Joël Cagnon

Atomically abrupt and unpinned Al2O3/In0.53Ga0.47As interfaces: Experiment and simulation

III-V semiconductor field effect transistors require an insulator/channel interface with a low density of electrically active defects and a minimal interface dipole to avoid Fermi level pinning. We demonstrate that an atomically abrupt and unpinned interface can be formed between an In0.53Ga0.47As (100) channel and an Al2O3 dielectric layer grown by atomic layer deposition (ALD) when oxidation of the substrate surface is prevented before and during oxide deposition. X-ray photoelectron spectra and electron microscopy indicate that in situ desorption of a protective As2 layer on the In0.53Ga0.47As (100)−4×2 surface followed by ALD of Al2O3 produced an atomically abrupt interface without Fermi level pinning. Temperature-dependent and frequency-dependent capacitance-voltage and conductance-voltage analysis of the resulting Pt/Al2O3/InGaAs capacitors are consistent with movement of the Fermi level through the InGaAs band gap. Moreover, the nearly ideal flat band voltages observed for gate metals of widely var...

Metal-oxide-semiconductor capacitors with ZrO2 dielectrics grown on In0.53Ga0.47As by chemical beam deposition

Zirconium oxide films were grown by chemical beam deposition with zirconium tert-butoxide as the source on (2×4) reconstructed, n-type In0.53Ga0.47As surfaces obtained after As decapping. Optimized growth conditions yielded ZrO2/In0.53Ga0.47As interfaces that were free of second phases. Capacitance-voltage (CV) measurements with different top electrodes showed a frequency dispersion of less than 2% per decade in accumulation. The accumulation capacitance and horizontal position of the CV curve were independent of temperature, while the inversion capacitance was strongly temperature dependent. Flat band voltages correlated with the work function of the metal electrode.

Strain relaxation in epitaxial Pt films on (001) SrTiO3

The relationship between strain relaxation and microstructure evolution of epitaxial, (001)-oriented Pt thin films on (001) SrTiO3 substrates is investigated as a function of Pt film thickness. X-ray diffraction shows that the Pt films gradually relax after film coalescence with increasing film thickness. The Pt film surfaces exhibit a cross-hatched surface pattern that increases in amplitude and density with film thickness and is due to progressive relaxation of the lattice mismatch strain by twinning. The potential of these Pt films as bottom electrodes for functional perovskite films is discussed.

Properties of dielectric dead layers for SrTiO3 thin films on Pt electrodes

Dielectric measurements as a function of temperature were used to characterize the properties of the dielectric dead layers in parallel-plate capacitors with differently textured SrTiO3 thin films and Pt electrodes. The apparent thickness dependence of the permittivity was described with low-permittivity passive (dead) layers at the interfaces connected in series with the bulk of the SrTiO3 film. Interfacial capacitance densities changed with the film microstructure and were weakly temperature dependent. Estimates of the dielectric dead layer thickness and permittivity were limited by the film surface roughness (∼5nm). The consequences for the possible origins of dielectric dead layers that have been proposed in the literature are discussed.Dielectric measurements as a function of temperature were used to characterize the properties of the dielectric dead layers in parallel-plate capacitors with differently textured SrTiO3 thin films and Pt electrodes. The apparent thickness dependence of the permittivity was described with low-permittivity passive (dead) layers at the interfaces connected in series with the bulk of the SrTiO3 film. Interfacial capacitance densities changed with the film microstructure and were weakly temperature dependent. Estimates of the dielectric dead layer thickness and permittivity were limited by the film surface roughness (∼5nm). The consequences for the possible origins of dielectric dead layers that have been proposed in the literature are discussed.

Temperature-dependent dielectric relaxation in bismuth zinc niobate thin films

We apply broadband measurement techniques to determine the dielectric permittivity of Bi1.5Zn1.0Nb1.5O7 (BZN) thin films over the frequency range 1 kHz to 40 GHz. At room temperature, the permittivity function shows relaxation at high frequencies (∼1 GHz), and as the temperature is reduced, the onset of relaxation rapidly moves to lower frequencies, reaching ∼1 kHz at 100 K. The observed frequency-dependent dielectric response of BZN thin films is quantitatively similar to the response of bulk ceramics, which suggests that the intrinsic disorder in the BZN material system can be conveniently explored via measurements on thin films.

High temperature stability of Hf-based gate dielectric stacks with rare-earth oxide layers for threshold voltage control

The thermal stability of DyOx∕HfSiON and HoOx∕HfSiON gate dielectric stacks on silicon was studied by scanning transmission electron microscopy techniques and correlated with their electrical characteristics. Intermixing of the rare-earth elements with the HfSiON was observed, but there was no diffusion into the interfacial SiO2. Rapid thermal annealing (1000°C) produced little detectable change in the concentration profile of the rare-earth elements but caused thinning of the interfacial SiO2 layer along with a corresponding increase in the rare-earth oxide layer thickness. These reactions could be explained with oxygen deficiency in the rare-earth oxide layer and its greater thermodynamic stability relative to SiO2. Negative flat band voltage shifts were observed relative to a control sample with no DyOx or HoOx. Mechanisms by which the observed microstructure changes could give rise to negative flatband voltage shifts are discussed.

Epitaxial SrTiO3 Tunnel Barriers on Pt/MgO Substrates

Tunnel junction devices employing epitaxial, (001)-oriented SrTiO3 barriers with thicknesses between 4 and 5 nm were fabricated by sputtering on (001) Pt/MgO substrates. The quality of the Pt/SrTiO3 interface was characterized by transmission electron microscopy and the current transport studied as a function of temperature and bias field. At low voltages the junctions showed excellent insulting properties and temperature dependent, non-linear current–voltage characteristics. If junctions were biased to high fields (>1.25 MV/cm) current hysteresis was observed. The hysteresis is shown to be due to time-dependent tunnel barrier properties at high fields.

Thickness Dependence of the Dielectric Properties of Epitaxial SrTiO3 Films on (001)Pt/SrTiO3

Epitaxial, (001)-oriented SrTiO3 thin films were grown by sputtering on (001)Pt/SrTiO3 substrates to thicknesses ranging from 20 to 160 nm. Their dielectric properties were studied using parallel-plate capacitor structures. For film thicknesses greater than 40 nm, the thickness dependence of the capacitance density could be described with a model of low-permittivity interfacial layers that are connected in series with the bulk of the film. Thinner films showed a deviation from the linear relationship between the inverse capacitance density and thickness. They also showed an increase in loss and a small, power-law frequency dependence of the capacitance. These changes were indicative of different bulk dielectric properties of the thinnest SrTiO3 films.

Metal-oxide-semiconductor capacitors with erbium oxide dielectrics on In0.53Ga0.47As channels

Erbium oxide dielectrics with a thickness of ∼6 nm were fabricated in situ on In0.53Ga0.47As channels. Leakage current and capacitance densities were characterized as a function of applied voltage using metal-oxide-semiconductor capacitors with two different top electrode materials, Pt and Al. Leakage current densities were less than 10−3 A/cm2 at gate voltages up to ±2 V. The capacitance densities were lower with the Al electrode, which was attributed to a low-permittivity aluminum oxide layer at the electrode interface. The capacitors with the Pt electrode showed a pronounced increase in the capacitance in the depletion region at frequencies as high as 1 MHz, which was not observed for the Al electrode. Possible origins of the differences in the capacitance-voltage characteristics with Pt and Al electrodes are discussed.

Electrical properties of epitaxial SrTiO3 tunnel barriers on (001) Pt/SrTiO3 substrates

Coherent, epitaxial Pt films with root-mean-square surface roughness values of less than one unit cell were grown on (001) SrTiO3 substrates by dc sputtering. These Pt films served as bottom electrodes for epitaxial SrTiO3 tunnel barriers grown by rf magnetron sputtering. The SrTiO3 barriers were free of pinholes and showed mean surface roughness values of less than one unit cell. Barriers with a thickness of 4.5 nm showed excellent insulating properties and nonlinear current-voltage characteristics. At high bias fields, a reproducible hysteresis and deviation from the ideal tunneling behavior were observed.