High permittivity dielectrics. Effects of nano and microstructures

Dielectric materials play a variety of roles in both electronics and electricity. In capacitors, they can be used both for energy storage and for decoupling electronic circuits. In field-effect transistors, they are essential for the design of gates, and their permittivity is decisive in defining the dimensions of this component.

Today, the manufacture of lead-free dielectrics has become a major issue due to the volatility of lead oxide (PbO) and its harmfulness to human health and the environment. With several European countries aiming to eliminate the use of lead-based products in the short term, alternative dielectric materials are being sought. In addition, PbO volatilization causes variations in the composition of ceramics, greatly altering their dielectric properties and making them more difficult to manufacture.

For the electronics industry, this restriction is compounded by other difficulties. Component minimization means that the design of new field-effect transistors, with dimensions of less than 100 nm, requires the use of very thin layers for the gate, as the aspect ratio of this component is decisive for its operation. However, very thin dielectrics allow electronic conduction by tunneling, which leads to problems of both power consumption and transistor overheating. However, the use of materials with higher dielectric constants means that gate thickness can be increased. This property is therefore essential for reducing the size of transistors and thus increasing their speed.

At the same time, reducing the size of capacitors is a necessity in order to reduce the distance between the passive and active components of electronic circuits. As this distance determines the time required to send an electrical signal, one of today's major challenges is to be able to produce thin-film capacitors directly on the printed circuit board. However, high permittivity ceramics have sintering temperatures of the order of 1,000°C, far higher than the maximum temperatures accepted by commonly used polymer substrates.

In addition, for energy storage applications, the optimization of geometric parameters often leads manufacturers to use a multiple thin-film design for high-capacity capacitors. However, few of the metals used as electrodes are compatible with the sintering temperatures of high permittivity ceramics. What's more, these ceramics are not compatible with less expensive processes for producing thin-film devices, such as ink printing.

This is why the search for new materials that offer both good performance and low environmental impact has turned to nano- and microstructuring. These techniques can either improve the properties of commonly used dielectrics, or introduce new materials for...