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Genuinely Ferroelectric Sub-1-Volt-Switchable Nanodomains in HfxZr(1–x)O2 Ultrathin Capacitors
journal contribution
posted on 2018-08-14, 00:00 authored by Igor Stolichnov, Matteo Cavalieri, Enrico Colla, Tony Schenk, Terence Mittmann, Thomas Mikolajick, Uwe Schroeder, Adrian M. IonescuThe
new class of fully silicon-compatible hafnia-based ferroelectrics
with high switchable polarization and good endurance and thickness
scalability shows a strong promise for new generations of logic and
memory devices. Among other factors, their competitiveness depends
on the power efficiency that requires reliable low-voltage operation.
Here, we show genuine ferroelectric switching in HfxZr(1–x)O2 (HZO)
layers in the application-relevant capacitor geometry, for driving
signals as low as 800 mV and coercive voltage below 500 mV. Enhanced
piezoresponse force microscopy with sub-picometer sensitivity allowed
for probing individual polarization domains under the top electrode
and performing a detailed analysis of hysteretic switching. The authentic
local piezoelectric loops and domain wall movement under bias attest
to the true ferroelectric nature of the detected nanodomains. The
systematic analysis of local piezoresponse loop arrays reveals a totally
unexpected thickness dependence of the coercive fields in HZO capacitors.
The thickness decrease from 10 to 7 nm is associated with a remarkably
strong decrease of the coercive field, with about 50% of the capacitor
area switched at coercive voltages ≤0.5 V. Our explanation
consistent with the experimental data involves a change of mechanism
of nuclei-assisted switching when the thickness decreases below 10
nm. The practical implication of this effect is a robust ferroelectric
switching under the millivolt-range driving signal, which is not expected
for the standard coercive voltage scaling law. These results demonstrate
a strong potential for further aggressive thickness reduction of HZO
layers for low-power electronics.
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voltageHZO capacitorsdomain wall movement500 mVswitchable polarizationthickness reductioncapacitor areaEnhanced piezoresponse force microscopypiezoresponse loop arrayssignalHZO layers10 nmthickness decrease800 mVHfGenuinely Ferroelectric Sub -1-Volt Nanodomainsthickness scalabilityZrapplication-relevant capacitor geometrypower efficiencypolarization domainssilicon-compatible hafnia-based ferroelectricsthickness dependence7 nmO 2sub-picometer sensitivityO 2 Ultrathin Capacitorsmemory devicesthickness decreasesanalysis
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