Electromagnetic Wave Absorbing Properties of High-Permittivity Ferroelectrics Coated with ITO Thin Films of 377 Ω

Abstract

For the aim of thin electromagnetic wave absorbers used in quasi-microwave frequency band, this study proposes the high-permittivity ferroelectrics of quarter wavelength thickness (λ/4 spacer) coated with ITO thin film of 377 Ω/sq (impedance transformer). For high-permittivity dielectrics, BaTiO3 (BT), 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (PMN-PT) and 0.8Pb(Mg1/3Nb2/3)O3-0.2Pb(Zn1/3Nb2/3)O3 (PMN-PZN) are prepared by conventional ceramic processing technique. The ferroelectric materials show high dielectric constant and dielectric loss in microwave frequency range and their dominant loss mechanism is considered to be domain wall relaxation or dynamics of polar clusters. The microwave absorbance (determined at 2 GHz) of BT, PMN-PT and PMN-PZN are found to be 65% (at a λ/4 thickness of 3.5 mm), 20% (2.5 mm) and 37% (2.5 mm), respectively. By coating ITO thin films on the ferroelectric substrates with a thickness of λ/4, the microwave absorbance is greatly improved. Particularly, when the sheet resistance of ITO films is closed to 377 Ω/sq, the reflection loss is reduced to −20 dB (99% power absorption). This is attributed to the wave impedance matching led by ITO thin film combined with a λ/4 thickness of high-permittivity dielectric spacer. It is, therefore, successfully proposed that the ITO/ferroelectrics structure with controlled electrical properties and thickness can be useful as thin microwave absorbers used in quasi-microwave frequency band.