Precursors for Ceramics used in Passive Components: SUPERAMIC™

• Passive Components
• Use of Rare-Earths

• Passive Components Passive electronic components contain a large number of products that perform functions that are supplementary or peripheral compared with the performance of active components or semi-conductors principally in amplification, commutation and calculation, display.

It might be said that semi-conductors perform the functions of decision and command, while passive components are in charge of preparation, protection and execution.

Resistors for instance, resist the passage of current to a greater or lesser degree, a portion of which is then transformed into heat. Capacitors (which stock electrical energy) are used for filtering, uncoupling, tuning, transformation, etc. They may be used in conjunction with coils and ferrites (also called magnetic components) and piezoelectronic components (quartz and ceramics) for tuning, filtration and time keeping.

The main functions of micro-wave filters and dielectric resonators are to filter electromagnetic waves in wireless communication devices to increasingly shorter wave lengths which are dedicated to the application.

Another type of electronic component is the oxygen sensor used in automotive exhaust gas systems. It is essential to maintain the oxygen content of the exhaust gas of gasoline engine vehicles in a narrow range in order for the three-way catalytic converter to function correctly. The oxygen sensor constantly measures this parameter & by means of a closed-loop system comprising the engine and the engine management system, it ensures that it remains in the required range.

• Use of Rare Earths

Precursors for Rare Earths based ceramics are used in numerous applications: microwave filters, capacitors, ferrites, resistors, varistors, oxygen tubes… Rare Earths are largely used because of their main valency (3+) and their specific ionic radius which allow them to be suitable with barium titanate and zirconia formulations.

Rhodia Electronics & Catalysis has developed a wide range of performance additives for electronic ceramics which brand name is: SUPERAMIC™. These additives are Rare Earths or zirconia salts or oxides. Their purity or their ability to disperse in ceramic formulations correspond to a new generation of passive components, e.g. reliability and miniaturization.

The SUPERAMIC™ range of performance products includes:

• Nd which is used widely in NPO capacitors, characterized by a great stability of the dielectric constant on the basis of temperature. The primary function of Nd in the titanium structure of barium is to flatten the DC / C = f(T) curve where C = capacity and T = temperature.
• Yttrium and other heavy Rare Earths which enable stabilization of the core/shell structures and to increase the durability of mulltilayers capacitors using NI or Cu based electrods.
• Pr, La or Sm, which acts on the same parameter as Nd or on other properties of dielectric composition.
• Zircona, which is an additive for barium titanate but also for piezoelectric PZT type.

The rapid development of mobile telecommunications is contributing to the increase in microwave components. Yttrium is used in YIGs (Yttrium - Iron - Garnets), which are ferrites, and YAGs (Yttrium - Aluminium - Garnets), used as resonators, circulators or filters in microwave equipment, particularly base stations for mobile telephones. Gadolinium is also a standard doping agent for these garnet structures. New generation filters and microwaves resonators are using Nd or Sm as a main component

The chemical and structural properties of Rare Earths are also beneficial in the technical ceramics industry. The best example is zircon, the crystalline structure of which is stabilized in quadratic or cubic form, or a mixture of the two, by adding determined quantities of yttrium oxide (1 to 10 % by mole). Depending on the circumstance, one then takes advantage of the ionic conductivity [induced by oxygen gap compensation for the difference in valence of the stabilizing cation (Y₃+) and zirconium (Zr4+)] and its variation with partial oxygen pressure, or even good mechanical properties, the origin of the use of stabilized zircon in the manufacture of cutting tools. Furthermore, when there is total stabilization of the cubic phase (for Y₂03 molar contents greater than 7 %), the light refraction properties approximate those of a diamond so closely that the cubic zirconium is the best imitation of it, and there is a high demand for its use in jewelry.

Praseodymium terbium oxides are used in the manufacture of ZnO based varistors - electronic components whose resistance decreases sharply when the tension applied reaches a certain value, to allow the protection of electronic devices or high-voltage circuits.

• Contacts

If you would like more informations, please contact:
ec-electronics@eu.rhodia.com