Characterizing Negative Capacitance in Ultrathin Ferroelectric HfO₂-ZrO₂ Towards Energy-Efficient Advanced Transistors

Negative capacitance (NC) [1] has emerged as a promising solution to overcome fundamental energy-efficiency limits in conventional electronics, in which internal ferroelectric order within the gate stack of a field-effect transistor can enable low-power operation. In particular, by swapping the conventional high-κ dielectric with a negative-κ ferroelectric gate stack, enhanced gate capacitance, i.e. lower equivalent oxide thickness (EOT), can be realized in advanced Si transistors, resulting in key performance benefits in transistors compared to established semiconductor foundry benchmarks [2-3]. We have previously stabilized NC in sub-2-nm HfO₂-ZrO₂ heterostructures [2-3], where we observe a capacitance enhancement, definitive proof of NC stabilization, over the SiO₂ interlayer [2-3] via small-signal capacitance measurements. However, the full internal polarization-electric field (<i>P-E_FE</i>) relation was not extracted for these NC gate oxides.<br/>In this work, ultrafast pulsed <i>I-V</i> measurements are used to map the ‘S’-shaped <i>P-E_FE </i>relation in various ultrathin (sub-2-nm) HfO₂-ZrO₂ NC gate stacks towards realizing both EOT and physical thickness scaling for power- and dimensional-scaling, respectively. The extracted <i>P-E_FE</i> relation shows a negative <i>dP/dE_FE</i> region, a clear signature of NC stabilization. Additionally, by integrating the <i>P-E_FE</i> relation, the characteristic ferroelectric double-well energy landscape was extracted and modelled with a Landau-Ginzburg-Devonshire framework. Both <i>P-E_FE</i>and energy landscapes were then used to quantify the degree of NC stabilization across the various gate stacks. Overall, this work further confirms NC stabilization in ultrathin HfO₂-ZrO₂ heterostructures via large-signal pulsed <i>I-V</i> measurements (as opposed to small-signal capacitance measurements) and provides a methodology to quantify the degree of NC stabilization.<br/>[1] S Salahuddin & S Datta. “Use of Negative Capacitance to Provide Voltage Amplification for Low Power Nanoscale Devices.” <i>Nano Lett</i>. 8, 405–410<br/>[2] S Cheema <i>et al</i>. “Ultrathin ferroic HfO₂–ZrO₂ superlattice gate stack for advanced transistors.” <i>Nature </i>604, 65 (2022).<br/>[3] N Shanker <i>et al.</i> “Ultralow equivalent oxide thickness via one nanometer ferroelectric negative capacitance.” <i>In preparation.</i>