Atomic Layer Deposition of SrTiO3 Thin Films from a Novel Strontium Precursor-Strontium-bis(tri-isopropyl cyclopentadienyl)

Effects of high-k gate dielectrics on the electrical performance and reliability of an amorphous indium-tin-zinc-oxide thin film transistor (a-ITZO TFT): an analytical survey

This study is a numerical simulation obtained by using Silvaco Atlas software to investigate the effect of different types of dielectric layers, inserted between the channel and the gate, on the performance and reliability of an a-ITZO TFT. Replacing the SiO2 oxide layer with a high-k dielectric layer gives the concept of the electrical thickness, known by the equivalent oxide thickness (EOT) in which the physical thickness (PT) can be increased to improve the device reliability without increasing the effective thickness of the gate dielectric. A range of different high-k dielectric materials was suggested. For low-k SiO2 (k = 3.9), the electrical parameters extracted are: Ci = 3.45 × 10-8 F cm-2, Ion = 2.23 × 10-6 A, Ioff = 2.17 × 10-13 A, Ion/Ioff = 1.02 × 107, EOT = 100 nm, VT = -0.61 V, μFE = 29.75 cm2 V-1 s-1, SS = 7.91 × 10-2 V per decade and Von = -0.95 V. Replacing SiO2 by a high-k dielectric material, such as SrTiO3 (k = 300), leads to effects similar to the effects of reducing the physical thickness of the gate dielectric but without actually reducing this physical thickness. This allows improving the outputs of the a-ITZO TFT as it leads to an increase in Ci, Ion and Ion/Ioff to the values Ci = 2.66 × 10-6 F cm-2, Ion = 2.86 × 10-4 A, and Ion/Ioff = 8.80 × 109, respectively, and the decrease in EOT, Ioff, VT, μFE, SS and Von to the values EOT = 1.3 nm, Ioff = 3.25 × 10-14 A, VT = -0.428 V, μFE = 26.66 cm2 V-1 s-1, SS = 6.12 × 10-2 V per decade and Von = -0.75 V, respectively, without leakage effects.

Effect of Growth Temperature during the Atomic Layer Deposition of the SrTiO3 Seed Layer on the Properties of RuO2/SrTiO3/Ru Capacitors for Dynamic Random Access Memory Applications

The atomic layer deposition process of SrTiO₃ (STO) films at 230 °C was studied with Sr(ⁱPr₃Cp)₂ and Ti(CpMe₅)(OMe)₃ (Pr, Cp, and Me are propyl, cyclopentadienyl, and methyl groups, respectively) on Ru substrates. The growth behavior and properties of STO films grown at 230 °C were compared with those deposited at 370 °C. With the limited over-reaction of the Sr precursor during the initial growth stage at a lower temperature, the cation composition was more controllable, and the surface morphology after crystallization annealing at 650 °C had more uniform grains with fewer defects. Here, the excess reaction of the Sr precursor means the chemical-vapor-deposition-like growth of the SrO component mediated through the thermal decomposition of the adsorbed Sr precursor molecules. It was by the reaction of the Sr precursor with the oxygen supplied from the partly oxidized Ru substrate. The second STO was grown at 370 °C (main layer) on the annealed first STO layer (crystallized seed layer) to lead to the in situ crystallization of the main layer. Due to the improved microstructure of STO films induced by the seed layer deposited at 230 °C, the bulk dielectric constant of 167 was obtained for the main layer, which was higher than the value of 101 where the seed layer was deposited at 370 °C, even though the crystallization annealing condition of the seed layer and the deposition condition of the main layer were consistent. The seed layer grown at 230 °C, however, had a lower dielectric constant of only ∼49, whereas the high-temperature seed layer had a dielectric constant of ∼106. Therefore, the low-temperature seed layer posed a severe limitation in acquiring an advanced capacitor property with the involvement of a low-dielectric interfacial layer.

Quantitative Analysis of the Incorporation Behaviors of Sr and Ti Atoms During the Atomic Layer Deposition of SrTiO3 Thin Films

The atomic layer deposition (ALD) of multication oxide films is complicated because the deposition behaviors of the component oxides are not independent of one another. In this study, the Ti and Sr atom incorporation behaviors during the ALD of SrTiO₃ films were quantitatively examined via the carefully designed ALD process sequences. H₂O and O₃ were adopted as the oxygen sources of the SrO subcycles, whereas only O₃ was used for the TiO₂ ALD subcycles. Apart from the general conjecture on the roles of the different types of oxygen sources, the oxygen source that was adopted for the subcycles of the other component oxide had almost complete control of the metal atom incorporation behaviors. This means that the first half-cycle of ALD played a dominant role in determining the metal incorporation rate, which revealed the critical role of the steric hindrance effect during the metal precursor injection for the ALD rate. O₃ had almost doubled its reactivity toward the Ti and Sr precursors compared with H₂O. Although these are the expected results from the common knowledge on ALD, the quantitative analysis of the incorporation behaviors of each metal atom provided insightful viewpoints for the ALD process of this technically important oxide material. Furthermore, the SrTiO₃ films with a bulk dielectric constant as high as 236 were obtained by the Ru-SrTiO₃-RuO₂ capacitor structure.

Ultrathin Ferroelectric Films: Growth, Characterization, Physics and Applications

Ultrathin ferroelectric films are of increasing interests these years, owing to the need of device miniaturization and their wide spectrum of appealing properties. Recent advanced deposition methods and characterization techniques have largely broadened the scope of experimental researches of ultrathin ferroelectric films, pushing intensive property study and promising device applications. This review aims to cover state-of-the-art experimental works of ultrathin ferroelectric films, with a comprehensive survey of growth methods, characterization techniques, important phenomena and properties, as well as device applications. The strongest emphasis is on those aspects intimately related to the unique phenomena and physics of ultrathin ferroelectric films. Prospects and challenges of this field also have been highlighted.

Synthesis and characterisation of cyclopentadienyl complexes of barium: precursors for atomic layer deposition of BaTiO3

Cyclopentadienyl complexes Ba(C5Me5)2(THF)2 (1), Ba(C5Me5)2(A) (A = THF, dien, trien, diglyme, triglyme) (2-5), Ba(Pr(i)3C5H2)2(THF)2 (6), Ba(Bu(t)3C5H2)2(THF) (7), Ba(Me2NC2H4C5Me4)2 (8) and Ba(EtOC2H4C5Me4)2 (9) were prepared and characterised with TGA/SDTA, NMR and MS. Crystal structures of 2, 4, 5, 7, 8 and 9 are presented. All complexes prepared sublime under reduced pressure and complexes 1, 6 and 7 showed volatility also under atmospheric pressure. Complexes 1, 6 and 7 lose the coordinated THF when evaporated while complexes 2-5 are sublimable as complete molecules under reduced pressure. Complexes with bulky cyclopentadienyl ligands (6 and 7) are the most thermally stable and volatile among the prepared barocenes. X-ray structure determinations reveal that all the complexes studied are monomeric. Complexes 1, 7 and 8 were successfully tested in BaTiO3 thin film depositions by atomic layer deposition (ALD).