Area Scaling of Nanosecond Switching Delay in HZO Capacitors with an Ultrathin ZrO2 Interlayer

Interfacial engineering can modify the electrical response of hafnium zirconium oxide capacitors, but separating polarization dynamics from circuit charging remains essential. We compare approximately 10 nm thick Hf0.5Zr0.5O2 (HZO) capacitors with otherwise identical capacitors containing an additional approximately 1 nm thick ZrO2 bottom interlayer (hereafter HZO–ZrO2 capacitors). Polarization–voltage measurements, cross-sectional scanning transmission electron microscopy, capacitance–voltage characterization, and switching/non-switching pulse measurements were combined across electrode areas of 25–10,000 μm2. Both stacks exhibit ferroelectric hysteresis and butterfly-shaped capacitance curves. At 2.5 V and 100 kHz, the HZO–ZrO2 capacitors have 10–15% higher capacitance. Their measured switching-onset delays are nevertheless lower at areas ≥ 400 μm2: 2.1, 5.6, and 23.0 ns at 400, 2500, and 10,000 μm2, compared with 3.2, 7.7, and 30.9 ns for HZO; the largest relative reduction is 34.4%, observed at 400 μm2, where the delay decreases from 3.2 ns to 2.1 ns. At 25 and 100 μm2, the measured differences (0.1 ns) are within the ≈0.1 ns timing resolution of the single-record measurement and are reported as descriptive values. Dividing the measured delay by the capacitance yields a quantity with resistance units that serves as a useful diagnostic for comparing devices, but it cannot be equated with a physical contact resistance. In particular, simply setting the delay equal to R × C with the nominal 100 Ω external resistance leads to an inconsistency for the largest HZO–ZrO2 capacitors, where it would imply a negative additional resistance. These results associate ZrO2 insertion with reduced operational delay while establishing the calibration requirements for interpreting its physical origin.