Ferroelectricity in hafnium oxide thin films

Abstract

We report that crystalline phases with ferroelectric behavior can be formed in thin films of SiO2 doped hafnium oxide. Films with a thickness of 10 nm and with less than 4 mol%. of SiO2 crystallize in a monoclinic/tetragonal phase mixture. We observed that the formation of the monoclinic phase is inhibited if crystallization occurs under mechanical encapsulation and an orthorhombic phase is obtained. This phase shows a distinct piezoelectric response, while polarization measurements exhibit a remanent polarization above 10 C/cm2 at a coercive field of 1 MV/cm, suggesting that this phase is ferroelectric. Ferroelectric hafnium oxide is ideally suited for ferroelectric field effect transistors and capacitors due to its excellent compatibility to silicon technology

Ferroelectricity in yttrium-doped hafnium oxide

“…This analogy to ferroelectric Si:HfO 2 supports the hypothesis that the structural origin of spontaneous polarization in doped HfO 2 is linked to the stabilization of this particular phase and does not originate from the dopant itself. 5 The anti-ferroelectric like behavior observed for the fully stabilized Si:HfO 2 , however, was not observed in the Y:HfO 2 system within our experimental conditions. Tomida et al 16 clearly distinguished the tetragonal Si:HfO 2 from the cubic Y:HfO 2 system.…”

“…reported for TiN=HfO 2 gate stacks 28 ) was identified to be the origin of the orthorhombic, ferroelectric, phase in SiO 2 -doped HfO 2 . 5 The increased P r observed in PMA samples at low YO 1.5 content suggests a larger ferroelectric phase fraction due to the suppressed monoclinic phase. However, even though PDA samples exhibit lower P r , they still show the presence of ferroelectricity, suggesting that the presence of a top electrode ("cap") is preferred, but not mandatory, for the formation of the ferroelectric phase in Y:HfO 2 thin films.…”

“…Recently, it has been demonstrated that doping of HfO 2 thin films with SiO 2 5 or ZrO 2 6 does not only stabilizes the tetragonal phase, but can also produce a spontaneous polarization at intermediate doping levels, that results in usable, ferroelectric hysteresis loops in these layers.…”

Interesting Evidence for Template‐Induced Ferroelectric Behavior in Ultra‐Thin Titanium Dioxide Films Grown on (110) Neodymium Gallium Oxide Substrates

“…[10] Properties such as induced ferromagnetism and superconductivity have been observed due to broken symmetries at the interface [11] between a LaAlO3 substrate and a SrTiO3 film. Recently, strain-induced ferroelectric behavior has been observed in ca 10nm thick films of HfO2 [12] and Zr0.5Hf0.5O2 [13] on silicon. The appearance of ferroelectricity in oxide thin films with such simple compositions, when compared with conventional oxide ferroelectrics such as PbZrxTi1-xO3 is particularly interesting, as it offers the possibility for much easier integration of materials with useful active properties such as piezoelectricity, pyroelectricity, switchable polarization etc.…”

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.…”