Jiang Li Cao

Hydrogen-induced degradation of PMN-based relaxor ferroelectrics during nickel electroplating

Abstract The effects of nickel electroplating on electrical properties of PMN-based relaxor ferroelectrics were studied by measuring the resistance and temperature dependence of dielectric constant and dissipation factor. It was found that the insulation resistivity of the specimens declined nonlinearly with electroplating time. Additionally, the dielectric constant and dissipation factor were reduced and enhanced respectively. X-ray photoelectron spectroscopy (XPS) analysis showed that Nb 5+ and Pb 2+ were partially reduced to Nb 4+ and metallic Pb by hydrogen during nickel electroplating, which consequently generated oxygen vacancies and conductive electrons in view of defect chemistry, thereby the conduction was enhanced. On the basis of our experiments, the degradation of electrical properties of PMN-based ferroelectrics was ascribed to resistive leakage resulting from Nb 5+ and Pb 2+ reductions to lower charge states by hydrogen.

Functional degradation of NiZnCu-based multilayer chip inductors during nickel electroplating

Functional degradation of NiZnCu-based multilayer chip inductors (MLCI) during nickel electroplating and subsequent lateral growth of metal coating on the ferrite substrate were studied. It was found that the resistivity of the NiZnCu ferrite and inductance of MLCI decreased continuously during the electroplating. Scanning electron microscopy (SEM) analysis showed that the surface morphology of the ferrite had changed significantly after the electroplating. However, the resistance-degraded specimens can be restored partially through air annealing at elevated temperature. Based on the results obtained, it was inferred that the ceramics surface had suffered hydrogen reduction during the electroplating, which led to the functional degradation of ferrite material and the lateral growth of nickel coating.

Hydrogen-Induced Lateral Growth of Nickel Coating on Ba3Co2Fe24 O 41 ( Co2 Z ) -Based Hexaferrite during the Electroplating of Multilayer Chip Inductors

In the present paper, electrical measurements, air-annealing experiments, and X-ray photoelectron spectroscopy (XPS) were used to study the lateral growth of nickel coating on the ceramics substrate during electroplating of Ba 3 Co 2 Fe 24 O 41 (Co 2 Z) hexaferrite multilayer chip inductors (MLCI). It was found that resistivity of the ferrite and inductance of MLCI decreased continuously during the electroplating. The lateral growth of metal coating occurred only after a certain time of electroplating, but not immediately. XPS analysis showed that a large part of Fe 3+ on the ferrite surface had been reduced to Fe 2+ during 20 min of nickel electroplating. However, the resistance-degraded specimens can be restored through 2 h of air annealing at 650°C during which all the Fe 2+ was reoxidized to Fe 3+ . Based on the results obtained, it was concluded that Fe 3+ reduction to Fe 2+ induced by hydrogen during electroplating must be responsible for the functional degradation of the ferrite, which then resulted in the lateral growth of metal coating on the ceramics surface.

Effect of Interactions at the Cofired Interface of Electrode/Ceramics on the Reliability of Lead-Based Multilayer Ceramic Capacitors

The increase of silver content in the internal electrodes was found to have a negative influence on accelerated-test life of lead magnesium niobate-based multilayer ceramic capacitors under direct current-voltage. Transmission electron microscopy (TEM) and auger electron spectroscopy (AES) analyses were carried out on the cofired electrode/ceramics interfaces to demonstrate the effect of Ag content in the electrode on the reliability of capacitors. The result showed that Ag could diffuse into the ceramic layers for more than one micrometer. We designed Ag-doping experiments to study the interactions between the ceramics and Ag. Temperature-humidity-bias (THB) tests on Ag-doped disc specimens revealed that the failure rate of the specimens increased with the Ag content in the ceramics. Based on these results, it was inferred that the deterioration of the multilayer ceramic capacitors with the increase of Ag content in the electrodes should be attributed to the Ag diffusion from the electrodes into the oxide ceramics.

Resistance Degradation of Lead Magnesium Niobate-Based Ceramics during Nickel Electroplating and Recovery Through Air Annealing

Resistance degradation of lead magnesium niobate (PMN)-based relaxor ferroelectrics during nickel electroplating, as well as the recovery of the degraded specimen through air annealing, were investigated by using resistance measurement and X-ray photoelectron spectroscopy (XPS). It was found that the resistivity of the ceramics declined nonlinearly with the electroplating time, and eventually, an obvious degradation occurred. The XPS results showed that parts of Pb 2+ and Nb 5+ were reduced to metallic Pb and Nb 4+ by hydrogen during electroplating. In view of defect chemistry, oxygen vacancies and free electrons were produced, leading to the resistance degradation. It was also found that the degraded PMN-based ceramics could regain its resistivity characteristics after being annealed in air at high temperatures. The correlation of Pb and Nb 4+ reoxidation and the resistivity recovery was clarified, which in turn confirmed that the generation of metallic Pb and Nb 4+ resulted in the resistance degradation of the ceramics during nickel electroplating.

Lateral growth of coating on Co2Z ferrite during electroplating of multilayer chip inductors

Lateral growth of nickel coating on a ferrite substrate during electroplating of multilayer chip inductors (MLCI) was investigated. It was found that the lateral growth occurred after a certain time of electroplating, but not at the initial stage. Resistivity of the ferrite and inductance of MLCI decreased continuously with electroplating time. Moreover, surface morphology of the ferrite changed significantly after electroplating, which indicated chemical reactions to take place during the plating process whereas corrosion effect of acid solution on the material can be neglected. Judging from the results obtained, it was inferred that the resistance degradation should be attributed to hydrogen reduction during electroplating, which consequently led to the lateral growth of on the ferrite.

Direct current-voltage failure in lead magnesium niobate-based multilayer ceramic capacitors

Resistance measurement, P-E hysteresis measurement, and transmission electron microscope and energy dispersive analysis of x-rays (TEM-EDAX) analysis were used to study the resistance failure of lead magnesium niobate-based multilayer ceramic capacitors (MLCC) under dc voltage. It was found that the failure rate of MLCC with 1/9 Pd/Ag internal electrodes was 10 times that of MLCC with 3/7 Pd/Ag electrodes after the temperature-humidity-bias test (THB). Voltage shifts of hysteresis loops showed that an internal bias field between electrodes of MLCC was formed after THB test. Ag diffusion from electrodes into the ceramics during cofiring was examined through TEM-EDAX analysis. It was also found that the degraded specimens could be partially restored after storing under natural condition. On the basis of these results, the failure mechanism was established that oxygen vacancies induced by Ag diffusion accumulated under the external bias field, which increased the concentration of electronic defects, thereby resulting in the resistance failure of MLCC.

Effect of nickel electroplating on the electrical properties of PMZNT relaxor ferroelectrics

Effect of nickel electroplating on insulation resistance and ferroelectricity of PMN-based relaxor ferroelectrics was investigated by resistivity and hysteresis measurements. Annealing experiments on the degraded specimens in air and argon at high temperature were also conducted. It was found that the insulation resistivity of the specimens and the hysteresis characteristic deteriorated after electroplating. Annealing experiments indicated that the degraded samples can recover totally through air annealing above 600 °C for 1 h while the argon annealing had almost no improvement on the degradation. It suggested that some metal elements in the PMN-based ferroelectrics may be reduced by hydrogen produced during electroplating thereby, oxygen vacancies and free electrons were generated, which led to the electrical degradation of the ceramics.

Mechanism of resistance degradation of lead magnesium Niobate-based ferroelectrics induced by hydrogen reduction during electroplating

Resistive leakage of lead magnesium niobate (PMN) based relaxor ferroelectrics after nickel electroplating was investigated through X-ray photoelectronic spectroscopy (XPS) analysis and annealing experiments in oxygen and argon. It was found that the resistivity of the ceramics declined nonlinearly with the electroplating time. XPS analysis suggested that the reduction of Nb5+ to Nb4+ by hydrogen during electroplating played an important role in the degradation. It was also noted that the degraded specimen can recover its properties completely after oxygen annealing at 600°C for 1 hour through the oxidation of Nb4+ to Nb5+. In contrast, almost no oxidization of Nb4+ and improvement of the degradation were observed for the degraded specimen after argon annealing. Therefore, it was concluded that the resistance degradation of the PMN-based relaxor ferroelectrics during electroplating must be ascribed to the oxygen loss and the reduction of Nb5+ to Nb4+.