Hafnium Compounds

Temperature dependent measurements have been used to examine transport mechanisms and energy band structure in MOS devices. In this study, a comparison between high-k HfO2 dielectrics and conventional SiO2 dielectrics is made to investigate dielectric specific thermally activated mechanisms. Temperature dependent measurements on large area n/pMOSFETs composed of SiO2 and HfO2/SiO2 gate dielectrics were performed from 5.6K to 300K. A large increase in the gate leakage current is observed at the formation of the minority carrier channel. The data indicate that gate leakage current prior to the formation of the minority channel is carrier rate limited while gate leakage current is tunneling rate limited above the threshold voltage. Gate leakage current measurements show two distinct Arrhenius transport regimes for both SiO2 and HfO2 gate dielectrics. The Arrhenius behavior of the gate leakage current is characterized by a strong temperature dependent regime and a weak temperature dependent regime. The activation energy of the strong temperature regime is found to vary with the applied gate voltage. Frenkel-Poole or other electric field models are able to explain the gate voltage dependence of the gate leakage current for the lowtemperature/voltage regime investigated. The data suggest that the variation of the activation energy for the Arrhenius behavior is weakly electric-field driven and strongly voltage, or Fermi energy level, driven. The weak electric field and strong voltage dependence of the thermal characteristics of the gate leakage current may point to trap densities within the HfO2 that vary in energy (hence applied voltage) as responsible for the observed activation energies. Trap assisted tunneling (or hopping) could be implicated as the transport mechanism.

The valence and conduction band densities of states for the HfO2∕SiO2∕Si structure are determined by soft x-ray photoemission and inverse photoemission. First principles calculations are used to help in assigning valence band maxima and conduction band minima. The energies of defect states at the band edges are estimated by comparing the theoretical and experimental results. Determinations of the local surface potentials before and after a forming gas anneal are used to help determine the possible location of the charge in the film.

High performance solution-processed n-channel organic field-effect transistors based on [6,6]-phenyl C61 butyric acid methyl ester with low operating voltages (3 V) are demonstrated using a high-k hafnium dioxide gate dielectric grown by atomic layer deposition. Devices exhibit excellent n-channel performance with electron mobility values up to 0.14 cm2/V s, threshold voltages of ∼0.3 V, current on/off ratios >105, and very low values of subthreshold slope (∼140 mV/decade).

In this paper, the first demonstration of a bow-tie antenna integrated with a metal-insulator-metal (MIM) diode for electromagnetic energy harvesting in the V-band (i.e., 40-75 GHz) is presented. We have designed, simulated, fabricated, and fully characterized a 60-GHz rectifying antenna (rectenna) based on a vertical Au-HfO 2-Pt MIM diode with reduced differential resistance. The dielectric used for the MIM structure is a 6-nm-thick amorphous HfO 2 grown by atomic layer deposition. For the fabricated MIM device, we report here a current density of 3 × 10 4 A/cm 2 that exceeds the previous values presented in the literature. The vertical MIM-based rectenna is able to efficiently harvest up to 250 µV from an impinging modulated millimeter-wave signal with −20 dBm of available power, thus offering a voltage responsivity of over 5 V/W. The reported results indicate that the proposed approach is well suited for future low-power solutions much sought after for the energetically autonomous 5G terminal equipment.

The reduction and removal of surface oxides from GaAs substrates by atomic layer deposition ͑ALD͒ of Al 2 O 3 and HfO 2 are studied using in situ monochromatic x-ray photoelectron spectroscopy. Using the combination of in situ deposition and analysis techniques, the interfacial "self-cleaning" is shown to be oxidation state dependent as well as metal organic precursor dependent. Thermodynamics, charge balance, and oxygen coordination drive the removal of certain species of surface oxides while allowing others to remain. These factors suggest proper selection of surface treatments and ALD precursors can result in selective interfacial bonding arrangements.

Gate-defined quantum dots in an InGaAs/InP heterostructure are realized by incorporating a high-HfO 2 material as a gate dielectric using atomic layer deposition. The fabricated quantum-dot devices show Coulomb blockade effect at low temperature. The Coulomb blockade current peaks are found to shift in pairs with the magnetic field applied perpendicular to the quantum-dot plane, due to the filling of electrons into spin-degenerate orbital states. When the magnetic field is applied parallel to the quantum-dot plane, spin splittings of orbital states are observed and the extracted effective g-factors are found to be different for different orbital states.

This paper presents the applications of the Hf 0.3 Zr 0.7 O 2 ferroelectric with a thickness of 10 nm for tuning high-frequency devices such as filters, phase shifters, and phased antenna arrays in the X band when the low bias voltages in the range À3 V-þ3 V are applied. In this respect, we show that a bandpass filter shifts its central frequency located at 10 GHz with 3 GHz, a phase shifter produces a phase difference of about 60 degrees in the X band, while the antenna array formed by two patched antennas is steering its lobe with 632 at 10 GHz. These results open the way for the tunability of high frequency devices for very low power applications, which represent one of the most challenging issues in applied physics. Published by AIP Publishing.

We have investigated the microstructures and electronic structures of a series of hafnium aluminate ͑HfAlO͒ films with Al concentration ranging from 0% to 100%. When the films evolve from pure HfO 2 to pure Al 2 O 3 by increasing the aluminum content, we find changes in their radial distribution functions, which disclose the short-range order of the materials, despite the amorphous nature of all films. The HfAlO films ͑with Al/ Hf ratio ranging from 0.25 to 5.8͒ appear to be a single glassy phase of Hf, Al, and O, instead of simple mixtures of HfO 2 and Al 2 O 3. The Hf ͑Al͒-O, Hf ͑Al͒-Al, and Hf-Hf bonds are observed to be insensitive to the amount of Al in the film, except when the Al concentration is large ͑Al/ Hfϳ 5.8͒, in which case the bonding is similar to that in pure Al 2 O 3. Although the local symmetry of Hf in amorphous HfO 2 is suggested by the electron energy-loss spectrum taken at an oxygen K edge, it is largely disrupted when Al is introduced. The valence electron energy-loss spectroscopy reveals three distinct evolving features as the Al content increases, which we discuss in terms of the electronic structure of HfO 2 .

In this paper, the first demonstration of a bow-tie antenna integrated with a metal-insulator-metal (MIM) diode for electromagnetic energy harvesting in the V-band (i.e., 40-75 GHz) is presented. We have designed, simulated, fabricated, and fully characterized a 60-GHz rectifying antenna (rectenna) based on a vertical Au-HfO 2-Pt MIM diode with reduced differential resistance. The dielectric used for the MIM structure is a 6-nm-thick amorphous HfO 2 grown by atomic layer deposition. For the fabricated MIM device, we report here a current density of 3 × 10 4 A/cm 2 that exceeds the previous values presented in the literature. The vertical MIM-based rectenna is able to efficiently harvest up to 250 µV from an impinging modulated millimeter-wave signal with −20 dBm of available power, thus offering a voltage responsivity of over 5 V/W. The reported results indicate that the proposed approach is well suited for future low-power solutions much sought after for the energetically autonomous 5G terminal equipment.

Gate-defined quantum dots in an InGaAs/InP heterostructure are realized by incorporating a high-HfO 2 material as a gate dielectric using atomic layer deposition. The fabricated quantum-dot devices show Coulomb blockade effect at low temperature. The Coulomb blockade current peaks are found to shift in pairs with the magnetic field applied perpendicular to the quantum-dot plane, due to the filling of electrons into spin-degenerate orbital states. When the magnetic field is applied parallel to the quantum-dot plane, spin splittings of orbital states are observed and the extracted effective g-factors are found to be different for different orbital states.

Strontium hafnium oxide (SrHfO3) has great potential as a high-k gate dielectric material, for use in memories, capacitors, CMOS and MOSFETs. We report for the first time the dielectric properties (relative permittivity and capacitance) of SrHfO3 nanoparticles (NPs), as opposed to thin films or sintered bulk ceramics. These monodisperse, ultra-small, perovskite-type SrHfO3 nanocrystals were synthesised through a non-aqueous sol–gel process under solvothermal conditions (at only 220 °C) using benzyl alcohol as a solvent, and with no other capping agents or surfactants. Advanced X-ray diffraction methods (whole powder pattern modelling, WPPM), CS-corrected high-resolution scanning transmission electron microscopy (HRSTEM), dielectric spectroscopy, and optical (UV-vis, Raman) and photoluminescent spectroscopy were used to fully characterise the NPs. These SrHfO3 NPs are the smallest reported and highly monodisperse, with a mean diameter of 2.5 nm, a mode of 2.0 nm and a small size distribution. The formation mechanism of the NPs was determined using NMR and GC-MS analysis of the species involved. Our SrHfO3 nanoparticles had a dielectric constant of 17, which is on par with literature data for bulk and thin film samples, and they also had a relatively large capacitance of 9.5 nF cm−2. As such, they would be suitable for applications as gate dielectrics for capacitors and in metal-oxide semiconductor field-effect transistor (MOSFET) technology.

Arsenic is of concern in water treatment because of its health effects. This research focused on incorporating hydrous ferric oxide (HFO) into granular activated carbon (GAC) for the purpose of arsenic removal. Iron was incorporated into GAC via incipient wetness impregnation and cured at temperatures ranging from 60 to 90 °C. X-ray diffractions and arsenic sorption as a function of pH were conducted to investigate the effect of temperature on final iron oxide (hydroxide) and their arsenic removal capabilities. Results revealed that when curing at 60 °C, the procedure successfully created HFO in the pores of GAC, whereas at temperatures of 80 and 90 °C, the impregnated iron oxide manifested a more crystalline form. In the column tests using synthetic water, the HFO-loaded GAC prepared at 60 °C also showed higher sorption capacities than media cured at higher temperatures. These results indicated that the adsorption capacity for arsenic was closely related to the form of iron (hydr)oxide for a given iron content. For the column test using a natural groundwater, HFO-loaded GAC (Fe, 11.7%) showed an arsenic sorption capacity of 26 mg As/g when the influent contained 300/μg/L As. Thus, the preloading of HFO into a stable GAC media offered the opportunity to employ fixed carbon bed reactors in water treatment plants or point-of-use filters for arsenic removal. © 2008 American Chemical Society.

http://pubs.acs.org/doi/abs/10.1021/es7025399