Oxygen nonstoichiometry and dielectric evolution of BaTiO3. Part II—insulation resistance degradation under applied dc bias

Abstract

The microchemical and microstructural origins of insulation-resistance degradation in BaTiO 3-based capacitors are studied by complementary impedance spectroscopy and analytical transmission electron microscopy. The degradation under dc-field bias involves electromigration and accumulation of oxygen vacancies at interfaces. The nonstoichiometric BaTiO 3−␦ becomes locally more conducting through increased oxygen vacancy concentration and Ti ion reduction. The symmetry across the dielectric layer and locally across each grain is broken during the degradation process. Locally, the nonstoichiometry becomes so severe that metastable lattice structures are formed. The degradation in insulation resistance at the grain boundaries and electrode interfaces is associated with the double Schottky-barrier potential lowering and narrowing. This may correlate with an effective decrease in net acceptor charge density at the grain boundaries.

Effect of Cr additions on the electrical properties of Ni–BaTiO3 ultra-thin multilayer capacitors

“…The p-type BaTiO 3 -Ni interface will have a hole accumulation and would show an ohmic contact [14]. Previous studies of BME-MLCC chips before and after the reoxidation treatment confirmed the formation of blocking Schottky barrier in either case [3,5]. This means that the BaTiO 3 -based dielectric is still n-type semiconducting even after the reoxidation treatment and different from the airfired cases.…”

“…Generally, the total impedance of actual MLCCs is modeled by a series of leaky capacitive components for the dielectric-electrode interfaces (E), dielectric grains (G) and dielectric grain boundaries (GB) [5,16,22,23]. The corresponding resistance for each element at low AC field (~50 mV), was calculated using this model and is summarized in Table 1.…”

“…One of the current issues in state-of-the-art base-metal electrode multilayer ceramic capacitors (BME MLCCs) with dielectric and electrode layer thicknesses around or below 1 μm is the discontinuity of Ni electrodes, which can affect the electrical performance and reliability of final products [1,2]. Recently, our investigations revealed the formation of an interfacial low-melting point (Ni,Ba,Ti) alloy with a melting point as low as 1000-1150°C at Ni-BaTiO 3 interfaces [3][4][5][6]. The reduction process to produce the metallic Ti and Ba components results from the presence of residual carbon content from the organics used in the tape casting and screen printing process steps.…”

Effect of Cr additions on the microstructural stability of Ni electrodes in ultra-thin BaTiO3 multilayer capacitors

“…Therefore, alloying is thermodynamically possible if BaTiO 3 undergoes significant reduction [16][17][18][19]. In fact, we recently identified the formation of discrete interfacial alloy layers consisting of Ni, Ba and Ti with a thickness of 5-15 nm between Ni electrodes and BaTiO 3 in commercial MLCCs [16][17][18][19]. The appearance of this alloy was attributed to the local reduction of the BaTiO 3 by residual carbon remaining from the binder burnout process.…”

A comparison study of solving diffusion equations with different algorithm methods

“…The resistance degradation rates of dopant, temperature, and voltage dependences in SrTiO 3 ceramics and single crystals were investigated by Waser et al 17,18 The oxygen vacancy concentration is critical in the resistance degradation, and it increased across the dielectric layers towards the cathode while decreased toward the anode region. 19 An accumulation of sub-stoichiometric points defects were observed at the cathode electrode. 20 Except experimental studies, theoretical studies focused on understanding the mechanism of resistance degradation [21][22][23][24] and bipolar switching behaviors.…”