# Evolution of Polymer Tantalum Capacitors
###### Abstract
The parts were baked out in the air at 125 \(\mathrm{\SIUnitSymbolCelsius}\) for 16 h, cooled down to 0 \(\mathrm{\SIUnitSymbolCelsius}\), and charged immediately to 28 V with a ramp of 120 V/s. As one can see in Figure 4, the average charge current in the Polymer Tantalum capacitors manufactured with conventional dielectric technology (Figure 4a) is about 10x the theoretical current \(\mathrm{I_{th}}=1.8\) mA calculated per (1), while it is about 2.5\(\times\) the theoretical current in the polymer tantalum capacitors manufactured with F-Tech (Figure 4b). Continuous improvements in the structure and chemical composition of the tantalum oxide dielectric will further reduce the charge current in the Polymer Tantalum capacitors, with the slurry PEDOT cathodes eventually eliminating the ACC in these capacitors. Polymer tantalum capacitors with lower working voltages are typically manufactured with a finer powder tantalum anode, thinner tantalum oxide dielectric, and hybrid in-situ PEDOT/slurry PEDOT cathode technology in order to cover the dielectric surface inside and outside the porous anodes. The F-Tech in the lower voltage polymer tantalum capacitors is based on the sintering of the pressed tantalum pellets in a deoxidizing atmosphere (deox-sintering) [4]. In this technology, a tantalum lead-wire is inserted into the pellet and is distorted during pressing at a high density in the region around the wire, providing a strong mechanical bond between the tantalum powder and lead-wire [12]. F-Tech with deox-sintering allows for combining a high reliability with record high volumetric charge efficiency CV/cc, the major advantage of tantalum capacitors in comparison with other types of the capacitors. Traditionally, high reliability capacitors are manufactured with a greater thickness of the dielectric for a given working voltage, and thus lose CV/cc as the capacitance is inversely proportional to the dielectric thickness. The formation of the thicker dielectric in tantalum capacitors requires larger sized powder particles in the tantalum anode, causing additional loss in CV/cc because of a reduction in the surface area of the tantalum anode. In polymer tantalum capacitors manufactured with F-Tech with deox-sintering, a high reliability is achieved without an increase in the thickness of the dielectric and related CV/cc loss. For example, Figure 5 shows the time-to-failure for accelerated tests at 105 \({}^{\circ}\)C and 1.3\(\times\) working voltage and CV/cc in D-case 220 \(\upmu\)F-16 V polymer tantalum capacitors manufactured with either conventional dielectric technology or F-Tech with deox-sintering. Both types of capacitors have similar thicknesses for the tantalum oxide dielectric and hybrid in-situ PEDOT/slurry PEDOT polymer cathode. Figure 4: Probability plots for the current distributions in D-case 15 \(\upmu\)F–35 V Polymer Tantalum capacitors with slurry PEDOT cathodes and either conventional dielectric technology (**a**) or F-Tech (**b**) charged to 28 V with a ramp of 120 V/s. According to Figure 5a, most of the Polymer Tantalum capacitors manufactured with conventional dielectric technology failed within relatively short time intervals (wear-out region), while only 1 out of 200 Polymer Tantalum capacitors manufactured with F-Tech with deoxy-sintering failed during this test. There were additional failures at higher accelerations and longer times, but no wear-out in the polymer tantalum capacitors manufactured with F-Tech with redox-sintering. The high reliability of the Polymer Tantalum capacitors manufactured with F-Tech with deoxy-sintering is accompanied by about a 30% increase in CV/cc in these capacitors in comparison with the CV/cc in the polymer tantalum capacitors manufactured with conventional dielectric technology (Figure 5b). This increase in the CV/cc is due to the unique morphology combining large necks between the sintered powder particles with large pores in the tantalum anodes [4].