Capacitor characteristics and application of niobium oxide

In recent years, new oxide solid acids have been reported, among which the fifth subgroup element (V, Nb, Ta) has always been the focus of solid acid research, the industry collectively referred to niobium pentoxide and tantalum pentoxide as soil acids. Hydrate tantalum oxide (Ta2O5) and niobium oxide (Nb2O5) were both potential solid acid catalysts with excellent properties. Niobium has very important research value, so we make a systematic overview of niobium and its compounds first.

Niobium and oxygen can form five oxides respectively: NbO, Nb02, Nb2O, Nb6O and Nb2O5, among which only Nb205 is the most stable, niobium pentaoxide exists in the structure of niobium oxyhexahedron. Niobium pentaoxide is widely used in various ceramic capacitors because of its good dielectric properties. Thin – film niobium oxide materials can be used to produce resistor – capacitance components in integrated circuits. Niobium pentoxide is also the manufacturing material of special optical glass, which can achieve high refractive index and low dispersion. Niobium can not only be used as a metal to form oxides, but also niobium pentaoxide can form similar niobate containing oxygen acid roots, like the fifth group P element. Most of niobate is insoluble in water, and among all niobate, potassium niobate has the greatest solubility. Many niobate crystals have the nature of spontaneous polarization and are good dielectric materials. Their nonlinear optical properties have been widely used in electronics industry.

Niobium oxide (Nb2O5) has many crystalline phases, nearly 15 of which have been reported. The most common crystal types are pseudohexagonal crystal system (TT-Nb2O5), orthogonal crystal system (T-Nb2O5) and monoclinic crystal system (H-Nb2O5). At different temperatures, each crystal phase transforms into each other. H-nb2o5 is the most stable crystal phase, which usually forms when heated above 1000℃, while TT- and M-Nb2O5 are the most unstable crystal phases. The basic electrical characteristics of NbO capacitors include: Capacity range: 10µF to 470µF, rated up to 1000µF, housing sizes meet EIA STANDARDS A through E. AVX’s OxiCapGeneric series NbO capacitors have a reliability of 0.5%/1000 hours (twice that of tantalum capacitors) and the Performance series has a reliability of 0.2%/1000 hours.

Reliability NbO capacitors have very effective self-healing properties, thus ensuring superior reliability over other commercial capacitor technologies. The Performance series has reliability specifications up to 0.2%/1000 hours, such as 500000 hours MTBF(mean time to failure). The Generic series has reliability of 0.5% over 1000 hours, such as 200,000 hours MTBF. This reliability level is higher than most existing commercial grade capacitors.

Anti-ignition failure mode
The ignition energy of niobium oxide is two grades higher than that of tantalum and niobium, and the specific heat is twice that of tantalum and niobium, and the ignition failure mode is significantly reduced (95%). In addition, the electrical stress in the medium is low (Nb 2o 5 is denser than Ta 2o 5 after applying the voltage, so Nb 2o 5 can operate at a lower field intensity at a given rated voltage), which can load a larger ripple current and reduce voltage loss in low-impedance circuits. Niobium oxide electrolytic capacitor has a high short-circuit failure resistance mechanism, and the oxide base significantly improves the thermal failure resistance of dielectric breakdown. In contrast to metallic tantalum or niobium capacitors, niobium oxide electrolytic capacitors offer true “no-burn” technology, regardless of whether they have a polymer electrolyte system.

Suitable for lead-free system
Lead-free assembly systems require higher reflux temperatures and thermo-mechanical stresses. These harsh conditions limit capacitor technology. Aluminum and foil capacitors are extremely sensitive to thermo-mechanical loads, especially for reflow temperature/time welding curves that can lead to severe electrical failure. Ceramic capacitors are most resilient to electrical overstress and are therefore suitable for lead-free assembly under thermo-mechanical load. However, larger ceramic parts are very sensitive to the curvature of the circuit board, so they must be done according to the manufacturer’s requirements. The common cause of ceramic failure is low insulation resistance or short circuit failure. The new niobium oxide capacitor is particularly notable in that, similar to ceramic capacitors, it shows excellent stability under thermo-mechanical stress and high temperature peak reflux conditions (lead-free assembly), while showing no reaction to mechanical weakness.

No piezoelectric effect
The high CV properties of barium titanate (the main ceramic material in most media systems) show a chattering effect. For example, when a DC bias is applied with a superimposed signal (e.g., a 1kHz sine wave), the Y5V capacitor will start to “buzz”. This process is also reversible, 1kHz external signals will also produce 1kHz noise to electrical signals. Although niobium oxide capacitors also use ceramic powder, but do not have this chattering effect.

Less weight
The proportion of niobium oxide powder is half that of tantalum powder, which will affect the total weight of the capacitor. For example, e-type niobium oxide capacitors are approximately 25% lighter than capacitors of the same size made from tantalum powder. The lighter weight also improves the drop test strength of the PCB for the same component occupying area, which is also an important parameter for practical applications.

ESR is smaller at higher temperatures
N b O capacitors have the same temperature-dependent characteristics as tantalum capacitors. ESR(effective series resistance) decreases with temperature due to improved MnO 2 (second electrode) conductivity. Therefore, the filtering performance at higher temperature is better than that at room temperature of 25℃.

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