Carrier Traps in Poly-p-Xylylene Thin Films

Abstract

Carrier traps in poly (p-xylylene), PPX thin films (0.7 µm) polymerized from the vapour phase are discussed from an analysis of the X-ray-induced thermally-stimulated current (TSC). PPX polymerized at room temperature is a semicrystalline polymer with a monoclinic lattice (α-form). The TSC spectrum from α-form PPX shows five groups of TSC peaks in the range -180 to 200°C. Thermal treatment of α-form PPX above 230°C producel β-form PPX with a trigonal crystal lattice, causing a change in the TSC spectrum, that is, a decrease in the TSC peaks at -150∼-90°C, -40°C, 120°C and 160°C. Annealing the α-form PPX while retaining its α-form crystal lattice increased the TSC's from 120–160°C and produced a new peak at 50–90°C which was not changed by further annealing, or even by the crystalline phase transition. Considering these facts, these traps were considered to be molecular irregularities at the surface or in the surface layer of the crystallite, molecular defects in the crystallite, and irregular molecules.