Date of Award

8-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Electrical Engineering

Advisor

Harrell, William R.

Committee Member

Poole , Kelvin F.

Committee Member

Freeman , Yuri

Committee Member

Greenstein , Joel

Abstract

Poly(3,4-ethylenedioxythiophene) (PEDOT), a conducting polymer, has been used since
the 1990s for the cathode of tantalum capacitors, which have a tantalum anode, and a layer of
tantalum pentoxide as the dielectric. Such capacitors are referred to as Polymer Ta capacitors.
The first method, an in situ polymerization technique, used to deposit the polymer resulted in
capacitors with a significant leakage current and breakdown voltages near 50 V. The second
method, a pre-polymerization (pre-poly) technique, resulted in capacitors that have a much lower
leakage current and a higher breakdown voltage than the in situ capacitors.
In this thesis, an accurate measurement technique for dielectric leakage current, also
referred to as the pre-breakdown current, was established for capacitors. Current versus time
measurements at constant voltage were performed at several voltages and the results were
compiled to obtain the current-voltage (I-V) characteristics of both in situ and pre-poly types of
capacitors. These characteristics were then modeled and analyzed, which led to the conclusion
that the pre-breakdown current is controlled by the Poole-Frenkel mechanism in the in situ
capacitors and by both the Poole-Frenkel and Schottky mechanisms in the pre-poly capacitors.
Current versus time measurements were also performed at various temperatures to obtain the
activation energy for the current in the capacitors and to verify the leakage mechanisms. Results
suggest the presence of shallow 0.15 eV traps in the dielectric of the in situ capacitor and deeper
0.75 eV traps in that of the pre-poly capacitor. Additionally, pre-poly capacitors also have a
0.54 eV Schottky barrier that limits the electrons from being emitted into the dielectric from the
electrode. Both the deep trap levels and the Schottky barrier explain the lower leakage current
and higher breakdown voltage observed in the pre-poly capacitors as compared to the in situ
capacitors.

Share

COinS