Ultrathin Hf_0.5Zr_0.5O₂ Ferroelectric Films on Si

Abstract

Because of their immense scalability and manufacturability potential, the HfO2-based ferroelectric films attract significant attention as strong candidates for application in ferroelectric memories and related electronic devices. Here, we report the ferroelectric behavior of ultrathin Hf0.5Zr0.5O2 films, with the thickness of just 2.5 nm, which makes them suitable for use in ferroelectric tunnel junctions, thereby further expanding the area of their practical application. Transmission electron microscopy and electron diffraction analysis of the films grown on highly doped Si substrates confirms formation of the fully crystalline non-centrosymmetric orthorhombic phase responsible for ferroelectricity in Hf0.5Zr0.5O2. Piezoresponse force microscopy and pulsed switching testing performed on the deposited top TiN electrodes provide further evidence of the ferroelectric behavior of the Hf0.5Zr0.5O2 films. The electronic band lineup at the top TiN/Hf0.5Zr0.5O2 interface and band bending at the adjacent n(+)-Si bottom layer attributed to the polarization charges in Hf0.5Zr0.5O2 have been determined using in situ X-ray photoelectron spectroscopy analysis. The obtained results represent a significant step toward the experimental implementation of Si-based ferroelectric tunnel junctions.

Scaling Effects in Perovskite Ferroelectrics: Fundamental Limits and Process‐Structure‐Property Relations

“…Recently, signatures of ferroelectricity were identified in thin polycrystalline HfO 2 ‐based films . The thicknesses and grain sizes associated with this observation are relatively small compared with other, more conventional, ferroelectrics with polarization switching and piezoelectric response measured in films with thicknesses as low as 5 nm and less, and lateral grain sizes between 20 and 30 nm . Ferroelectricity in these materials is reported to stem from the stabilization of a noncentrosymmetric orthorhombic phase.…”

Giant tunnelling electroresistance in metal/ferroelectric/semiconductor tunnel junctions by engineering the Schottky barrier

“…In the present work, coherent growth of BTO on lattice-matched NbSTO may greatly suppress the interfacial states2448 and the observed TER is from the modulation on the depleted space charge region and hence the Schottky barrier with the polarization reversal. Recently, high-quality HfO 2 -based ferroelectric ultrathin films have been elaborated directly on Si substrates495051. With appropriate choice of material parameters, the proposed ferroelectric-modulated Schottky junctions may have potential applications for Si-based memories compatible to the current technology.…”

Analysis of Performance Instabilities of Hafnia‐Based Ferroelectrics Using Modulus Spectroscopy and Thermally Stimulated Depolarization Currents

“…100 nm thick 2% Fe-doped 30/70 PZT samples were fabricated by chemical solution deposition processing of a butanol-based precursor solution which was synthesized according to a route published elsewhere. [47] Under the given ALD conditions, HZO films with an Hf:Zr ratio of 0.5:0.5 were deposited applying an HfO 2 :ZrO 2 ALD cycle ratio of 1:1 and using H 2 O as the oxygen source. The 0.3 mol L −1 coating solution was applied to the platinized silicon substrate at room temperature by spin-coating at 3000 rpm for 30 s. Subsequently, the as-deposited layer was pyrolyzed at 350 °C for 2.5 min on a hot plate.…”

“…[17] Then, 10-30 nm thick Hf 0.5 Zr 0.5 O 2 films were grown in an Oxford Instruments OpAL ALD tool using Hf-and Zr-metalorganic precursors similar to the ones used in previous publications. [47] Under the given ALD conditions, HZO films with an Hf:Zr ratio of 0.5:0.5 were deposited applying an HfO 2 :ZrO 2 ALD cycle ratio of 1:1 and using H 2 O as the oxygen source. As reported before, TiN electrodes were deposited before and after dielectric deposition.…”