Structure, properties, and thermal stability of nanocrystallite Fe-Ti-N soft magnetic films

We deposited Fe-Ti-N magnetic films with a high sputtering power of 7 W/cm/sup 2/. When the composition of the films was in the range of Fe-Ti(3.9 at.%)-N(8.8 at.%) to Fe-Ti(3.3 at.%)-N(13.5 at.%), the films were composed of /spl alpha/' and Ti/sub 2/N precipitates. With the addition of nitrogen, 4/spl pi/M/sub s/ became higher than that of pure iron, reaching a maximum of 23.8 kG. At the same time, H/sub c/ was reduced to a minimum of 1.12 Oe. The best films can meet the needs of the recording head in dual-element giant magnetoresistive/inductive heads, yielding high storage density (10 Gb/in/sup 2/). The incorporation of N in /spl alpha/-Fe brought about the /spl alpha/' phase with its higher saturation magnetization. Ti additions inhibited the equilibrium decomposition /spl alpha/'/spl rarr//spl alpha/+/spl gamma/'. Because H/sub C//sup D//spl prop/D/sup 6/, where D is average grain diameter, grain size control is very important. The nitrogen induces severe distortion of the /spl alpha/' lattice, which can cause the grains to break into pieces and reduce the grain size. High sputtering power also led to the formation of fine grains, with diameter in the order of 14 nm. Probably Ti/sub 2/N is preferentially precipitated on the grain boundary, pinning the grain boundary and stabilizing the grain size during high-temperature heat treatment. The temperature limit for stability of the structure and its associated low coercivity was not less than 520/spl deg/C.     

Shear mode coupling and tilted grain growth of AlN thin films in BAW resonators

Polycrystalline AlN thin films were deposited by RF reactive magnetron sputtering on Pt(111)/Ti electrode films. The substrates were tilted by an angle ranging from 40/spl deg/ to 70/spl deg/ with respect to the target normal. A low deposition temperature and a high sputter gas pressure were found ideal for tilted growth. The resulting grain tilt angle amounts to about half the substrate tilt angle. For coupling evaluation, 5 GHz solidly mounted resonator structures have been realized. The tilted grain AlN films exhibited a permittivity in the 9.5-10.5 range and loss tangent of 0.3%. Two shear modes as well as the longitudinal mode could be clearly identified. The coupling coefficient k/sub eff//sup 2/, of the fundamental thickness shear mode (TSO) was found to be about 0.5%, which is compatible with a c-axis tilt of about 6/spl deg/.     

Optical and electrical H/sub 2/- and NO/sub 2/-sensing properties of Au/In/sub x/O/sub y/N/sub z/ films

In this paper, we describe the optical and electrical gas-sensing properties of In/sub x/O/sub y/N/sub z/ films with an ultrathin gold promoter overlayer. We have fabricated In/sub x/O/sub y/N/sub z/ films with a nanocrystalline porous structure by RF-sputtering in Ar/N/sub 2/ followed by an annealing process. Gold particles with 20-30-nm diameter have been formed on top of the In/sub x/O/sub y/N/sub z/ films by dc sputtering and an annealing process. We have investigated the optical H/sub 2/and NO/sub 2/-sensing properties (change of absorbance) and also the electrical sensing effect (change of electrical resistance) for these two gases. A combined optical/electrical sensor for H/sub 2//NO/sub 2/ is proposed.     

Nanometer surface roughness effect on the magnetic properties of CoFeHfO thin films

This article reports the effects of nanometer surface roughness on the magnetic properties of CoFeHfO thin films, as deposited on Si (100) substrates. The surface roughness was controlled via the working pressure during the sputtering time. When the working pressure increases from 0.5 to 3 mT, the surface roughness (R) of CoFeHfO thin films, formed by islands with the average high R, increases from 0.25 nm to 4.66 nm, respectively. At surface roughness (R) = 4.66 nm, coercivity (H(c)) reaches the highest value of 0.42 Oe and magnetic anisotropy (H(k)) drops to the lowest value of 33 Oe. This suggests that the quality of the soft magnetic properties of thin film decrease due to the increase in surface roughness. However, at very low working pressure, thin films become a homogeneous structure which also exhibits poor soft magnetic properties. The optimum value, with H(c) of 0.10 Oe and H(k) of 50 Oe, were obtained at 1.5 mT of working pressure. The model of the roughness effect on the magnetic properties is introduced and discussed.     

High coercivity and high saturation magnetization Mn-Al thin films

Mn-Al thin films with the composition of 31-68 at.% Mn were prepared by rf magnetron sputtering at various substrate temperatures then annealed in vacuum. Effects of the chemical composition, substrate temperature and annealing temperature on the magnetic properties of Mn-Al films have been investigated. The analysis of X-ray diffraction and magnetic measurement indicate that τ-phase was synthesized at a composition range of 40-60 at.% Mn. However, the formation of large amount of τ-phase occurred for Mn₅₀-Al₅₀ films, which have a high coercivity up to about 3000 Oe and a fairly large saturation magnetization of about 420 emu/cc     

Effect of dopants on the soft magnetic properties and high frequency characteristics of FeCoBM (M = Ti, Nb, Hf, and Ta) thin films

Effect of dopants on the soft magnetic properties and high frequency characteristics of FeCoBM thin films (M = Ti, Nb, Hf, and Ta) have been studied. For (Fe0.55Co0.45)(100-x)B(x) (x = 5-15) thin films, with the increase of B content, the resistivity was increased because B could decrease the crystallinity of the films. The (Fe0.55Co0.45)90B10 thin film showed the optimum properties, where 4piM(s) = 16.1 kG, H(ce) = 64.2 Oe, H(ch) = 13.5 Oe, H(k) = 310 Oe and p = 338 microomega-cm. To reduce the coercivity of the film, the elements M, including Ti, Nb, Hf, and Ta, were selected to substitute for B in the FeCoB films. It was found that (Fe0.55Co0.45)90B6Ti2Nb2 thin film after annealing at a temperature of 200 degrees C for 30 min showed the optimal properties, where 4piM(s) = 15.8 kG, H(ce) = 4.8 Oe, H(ch) = 3.6 Oe, H(k) = 224 Oe and p = 290 microomega-cm. The theoretically calculated ferromagnetic resonance frequency of the developed films can be higher than 5 GHz.     

Preparation of ferroelectric Ba(Ti/sub 0.85/Sn/sub 0.15/)O/sub 3/ thin films by metal-organic decomposition

Ferroelectric Ba(Ti/sub 0.85/Sn/sub 0.15/)O/sub 3/ (BTS/sub 15/) thin film is newly prepared on the Pt/Ti/SiO/sub 2//Si substrate by metal-organic decomposition. The firing condition is determined by thermogravimetric and differential thermal analysis. The BTS/sub 15/ thin film with a flat surface and uniform thickness is obtained by spin coating in N/sub 2/ atmosphere that avoids moisture. The BTS/sub 15/ film has a perovskite phase and a preferential [110] texture. It is also found that the crystalline structure is cubic at 24/spl deg/C with a lattice constant of 4.01 /spl Aring/, and a grain size of about 30 nm was estimated by Scherrer equation and SEM image. From P-E hysteresis loop at 20/spl deg/C, the polarization at E=0 and the electric field at P=0 are found to be 1.07 /spl mu/C/cm/sup 2/ and 24.0 kV/cm, respectively. It is observed that the dielectric constant decreases monotonously from about 830 to 630 with increasing temperature ranging from 20/spl deg/C to 50/spl deg/C. Finally, it is found that the BTS/sub 15/ thin film shows a sufficient ferroelectricity and is an attractive material for functional ferroelectric devices, such as thermal-type infrared sensors.     

The electrical properties of resistive and dielectric thin films prepared by reactive sputtering from a tantalum-titanium composite target

Resistive thin films of TaTiN and dielectric thin films of TaTiO prepared by reactive co-sputtering in ArN₂ or ArO₂ mixtures from a TaTi composite target were investigated in an effort to extend the data on the electrical properties of films prepared by reactive sputtering from tantalum targets. The composition of the thin films was controlled by changing the ratio of the tantalum area to the titanium area on the composite target surface.For the TaTiN films the resistivity, the temperature coefficient of resistance and the Hall coefficient were investigated as functions of the nitrogen partial pressure and the composition of the films.The dielectric constant, the temperature coefficient of capacitance and tan δ were studied as functions of composition in films of the TaTiO system.The resistivities of TaTiN films sputtered at a nitrogen partial pressure of 4 × 10^?4 Torr varied linearly from 50 to 270 μω cm as the tantalum weight percentage of the films increased from 10 to 90%. The temperature coefficient of resistance for these films decreased, again linearly, from 1000 to ?50 ppm °C^?1 over the same range of tantalum weight percentage.As the titanium weight percentage of the films increased from 10 to 90%, the dielectric constant and tan δ for the TaTiO films varied linearly from 30 to 70 and from 0.008 to 0.025 respectively.It is believed that these resistive and dielectric thin films will be valuable for producing thin film passive elements in hybrid integrated circuits.     

Ceramic temperature sensors for harsh environments

A ceramic thermocouple based on indium-tin-oxide (ITO) thin films is being developed to measure the surface temperature of gas turbine engine components employed in power and propulsion systems that operate at temperatures in excess of 1500/spl deg/C. By fabricating ITO elements with substantially different charge carrier concentrations, it was possible to construct a robust ceramic thermocouple. A thermoelectric power of 6.0 /spl mu/V//spl deg/C, over the temperature range 25-1250/spl deg/C, was realized for an unoptimized ITO ceramic thermocouple. The charge carrier concentration difference in the legs of the ITO thermocouple was established by r.f. sputtering in oxygen-rich and nitrogen-rich plasmas. SEM micrographs revealed that after high-temperature exposure, the surfaces of the nitrogen prepared ITO films exhibited a partially sintered microstructure with a contiguous network of ITO nanoparticles. Thermal cycling of ITO films in various oxygen partial pressures showed that the temperature coefficient of resistance was nearly independent of oxygen partial pressure at temperatures above 800/spl deg/C and eventually became independent of oxygen partial pressure after repeated thermal cycling below 800/spl deg/C. Based on these results, a versatile ceramic sensor system has been envisioned where a ceramic thermocouple and strain sensor can be combined to yield a multifunctional ceramic sensor array.     

Ultrahigh-sensitive tin-oxide microsensors for H/sub 2/S detection

Ultrahigh-sensitivity SnO/sub 2/-CuO sensors were fabricated on Si(100) substrates for detection of low concentrations of hydrogen sulfide. The sensing material was spin coated over platinum electrodes with a thickness of 300 nm applying a sol-gel process. The SnO/sub 2/-based sensors doped with copper oxide were prepared by adding various amounts of Cu(NO/sub 3/)/sub 2/.3H/sub 2/O to a sol suspension. Conductivity measurements of the sensors annealed at different temperatures have been carried out in dry air and in the presence of 100 ppb to 10-ppm H/sub 2/S. The nanocrystalline SnO/sub 2/-CuO thin films showed excellent sensing characteristics upon exposure to low concentrations of H/sub 2/S below 1 ppm. The 5% CuO-doped sensor having an average grain size of 20 nm exhibits a high sensitivity of 2.15/spl times/10/sup 6/ (R/sub a//R/sub g/) for 10-ppm H/sub 2/S at a temperature of 85/spl deg/C. By raising the operating temperature to 170/spl deg/C, a high sensitivity of /spl sim/10/sup 5/ is measured and response and recovery times drop to less than 2 min and 15 s, respectively. Selectivity of the sensing material was studied toward various concentrations of CO, CH/sub 4/, H/sub 2/, and ethanol. SEM, XRD, and TEM analyses were used to investigate surface morphology and crystallinity of SnO/sub 2/ films.     

Fabrication of resonant-tunneling diodes by Sb surfactant modified growth of Si films on CaF/sub 2//Si

Molecular beam epitaxy growth of Si thin films on CaF/sub 2//Si(111) substrates has been studied. A surfactant-modified solid-phase epitaxy method, where the room temperature Si deposition was followed by annealing under Sb flux, resulted in a continuous, smooth epitaxial crystalline Si film with a sharp (/spl radic/3/spl times//spl radic/3)R30/spl deg/ reconstruction and a surface roughness of 0.15-nm rms for a 2.8-nm Si thin film. This growth technique was used to fabricate CaF/sub 2//Si/CaF/sub 2/ double-barrier resonant tunneling diodes in SiO/sub 2/ windows patterned on Si(111) substrates. A negative differential resistance (NDR) peak was found at /spl sim/0.35 V at 77 K, and the current density at the NDR peak was estimated to be 3-4 orders of magnitude higher than in earlier reports.     

Magnetic properties, microstructures, and corrosion resistance ofhigh-saturation FeMoN and FeRhN films for recording heads

We have investigated high-saturation FeMoN and FeRhN films, deposited by radio frequency-diode reactive sputtering on alumina-TiC substrates, for inductive head applications. A minimum coercivity of ~1.2 Oe is obtained in (Fe_97.8Mo_2.2)N films at a N ₂/Ar flow ratio of ~6.2%. A minimum coercivity of ~1.6 Oe is obtained in (Fe_96.9Rh_3.1)N films at a N₂/Ar flow ratio of ~4.6%. The films mainly consist of α-Fe phase and γ'-Fe₄N phase; The magnetic properties of these films are stable under easy axis field annealing up to 350°C. Addition of Rh or Mo to FeN has resulted in a significant improvement in corrosion resistance over that of FeN. The localized corrosion resistance of FeRhN and FeMoN can be comparable to that of Permalloy. In contrast, their intrinsic corrosion resistance is inferior to that of Permalloy, but it can be adjusted and controlled by pH level     

Iridium oxide as low temperature NO/sub 2/-sensitive material for work function-based gas sensors

This paper presents the results on work function-based NO/sub 2/-sensing properties of iridium-oxide thin films at 130/spl deg/C. Films of 20-nm and 100-nm thickness were deposited on silicon substrates using dc sputtering followed by annealing in oxygen ambient. Sensitivity of these films to different concentrations of NO/sub 2/, H/sub 2/, CO, Cl/sub 2/, and NH/sub 3/ in synthetic air was measured using a Kelvin probe. It was observed that work function of 20-nm-thick iridium-oxide film changed by /spl sim/100 mV on exposure to 5-ppm NO/sub 2/ (German safety limit). Cross sensitivity to other gases (except NH/sub 3/) and interference of humidity was found to be negligibly small. The film was incorporated as a gate electrode in a hybrid suspended gate field effect transistor (HSGFET) structure to examine its suitability in FET-type sensors. The films were characterized using Rutherford backscattering spectroscopy, X-ray diffraction analysis, and scanning electron microscopy to determine their composition, phase, and surface morphology. The results suggest that iridium-oxide film is a promising material for the realization of a FET-based NO/sub 2/ sensor.     

Chemically synthesized FePt nanoparticle material for ultrahigh-density recording

We have examined the magnetic anisotropy of the "heat-treated FePt nanoparticles" annealed in a magnetic field. The magnetic easy axis of the "heat-treated FePt nanoparticles" is found to be three-dimensional (3-D) random and a partial ordering fct structure is observed before annealing in the presence of a magnetic field. The value of M/sub r//M/sub s/ obtained is 0.5. After annealing in the presence of a magnetic field, the M-H loop indicates that the easy axis is oriented preferably in the perpendicular direction than along the in-plane direction. The value of H/sub c/(//)/H/sub c/(/spl perp/) at 10 K is 0.62 (1410 Oe/2250 Oe). The value of M/sub r//M/sub s/(/spl perp/) is 0.58 at 10 K larger than the value of M/sub r//M/sub s/(//). Therefore, a weak magnetic easy axis orientation is fundamentally possible on the chemically synthesized FePt nanoparticles. We have studied the recording characteristics of a 3-D random nanoparticle medium using a GUZIK spinstand and observed the recorded patterns for the medium by imaging with a magnetic force microscopy.     

Influence of grain boundaries and voids on the saturated magnetization in Fe/sub 3/O/sub 4/ films at a low magnetic field

We report the magnetic behaviors of Fe/sub 3/O/sub 4/ thin films grown by zero field growth (ZFG) and field growth (FG) techniques during the sputtering process. In FG conditions, an in situ 300 Oe field during growth is applied to a substrate, inducing an easy axis of magnetization. Structural observations obtained by high-resolution transmission electron microscopy measurements clearly depicted a significant reduction of the grain boundaries and voids in the Fe/sub 3/O/sub 4/ films grown under FG conditions, thus explaining the saturated magnetization of the Fe/sub 3/O/sub 4/ films at about 0.01 T. This behavior was expected due to a remarkable reduction of the antiferromagnetic exchange couplings between grains for FG conditions. In addition, the zero-field-cooled magnetization of the ZFG samples showed an abrupt change at about 285 K, confirming the existence of defects or other phases in the ZFG films.     

Magnetic and structural properties of Co ion-implanted GaN

A GaN epilayer was grown on Al/sub 2/O/sub 3/ substrate by metal-organic chemical vapor deposition, and Co/sup -/ ions with a dose of 3/spl times/10/sup 16/ cm/sup -2/ were implanted into GaN at 350/spl deg/C. The implanted samples were postannealed at 700/spl deg/C-900/spl deg/C to recrystallize the samples and to remove implantation damage. We have investigated the magnetic and structural properties of Co ion-implanted GaN by using X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, and X-ray photoelectron spectroscopy (XPS). XRD results did not show any peaks associated with the second phase formation, and only the diffraction from the GaN layer and substrate structure were observed. The temperature dependence of magnetization taken in zero-field-cooling and field-cooling conditions showed the features of superparamagnetic system in films annealed at 700/spl deg/C-900/spl deg/C. The magnetization curves at 5 K for samples annealed at 700/spl deg/C-900/spl deg/C exhibits ferromagnetic hysteresis loops, and the highest residual magnetization (M/sub R/) and coercivity (H/sub c/) of M/sub R/=1.5/spl times/10/sup -4/ emu/g and H/sub c/=107 Oe were found in the 800/spl deg/C annealed sample. XPS measurement showed the metallic Co 2p core levels and the metallic valence band spectra for as-implanted and 700/spl deg/C-900/spl deg/C annealed samples. From these, it could be explained that the magnetic property of our films originated from Co and CoGa magnetic clusters.     

磁控溅射制备ITO薄膜光电性能的研究

采用直流磁控溅射方法在玻璃基底上制备了ITO薄膜.分别用分光光度计和四探针仪测试了所制备ITO薄膜在可见光区域内的透过率和电阻率,研究了溅射气压、氧氩流量比和溅射功率三个工艺参数对ITO薄膜光电性能的影响.研究结果表明,制备ITO薄膜的最佳工艺参数为:溅射气压0.6 Pa,氧氩流量比1:40,溅射功率108 W.采用此工艺参数制备的ITO薄膜在可见光区平均透过率为81.18％,薄膜电阻率为8.9197×10-3Ω·cm.     

Photoacoustic measurement of thermal properties of TiN thin films

Titanium nitride (TiN) thin films were prepared by reactive DC magnetron sputtering under different nitrogen flow rates and at constant substrate temperature as well as at constant nitrogen flow rate and at different substrate temperatures. Photoacoustic measurement of the thermal properties of the films revealed that the thermal diffusivity and thermal conductivity of the TiN thin films are significantly lower than the bulk values and that the grain size of the films has substantial influence on the thermal properties of TiN thin films. The thermal conductivity of the films decreases with increasing nitrogen flow rates and increases with increasing substrate temperature. The above opposing behaviour in the thermal properties is found to be related to the microstructure, especially, the grain size of the films.     

氮流量比对磁控溅射(CoCrFeNi)Nx高熵合金薄膜的组织和性能的影响

采用直流磁控溅射法制备(CoCrFeNi)N_x高熵薄膜,研究了氮流量比对薄膜的力学性能和电磁性能的影响。结果表明,在不同氮流量比条件下制备的(CoCrFeNi)N_x薄膜,都具有致密的组织、简单的FCC结构并呈现(200)择优取向。随着氮流量比从10%提高到30%,薄膜的硬度和弹性模量随之增大,其最大值达到14 GPa和212 GPa;电阻率基本上呈增大的趋势,最大值达到138 μΩ?cm;饱和磁化强度和磁导率随之减小,薄膜饱和磁化强度最高为427.43 emu/cm³。薄膜的矫顽力约为0。