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Showing papers on "Dielectric published in 2001"


Journal ArticleDOI
27 Jul 2001-Science
TL;DR: Optical conductivity measurements on the perovskite-related oxide CaCu3Ti4O12 provide a hint of the physics underlying the observed giant dielectric effect in this material, suggesting the presence of a strong absorption at very low frequencies due to dipole relaxation.
Abstract: Optical conductivity measurements on the perovskite-related oxide CaCu3Ti4O12 provide a hint of the physics underlying the observed giant dielectric effect in this material. A low-frequency vibration displays anomalous behavior, implying that there is a redistribution of charge within the unit cell at low temperature. At infrared frequencies (terahertz), the value for the dielectric constant is approximately 80 at room temperature, which is far smaller than the value of approximately 10(5) obtained at lower radio frequencies (kilohertz). This discrepancy implies the presence of a strong absorption at very low frequencies due to dipole relaxation. At room temperature, the characteristic relaxation times are fast (less than or approximately 500 nanoseconds) but increase dramatically at low temperature, suggesting that the large change in dielectric constant may be due to a relaxor-like dynamical slowing down of dipolar fluctuations in nanosize domains.

1,540 citations


Journal ArticleDOI
TL;DR: In this paper, a large variety of polymers have been proposed for use as materials with low dielectric constants for applications in microelectronics, including polyimides, heteroaromatic polymers, poly(aryl ether)s, fluoropolymers, hydrocarbon polymers without any polar groups, films deposited from the gas phase by chemical vapor deposition, plasma enhanced chemical vapor (PEVD) and other techniques.

949 citations


Journal ArticleDOI
TL;DR: In this article, the present state of knowledge of the chemistry, structure, and dielectric properties of these materials, as well as examples of our own work, are described and compared.
Abstract: Dielectric ceramic materials have been studied for decades due to both their application in important technologies and the fundamentally interesting relationships among their crystal chemistry, crystal structures, and physical properties. Recent dramatic changes in microelectronics and in particular wireless communications technologies have made the importance of materials with the unusual combination of high dielectric constant, low dielectric loss and low temperature dependence of dielectric constant of great interest. In this review, the present state of knowledge of the chemistry, structure, and dielectric properties of these materials, as well as examples of our own work, are described.

528 citations


Journal ArticleDOI
TL;DR: In this paper, the extrinsic contribution to the dielectric constant of PZT films was mainly attributed to 180° domain wall motion, which increased with both film thickness and grain size.
Abstract: In this article, domain wall motion and the extrinsic contributions to the dielectric and piezoelectric responses in sol–gel derived lead zirconate titanate (PZT) films with compositions near the morphotropic phase boundary were investigated. It was found that although the films had different thicknesses, grain sizes, and preferred orientations, similar intrinsic dielectric constants were obtained for all films between 0.5 and 3.4 μm thick. It was estimated that about 25%–50% of the dielectric response at room temperature was from extrinsic sources. The extrinsic contribution to the dielectric constant of PZT films was mainly attributed to 180° domain wall motion, which increased with both film thickness and grain size. In studies on the direct and converse longitudinal piezoelectric coefficients of PZT films as a function of either stress or electric driving field, it was found that the ferroelastic non-180° domain wall motion was limited. Thus extrinsic contributions to the piezoelectric response were small in fine grain PZT films (especially those under 1.5 μm in thickness). However, as the films became thicker (>5μm), nonlinear behavior between the converse piezoelectric coefficient and the electric driving field was observed. This indicated that there was significant ferroelectric non-180° domain wall motion under high external excitation in thicker films. The activity of the non-180° domain walls was studied through non-180° domain switching. For fine grain films with film thicknesses less than 2 μm, non-180° switching was negligible. Transmission electron microscopy plan-view micrographs evidenced non-180° domain fringes in these films, where the vast majority of grains were 50–100 nm in diameter and showed a single set of domain fringes. Taken together, these measurements suggest that the pinning of non-180° domain walls is very strong in films with thickness less than 2 μm. In thicker films, non-180° domain switching was evidenced when the poling field exceeded a threshold field. The threshold field decreased with an increase in film thickness, suggesting more non-180° domain wall mobility in thicker films. Non-180° domain switching in large grained PZT films was found to be much easier and more significant than in the fine grained PZT films.

480 citations


Proceedings ArticleDOI
16 Jul 2001
TL;DR: In this article, the authors discuss the fundamentals of dielectric elastomer generators, experimental verification of the phenomenon, practical issues, and potential applications, and discuss the operating conditions and materials required for high efficiency.
Abstract: Dielectric elastomers have shown great promise as actuator materials. Their advantages in converting mechanical to electrical energy in a generator mode are less well known. If a low voltage charge is placed on a stretched elastomer prior to contraction, the contraction works against the electrostatic field pressure and raises the voltage of the charge, thus generating electrical energy. This paper discusses the fundamentals of dielectric elastomer generators, experimental verification of the phenomenon, practical issues, and potential applications. Acrylic elastomers have demonstrated an estimated 0.4 J/g specific energy density, greater than that of piezoelectric materials. Much higher energy densities, over 1 J/g, are predicted. Conversion efficiency can also be high, theoretically up to 80-90%; the paper discusses the operating conditions and materials required for high efficiency. Practical considerations may limit the specific outputs and efficiencies of dielectric elastomeric generators, tradeoffs between electronics and generator material performance are discussed. Lastly, the paper describes work on potential applications such as an ongoing effort to develop a boot generator based on dielectric elastomers, as well as other applications such as conventional power generators, backpack generators, and wave power applications.

474 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of experimental evidence and present understanding of nonlinear dielectric, elastic and piezoelectric relationships in PEG ceramics.
Abstract: The paper presents an overview of experimental evidence and present understanding of nonlinear dielectric, elastic and piezoelectric relationships in piezoelectric ceramics. This topic has gained an increasing recognition in recent years due to the use of such materials under extreme operating conditions, for example in electromechanical actuators and high power acoustic transducers. Linear behaviour is generally confined to relatively low levels of applied electric field and stress, under which the dielectric, elastic and piezoelectric relationships are described well by the standard piezoelectric constitutive equations. Nonlinear relationships are observed above certain ‘threshold’ values of electric field strength and mechanical stress, giving rise to field and stress-dependent dielectric (e), elastic (s) and piezoelectric (d) coefficients. Eventually, strong hysteresis and saturation become evident above the coercive field/stress due to ferroelectric/ferroelastic domain switching. The thermodynamic method provides one approach to describing nonlinear behaviour in the ‘intermediate’ field region, prior to large scale domain switching, by extending the piezoelectric constitutive equations to include nonlinear terms. However, this method seems to fail in its prediction of the amplitude and phase of high frequency harmonic components in the field-induced polarisation and strain waveforms, which arise directly from the nonlinear dielectric and piezoelectric relationships. A better fit to experimental data is given by the empirical Rayleigh relations, which were first developed to describe nonlinear behaviour in soft magnetic materials. This approach also provides an indication of the origins of nonlinearity in piezoelectric ceramics, in terms of ferroelectric domain wall translation (at intermediate field/stress levels) and domain switching (at high field/stress levels). The analogy with magnetic behaviour is also reflected in the use of Preisach-type models, which have been successfully employed to describe the hysteretic path-dependent strain-field relationships in piezoelectric actuators. The relative merits and limitations of the different modelling methods are compared and possible areas of application are identified.

447 citations


Journal ArticleDOI
TL;DR: The elastic, piezoelectric, and dielectric constants of 0.67Pb(Mg1/3Nb2/3)O3 and 0.33PbTiO3 domain engineered single crystal were determined experimentally by using ultrasonic and resonance methods as mentioned in this paper.
Abstract: The elastic, piezoelectric, and dielectric constants of 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 domain engineered single crystal were determined experimentally by using ultrasonic and resonance methods. It was confirmed that the single crystal system has large electromechanical coupling coefficient k33 (∼94%) and piezoelectric constant d33 (∼2800 pC/N) if the poling is done along the [001] of pseudocubic directions. A soft shear mode with a velocity of 880 m/s was observed in the [110] direction with displacement in [110]. Using the measured data, the orientation dependence of phase velocities and electromechanical coupling coefficients were calculated. The origin of experimental errors and their influence on measured results are also examined.

422 citations


Patent
22 Feb 2001
TL;DR: In this paper, a conformal capacitor dielectric over textured silicon electrodes for integrated memory cells is presented, where the first electrodes include hemispherical grain (HSG) silicon for increasing the capacitor plate surface area.
Abstract: Method and structures are provided for conformal capacitor dielectrics over textured silicon electrodes for integrated memory cells. Capacitor structures and first electrodes or plates are formed above or within semiconductor substrates. The first electrodes include hemispherical grain (HSG) silicon for increasing the capacitor plate surface area. The HSG topography is then exposed to alternating chemistries to form monolayers of a desired dielectric material. Exemplary process flows include alternately pulsed metal organic and oxygen source gases injected into a constant carrier flow. Self-terminated metal layers are thus reacted with oxygen. Near perfect step coverage allows minimal thickness for a capacitor dielectric, given leakage concerns for particular materials, thereby maximizing the capacitance for the memory cell and increasing cell reliability for a given memory cell design. Alternately pulsed chemistries are also provided for depositing top electrode materials with continuous coverage of capacitor dielectric, realizing the full capacitance benefits of the underlying textured morphology.

399 citations


Journal ArticleDOI
01 Oct 2001-Fuel
TL;DR: In this paper, the relative real permittivity of coal is greater than most composite mineral matter with the exception of pyrite, which may increase the bulk coal electric permittivities if present in sufficient quantity.

397 citations


Journal ArticleDOI
TL;DR: An overview of recent work on ultrathin (, 100 A) films of metal oxides deposited on silicon for advanced gate dielectrics applications is presented in this article, where the authors illustrate the 23 2 2 2 3 complex processing, integration and device related issues for high dielectric constant ('high-K') materials.

376 citations


Patent
05 Nov 2001
TL;DR: In this paper, a method of depositing and etching dielectric layers has been proposed for the formation of horizontal interconnects by varying the concentration of a carbon:oxygen gas such as carbon monoxide.
Abstract: A method of depositing and etching dielectric layers having low dielectric constants and etch rates that vary by at least 3:1 for formation of horizontal interconnects The amount of carbon or hydrogen in the dielectric layer is varied by changes in deposition conditions to provide low k dielectric layers that can replace etch stop layers or conventional dielectric layers in damascene applications A dual damascene structure having two or more dielectric layers with dielectric constants lower than about 4 can be deposited in a single reactor and then etched to form vertical and horizontal interconnects by varying the concentration of a carbon:oxygen gas such as carbon monoxide The etch gases for forming vertical interconnects preferably comprises CO and a fluorocarbon, and CO is preferably excluded from etch gases for forming horizontal interconnects

Patent
31 Dec 2001
TL;DR: A process for fabrication of a semiconductor device including a modified ONO structure is described in this article, where the modified ono structure is formed by providing a substrate, forming a first oxide layer on the semiconductor substrate, depositing a layer comprising a high-K dielectric material on the oxide layer, and forming a top oxide layer.
Abstract: A process for fabrication of a semiconductor device including a modified ONO structure, including forming the modified ONO structure by providing a semiconductor substrate; forming a first oxide layer on the semiconductor substrate; depositing a layer comprising a high-K dielectric material on the first oxide layer; and forming a top oxide layer on the layer comprising a high-K dielectric material The semiconductor device may be, eg, a MIRRORBIT™ two-bit EEPROM device or a floating gate flash device including a modified ONO structure


Journal ArticleDOI
TL;DR: In this paper, the dielectric constant of quantum paraelectric (e.g., EuTiO) has been measured under a magnetic field and shown to be dominated by the pair correlation of the nearest neighbor Eu spins, likely via the variation of the soft-phononmode frequency.
Abstract: The dielectric constant of quantum paraelectric ${\mathrm{EuTiO}}_{3},$ which contains ${\mathrm{Eu}}^{2+}$ with $S=7/2$ spin and ${\mathrm{Ti}}^{4+},$ has been measured under a magnetic field. The dielectric constant shows a critical decrease at the antiferromagnetic ordering of the Eu spins at 5.5 K, as well as a substantial change under a magnetic field (by $\ensuremath{\sim}7%$ with 1.5 T), indicating a strong coupling between the Eu spins and dielectric properties. We show that the variation of the dielectric constant is dominated by the pair correlation of the nearest-neighbor Eu spins, likely via the variation of the soft-phonon-mode frequency.

Patent
28 Jun 2001
TL;DR: The use of these nitrate-based precursors is well suited to forming high dielectric constant materials on hydrogen passivated silicon surfaces, such as nanolaminates of hafnium oxide and zirconium oxide.
Abstract: Methods of forming hafnium oxide, zirconium oxide and nanolaminates of hafnium oxide and zirconium oxide are provided. These methods utilize atomic layer deposition techniques incorporating nitrate-based precursors, such as hafnium nitrate and zirconium nitrate. The use of these nitrate based precursors is well suited to forming high dielectric constant materials on hydrogen passivated silicon surfaces.

Journal ArticleDOI
TL;DR: In this paper, the growth and properties of both epitaxial and amorphous films of Gd2O3 (κ=14) and Y2O 3 (κ = 18) as the alternative gate dielectrics for Si were presented.
Abstract: We present the materials growth and properties of both epitaxial and amorphous films of Gd2O3 (κ=14) and Y2O3 (κ=18) as the alternative gate dielectrics for Si. The rare earth oxide films were prepared by ultrahigh vacuum vapor deposition from an oxide source. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single domain films in the Mn2O3 structure. Compared to SiO2 gate oxide, the crystalline Gd2O3 and Y2O3 oxide films show a reduction of electrical leakage at 1 V by four orders of magnitude over an equivalent oxide thickness range of 10–20 A. The leakage of amorphous Y2O3 films is about six orders of magnitude better than SiO2 due to a smooth morphology and abrupt interface with Si. The absence of SiO2 segregation at the dielectric/Si interface is established from infrared absorption spectroscopy and scanning transmission electron microscopy. The amorphous Gd2O3 and Y2O3 films withstand the high temperature anneals to 850 °C and remain electrically and chemically intact.

Journal ArticleDOI
TL;DR: In this paper, a series of molecular dynamics simulations of aqueous NaCl and KCl solutions at different concentrations, ranging from 0 M to 4.5 M, were performed to investigate the effects of ion concentration on the single-particle, pair, and collective dynamical properties of an electrolyte solution.
Abstract: We have performed a series of molecular dynamics simulations of aqueous NaCl and KCl solutions at different concentrations, ranging from 0 M to 4.5 M, to investigate the effects of ion concentration on the single-particle, pair, and collective dynamical properties of aqueous electrolyte solutions. The SPC/E model is used for water and the ions are modeled as charged Lennard-Jones particles. The single-particle dynamics is investigated by calculating the self-diffusion coefficients of ions and water molecules and also the orientational relaxation times. The pair dynamics is studied by evaluating the ion–water residence and water–water hydrogen bond time correlation functions. The relaxation of relative velocity autocorrelation function and the cross velocity correlation function of two hydrogen bonded water molecules are also investigated at varying ion concentration. Finally, we explore the collective dynamical properties by calculating the frequency dependent dielectric function and conductivity. It is found that the self and relative diffusion coeffcients decrease and the orientational relaxation times increase with ion concentration. The residence times of water molecules near ions and also the structural relaxation time of water–water hydrogen bonds show an increasing trend as the ion concentration is increased. The dielectric relaxation time is found to decrease with ion concentration for the solutions investigated here. The static conductivity of concentrated solutions shows significant departure from the Nernst–Einstein behavior due to formation of ion pairs. With an increase of frequency, the conductivity first increases substantially and then decreases at very high frequency. The initial increase of conductivity is attributed to the disruption of ion pairs on application of high frequency electric fields.

Patent
31 Aug 2001
TL;DR: In this article, a method of forming a low dielectric constant interlayer interlayer Dielectric film on a substrate by reacting, under chemical vapor deposition conditions sufficient to deposit the film on the substrate, an organosilicon precursor comprising a silyl ether, a SilyL ether oligomer, or an organosailicon compound containing one or more reactive groups was proposed.
Abstract: A method of forming a low dielectric constant interlayer dielectric film on a substrate by reacting, under chemical vapor deposition conditions sufficient to deposit the film on the substrate, an organosilicon precursor comprising a silyl ether, a silyl ether oligomer, or an organosilicon compound containing one or more reactive groups, to form an interlayer dielectric film having a dielectric constant of 3.5 or less. The films formed by the above method.

Journal ArticleDOI
TL;DR: It is found that heat generation at off-resonance is caused mainly by dielectric loss tan /spl delta/' (i.e., P-E hysteresis loss), not by mechanical loss, and that a significant decrease in mechanical Q/sub m/ with an increase of vibration level was observed in resonant piezoelectric ceramic devices.
Abstract: Losses in piezoelectrics are considered in general to have three different mechanisms: dielectric, mechanical, and piezoelectric losses. This paper deals with the phenomenology of losses first, then how to measure these losses separately in experiments. We found that heat generation at off-resonance is caused mainly by dielectric loss tan /spl delta/' (i.e., P-E hysteresis loss), not by mechanical loss, and that a significant decrease in mechanical Q/sub m/ with an increase of vibration level was observed in resonant piezoelectric ceramic devices, which is due to an increase in the extensive dielectric loss, not in the extensive mechanical loss. We propose the usage of the antiresonance mode rather than the conventional resonance mode, particularly for high power applications because the mechanical quality factor Q/sub B/ at an antiresonance frequency is larger than Q/sub A/ at a resonance frequency.

Journal ArticleDOI
TL;DR: In this paper, the authors reported the ferroelectric and electromechanical properties of poly(vinylidene-fluoride-trifluoroethylene-chlorotrifluorethylene) terpolymer, which exhibits a slim polarization hysteresis loop and a high electrostrictive strain at room temperature.
Abstract: This letter reports the ferroelectric and electromechanical properties of a class of ferroelectric polymer, poly(vinylidene-fluoride–trifluoroethylene–chlorotrifluoroethylene) terpolymer, which exhibits a slim polarizationhysteresis loop and a high electrostrictive strain at room temperature. The dielectric and polarization behaviors of this terpolymer are typical of the ferroelectric relaxor. The x-ray and Fourier transform infrared results reveal that the random incorporation of bulky chlorotrifluoroethylene (CTFE) ter-monomers into polymer chains causes disordering of the ferroelectric phase. Furthermore, CTFE also acts as random defect fields which randomize the inter- and intrachain polar coupling, resulting in the observed ferroelectric relaxor behavior.

Journal ArticleDOI
TL;DR: The dielectric constant of water confined in a nanodimensional spherical cavity is calculated by means of molecular dynamics simulations as mentioned in this paper by using two different water models: soft sticky dipole and simple point charge/extended.
Abstract: The dielectric constant of water confined in a nanodimensional spherical cavity is calculated by means of molecular dynamics simulations The simulations are carried out by using two different water models: soft sticky dipole and simple point charge/extended Three different sizes of the confining cavity are considered for each water model For both the models, the dielectric constant of water in the cavity is found to be significantly smaller than that of bulk water A nearly 50% decrease of the dielectric constant is observed when water is confined in a cavity of about 12 A in diameter In the present models, there is no electrostatic interaction between water and the cavity surface, and thus, the reduction of the dielectric constant observed in this study is purely a result of confinement

Patent
11 Sep 2001
TL;DR: In this paper, a high-k dielectric material is sandwiched between two layers of aluminum oxide or lanthanide oxide in the formation of a transistor gate or memory cell.
Abstract: An ultrathin aluminum oxide and lanthanide layers, particularly formed by an atomic layer deposition (ALD) type process, serve as interface layers between two or more materials. The interface layers can prevent oxidation of a substrate and can prevent diffusion of molecules between the materials. In the illustrated embodiments, a high-k dielectric material is sandwiched between two layers of aluminum oxide or lanthanide oxide in the formation of a transistor gate dielectric or a memory cell dielectric. Aluminum oxides can serve as a nucleation layer with less than a full monolayer of aluminum oxide. One monolayer or greater can also serve as a diffusion barrier, protecting the substrate from oxidation and the high-k dielectric from impurity diffusion. Nanolaminates can be formed with multiple alternating interface layers and high-k layers, where intermediate interface layers can break up the crystal structure of the high-k materials and lower leakage levels.

Journal ArticleDOI
TL;DR: In this article, a series of BaTiO3/monomer suspensions were photocured into thin wafers, and the dielectric permittivity of the composites was investigated at frequencies from 100 Hz to 10 GHz and at temperatures from −140 to +150 °C.
Abstract: Dielectric properties of model BaTiO3/polymer composites were measured over a broad frequency and temperature range. A series of BaTiO3/monomer suspensions were photocured into thin wafers. The wafers were equipped with aluminum electrodes, and the dielectric permittivity of the composites was investigated at frequencies from 100 Hz to 10 GHz and at temperatures from −140 to +150 °C. It has been found that for the same BaTiO3 loading dielectric characteristics of the composites strongly depend of the type of polymer. Polar polymers increase dielectric constant of the composites at low frequencies but have little effect at gigahertz frequencies. Dielectric losses of the composites show a maximum at some intermediate frequency within megahertz to gigahertz range that reflects the relaxation behavior of the polymer matrix. The magnitude of the losses increases with increasing polarity of the polymer component. At constant frequency and temperature, the composites follow a linear relationship between logarith...

Journal ArticleDOI
TL;DR: In this paper, carbon-doped oxide materials (SiCOH films) with ultralow dielectric constants have been prepared by plasmaenhanced chemical vapor deposition (PECVD) from mixtures of SiCOH precursors with organic materials.
Abstract: Carbon-doped oxide materials (SiCOH films) with ultralow dielectric constants have been prepared by plasma-enhanced chemical vapor deposition (PECVD) from mixtures of SiCOH precursors with organic materials. The films have been characterized by Rutherford backscattering and forward recoil elastic scattering analysis, Fourier transform infrared spectroscopy and index of refraction measurements, and measurement of step heights in the films. The electrical properties of the films have been measured on metal–insulator–silicon structures. By proper choice of the precursor and deposition conditions, the dielectric constants of the SiCOH films can be reduced to values below 2.1, demonstrating the extendibility of PECVD-prepared carbon-doped oxides as the interconnect dielectrics for future generation of very large scale integrated chips.

Journal ArticleDOI
TL;DR: The dielectric properties of ten rat tissues at six different ages were measured using an open-ended coaxial probe and a computer controlled network analyser to provide some insight into possible differences in the assessment of exposure for children and adults.
Abstract: The dielectric properties of ten rat tissues at six different ages were measured at 37 °C in the frequency range of 130 MHz to 10 GHz using an open-ended coaxial probe and a computer controlled network analyser. The results show a general decrease of the dielectric properties with age. The trend is more apparent for brain, skull and skin tissues and less noticeable for abdominal tissues. The variation in the dielectric properties with age is due to the changes in the water content and the organic composition of tissues. The percentage decrease in the dielectric properties of certain tissues in the 30 to 70 day old rats at cellular phone frequencies have been tabulated. These data provide an important input in the provision of rigorous dosimetry in lifetime-exposure animal experiments. The results provide some insight into possible differences in the assessment of exposure for children and adults.

Journal ArticleDOI
TL;DR: In this article, the authors explore the theory of thin-film low-macroscopic-field (LMF) electron emitters, starting from the need to understand the behaviour of emitters based on amorphous carbon films.
Abstract: Thin flat dielectric films can be low-macroscopic-field (LMF) electron emitters, able to generate electrons when subject to a macroscopic electric field in the range 1–50 V μm −1 . This phenomenon is a known cause of pre-breakdown currents in high-voltage vacuum breakdown, and is now the basis of a broad-area electron-source technology, using carbon-based thin films and other materials. The phenomenon occurs because the dielectric film is, or becomes, an electrically nanostructured heterogeneous (ENH) material, with quasi-filamentary conducting channels between its surfaces. These channels connect to emitting features near or on the film/vacuum surface, or act as electron emitters themselves. The film may contain conducting or semiconducting particles that assist with conductivity and/or act as emitting features. Several forms of thin-film LMF emitter exist: in each case the situation geometry ensures that sufficient field enhancement occurs at the ‘tip’ of the emitting feature for the emission process to be some form of tunnelling field electron emission (probably ‘cold’ in some cases, ‘hot’ in others). This paper explores aspects of the theory of thin-film LMF emission, starting from the need to understand the behaviour of emitters based on amorphous carbon films. A summary review, with extensive references, is given of relevant past work outside the immediate ‘carbon field emission’ context. Relevant aspects of semiconductor field emission theory are noted. Comment is made on the original experiments on diamond field emission, and on theoretical misconceptions in the carbon field emission literature. Analysis of carbon-film emitter behaviour suggests that emission must primarily be due to geometrical field enhancement, that in at least some cases arises from conducting nanostructure inside the film. In one case, published film characteristics can be used to show that sufficient field enhancement should be available. Some problems with an ‘internal field enhancement’ hypothesis are considered and disposed of. Difficulties with Latham’s theory of field-induced emission from ENH materials are pointed out: a new theory, largely qualitative at this stage, can explain longstanding problems: this assumes that dielectric films must be treated as ‘hopping conductors’ not semiconductors. Electron emission takes place via localised surface states: transition to a channel-limited current regime takes place when the surface states no longer have high enough occupation probability to screen the external field, and is accompanied by anomalous band bending at the channel tip. Mathematical theories of band bending and field emission for hopping conductors are required. Some consequences for the design of LMF emitters are noted.

Journal ArticleDOI
TL;DR: In this article, available data on microwave absorbing materials finding engineering applications or potentially attractive for use in dielectric, magnetic, and ferroelectric-seignettomagnetic absorbers are summarized.
Abstract: Available data on microwave absorbing materials finding engineering applications or potentially attractive for use in dielectric, magnetic, and ferroelectric–seignettomagnetic absorbers are summarized.

Journal ArticleDOI
TL;DR: In this paper, the structures, morphologies, and dielectric properties of thin films with two compositions, Bi1.5Zn0.5 and Bi2(Zn1/3Nb2/3)2O7, were investigated.
Abstract: Bi2O3–ZnO–Nb2O5 pyrochlore thin films were prepared on platinum coated Si wafers using a metalorganic deposition process. The structures, morphologies, and dielectric properties of films with two compositions: (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 and Bi2(Zn1/3Nb2/3)2O7, were investigated. Thin films of (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 have a cubic pyrochlore phase when crystallized at 550 °C or higher. The crystal structure of Bi2(Zn1/3Nb2/3)2O7 thin films was dependent on the firing temperature; the films showed the cubic pyrochlore phase at temperatures below 650 °C, and a pseudo-orthorhombic pyrochlore structure at 750 °C. A mixture of cubic and pseudo-orthorhombic structures was found in thin films crystallized at 700 °C. (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 films fired at 750 °C had a dielectric constant of ∼150 and a negative temperature coefficient of capacitance of −400 ppm/°C. Bi2(Zn1/3Nb2/3)2O7 thin films fired at 750 °C had a smaller dielectric constant of ∼80 and a positive temperature coefficient of capacitance of 150...

Patent
06 Mar 2001
TL;DR: In this paper, a graded gate dielectric is provided, even for extremely thin layers, whereby the composition of the film can be varied from monolayer to monollayer during cycles including alternating pulses of self-limiting chemistries.
Abstract: Thin films are formed by atomic layer deposition, whereby the composition of the film can be varied from monolayer to monolayer during cycles including alternating pulses of self-limiting chemistries. In the illustrated embodiments, varying amounts of impurity sources are introduced during the cyclical process. A graded gate dielectric is thereby provided, even for extremely thin layers. The gate dielectric as thin as 2 nm can be varied from pure silicon oxide to oxynitride to silicon nitride. Similarly, the gate dielectric can be varied from aluminum oxide to mixtures of aluminum oxide and a higher dielectric material (e.g., ZrO 2 ) to pure high k material and back to aluminum oxide. In another embodiment, metal nitride (e.g., WN) is first formed as a barrier for lining dual damascene trenches and vias. During the alternating deposition process, copper can be introduced, e.g., in separate pulses, and the copper source pulses can gradually increase in frequency, forming a graded transition region, until pure copper is formed at the upper surface. Advantageously, graded compositions in these and a variety of other contexts help to avoid such problems as etch rate control, electromigration and non-ohmic electrical contact that can occur at sharp material interfaces.

Journal ArticleDOI
TL;DR: In this article, a general model for calculating the static dielectric constant of mixed-solvent electrolyte solutions is developed for mixtures of solvents without electrolyte components, based on an empirical modification of the Kirkwood theory for multicomponent systems.