Modification of work function of Ti by self-assembled monolayer molecules on SiO2∕p-Si

Abstract

A method was used to change the work function of Ti (ϕTi) using self-assembled monolayer (SAM) molecules of dipolar, aminopropyl triethoxy silane, a change attributed to the change in the electrical potential at the Ti∕SAM interface. The SAM was deposited on SiO2∕Si followed by Ti electrode evaporation to form a Ti∕SAM∕SiO2∕p-Si stack for capacitance-voltage (C–V) analyses. The binding of SAM on the SiO2 surface was confirmed using Fourier-transform infrared spectroscopy, and the surface coverage of SAM was determined by the change in the flat-band voltages VFB with deposition time. After 1h of deposition time, an independence of the total capacitance Ctotal and VFB was indicative of saturated surface coverage of SAM on the SiO2 surface. A relationship between the fraction x (where 0<x<1 and x=1 correspond to a monolayer) of the SiO2 surface covered with SAM, at saturated surface coverage, and the dielectric permittivity of SAM (KSAM) was found to be x=0.15KSAM+0.09; if KSAM is assumed to be 3, x is estimated to be 0.54. The ϕTi on the bare SiO2 surface as well as on the SiO2 surface covered with SAM at saturated surface coverage were determined from VFB versus total equivalent oxide thickness plots. The maximum change in ϕTi from Ti∕SiO2∕p-Si to Ti∕SAM∕SiO2∕p-Si configuration was found to be 0.2V.