Purpose: 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. Design/methodology/approach: 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. Findings: 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. Originality/value: 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.

This paper presents a detailed analysis of aluminium-doped zinc oxide (AZO) thin films and considers them a promising alternative to indium tin oxide in transparent electrodes. The study focusses on critical properties of AZO, including optical, electrical, and mechanical properties, with potential applications in displays, photovoltaic cells, and protective coatings. The deposited AZO thin films are characterised by excellent optical and electrical parameters, with transparency in the visible light range exceeding 80% and resistivity of 10⁻³ Ω·cm, which gives a high value of figure of merit of 63. Structural analysis confirms the nanocrystalline nature of as-deposited AZO thin films, featuring hexagonal ZnO, orthorhombic Al₂O₃, and cubic Al₂ZnO₄ phases. The study includes nanoindentation measurements, which reveal exceptional hardness (11.4 GPa) and reduced elastic modulus (98 GPa), exceeding typical values reported in the literature, highlighting their protective potential. Abrasion tests have shown extraordinary scratch resistance due to the lack of impact on topography and surface roughness up to 10,000 cycles. This comprehensive study demonstrated that as-deposited AZO thin films are multifunctional materials with exceptional optical, electrical, and mechanical properties. The findings open up possibilities for a variety of applications, especially in protective coatings, where the combination of hardness, scratch resistance, and transparency is both rare and valuable.

Correct operation of electronic circuits (including those made with the ink-jet printing technique) requires the electrical parameters of the structures to be constant or to be changeable, but in a predictable way. Due to that, the flexible, ink-jet printed interdigital capacitors (IDSs) were made and then tested in various conditions. We used the conductive silver-based Amepox AX JP-60n ink. As a substrate, we chose the transparent, flexible Melinex OD foil with a thickness of 125 µm. The IDCs were designed and their capacitances were simulated using Comsol Multiphysics Software. Then the test structures were fabricated by the ink-jet printing process using Dimatix DMP 2831 printer. The printed structures were subjected to environmental exposures in a climate chamber to check the influence of temperature and humidity on the tested samples. The IDCs were also subjected to cyclic bending and straightening tests to analyze the outflow of tensile forces on the printed structures, which are exposed to the common factors, that could diminish the quality of the printed and flexible devices. Due to the small capacitance values of the designed and made IDSs, the measurements showed the key importance of the measuring table on which flexible substrates with IDC capacitors were placed for their capacitance value. Performed tests also demonstrated that in most cases, the capacitors are characterized by an increase in capacitance by a few to a dozen or so % after the ageing tests. Obtained results could be a good groundwork for further research, that will include ways of preventing the creation of discontinuities—or minimizing their impact on the printed device performance.

In this paper we compare the influence of two printing techniques on wideband performance of a microstrip line on LTCC substrate. The inkjet printing and screen printing techniques are compared. The quality of conductive layers is analyzed in terms of material type (paste and ink), their thickness, roughness and shape of pattern edges. Finally, microstrip line performance is characterized for frequencies up to 20 GHz. We show that microstrip lines made of two layers of nanosilver ink performs poorly. In this case the insertion loss can be several times higher (in dB) in comparison to insertion loss introduced by silver paste-made microstrip lines.