Damoon Sohrabi Baba Heidary

Electrical characterization and analysis of the degradation of electrode Schottky barriers in BaTiO3 dielectric materials due to hydrogen exposure

Hydrogen gas creates a highly damaging environment that degrades electrical properties in oxide based dielectrics and piezoelectrics. In this study, the degradation resistivity due to hydrogen gas in a barium titanate X7R dielectric is designed and processed for base metal electrode capacitors. The present paper is devoted to I-V measurements and the loss of resistivity in the electrode Schottky barriers. The DC degradation and asymmetries noted in I-V forward and reverse biasing conditions were assumed to be hydrogen ion interstitials, locally creating donor substitutions. Thermionic and field emission conductivity mechanisms are applied to model the I-V data; the conductivity is controlled by the Schottky barrier heights and hydrogen ions localizing at the interfaces. Finally, a mechanism was proposed for resistivity degradation due to exposure to hydrogen gas. The proposed mechanism predicts the degradation should be reversible, and its validity was examined by recovery tests.

Evaluating the merit of ALD coating as a barrier against hydrogen degradation in capacitor components

The degradation of the properties of electronic materials due to exposure to hydrogen gas is a common problem in electro-ceramic device components. In this study, we explore atomic layer deposition (ALD) coatings as a potential barrier against hydrogen gas. Three ALD chemistries of ZnO, Al2O3, and HfO2 with different thicknesses were coated onto BaTiO3 capacitors, and their merit as hydrogen gas barriers at high temperatures was evaluated by I–V and impedance spectroscopy which could monitor the degradation of resistivity. These experimental investigations provide the temperature of merit (T0) and the proton (H-ion) diffusion coefficients of the ALD layers, which can be used to evaluate their barrier effectiveness. Transmission electron microscopy (TEM) analysis was applied to examine the ALD layers before and after the I–V tests and find out the physical dimensions, conformity, and structure (amorphous and crystalline) of the ALD layers. We determine that the failure of the barrier characteristics at elevated temperatures is due to crystallization. The diffusion coefficient associated with protons before and after crystallizations in ALD layers was determined. Within the chemistries investigated here, the most effective ALD layers are made of HfO2 with an amorphous structure.

Study on the behavior of atomic layer deposition coatings on a nickel substrate at high temperature

Although many techniques have been applied to protect nickel (Ni) alloys from oxidation at intermediate and high temperatures, the potential of atomic layer deposition (ALD) coatings has not been fully explored. In this paper, the application of ALD coatings (HfO2, Al2O3, SnO2, and ZnO) on Ni foils has been evaluated by electrical characterization and transmission electron microscopy analyses in order to assess their merit to increase Ni oxidation resistance; particular consideration was given to preserving Ni electrical conductivity at high temperatures. The results suggested that as long as the temperature was below 850 °C, the ALD coatings provided a physical barrier between outside oxygen and Ni metal and hindered the oxygen diffusion. It was illustrated that the barrier power of ALD coatings depends on their robustness, thicknesses, and heating rate. Among the tested ALD coatings, Al2O3 showed the maximum protection below 900 °C. However, above that temperature, the ALD coatings dissolved in the Ni substrate. As a result, they could not offer any physical barrier. The dissolution of ALD coatings doped on the NiO film, formed on the top of the Ni foils. As found by the electron energy loss spectroscopy (EELS), this doping affected the electronic transport process, through manipulating the Ni(3+)/Ni(2+) ratio in the NiO films and the chance of polaron hopping. It was demonstrated that by using the ZnO coating, one would be able to decrease the electrical resistance of Ni foils by two orders of magnitude after exposure to 1020 °C for 4 min. In contrast, the Al2O3 coating increased the resistance of the uncoated foil by one order of magnitude, mainly due to the decrease in the ratio of Ni(3+)/Ni(2+).

Li2CO3-Coated Ni Particles for the Inner Electrodes of Multilayer Ceramic Capacitors: Evaluation of Lifetime

In previous work, it was demonstrated that using Li2CO3-coated Ni particles in the manufacturing of multilayer ceramic capacitor (MLCC) devices could improve both the permittivity and dissipation factors. However, adding Li+ ions to the system gave rise to the concern that ions could migrate under sustained electrical fields and thereby increase the degradation rates of the insulation resistance in MLCCs. In this paper, thermally stimulated depolarization current and highly accelerated lifetime testing were both utilized to evaluate the oxygen vacancy space-charge regions and migration in MLCCs. The results suggested that three parameters (the sintering schedule, Li2CO3 coatings, and oxygen flow during sintering) determine the overall resilience to the degradation. The Li+ ions did not migrate during degradation, as verified by time-of-flight secondary-ion mass spectrometry mapping; however, the Li ions enter the perovskite structure as an acceptor and, if ionically compensated for, could introduce more oxygen vacancies to the system and decrease the lifetime of the MLCCs. Nevertheless, it was demonstrated that the relative lifetimes of the newly designed MLCCs significantly improve relative to the conventional samples.