Ferroelectric hafnium
zirconium oxide holds great promise for a
broad spectrum of complementary metal–oxide–semiconductor
(CMOS) compatible and scaled microelectronic applications, including
memory, low-voltage transistors, and infrared sensors, among others.
An outstanding challenge hindering the implementation of this material
is polarization instability during field cycling. In this study, the
nanoscale phenomena contributing to both polarization fatigue and
wake-up are reported. Using synchrotron X-ray diffraction, the conversion
of non-polar tetragonal and polar orthorhombic phases to a non-polar
monoclinic phase while field cycling devices comprising noble metal
contacts is observed. This phase exchange accompanies a diminishing
ferroelectric remanent polarization and provides device-scale crystallographic
evidence of phase exchange leading to ferroelectric fatigue in these
structures. A reduction in the full width at half-maximum of the superimposed
tetragonal (101) and orthorhombic (111) diffraction reflections is
observed to accompany wake-up in structures comprising tantalum nitride
and tungsten electrodes. Combined with polarization and relative permittivity
measurements, the observed peak narrowing and a shift in position
to lower angles is attributed, in part, to a phase exchange of the
non-polar tetragonal to the polar orthorhombic phase during wake-up.
These results provide insight into the role of electrodes in the performance
of hafnium oxide-based ferroelectrics and mechanisms driving wake-up
and fatigue, and demonstrate a non-destructive means to characterize
the phase changes accompanying polarization instabilities.
Ferroelectric/ferroelastic domain reorientation was measured in a 1.9 m thick tetragonal{001} oriented PbZr0.3Ti0.70O3 thin film doped with 1% Mn under different mechanical boundary constraints. Domain reorientation was quantified through the intensity changes in the 002/200 Bragg reflections as a function of applied electric field. To alter the degree of clamping, films were undercut from the underlying substrate by 0%, ~25%, ~50%, or ~75% of the electrode area. As the amount of declamping from the substrate increased from 0% to ~75%, the degree of ferroelectric/ferroelastic domain reorientation in the films increased more than six fold at three times the coercive field. In a film that was ~ 75% released from the substrate, approximately 26% of 90° domains were reoriented under the maximum applied field; this value for domain reorientation compares favorably to bulk ceramics of similar compositions. An estimate for the upper limit of 90° domain reorientation in a fully released film under these conditions was determined to be 32%. It was also found that the different clamping conditions strongly influence the amount of reorientation upon removing the applied field, with higher remanence of preferred domain orientations observed in declamped films.
The frequency-dependent ferroelectric properties of 45 nm (Al,Sc)N films sputter deposited on complementary metal-oxide-semiconductor (CMOS)-compatible Al metal electrodes are measured and compared. Low in-plane compressive stress (À10 AE 20 MPa) is observed in (Al,Sc)N thin films deposited on Al electrodes. The (Al,Sc)N films exhibit an imprint in the measured coercive fields (E c ) of À4.3/þ5.3 MV cm À1 at 10 kHz. Utilizing positive-up negative-down (PUND) measurements, ferroelectric switching is observed within %200 ns of an applied voltage pulse, which demonstrates the ability of ferroelectric (Al,Sc)N to achieve the fast read/write speeds desired in memory devices.
The origins of high piezoelectric properties in the lead-free (K,Na)NbO 3-based tetragonal composition (K 0.44 Na 0.52 Li 0.04)(Nb 0.86 Ta 0.10 Sb 0.04)O 3 (KNL-NTS) is investigated by quantifying the intrinsic and extrinsic contributions from high energy X-ray diffraction measurements. The applied methodology, which allows discerning between the intrinsic contribution, related to the field induced lattice distortion, and the extrinsic contributions, related to non-180° domain wall motion, is widely described in this work. The non-180° domain reorientation of the KNL-NTS piezoceramic is quantify from the integrated intensities of the 002 and 200 reflections obtained from line profile, while the shifts in peak position versus the applied electric field is used to obtain the lattice strain contribution. Large non-180° domain wall contribution to the electric field induced macroscopic strain (80% of the macroscopic strain) is verified in KNL-NTS.
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