Doped Hafnium Research Articles

Improvement in the Bias Stability of Zinc-Tin Oxide Thin-Film Transistors by Hafnium Doping

The influence of hafnium (Hf) doping on negative-bias temperature instability in zinc-tin oxide thin-film transistors was studied. Hafnium-zinc-tin oxide TFTs exhibited a turn-on voltage (V ON) that shifted from 0 V to −1 V with negligible changes in the subthreshold swing and field-effect mobility after 3 h of total stresses. The enhanced improvement of the V ON shift (ΔV ON) was attributed to the reduction in the interface trap density, which may result from the suppression of oxygen-vacancy-related defects by the Hf ions.

Improvement in the negative bias stability of zinc oxide thin-film transistors by hafnium doping

Thin-film transistors (TFTs) with hafnium-doped zinc oxide (HZO) channels were fabricated and the effects of Hf content on the performance of ZnO-based TFT were investigated. HZO TFTs exhibit improved electrical characteristics, with increased ION/IOFF and decreased subthreshold swing. We also investigated the influence of hafnium doping on the bias stability of ZnO TFTs. HZO TFTs exhibited turn-on voltage (VON) shifts of −1 V in negative stress bias, compared with −8 V for intrinsic ZnO TFTs. The improvement in the VON shift may be due to a reduction in the total trap density resulting from the suppression of the defect-related oxidation state of the Zn ions caused by the high binding energy of Hf ions.

Characterization of the Sno2 Based Thin Film Transistors with Ga, In and Hf Doping

We investigated the effects of doping tin oxide thin film transistors (TFTs) with Ga, In, and Hf. The quantity of doping impurities added to the SnO2-TFT channel layer was as follows: Ga (6.3-21.4 at.%), In (9.6-55.6 at.%), and Hf (1.2-2.7 at.%). Hafnium and gallium doping of SnO2 thin film decreased the carrier concentration, possibly due to a decrease in field effect mobility, and reduced oxygen vacancy-related defects. Indium-doped SnO2-TFTs exhibited high performance with a high field-effect mobility of > 20 cm2 V(-1) s(-1). The current on/off ratio and the subthreshold swing of In-doped SnO2-TFTs was 1 x 10(9) and 0.5 V/decade, respectively. These results demonstrate that Ga, In, and Hf doping can effectively enhance the performance of SnO2-based TFT devices.

First principle study of the electronic structure of hafnium-doped anatase TiO2

Crystal structures and electronic structures of hafnium doping anatase TiO2 were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on the density functional theory within the generalized gradient approximation. The calculated results show that the lattice parameters a and c of Hf-doped anatase TiO2 are larger than those of intrinsic TiO2 under the same calculated condition. The calculated band structure and density of states show that the conduction band width of Hf-doped TiO2 is broadened which results in the band gap of Hf-doped being smaller than the band gap of TiO2.

Phase diagram and spin-glass phenomena in electron-doped La1−xHfxMnO3 (0.05 ≤ x ≤ 0.3) manganite oxides

The effects of tetravalent hafnium doping on the structural, transport, and magnetic properties of polycrystalline La1−xHfxMnO3 (LHMO) (0.05 ≤ x ≤ 0.3) were investigated systematically. LHMO exhibited a typical colossal magnetoresistance effect via the double-exchange between Mn2+ and Mn3+ ions, instead of that between Mn3+ and Mn4+ ions in hole-doped manganites. A phase diagram was obtained for the first time through magnetization and resistance measurements in a broad temperature range. As the Hf concentration varied from x = 0.05 to 0.3, the Curie point and metal-to-insulator transition temperature increased significantly, whereas the magnetization and resistivity decreased remarkably. An abnormal enhancement of the magnetization was observed at about 42 K. It was further confirmed that a second magnetic phase MnO2 in LHMO gives rise to such a phenomenon. The possible causes are discussed in detail. The dynamic magnetic properties of LHMO, including relaxation and aging processes, were studied, demonstrating a spin-glass state at low temperature accompanied by a ferromagnetic phase.

Improvement in the bias stability of tin oxide thin-film transistors by hafnium doping

Thin-film transistors (TFTs) were fabricated with hafnium doped tin oxide (HTO) channels, and the effects of Hf content on the device performance of SnO x based TFTs was investigated. HTO TFTs exhibit improved electrical properties with increased field effect mobility and decreased subthreshold swing. We also investigated the influence of hafnium doping on bias stability in SnO x TFTs. HTO TFTs exhibited turn-on voltage (V ON) shifts of + 7 V for positive stress bias, compared with + 18 V for SnO x TFTs. The improvement in the V ON shift may be due to reduction in total trap density resulting from the suppression of defects related oxidation state of the Sn ion caused by the high binding energies of Hf ions.

Superconductivity, structure visualization, mechanical strength promotion and Raman spectra of hafnium-doped-123-YBCO synthesized via urea precursor route

The pure YBCO (YBa2Cu3O7) and its variant hafnium containing superconductors with general formula: Y1−xHfxBa2Cu3Oz, where x=0.1, 0.2, and 0.4mole, respectively, were synthesized by solution route using urea as precursor forming agent. X-ray measurements indicated that Hf4+ ions have a negligible effect on the main crystalline structure and substitute Y-sites successfully in lattice structure of 123-YBCO at low levels of hafnium doping (x=0.1→0.2mole). From SE-microscopy mapping and EDX elemental analysis Hf4+ was detected qualitatively with good approximation to the actual molar ratio but not observed at 123-YBCO grain boundaries which confirm that hafnium (IV) has diffused regularly into material bulk of superconducting 123-YBCO-phase at low levels of concentrations. Structure visualization of Hf-doped-123-YBCO was made to confirm success of hafnium substitutions inside crystal lattice on Y-sites of 123-YBCO superconductors. Hafnium dopings affected sharply on the main vibrating modes of YBCO regime particularly on the apical oxygen (O4) vibrational mode A1g. Magnetic susceptibility measurements proved that hafnium dopings have strong effect on the transport properties of YBCO-composites regime. Hafnium promotes mechanical tensile coefficient recording maxima 35.7MPa for x=0.4mole.

Improvement in the negative bias temperature stability of ZnO based thin film transistors by Hf and Sn doping

We assessed the performance of ZnO TFTs using Si 3N 4 gate dielectrics after various treatments. A remarkable improvement in the transfer characteristics was obtained for the O 2 plasma treated ZnO TFT and SiO 2 interlayer deposited ZnO TFT. Also, we developed amorphous hafnium–zinc–tin oxide (HZTO) thin film transistors (TFTs) and investigated the influence of hafnium (Hf) doping on the electrical characteristics of the hafnium–zinc oxide (HZO) thin film transistors. Doping with Hf can decrease the carrier concentration, which may result from a decrease of the field effect mobility, and reduce oxygen vacancy related defects in the interfacial layer. Adding tin (Sn) can suppress the growth of a crystalline phase in the HZTO films. The HZTO TFTs exhibited good electrical properties with a field effect mobility of 14.33 cm 2/Vs, a subthreshold swing of 0.97 V/decade, and a high I ON/OFF ratio of over 10 9.

Narrow Range of Hafnium Doping for Promoted Mechanical Properties and Critical Current Density (J c ) Values of Mg1−x Hf x B2 Superconductor

Hafnium was used as a softener dopant to replace at magnesium sites of Mg1−xHfxB2 regime (where x=0.0, 0.05, 0.1, 0.2, and 0.4 mole). Samples were prepared via high temperature solid state reaction technique depending upon diffusion mechanism of Mg-vapor ions through hafnium–boron matrix. The maximum solubility limit of hafnium (n) was found to be ∼0.22 mole. The crystalline lattice constants exhibit slight elongation in the case of the c-axis as x increases. Furthermore, the effect of Hf-doping on the microstructure properties of the MgB2 system was investigated carefully. The SE-microscopic analysis indicated that hafnium ions diffuse regularly through surface and bulk in case of (x=0.05–0.2 mole). The grain size was estimated and found to be between 0.33 and 1.34 μm. The mechanical tensile strength of the samples was clearly improved linearly as Hf-content increased, recording the maximum tensile strength of 34.8 MPa for the sample with x=0.4 mole. A visualization of the Hf-doped MgB2 structure was constructed and investigated to confirm the success of hafnium substitutions at the Mg-sites of the MgB2 superconductor.

The influence of hafnium doping on bias stability in zinc oxide thin film transistors

We investigated the influence of hafnium doping on negative bias temperature instability (NBTI) and positive bias temperature instability (PBTI) in zinc oxide thin film transistors (TFTs). Hafnium zinc oxide (HZO) TFTs exhibited turn-on voltage (V ON) shifts of 0 V for negative stress bias and + 3 V for positive stress bias, compared with −5 V and + 9 V, respectively, for ZnO TFTs. The enhanced improvement of the V ON shift may be due to a reduction in interface trap density resulting from the suppression of oxygen vacancy related defects caused by the high binding energy of Hf ions.

Solvothermal and surfactant-free synthesis of crystalline Nb2O5, Ta2O5, HfO2, and Co-doped HfO2 nanoparticles

A simple route to niobium, hafnium and tantalum oxide nanocrystals using a nonaqueous sol-gel route based on the solvothermal reaction of the corresponding metal chlorides with benzyl alcohol is presented. This approach can easily be extended to the preparation of high quality Co-doped HfO(2) nanoparticles of uniform size and shape and with a homogenous distribution of the magnetic ions. The structural characterization of all these nanomaterials as well as the magnetic properties of pure and doped hafnia, with special attention to the doping efficiency, are discussed. The obtained Co-doped hafnia exhibits paramagnetic properties with very weak antiferromagnetic interactions between Co ions moments.

Thermodynamics of solid electrolytes and related oxide ceramics based on the fluorite structure

Oxides based on the fluorite structure are important as electrolytes in solid oxide fuel cells, thermal barrier coatings, gate dielectrics, catalysts, and nuclear materials. Though the parent fluorite structure is simple, the substitution of trivalent for tetravalent cations, coupled with the presence of charge-balancing oxygen vacancies, leads to a wealth of short-range and long-range ordered structures and complex thermodynamic properties. The location of vacancies and the nature of clusters affect the energetics of mixing in rare earth doped zirconia, hafnia, ceria, urania, and thoria, with systematic trends in energetics as a function of cation radius. High temperature oxide melt solution calorimetry has provided direct measurement of formation enthalpies of these refractory materials. Surface and interfacial energies have also been measured in yttria stabilized zirconia (YSZ) nanomaterials. Other ionic conductors having perovskite, apatite, and mellilite structures are discussed briefly.

The Influence of the Hafnium Doping on Negative Bias Stability in Zinc Oxide Thin Film Transistor

The influence of hafnium doping on negative bias temperature instability in zinc oxide thin film transistors (TFTs) was investigated. The hafnium zinc oxide TFTs showed that the turn-on voltage (V ON ) shifted from -2 to -7 V with negligible changes in the subthreshold swing and field effect mobility (μ FE ) after a time of total stress. The enhanced improvement of the V ON shift was attributed to the reduction in interface trap density, which might result from the suppression of oxygen vacancy related defects due to the role of Hf ions.

Ion-conducting, sub-100 nm-thick film of amorphous hafnium silicate

Ceramic electrolytes operating in the temperature range of 200 to 500 °C under dry atmosphere are a key material for the next-generation fuel cell and related applications. We discovered that nanometer-thick films of amorphous hafnium silicate (Hf n Si 1 − n O x ) exhibited efficient ionic conduction at 100–400 °C in dry air. When the fraction of hafnium doping was around 0.1, the nanofilm showed a low area-specific-resistance (< 0.15 Ω cm 2) at around 350 °C that was small enough for the practical fuel cell application. The sub-100 nm-thick membranes of Hf 0.13Si 0.87O x , could be fabricated on porous Pt/alumina substrate to provide gas concentration cells. The electromotive force observed with H 2 concentration cell indicated that the ceramic nanomembrane acted as predominant proton conductor without permeation of H 2 gas. In addition, the Hf 0.13Si 0.87O x and Zr 0.11Si 0.89O x membranes responded to the change of O 2 pressures in O 2 concentration cells, while the Al 0.16Si 0.84O x and Ce 0.06Si 0.94O x membranes did not produce the electrical voltage by gradient of O 2 pressure. We conclude that Hf 0.13Si 0.87O x nanomembrane is promising as electrolyte material for fuel cells and related ionics devices.

Erratum: “Synthesis of nitrogen passivated rare-earth doped hafnia thin films and high temperature electrochemical conduction studies” [J. Vac. Sci. Technol. B 26, L33 (2008)

Erratum: “Synthesis of nitrogen passivated rare-earth doped hafnia thin films and high temperature electrochemical conduction studies” [J. Vac. Sci. Technol. B 26, L33 (2008)

Effect of Rare-Earth Doping and Nitrogen Passivation Treatments on the Properties of Ultra-thin Hafnia Films

Rare-earth doped hafnia films are of great interest as higher-k dielectrics that could potentially function as alternate gate dielectrics on Si and other high-mobility semiconductor channels. We present results on the effect of nitridation on electrical and dielectric properties of hafnia films prepared by physical vapor deposition. Particular emphasis is placed on passivation of point defects by nitrogen studied through high temperature electrochemical conductivity measurements.

Synthesis of nitrogen passivated rare-earth doped hafnia thin films and high temperature electrochemical conduction studies

The authors report on the synthesis, electrical characterization, and high temperature electrochemical conductivity of nitrogen passivated crystalline rare-earth doped hafnia thin films with high-dielectric constant (∼30) and low leakage currents. High temperature electrochemical conductivity of the Re-doped nitrided hafnia thin films are comparable to one another. The results are of potential significance to synthesis of crystalline oxides on semiconductor surfaces with tailored functionality.

NMOS Compatible Work Function of TaN Metal Gate With Erbium-Oxide-Doped Hafnium Oxide Gate Dielectric

This letter demonstrates reduction in effective work function of tantalum-nitride (TaN) metal gate with erbium-oxide-doped hafnium oxide. We report that TaN effective metal-gate work function can be tuned from Si midgap to the conduction band to meet the work-function requirement of NMOSFETs by incorporating ErO in HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with an equivalent oxide thickness as low as 1.15 nm. Several other lanthanide-oxide doped hafnium oxides show similar characteristics.

Reactively sputtered doped hafnium nitride coatings

Doping of hafnium nitride (HfN) coatings increases the hardness by as much as 50% over that of undoped coatings. Pure hafnium nitride coatings prepared via-high-rate reactive sputtering are already considerably harder than bulk HfN material. The Vickers microhardness (100 gf) of reactively-sputtered HfN has an optical hardness of 3280 kgf mm -2 compared with 1600 kgf mm -2 for the bulk material. Powder metal Research S-Gun targets were prepared with 1 at.% of phosphorus, arsenic, antimony and bismuth in them. These doped targets were reactively sputtered in a nitrogen atmosphere onto M-2 high speed steel, and the hardness, crystallographic structure and chemical composition of these doped HfN coatings were measured. In all cases, the crystal structure remained basically f.c.c. with a lattice parameter of 4.56 Å. Electron beam microprobe analysis was not able to detect any of the dopants in the coatings, but the hardness measurements did show a difference that was dependent on the particular dopant. The measured Vickers (100 gf) optical microhardnesses for HfN:P, HfN:As, HfN:Sb and HfN:Bi were 3570 kgf mm -2, 3850 kgf mm -2, 4920 kgf mm -2 and 4370 kgf mm -2 respectively.