Origin of Abnormal Dielectric Behavior and Chemical States in Amorphous CaCu₃Ti₄O₁₂ Thin Films on a Flexible Polymer Substrate

High dielectric constant thin films processable at nearly room temperature have been demanded for various flexible electronic devices. Here, we explore the origin of abnormal dielectric behavior of amorphous CaCu₃Ti₄O₁₂ (CCTO) thin films having an exceptionally high dielectric constant, in conjunction with chemical states and unusual ferroelectricity in the amorphous state. As an optimal example, the amorphous CCTO film sputtered at room temperature under an oxygen partial pressure of 3.6 mTorr exhibits a dielectric constant of ∼192 and a dielectric loss of <0.1 at 100 Hz. The promising dielectric characteristics are unexpectedly found to originate from the evolution of ferroelectric domains, even in the amorphous state. Strong dependence of oxygen partial pressure on chemical states, vacancy formation, and ferroelectric polarization is very critical for the unexpected dielectric behavior. This may be the very first example of exploring the origin of amorphous dielectric behavior for a material that possesses space charge polarization.