High Leakage Current Density Research Articles

Langmuir–Blodgett Fabrication of Nanosheet-Based Dielectric Films without an Interfacial Dead Layer

Langmuir–Blodgett (LB) deposition was employed to fabricate high-κ dielectric nanofilms of titania nanosheets. The LB-based layer-by-layer approach using an atomically flat SrRuO3 substrate is effective for the fabrication of atomically uniform and highly dense nanofilms. These films exhibited both high dielectric constant (κ∼123) and low leakage current density (J< 10-7 A cm-2) for thicknesses down to 5 nm, while eliminating the size-effect problems encountered in current high-κ films. From analyses of interfacial structures by transmission electron microscopy and hard X-ray photoelectron spectroscopy, we have clarified that the films are composed of a well-ordered lamellar structure without an interfacial dead layer. According to first-principles calculations, a highly polarizable nature of titania nanosheets can bring improved dielectric properties, yielding high-κ values even in an ultrathin geometry (<10 nm).

Effect of Oxygen Pressure on the Electrical Properties of $\hbox{Bi}_{5} \hbox{Nb}_{3}\hbox{O}_{15}$ Films Grown by RF Magnetron Sputtering

Bi5Nb3O15 (B5N3) films grown under a low oxygen partial pressure (OP) of 1.7 mtorr showed a high leakage current density of 0.1 A/cm2 at 1.0 MV/cm. However, the leakage current density decreased with increasing OP to a minimum of 5.8 times 10-9 A/cm2 for the film grown under 5.1 mtorr due to the decreased number of oxygen vacancies. This film also showed an improved breakdown field of 2.2 MV/cm and a large capacitance density of 24.9 fF /mum2. The electrical properties of the film, however, deteriorated with a further increase in OP, which is probably due to the formation of oxygen interstitial ions. Therefore, superior electrical properties for the B5N3 film can be obtained by careful control of OP.

Low-voltage high-performance C60 thin film transistors via low-surface-energy phosphonic acid monolayer/hafnium oxide hybrid dielectric

C 60 -based organic thin film transistors (OTFTs) have been fabricated using a n-octadecylphosphonic acid self-assembled monolayer/sol-gel processed hafnium oxide hybrid dielectric. With the combination of high capacitance (580 nF/cm2) and low leakage current density (8×10−9 A/cm2), this hybrid dielectric yields C60 OTFTs operating under 1.5 V with an average n-channel saturation field-effect mobility of 0.28 cm2/V s, high on-off current ratio of 105, and low subthreshold slope of 100 mV/decade. The low surface energy of the n-octadecylphosphonic acid allows C60 to form a thin film with large grains that provide an efficient charge carrier pathway for the low-voltage OTFTs.

Dependence of ferroelectric and magnetic properties on measuring temperatures for polycrystalline BiFeO3 films

A multiferroic BiFeO(3) film was fabricated on a Pt/Ti/SiO(3)/Si(100) substrate by a chemical solution deposition (CSD) method, and this was followed by postdeposition annealing at 923 K for 10 min in air. X-ray diffraction analysis indicated the formation of the polycrystalline single phase of the BiFeO(3) film. A high remanent polarization of 89 microC/cm(2) was observed at 90 K together with a relatively low electric coercive field of 0.32 MV/cm, although the ferroelectric hysteresis loops could not be observed at room temperature due to a high leakage current density. The temperature dependence of the ferroelectric hysteresis loops indicated that these hysteresis loops lose their shape above 165 K, and the nominal remanent polarization drastically increased due to the leakage current. Magnetic measurements indicated that the saturation magnetization was less than 1 emu/cm(3) at room temperature and increased to approximately 2 emu/cm(3) at 100 K, although the spontaneous magnetization could not appear. The magnetization curves of polycrystalline BiFeO3 film were nonlinear at both temperatures, which is different with BiFeO3 single crystal.

Complete prevention of reaction at HfO 2/Si interfaces by 1 nm silicon nitride layer

When hafnium oxide (HfO 2) is directly deposited on Si by the RF sputtering method, Hf silicide is formed and post-deposition anneal (PDA) at 400 °C transforms Hf silicide to Si suboxide plus Hf suboxide. The leakage current density for the 〈aluminum (Al)/HfO 2/Si(1 0 0)〉 diodes without PDA is high due to the high density interface states near the Fermi level (0.86 eV above the Si valence band maximum, VBM) and minute conduction channels. PDA at 400 °C eliminates the interface states and the conduction channels, and improves the characteristics of the HfO 2 layer, but interface states are newly formed at 0.53 eV above the VBM, resulting in still high leakage current density. Silicon nitride (SiN) layers formed by Si nitridation using N 2-plasma generated by the low energy electron impact method possess a high nitrogen atomic concentration ratio, N/(N + O) of 0.65. When a 1.0 nm SiN layer is inserted between HfO 2 and Si, interfacial reaction is completely prevented, resulting in a smaller effective oxide thickness, EOT of 1.4 nm. In spite of the smaller EOT, the leakage current density is nearly the same as that with no SiN layer, possibly due to the prevention of the formation of the conduction channels. PDA at 400 °C improves HfO 2 characteristics without causing the interfacial reaction, leading to a decrease in the leakage current density.

Solution-Based Fabrication of High-κ Dielectric Nanofilms Using Titania Nanosheets as a Building Block

We have demonstrated a novel procedure for fabricating high-κ dielectric nanofilms by using a titania nanosheet as a building block. The layer-by-layer assembly of titania nanosheets using an atomically flat SrRuO3 substrate is advantageous as a means of fabricating atomically uniform multilayer high-κ nanofilms. High-resolution transmission electron microscopy revealed that these multilayer nanofilms are composed of a well-ordered lamellar structure without an interfacial dead layer. These nanofilms exhibited both high dielectric constant (εr∼125) and low leakage current density (J<10-7 A/cm2) even for thicknesses as low as 10 nm. These results indicate that the titania nanosheet is a very promising candidate as a high-κ nanoblock, and its bottom-up fabrication provides new opportunities for the development of high-κ devices.

Electrical Characteristics of Strontium Titanate Films Prepared by Liquid Phase Deposition

In this study, strontium titanate precursor was prepared by liquid phase deposition with aqueous solutions of ammonium hexafluoro-titanate, strontium nitrate and boric acid. Its polycrystalline structure shows high leakage current density and low dielectric constant. After thermal annealing in O2 ambient, the strontium titanate precursor is transformed gradually into strontium titanate film, as determined by X-ray diffraction (XRD). The leakage current and dielectric constant are improved. In order to further improve the leakage current, a thermal ultrathin SiO2 layer is added between strontium titanate and silicon. The leakage current density can be improved to 2.23×10-4 A/cm2 at 0.38 MV/cm and the dielectric constant is 39.

Structural, magnetic, and ferroelectric properties of multiferroic BiFeO3 film fabricated by chemical solution deposition

Polycrystalline BiFeO3 film has been fabricated by a chemical solution deposition on Pt∕Ti∕SiO2∕Si(100) substrates. A ferroelectric hysteresis loop showed a high remanent polarization of 47μC∕cm2 at room temperature. Leakage current density was on the order of 10−1A∕cm2 at 100kV∕cm, indicating the high leakage current density in the present BiFeO3 film. The leakage current mechanism could be considered as follows: Ohmic conduction at low electric field and Poole-Frenkel trap-assisted conduction appeared as the electric field increased, and space-charge-limited current started at a high electric field. Weak ferromagnetism was observed at room temperature, and magnetic coercivity increased to 0.5kOe with small remanent magnetization of 2emu∕cm3 at 10K. In order to investigate the magnetoelectric effect of the BiFeO3 film, the ferroelectric hysteresis loop was measured under the magnetic field of 5kG at room temperature.

Porosity Effects on Properties of Mesoporous Silica Low-k Films Prepared Using Tetraethylorthosilicate with Different Templates

A series of mesoporous silica films with different porosities and different pore sizes were prepared using different templates or different template concentrations in tetraethylorthosilicate colloid solutions. The amphiphilic templates such as cetyltrimethylammonium bromide (), Brij-56, Tween80, and Pluronic P123 were used. To investigate the effect of self-assembly surfactants on the film properties and to make a comparison, polyethylene glycol (molecular weight = 1450) which is not a surfactant was also used as a template in this research. Various film properties such as porosity, refractive index, dielectric constant, leakage current density, flatband voltage, hardness, and Young’s modulus were measured. For the film templated with , the high leakage current density and positive flatband voltage were attributed to the residual bromide in the framework, which was from bromine in after the calcination process. Moreover, its abnormally low dielectric constant was mainly due to the high leakage current density. For the films made with nonionic templates, the dielectric constant and the refractive index can be reduced linearly by increasing the film porosities; in other words, they are strongly related to the porosity rather than the pore size or the ordering of pore structure. However, the larger leakage current density and the weaker mechanical strength for more porous films are the drawbacks. According to higher values of flatband voltage, the elevation of leakage current densities are attributed to more silanol groups in the films. It was shown that the films with more ordered structures or thicker pore wall possessed better mechanical strength. Nevertheless, the porosity is the most influential factor upon mechanical strength of the films.

Characterization of Laminated CeO2 – HfO2 High-k Gate Dielectrics Grown by Pulsed Laser Deposition

The electrical and physical properties of nanolaminates on Si(100), by pulsed laser deposition, are investigated. Layers were deposited using pure and targets at various substrate temperatures ranging from at and and in situ postdeposition anneal of nanolaminates performed by controlled cooling from deposition temperature to room temperature under high oxygen pressure. After layer growth and anneal, top and bottom Au electrodes were deposited by sputtering. Electrical characterization was done by and measurements. The highest value of 30 was found for the laminates deposited at in ambient. It is found that the properties of nanolaminates deposited at reducing atmosphere are dependent on the layer thickness. Thicker layers showed a higher dielectric constant and higher leakage current densities than thinner layers.

A comparison of pulsed-laser-deposited and ion-beam-enhanced-deposited AlN thin films for SOI application

Aluminum nitride (AlN) thin films have attracted interests as the buried dielectric layer in silicon-on-insulator (SOI) substrates. The precondition for this application is that AlN films have smooth surfaces for wafer bonding and excellent insulation properties. In this work, AlN films synthesized by pulsed-laser deposition (PLD) and ion-beam-enhanced deposition (IBED) techniques are compared under the concern of their suitability for SOI application. Both PLD-deposited and IBED-deposited AlN films exhibit smooth surface morphologies. However, AlN films show quite different electrical properties due to different microstructures: microcrystalline wurtzite by PLD but amorphous by IBED. PLD AlN films have high leakage current and high dynamic charge densities. In contrast, IBED films have low leakage current and the breakdown field is about 2.1 MV/cm. Moreover, after postannealing at 800–1100 °C, the breakdown field exceeds 4 MV/cm and the leakage current is reduced nearly two orders in magnitude. We conclude that IBED is more suitable technique to fabricate AlN films as buried insulators in SOI substrates.

Microstructure development and nonlinear electrical characteristics of the SnO2·CuO·Ta2O5 based varistors

The microstructure development of SnO2·CuO based ceramic material was analyzed by XRD and SEM and the electrical properties were investigated by J-E relation. The secondary phases of copper oxide were found by the XRD. Copper oxide could make tin oxide densify and advance the grain growth, while tantalum oxide would retard the grain growth. Excess copper would centralize at the grain boundaries and prevent the mass transport. The high nonlinear coefficient (α = 27.3) and low leakage current density (JL = 16 μA cm−2) for the 0.05 mol% Ta2O5-doped SnO2·CuO based varistor sample were obtained. The modified defect barrier model for CuO and Ta2O5-doped SnO2 based varistors was introduced.

Effects of substrate temperature on properties of pulsed dc reactively sputtered tantalum oxide films

The effects of substrate heating on the stoichiometry and the electrical properties of pulsed dc reactively sputtered tantalum oxide films over a range of film thickness (0.14to5.4μm) are discussed. The film stoichiometry, and hence the electrical properties, of tantalum oxide films; e.g., breakdown field, leakage current density, dielectric constant, and dielectric loss are compared for two different cases: (a) when no intentional substrate/film cooling is provided, and (b) when the substrate is water cooled during deposition. All other operating conditions are the same, and the film thickness is directly related to deposition time. The tantalum oxide films deposited on the water-cooled substrates are stoichiometric, and exhibit excellent electrical properties over the entire range of film thickness. “Noncooled” tantalum oxide films are stoichiometric up to ∼1μm film thickness, beyond that the deposited oxide is increasingly nonstoichiometric. The presence of partially oxidized Ta in thicker (&amp;gt;∼1μm) noncooled tantalum oxide films causes a lower breakdown field, higher leakage current density, higher apparent dielectric constant, and dielectric loss. The growth of nonstoichiometric tantalum oxide in thicker noncooled films is attributed to decreased surface oxygen concentration due to oxygen recombination and desorption at higher film temperatures (&amp;gt;∼100°C). The quantitative results presented reflect experience with a specific piece of equipment; however, the procedures presented can be used to characterize deposition processes in which film stoichiometry can change.

Leakage current and charge carriers in (Na0.5Bi0.5)TiO3 thin film

A sodium bismuth titanate (Na0.5Bi0.5)TiO3 (NBT) thin film of perovskite structure, synthesized by radio-frequency magnetron sputtering, exhibited a remanent polarization of 11.9 µC cm−2 and a coercive field of 37.9 kV cm−1 at room temperature. It however showed a rather high leakage current density of ∼6 × 10−5 A cm−2 at an applied electric field of 100 kV cm−1. There occurs a change in the controlling mechanism of the electrical behaviours of the NBT thin film from grain interiors to grain boundaries with increasing temperature. The ac conductivity obeys the Jonscher relation. The activation energies for dc conductivity and hopping frequency of the charge carriers are calculated to be 0.92 eV and 1.00 eV, respectively, suggesting oxygen vacancies are the most likely charge carriers at high temperatures. Hopping of oxygen vacancies trapped at the grain boundaries and excitation of polarons in the grain interior are responsible for the relatively high dielectric loss and high dc conductivity. The contribution of hopping charge carriers to the dielectric response is demonstrated by the frequency dispersion observed for the relative permittivity in the low frequency region.

A comparative study of low dielectric constant barrier layer, etch stop and hardmask films of hydrogenated amorphous Si-(C, O, N)

New barrier layer, etch stop and hardmask films, including hydrogenated amorphous a-SiC x :H (SiC), a-SiC x O y :H (SiCO), and a-SiC x N y :H (SiCN) films with a dielectric constant ( k) approximately 4.3, are produced using the plasma-enhanced chemical vapor deposition technique. The chemical and structural nature, and mechanical properties of these films are characterized using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and nano-indentation. The leakage current density and breakdown electric field are investigated by a mercury probe on a metal-insulator-semiconductor structure. The properties of the studied films indicate that they are potential candidates as barrier layer, etch stop and hardmask films for the advanced interconnect technology. The SiC film shows a high leakage current density (1.3×10 −7 A/cm 2 at 1.0 MV/cm) and low breakdown field (1.2 MV/cm at 1.0×10 −6 A/cm 2). Considering the mechanical and electrical properties requirements of the interconnect process, SiCN might be a good choice, but the N content may result in via poison problem. The low leakage current (1.2×10 −9 A/cm 2 at 1.0 MV/cm), high breakdown field (3.1 MV/cm at 1.0×10 −6 A/cm 2), and relative high hardness (5.7 GPa) of the SiCO film indicates a good candidate as a barrier layer, etch stop, or hardmask.

Deep depletion phenomenon of SrTiO3 gate dielectric capacitor

SrTiO 3 (STO) thin films were deposited on p-type silicon substrate by radio-frequency (rf) magnetron sputtering in an Ar–O2 and Ar–N2 mixed ambient to form metal/insulator/semiconductor (MIS) structure. We found the Schottky emission and Fowler–Nordheim tunneling mechanisms as responsible for the leakage current in the STO-based MIS structures at low and high electric fields under negative bias voltage, respectively. On the other hand, it was also observed that the generation current dominated the leakage mechanism at the high electric field under positive bias voltage due to the highly leaky insulator and lack of electrons. To maintain the leakage current at the higher electric field, the depletion width would broaden to generate more electrons, which is called deep depletion. Therefore, deep depletion was induced by high leakage current density under positive bias voltage. We also investigated the correlation between deep depletion and the leakage mechanism in STO-based gate dielectric capacitors under positive bias voltage to extract the generation lifetime of silicon substrates. The extracted generation lifetime can be used to examine the quality of silicon substrates after different processing conditions.

Ferroelectric Characteristics of Sr&lt;sub&gt;x&lt;/sub&gt;Bi&lt;sub&gt;2.4&lt;/sub&gt;Ta&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;9&lt;/sub&gt; Thin Films and Electrical Properties of the Pt/Sr&lt;sub&gt;x&lt;/sub&gt;Bi&lt;sub&gt;2.4&lt;/sub&gt;Ta&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;9&lt;/sub&gt;/TiO&lt;sub&gt;2&lt;/sub&gt;/Si Structure

Ferroelectric characteristics of the 400 nm-thick SrxBi2.4Ta2O9(0.7≤x≤1.3) thin films processed by metalorganic decomposition were investigated, and electrical properties of the Pt/Sr0.85Bi2.4Ta2O9/TiO2/Si structure prepared using TiO2 buffer layer were characterized. The Sr-deficient SrxBi2.4Ta2O9 films exhibited well-developed ferroelectric hysteresis curves compared to those of the Sr-excess films. The Sr0.85Bi2.4Ta2O9 film exhibited optimum ferroelectric properties, such as high remanent polarization and low leakage current density, among SrxBi2.4Ta2O9 films. A memory window of the Pt/SrxBi2.4Ta2O9/TiO2/Si structure was dependent upon the coercive field of the SrxBi2.4Ta2O9 film, and the Pt/SrxBi2.4Ta2O9/TiO2/Si exhibited a maximum memory window of 1.3 V at the sweeping voltage of ±5 V.

Influence of Precursor Solutions on the Ferroelectric Properties of Sol-Gel-Derived Lanthanum-Modified Lead Titanate (PLT) Thin Films

Precursor chemistry was found to have a dominant effect on the electrical properties of sol-gel-derived Pb0.85La0.15TiO3 (PLT15) thin films prepared using different precursor sources for lanthanum, namely, lanthanum acetate dissolved in acetic acid (LAA) and lanthanum 2-methoxyethoxide in 2-methoxyethanol (LMM). The LMM-derived PLT15 films had lower dielectric constants (KLMM= 394, KLAA= 548, measured at 100 kHz, applying 500 mV oscillation voltage), poorer polarization hysteresis characteristics, and higher leakage current densities (JLMM∼ 1.5 × 10−7 A/cm2, JLAA∼ 2 × 10−9 A/cm2, measured at 10 kV/cm field). Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) measurements in conjunction with Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicate that better removal of C–O moieties are the key step to yield improved electrical properties in these films. Possibly, C–O moieties reduce the metallic oxides to their corresponding metals and the presence of the metallic constituent(s) (e.g., lead), in turn deteriorate the electrical properties. In line with these postulations it was found that, when the pyrolysis temperature is increased from 450° to 550°C, the organic contents of LMM-derived films are reduced and their electrical properties are indeed comparable to that of the LAA-derived films.

Lead Content Control in (Pb, La)(Zr, Ti)O3 Films Using Ar/O2 Sequential Rapid Thermal Process

A new method of controlling the lead (Pb) profile in (Pb, La)(Zr, Ti)O3 (PLZT) capacitor films with top and bottom SrRuO3 (SRO) electrodes has been developed using an Ar/O2 sequential crystallization process. This new technique makes it possible to realize good fatigue properties and a low leakage current density in the films. We found that the gas ambient of the rapid thermal process (RTP) affects Pb evaporation behavior during PLZT crystallization; an Ar ambient promotes Pb evaporation more than an O2 ambient. The Ar/O2 sequential RTP was introduced on the basis of the optimum design of the Pb profile in crystallized PLZT films. A good ferroelectric capacitor with a Pt/SRO/PLZT/SRO/Pt structure was achieved by controlling the Pb composition in the bulk of PLZT films as well as at the interfaces to the electrodes, resulting in high endurance and low leakage current density.

The effect of substrate temperature on the physical properties of tantalum oxide thin films grown by reactive radio-frequency sputtering

Thin films of TaO x were deposited on Si(1 0 0) by radio-frequency magnetron sputtering at substrate temperatures of 25, 100, 200, 300, 400, and 500 °C. The properties of TaO x thin films deposited with different oxygen-to-argon gas ratios and substrate temperatures were evaluated. The results show that the films with lowest leakage current density were obtained at ambient temperature with an oxygen mixture ratio (OMR) of 60% and the oxygen-to-tantalum ratio has a minimum with increasing deposition substrate temperature. From the current–voltage ( I– V) characteristics of the TaO x thin films as a function of deposition substrate temperature, we found that the leakage current density in the TaO x thin films increases with increasing deposition substrate temperature. The higher leakage current density in the TaO x films is correlated to the oxygen deficiency in TaO x films and crystallization at higher deposition temperature.