Distinct Clockwise Capacitance−Voltage Hysteresis in Aminopropyl-silsesquioxane Thin Films

Aminopropyl-silsesquioxane resins and thin films were synthesized from aminopropyltrimethoxysilane (APTMS). To investigate the changes in the molecular structure of the film with increasing curing temperature, Fourier transform infrared spectroscopy (FT-IR) was performed. The dielectric properties of the thin films were investigated by capacitance−voltage (C−V) measurements in a metal−insulator−semiconductor (MIS) structure. To explain the spectral changes in the FT-IR results, it is proposed that the Si−OH and aminopropyl groups freely exist without hydrogen bonding interactions in the curing temperature range 100−200 °C, while molecular structures such as N(Si≡)3, N(Si≡)2, and O(Si≡)2 are formed at higher temperatures in the range 250−300 °C. The dielectric constant values and dissipation factors are regarded as being suitable for electronic applications, e.g., the gate insulators of organic thin film transistor (OTFT) devices. Interestingly, amphoteric charge trap behavior, such as a distinct clockwise C−V hysteresis, was observed in the sample cured at 300 °C. It is proposed that this originates from the coexistence of N(Si≡)2 and E′ centers in the cured films, into which positive charges or negative charges originating from the metal gate electrode are trapped, depending on the polarity of the applied electric field. It seems that the nitrogen-related molecular defects act as electron trap centers in the aminopropyl-silsesquioxane thin films.