glass. The gas-sensitive films were tested with changing concentrations of reducing and oxidising gases in air. The necessary sensor working temperature was obtained and stabilised using a custom-built digital controller. The low heat capacity of the sensor structure enabled also a sinusoidal temperature control. The satisfactory results obtained by the authors indicate that the connection of LTCC and thin film technologies can lead to the fabrication of good quality gas sensors.

A drop-on band-pass filter for millimeter-wave multichip modules on LTCC

Low-temperature cofired ceramic (LTCC) is increasingly used to realize multichip modules (MCMs), even in the millimeter (mm)-wave frequency range. Fabrication tolerances of standard LTCC structures, however, still are limiting the performance of band-pass filters integrated directly on the LTCC substrate. This contribution therefore describes the design and the performance of a separate filter chip based on alumina which simply is placed on top and glued to the LTCC substrate using nonconductive epoxy. A special electromagnetic field coupling is used to provide both the interconnect of signal lines and filter ground. The design includes special measures to reduce the tolerance requirement for filter placement and glue thickness.

Optimization of thermal distribution in ceramics and LTCC structures applied to sensor elements

Thermal properties of Pt or RuO2 thick‐film heaters made on alumina, aluminum nitride or low temperature co‐fired ceramics (LTCC) were compared in the first step of our work. Special holes to improve the heat distribution were included. Several heater layouts were analysed. The heat distribution was measured by an infrared camera, at different heating power. Second, the optimization of LTCC constructions was carried out. The simple structure of LTCC permitted the achievement of a high package density. It was possible to integrate a heating element made from special thick‐film ink as a buried film, inside a substrate. An important step in our technology was the making of the holes. A pattern of holes (achieved by punching or laser cutting) around the heating area permitted a changeable heat gradient. The quality of lamination and the structure of the buried elements were investigated with an ultrasonic microscope.

A low cost manufacturing process for high density hybrid components based on multilayer polyimide/ceramic structures

The authors describe a multichip module component manufacturing process combining multilayer polyimide and multilayer low-temperature cofired ceramic structures, using the latter as the encapsulation support. A first characterization of the results is also reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>