We demonstrate ferroelectricity in Mg-substituted ZnO thin films with the wurtzite structure. Zn1−xMgxO films are grown by dual-cathode reactive magnetron sputtering on (111)-Pt // (0001)-Al2O3 substrates at temperatures ranging from 26 to 200 °C for compositions spanning from x = 0 to x = 0.37. X-ray diffraction indicates a decrease in the c-lattice parameter and an increase in the a-lattice parameter with increasing Mg content, resulting in a nearly constant c/a axial ratio of 1.595 over this composition range. Transmission electron microscopy studies show abrupt interfaces between Zn1−xMgxO films and the Pt electrode. When prepared at pO2 = 0.025, film surfaces are populated by abnormally oriented grains as measured by atomic force microscopy for Mg concentrations >29%. Raising pO2 to 0.25 eliminates the misoriented grains. Optical measurements show increasing bandgap values with increasing Mg content. When prepared on a 200 °C substrate, films display ferroelectric switching with remanent polarizations exceeding 100 μC cm−2 and coercive fields below 3 MV cm−1 when the Mg content is between ∼30% and ∼37%. Substrate temperature can be lowered to ambient conditions, and when doing so, capacitor stacks show only minor sacrifices to crystal orientation and nearly identical remanent polarization values; however, coercive fields drop below 2 MV/cm. Using ambient temperature deposition, we demonstrate ferroelectric capacitor stacks integrated directly with polymer substrate surfaces.
REFERENCES
1.
Z.
Fan
, J.
Chen
, and J.
Wang
, “Ferroelectric HfO2-based materials for next-generation ferroelectric memories
,” J. Adv. Dielectr.
6
, 1630003
(2016
). 2.
K.
Florent
et al., “Understanding ferroelectric Al:HfO2 thin films with Si-based electrodes for 3D applications
,” J. Appl. Phys.
121
, 204103
(2017
). 3.
J. F.
Scott
, L. D.
McMillan
, and C. A.
Araujo
, “Switching kinetics of lead zirconate titanate sub-micron thin-film memories
,” Ferroelectrics
93
, 31
–36
(1989
). 4.
T. P.
Ma
and J. P.
Han
, “Why is nonvolatile ferroelectric memory field-effect transistor still elusive?
,” IEEE Electron Device Lett.
23
, 386
–388
(2002
). 5.
H.
Kohlstedt
et al., “Current status and challenges of ferroelectric memory devices
,” Microelectron. Eng.
80
, 296
–304
(2005
). 6.
Y. S.
Kim
et al., “Critical thickness of ultrathin ferroelectric BaTiO3 films
,” Appl. Phys. Lett.
86
, 102907
(2005
). 7.
V.
Nagarajan
et al., “Misfit dislocations in nanoscale ferroelectric heterostructures
,” Appl. Phys. Lett.
86
, 192910
(2005
). 8.
J. F.
Ihlefeld
et al., “Scaling effects in perovskite ferroelectrics: Fundamental limits and process-structure-property relations
,” J. Am. Ceram. Soc.
99
, 2537
–2557
(2016
). 9.
A.
von Hippel
, “Piezoelectricity, ferroelectricity, and crystal structure
,” Z. Phys.
133
, 158
–173
(1952
). 10.
11.
12.
J.
Müller
et al., “Ferroelectricity in yttrium-doped hafnium oxide
,” J. Appl. Phys.
110
, 114113
(2011
). 13.
S.
Fichtner
, N.
Wolff
, F.
Lofink
, L.
Kienle
, and B.
Wagner
, “AlScN: A III-V semiconductor based ferroelectric
,” J. Appl. Phys.
125
, 114103
(2019
). 14.
J.
Hayden
et al., “Ferroelectricity in boron-substituted aluminum nitride thin films
,” Phys. Rev. Mater.
5
, 044412
(2021
). 15.
R. F.
Cava
, W. F.
Peck
, and J. J.
Krajewski
, “Enhancement of the dielectric constant of Ta2O5 through substitution with TiO2
,” Nature
377
, 215
–217
(1995
). 16.
G. L.
Brennecka
and D. A.
Payne
, “Preparation of dense Ta2O5-based ceramics by a coated powder method for enhanced dielectric properties
,” J. Am. Ceram. Soc.
89
, 2089
–2095
(2006
). 17.
H.
Moriwake
et al., “Ferroelectricity in wurtzite structure simple chalcogenide
,” Appl. Phys. Lett.
104
, 242909
(2014
). 18.
K.
Koike
et al., “Molecular beam epitaxial growth of wide bandgap ZnMgO alloy films on (1 1 1)-oriented Si substrate toward UV-detector applications
,” J. Cryst. Growth
278
, 288
–292
(2005
). 19.
X.
Kang
et al., “Enhanced dielectric and piezoelectric responses in Zn1−xMgxO thin films near the phase separation boundary
,” Appl. Phys. Lett.
110
, 042903
(2017
). 20.
P.
Kumar
, H. K.
Malik
, A.
Ghosh
, R.
Thangavel
, and K.
Asokan
, “Bandgap tuning in highly c-axis oriented Zn1−xMgxO thin films
,” Appl. Phys. Lett.
102
, 221903
(2013
). 21.
T.
Minemoto
, T.
Negami
, S.
Nishiwaki
, H.
Takakura
, and Y.
Hamakawa
, “Preparation of Zn1−xMgxO films by radio frequency magnetron sputtering
,” Thin Solid Films
372
, 173
–176
(2000
). 22.
A.
Ohtomo
et al., “MgxZn1−xO as a II-VI widegap semiconductor alloy
,” Appl. Phys. Lett.
72
, 2466
(1998
). 23.
A.
Onodera
, N.
Tamaki
, Y.
Kawamura
, T.
Sawada
, and H.
Yamashita
, “Dielectric activity and ferroelectricity in piezoelectric semiconductor Li-doped ZnO
,” Jpn. J. Appl. Phys.
35
, 5160
–5162
(1996
). 24.
A.
Onodera
, N.
Tamaki
, K.
Jin
, and H.
Yamashita
, “Ferroelectric properties in piezoelectric semiconductor Zn1−xMxO (M = Li, Mg)
,” Jpn. J. Appl. Phys.
36
, 6008
(1997
). 25.
Y.-H.
Lin
, M.
Ying
, M.
Li
, X.
Wang
, and C.-W.
Nan
, “Room-temperature ferromagnetic and ferroelectric behavior in polycrystalline ZnO-based thin films
,” Appl. Phys. Lett.
90
, 222110
(2007
). 26.
M.
Joseph
, H.
Tabata
, and T.
Kawai
, “Ferroelectric behavior of Li-doped ZnO thin films on Si(100) by pulsed laser deposition
,” Appl. Phys. Lett.
74
, 2534
–2536
(1999
). 27.
A.
Onodera
and M.
Takesada
, “Ferroelectricity in simple binary crystals
,” Crystals
7
, 232
(2017
). 28.
N. W.
Emanetoglu
et al., “MgxZn1−xO: A new piezoelectric material
,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control
50
, 537
–543
(2003
). 29.
T.
Minemoto
et al., “Preparation of Zn1−xMgxO films by radio frequency magnetron sputtering
,” Thin Solid Films
372
, 173
–176
(2000
). 30.
M.
Rouchdi
, E.
Salmani
, B.
Fares
, N.
Hassanain
, and A.
Mzerd
, “Synthesis and characteristics of Mg doped ZnO thin films: Experimental and ab-initio study
,” Results Phys.
7
, 620
–627
(2017
). 31.
H.
Hayashi
et al., “Zn1−xMgxO second buffer layer of Cu2Sn1−xGexS3 thin-film solar cell for minimizing carrier recombination and open-circuit voltage deficit
,” Sol. Energy
204
, 769
–776
(2020
). 32.
O.
Gencyilmaz
, F.
Atay
, and I.
Akyuz
, “Fabrication and characterization of Zn1−xMgxO films for photovoltaic application
,” in Progress in Clean Energy
(Springer
, Cham
, 2015
), Vol. 1, pp. 1
–968
.33.
M.
Akiyama
et al., “Enhancement of piezoelectric response in scandium aluminum nitride alloy thin films prepared by dual reactive cosputtering
,” Adv. Mater.
21
, 593
–596
(2009
). 34.
M.
Akiyama
, T.
Kamohara
, K.
Kano
, A.
Teshigahara
, and N.
Kawahara
, “Influence of oxygen concentration in sputtering gas on piezoelectric response of aluminum nitride thin films
,” Appl. Phys. Lett.
93
, 021903
(2008
). 35.
S.-H.
Jang
and S. F.
Chichibu
, “Structural, elastic, and polarization parameters and band structures of wurtzite ZnO and MgO
,” J. Appl. Phys.
112
, 073503
(2012
). 36.
S.
Gowrishankar
, L.
Balakrishnan
, and N.
Gopalakrishnan
, “Band gap engineering in Zn(1−x)CdxO and Zn(1−x)MgxO thin films by RF sputtering
,” Ceram. Int.
40
, 2135
–2142
(2014
). 37.
I. S.
Kim
and B. T.
Lee
, “Structural and optical properties of single-crystal ZnMgO thin films grown on sapphire and ZnO substrates by RF magnetron sputtering
,” J. Cryst. Growth
311
, 3618
–3621
(2009
). 38.
M. M.
Fan
et al., “Realization of cubic ZnMgO photodetectors for UVB applications
,” J. Mater. Chem. C
3
, 313
–317
(2015
). 39.
J.-L.
Yang
, K.-W.
Liu
, and D.-Z.
Shen
, “Recent progress of ZnMgO ultraviolet photodetector
,” Chin. Phys. B
26
, 047308
(2017
). 40.
R.
Ondo-Ndong
, H.
Essone-Obame
, Z. H.
Moussambi
, and N.
Koumba
, “Capacitive properties of zinc oxide thin films by radiofrequency magnetron sputtering
,” J. Theor. Appl. Phys.
12
, 309
–317
(2018
). 41.
J. S.
Thorp
, N. E.
Rad
, D.
Evans
, and C. D. H.
Williams
, “The temperature dependence of permittivity in MgO and Fe-MgO single crystals
,” J. Mater. Sci.
21
, 3091
–3096
(1986
). 42.
H.
Ono
, M.
Nakahata
, F.
Tsukihashi
, and N.
Sano
, “Determination of standard Gibbs energies of formation of MgO, SrO, and BaO
,” Metall. Trans. B
24
, 487
–492
(1993
). 43.
Y.
Li
and X.
Wu
, “The standard molar enthalpies of formation of nano-ZnO particles with different morphologies
,” J. Nanomater.
2015
, 738909
. 44.
J.
Lettieri
, J. H.
Haeni
, and D. G.
Schlom
, “Critical issues in the heteroepitaxial growth of alkaline-earth oxides on silicon
,” J. Vac. Sci. Technol. A
20
, 1332
–1340
(2002
). 45.
S.
Okamura
, M.
Takaoka
, T.
Nishida
, and T.
Shiosaki
, “Increase in switching charge of ferroelectric SrBi2Ta2O9 thin films with polarization reversal
,” Jpn. J. Appl. Phys.
39
, 5481
–5484
(2000
). 46.
D.
Zhou
et al., “Wake-up effects in Si-doped hafnium oxide ferroelectric thin films
,” Appl. Phys. Lett.
103
, 192904
(2015
). 47.
M.
Andritschky
, F.
Guimarães
, and V.
Teixeira
, “Energy deposition and substrate heating during magnetron sputtering
,” Vacuum
44
, 809
–813
(1993
). 48.
R. H.
Reuss
et al., “Macroelectronics: Perspectives on technology and applications
,” Proc. IEEE
93
, 1239
–1256
(2005
). 49.
V.
Lumelsky
, M.
Shur
, S.
Wagner
, and M.
Ding
, “Special issue on sensitive skin
,” Int. J. High Speed Electron. Syst.
10
, 413
(2000
). 50.
S. R.
Forrest
, “Electronic appliances on plastic
,” Nature
428
, 911
–918
(2004
). 51.
J.
Rho
, S.
Kim
, N. E.
Lee
, H. S.
Lee
, and J. H.
Ahn
, “PbZrxTi1−xO3 ferroelectric thin-film capacitors for flexible nonvolatile memory applications
,” IEEE Electron Device Lett.
31
, 1017
–1019
(2010
). 52.
R. D.
Shannon
, and C. T.
Prewitt
, “Effective ionic radii in oxides and fluorides
,” Acta Cryst. B
25
, 925
–946
(1969
). © 2021 Author(s). Published under an exclusive license by AIP Publishing.
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