Sigma Technologies is a leading independent polymer capacitor technology group. Sigma is actively developing capacitor technology for high energy density pulse power applications, and electrostatic super-capacitors for battery back-up applications
POLYMER MULTILAYER (PML) CAPACITORS
Sigma has developed a high energy density, solid state, polymer multilayer capacitor technology, with nano-thick acrylate dielectrics and metallized aluminum electrodes. It is a unique technology where a $3-$5/lb liquid monomer and $4/lb aluminum wire are introduced into a large process machine which produces multilayer capacitor material with 1000s of nano-dielectric and electrode layers. The PML capacitor technology has been licensed to multinational capacitor OEMs, who are producing millions of PML capacitors for electronic consumer equipment (digital cameras, audio and video equipment).
The schematic above outlines the PML capacitor manufacturing process. A large area (10-20 sq.ft.) “mother capacitor” sheet is produced in a vacuum chamber using a continuous inline deposition process of polymer dielectric and metallized electrodes. A monomer dielectric is flash evaporated and condensed onto the drum where it is polymerized using a electron beam curtain. A mask in front of the aluminum station produces multiple capacitor lanes. The mask shifts on every revolution to produce opposite polarity electrodes. Capacitors with 2000-10000 dielectric layers are produced with this method.
PML Capacitor Properties include
- High temperature polymer dielectrics >200C
- High breakdown strength dielectrics 1000V/mm
- Self healing properties- open failure mechanism
- Low ESL - prismatic shape
- Low ESR – 1000 of aluminum electrodes in parallel
- Pin-hole free dielectrics
- High resistance to vibration damage
- Low cost materials
HYBRID METALLIZED FILM CAPACITORS
The hybrid PP film is an extension of the multilayer PML capacitor technology and it was originally developed by Sigma to selectively alter the properties of polymer film dielectrics, such as PPS and PVDF. Sigma demonstrated that when coating PPS films with thin acrylate dielectrics, the self healing properties of PPS and PVDF improved, leading to capacitors with higher energy density and lower leakage current. During a self healing event the aluminum melts and evaporates away from the breakdown site leaving behind a small hole with surface tracking damage around the hole. When the arc generated tracks incorporate high levels of carbon, the capacitor leakage current increases. The chemistry of acrylate polymers used in hybrid film applications can be selected with high O:C and H:C ratios, which aids the formation of Al2O3, CO, CO2, CH3, C2H6 during the surface tracking process. This removes carbon from the breakdown site aiding the self healing process and allowing the application of higher voltages for a given dielectric thickness.
Key properties of Hybrid films when compared to the based polymer films, include the following:
- Superior self healing properties
- Higher breakdown strength
- Improved termination
- Lower ESR
- Superior current carrying ability
- Improved dv/dt and di/dt performance
- Higher energy density
- Improved life at in high frequency applications
The hybrid film process is shown in the figure above. A liquid monomer formulation is flash evaporated and converted into a monomer vapor that is deposited onto the polymer film where it is polymerized using an electron beam curtain. A demetalization oil based mask is printed onto the hybrid PP film prior to the electrode metallization.