Ferroelectric phenomena in Si-doped HfO2 thin films with TiN and Ir electrodes

Abstract

Ferroelectric HfO2 is an attractive candidate for future ferroelectric random access memory devices due to its compatibility with the complementary metal-oxide-semiconductor process, conformal deposition, and scaling ability. Crystallization of HfO2 with different dopants and annealing conditions can produce the stabilization of the monoclinic, tetragonal, cubic, or orthorhombic crystal phases. In this work, the authors observe ferroelectric behavior in Si-doped hafnium oxide with TiN and Ir electrodes. Atomic layer deposited 10 nm HfO2 capacitors doped with varying concentrations of SiO2 have been fabricated in the metal–ferroelectric–insulator–semiconductor (MFIS) structure. The ferroelectric characteristics of thin film HfO2 are compared in the MFIS and metal–ferroelectric–metal configurations. Post-metallization anneals were applied to all thin film ferroelectric HfO2 capacitors, resulting in a remanent polarization of up to 22 μC/cm2 and a range of observed coercive voltages, emphasizing the importance of the annealing conditions, electrode materials, and device structure on the ferroelectric properties of thin film HfO2.

Causes of ferroelectricity in HfO2-based thin films: an ab initio perspective

“…These studies have generally found that, when the HfO 2 films are doped with a few percent of a wide range of dopants or with ∼50% Zr, grown to be ∼ 5 − 20 nm thick between two metal electrodes, and annealed at ∼ 800 − 1000°C, they can display ferroelectricity. Some of the studies [11,16,17,21] have shown that for TiN/HfO 2 /TiN stacks, if the film is annealed before the deposition of the top electrode, then the ferroelectric behavior is significantly suppressed, which indicates that the confinement provided by the top electrode during annealing is crucial for ferroelectricity.…”

Induction of ferroelectricity in nanoscale ZrO2/HfO2 bilayer thin films on Pt/Ti/SiO2/Si substrates

“…The insertion of Al 2 O 3 interlayers into the Hf 0.5 Zr 0.5 O 2 thin films was adopted to inhibit the growth of HZO nanocrystals, which in turn promoted the formation of the ferroelectric O-III phase [26]. Overall, several parameters have been identified to influence the stability and amount of the O-III phase in nanoscale HZO thin films, including atmospheric conditions [27,28], annealing temperature [23,29] and grain size [26].…”

On the structural origins of ferroelectricity in HfO2 thin films

“…3 Combined with controlled doping, the response is further influenced by dimensional confinement introduced through capping layers including TiN, 1 TaN, 4 RuO 2 , 5 Pt, 5,6 or Ir. [7][8][9] While these HfO 2 thin film structures show promise as candidates for non-volatile memory applications, 10 direct identification of the phase responsible for spontaneous polarization has remained experimentally elusive.…”