Molecular-scale charge trap medium for organic non-volatile memory transistors

In this work, we introduce a molecular-scale charge trap medium for an organic non-volatile memory transistor (ONVMTs). We use two different types of small molecules, 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), which have the same triphenylene cores with either hydroxyl or methoxy end groups. The thickness of the small molecule charge trap layer was sophisticatedly controlled using the thermal evaporation method. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) analysis revealed that there were negligible differences in the chemical structures of both small molecules before and after thermal deposition process. The ONVMTs with a 1-nm-thick HHTP charge trap layer showed a large hysteresis window, approximately 20 V, under a double sweep of the gate bias between 40 V and -40 V. The HMTP-based structure showed a negligible memory window, which implied that the hydroxyl groups affected hysteresis. The number of trapped charges on the HHTP charge trap layer was measured to be 4.21 × 10¹² cm^-2. By varying the thickness of the molecular-scale charge trap medium, it was determined that the most efficient charge trapping thickness of HHTP charge trap layer was approximately 5 nm.