# Evolution of Polymer Tantalum Capacitors
###### Abstract
The slurry PEDOT technology does not have any byproducts that can contaminate the polymer cathode and its interface with the dielectric. The combination of flawless dielectric and slurry PEDOT technologies in the manufacturing of polymer tantalum capacitors radically changed DC leakage/voltage and breakdown voltage (BDV)/dielectric thickness characteristics in comparison with these characteristics in the polymer tantalum capacitors manufactured with conventional dielectric technology and in-situ PEDOT (Figure 3). Figure 3a shows the DC leakage increases rapidly with the voltage in the Polymer Tantalum capacitors manufactured with conventional dielectric technology and in-situ PEDOT, while it remains low in a broad range of voltages in the Polymer Tantalum capacitors manufactured with F-Tech and slurry PEDOT, providing sharp decrease in DC leakage. In Figure 3b, the BDV flattens at about 50 V with an increase in the dielectric thickness in the Polymer Tantalum capacitors manufactured with conventional dielectric technology and in-situ PEDOT, while it continuously increases with the dielectric thickness in the Polymer Tantalum capacitors manufactured with F-Tech and slurry PEDOT, providing a sharp increase in working voltages. A combination of flawless dielectric and slurry PEDOT technologies provide record low DC leakage and record high working voltage in the presently manufactured Polymer Tantalum capacitors [8]. The potential barrier at the dielectric/polymer interface plays an important role in the differences in DC leakage/voltage and BDV-/dielectric thickness characteristics in Polymer Tantalum capacitors manufactured with either conventional dielectric technology and in-situ PEDOT or F-Tech and slurry PEDOT, as shown in Figure 3[9; 10]. This barrier increases with voltage at a normal polarity (plus on tantalum anode) and blocks DC leakage when F-Tech eliminates the defects that shunt the dielectric, and slurry PEDOT eliminates contamination of the polymer cathode that pins the potential barrier at the dielectric/polymer interface. Figure 3: DC leakage/voltage characteristic with a 230 nm dielectric thickness (**a**) and breakdown voltage (BDV) dependence on the dielectric thickness (**b**) in Polymer Tantalum capacitors manufactured with conventional dielectric technology and in-situ PEDOT, and F-Tech and slurry PEDOT. When polymer tantalum capacitors with a slurry PEDOT cathode (KV2 from Heraeus) are subjected to thorough drying, they exhibit anomalous charge current (ACC) exceeding the theoretical charge current (\(\mathrm{I_{th}}\)), which is calculated as follows:  
\[\mathrm{I_{th}}=\mathrm{C*\frac{dV}{dt}} \tag{1}\]  
where C is the capacitance and \(\mathrm{dV/dt}\) is the voltage ramp. ACC increases at higher applied voltages and lower ambient temperatures. In low voltage polymer tantalum capacitors with slurry PEDOT cathodes, the ACC is explained by the reorientation of the dipoles in charged polymer chains in the conductive polymer cathode at the dielectric/polymer interface [11]. This reorientation takes a longer time, with the slurry PEDOT having larger sized molecules of dopant poly(styrenesulfonate) (PSS) added to increase conductivity of the polymer cathode and to prevent the agglomeration of the pre-polymerized PEDOT particles in the water-based dispersion. Humidity in the polymer cathode plays the role of a plasticizer, reducing the reorientation time for the polymer chains and thus eliminating the ACC in the Polymer Tantalum capacitors. F-Tech provides a significant reduction in ACC in higher voltage polymer tantalum capacitors with slurry PEDOT cathodes in comparison with the ACC with conventional dielectric technology. For example, Figure 4 shows the charge current distributions in D-case 15 \(\mathrm{\SIUnitSymbolMicro\text{$\mu$F}}\)-35 V Polymer Tantalum capacitors manufactured with slurry PEDOT cathodes and either conventional dielectric technology or F-Tech.