K. Hušeková

Growth of High-Dielectric-Constant TiO2 Films in Capacitors with RuO2 Electrodes

Titanium dioxide thin films were grown on RuO 2 layers by atomic layer deposition. The stabilizing effect of the bottom rutile-type RuO 2 layer resulted in growth of the TiO 2 rutile films at temperatures above 275°C. Stabilization of the TiO 2 rutile phase occurred due to local epitaxial growth of the polycrystalline RUO 2 /TiO 2 /RUO 2 structure, as revealed by transmission electron microscopy. A dielectric constant as high as 155 and equivalent oxide thickness (EOT) as low as 0.5 nm were determined from the capacitance-voltage measurements for the TiO 2 films grown above 275°C. A leakage current density of 10 -3 A/cm 2 at 1 V bias voltage was obtained for the films with EOT equal to 0.5 nm.

High-permittivity metal-insulator-metal capacitors with TiO2 rutile dielectric and RuO2 bottom electrode

We describe properties of MIM capacitor structures with the RuO2 bottom electrode, TiO2 dielectric film and various top electrodes. The TiO2 films were grown by atomic layer deposition (ALD) at temperature 425 °C on metal organic chemical vapour deposited (MOCVD) RuO2 bottom electrodes grown at 300 °C. Due to local epitaxial growth on the RuO2 rutile structure, TiO2 films with the permittivity 135 and equivalent oxide thickness 0.58 nm were obtained. Capacitance density as high as 60 fF/μm2 was achieved. Au and Ni films for top electrodes were prepared by evaporation at room temperature. RuO2 films for top electrodes were grown by MOCVD. Strong effect of top electrode material on capacitance and leakage currents was observed. In addition, the stacks with TiO2 dielectric were found to be very sensitive to oxygen post-deposition treatment.

Impact of plasma treatment on electrical properties of TiO2/RuO2 based DRAM capacitor

In this work, we systematically studied the influence of the plasma treatment (PT) on the structural and electrical properties of Pt/rutile-TiO2/RuO2 metal–insulator–metal capacitors. The leakage current of the 12 nm thick TiO2 dielectrics prepared by atomic layer deposition was reduced below 10−7 A cm−2 while the capacitance equivalent thickness was kept below 0.5 nm using oxygen PT of the bottom RuO2 electrode. Reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy analyses allowed the conclusion that O2 plasma smoothened the RuO2 surface and increased its oxygen content through plasma induced surface reconstruction. The nucleation of TiO2 on the plasma-treated surface was faster while the thickness of the capacitor dead layer at the TiO2/RuO2 interface was reduced.

Nanoscale Characterization of TiO2 Films Grown by Atomic Layer Deposition on RuO2 Electrodes

Topography and leakage current maps of TiO2 films grown by atomic layer deposition on RuO2 electrodes using either a TiCl4 or a Ti(O-i-C3H7)4 precursor were characterized at nanoscale by conductive atomic force microscopy (CAFM). For both films, the leakage current flows mainly through elevated grains and not along grain boundaries. The overall CAFM leakage current is larger and more localized for the TiCl4-based films (0.63 nm capacitance equivalent oxide thickness, CET) compared to the Ti(O-i-C3H7)4-based films (0.68 nm CET). Both films have a physical thickness of ∼20 nm. The nanoscale leakage currents are consistent with macroscopic leakage currents from capacitor structures and are correlated with grain characteristics observed by topography maps and transmission electron microscopy as well as with X-ray diffraction.

InAlN∕GaN metal-oxide-semiconductor high electron mobility transistor with Al2O3 insulating films grown by metal organic chemical vapor deposition using Ar and NH3 carrier gases

Al2O3 thin films were deposited by a metal organic chemical vapour deposition on InAlN∕GaN heterostructures using Ar or NH3 as a carrier gas. Effects of NH3 and Ar carrier gases on the electrical and structural properties of Al2O3∕InAlN∕GaN HEMT devices were investigated by current voltage, current collapse, and Auger electron spectroscopy measurements. Al2O3 deposited using Ar as a carrier gas leads to a substantial gate leakage current reduction with no increase of the current collapse compare to Schottky gate based HEMT. On the other hand, HEMT electrical performance shows degradation if NH3 carrier gas is used. Similarly, Auger electron spectroscopy revealed presence of carbon on InAlN surface when NH3 carrier gas was applied. It is suggested that the formation of carbon-related traps on the InAlN surface takes place in the early stages of the Al2O3 deposition with NH3 carrier gas that strongly influences the HEMT performance.

Gate oxide thickness dependence of the leakage current mechanism in Ru/Ta2O5/SiON/Si structures

Leakage conduction mechanisms in Ru/Ta2O5/SiON/Si structures with rf-sputtered Ta2O5 with thicknesses ranging from 13.5 to 1.8 nm were systematically studied. Notable reaction at the Ru/Ta2O5 interface was revealed by capacitance–voltage measurements. Temperature-dependent current–voltage characteristics suggest the bulk-limited conduction mechanism in all metal-oxide–semiconductor structures. Under gate injection, Poole–Frenkel emission was identified as a dominant mechanism for 13.5 nm thick Ta2O5. With an oxide thickness decreasing down to 3.5 nm, the conduction mechanism transforms to thermionic trap-assisted tunnelling through the triangular barrier. Under substrate injection, the dominant mechanism gradually changes with decreasing thickness from thermionic trap-assisted tunnelling to trap-assisted tunnelling through the triangular barrier; Poole–Frenkel emission was not observed at all. A 0.7 eV deep defect level distributed over Ta2O5 is assumed to be responsible for bulk-limited conduction mechanisms and is attributed to H-related defects or oxygen vacancies in Ta2O5.

Defect states characterization of non-annealed and annealed ZrO2/InAlN/GaN structures by capacitance measurements

InAlN/GaN metal-oxide-semiconductor structures with non-annealed and annealed ZrO2 gate insulators were characterized by capacitance-voltage (C−V) measurements. A significant capacitance hysteresis in both channel depletion and barrier accumulation regions was observed on the non-annealed structures. Fixed positive charge in the gate insulator was identified from the negative shift of the C−V curves. The C−V hysteresis was negligible and the threshold voltage decreased with a corresponding increase of the sheet charge density by 6 × 1012 cm−2 after annealing. The C−V slope in the accumulation region increased and the flat-band voltage decreased with decreased frequency. This confirms a decrease of the oxide/barrier interface trap state density with increased their activation energy. Capacitance saturation in the accumulation region occurs at lower values than it is in the insulator capacitance. Measurements at increased temperature up to 150 °C show a shift of the flat-band voltage to lower values. Both f...

ZrO2/InAlN/GaN Metal?Oxide?Semiconductor Heterostructure Field-Effect Transistors with InAlN Barrier of Different Compositions

We report on InAlN/GaN heterostructure metal-oxide-semiconductor field-effect transistors (MOSHFETs) with an InAlN barrier layer of different compositions (x(InN) 13, 17, and 21%) and ZrO2 gate-insulator/passivation. Static measurements yielded higher drain currents than those on unpassivated HFET counterparts and the currents increased with decreased x(InN). Post deposition annealing of the ZrO2 insulator had less influence on the static performance but remarkable changes were observed on the capacitance-voltage characteristics. The capacitance hysteresis in both channel depletion and barrier accumulation regions was significantly suppressed after annealing. This indicates a reduction of the interfacial trap states and of fixed charge in the oxide. Pulsed current-voltage measurements confirmed this conclusion-the gate lag of only similar to 80% was evaluated for 200 ns pulse width, independently on the composition of the InAlN barrier layer. These results support an application of high permittivity ZrO2 gate-insulator/passivation for the preparation of high-performance InAlN/GaN MOSHFETs

RuO 2 /TiO 2 based MIM capacitors for DRAM application

MIM capacitors with MOCVD-grown RuO<inf>2</inf> bottom electrode, ALD-grown TiO<inf>2</inf> rutile dielectric and RuO<inf>2</inf> and Pt top electrodes were prepared and characterised by the means of C-V and J-V measurements. Dielectric constants were in the range of 140, which correspond to EOT of 0.5 nm and leakage current density as low as 1.5*10⁻⁶ A/cm² was achieved. Strong influence of TiO<inf>2</inf> stoichiometry on the leakage currents was found and analysed.

Resistive switching in RuO 2 /TiO 2 /RuO 2 MIM structures for non-volatile memory application

In this paper we describe resistive switching in RuO<inf>2</inf>/TiO<inf>2</inf>/RuO<inf>2</inf> structures. Electrodes (RuO<inf>2</inf>) were grown by metal organic chemical vapor deposition and dielectric TiO<inf>2</inf> switching layers with rutile structure were prepared by atomic layer deposition. After proper nitrogen annealing of as-grown samples followed by an electro-forming procedure and forming procedure bipolar resistive switching was observed. For various switching parameters 100 switching cycles were performed to test retention characteristics. Ratio of high to low resistance up to 10³ was obtained for reading voltage of −0.3 V.