The driving force in the evolution of Ta capacitors from Wet to Solid MnO2 to Polymer was reducing equivalent series resistance (ESR), which enabled higher frequency applications and increased ripple current capability. At the same time, there was heavy price to pay for lower ESR. In comparison to Wet, MnO2 and Polymer Ta capacitors have lower volumetric efficiency, the key selling point of Ta capacitors, as well as lower working voltages, and higher d.c. leakage current (DCL).
Recently, KEMET introduced a new type of Ta capacitor, Polymer Hermetic Sealed (PHS), which combines the highest volumetric efficiency and working voltage inherent to Wets with the lowest ESR inherent to Polymers. PHS Ta capacitors demonstrate extremely high capacitance stability over a broad range of frequency and temperature. “This is the most capacitance efficient capacitor we’ve ever tested. We can use fewer parts and get better results”, said a design engineer with one of KEMET’s customers after testing the PHS samples. Besides that, PHS Ta capacitors have low DCL, high ripple current capability, high reliability, benign failure mode, and low weight, which is critical for aerospace applications.
Scientific foundation for PHS Ta capacitors was developed jointly by KEMET, led by Dr. Yuri Freeman, Vice President/Technical Fellow, and ECE professor Rod Harrell's research group using Metal – Insulator – Semiconductor (MIS) theory underlying digital electronics. In this case M stands for the Ta anode, I stands for the Ta2O5 dielectric , and S stands for the semiconductor polymer cathode. The Journal of the Electrochemical Society published this work in Issue 7 in 2010 and accepted a second manuscript co-authored with the Clemson group for publication in the Fall of 2012. CARTS International honored the KEMET-Clemson team for this work with the John Moynihan Best Paper Award in February 2012.
The technology of PHS Ta capacitors comprises the most advanced processes and techniques such as F1 Ta anode, tetraglyme formation, slurry polymer, and simulated breakdown screening. Utilizing moisture inside the hermetic sealed design provides space level longevity to these capacitors. PHS technology is covered by seven KEMET patents and patent applications, including a patent application on general PHS design, which was allowed by the US Patent Office in April 2012.
PHS is not just a substitute for Wet. It is a revolutionary step in the history of Ta capacitors which opens the door to the most challenging applications never dreamed about before.
The continued collaboration between Clemson University ECE Department and KEMET, largely based on joint publications, has also helped KEMET attract Apple as a major customer for polymer capacitors.