Ultrathin ferroic HfO2-ZrO2 superlattice gate stack for advanced transistors

Abstract

With the scaling of lateral dimensions in advanced transistors, an increased gate capacitance is desirable both to retain the control of the gate electrode over the channel and to reduce the operating voltage¹. This led to a fundamental change in the gate stack in 2008, the incorporation of high-dielectric-constant HfO₂ (ref. ²), which remains the material of choice to date. Here we report HfO₂-ZrO₂ superlattice heterostructures as a gate stack, stabilized with mixed ferroelectric-antiferroelectric order, directly integrated onto Si transistors, and scaled down to approximately 20 ångströms, the same gate oxide thickness required for high-performance transistors. The overall equivalent oxide thickness in metal-oxide-semiconductor capacitors is equivalent to an effective SiO₂ thickness of approximately 6.5 ångströms. Such a low effective oxide thickness and the resulting large capacitance cannot be achieved in conventional HfO₂-based high-dielectric-constant gate stacks without scavenging the interfacial SiO₂, which has adverse effects on the electron transport and gate leakage current³. Accordingly, our gate stacks, which do not require such scavenging, provide substantially lower leakage current and no mobility degradation. This work demonstrates that ultrathin ferroic HfO₂-ZrO₂ multilayers, stabilized with competing ferroelectric-antiferroelectric order in the two-nanometre-thickness regime, provide a path towards advanced gate oxide stacks in electronic devices beyond conventional HfO₂-based high-dielectric-constant materials.