Optimization of N2/Ar gas flow ratio for the realization of nitrogen-doped p-type ZnCdO thin films synthesized by RF magnetron sputtering

Nitrogen doped ZnCdO films [ZCO:N] have been grown on quartz substrates by radio frequency (RF) reactive magnetron sputtering technique, and the effect of the ratio of nitrogen to argon gas flow [N₂:Ar] on their electrical, microstructure and optical properties were investigated by Hall effect, energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscope (TEM), optical absorbance and photoluminescence (PL) measurements. The results indicate that all the ZCO:N films are of hexagonal wurtzite structure with highly (002) preferential orientation. As the N₂:Ar increases from 0:1 to 4:1, the absorption edge for the samples exhibits blue shift. Hall effect measurement results indicate that the N₂:Ar exerts an immense influence on the p-type conduction conversion for ZCO:N film. It is found that ZCO:N film deposited at the N₂:Ar of 1:2 shows the optimal p-type behavior, which has a carrier concentration of 1.10×10¹⁷ cm⁻³, a mobility of 3.28 cm²V⁻¹s⁻¹ and a resistivity of 17.3 Ω cm. Compared with the other samples, ZCO:N film fabricated at the relatively lower N₂:Ar possesses the superior crystal quality, luminescent and electrical properties. Additionally, a possible mechanism of p-type conduction for ZCO:N film was discussed in this work.     

Effect of substrate biasing and temperature on AlN thin film deposited by cathodic arc ion

Aluminum nitride (AlN) films have been grown in pure N₂ plasma using cathodic arc ion deposition process. The films were prepared at different substrate bias voltages and temperatures. The aim was to investigate their influence on the Al macro-particles, structural and optical properties of deposited films. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Scanning electron microscope (SEM) and Rutherford backscattering spectrometry (RBS) were employed to characterize AlN thin films. XRD patterns indicated the formation of polycrystalline (hexagonal) films with preferential orientation of (002), which is suppressed at higher substrate bias voltage. FTIR and Raman spectroscopic analysis were used to assess the nature of chemical bonding and vibrational phonon modes of AlN thin films respectively. FTIR spectra depicted a dominant peak around 850 cm^?1 corresponding to the longitudinal optical (LO) mode of vibration. A shift in this LO mode peak towards higher wavenumbers was observed with the increase of substrate bias voltage and temperature, showing the upsurge of nitrogen concentration in the deposited film. Raman spectra illustrated a peak at 650 cm^?1 corresponding to E₂ (high) phonon mode depicting the c-axis oriented (perpendicular to substrate) AlN film. SEM analysis showed the AlN film deposited at higher substrate bias voltage contains fewer amounts of Al macro-particles.     

Composition,structure and electrical properties of DC reactive magnetron sputtered Al2O3 thin films

Thin films of alumina (Al₂O₃) were deposited over Si 〈1 0 0〉 substrates at room temperature at an oxygen gas pressure of 0.03 Pa and sputtering power of 60 W using DC reactive magnetron sputtering. The composition of the as-deposited film was analyzed by X-ray photoelectron spectroscopy and the O/Al atomic ratio was found to be 1.72. The films were then annealed in vacuum to 350, 550 and 750 °C and X-ray diffraction results revealed that both as-deposited and post deposition annealed films were amorphous. The surface morphology and topography of the films was studied using scanning electron microscopy and atomic force microscopy, respectively. A progressive decrease in the root mean square (RMS) roughness of the films from 1.53 nm to 0.7 nm was observed with increase in the annealing temperature. Al–Al₂O₃–Al thin film capacitors were then fabricated on p-type Si 〈1 0 0〉 substrate to study the effect of temperature and frequency on the dielectric property of the films and the results are discussed.     

Investigation on Na-N dual acceptors doped p-type ZnCdO thin films synthesized by RF magnetron sputtering

Sodium and nitrogen dual acceptors doped ZnCdO [ZCO:(Na, N)] have been prepared by radio frequency (RF) reactive magnetron sputtering followed by rapid annealing treatment, and the influence of the ratio of argon to nitrogen gas flow (Ar:N₂) on the electrical, structure and optical properties of ZCO:(Na, N) films were investigated in detail. Hall-effect measurement results reveal that Na–N dual acceptors doping method is an effective path to realize the p-type conversion of ZnCdO (ZCO). When the Ar:N₂ was set to 1:2 (S3), ZCO:(Na, N) film possesses the optimal p-type conduction properties with carrier concentration of 7.84 × 10¹⁸ cm⁻³ and the resistivity of 30.9 Ω cm. It is demonstrated that the presence of Na_Zn and N_o acceptors are answerable for the p-type behavior in ZCO:(Na, N) film by the analysis of X-ray photoelectron spectroscopy (XPS) results. All the ZCO:(Na, N) films are of hexagonal wurtzite crystal structure with highly (002) preferential orientation. As Ar:N₂ increases from 1:4 (S1) to 2:1 (S5), the absorption edge gradually shifted to longer wavelength side. The observed p-type ZCO:(Na, N) films will open the door for practical applications in various optoelectronic devices.     

Effects of oxygen concentration on the properties of Al-doped ZnO transparent conductive films deposited by pulsed DC magnetron sputtering

The effect of oxygen concentration on the properties of Al-doped ZnO (AZO) transparent conductive films has been investigated on the films deposited by pulsed DC magnetron sputtering using a cylindrical ZnO target containing 2 wt% Al. AZO films were deposited at 230 °C to the thickness of about 1000 nm and the oxygen concentration was controlled by varying the O₂/Ar supply ratio from 0 to 0.167. With the increasing O₂/Ar ratio, crystallinity of the AZO films deteriorated while the film surface became smooth. Accompanying this, electrical properties also deteriorated significantly. When the O₂/Ar ratios were 0 and 0.033, the AZO films showed metallic conduction behavior with the electrical resistivity in the mid 10^?4 Ω cm range. However, when the ratios were 0.100 and 0.167, the films showed poor electrical conduction behavior similar to semiconductors as deduced from the transmittance behavior. Spectroscopic analysis showed that such deteriorating properties are due to the formation of condensed oxide group through the reaction between excess oxygen and dopant aluminum.     

Effect of processing parameter on structural,optical and electrical properties of photovoltaic chalcogenide nanostructured RF magnetron sputtered thin absorbing films

The aim of this work was to develop high quality of CuIn_1−xGa_xSe₂ thin absorbing films with x (Ga/In+Ga)<0.3 by sputtering without selenization process. CuIn_0.8Ga_0.2Se₂ (CIGS) thin absorbing films were deposited on soda lime glass substrate by RF magnetron sputtering using single quaternary chalcogenide (CIGS) target. The effect of substrate temperature, sputtering power & working pressure on structural, morphological, optical and electrical properties of deposited films were studied. CIGS thin films were characterised by X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), Energy dispersive X-ray spectroscopy (EDAX), Atomic force microscopy (AFM), UV–vis–NIR spectroscopy and four probe methods. It was observed that microstructure, surface morphology, elemental composition, transmittance as well as conductivity of thin films were strongly dependent on deposition parameters. The optimum parameters for CIGS thin films were obtained at a power 100 W, pressure 5 mT and substrate temperature 500 °C. XRD revealed that thin film deposited at above said parameters was polycrystalline in nature with larger crystallite size (32 nm) and low dislocation density (0.97×10¹⁵ lines m⁻²). The deposited film also showed preferred orientation along (112) plane. The morphology of the film depicted by FE-SEM was compact and uniform without any micro cracks and pits. The deposited film exhibited good stoichiometry (Ga/In+Ga=0.19 and In/In+Ga=0.8) with desired Cu/In+Ga ratio (0.92), which is essential for high efficiency solar cells. Transmittance of deposited film was found to be very low (1.09%). The absorption coefficient of film was ~10⁵ cm⁻¹ for high energy photon. The band gap of CIGS thin film evaluated from transmission data was found to be 1.13 eV which is optimum for solar cell application. The electrical conductivity (7.87 Ω⁻¹ cm⁻¹) of deposited CIGS thin film at optimum parameters was also high enough for practical purpose.     

Influence of processing and annealing steps on electrical properties of InAlN/GaN high electron mobility transistor with Al2O3 gate insulation and passivation

We report on preparation and electrical characterization of InAlN/AlN/GaN metal–oxide–semiconductor high electron mobility transistors (MOS HEMTs) with Al₂O₃ gate insulation and surface passivation. About 12 nm thin high-κ dielectric film was deposited by MOCVD. Before and after the dielectric deposition, the samples were treated by different processing steps. We monitored and analyzed the steps by sequential device testing. It was found that both intentional (ex situ) and unintentional (in situ before Al₂O₃ growth) InAlN surface oxidation increases the channel sheet resistance and causes a current collapse. Post deposition annealing decreases the sheet resistance of the MOS HEMT devices and effectively suppresses the current collapse. Transistors dimensions were source-to-drain distance 8 μm and gate width 2 μm. A maximum transconductance of 110 mS/mm, a drain current of ～0.6 A/mm (V_GS = 1 V) and a gate leakage current reduction from 4 to 6 orders of magnitude compared to Schottky barrier (SB) HEMTs was achieved for MOS HEMT with 1 h annealing at 700 °C in forming gas ambient. Moreover, InAlN/GaN MOS HEMTs with deposited Al₂O₃ dielectric film were found highly thermally stable by resisting 5 h 700 °C annealing.     

Characterization of TiAl alloy films for potential application in MEMS bimorph actuators

In this letter, we demonstrate the feasibility of applying TiAl alloy film for the fabrication of bimorph actuators. The TiAl alloy films were prepared by thermal annealing at 400°C of Ti/Al multilayers, which were deposited by DC magnetron sputtering from Ti and Al targets. The microstructure and surface morphology of TiAl alloy films were analyzed by X-ray diffraction and scanning electron microscopy, which showed that TiAl alloy film is formed in the mixed phases of TiAl₃ and Ti₃₆Al₆₄, depending on the deposition conditions. The resistivity of TiAl film is about 9 μΩ cm, and the stress is about 200 MPa. Our nano-indentation measurements showed that the Young's modulus and hardness of TiAl alloy films are 175 and 6.5 GPa, respectively, which are larger than that of Al and comparable to Si. We have successfully fabricated the bimorph actuators based on the TiAl alloy films and our test cantilevers up to 500 μm long showed very straight with tip bending as small as ±5 μm, indicating negligible stress gradient in TiAl film. Our preliminary testing results indicated that TiAl alloy film has potential application for bimorph actuators.     

Effect of different sputtering gas mixtures on the structural,electrical, and optical properties of p-type NiO thin films

We investigated how mixtures of Ar and O₂ or N₂ gases affect the structural, electrical and optical properties of RF-magnetron-sputtered NiO films. It is shown that the addition of O₂ gas to Ar ambient (namely, Ar:O₂=2:1 to 1:2) slightly reduces the (2 0 0) texturing of the NiO films. The introduction of N₂ gas (from 0 to 2 sccm) to Ar:O₂ (2:1) mixture enhances the (2 0 0) texturing, while the addition of N₂ gas (from 0 to 2 sccm) to Ar ambient slightly weakens the (1 1 1) texturing. The deposition rate is reduced from 6.1 to 1.5 nm/min when O₂ gas is added to Ar ambient. The addition of N₂ gas to the Ar:O₂ (2:1) mixture slightly increases the deposition rate from 1.8 to 2.6 nm/min, whereas adding N₂ gas to Ar only ambient somewhat reduces the rate from 6.1 to 4.4 nm/min. The carrier concentration of the films is increased and the mobility is decreased as the O₂ flow rate in the Ar:O₂ mixture is increased. The addition of N₂ gas to the Ar:O₂ (2:1) mixture increases the resistivity of the films, while adding N₂ gas to Ar ambient decreases the resistivity. The transmittance and optical bandgap of the films are reduced (from 58.4 to 45.5% at 550 nm and from 3.5 to 3.3 eV, respectively) with increasing O₂ flow to Ar ambient. When N₂ gas is added to the Ar:O₂ (2:1) mixture, the transmittance in the visible wavelength range increases from 58.4 to 71.3% and the optical bandgap increases from 3.5 to 3.6 eV. However, adding N₂ gas to the Ar only ambient results in decrease in the transmittance in the visible wavelength region (from 69.3 to 56%) and the optical bandgap (from 3.7 to 3.5 eV).     

Structural,surface morphology and optical properties of sputter-coated CaCu3Ti4O12 thin film: Influence of RF magnetron sputtering power

This study focusses on the investigation of RF power variations (100–300 W) effects on structural, morphological and optical properties of CaCu₃Ti₄O₁₂ thin film deposited on ITO/glass substrate in a non-reactive atmosphere (Ar). The increase of RF power from 100 W to 300 W led to evolution of (112), (022), (033), and (224) of CCTO XRD peaks. The results indicated that all the films were polycrystalline nature with cubic structure. The crystallite size increased from 20 nm to 25 nm with increasing RF power. FESEM revealed that the films deposited were uniform, porous with granular form, while the grain size increased from 30 to 50 nm. AFM analysis confirmed the increment in surface roughness from 1.6 to 2.3 nm with increasing film grain size. Besides, optical transmittance values decreased to minimum 70% with increasing RF power while optical energy bandgap increased from 3.20 eV to 3.44 eV. Therefore, favorable CCTO thin film properties can be possibly obtained for certain application by controlling RF magnetron sputtering power.     

The influence of nitrogen and fluorine on the dielectric constant of hydrogenated amorphous carbon (a-C:H) films

The possibility to use diamond-like carbon (DLC) film as dielectric in CIs has been motivating the study of this material. In this work, an analysis focused on the influence of the nitrogen and fluorine on the dielectric constant of the a-C:H films deposited by a reactive RF magnetron sputtering with a graphite target is reported. Different mixtures (CH₄/N₂ and CH₄/CF₄) were used in the depositions. The working pressure process was 5 mTorr and the RF power was 150 W. RBS and FTIR spectra were used to investigate the chemical composition and chemical bonding structure of the films, respectively. As verified in this study, the effect caused by nitrogen and fluorine on the chemical bonding structure of the a-C:H film have a fundamental role on the dielectric constant of this material.     

Effect of AlN buffer layer thickness on the properties of GaN films grown by pulsed laser deposition

The GaN films are grown by pulsed laser deposition (PLD) on sapphire, AlN(30 nm)/Al₂O₃ and AlN(150 nm)/Al₂O₃, respectively. The effect of AlN buffer layer thickness on the properties of GaN films grown by PLD is investigated systematically. The characterizations reveal that as AlN buffer layer thickness increases, the surface root-mean-square (RMS) roughness of GaN film decreases from 11.5 nm to 2.3 nm, while the FWHM value of GaN film rises up from 20.28 arcmin to 84.6 arcmin and then drops to 31.8 arcmin. These results are different from the GaN films deposited by metal organic chemical vapor deposition (MOCVD) with AlN buffer layers, which shows the improvement of crystalline qualities and surface morphologies with the thickening of AlN buffer layer. The mechanism of the effect of AlN buffer layer on the growth of GaN films by PLD is hence proposed.     

The effects of carrier gas and substrate temperature on ZnO films prepared by ultrasonic spray pyrolysis

ZnO films were deposited on glass substrates in the temperature range of 350–470 °C under an atmosphere of compressed air or nitrogen (N₂) by using ultrasonic spray pyrolysis technique. Structural, electrical and optical properties of the ZnO films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical two-probe and optical transmittance measurements. The ZnO films deposited in the range of 350–430 °C were polycrystalline with the wurtzite hexagonal structure having preferred orientation depending on the substrate temperature. The ZnO films deposited below 400 °C had a preferred (100) orientation while those deposited above 400 °C mostly had a preferred (002) orientation. The resistivity values of ZnO films depended on the types of carrier gas. The ZnO thin films deposited under N₂ atmosphere in the range of 370–410 °C showed dense surface morphologies and resistivity values of 0.6–1.1 Ω-cm, a few orders of magnitude lower than those deposited under compressed air. Hydrogen substition in ZnO possibly contributed to decreasing resistivity in ZnO thin films deposited under N₂ gas. The Hall measurements showed that the behavior of ZnO films deposited at 410 °C under the N₂ atmosphere was n-type with a carrier density of 8.9–9.2×10¹⁶ cm^-3 and mobility of ～70 cm²/Vs. ZnO thin films showed transmission values at 550 nm wavelength in a range of 70–80%. The values of band gaps extrapolated from the transmission results showed bandgap shrinkage in an order of milli electron volts in ZnO films deposited under N₂ compared to those deposited under compressed air. The calculation showed that the bandgap reduction was possibly a result of carrier–carrier interactions.     

Sol–gel synthesized Titania nanoparticles deposited on porous polycrystalline silicon: Improved carbon dioxide sensor properties

Titania nanoparticles (TNPs) were synthesized by a sol–gel method in our laboratory using titanium tetrachloride as the precursor and isopropanol as the solvent. The particles׳ size distribution histogram was determined using ImageJ software and the size of TNPs was obtained in the range of 7.5–10.5 nm. The nanoparticle with the average size of 8.5 nm was calculated using Scherrer׳s formula. Homogeneous and spherical nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy (UV–vis). The X-ray powder diffraction analysis showed that the prepared sample (TNPs) has pure anatase phase. TNPs were deposited on porous polycrystalline silicon (PPS) substrate by electron beam evaporation. The TNPs thickness was 23±2 nm at 10⁻⁵ mbar pressure at room temperature. Porosity was performed by an anodization method. Since polycrystalline silicon wafers consist of different grains with different orientations, the pore size distribution in porous layer is non-uniform [1]. Therefore, the average diameter of pores can be reported in PPS layer analysis. Average diameter of pores was estimated in the range of 5 μm which was characterized by FESEM. The nanostructured thin films devices (Al/Si/PPS/TNPs/Al and Al/Si/PPS/Al) were fabricated in the sandwich form by aluminum (Al) electrodes which were also deposited by electron beam evaporation. Electrical measurements (I–V curves) demonstrated the semiconducting behavior of thin film devices. The gas sensitivity was studied on exposure to 10% CO₂ gas. As a result, conductivity of devices increased on exposure to CO₂ gas. The device with TNPs thin film (Al/Si/PPS/TNPs/Al) was more sensitive and, had better response and reversibility in comparison with the device without TNPs thin film (Al/Si/PPS/Al).     

Effect of Al dopant concentration on structural,optical and photoconducting properties in nanostructured zinc oxide thin films

Thin films of undoped and doped ZnO, with different Al concentrations (1–5 wt%) were deposited onto glass substrates, by the sol–gel spin coating method. Grazing incidence X-ray diffraction (GIXRD) studies confirmed the nature of films as poly-crystalline, with typical hexagonal wurtzite structure. The films showed variation in crystallite size and change in relative intensities, upon different Al doping concentrations. The surface morphology of the films examined using FE-SEM, showed the grain size becoming smaller upon Al doping. The influence of Al with different concentrations, onto ZnO on the optical absorption and transmittance was studied using UV–Vis–NIR spectrophotometer in the wavelength range 300–2500 nm. The UV absorption shifted towards shorter wavelength upon Al doping. The average transmittance in the visible region increased for Al doped films up to 1–2 wt% and decreased for other concentration. The dark and photo conductivity measurements of the films indicated increase in the current values upon doping up to 1–2 wt% of Al and decreased for further concentrations. The rise and decay time measured from the photoresponse study, indicate larger values of rise time for the doped films compared to undoped ZnO. However, the film with 1–2 wt% doping of Al showed better response within the doping concentration. The thermal activation energy obtained from temperature-dependant conductivity showed decrease in the value upon Al doping up to 2 wt% and increased beyond this concentration in the temperature range 300–400 K.     

Effects of thermal annealing on the morphology of the AlxGa(1−x)N films

Effects of thermal annealing on the morphology of the Al_xGa_(1−x)N films with two different high Al-contents (x=0.43 and 0.52) have been investigated by atomic force microscopy (AFM). The annealing treatments were performed in a nitrogen (N₂) gas ambient as short-time (4 min) and long-time (30 min). Firstly, the films were annealed as short-time in the range of 800–950 °C in steps of 50–100 °C. The surface root-mean-square (rms) roughness of the films reduced with increasing temperature at short-time annealing (up to 900 °C), while their surface morphologies were not changed. At the same time, the degradation appeared on the surface of the film with lower Al-content after 950 °C. Secondly, the Al_0.43Ga_0.57N film was annealed as long-time in the range of 1000–1200 °C in steps of 50 °C. The surface morphology and rms roughness of the film with increasing temperature up to 1150 °C did not significantly change. Above those temperatures, the surface morphology changed from step-flow to grain-like and the rms roughness significantly increased.     

Enhancement in electrical performance of indium gallium zinc oxide-based thin film transistors by low temperature thermal annealing

We have studied the characteristics of transparent bottom-gate thin film transistors (TFTs) using In–Ga–Zn–O (IGZO) as an active channel material. IGZO films were deposited on SiO₂/Si substrates by DC sputtering techniques. Thereafter, the bottom-gate TFT devices were fabricated by depositing Ti/Au metal pads on IGZO films, where the channel length and width were defined to be 200 and 1000 μm, respectively. Post-metallization thermal annealing of the devices was carried out at 260, 280 and 300 °C in nitrogen ambient for 1 h. The devices annealed at 280 °C have shown better characteristics with enhanced field-effect mobility and high on–off current ratio. The compositional variation of IGZO films was also observed with different annealing temperatures.     

Investigations on phosphorus doped amorphous/nanocrystalline silicon films deposited by a filtered cathodic vacuum arc technique in the presence of hydrogen gas

Phosphorus doped amorphous/nanocrystalline silicon (a-Si:H/nc-Si:H) thin films have been deposited by a filtered cathodic vacuum arc (FCVA) technique in the presence of hydrogen gas at different substrate temperatures (T_s) ranging from room temperature (RT) to 350 °C. The films have been characterized by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dark conductivity (σ_D), activation energy (ΔE), optical band gap (E_g) and secondary ion mass spectroscopy. The XRD patterns show that RT grown film is amorphous in nature but high temperature (225 and 350 °C) deposited films exhibit nanocrystalline structure with (111) and (220) crystal orientations. The crystallite size of higher temperature grown silicon film evaluated was between 13 and 25 nm. Raman spectra reveal the amorphous nature of the film deposited at RT, whereas higher temperature deposited films show crystalline nature. The crystalline volume fraction of the silicon film deposited at higher temperatures (225 and 350 °C) was estimated to be 58 and 72%. With the increase of T_s, the bonding configuration changes from mono-hydride to di-hydride as revealed by the FTIR spectra. The values of σ_D, ΔE and E_g of silicon films deposited at different T_s were found to be in the range of 5.37×10⁻⁴–1.04 Ω⁻¹ cm⁻¹, 0.05–0.45 eV and 1.42–1.83 eV, respectively. Photoconduction of 3.5% has also been observed in n-type nc-Si:H films with the response and recovery times of 9 and 12 s, respectively. A n-type nc-Si:H/p-type c-Si heterojunction diode was fabricated which showed the diode quality factor between 1.6 and 1.8.     

Residual strain and electrical resistivity dependence of molybdenum films on DC plasma magnetron sputtering conditions

Sputter deposited molybdenum (Mo) thin films are used as back contact layer for Cu(In_1−xGa_x)(Se_1−yS_y)₂ based thin film solar cells. Desirable properties of Mo films include chemical and mechanical inertness during the deposition process, high conductivity, appropriate thermal expansion coefficient with contact layers and a low contact resistance with the absorber layer. Mo films were deposited over soda-lime glass substrates using DC-plasma magnetron sputtering technique. A 2³ full factorial design was made to investigate the effect of applied power, chamber pressure, and substrate temperature on structural, morphological, and electrical properties of the films. All the films were of submicron thickness with growth rates in the range of 34–82 nm/min and either voided columnar or dense growth morphology. Atomic force microscope studies revealed very smooth surface topography with average surface roughness values of upto 17 nm. X-ray diffraction studies indicated, all the films to be monocrystalline with (001) orientation and crystallite size in the range of 4.6–21 nm. The films exhibited varying degrees of compressive or tensile residual stresses when produced at low or high chamber pressure. Low pressure synthesis resulted in film buckling and cracking due to poor interfacial strength as characterized by failure during the tape test. Measurement of electrical resistivity for all the films yielded a minimum _value of 42 μΩ cm for Mo films deposited at 200 W DC power.     

Fabrication of NbN/AlN/NbN junctions with Al embedding circuits on Si membrane for 1.5 THz SIS mixers

A process has been developed to fabricate NbN tunnel junctions and 1.5 THz SIS mixers with Al electrodes and Al/SiO₂/Al microstrip tuning circuits on thin Si membranes patterned on silicon on insulator wafers (SIMOX). High Josephson current density (J_c up to 2×10⁴ A/cm²) NbN/AlN/NbN and NbN/MgO/NbN SIS junctions have been fabricated with a reasonably good V_m quality factor and energy gap values close to 5 meV at 4.2 K on (100) oriented 3 inches SIMOX wafers covered by a thin (∼8 nm) MgO buffer layer. The sputtering conditions critically influence the dielectric quality of both AlN and MgO tunnel barriers as well as the surface losses of NbN electrodes. 0.6-μm Si/SiO₂ membranes are obtained after processing of a whole wafer and etching the individual chips in EDP. Such a technology is applied to the development of a waveguide/membrane SIS mixer for use around 1.5 THz.