Dipole-induced modulation of effective work function of metal gate in junctionless FETs

In this work, a metal gate with a high effective work function (Weff) that is suitable for junctionless field-effect transistors (JLFETs) has been fabricated. Weff is modulated by inserting an Al interfacial layer with different thicknesses between the HfO2 dielectric layer and the Pt gate metal. Transmission electron microscopy together with capacitance–voltage (C–V) measurement is used to investigate the underlying mechanism of this phenomenon. It is suggested that the oxygen scavenging from HfO2 by the Al layer leads to the formation of interface dipoles, which effectively modulate Weff. By varying the Al layer thickness, it is found that Weff first increases and then decreases as the Al thickness increases above ∼2.5 nm, and the largest increase in Weff is about 0.56 eV. Based on these results, our work provides a useful method using interface dipoles to adjust Weff to the desired value for JLFETs, which is otherwise difficult to achieve using a single metal.