Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...

Low loss dielectric materials for LTCC applications: a review

Nanomaterials are at the leading edge of the emerging field of nanotechnology. Their unique and tunable size-dependent properties (in the range 1–100 nm) make these materials indispensable in many modern technological applications. In this Review, we summarize the state-of-art in the manufacture and applications of inorganic nanoparticles made using continuous hydrothermal flow synthesis (CHFS) processes. First, we introduce ideal requirements of any flow process for nanoceramics production, outline different approaches to CHFS, and introduce the pertinent properties of supercritical water and issues around mixing in flow, to generate nanoparticles. This Review then gives comprehensive coverage of the current application space for CHFS-made nanomaterials including optical, healthcare, electronics (including sensors, information, and communication technologies), catalysis, devices (including energy harvesting/conversion/fuels), and energy storage applications. Thereafter, topics of precursor chemistry and ...

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Continuous Hydrothermal Synthesis of Inorganic Nanoparticles: Applications and Future Directions

The recent rapid advances in wireless telecommunication, Internet of Things, the Tactile Internet (5th generation wireless systems), the Industrial Internet, electronic warfare, satellite broadcasting, and intelligent transport systems demand low loss dielectric materials with ultra-low sintering temperatures with modern component fabrication techniques. Properties of microwave ceramics depend on several parameters including their composition, the purity of starting materials, processing conditions, and their ultimate densification/porosity. The preparation, characterization and properties of important materials families such as glass ceramics and molybdates, tellurates, tungstates and vanadates, in combination with Bi, K, Na, Ag, Li, Ba, Ca, etc. with ultra-low sintering temperatures are discussed. In this review the data for all reported low-loss microwave dielectric ceramic materials with ultra-low sintering temperatures are collected and tabulated. The table of these materials gives the relative permittivity, quality factor (tan  δ ), temperature variation of the resonant frequency, crystal structure, sintering temperature, measurement frequency and references. The data arranged in the order of increasing relative permittivity will be very useful for scientists, industrialists, engineers and students working on current and emerging applications of microelectronics.

Low temperature co-fired ceramics with ultra-low sintering temperature: A review

Sintering is a common technique for the production of ceramic, metallic and composite bodies and components. During this process it is known that internal stresses can arise from external constraint or from differential densification. These stresses can give rise to significant strain rate changes, distortions and damage in the fired parts. For quality control of sintered bodies, it is necessary to measure or predict the changes in deformation behaviour that occurs as the porous starting bodies undergo densification. Contributions of the continuum mechanical approach to this problem of constrained sintering are reviewed. Theoretical predictions as well as experimental techniques and results are detailed. Special emphasis is given to the development of anisotropy that can develop in the microstructure of a sintering body in response to the internal stresses.

Constrained sintering: A delicate balance of scales

The use of microwaves for heating is well established in society, being used in domestic and some industrial processes. However, there is potential for this technology to be introduced and applied to many other industrial heating processes, which offers unique advantages not attained with conventional heating. In this sense, microwave technology is being explored as one method to assist in waste management. Currently, significant quantities of hazardous wastes are generated from a multitude of products and processes. The increase in both the quantity and of the diversity of waste production is now posing significant problems for their effective management. New technologies are being investigated to develop systems which shall support the safe handling, transportation, storage, disposal and destruction of the hazardous constituents of this waste. The recent interest in microwave technologies appears to offer the best solution to waste management, whereby a variety of microwave systems can be designed, developed and tailored to process many waste products. It is possible that microwave technologies shall provide for: (i) a reduction in waste volume, (ii) rapid heating, (iii) selective heating, (iv) enhanced chemical reactivity, (v) the ability to treat waste in-situ, (vi) rapid and flexible processes that can also be controlled remotely, (vii) ease of control, (viii) energy savings, (ix) overall cost effectiveness, (x) portability of equipment and processes, (xi) cleaner energy source compared to some more conventional systems, etc. From existing processes for the harnessing of energy and raw materials from waste, thermochemical conversion routes are suitable candidates for the application of microwave technology. One of the thermochemical processes which is rapidly gaining in importance in this field is pyrolysis. This process not only allows for higher energy recovery from the waste, but it also generates a wide spectrum of products. Hitherto, most published work on the pyrolysis process has dealt with conventional heating systems, although recent interest in microwave-assisted pyrolysis (MP) has highlighted its unique advantages, not within the scope of traditional methods. The aim of this chapter is to emphasize the principles of MP and to show recent research on the application of this technology to waste treatment. As an introduction to the topic, a brief background on the pyrolysis process and the fundamentals of microwave irradiation as an energy source are presented.

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Microwave Heating Applied to Pyrolysis

Advanced materials of rare earth derived glass and reactive bonded glass-ceramic composites are exceptionally interesting for 1C packaging, radar, antennas and wireless technologies for the next generation of miniature electronic devices. Glass ceramic composites in the system 1:1:4 BaO-Nd 2 O 3 -TiO 2 and modified rare earth glasses based on boron oxide for passive integration in LTCC demonstrate excellent dielectric properties in the middle permittivity F range of 20/70 with high quality factor Q and low temperature coefficient TCf at microwave frequencies. Depending on the glass-ceramic system, concentration, significant processing parameters e.g. powder preparation techniques and sintering of dense composite at temperatures < 900 C were achieved. Dielectric properties were studied by a cavity resonator method at frequencies 1-6 GHz in correlation of the crystalline microstructure. This work was supported by tridimensional modeling systems to estimate dielectric behavior of multiphase glass ceramic composites.

LTCC glass-ceramic composites for microwave application

The miniaturisation potential of LTCC devices would be drastically improved, if inductances could be directly integrated into the multilayer structure. Co-firing of ferrite green tapes in combination with dielectric green tapes, which offers this possibility, is the focus of the paper. Commercial dielectric LTCC tape and a new developed ferrite green tape on the basis of BaFe 12 O 19 were characterised. To manufacture composite structures of these two types of green tape via LTCC technology, the ferrite tape must densify at temperatures around 900 °C. The characterisation of the tapes included the green tape structure and shrinkage behaviour by means of density measurements, thermogravimetry, thermomechanical analysis, optical dilatometery and microstructure investigations. The shrinkage and warpage behaviour of both single tapes and composites was characterised. By combination of the different tapes a constrained sintering behaviour could be generated. Stress effects during sintering and cooling cycles could be related to occurring defects.

http://web1.see.asso.fr/electroceramics/html/cdrom/pdf/Papers/A04-03-Ora.pdf

Constrained sintering of dielectric and ferrite LTCC tape composites

Hexaferrites are usually prepared according to the standard mixed oxide method with high sintering temperatures of up to 1350°C, which are not suitable for low temperature cofired ceramics (LTCC) technology. In this work, the sintering temperature of BaFe 12 O 19 was reduced to 900°C by the development of reaction-bonded glass ceramics systems for LTCC-hexaferrites. Low amounts of reactive glasses (<7 vol.%) based on boron and zinc oxide were used as sintering additives to achieve full densification at 900 °C. The influence of variation in glass-ceramics compositions, different processing parameters, advanced powder preparation by using high-energy milling and the calcination temperature on achieving high-μ ferrites at 900°C was studied. The magnetic properties of these LTCC-hexaferrites were characterized by a coaxial airline method and impedance measurements in the frequency range of 0.1-10 GHz. The influence of phase composition and microstructure on magnetic properties was also discussed.

http://web1.see.asso.fr/electroceramics/html/cdrom/pdf/Papers/A02-04-Ora.pdf

New LTCC-hexaferrites by using reaction bonded glass ceramics

The invention relates to a glass ceramic mass, comprising at least one oxide ceramic, containing barium, titanium and at least one rare earth metal Rek and at least one glass material, containing at least one oxide with boron and at least one oxide of a rare earth metal Reg. The glass material further contains either an oxide of a tetravalent metal Me4+, or at least one oxide of a pentavalent metal Me5+. A compression of the glass ceramic mass occurs above all by viscous flow. A low vitrification temperature can thus be achieved. Crystallisation products are produced during and/or after the compression. The rare earth oxide and the crystallisation products can be used to pre-determine each of a dielectric material property of the glass ceramic mass in a wide range such as permittivity (15 - 80), Q (350 - 5000) and Tf value (± 20 ppm/K). The glass ceramic mass is characterised by a vitrification temperature of below 850 °C and can thus find application in LTCC (low temperature cofired ceramics) technology for the integration of a passive electrical component in the volume of a ceramic multi-layer body. Suppression of a lateral shrinkage may be achieved in a composite with a ceramic film blank made from another ceramic material compressed at a higher temperature.

Glass ceramic mass and use thereof

The invention relates to a plastic compound comprising at least one polymer, at least one organic starting compound of a ceramic active ingredient and at least one glass material for forming a glass ceramic with the aid of said ceramic active ingredient, said material containing glass and/or a starting material of glass. The plastic compound is characterised in that the glass has a glass transition point Tg, which essentially corresponds to a decomposition temperature Tz of the organic starting compound. The organic starting compound is preferably a polyorganosiloxane. The thermal decomposition of the polyorganosiloxane leads to the formation of a porous parent structure consisting of silicon oxide, which is infiltrated by the glass, which is molten at the decomposition temperature. In addition, a dense, mechanically stable glass ceramic layer is formed. Said layer is electro-insulating so that a cable retains its function in the event of fire. The plastic compound is thus used to electrically insulate products that are exposed to fire-risks, for example cables or domestic appliances.

Oliver Dernovsek

Papers

LTCC glass-ceramic composites for microwave application

Constrained sintering of dielectric and ferrite LTCC tape composites

New LTCC-hexaferrites by using reaction bonded glass ceramics

Glass ceramic mass and use thereof

Plastic compound, product composed of said compound and use of said compound