Low Temperature Co-fired Ceramics (LTCC) is one of the microelectronic techniques. This technology was initially developed as an alternative to Printed Circuit Boards (PCB) and classical thick-film technology, and it has found application in the fabrication of multilayer ceramic boards for electronic devices. Fast and wide development of this technology permitted the fabrication of 3D mechanical structures and integration with various different processes. Thanks to this, LTCC has found application in the manufacturing of various microelectronic devices. This paper presents an overview on LTCC technology and gives a detailed summary on physical quantity sensors fabricated using LTCC technique.

Electrocaloric (EC) materials have shown the potential to replace some of the technologies in current commercial refrigeration systems. The key problem when fabricating an efficient EC refrigerator is the small adiabatic temperature change that current bulk materials can achieve. Therefore, such a solid-state EC refrigerator should be engineered to enhance the EC temperature change by rectifying the induced EC heat flow. Here, we present a numerical study of a device that couples the EC and electromechanical (EM) effects in a single active material. The device consists of several elements made from a functional material with coupled EC and EM properties, allowing the elements to bend and change their temperature with the application of an electric field. The periodic excitation of these elements results in a temperature span across the device. By assuming heat exchange with the environment and a low thermal contact resistivity between the elements, we show that a device with 15 elements and an EC effect of 1.2 K achieves a temperature span between the hot and cold sides of the device equal to 12.6 K. Since the temperature span can be controlled by the number of elements in the device, the results suggest that in combination with the so-called “giant” EC effect (ΔTEC ≥ 10 K), a very large temperature span would be possible. The results of this work should motivate the development of efficient EC refrigeration systems based on a coupling of the EC and EM effects.

Laminated 3D structures made using lowtemperature co-fired ceramic (LTCC) technology are practical for ceramic micro-electro-mechanical systems (C-MEMS). The sensors for mechanical quantities, and/or actuators, are fundamental parts of MEMS. Thick-film resistors can be used to sense the mechanical deformations, and thick-film piezoelectric materials can be used as electro-mechanical transducers in a C-MEMS structure. The integration of these thick-film materials on LTCC substrates is in some cases difficult to realise due to interactions with the rather glassy LTCC substrates. The subject of our work is an investigation of thick-film materials for electro-mechanical transducers (sensors and actuators) and their compatibility with LTCC substrates. Resistors made with commercial thick-film resistor materials for use as sensors on LTCC substrates have been investigated and evaluated. Ferroelectric ceramic materials based on solid solutions of lead zirconate titanate (PZT) with low firing temperatures around 850°C were developed for thick-film technology and evaluated on LTCC substrates.

The influence of thermal stresses versus the phase composition for 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (0.65PMN–0.35PT) thick films is being reported. The thermal residual stresses in the films have been calculated using the finite-element method. It has been observed that in 0.65PMN–0.35PT films a compressive stress enhances the thermodynamic stability of the tetragonal phase with the space group P4mm.

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LTCC-based pressure sensors are promising candidates for wet-wet applications in which the effect of the surrounding media on the sensor's characteristics is of key importance. The effect of humidity on the sensor's stability can be a problem, particularly in the case of capacitive sensors. A differential mode of operation can be a good solution, but manufacturing the appropriate sensing capacitors remains a major challenge. In the case of piezoresistive sensors the influence of humidity is less critical, but it still should be considered as an important parameter when designing sensors for low-pressure ranges. In this paper we discuss the stability of the sensors' offset characteristics, which was inspected closely using experimental and numerical analyses.

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