Showing papers on "Field effect published in 1997"

Ferroelectric Field Effect Transistor Based on Epitaxial Perovskite Heterostructures

Abstract: Ferroelectric field effect devices offer the possibility of nonvolatile active memory elements. Doped rare-earth manganates, which are usually associated with colossal magnetoresistive properties, have been used as the semiconductor channel material of a prototypical epitaxial field effect device. The carrier concentration of the semiconductor channel can be "tuned" by varying the manganate stochiometry. A device with La0.7Ca0.3MnO3 as the semiconductor and PbZr0.2Ti0.8O3 as the ferroelectric gate exhibited a modulation in channel conductance of at least a factor of 3 and a retention loss of 3 percent after 45 minutes without power.

Field effect devices and capacitors with improved thin film dielectrics and method for making same

Abstract: In accordance with the invention an electronic device is provided with a thin film dielectric layer of enhanced reliability. The dielectric comprises a thin film of silicon oxide having maximum concentrations of nitrogen near its major interfaces. In a field effect device, the maximum adjacent the gate enhances resistance to penetration of dopants from the gate. The secondary maximum near the channel enhances resistance to current stress. The maximum near the channel is preferably displaced slightly inward from the channel to minimize effects on carrier mobility.

Ferroelectric field effect in ultrathin SrRuO3 films

Abstract: We report the observation of a ferroelectric field effect in the conducting oxide SrRuO3 using Pb(Zr0.52Ti0.48)O3/SrRuO3 epitaxial heterostructures. Upon reversing the polarization of the ferroelectric Pb(Zr0.52Ti0.48)O3 layer, we measured a 9% change in the resistance of a nominally 30 A SrRuO3 film at room temperature. This change was nonvolatile for a period of several days. Conductivity measurements taken between 4.2 and 300 K are consistent with n-type conduction throughout this temperature range. Hall effect measurements also yield n-type conduction, with n≈2×1022 electrons/cm3, and furthermore allow us to understand quantitatively the magnitude of the observed resistivity change.

Single-chip fused hybrids for acousto-electric and acousto-optic applications

Abstract: The combination of the electronic and optical properties of a semiconductor hetero-junction and the acoustic properties of a piezoelectric substrate material yields a new class of very promising hybrids for potential acousto-electric and acousto-optic applications. LiNbO3/GaAs hybrids have been fabricated using the epitaxial lift-off technique resulting in unusually large acousto-electric and acousto-optic interaction between the quasi two-dimensional electron system in the semiconductor and surface acoustic waves on the piezoelectric substrate. Field effect tunability of the interaction at room temperature is demonstrated and possible device applications are discussed. Photoluminescence measurements show the influence of the acousto-electric fields on the optical properties of quantum well structures.

Field-effect-induced gas sensitivity changes in metal oxides

Abstract: The sensitivity of micromachined gas sensor elements with respect to CO, NO, NO2, CH4, H2O and oxygen partial pressure changes was investigated. The microsensors consisted of thin films of RGTO-SnO2 deposited on top of resistively heated Si3N4 membranes. The electrical insulation between the Pt heater and SnO2 sensing layer circuits was provided by a thin dielectric layer. Applying a bias voltage across this layer, field-effect-induced changes in the gas sensing properties could be studied. We find that bias voltage changes can be used to systematically modify the cross-sensitivity of identically prepared sensor elements. These results are relevant for the realisation of monolithically integrated gas sensor arrays.

Evaluation of Electrical Properties of Evaporated Thin Films of Metal-Free, Copper and Lead Phthalocyanines by In-Situ Field Effect Measurements.

Abstract: We have fabricated thin-film transistors consisting of evaporated thin films of metal-free, copper and lead phthalocyanines, and estimated the electrical parameters of carrier mobility, carrier concentration and electrical conductivity by in-situ field effect measurements. We have also investigated the effect of introducing of oxygen gas into the vacuum chamber and of thermal annealing on the electrical parameters of the films. We found that the carrier concentration and carrier mobility are strongly influenced by the metals in the phthalocyanine molecules and by oxygen gas exposure.

Dielectric and field-induced strain behaviour of (Pb1−xBax) ZrO3 ceramics

Abstract: The effects of Ba2+ substitution on the dielectric properties and induced strain behaviour of the (Pb1−xBax) ZrO3 ceramics (0.05≤x≤0.3) have been investigated as a function of x. A new phase diagram of the (Pb1−xBax) ZrO3 system, indicating the field effect on the phase transition, is also presented. As the Ba2+ content increases, the Curie temperature decreases linearly, whereas maximum dielectric constant increases for up to 20 mol% Ba2+ addition, and then decreases with further Ba2+ addition. Based on the hysteresis loops, the temperature range of the ferroelectric phase as an intermediate phase between the antiferroelectric and paraelectric phases, increases with increasing electric field and Ba2+ content. The ferroelectric loops are induced at room temperature for the specimens containing above 10 mol% Ba2+ by applying an electric field up to ∼25 kV cm−1. However, for the 5 mol% Ba2+-substituted specimen, no ferroelectric loop is induced, even with applied fields up to 55 kV cm−1. The phase transition due to electric field and Ba2+ addition is also confirmed by the measurement of the field-induced longitudinal strain.

Gallium nitride junction field-effect transistor

Abstract: An all-ion implanted gallium-nitride (GaN) junction field-effect transistor (JFET) and method of making the same. Also disclosed are various ion implants, both n- and p-type, together with or without phosphorous co-implantation, in selected III-V semiconductor materials.

Microscopic theory of the intracollisional field effect in semiconductor superlattices

Abstract: A detailed analysis of the optical and transport properties of semiconductor superlattices in the high-field regime is presented. Electronic Bloch oscillations and the resulting terahertz emission signals are computed including phonon damping in the presence of the electric field. The modifications of the phonon-induced terahertz signal decay are analyzed including the movement of the carriers in the field (intracollisional field effect). For elevated fields it is shown that the interplay between electric field and electron-phonon interaction leads to resonance structures in the terahertz damping rate.

Semiconductor non-volatile memory device and manufacture thereof

Abstract: PROBLEM TO BE SOLVED: To enable a semiconductor non-volatile memory device to be lessened in operating voltage such as an erase voltage by a method wherein a field effect memory transistor possessed of a charge storage layer is provided between a control gate and a channel forming region in a semiconductor layer. SOLUTION: A floating gate 32a has a function to retain electrical charge in a film, and a tunnel insulating film 22a and an intermediate insulating film 23a serve to confine electrical charge in the floating gate 32a. A proper potential is applied to a control gate 32a and a source drain diffusion layer inside a semiconductor layer 31b, whereby a Fowler Nordheim tunnel current is generated, and electrons are injected from the semiconductor layer 31b into the floating gate 32a through the tunnel insulating film 22a or electrons are discharged from the floating gate 32a into the semiconductor layer 31b. When charge is accumulated in the floating gate 32a, an electrical field is generated by the accumulated charge, so that a transistor is changed in threshold voltage to store data.

Field-Effect Mobility of Molecularly Doped Poly(3-hexylthiophene)

Abstract: Thin film field-effect transistors (TFTs) utilizing poly(3-hexylthiophene) (PAT6) doped with the electron transporting molecule N,N'-bis(2,5-di- tert -butylphenyl)-3,4,9,10-perylene dicarboximide (BPPC), have been fabricated and characterized. Bipolar transport characteristics have been found in these TFTs, for which the mobilities of both the hole and the electron have been evaluated. Observed unique BPPC concentration dependence of the field-effect electron mobilities has been interpreted in terms of the percolation model.

Charge Transport in Thin Organic Semiconducting Films: Seebeck and Field Effect Studies

Abstract: We have investigated the charge transport properties of vapor-deposited thin organic films, using the Seebeck effect for determining conduction type and Fermi energy and the field effect to measure mobility and total charge carrier density. We show that the combination of both techniques gives a complete picture of the electrical properties of the films.

Electrical AC loss measurements in superconducting coils

Abstract: Electromagnetic losses occur in superconducting wires when they are exposed to time-varying fields or currents. The total losses are the sum of the hysteresis component, the coupling currents in the resistive matrix, the self field effect... In order to separate these different contributions, an electrical measurement method has been developed. The self field effect signal is analysed in LTc multifilamentary superconducting wires. The influence of the current wave shape (sinusoidal, triangular) is shown, To compare the loss mechanisms in HTS, a high temperature superconducting Bi coil has been studied. As for LTc material, they seem to be governed by the self field effect, but the eddy currents are no longer negligible and may be predominant at high frequencies.

Characterization of the electrical properties of semimetallic Bi films by electrical field effect

Abstract: The electrical field effect (EFE) was used to investigate and to characterize the electrical properties of Bi films The samples were prepared in a capacitor configuration with Al as the gate electrode, Al2O3 as the dielectric and the thin (∼1300 A) thermal-evaporation deposited Bi film sample serving as the other electrode The dependence of EFE on the electrical field (up to electrical displacements ∼107 V/cm or ≈1013[e]/cm2 “surface” charge) and on temperature (15–300 K), and also the temperature dependence of Hall constant, were determined The experimental results are shown to be consistent with the EFE theory of a semimetal film, assuming that: (1) the film has an interface “dead layer” (∼600 A) that does not contribute markedly to EFE due to its extremely low carrier mobilities Only in the rest, “good” part of the film, the electroconductivity is modulated and leads to a measurable EFE; (2) the temperature behavior of EFE follows the temperature dependence of the electron and hole mobilities and i

Ferroelectric field effect in (La,Sr)CoO3/Pb(Zr,Ti)O3/(La,Sr)CoO3 heterostructures

Abstract: Epitaxial LaCoO3/Pb(Zr,Ti)O3/(La,Sr)CoO3 (LSCO) heterostructures have been grown on LaAlO3 by pulsed laser deposition for investigating ferroelectric field effect. In the heterostructure, semiconducting LaCoO3 was used as a conducting channel layer, instead Si. The resistivity of the LaCoO3 (LCO) channel layer was found to be dependent on an oxygen ambient, primarily the ambient oxygen pressure during deposition. The resistivity of the LCO layer varied in the range of 0.1 – 100 Ω cm. Ferroelectric field effect induced in LaCoO3 layer was observed by measuring the resistance modulation of the LCO layer with respect to the polarized state of the PZT layer. The resistance modulation of 9% was obtained in the 680 A thick LCO layer. Further the resistance modulation was improved up to 45% after applying dc bias. It is suggested that the LCO/PZT/LSCO heterostructure can be used as a ferroelectric field effect transistor.

Theoretical study of hyperpolarizabilities in crystalline m-nitroaniline

Abstract: A variational−perturbation method in terms of molecular orbitals (MOs) has been developed to study the effect of a permanent crystal field on hyperpolarizability (β) in van der Waals organic crystals. The method has the advantage of giving a numerical value of the dipole moment for each fragment molecule in a weakly interacting system with an accuracy comparable to the supermolecule method. Our method has been applied to a m-nitroaniline molecule in different model crystal environments to analyze the crystal field effect on the β-values. The results indicate that the crystal field induces the intramolecular charge transfer (CT) of the π-electrons from an NH2 group to a NO2 group in the highest occupied MO while the lowest unoccupied MO almost remains unchanged. From a net atomic charge analysis, the CT will be derived from the reversed polarization of the σ-electrons due to the polarized π-electrons and it will then contribute to the enhancement of the βx-value additively (βadd). The effect of the differe...

Electric field effect in (BiPb)2Sr2Ca2Cu3Ox superconductor bars

Abstract: An experimental study has been made of the electric field effect in an electrode/insulator/superconductor system on the critical current ( I c ) and the current-voltage ( I – V ) characteristics at 77 K of large, c-axis-textured (BiPb) 2 Sr 2 Ca 2 Cu 3 O x superconductor bars. In strong electric fields (120 MV/m), the current and conductivity of bars at current I > I c increased. The electric field effect was reversible and was observed in various field orientations with respect to the pressing direction of the bars. New peculiarities of the field effect were observed in the presence of current-voltage hysteresis.

Back contact effects on junction photoluminescence in CdTe/CdS solar cells

Abstract: Studies of junction photoluminescence in CdTe/CdS solar cells reveal that back-contact application produces a dramatic qualitative change in the junction PL spectrum. Prior to contact application, the spectrum has two peaks at energies of 1.508 eV and 1.45 eV, corresponding to recombination in bulk CdTe, and in a CdTeS alloy with 9% sulfur content, respectively. After contact application, the spectrum consists of a single broad peak at 1.48 eV. Previous studies have shown that the nitric-phosphoric (NP) etch used in the contact procedure produces a layer of elemental Tellurium (Te) on the CdTe surface. The authors' measurements utilizing Auger electron spectroscopy (AES) show that this Te layer penetrates grain boundaries down to the CdTe/CdS interface. It appears that the change in the near-junction PL spectrum is caused by a "grain boundary field effect" due to perturbations of the grain boundary conductivity and Fermi level.

Near-intrinsic microcrystalline silicon for use in thin-film transistors

Abstract: Inverted-staggered thin film transistors (TFTs) incorporating hydrogenated microcrystalline silicon for both contact and channel regions have been fabricated by plasma enhanced chemical vapour deposition (PECVD) using the high hydrogen-dilution method. The deposition parameters for the channel region were chosen to yield near-intrinsic material with a dark conductivity activation energy of 0.7 eV and a Tauc gap of 1.98 eV, while the doped contact layer was optimised to produce a high dark conductivity of 10 S/cm. These devices exhibit a low off-current but the field effect mobility is found to be lower than that of similar devices incorporating an optimised amorphous silicon channel region. The mobility activation energy in these devices is similar to those incorporating an amorphous channel, but the mobility pre-factor is reduced. We propose that this is due to inhomogeneous conduction through a microcrystalline region with a smaller grain size at the dielectric/channel interface.

Field-effect trap-level-distribution model of dynamic random access memory data retention characteristics

Abstract: Dynamic random access memory data retention characteristics were investigated as a function of operating voltage. Based on a statistical process, called the trap-level-distribution model, which was proposed in our previous report, we further assumed that the junction leakage current by Shockley–Read–Hall process is enhanced by an electric field through the trap-assisted-tunneling process. We incorporated into the model two processes that cause variation in the electric field at the traps; the variation of electric field itself and the spatial trap distribution. By comparing the Monte Carlo and analytical calculations with the experimental results, we found that the retention time distribution is not only caused by the energy level and spatial distributions of the traps, but by the space-charge-region field distribution among the cells. A possible origin of the field distribution is the variation of dopant profile among the junctions.

Method for manufacturing compound semiconductor field-effect transistors with improved DC and high frequency performance

Abstract: A method for making compound semiconductor devices including the use of a p-type dopant is disclosed wherein the dopant is co-implanted with an n-type donor species at the time the n-channel is formed and a single anneal at moderate temperature is then performed. Also disclosed are devices manufactured using the method. In the preferred embodiment n-MESFETs and other similar field effect transistor devices are manufactured using C ions co-implanted with Si atoms in GaAs to form an n-channel. C exhibits a unique characteristic in the context of the invention in that it exhibits a low activation efficiency (typically, 50% or less) as a p-type dopant, and consequently, it acts to sharpen the Si n-channel by compensating Si donors in the region of the Si-channel tail, but does not contribute substantially to the acceptor concentration in the buried p region. As a result, the invention provides for improved field effect semiconductor and related devices with enhancement of both DC and high-frequency performance.

Field-effect type photoelectric energy converter

Abstract: PROBLEM TO BE SOLVED: To increase an electric field in a semiconductor in the vicinity of a ferroelectric, and to inhibit the recombination of an electron-hole pair generated by light by forming a comb-shaped electrode and a ferroelectric layer on a hydrogenated amorphous silicon layer. SOLUTION: A lower electrode 32 is formed onto a substrate 31, a p-type hydrogenated amorphous silicon layer 33, an i-type hydrogenated amorphous silicon layer 34 and an n-type hydrogenated amorphous silicon layer 35 are growm successively on the lower electrode 32. The hydrogenated amorphous silicon layers may also have n-i-p structure, and the hydrogenated amorphous silicon layers excepting the uppermost layer 35 may also have only i-p structure and i-n structure. Comb-shaped electrodes 36 are formed onto the n-type hydrogenated amorphous layers 35, and a ferroelectric layer 37 is grown on the electrodes 36. A transparent conductive film 38 as an upper electrode is formed onto a surface. According to such constitition, an electric field is induced to the hydrogenated amorphous silicon layer by the spontaneous polarization effect of the ferroelectric layer. Consequently, the recombination of electrons and holes is inhibited by the increase of the electric field induced by the spontaneous polarization effect of a ferroelectric.

Insulating gate field effect semiconductor device and method of manufacturing the same

Abstract: An insulating gate field effect semiconductor device having a gate insulating film of high resistance to moisture adsorption, wherein trap densities in the gate insulator film and at the interface between a channel semiconductor film and the gate insulator film are lowered, and causing no degradation of device characteristics and no lowering of reliability are caused. A SiO 2 film including fluorine atoms is used as the gate insulator film to compensate defects in the gate insulator film and at the interface between the channel semiconductor film and the gate insulator film.

An investigation of conduction mechanisms at high-field in PET

Abstract: The high-field electrical conduction, up to 60 kV/mm, of PET films is investigated in this paper. The behavior of time-to-peak, observed in transient charging current, vs electrical field fits well with the SCLC model, showing a power relationship. An exponential law is obtained between time-to-peak and temperature. Steady state regime provides charging-current density vs. electrical field plots which show clear transition from an ohmic behavior, at low field, to the SCLC mechanism. The threshold for this transition is a function of temperature.

Manufacture of field emission electron source

Abstract: PROBLEM TO BE SOLVED: To provide a field emission electron source which can provide high electric current density. SOLUTION: A conductive projected fine structure 3 is formed on the surface of an electrode 2 formed on the surface of a substrate 1 and an electrode layer 6 to be a gate is formed in the peripheral area through an insulating layer 5. A plurality of projected parts 4 to be a cold cathode are formed in the surface of the projected fine structure 3. Positive voltage is applied to the cathode and to the gate electrode, a large quantity of electrons are emitted out of the tip parts of a plurality of the projected parts 4 due to the field effect.