Hafnium Silicate Research Articles

Ultrasensitive Pressure-Induced Optical Materials: Europium-Doped Hafnium Silicates with a Khibinskite Structure for Optical Pressure Sensors and WLEDs.

Ultrasensitive pressure-induced optical materials are of great importance owing to their potential applications in optical pressure sensors. However, the lack of outstanding pressure sensitivity, observable color evolution, and structure reliability limits their further development in both practical applications and luminescence theory. To overcome the above problems, an enlightening methodology is proposed to explore the high sensitivity and phase stability of hafnium silicate K2HfSi2O7 (KHSO) phosphor with a Khibinskite structure. By employing X-ray diffraction (XRD) Rietveld refinement, cryogenic spectroscopy, and ancillary calculations, information on Eu2+ ion occupation is completely obtained at atmospheric pressure. The remarkable pressure sensitivity (dλ/dP = 3.25 nm/GPa-1) and excellent phase stability up to 20 GPa, along with the reproducible color hue variation, exhibit unprecedented superiority when used in optical pressure sensors. These advantages can be assigned to the pressure-induced Eu2+-selective occupation and the unique properties of 5d-4f transition (Stokes shift, nephelauxetic effect, and intense crystal field strength), which are clearly proved by measuring the XRD patterns, Raman spectra, and Gaussian fitting spectra under compression and decompression processes. The excellent luminescence property manifests that KHSO/Eu2+ can be considered as a potential luminescent material for solid-state lighting and optical pressure sensors.

Thermochemical degradation of HfSiO4 by molten CMAS

The thermochemical degradation of hafnium silicate (HfSiO4) was investigated with a molten calcium-magnesium-aluminosilicate (CMAS) glass relevant to gas turbine engine applications. Sintered HfSiO4 coupons were fabricated, within which wells were drilled and filled with CMAS glass powder at a loading of ∼35 mg/cm2. Samples were heat treated at 1200°C, 1300°C, 1400°C, and 1500°C for 1 h, 10 h, and 50 h. At 1200°C and 1300°C, slow formation of a Ca2HfSi4O12 cyclosilicate phase was observed at the HfSiO4-CMAS interface. At 1300°C and higher, rapid infiltration of CMAS into the material along the grain boundaries was observed. Initial conjecture into CMAS degradation mechanisms of HfSiO4 are presented herein.

Properties of Hafnium and Aluminium Silicates Coatings Obtained by PLD

We report on the deposition and characterization of hafnium silicate and aluminium silicate thin films for different applications in optics and electronics. Pulsed laser deposition in a controllable oxygen atmosphere was used as a processing technique, with optimized parameters in terms of laser wavelength, laser fluence and oxygen pressure. The thin films were investigated using atomic force microscopy, spectroscopic ellipsometry, UV–VIS spectroscopy and X-ray photoelectron spectroscopy. The morphological investigations evidenced uniform layers with low roughness (in the order of nanometres). The optical investigations revealed that aluminium silicate layers with low roughness and low absorption in the infrared (IR) range can be obtained at high substrate temperatures (600 °C). The behaviour of the silicate thin films with respect to the nanosecond IR laser irradiation revealed that aluminium silicate layers have higher laser-induced damage threshold values in comparison with hafnium silicate.

Combined Implications of UV/O3 Interface Modulation with HfSiOX Surface Passivation on AlGaN/AlN/GaN MOS-HEMT

Surface passivation is critically important to improve the current collapse and the overall device performance in metal-oxide semiconductor high-electron mobility transistors (MOS-HEMTs) and, thus, their reliability. In this paper, we demonstrate the surface passivation effects in AlGaN/AlN/GaN-based MOS-HEMTs using ultraviolet-ozone (UV/O3) plasma treatment prior to SiO2 -gate dielectric deposition. X-ray photoelectron spectroscopy (XPS) was used to verify the improved passivation of the GaN surface. The threshold voltage (VTH) of the MOS-HEMT was shifted towards positive due to the band bending at the SiO2/GaN interface by UV/O3 surface treatment. In addition, the device performance, especially the current collapse, hysteresis, and 1/f characteristics, was further significantly improved with an additional 15 nm thick hafnium silicate (HfSiOX) passivation layer after the gate metallization. Due to combined effects of the UV/O3 plasma treatment and HfSiOX surface passivation, the magnitude of the interface trap density was effectively reduced, which further improved the current collapse significantly in SiO2-MOS-HEMT to 0.6% from 10%. The UV/O3-surface-modified, HfSiOX-passivated MOS-HEMT exhibited a decent performance, with IDMAX of 655 mA/mm, GMMAX of 116 mS/mm, higher ION/IOFF ratio of approximately 107, and subthreshold swing of 85 mV/dec with significantly reduced gate leakage current (IG) of 9.1 ×10−10 A/mm.

Analysis of dielectric and temperature impact on co-axial CNTFET characteristics using NEGF

Carbon nanotube (CNT) is one of the promising materials for MOS technology. In this study, the impact of dielectric materials and temperature for a certain diameter of CNT has been discussed related to ballistic CNTFET by using non-equilibrium Green’s function (NEGF) formalism. With the dielectric materials like polyethylene (2.25), hafnium silicate (11), zirconium dioxide (19) and titanium dioxide (40) the device characteristics such as drain induced barrier lowering (DIBL), Sub threshold swing (SS), carrier injection velocity (V_inj), output conductance (gm), voltage gain (AV), transconductance (gm) have been investigated.

Low-temperature Hf-silicate prepared with various thermal budgets

In this study, the influence of thermal budget on preparing hafnium silicate (HfSiO) and metal–insulator–semiconductor (MIS) structures with tetragonal hafnium oxide (HfO2) films was investigated. Amorphous silicon (a-Si) was used as a sacrificial layer for HfSiO formation. Rapid thermal annealing (RTA) could efficiently drive the oxidation of a-Si with HfO2. The RTA-produced HfSiO film thicker than that produced through furnace annealing could suppress gate leakage in MIS devices, and aid in maintaining a high dielectric constant of the gate insulator. The combination of sacrificial a-Si film use and RTA application resulted in a HfSiO/HfO2 structure (named as hybrid HfO2), which demonstrated a high dielectric constant and strength (29.5 and 21.2 MV cm−1, respectively). MIS devices integrated with this hybrid HfO2 achieved a hysteresis value of only 0.11 V on a flat-band voltage measured at a 50 mV s−1 sweep rate with an applied voltage between −5 and 5 V.

Hafnium silicate formation during oxidation of a permeable silicon + HfO2 powder composite system

Silicon bond coats, applied to silicon carbide composites used in gas turbine engines as a part of an environmental barrier coating (EBC) system, arrest the transport of oxidizing species to the SiC composite by forming a SiO2 thermally grown oxide. Above 1200°C, a crystalline ß-cristobalite SiO2 phase is formed that subsequently undergoes a large thermal contraction during its ß→α-cristobalite transformation upon cooling, leading to oxide layer cracking and eventual EBC delamination. A model system of silicon particles in a highly porous HfO2 particle matrix is used to investigate the rate and mechanism by which ß-cristobalite SiO2 is dynamically converted to hafnium orthosilicate (HfSiO4; Hafnon) when oxidizing silicon is in contact with m-HfO2. The study compares the net rate of SiO2 formation in the model silicon + HfO2 system with that on only silicon particles, and finds that the thickness of the SiO2 layer that forms during high temperature (1250–1316°C) oxidation can be greatly reduced by the hafnon formation reaction. The study also investigates the mechanism by which hafnon forms, and reports a SiO2 rumpling process when its outward (radial) growth is locally constrained by HfO2 particles. Since hafnon is phase stable over the temperature range of EBC interest, and has a thermal expansion coefficient similar to silicon, the dynamic conversion of SiO2 to hafnon provides a promising approach for controlling the delamination of EBC systems that use silicon bond coats.

Hafnium silicate formation during the reaction of β‐cristobalite SiO2 and monoclinic HfO2 particles

AbstractHafnium silicate (HfSiO4; hafnon) is under consideration as an environmental barrier coating material for high‐temperature applications. However, its rate of formation from mixtures of monoclinic HfO2 and crystalline (β‐cristobalite) SiO2 powders is unknown. Here it has been synthesized and its formation rate measured during their solid‐state reaction at temperatures from 1250°C to 1400°C. Rietveld refinement of X‐ray diffraction patterns indicates that at 1250°C the hafnon phase fraction increases linearly with time, while at the highest reaction temperature, the hafnon phase fraction exhibited a parabolic dependence upon time. Between these two limiting temperatures, a region of linear behavior preceded a transition to parabolic kinetics, with the transition occurring at an earlier time as the reaction temperature increased. Arrhenius relations fitted the kinetics of hafnium silicate formation in both the linear and parabolic regimes. Scanning electron microscopy indicated that the reaction proceeded by diffusion of SiO2 into HfO2, similar to the mechanism by which zirconium silicate has been formed from vitreous SiO2 and tetragonal ZrO2. The initial linear rate of reaction is consistent with the growth of the contact area between the SiO2 and HfO2 particles combined with rapid permeation of the Si4+ and O2− through the initial, incompletely formed hafnon. After a thin hafnon layer had formed between the reactants, the rate of hafnium silicate growth slowed and further growth was governed by the rate of diffusion of Si4+ and O2− through the reaction product consistent with the observed parabolic dependence of the phase fraction upon time.

Gate controllability of HfSiOx/AlGaN/GaN MOS high-electron-mobility transistor

Hafnium silicate (HfSiOx) has been applied to AlGaN/GaN high-electron-mobility transistors (HEMTs) as a high κ gate dielectric. The (HfO2)/(SiO2) laminate structure was deposited on the AlGaN surface by a plasma-enhanced atomic layer deposition, followed by a post-deposition annealing at 800 °C. The HfSiOx-gate HEMT showed good transfer characteristics with a high transconductance expected from its κ value and a subthreshold swing of 71 mV/decade. For the metal–oxide-semiconductor (MOS) HEMT diode, we observed excellent capacitance–voltage (C–V) characteristics with negligible frequency dispersion. The detailed C–V analysis showed low state densities on the order of 1011 cm−2 eV−1 at the HfSiOx/AlGaN interface. In addition, excellent operation stability of the MOS HEMT was observed at high temperatures up to 150 °C.

Plasma-enhanced atomic layer deposition of hafnium silicate thin films using a single source precursor

A single source precursor containing both Hf and Si was employed with oxygen plasma to deposit hafnium silicate thin films using plasma-enhanced atomic layer deposition (PEALD). The self-limiting growth features were observed between 210 °C-280 °C with a constant growth rate of 1.45 Å/cycle. The deposited hafnium silicate thin films were amorphous with a composition of Hf0.33Si0.66O2. The mechanism for the surface adsorption of the precursor was investigated by density functional theory (DFT) calculations, which show adsorption reactions of both Hf and Si atoms are viable. Bottom-gated InGaZnO channel thin-film transistors (TFTs) were fabricated to evaluate the electrical characteristics of PEALD hafnium silicate thin films as gate dielectrics. Compared to the conventional SiO2 gate dielectric, TFTs with PEALD hafnium silicate gate dielectric exhibited an improved switching performance, where the turn-on voltage, threshold voltage, saturation mobility, subthreshold slope, and on-off current ratio were −0.456 V, 3.202 V, 15.83 cm2/V·sec, 0.196, and 1.34 × 109, respectively.

Comparative analysis of silicon nano tube FET for switching applications using high K and work function modulation

In this paper we studied the impact of variation of dielectric constant and alternation of gate work function on silicon nanotube FET for low power and high speed switching applications. The silicon nano tubular structure offers better immunity towards short channel effects. Due to the gate engineered structure high K value structures possess high value of electron velocity. In this paper we have considered a silicon dioxide (SiO2), silicon nitride (Si3N4), hafnium oxide (HfO2), hafnium silicate (HfSiO4), tin oxide (SnO2) and titanium oxide (TO2) as a gate dielectric. Further by tuning the gate work function of the device we can able to achieve multiple threshold voltages and optimise the performance of the device. In this paper we discuss the impact of work function variation on ON-current, OFF-current and threshold voltage. From the analysis it has been found that HfO2 in SINTFET will be a superior alternative for future tubular FET devices and by tuning the gate work function nearby to 4.8 eV the silicon nano tube shows optimised better performance among all other values.

Hafnium silicate gate dielectrics in GaN metal oxide semiconductor capacitors

Characteristics of hafnium silicate as gate dielectric in n-GaN capacitors were investigated. The Hf0.57Si0.43Ox, Hf0.64Si0.36Ox and HfO2 films exhibited high dielectric constants of 15.4, 15.9, and 17.6, respectively. The Hf0.57Si0.43Ox and Hf0.64Si0.36Ox films, which had an amorphous structure, showed superior properties, including a minimal flatband voltage (Vfb) hysteresis (≤70 mV) and a small Vfb shift (≤−0.45 V), as well as a low interface state density (~4 × 1011 cm−2 eV−1 at −0.4 eV from conduction band), and a high breakdown electric field (≥8.6 MV cm−1) compared to those of a polycrystalline HfO2 film.

Interface properties study on SiC MOS with high-k hafnium silicate gate dielectric

High k dielectrics, such as Al2O3, has attracted increasing research attention for its use as the gate dielectric of 4H-SiC MOS capacitors. Since the dielectric constant of Al2O3 is not high enough, many other high-k dielectrics are actively explored. In this letter, a report of the interface properties of 4H-SiC MOS capacitors with Hafnium silicate (HfSiOx) dielectric is presented. The HfSiOx dielectric was deposited by thermal atomic layer deposition. A systematic study of I-V and multi-frequency C-V characteristics were carried out and the results showed HfSiOx gate dielectric could effectively increase dielectric constant. A thin layer of SiO2 in between SiC and high k dielectric can further improve interface properties. These results indicate that HfSiOx could be a promising candidate as suitable gate dielectric material for future 4H-SiC MOS capacitors and MOSFETs.

Performance Analysis of CNFET Based 6T SRAM

CNFET is an emerging device which facilitates continuing feature size scaling trend. This novel device is predicted to outperform existing planer devices in near future owing to its unique features like ballistic transport operation, excellent carrier mobility, high current carrying capability, high stability, one dimensional band structure. In this paper, the performance of CNFET based six transistor (6T) SRAM cell has been analyzed. The effects of variations in dielectric material, oxide thickness, metal gate and CNT work function, Fermi level and chiral vector on power delay product (PDP) and static noise margin (SNM) are comprehensively analyzed. It is observed that Hafnium Silicate (HfSiO4) as dielectric material at 1nm oxide thickness yields best results in terms of stability and energy efficiency. CNT work function of 4.65eV yields most optimum PDP value of 63.59 zepto Joule.

Origin of Pr3+ luminescence in hafnium silicate films: combined atom probe tomography and TEM investigations

Structural, chemical, and luminescence properties of Pr3+-doped HfSiOx layers fabricated by radio-frequency magnetron sputtering were examined as a function of annealing temperature. Phase separation between SiO2 and HfO2 as well as the location of Pr3+ dopants were investigated using atom probe tomography and transmission electron microscopy while optical properties of Pr3+ ions were studied using photoluminescence measurements. As a result, (i) we evidenced the location of the Pr3+ dopants in the HfO2 phase while the SiO2 phase was discovered to be free of these dopants, (ii) the HfO2 phase was identified to crystallize in the cubic phase until 1050 °C annealing, (iii) no Pr clusters were detected as function of annealing, and (iv) luminescence properties were discussed in regard to the location of Pr in the HfO2 cubic phase.

Low temperature synthesis of pure and Fe-doped HfSiO4: Determination of Si and Fe fractions by neutron activation analysis

A new method of synthesis of hafnium silicate HfSiO4 (also known as hafnon) is reported. We observed a self-controlled incorporation of SiO2 from the quartz tube in which a sample of hafnium oxide nanoparticles was heated. This approach was then adapted to Fe-doped hafnon production. Sample structure, morphology and composition were characterized by X-ray diffraction, electron microscopy and neutron activation analysis. Diffraction data has shown that lattice parameters of doped HfSiO4 thus obtained are very close to those previously known for bare hafnon. The hafnon-like phase stabilized at T = 900 °C which is about 500 °C lower than the corresponding transition of bare bulk hafnium silicate. The fractions of Si and Fe in the composite matrices were determined with neutron activation analysis. These results completed by X-ray diffraction data allowed to assume that (i) Fe initially substituted Hf in the HfO2 lattice; (ii) there was no migration of iron atoms from Hf to Si sites at the formation of hafnon-like phase; (iii) doped and undoped hafnium oxide has taken as much Si from the quartz as was needed for the arrangement of Fe1-xHfxSiO4 tetragonal system, 0≤x<0.2. Our results are consistent with those obtained for similar materials, such as metal (Fe,V) doped zircon, where the dopant also demonstrated catalytic effect on phase stabilization.

High-temperature thermal barrier-coated Sylramic-iBN/pyrolytic carbon/chemical vapor infiltration silicon carbide ceramic matrix composite behavior in a combustion environment

An environmental barrier-coated Sylramic-iBN/pyrolytic carbon/chemical vapor infiltration silicon carbide ceramic matrix composite was characterized in a harsh combustion environment under two conditions; (i) with a coating surface temperature of 1480℃, and (ii) with a combustion flame distance of 120 mm (constant flux). Three coating systems were evaluated; Coating “A” (ytterbium silicate using hafnium–silicate bond), Coating “B” (ytterbium silicate using alumina bond), and Coating “C” (ytterbium–silica compounds using alumina bond). All three coatings survived with essentially no mass loss up to 25 h when tested at 1480℃. At a flame distance of 120 mm coatings “A” and “B” experienced extensive degradation and strength loss while coating “C” had practically no degradation in retained strength. Coating “C” outperformed the other two coatings exposed to the harsh combustion environment. It performed best in terms of material loss, thermal barrier capability, and residual tensile strength.

Oxygen vacancy induced structure change and interface reaction in HfO2 films on native SiO2/Si substrate

The HfO2 films were deposited on SiO2 (native)/n-Si (100) substrates by electron beam evaporation (EBE) technology. The structural evolution of the films during thermal annealing were studied by using grazing incidence X-ray diffraction (GIXRD), Raman spectra and Auger electron spectroscopy (AES), while the change of bonding structure and interface products were obtained by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The existence of oxygen vacancies in the surface layer of the as-deposited HfO2 film was confirmed by Auger line shapes, which could facilitate the adsorption of ambient oxygen on the free surface and induce the diffusion of oxygen atoms to the surface layer during thermal annealing. Meanwhile, the newly formed defects in the films could provide more passageways for the diffusion of oxygen atoms to the film-substrate interface layer. The oxygen that diffused to the interface layer was the key factor of the change in the interface structure, which participated in the interface reaction. In addition, the formation amount and bonding structure of the interface products such as suboxide of silicon and hafnium silicate were influenced by the oxygen concentration of the external environment.

Out-of-Plane Strain Effects on Physically Flexible FinFET CMOS

We present a comprehensive electrical performance assessment of hafnium silicate (HfSiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) high-κ dielectric and titanium-nitride (TiN) metal-gate-integrated FinFET-based complementary-metal-oxide-semiconductor (CMOS) on flexible silicon on insulator. The devices were fabricated using the stateof-the-art CMOS technology and then transformed into flexible form by using a CMOS-compatible maskless deep reactive-ion etching technique. Mechanical out-of-plane stresses (compressive and tensile) were applied along and across the transistor channel lengths through a bending range of 0.5-5 cm radii for n-type and p-type FinFETs. Electrical measurements were carried out before and after bending, and all the bending measurements were taken in the actual flexed (bent) state to avoid relaxation and stress recovery. Global stress from substrate bending affects the devices in different ways compared with the well-studied uniaxial/biaxial localized strain. The global stress is dependent on the type of channel charge carriers, the orientation of the bending axis, and the physical gate length of the device. We, therefore, outline useful insights on the design strategies of flexible FinFETs in future free-form electronic applications.

Comparison of HfCl4, HfI4, TEMA-Hf, and TDMA-Hf as precursors in early growing stages of HfO2 films deposited by ALD: A DFT study

The final structure of HfO2 films grown by atomic layer deposition (ALD) after reaction with OH− ions has been analyzed by DFT (density functional theory). The interaction of the precursors: HfCl4 (hafnium tetrachloride), HfI4 (hafnium tetraiodide), TEMA-Hf (tetrakis-ethylmethylamino hafnium), and TDMA-Hf (tetrakis-dimethylamino hafnium) with HO–H was studied employing the B3LYP (Becke 3-parameter, Lee–Yang–Parr) hybrid functional and the PBE (Perdew–Burke–Ernzerhof) generalized gradient functional. The structural evolution at the Si(100) surface has been analyzed by LDA (local density approximation). The structural parameters: bond length and bond angle, and the vibrational parameters for the optimized structures are also reported. The presence of hafnium silicate at the interface was detected. The infrared spectra and structural parameters obtained in this work agree with previously reported experimental results.