Electrical Sheet Resistance Research Articles

High figure-of-merit ultrathin metal transparent electrodes incorporating a conductive grid

It is known that ultrathin (<10 nm) metal films (UTMFs) can achieve high level of optical transparency at the expense of the electrical sheet resistance. In this letter, we propose a design, the incorporation of an ad hoc conductive grid, which can significantly reduce the sheet resistance of UTMF based transparent electrodes, leaving practically unchanged their transparency. The calculated highest figure-of-merit corresponds to a filling factor and a grid spacing-to-linewidth ratio of 0.025 and 39, respectively. To demonstrate the capability of the proposed method the sheet resistance of a continuous 2 nm Ni film (>950 Ω/◻) is reduced to ∼6.5 Ω/◻ when a 100 nm thick Cu grid is deposited on it. The transparency is instead maintained at values exceeding 75%. These results, which can be further improved by making thicker grids, already demonstrate the potential in applications, such as photovoltaic cells, optical detectors and displays.

Optoelectronic properties of graphene thin films prepared by thermal reduction of graphene oxide

Graphene thin films have been prepared by thermal reduction of graphene oxide. Raising the reduction temperature results in a red-shift of the G peak in Raman spectra. The reduction temperature turns out to strongly affect the morphology of the prepared graphene film. Photoluminescence (PL) results show that the band gap of graphene can be tuned by varying the reduction temperature. The thermal reduction process has been optimized in an effort to minimize the formation of wrinkles/folds on the graphene surface leading to enhanced PL and Raman peak intensities and reduced electrical sheet resistance.

Patterning of nanoparticulate transparent conductive ITO films using UV light irradiation and UV laser beam writing

Indium tin oxide (ITO) thin film is one of the most widely used as transparent conductive electrodes in all forms of flat panel display (FPD) and microelectronic devices. Suspension of already crystalline conductive ITO nanoparticles fully dispersed in alcohol was spun, after modifying with coupling agent, on glass substrates. The low cost, simple and versatile traditional photolithography process without complication of the photoresist layer was used for patterning ITO films. Using of UV light irradiation through mask and direct UV laser beam writing resulted in an accurate linear, sharp edge and very smooth patterns. Irradiated ITO film showed a high transparency (∼85%) in the visible region. The electrical sheet resistance decrease with increasing time of exposure to UV light and UV laser. Only 5 min UV light irradiation is enough to decrease the electrical sheet resistance down to 5 kΩ□.

Aggregation in thin-film silver: Induced by chlorine and inhibited by alloying with two dopants

The Ag aggregation mechanism triggered by chlorine (Cl) is discussed. The frontier orbital theory by K. Fukui is applied in order to determine the growing point in the silver (Ag) cluster. Ag in the thin-film silver would grow to Ag n Cl and stack, triggered by Cl from the outside according to the mechanism described. This would lead to an aggregate with a high Ag density. It is suggested that this would be the generating mechanism of the silver-gray aggregate consisting mostly of Ag, which is generated by exposing it to Cl. Two tactics in order to prevent restrain aggregation induced by Cl according to the mechanism are proposed. Tactic 1 is a restraining of structure change to a plane in the process of Ag 6Cl + Ag → Ag 7Cl. Tactic 2 is the trapping of Cl before it generates a bond to Ag. The ability of the two combined dopants with the abilities of tactics 1 and 2, such as in an Ag alloy including palladium and copper (APC), and including neodymium and gold (ANA) is expected to be very high. The aggregation resistance of an Ag alloy including two dopants is evaluated by a salt water immersion test. The APC and ANA demonstrated a very high resistance to Cl, because of the combination of the dopants working with tactic 1 (Pd, Au) and tactic 2 (Cu, Nd). The multilayer sputter coating with an ANA layer demonstrated a very interesting profile where the light transmittance and the electrical sheet resistance are almost the same as the multilayer sputter coating with a pure Ag. The multilayer sputter coating with AIS also demonstrates a very interesting profile, where the light transmittance is higher than the multilayer sputter coating with a pure Ag.

High-rate, room temperature plasma-enhanced deposition of aluminum-doped zinc oxide nanofilms for solar cell applications

A custom-designed inductively coupled plasma (ICP)-assisted radio-frequency magnetron sputtering deposition system has been employed to synthesize aluminium-doped zinc oxide (ZnO:Al) nanofilms on glass substrates at room temperature. The effects of film thickness and ZnO target (partially covered by Al chips) power on the structural, electrical and optical properties of the ZnO:Al nanofilms are studied. A high growth rate (∼41 nm/min), low electrical sheet resistance (as low as 30 Ω/□) and high optical transparency (>80%) over the visible spectrum has been achieved at a film thickness of ∼615 nm and ZnO target power of 150 W. The synthesis of ZnO:Al nanofilms at room temperature and with high growth rates is attributed to the unique features of the ICP-assisted radio-frequency magnetron sputtering deposition approach. The results are relevant to the development of photovoltaic thin-film solar cells and flat panel displays.

Optical properties of SnO2:F films deposited by atmospheric pressure CVD

Atmospheric pressure chemical vapor deposition (APCVD) system, designed for the deposition of F-doped SnO 2 thin films, is compatible with industrial requirements such as high process speed, scaling to wide substrate widths and low costs. Precise method for measuring the optical absorptance in the spectral range 300–1700 nm combines transmittance, reflectance and photothermal deflection (PDS) spectra measured on the same spot of the sample immersed in the transparent liquid with a relatively high index of refraction. The effects of the film thickness, doping gas addition and the susceptor temperature on the optical absorptance and electrical resistivity of the TCO films are assessed. We show that the doping gas concentration and the susceptor temperature influence both the incorporation ratio of dopants into SnO 2 film as well as the defect concentration. The SnO 2 films growth at optimum APCVD conditions have thickness 0.7 µm, average surface roughness about 40 nm, sheet electrical resistance 10 Ω/sq and the optical absorption 1% at 500 nm and about 5% at 1000 nm.

Structural Stability and Phase-Change Characteristics of Ge[sub 2]Sb[sub 2]Te[sub 5]∕SiO[sub 2] Nano-Multilayered Films

The phase-change characteristics of Ge 2 Sb 2 Te 5 /SiO 2 multilayered films with various bilayer thicknesses were investigated using high-resolution transmission electron microscopy. The change in the electrical sheet resistance of the films shows that the metastable face-centered cubic (fcc) structure formation was significantly affected by the bilayer thickness of the multilayer film. That is, compared with the single-layered Ge 2 Sb 2 Te 5 film, the multilayered films transformed to hexagonal at lower temperatures. In particular, the transition temperature region of the fcc structure with semiconductor properties was significantly reduced. We observed that as the bilayer thickness decreased and annealing temperature increased, the structure of the multilayer film was transformed into Ge-deficient and hexagonal phases such as GeSb 2 Te 4 and Sb 2 Te 3 . This behavior was induced by the out-diffusion of Ge atoms from the outer surface layer, which can be caused by a difference in thermal strain at the interface between the Ge 2 Sb 2 Te 5 and SiO 2 films.

Effect of Heating Rate on the Activation Energy for Crystallization of Amorphous Ge[sub 2]Sb[sub 2]Te[sub 5] Thin Film

The crystallization of the amorphous Ge 2 Sb 2 Te 5 film was investigated by in situ electrical sheet resistance measurement. The crystallization start temperature increases logarithmically with heating rate and is equated. The effective activation energy E A of the crystallization is 2.34 eV at slow heating rates below 40°C/min and decreases to 0.49 eV at higher heating rates because of the reduced activation energies for both nucleation and growth of the crystalline face-centered cubic phase by overheating at high heating rates.

Indium tin oxide films deposited on polyethylene naphthalate substrates by radio frequency magnetron sputtering

Indium tin oxide (ITO) thin films were deposited on unheated polyethylene naphthalate substrates by radio-frequency (rf) magnetron sputtering from an In 2O 3 (90 wt.%) containing SnO 2 (10 wt.%) target. We report the structural, electrical and optical properties of the ITO films as a function of rf power and deposition time. Low rf power values, in the range of 100–130 W, were employed in the deposition process to avoid damage to the plastic substrates by heating caused by the plasma. The films were analyzed by X-ray diffraction and optical transmission measurements. A Hall measurement system was used to measure the carrier concentration and electrical resistivity of the films by the Van der Pauw method. The X-ray diffraction measurements analysis showed that the ITO films are polycrystalline with the bixbite cubic crystalline phase. It is observed a change in the preferential crystalline orientation of the films from the (222) to the (400) crystalline orientation with increasing rf power or deposition time in the sputtering process. The optical transmission of the films was around 80% with electrical resistivity and sheet resistance down to 4.9 × 10 - 4 Ωcm and 14 Ω/sq, respectively.

Activation level in boron-doped thin germanium-on-insulator (GeOI): Extraction method and impact of mobility

We hereby present a non-destructive method for extracting the activation level on boron-doped germanium-on-insulator (GeOI) wafers, with a discussion on the impact of the hole mobility model. This method combines Monte Carlo boron profile simulations with optical Ge layer thickness T Ge and electrical sheet resistance R sh measurements. As B atoms are known not to diffuse in Ge for the usual activation temperatures (<800 °C), we can assume that the as-implanted dopant profile remains unchanged after annealing (no modelling of boron diffusion required). We highlight that the knowledge of the hole mobility dependence on activated impurities concentration in Ge is of paramount importance. Several experimental and theoretical models are available in the literature. After relative validity assessments, all of them have been implemented for extraction and unfortunately yield different values scattered over nearly one decade. Still, the lower-bound concentration 2.7×10 19 cm −3 is in the range of the state-of-the-art values for B-implanted crystalline Ge and has proven suitable for functional GeOI pMOSFET demonstration.

Growth study of Ge xSb yTe z deposited by MOCVD under nitrogen for non-volatile memory applications

We report on the bubbler-type MOCVD growth of Ge x Sb y Te z (GST) on SiO 2/Si substrates, potentially transferable to phase change memory (PCM) devices. Pure nitrogen was used as the process gas in order to reduce toxicity whilst increasing the simplicity of the process. This systematic study allowed the modification of the growth parameters on SiO 2 to move through initial sub-micrometric crystalline grain deposition on to lateral island growth. Temperature was observed to play a critical role in film quality with strong morphology and island shape/size changes for small thermal variations. Eventually, continuous layers of GST in the hcp phase and composition close to the 2:2:5 were studied. The deposition on different substrates was also investigated. Although crystal nucleation is still far from achieving the target step coverage required for uniform coating of patterned substrates, the electrical sheet resistance of GST films exhibited values corresponding to those expected for chalcogenide materials suitable to be integrated into PCM devices.

Optical and electrical properties of ZnO thin film containing nano-sized Ag particles

Low-temperature crystallized ZnO thin film was achieved by sol–gel process using zinc acetate dihydrate and 2-methoxyethanol as starting precursor and solvent, respectively. Ag nanoparticles were prepared with uniform size at 4.4 nm by spontaneous reduction method of Ag 2-ethylhexanoate in dimethyl sulfoxide (DMSO). The optical and electrical properties of ZnO thin films containing various contents of Ag-nanoparticles were monitored. Light scattering and charge emission and scattering behaviors of Ag nanoparticles in ZnO film were found. The incorporation of Ag nanoparticles into Al-doped ZnO film was also investigated. The optical transmittance was not degraded but the increase of electrical sheet resistance was found. The effect of Al-dopant on the transmittance and electrical sheet resistance of ZnO film was found too great to distinguish the positive effect of the incorporation of Ag nanoparticles into Al-doped ZnO thin films.

Fabrication of CNTs/Cu composite thin films for interconnects application

Carbon nanotubes/copper (CNTs/Cu) composite thin films were fabricated by combined electrophoresis and electroplating techniques. Electrical properties and structure of both CNTs/Cu thin films and the reference pure Cu thin films were investigated after annealing at different temperatures. The sheet electrical resistance of CNTs/Cu films decreases faster than that of pure Cu films with increase of annealing temperature. The grain size of CNTs/Cu film becomes much larger than that of pure Cu film at the same annealing temperature. The peak relative intensity of Cu (1 1 1) plane in CNTs/Cu film was stronger than that of pure Cu film. CNTs/Cu composite thin films, with better electrical properties than that of conventional pure Cu thin films, have been fabricated by electrophoresis and electroplating deposition techniques.

SnO 2/ZnO double-layer thin films: A novel economical preparation and investigation of sensitivity and stability of double-layer gas sensors

A double-layer SnO 2/ZnO gas sensor was produced by utilization of SnO 2 and ZnO thin films. Top layer consisted of SnO 2 produced by a sol–gel controlled-annealing technique. Bottom coating consisted of ZnO thin film precipitated by two-stage chemical deposition (TSCD) from an aqueous zinc containing solution. Both top and bottom coatings were analyzed by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and electron dispersive elemental analysis (EDAX). Auger electron spectroscopy (AES) was also used to investigate the growth of tin oxide films on zinc oxide films and their interface. Gas sensitivity of the SnO 2/ZnO double layer was determined by electrical sheet resistance measurements. Although sensitivity was slightly reduced by double-layer formation, selectivity and stability were considerably improved by combination of the two thin layers. The existence of an interfacial transition layer between SnO 2 and ZnO and stabilization mechanism of the SnO 2/ZnO double layer were rigorously investigated in this research.

Morphology evolution in TiN/Al–0.5Cu/Ti interconnection during chamber long stay and post-deposition annealing correlated to defect formation in metallization processing

TiN/Al–0.5Cu/Ti film stacks deposited on SiO 2 substrate were studied by X-ray diffraction and electron microscopy to clarify the effects of the chamber long stay and post-deposition annealing on the morphology evolution. Experimental results indicated that the chamber idleness at 270 °C resulted in significant Al 2Cu precipitation and hillock growth for the Al–Cu films, which enhanced the occurrence rate of the microcorrosion-induced bridging defects and caused yield degradation on production line while post-deposition annealing at 400 °C for 30 min was proven to effectively regain good yield for the chamber-idled wafers. The yield recovery could be attributed to the fast Al 2Cu dissolution and hillock mitigation at the annealing temperature. The electrical sheet resistance of the Al–Cu films would somewhat increase due to the formation of the Al 3Ti phase during annealing, but the Al 2Cu precipitates and surface hillocks formed during chamber idleness would scarcely change the electrical property of the films. This study suggests that the evolutions of second phase and surface hillocks can be controlled by the processing duration and post-deposition treatment rather than the deposition temperature or Cu addition amount of Al–Cu alloy.

Photothermal Activation of Shallow Dopants Implanted in Silicon

Dopant impurities were implanted at high dose and low energy (1015 cm−2, 0.5–2.2 keV) into double-side polished 200 mm diameter silicon wafers and electrically activated to form p–n junctions by 10 s anneals at temperatures of 1,025, 1,050, and 1,075°C by optical heating with tungsten incandescent lamps. Activation was studied for P, As, B, and BF2 species implanted on one wafer side and for P and BF2 implanted on both sides of the wafer. Measurements included electrical sheet resistance (Rs) and oxide film thickness. A heavily boron-doped wafer, which is optically opaque, was used as a hot shield to prevent direct exposure to lamp radiation on the adjacent side of the test wafer. Two wafers with opposing orientations with respect to the shield wafer were annealed for comparison of exposure to, or shielding from, direct lamp illumination. Differences in sheet resistance for the two wafer orientations ranged from 4% to 60%. n-Type dopants implanted in p-type wafers yielded higher Rs when the implanted surface was exposed to the lamps, as though the effective temperature had been reduced. p-Type dopants implanted in n-type wafers yielded lower Rs when the implanted surface was exposed to the lamps, as though the effective temperature had been increased. Effective temperature differences larger than 5°C, which were observed for the P, B, and BF2 implants, exceeded experimental uncertainty in temperature control.

Polymer-based microsensor for soil moisture measurement

A moisture microsensor based on poly(3,4-ethylenedioxythiophene–poly(styrene-sulfonate) (PEDOT–PSS) conductive polymer is developed and presented in this paper. The change in electrical characteristics of the PEDOT–PSS polymer film is used to determine its sensitivity and working mechanism when exposed to different levels of moisture content. The output characteristics, the change in electrical sheet resistance of the PEDOT–PSS film versus the percentage change in relative humidity (%RH), show that the conductivity of the film decreases when it is exposed to increasing levels of moisture content. The moisture sensors thus fabricated based on the PEDOT–PSS thin film were used to detect the gravimetric water content present in highly plastic (CH) soil samples (Buckshot Clay) for geological and geotechnical engineering applications. The Fourier transform infrared spectroscopy (FT-IR) study of the PEDOT–PSS film on a glass substrate showed the incorporation of OH molecules in the film when it was exposed to moisture environment. This incorporation of OH molecules caused the change in resistance of the PEDOT–PSS film when exposed to moisture content. The change in the output resistance of the sensor device was observed to be from 2.5 to 4.0 M ohm when exposed to soil samples with 15–35% change in gravimetric water content.

Optical and electrical properties between 04 and 12 μm for Sn-doped In_2O_3 films by pulsed laser deposition and cathode sputtering

Optical properties of Sn-doped In(2)O(3) (ITO) have been studied in the optical range of 0.4-12 microm. A deposition has been made on BK7 glass, magnesium fluoride, sapphire, and zinc sulfide substrates. The layers have been characterized by their optical properties, DC electrical sheet resistivity, and Hall mobility. Sheet resistivity lies in the range of 6.8-318 Omega/sq for thicknesses between 16 and 280 nm. The best carrier mobility is obtained on BK7 and sapphire substrates, up to approximately 50 cm(2)/V s. The material shows good infrared transparency in the 3-5 microm range on magnesium fluoride and 0.4-4 microm on sapphire, and it is usable for practical applications up to 12 microm on zinc sulfide. Simulations have been carried out for optical indices and spectra calculations. The Drude model has been used to exploit the results in either direction: from electrical measured data to the simulation of optical spectra and indices, and from measured optical spectra to simulated optical indices and electrical parameters (mobility, carrier density). Hall mobility is considered a worthy and convenient material quality criteria for materials aimed at optics.

Study of titanium nitride for low-e coating application

The paper reports our novel work on chemical vapor deposition coating of titanium nitride (TiN) thin film on glass for energy saving. TiN films were deposited on glass substrates by atmospheric pressure chemical vapor deposition (APCVD) using titanium tetrachloride (TiCl4) and ammonia (NH3) as precursors. As a result, TiN films with a thickness of 500 nm were obtained. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), four-point probe method and optical spectroscopy were respectively employed to study the crystallization, microstructure, surface morphology, electrical and optical properties of the coated TiN films. The deposited TiN films are of NaCl structure with a preferred (200) orientation. The particles in the film are uniform. The reflectivity of the TiN coating in the near-infrared (NIR) band can reach over 40%, the visible transmittance is approximately 60%, and the visible reflectivity is lower than 10%. The sheet electrical resistance is 34.5 Ω. According to Drude theory, the lower sheet resistance of 34.5 Ω gives a high reflectivity of 71.5% around middle-far infrared band. The coated films exhibit good energy-saving performance.

Characteristics of Cu/C films on polymer substrates prepared by ECR–MOCVD

Cu/C films were prepared at ambient temperature under a Cu(hfac)2-Ar-H2 atmosphere in order to obtain metallized polymer by using electron cyclotron resonance metal organic chemical vapor deposition(ECR-MOCVD) coupled with a direct current (DC) bias system. DC bias selectively attracts the positively charged copper ions and then makes them deposit on the polymer substrate. Structural analysis of the films by ECR showed that fine copper grains were embedded in an amorphous polymer matrix. The electrical properties of the films were closely related to the process parameters such as microwave power, magnet current, H2/Ar mole ratio and periodic negative voltage. The increase in H2 contents, microwave power, magnet current and the negative voltage brought on copper-rich film formation with low electrical resistance. On the other hand carbon-rich films with low sheet electrical resistance were prepared with lower values for process parameters described above. Formation of Cu/C films depends strongly on the periodic negative pattern of DC bias and the electrical sheet resistance of the films was controlled in the 108–100 ohm/sq range by process parameters of the ECR-MOCVD system.