TiN-coated Si Research Articles

A facile control of epitaxial-like barium strontium titanate thin films with various Ba/Sr ratios synthesized by a hydrothermal-galvanic couple method

Barium strontium titanate (BaxSr1-xTiO3; BST) thin films exhibiting superior dielectric tunability have many technological applications. BST thin films with various Ba/Sr ratios were facilely produced on TiN-coated Si substrates by a hydrothermal-galvanic couple (HT-GC) method in mixed Ba(CH3COO)2 and Sr(CH3COO)2 alkaline solutions. A cubic single phase of BST films with the perovskite structure was obtained. Epitaxial-like growth in that strongly preferred (111) BST films grew over (111)-oriented TiN underlayer was observed for all the obtained films. When increasing the mole fraction of Ba2+ in the reaction solutions, the (111) diffraction peak of BST films shifted toward lower Bragg's angles, indicating a transition from Sr-rich to Ba-rich BST. From the X-ray photoelectron spectroscopy and electron probe for microanalysis, BST films with a full range of Ba/Sr ratios were obtained. The Sr ions were more readily incorporated into the films than Ba ions, which is associated with the lower formation energy of SrTiO3. Field-emission scanning electron microscopy revealed a spherical-particulate microstructure of the BST films. The formation mechanisms of the films by such a method were also discussed. The obtained BST films exhibited a promising dielectric tunability that could reach as high as 92%.

A facile growth control of perovskite SrTiO3 thin films by tailoring surface morphologies of TiN seeding layers in the hydrothermal-galvanic couple synthesis

Growth control of cubic perovskite structure strontium titanate (SrTiO3) thin films was facilely achieved by tailoring surface morphologies of the TiN seeding layer in the hydrothermal-galvanic couple (HT-GC) synthesis. Two types of TiN thin films with pyramidal (P-TiN) and granular (G-TiN) surface morphologies were deposited on Si substrates by sputtering. The TiN-coated Si working electrodes were then directly connected to the Pt counter electrode without applying any external power source and soaked in 0.1 M Sr(CH3COOH)2 mixed with 2 M NaOH at 80 °C for 1–60 min. Significant galvanic currents were detected during the HT-GC synthesis. Directional oriented cubic SrTiO3 thin films grew over the two types of highly preferred oriented TiN seeding layers. The growth kinetics of SrTiO3 was deduced by fitting the coverage of the oxide over the two types of TiN at different reaction times to a modified Avrami equation. It was shown that galvanic currents, relative peak integrated intensities, and growth rates of SrTiO3 over the P-TiN were much higher than those on the G-TiN, while the grain sizes of SrTiO3 over the P-TiN were smaller. The faceted surfaces with fewer phase boundaries for P-TiN could yield a different rate-limiting step during the HT-GC synthesis and enhance significantly the growth of the oxide. This facile growth control could also be applied to similar perovskite oxide/conductive nitride systems.

Formation of Ba x Sr 1-x TiO 3 films on TiN-coated substrates by plasma electrolytic oxidation

Abstract Barium strontium titanate (Ba x Sr 1−x TiO 3 ; BST) films with compositions varying from x=0 to 1 were produced on TiN-coated Si substrates by plasma electrolytic oxidation (PEO). Mixed Ba(OH) 2 and Sr(OH) 2 solutions with different Ba/Sr ratios in a total of 0.5 M were used as the electrolytes. PEO was conducted with a potentiostatic mode at an applied voltage of 65 V for 1 min. Spark plasma discharges occurred at the working electrodes and lasted for about 10–15 s during PEO for all the specimens. Single phase cubic BST films were gained at the [Ba/(Ba+Sr)] ratios above 0.6 while cubic BST accompanying partly anatase TiO 2 were present at the [Ba/(Ba+Sr)] ratios below 0.4. Sintered-like porous morphologies with nanolayered structures were obtained. More Sr ions were readily incorporated into BST films at fixed [Ba/(Ba+Sr)] ratios of the electrolytes. On the other hand, more Ba ions in the electrolytes would enhance the ionic conductivity and the crystallinity of the films. The measured dielectric constants and dielectric losses of the BST films were compatible with those reported in the related literature. Reaction routes and formation mechanisms of the BST films have also been proposed.

Atomic Layer Deposited Oxide-Based Nanocomposite Structures with Embedded CoPtx Nanocrystals for Resistive Random Access Memory Applications.

Al2O3- or HfO2-based nanocomposite structures with embedded CoPtx nanocrystals (NCs) on TiN-coated Si substrates have been prepared by combination of thermal atomic layer deposition (ALD) and plasma-enhanced ALD for resistive random access memory (RRAM) applications. The impact of CoPtx NCs and their average size/density on the resistive switching properties has been explored. Compared to the control sample without CoPtx NCs, ALD-derived Pt/oxide/100 cycle-CoPtx NCs/TiN/SiO2/Si exhibits a typical bipolar, reliable, and reproducible resistive switching behavior, such as sharp distribution of RRAM parameters, smaller set/reset voltages, stable resistance ratio (≥102) of OFF/ON states, better switching endurance up to 104 cycles, and longer data retention over 105 s. The possible resistive switching mechanism based on nanocomposite structures of oxide/CoPtx NCs has been proposed. The dominant conduction mechanisms in low- and high-resistance states of oxide-based device units with embedded CoPtx NCs are Ohmic behavior and space-charge-limited current, respectively. The insertion of CoPtx NCs can effectively improve the formation of conducting filaments due to the CoPtx NC-enhanced electric field intensity. Besides excellent resistive switching performances, the nanocomposite structures also simultaneously present ferromagnetic property. This work provides a flexible pathway by combining PEALD and TALD compatible with state-of-the-art Si-based technology for multifunctional electronic devices applications containing RRAM.

Excellent resistive switching properties of atomic layer-deposited Al2O3/HfO2/Al2O3 trilayer structures for non-volatile memory applications.

We have demonstrated a flexible resistive random access memory unit with trilayer structure by atomic layer deposition (ALD). The device unit is composed of Al2O3/HfO2/Al2O3-based functional stacks on TiN-coated Si substrate. The cross-sectional HRTEM image and XPS depth profile of Al2O3/HfO2/Al2O3 on TiN-coated Si confirm the existence of interfacial layers between trilayer structures of Al2O3/HfO2/Al2O3 after 600°C post-annealing. The memory units of Pt/Al2O3/HfO2/Al2O3/TiN/Si exhibit a typical bipolar, reliable, and reproducible resistive switching behavior, such as stable resistance ratio (>10) of OFF/ON states, sharp distribution of set and reset voltages, better switching endurance up to 103 cycles, and longer data retention at 85°C over 10 years. The possible switching mechanism of trilayer structure of Al2O3/HfO2/Al2O3 has been proposed. The trilayer structure device units of Al2O3/HfO2/Al2O3 on TiN-coated Si prepared by ALD may be a potential candidate for oxide-based resistive random access memory.

Hydrothermal–galvanic couple synthesis of directionally oriented BaTiO3 thin films on TiN-coated substrates

BaTiO3 films were synthesized on TiN-coated Si substrate below 100°C by a hydrothermal–galvanic couple technique in barium contained alkaline solutions. X-ray diffraction and electron backscatter diffraction results show that the BaTiO3 thin films were directionally oriented grown on the TiN/Si substrates, i.e., (111) BaTiO3 over (111) TiN. The surface morphologies revealed that BaTiO3 nucleated and grew over the TiN surface with a single layer. From kinetic analyses, the growth rates of BaTiO3 films prepared by the hydrothermal–galvanic couple technique were faster than a hydrothermal method. The galvanic effects were confirmed by investigating the induced currents and energies. The galvanic currents were generated and controlled by both the dissolution of TiN and the formation of BaTiO3. The output electric energies increased rapidly with the reaction time and leveled off at the full coverage of BaTiO3.

Electrochemical deposition of barium titanate thin films on TiN/Si substrates

Barium titanate (BaTiO3) films were synthesized on TiN-coated Si substrates by electrochemically anodic oxidation in mixed alkaline electrolytes of 0.5M Ba(CH3COO)2 and 2M NaOH. A potentiostatic mode was conducted to make the films with the voltages ranging from 2 to 60V at 70°C for only 1min. X-ray diffraction results show that cubic BaTiO3 films were successfully prepared on TiN-coated substrates at the reaction voltages above 2V. Field-emission scanning electron microscopy revealed that the obtained BaTiO3 films possessed uniformly distributed spherical-particulate surface morphology with a nanolayered feature. The thickness of BaTiO3 could reach about 4μm after electrochemical oxidation with the voltage of 60V. The growth rate of BaTiO3 films synthesized by the electrochemical oxidation was much faster than that of the films prepared by the previously reported hydrothermal and hydrothermal–galvanic couple methods where only a single layer was produced. Potentiodynamic polarization reveals that the corrosion resistance of TiN-coated substrates was greatly improved by electrochemical deposition of the dense and thick BaTiO3 films over the substrates.

Thermally induced interfacial interactions between various metal substrates and a-SiC thin films deposited by a polymer-source chemical vapor deposition

Amorphous silicon carbide (a-SiC) thin films have been deposited onto a variety of substrates, including silicon, SiO 2, Si 3N 4, Cr, Ti and refractory metal-coated silicon, by means of a polymer-source chemical vapor deposition (PS-CVD), at a substrate temperature of 800 °C. The poly(dimethylsilane) (PDMS) was used as a high-density single-source molecular precursor for the PS-CVD process. Capacitance–voltage ( C– V) measurements were systematically used to evaluate the impurity level of the deposited a-SiC films. In addition, elastic recoil detection (ERD) and X-ray photoelectron spectroscopy (XPS) techniques were used to determine the elemental composition of the films and their interface with substrates. Scanning electron and atomic force microscopies were also employed to characterize the surface morphology of the films. The impurity levels of the a-SiC films were found to be clearly correlated with the nature of the underlying substrates. The Pt–Rh and TiN-coated Si substrates are shown to lead to the lowest impurity level (∼1 × 10 13 cm −3) in the PS-CVD grown a-SiC films, while Cr and Ti-coated Si substrates induce much higher impurity concentrations. Such high impurity levels are shown to be a consequence of a strong metallic diffusion of the metallic species (Cr or Ti). In contrast, no diffusion was observed at the interface of a-SiC with either Pt–Rh or TiN. Our results pinpoint TiN-coated Si as the electrode material of choice that satisfies best all the criteria required for the integration of a-SiC into opto-electronic devices.

Emission characteristics of TiN-coated silicon field emitter arrays

We observed the emission characteristics and stability of TiN-coated Si field emitter arrays (FEAs) with a TiW gate structure. The TiN layer on Si tips was formed by a two-step rapid thermal nitridation process in an NH3 ambient by which a Ti layer was thermally converted to a TiN/ TiSi2 bilayer. This process could suppress the formation of TiO2 on the surface and make the TiN layer thicker than a one-step process. By coating Si tips with TiN, the operating voltage of the TiN-coated Si FEAs was reduced by about 20 V compared with non-coated ones. Also, the TiN-coated Si FEAs showed thermally stable electron emission compared with non-coated ones.