Wooho Jeong

Characteristics of the ZnO thin film transistor by atomic layer deposition at various temperatures

ZnO thin films were deposited by atomic layer deposition (ALD) at various temperatures and the resulting electrical and chemical properties were examined. The fraction of O–H bonds in ZnO films decreased from 0.39 to 0.24 with increasing processing temperatures. The O/Zn ratio decreased from 0.90 at 70 °C to 0.78 at 130 °C. The carrier concentration and resistivity changed sharply with decreasing temperature. The ZnO thin film transistors (TFTs) were fabricated at processing temperatures of 70 to 130 °C and the electrical properties of the TFT were as follows: the field-effect mobility ranged from 8.82 × 10−3 to 6.11 × 10−3 cm2 V−1 s−1, the on/off current ratio ranged from 1.28 × 106 to 2.43 × 106, the threshold voltage ranged from −12.5 to 14.7 V and the subthreshold swing ranged from 1.21 to 24.1 V/decade. The electrical characteristics of the ZnO TFT were enhanced as the processing temperature decreased.

Structural and Electrical Properties of ZnO Thin Films Deposited by Atomic Layer Deposition at Low Temperatures

In this study, ZnO thin films were deposited by atomic layer deposition (ALD) at various process temperatures. The purpose of this paper was to investigate the controllability of the preferred orientations of ZnO thin films by varying the process temperature and to determine the effect of the preferred orientations on the electrical properties of the films. The process temperature was varied from 70 to 250°C at several increments while the other ALD process parameters were fixed. The deposition rates and uniformities, crystal structures, and electrical properties of these films were evaluated at the various process temperatures. At process temperatures of 70 and 90°C, ZnO thin films showed strong (002) preferred orientations with cylindrical, fine, columnar crystal structures, almost a 1:1 stoichiometric chemical ratio of Zn to O, and n-type carrier concentrations in the range of 10 16 cm -3 with resistivities of 0.1-1 Ω cm. ZnO thin films deposited at temperatures higher than 110°C had wedge-shaped crystal structures, high oxygen deficiencies, and higher n-type carrier concentrations up to 10 20 cm -3 than the films deposited at lower temperatures.

Characteristics of Cobalt Thin Films Deposited by Remote Plasma ALD Method with Dicobalt Octacarbonyl

Cobalt thin films were deposited by a remote plasma atomic layer deposition (ALD) system with a metalorganic precursor of dicobalt octacarbonyl (Co 2 (CO) 8 ). To investigate the reaction kinetics and the characteristics of the Co films, we carried out experiments, varying parameters such as precursor flow rate and injection time, reactant gas flow rate, plasma power, and substrate temperature. The deposition rate of Co films was ∼ 1.2 A/cycle in the ALD window of 75-110°C. The extent of impurity content such as oxygen and carbon was highly affected by plasma power. Two Co films deposited with a plasma power of 50 and 300 W showed different compositional variations. The carbon content of the samples was about ∼ 22% and ∼ 15%, and oxygen content was about ∼ 15% and ∼ 2%, for deposition with plasma powers of 50 and 300 W, respectively. The incorporation of impurities was caused by the incomplete decomposition of Co-CO and suppressed Co reaction on Si substrate, retarding silicide formation.

Investigation of the effects of interface carrier concentration on ZnO thin film transistors fabricated by atomic layer deposition

Thin films of ZnO were deposited by atomic layer deposition (ALD) at different process temperatures and the resulting chemical and electrical characteristics were investigated. As the process temperature increased, the ZnO film exhibited an increase in carrier concentration from 1.3 × 1015 to 2.1 × 1019 cm−3, and a decrease in resistivity from 6.7 × 103 to 8.2 × 10−3 Ω cm. We utilized this temperature dependence of the electrical properties and fabricated thin film transistors (TFTs) at different temperatures with both single and double channel layers. In the ZnO-TFT with a single channel layer, the overall device performance of the ZnO-TFT, such as the Ion/Ioff ratio and subthreshold swing (SS), was degraded as the entire channel resistance decreased. In contrast, the ZnO-TFT with a double channel layer could control the turn-on voltage and threshold voltage by suppressing the increase in the off-current. The Ion/Ioff ratios were 8.6 × 105, 2.2 × 106 and 4.7 × 105 and the subthreshold swings exhibited 0.60 V/decade, 0.71 V/decade and 0.68 V/decade for the TFT with interface channel layers deposited at 120 °C, 140 °C and 160 °C, respectively. The saturation mobility slightly increased from 1.267 to 1.912 cm V−1s−1 as the process temperature of the interface channel layer increased.

Al2O3 buffer in a ZnO thin film transistor with poly-4-vinylphenol dielectric

We compared the characteristics of bottom-gate ZnO-thin film transistors using poly-4-vinylphenol (PVP) and PVP/Al2O3 dielectrics. The PVP dielectric is more hydrophobic than the PVP/Al2O3 dielectric and is not useful for TFT devices because of its high leakage current density, but this leakage current density can be significantly reduced by inserting Al2O3. We deposited ZnO and Al2O3 films by atomic layer deposition (ALD) because it is a low-temperature process. The ZnO-TFTs with either a PVP or a PVP/Al2O3 dielectric exhibit typical field-effect transistor characteristics with n-channel properties. The ZnO-TFT containing PVP/Al2O3 exhibits clear pinch-off and excellent saturation with an enhanced mode operation. The on/off ratio of 7.9 × 104 for the device containing the hybrid dielectric is about three orders of magnitude higher than the ratio of 47 for the device containing PVP. The subthreshold gate swings are 12 V/decade for the TFT containing PVP and 1.2 V/decade for the TFT containing PVP/Al2O3. The density of the interface trap state is significantly lower in the device containing PVP/Al2O3 than in the ZnO-TFT containing PVP. The saturation mobility was 0.05 and 0.8 cm2 V−1 s−1, respectively, in the TFTs containing PVP and PVP/Al2O3.

Physical and Electrical Properties of Hafnium–Zirconium–Oxide Films Grown by Atomic Layer Deposition

We deposited HfO 2 , ZrO 2 , and Zr x Hf 1-x O 2 films having different ZrO 2 contents on Si substrates by atomic layer deposition at 300°C and investigated their physical and electrical characteristics. The HfO 2 and ZrO 2 films with thicknesses of about 20 nm exhibited crystalline structures composed of monoclinic and tetragonal phases, respectively. As the ZrO 2 content in the hafnium-zirconium-oxide was increased, the ratio of the tetragonal phase seen in the crystal increased. These changes in crystal phase led to changes in electrical properties. The crystalline phases and electrical properties of the hafnium-zirconium-oxide films exhibited a strong dependence on their Hf/Zr composition ratio.

Characteristics of Hafnium–Zirconium–Oxide Film Treated by Remote Plasma Nitridation

Characteristics of hafnium-zirconium-oxide films, with and without remote plasma nitridation, have been investigated. The films were created by atomic layer deposition. After deposition, remote plasma nitridation was performed. Nitrogen atoms were successfully incorporated into the hafnium-zirconium-oxide films. As-deposited hafnium-zirconium-oxide film showed a partially crystallized structure. Remote plasma treatment of the hafnium-zirconium-oxide film can effectively suppress the crystallization of the film during rapid thermal annealing. The annealed hafnium-zirconium-oxide film treated by remote plasma nitridation showed a lower equivalent oxide thickness (EOT) and a lower leakage current density than a non-nitrided sample with the same physical thickness. The EOTs of the mixed oxide films with and without nitridation were approximately 1.8 and 2.0 nm, respectively, and the leakage current densities of the films were 5.5 X 10 -8 and 9.2 X 10 -6 A/cm 2 , respectively.

Atomic layer deposited HfO2/HfSixOyNz stacked gate dielectrics for metal-oxide-semiconductor structures

HfSixOyNz layers were grown on Si substrates prior to HfO2 growth in order to investigate the growth of an interfacial layer between HfO2 and Si substrate and the chemical composition changes at the interfacial region. The effects of the HfSixOyNz buffer layers were also investigated. The HfSixOyNz and HfO2 films were grown by remote plasma atomic layer deposition using N2/O2 plasma and O2 plasma, respectively. The HfSixOyNz films were grown using a TDEAH precursor and N2/O2 mixed plasma. The Hf-N and N-O bonds of the HfSixOyNz layers were easily broken by annealing at 800 °C in N2 ambient because their bonds were relatively weak. The peak intensities of the Si-O-N, Hf-O-Si, and Si-O bonds at the interfacial region increased after annealing. The excess N atoms due to the breaking of the Hf-N and N-O bonds can form bonds with Si atoms in the interfacial region and cause the growth of SiOxNy or SiNx. The excess Hf and O atoms can grow HfSixOy or SiO2 due to interactions with Si atoms. The formation of the H...