Low dielectric constant polymers as novel charge electrets

Research project P 14116 Low dielectric constant polymers as novel change electrets Siegfried BAUER 24.01.2000 Charge electrets are dielectric materials exhibiting a quasi-permanent electrical charge. The presently best known polymer charge electrets are based on polytetrafluoroethylene and its copolymers, materials that cannot be prepared as films on substrates by conventional techniques. Novel charge electrets that can be easily processed as thin films on substrates are highly demanded for advanced electret devices, such as microphones, dosimeters, micro-relay switches, for the electrostatic anchoring of molecules in nanotechnology etc. They are also interesting for fundamental research in order to better understand charge trapping mechanisms in polymers. The best polymer charge electrets are mostly semicrystalline with a complex morphology, thereby making a correlation between charge stability, chemical structure, morphology and molecular mechanisms extremely difficult. Materials with low dielectric constant (low-k dielectrics) are currently investigated world-wide for microelectronics applications. Low-k polymers are essentially nonpolar with exceptional thermal stability, in cross-linking networks glass transitions above 400`C are common. Preparation techniques include spin-coating and plasma-polymerization, established industrial techniques. Due to the high purity and the exceptional thermal stability, this class of polymers seems promising for new charge electrets. Moreover, their relatively simple chemical repeat units may lead to a better understanding of fundamental charge-trapping processes. Yet no attempt to investigate the charge electret properties of these material class has been reported. The aim of this project is to identify new charge electrets from the large class of low-k dielectrics, to study molecular motions in nonpolar materials with newly developed experimental techniques, to investigate polymers with similar chemical structure but different morphology, and to correlate the charge stability with chemical structure, morphology and molecular motions. The results of the project may lead to new applications in advanced electret devices. From a fundamental point of view, new insights are expected in charge trapping in polymers, as well as in the characterization of softening and glass transitions in nonpolar thermoplastic and thermoset polymers. The results may be also applicable to materials in other fields, such as glues, dental resins, etc.