# Evolution of Polymer Tantalum Capacitors
###### Abstract  
The major advantage of Polymer Tantalum capacitors over other types of tantalum capacitors is their low equivalent series resistance (ESR), providing a higher capacitance stability with frequency and ripple current capability. When Polymer Tantalum capacitors were introduced to the market in mid 1990s, they were low voltage, leaky, and unreliable, which limited their applications to commercial electronics. Today, some types of polymer tantalum capacitors demonstrate the highest working voltage, lowest DC leakage, and highest reliability ever achieved in tantalum capacitors. These Polymer Tantalum capacitors combine outstanding performance and reliability with superior volumetric charge efficiency, which makes them cost effective and attractive for numerous applications, including mission critical ones. This paper is dedicated to the major technological breakthroughs and scientific discoveries that enabled the radical evolution of Polymer Tantalum capacitors. tantalum capacitor; conducting polymer; working voltage; charge efficiency; reliability; cost  
Polymer Tantalum capacitors with a sintered tantalum powder anode, an anodic oxide film of tantalum as the dielectric, and a polymer cathode were developed by NEC Corporation, Japan, and introduced to the market in mid 1990's [1]. The inherently conductive poly(3_A_-ethylenedioxytheophene) (PEDOT) is the most commonly used cathode in polymer tantalum capacitors [2]. The conductivity of the PEDOT cathode is higher than the conductivity of the liquid electrolyte cathode in Wet Tantalum capacitors and the MnO\({}_{2}\) cathode in Solid Electrolytic Tantalum capacitors. This results in a lower equivalent series resistance (ESR), and thereby a higher capacitance stability with a frequency and ripple current capability in Polymer Tantalum capacitors in comparison with these characteristics in Wet and Solid Electrolytic Tantalum capacitors. There were major improvements in the performance and reliability of Polymer Tantalum capacitors since they were introduced to the market, including a sharp increase in the working voltage and a decrease in DC leakage (Figure 1). Figure 1 shows that original Polymer Tantalum capacitors had low working voltages and high DC leakage making them usable only in commercial electronics, while the current polymer tantalum capacitors have high working voltages and low DC leakage and are broadly used in high reliability applications [3]. There were major improvements in the technology of the Polymer Tantalum capacitors that enabled these radical changes in their performance and reliability. One of the most important improvements was flawless dielectric technology (F-Tech) [4]. The typical defects in the dielectric of tantalum capacitors are crystalline inclusions in the amorphous matrix of tantalum pentoxide (Ta\({}_{2}\)O\({}_{5}\)). These inclusions are initiated at the formation of the oxide dielectric, and continue to grow during the manufacturing, testing, and field application of tantalum capacitors. As the density of the crystalline Ta\({}_{2}\)O\({}_{5}\) is higher than the density of the amorphous Ta\({}_{2}\)O\({}_{5}\), the growth of the crystalline inclusions generates mechanical stress in the amorphous matrix that eventually causes cracks in the dielectric and failures of the capacitors. These crystalline inclusions start to grow from the small crystalline seeds atthe dielectric interface with the tantalum anode. Figure 2 shows the transmission electron microscopy (TEM) image and electron diffraction pattern of the Ta\({}_{2}\)O\({}_{5}\) crystalline seeds on the surface of a tantalum anode after the amorphous matrix of the Ta\({}_{2}\)O\({}_{5}\) dielectric was removed by etching in dilute hydrofluoric acid. Figure 2 shows that crystalline seeds develop on the local sites in the tantalum anodes contaminated with impurities such as oxygen, carbon, and transition metals.