Phase Transition and Microstructural Changes of Sol–Gel Derived ZrO₂/Si Films by Thermal Annealing: Possible Stability of Tetragonal Phase without Transition to Monoclinic Phase

Stabilization of high-temperature phases such as tetragonal (<i>t</i>-) or cubic phases has been a pivotal issue for technological applications of polymorphic ZrO₂. In this work, we fabricated ZrO₂/Si films using a sol–gel deposition route and investigated the phase transformation, microstructural evolution, surface morphological changes, and interfacial chemical structures by thermal annealing. The ZrO₂ precursor solution was prepared using a zirconium acetylacetonate, coated, dried on Si substrates, and finally annealed at 300–950 °C in ambient air. The sol–gel-derived ZrO₂ layer crystallized into the <i>t</i>-phase as the annealing temperature increased. Despite high-temperature annealing, the <i>t</i>-phase was stabilized without a noticeable transition to the monoclinic phase, probably because of the relatively low film thickness (∼15 nm), enlarged surface/interface area due to thermal grooving, and strain effects. The probable <i>t</i>(112) orientation was developed after annealing at ≥800 °C, which could be related to minimization of the sum of the surface, interface, and strain energies. High-temperature thermal annealing resulted in the contraction of the ZrO₂ layer as a result of the pyrolysis of the remnant organics, surface roughening by thermal grooving, and thickening of the amorphous interface layer (predominantly SiO_<i>x</i>) between the ZrO₂ and Si

Effect of Al₂O₃ Deposition on Performance of Top-Gated Monolayer MoS₂‑Based Field Effect Transistor

Deposition of high-<i>k</i> dielectrics on two-dimensional MoS₂ is an important process for successful application of the transition-metal dichalcogenides in electronic devices. Here, we show the effect of H₂O reactant exposure on monolayer (1L) MoS₂ during atomic layer deposition (ALD) of Al₂O₃. The results showed that the ALD-Al₂O₃ caused degradation of the performance of 1L MoS₂ field effect transistors (FETs) owing to the formation of Mo–O bonding and trapping of H₂O molecules at the Al₂O₃/MoS₂ interface. Furthermore, we demonstrated that reduced duration of exposure to H₂O reactant and postdeposition annealing were essential to the enhancement of the performance of top-gated 1L MoS₂ FETs. The mobility and on/off current ratios were increased by factors of approximately 40 and 10³, respectively, with reduced duration of exposure to H₂O reactant and with postdeposition annealing

Tailored Self-Assembled Monolayer using Chemical Coupling for Indium–Gallium–Zinc Oxide Thin-Film Transistors: Multifunctional Copper Diffusion Barrier

Controlling the contact properties of a copper (Cu) electrode is an important process for improving the performance of an amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistor (TFT) for high-speed applications, owing to the low resistance–capacitance product constant of Cu. One of the many challenges in Cu application to a-IGZO is inhibiting high diffusivity, which causes degradation in the performance of a-IGZO TFT by forming electron trap states. A self-assembled monolayer (SAM) can perfectly act as a Cu diffusion barrier (DB) and passivation layer that prevents moisture and oxygen, which can deteriorate the TFT on–off performance. However, traditional SAM materials have high contact resistance and low mechanical-adhesion properties. In this study, we demonstrate that tailoring the SAM using the chemical coupling method can enhance the electrical and mechanical properties of a-IGZO TFTs. The doping effects from the dipole moment of the tailored SAMs enhance the electrical properties of a-IGZO TFTs, resulting in a field-effect mobility of 13.87 cm2/V·s, an on–off ratio above 107, and a low contact resistance of 612 Ω. Because of the high electrical performance of tailored SAMs, they function as a Cu DB and a passivation layer. Moreover, a selectively tailored functional group can improve the adhesion properties between Cu and a-IGZO. These multifunctionally tailored SAMs can be a promising candidate for a very thin Cu DB in future electronic technology