Exploration of Breakdown Strength Decrease and Mitigation of Ultrathin Polypropylene.

Area of Science:

• Materials Science
• Electrical Engineering
• Polymer Science

Background:

• Polypropylene film is a key organic dielectric in capacitor technology.
• Miniaturization in power electronics demands thinner dielectric films.
• Commercial biaxially oriented polypropylene (BOPP) films lose breakdown strength as thickness decreases below 5 microns.

Purpose of the Study:

• To investigate the breakdown strength of polypropylene films between 1 and 5 microns.
• To identify the causes of reduced dielectric strength in thin BOPP films.
• To enhance the dielectric strength and high-temperature performance of thin BOPP films.

Main Methods:

• Fabrication and testing of polypropylene films in the 1-5 micron thickness range.
• Analysis using Differential Scanning Calorimetry (DSC), X-ray, and Scanning Electron Microscopy (SEM).
• Application of Atomic Layer Deposition (ALD) oxide coating on BOPP films.

Main Results:

• Breakdown strength rapidly decreases for films thinner than 5 microns, hindering energy density targets.
• Defects like non-uniform fibers and voids, not crystallographic properties, cause premature breakdown in thin films.
• ALD oxide coating successfully augmented the dielectric strength of BOPP films below 5 microns without degrading physical properties.

Conclusions:

• Overstretching during BOPP film production introduces defects that limit dielectric performance at small thicknesses.
• ALD oxide coating is an effective strategy to overcome the dielectric strength reduction in thin BOPP films.
• This enhancement is crucial for maintaining high energy density in miniaturized capacitors for power electronics.