Origin of Ferroelectric Phase in Undoped HfO₂ Films Deposited by Sputtering

Abstract

Thin film metal-insulator-metal capacitors with undoped HfO2 as the insulator are fabricated by sputtering from ceramic targets and subsequently annealed. The influence of film thickness and anneal temperature is characterized by electrical and structural methods. After annealing, the films show distinct ferroelectric properties. Grazing incidence x-ray diffraction measurements reveal a dominant ferroelectric orthorhombic phase for thicknesses in the 10-50 nm range and a negligible non-ferroelectric monoclinic phase fraction. Sputtering HfO2 with additional oxygen during the deposition decreases the remanent polarization.Overall, the impact of oxygen vacancies and interstitials in the HfO2 film during deposition and anneal is correlated to the phase formation process.

Structure and microwave dielectric characteristics of Hf1‐xTixO2 ceramics

“…4,5 Recently, HfO 2 has attracted extensive scientific interest as a promising oxide material, especially for the unique ferroelectricity in HfO 2 -based films. 6 Ferroelectricity in Si, Y, and Al doped HfO 2 films, [6][7][8][9][10] even undoped HfO 2 films, 11 has been reported on. However, there is little research on HfO 2 ceramics, and no ferroelectricity has been reported in HfO 2 -based ceramics.…”

Impact of vacancies and impurities on ferroelectricity in PVD- and ALD-grown HfO2 films

“…6 For PVD samples, the oxygen vacancies likely take this function. 4 In HAXPES spectra, oxygen vacancies V 0 manifest themselves as a small Hf 3þ component at the low binding energy side of Hf 4f spectra (see Fig. 3).…”

“…Oxygen vacancies are recognized as those defects, which have a positive impact on the stabilization of the ferroelectric orthorhombic phase in undoped HfO 2 . [4][5][6] Here, we present a comparative study of both ALD-and PVD-grown HfO 2 thin films interfaced with TiN bottom/top electrodes (BE/TEs) integrated into TiN/HfO 2 /TiN capacitors. We apply hard x-ray photoelectron spectroscopy (HAXPES) as an equally depth-sensitive and element-specific chemical characterization technique, 7,8 which allows us to gain a comprehensive picture of the chemical state of the HfO 2 layers.…”

“…30 As highlighted before, oxygen vacancies are essential for stabilizing the ferroelectric phase in HfO 2 films and also determine the onset of the wake-up effect during electric field cycling of the TiN/HfO 2 /TiN capacitors. 4,5,34,35 A key parameter is the mobility of the oxygen vacancies under the application of an electric field. It determines their spacial redistribution and increases the ferroelectric polarization during the wake-up cycling.…”

Ferroelectric Switching in Trilayer Al2O3/HfZrOx/Al2O3 Structure

“…It has been believed that the observation of the ferroelectricity in hafnia films were contributed by a formation of a non-centrosymmetric Pca2 1 orthorhombic phase [ 19 , 20 ]. The ferroelectricity was also observed in the undoped HfO 2 film [ 21 ], but incorporating the optimized dopants seems to make the phase transformation more effective and easier.…”