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This paper aims to focus on the application of low temperature co-fired ceramic (LTCC) technology in the fabrication of a microfluidic module with integrated microwave components. The design, technology and performance of such an LTCC-based module is investigated. The rapid heating of liquid samples on a microliter scale is shown to be possible with the use of microwaves.

The developed microwave-microfluidic module was fabricated using well-known LTCC technology. The finite element method was used to design the geometry of the microwave circuit. Various numerical simulations for different liquids were performed. Finally, the performance of the real LTCC-based microwave-microfluidic module was examined experimentally.

LTCC materials and technology can be used in the fabrication of microfluidic modules which use microwaves in the heating of the liquid sample. LTCC technology permits the fabrication of matching circuits with appropriate geometry, whereas microwave power can be used to heat up the liquid samples on a microliter scale.

The main limitation of the presented work is found to be in conjunction with LTCC technology. The dimensions and shape of the deposited conductors (e.g. microstrip line, matching circuit) depend on the screen-printing process. A line with resolution lower than 75 µm with well-defined edges is difficult to obtain. This can have an effect on the high-frequency properties of the LTCC modules.

The presented LTCC-based microfluidic module with integrated microwave circuits provides an opportunity for the further development of various micro-total analysis systems or lab-on-chips in which the rapid heating of liquid samples in low volumes is needed (e.g. miniature real-time polymerase chain reaction thermocycler).

Examples of the application of LTCC technology in the fabrication of microwave circuits and microfluidic systems can be found in the available literature. However, the LTCC-based module which combines microwave and microfluidic components has yet to have been reported. The preliminary work on the design, fabrication and properties of the LTCC microfluidic module with integrated microwave components is presented in this paper.

The main purpose of this study is to test the performance of the ink-jet printed microwave resonant circuits on Low temperature co-fired ceramics (LTCC) substrates combined with microfluidic channels for sensor applications. Normally, conductive patterns are deposited on an LTCC substrate by means of the screen-printing technique, but in this paper applicability of ink-jet printing in connection with LTCC materials is demonstrated.

A simple microfluidic LTCC sensor based on the microstrip ring resonator was designed. It was assumed the micro-channel, located under the ring, was filled with a mixture of DI water and ethanol, and the operating frequency of the resonator was tuned to 2.4 GHz. The substrate was fabricated by standard LTCC process, and the pattern of the microstrip ring resonator was deposited over the substrate by means of an ink-jet printer. Performance of the sensor was assessed with the use of various volumetric concentrations of DI water and ethanol. Actual changes in concentration were detected by means of microwave measurements.

It can be concluded that ink-jet printing is a feasible technique for fast fabrication of micro-strip circuits on LTCC substrates, including microfluidic components. Further research needs to be conducted to improve the reliability, accuracy and performance of this technique.

The literature shows the use of ink-jet printing for producing various conductive patterns in different applications. However, the idea to replace the screen-printing with the ink-jet printing on LTCC substrates in connection with microwave-microfluidic applications is not widely studied. Some questions concerning accuracy and reliability of this technique are still open.

The low-temperature co-fired ceramics (LTCC) microfluidic-microwave devices fabrication requires careful consideration of two main factors: the accuracy of deposition of conductive paths and the modification needed to the standard process of the LTCC technology. Neither of them are well-described in the literature.

The first part of this paper deals with the individual impact of screen parameters such as aperture, photosensitive emulsion thickness and mounting angle on the precision of the screen-printed conductive paths fabrication. For the quantitative analysis purposes, the design of experiment method with Taguchi orthogonal array and analysis of variance was used. The second part contains the characterization of the complex permittivity measured for different values of LTCC substrates lamination pressure.

It can be concluded, that the combination of aperture, equal to 24 µm, emulsion thickness 20 µm and mounting angle 22.5° ensures the highest quality of printed conductive metallization. Furthermore, the obtained results indicate, that the modification of the lamination pressure does not affect significantly the dielectric parameters of the LTCC substrates.

This paper shows two aspects of the fabrication of the microfluidic-microwave LTCC devices. First, the resolution of the applied metallization is critical in manufacturing high-frequency structures. The obtained experimental results have shown that optimal screen parameters, in terms of conductive pattern quality, can be found. Second, the received outcomes indicate that the changes in the lamination pressure do not affect significantly the electrical parameters of the substrate. Hence, this effect does not need to be taken into account.

The purpose of this paper was to investigate the influence of non-uniform temperature distribution inside a box furnace during the firing process on electrical properties of the low-temperature co-fired ceramic (LTCC) materials used in radio frequency (RF)/microwave applications.

The authors studied the change in dielectric constant of two popular LTCC materials (DP 951 and DP 9K7) depending on the position of their samples inside the box furnace. Before firing of the samples, temperature distribution inside the box furnace was determined. The dielectric constant was measured using the method of two microstrip lines.

The findings showed that non-uniform temperature distribution with spatial difference of 6°C can result in 3-4 per cent change of the dielectric constant. It was also found that dielectric constant of the two tested materials shows disparate behavior under the same temperature distribution inside the box furnace.

The dielectric constant of the substrate materials is crucial for RF/microwave applications. Therefore, it was shown that 3-4 per cent deviation in dielectric constant can result in considerable detuning of microwave circuits and antennas.

To the best of the authors’ knowledge, the quantitative description of the impact of temperature distribution inside a box furnace on electrical properties of the LTCC materials has never been published in the open literature. The findings should be helpful when optimizing production process for high yield of reliable LTCC components like filters, baluns and chip antennas.