Method for low ESR, high frequency tantalum capacitors
Disclosed is a method for low effective series resistance (ESR),
high frequency tantalum (Ta) capacitors. Benefits include improved performance
and improved design flexibility.
Background
Fabrication
of Ta capacitors starts with high surface area Ta powders. After power
compaction and insertion of Ta wires, an anodization process is used to form
Ta2O5 dielectric. Cathods are made with either MnO2 or a conducting polymer.
One of the main advantages for using Ta capacitors is the high capacitance
density due to the high surface area generated by fine Ta powders (see Figure
1). However, a higher ESR and resistance capacitance (RC) ladder effect is the
by-product as high resistance and series resistance occur along the powders
linked by the neck region formed by compaction.
Ta capacitors offer high capacitance
density and good high temperature performance. However, high ESR and
significant capacitance rolloff at high frequency (100 KHz and above) have
prevented them from being used for voltage regulation for high-performance
CPUs. To achieve lower ESR and improve capacitance rolloff, Ta capacitor
suppliers conventionally use multiple anodes and conducting polymer (instead of
MnO2, which has a lower conductivity). Multiple anodes result in a higher cost.
Conducting polymer helps to improve the ESR and high-frequency performance to
some extent but further improvement is still required to catch up with an
increasing demand for voltage regulation.
General description
The disclosed method is a design to
use Ta capacitors with lower ESR and improved high-frequency
performance.
The key elements of the method
include:
·
Ta capacitors using different Ta power morphology, such as plate or
cube shape, which provides a greater surface contact after compaction
·
Ta capacitors using doped/coated Ta powder with conducting metals (such
as Al, Ag, and Cu)
·
Ta capacitors using conducting polymer mixed/doped with conducting
metal powders/flakes (such as Al, Ag, C, and Cu)
Advantages
The
disclosed method provides advantages including:
·
Improved ESR and high-frequency performance for Ta
capacitors
·
Im...
