Ferroelectricity and Antiferroelectricity of Doped Thin HfO₂‐Based Films

Abstract

The recent progress in ferroelectricity and antiferroelectricity in HfO2-based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O3, BaTiO3, and SrBi2Ta2O9, which are considered to be feasible candidate materials for non-volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si-compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si-doped HfO2 thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferro-electricity or antiferroelectricity in thin HfO2 films. They have large remanent polarization of up to 45 μC cm(-2), and their coercive field (≈1-2 MV cm(-1)) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin (<10 nm) and have a large bandgap (>5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric field-effect-transistors and three-dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid-state-cooling, and infrared sensors.

The origin of ferroelectricity in Hf1−xZrxO2: A computational investigation and a surface energy model

“…After the observation of a remanent polarization and hysteresis in 10 nm thick films of 3 % Si doped HfO2 films 1 in a TiN-HfO2-TiN stack, the effect was additionaly found in Al-and Y-doped films 8,9 grown on TiN as well. More suitable dopants have been discovered since 10 . Furthermore, ferroelectricity was found in the 9 nm mixed oxide thin film Hf0.5Zr0.5O2 (HZO) 2 deposited on TiN electrodes, although neither the pure HfO2 nor the pure ZrO2 film exhibit ferroelectricity.…”

“…Müller 11 showed, that ZrO2 behaves antiferroelectric: above a critical field in the order of 1 MV/cm, a temperature dependent field induced phase transformation to the f-phase occurs. A recent review of the current status of HfO2, ZrO2 and HZO based ferroelectric films can be found in 10 .…”

Intrinsic electron traps in atomic-layer deposited HfO2 insulators

“…In recent years, hafnium dioxide (HfO 2 ) based insulators have emerged as the primary contenders to replace traditional SiO 2 in a variety of nano-electronic devices ranging from deep-scaled transistors to DRAM 1,2 and non-volatile memory cells. 3,4 Furthermore, thanks to the ferroelectricity property of both doped 5,6 and pure 7 HfO 2 , novel applications including memories 8 and high sub-threshold slope transistors 9 are envisioned. However, the reliability of the dielectric associated with electron trapping appears to be the "show stopper": It has already been shown that the positive bias-temperature instability (PBTI) limits the gate oxide scaling in metal-HfO 2 -Si transistors [10][11][12][13] while in flash cells, electron trapping in the intergate HfO 2 insulator degrades the program/erase window, retention, and endurance.…”

Prediction of new metastable $$\hbox {HfO}_{2}$$ HfO 2 phases: toward understanding ferro- and antiferroelectric films

“…However, precise identification of the phase(s) in these films is problematic due to experimental limitations such as the broadness of the thin-film diffraction spectra, unknown film texture and strain fields, and possible presence of multiple phases within a single film. Even the most conclusive phase determination to date [3], combining multiple characterization techniques, has had to rely on a pre-postulated set of possible structural candidates, which in turn has relied on a prior theoretical structure prediction study identifying possible metastable phases [15]. While the detailed investigation in Ref.…”

“…This discovery is of great interest to the semiconductor industry and has led to intensive experimental [3][4][5][6][7][8][9][10][11][12][13][14] and theoretical [9,[15][16][17][18][19][20][21][22] research, because these materials are believed to avoid the problems typical for the traditional ferroelectric materials (such as lead zirconate titanate) during integration into microelectronic devices. However, precise identification of the phase(s) in these films is problematic due to experimental limitations such as the broadness of the thin-film diffraction spectra, unknown film texture and strain fields, and possible presence of multiple phases within a single film.…”