Leakage Current Characteristics of Lead-Free K_0.5Na_0.5NbO₃ Ferroelectric Thin Films with (K,Na) Excess and Li Substitution

Abstract

K0.5Na0.5NbO3 thin films with (K,Na) excess and LiNbO3 substitution were fabricated on a Pt substrate by a chemical solution deposition method. The K0.5Na0.5NbO3 thin films with (K,Na) 10 mol % excess and LiNbO3 5 mol % substitution showed a saturated ferroelectric polarization–electric field (P–E) hysteresis loop and the estimated remanent polarization (P r) and coercive field (E c) were 8.6 µC/cm2 and 40 kV/cm at 280 kV/cm, respectively. Compared to pure K0.5Na0.5NbO3 thin films, the ferroelectric polarization of the thin film was improved and leakage current densities were decreased. Moreover, the ferroelectric polarization and leakage current characteristics are stable for higher applied electric fields and elevated temperatures. The conduction behaviours of these films were analyzed by Schottky and Poole–Frenkel emission.

Temperature-dependent leakage current behavior of epitaxial Bi0.5Na0.5TiO3-based thin films made by pulsed laser deposition

“…This is in agreement with previously reported findings on the leakage current behavior of lead-free thin films where the ohmic conduction is responsible for electrical charge transport at low voltages. 12,14,15,21,22 In the ohmic region, when the electrodes are well adhered to the film and form an ohmic contact with infinite supply of charge carriers, the current density can be expressed by 26…”

“…21 Some other leakage current mechanisms including bulkcontrolled Poole-Frenkel (PF) and interface-controlled Schottky mechanisms have also been suggested as fundamental conduction mechanisms in ferroelectric thin films. 12,14,15,19,29 PF mechanism, quantitatively expressed in Eq. (3), describes the thermal emission of charge carriers from trapped centers under high electric fields, 28,30,31…”

“…The leakage current behavior in some of the lead-free thin films such as (K,Na) 0.5 NbO 3 (KNN) [11][12][13][14] and BiFeO 3 (BFO)-based [15][16][17][18][19] compositions has been extensively investigated. On the other hand, published literatures pertaining to BNT-based systems have mainly focused on the ferroelectric and piezoelectric properties of these thin films.…”

Growth and physical properties of highly oriented La-doped (K,Na)NbO3 ferroelectric thin films

“…Alkaline niobate-based compounds, especially (K 0.5 Na 0.5 )NbO 3 (KNN), are nowadays being considered as one of the promising lead-free piezoelectric materials because of their good piezoelectricity and a high Curie point [4]. However, serious problems exist for obtaining KNN polycrystalline thin films, because they are usually obtained with high leakage current, and thus with poor ferroelectric properties [5,6]. Moreover, it is important to take special care of the Na/K relationship to obtain high quality thin films [7,8], otherwise low quality ferroelectric properties are obtained.…”

Optical and Electric Properties of Bi0.5Na0.5TiO3-Based Thin Films Grown on Indium–Tin-Oxide-Coated Glass Substrates

“…Most of the reports focus on the synthesis and electric properties of the lead-free materials in bulk form, whereas only a few focus on thin films counterparts that can be easily used in various electronic devices. [3][4][5][6][7][8][9][10][11][12][13][14] This might be at least partly due to that the electric properties of thin film form are not as good as that of their bulk counterparts. Furthermore, the literatures dealing with lead-free thin films mainly focus on electric properties but seldom on their optical properties.…”