Schottky Emission Mechanism Research Articles

The Leakage Current Conduction Mechanisms of Cu/Porous Silica Damascene Schemes with Nano-cluster TaSix Barrier

Leakage current conduction mechanisms of Cu/porous silica damascene structures with TaSix (20 nm) barrier were investigated. Polycrystalline TaSi0.54 and nano-cluster TaSi0.42 barriers were prepared by dc sputtering with various power and pressure. The newly developed silica based slurry was employed for the metal-CMP of TaSix films. The incorporation of traditional NH4OH solution and megasonic were applied to perform post-CMP cleaning. Auger mapping revealed clearly straight Cu and Ta lines in these TaSix samples. The line-to-line leakage current density (JL) was plotted versus the electric field (E) at various temperatures. The Ln(JL)–(E)1/2 plots showed that Ln(JL) is linearly dependent on (E)1/2, corresponding to Schottky emission mechanism. The slope of straight lines were determined from the data points of the Ln(JL/T2)–(1000/T) plots. It revealed the magnitude of barrier height. The maximum height of the potential barrier of nano-cluster TaSix/porous silica is about 0.12–0.30 eV. The bias-temperature-stress induced leakage current was measured for reliability study.

Microwave loss mechanisms in Ba0.25Sr0.75TiO3 thin film varactors

Parallel-plate Au(Pt)∕Ba0.25Sr0.75TiO3∕(Pt)Au thin film varactors were fabricated on high resistance Si substrates and characterized at dc, rf, and microwave frequencies. In the frequency range 10–45 GHz the varactors show relatively low losses, with loss tangent less than 0.025 at 45 GHz. Due to the thick and highly conductive Pt/Au electrodes the metal losses are less than 10%. However, the loss tangent of the ferroelectric film is still three to five times higher than that in Ba0.27Sr0.73TiO3 single crystal. The analysis of the dc field dependences of loss tangent and permittivity in a wide frequency range shows that these additional losses are mainly due to the charged defects. Extrapolation of measured low frequency (1 MHz) loss tangents to the microwave region using the power law ω1∕3 is in good agreement with experiment. The dc current through the varactor is found to be controlled by Schottky emission and Poole-Frenkel mechanisms depending on the polarity. The Poole-Frenkel mode is associated with field enhanced thermal excitation of charge carriers from internal traps. The trap activation energy (about 0.15 eV) determined from the Poole-Frenkel mode agrees well with the energy level of the oxygen vacancy. We assume that the oxygen vacancies within the grain boundaries of the ferroelectric film act as charged defects and cause additional (extrinsic) microwave losses. The possible correlation between the film’s internal strains and density of the oxygen vacancies are discussed. The knowledge of the extrinsic loss mechanism and corresponding microstructure defects is useful in optimization of the varactor design, deposition, annealing process, and further improvement of the varactor performance.

Structural and Electrical Properties of Barium StrontiumTitanate Thin Film on Conductive La1−xSrxMnO3 Bottom Layer

Ferroelectrics and colossal magnetoresistance heterostructureBa1−xSrxTiO3(BST)/La1−xSrxMnO3 (LSMO) have beenfabricated on a LaAlO3 substrate by the pulse laser depositionmethod. The dielectric measurements show that at room temperature and100 kHz, the dielectric constant and loss tangent are about 990 and0.012, respectively; the highest tunability is about 45% near 200 Kunder the applied electric field of 200 kV/cm. Further studyindicates that the leakage current for the BST/LSMO heterostructureobeys the Schottky emission mechanism in the electric field regionhigher than 100 kV/cm at room temperature.

04/00859 Method of and apparatus for producing power from solar energy: Sugarmen, C. et al. U.S. Pat. Appl. Publ. US 2003 97,843 (Cl. 60–780; F02C3/28), 29 May 2003, Appl. 993,305

Nanostructure thin film of InSe deposited on p-Si single crystal to fabricate n-InSe/p-Si heterojunction. Electrical and photoelectrical have been studied by the current density–voltage (J–V). The fabricated cell exhibited rectifying characteristics. Analyzing the results of dark forward J–V shows that there are differrent conduction mechanisms. At low voltages, the current density is controlled by a Schottky emission mechanism. While at a relatively high voltage, a space charge-limited-conduction mechanism is observed with a single trap level. The cell also exhibited a photovoltaic characteristic with a power conversion efficiency of 3.42%. Moreover, artificial neural networks (ANNs) are adopted to model the J–V through the obtained functions. Different network configurations and many runs were trying to achieve good performance and finally obtained the current density, J, as a function of the junction temperature, T, and applied voltage, V. In all cases studied, we compared our obtained functions produced by the ANN technique with the corresponding experimental data and the excellent matching was so clear.

Transport properties of zirconium alloy oxide films

Abstract The conductivity mechanism of oxide films on tubes of various zirconium alloys grown in water and steam was investigated by I–V measurements. Electrodes of Ga, Ag, graphite and Au gave different results. The current decrease at voltage application was due to formation of space charge, which could be extracted again as short-circuit current. The positive branch of the I–V characteristics could be fitted by a second-order polynomial. Neither the Schottky emission mechanism nor the Poole–Frenkel effect could be proved. A high invariable carrier concentration with extremely low, but temperature dependent mobility could be proved using the Mott–Guerney relation. The carriers originate from oxygen vacancies in a substoichiometric black oxide layer near the metal–oxide interface. The conduction mechanism is believed to be a hopping process of electrons between oxygen-vacancy traps. There exists a small ionic conduction part, building up an open-circuit voltage so that the I–V characteristics do not pass through the origin. The Meyer–Neldel rule applies.

Dielectric properties and schottky barriers in silver tantalate-niobate thin film capacitors

Submicron thick ferroelectric Ag(Ta,Nb)O3 films have been pulsed laser deposited on the bulk Pt80lr20 polycrystalline substrates. They are ferroelectric at temperatures below 125 K with the remnant polarization of 0.4 μC/cm2 @ 77K and paraelectric at higher temperatures with tanδ@ 100 kHz as low as 0.015. Extensive I-V characterization has been performed in a wide temperature range 77 K to 350 K for vertical Me/Ag(Ta,Nb)O3/Pt80Ir20 capacitive cells, where the metals Me = Pd, Au, Cr, and Al have been used as a top electrode. The electronic transport in thin Me/Ag(Ta,Nb)O3/Pt80Ir20 capacitors follows the Schottky emission mechanism with the barrier height for the Pd, Au, Cr, and Al of 0.85, 0.8, 0.74, and 0.69 eV, respectively.

Analysis of current–voltage characteristics of organic light emitting diodes having a LiF/Al cathode and an Al–hydroxyquinoline/diamine junction

The electron injection from the composite cathode consisting of a very thin LiF layer and an Al layer (LiF/Al) into Al–hydroxyquinoline (ALQ) layers showed the voltage and temperature dependence, which is characteristic to the Schottky emission mechanism. The barrier formed at the interface is lower than that formed at the interfaces between the conventional cathodes and the ALQ layer. The current–voltage characteristics of the light emitting diodes having the LiF/Al cathode and the ALQ/diamine junction were well explained on the basis of the properties of the electron injection into the ALQ layer and the hole injection into the diamine layer.

D.c. conductivity and I–V characteristics in Fe-doped cellulose acetate films

D.c. electrical conductivity and current-voltage characteristics of Fe-doped cellulose acetate films (2 μm thick) have been studied as a function of applied bias field and film temperature. The temperature variation of conductivity shows three regions against two observed for undoped films. Log I vs. 1/ T plots for doped films are characterised by two regions of sharply increasing conductivity in the low and high temperature regions. It is suggested that electronic conduction is the dominant charge transport mechanism. Studies on current-voltage characteristics indicate that a Schottky emission mechanism is responsible for thegeneration and transport of charges in the polymer. The decrease in electrical conductivity owing to doping has been attributed to the formation of molecular aggregates of the dopant in the polymer matrix. The observation of two additional adsorption bands at 315 nm and 364 nm in doped specimens lends support to the formation of molecular aggregates.

Characterization of Electrodeposited Molybdenum Black Surface Coatings

Molybdenum black has been produced in thin coating form (3 μm) on prepared aluminium surfaces by the method of electrodeposition. The microstructure of the coating has been identified as one of flat irregular platelets belonging to a material which can be described as quasi-amorphous. Its chemical composition is 90 wt% MoO2 · 2 H2O and 10 wt% Ni(OH)2 · Mo-black appears to be a good absorber of solar radiation. Absorbance values as high as 93% have been measured for the visible region of the solar energy spectrum. It has been identified that the coating is of semiconducting nature and that the dominant conduction mechanism is the Schottky emission mechanism. Photoelectrochemical measurements have finally provided evidence for photon-induced electrochemical processes at the Mo-black electrodes.

Electrical conduction mechanism in solution grown thin polyvinylchloride (PVC) films

The electrical transport behaviour of thin polyvinylchloride (PVC) films deposited by the solution growth technique has been investigated. The current transport in PVC films of 2500 Å thickness at temperatures below 250 K is ascribed to hopping mechanisms. The weak temperature dependence of the conductivity is attributed to interchain hopping, whereas the strong temperature dependence is attributed to the trap hopping process. The conductivity of PVC films is increased on doping with iodine. This is interpreted on the basis of the formation of charge transfer complexes in the film. The activation energy for conduction increases from 0.7 to 1.22 eV at 315 K and decreases from 2.2 to 0.8 eV at 375 K on doping PVC films with iodine (0.7 g of iodine per 100 ml PVC solution). At high (≧5 × 10 4 V cm -1) fields and at higher (≧350 K) temperatures, the observed conduction behaviour can be described by the Schottky emission mechanism. The height of the Schottky barrier is found to depend on the type of the metal electrode and the direction of the current. The barrier height decreases with increasing iodine concentration in the PVC films.

Quantum-mechanical tunneling in thin films of chlorophyll a

Thin dielectric films of chlorophyll a deposited onto a tin electrode by the Langmuir-Blodgett technique were investigated with regard to quantum-mechanical tunneling and Schottky emission conductivity mechanisms. The films exhibited conduction characteristics in which the current was directly proportional to the applied voltage, but independent of temperature, in the region 50–500 mV. From a consideration of the nature of the conduction it is concluded that tunneling is the most likely conduction mechanism in this voltage range. At higher voltages, the conduction data is consistent with tunneling, Schottky emission or Frenkel-Poole conduction mechanisms. The significance of tunneling in thin films of chlorophyll with respect to photosynthesis is discussed.

Electrical Conduction through SiO Films

The voltage—current characteristics for evaporated SiO films sandwiched between Al electrodes is suggestive of the Schottky emission mechanism for film thickness between 1000 and 10 000 Å. The temperature dependence of the voltage—current characteristics and the photoresponse as a function of photon energy were measured to investigate the mechanism of current flow. The results show that the current density through the SiO film can be described by the following empirical equation: J=αa exp(βV12−γ/kT)[1−exp(−β2V)],where α and γ are constants and a is the SiO film thickness. The most important conclusion is that even though the functional form is similar to that which is obtained for the Schottky emission mechanism, the pre-exponential factor is not the Richardson constant times T2 and γ is not a barrier height corresponding to the threshold for photoresponse. The transient behavior of these films is suggestive of trapping and the resultant voltage—current characteristic may be due to space-charge buildup in the film as described by O'Dwyer.

Schottky Emission and Conduction in Some Organic Insulating Materials

Voltage-current curves of such organic insulators as polyethylene-terephthalate and polyvinylformal display the familiar Richardson-Schottky characteristics for fields between 20 and 200 kV/cm and temperatures from 25° to 100°C. Assuming the Schottky emission mechanism being the limiting factor in establishing the steady-state current, comparison between measured values and the Richardson-Schottky equation yields data on the work function of these materials. 0.88 eV was found for polyethylene-terephthalate and 1.24 eV for polyvinylformal. The calculations indicate an increase of the electric field at the injecting electrode over the value which would apply to an ideal, nonconducting insulator. This increase may be caused by space-charge effects.