Low-Temperature Atomic Layer Deposition of Hafnium Oxide for Gating Applications

Abstract

We present a novel low-temperature (30 °C) atomic layer deposition process for hafnium oxide and apply the layers as gate dielectric to fabricate devices out of the thermally sensitive topological insulator HgTe. The key to achieving self-limiting growth at these low temperatures is the incorporation of sufficiently long purge times ( ≥150 s) in the deposition cycles. We investigate the structural and compositional properties of these thin films using X-ray reflectometry and photoelectron spectroscopy, finding a growth rate of 1.6 Å per cycle and an atomic ratio of Hf/O of 1:1.85. In addition, we report on the transport properties of the microstructured devices, which are much enhanced compared to previous device generations. We determine a relative permittivity of ∼15 for our HfO2 layers. Our process considerably reduces the thermal load of the samples during microfabrication and can be adapted to a broad range of materials, enabling the fabrication of high-quality gate insulators on various temperature-sensitive materials.

Atomic Layer Deposition of Defective Amorphous TiOx Thin Films with Improved Photoelectrochemical Performance

“…Figure d shows the GPCs of ALD-TiO x thin films formed at different growth temperatures after 900 cycles. The GPC of ALD-TiO x thin films depends on the growth temperature and gradually decreases from 0.061 to 0.044 nm/cycle as the growth temperature increases from 120 °C to 200 °C, respectively (Table S1), because of the increased desorption of the surface hydroxyl (−OH) groups with an increase in growth temperatures, which is frequently observed in many oxide-based ALD processes . Thus, Figure c,d collectively validates that the ALD recipe, established by fine-tuning of pulse and purge times of the precursor and reactant, enables a stable and uniform ALD process.…”

Thickness dependence of the crystallization and phase transition in ZrO 2 thin films

“…Hafnia (HfO 2 ) and zirconia (ZrO 2 ), as typical fluoritestructure binary oxides, exhibit a range of intriguing physical properties, and attract considerable research interest for the applications of thermal barrier coatings [1], high-k dielectric materials [2], and diluted i.e., monoclinic (m)-phase (space group: P2 1 /c), tetragonal (t)-phase (space group: P4 2 /nmc), and cubic (c)-phase (space group: Fm3m) [12,13]. The emerging ferroelectricity, however, is attributed to a polar structure, a non-centrosymmetric orthorhombic (o)-phase (space group: Pca2 1 ) [12,14] that is thermodynamically unstable with free energy higher than that of the m-phase.…”

Overlapping top gate electrodes based on low temperature atomic layer deposition for nanoscale ambipolar lateral junctions

“…Subsequently, a second gate electrode is defined by (optical or electron-beam) lithography and metallized with a small lateral overlap of a few micrometer with the underlying gate electrode. As a result, the gate electrode separation in the overlapping region is purely defined by the thickness of the dielectric, typically ∼14.5 nm [18], which is well below the smallest separation that can be reliably achieved for lithographically defined split gates, as will be discussed in detail later. The process is also compatible with thinner or thicker dielectric layers as long as a conformal coating of the side walls is achieved.…”

“…Figure 1(a) shows a cross sectional image of the overlapping gate structure on top of the mercury telluride quantum well. Here, hafnium oxide grown by a low-temperature atomic layer deposition process (deposition temperature 30 • C, see [18] for details) is employed as a dielectric. The thickness of both hafnium oxide layers is ∼14.5 nm (90 growth cycles), and each gate electrode consists of a titanium adhesion layer (∼2 nm) and ∼70 nm gold.…”