Reducing the edge deformation of thin electrical steel sheet

The edge deformation of cold-rolled electrical-steel sheet in finishing is studied, as well as the change in flatness of the sheet in rolling and heat treatment. The influence of these processes on the edge deformation is determined. The edge deformation is largely due to thermal deformation occurring when coils of strip are heated in cupola furnaces. Quantitative analysis indicates that the thermal deformation is due to the temperature gradients in the coils. Cold-rolling conditions that minimize edge deformation are proposed and tested.     

Formation of internal structure in the rolling of a bcc (110)[001] single crystal

The stages of structure formation during cold rolling are investigated in bcc (110)[001] single crystals of Fe–3% Si alloy, within the deformation zone. To obtain a visible deformation zone, the laboratory mill is abruptly stopped at the instant of sample rolling. To reduce the frictional coefficient, lubricant is used for some of the samples. The deformational structure is studied by metallography and orientational electron microscopy (EBSD). Deform-3D software is used to analyze the relation between the experimental data and the calculated stress state in rolling, for various values of the frictional coefficient. Depending on the frictional coefficient, the stress state may significantly affect the mesostructure formation and the texture development. In a single crystal rolled with elevated friction, when the deformation is relatively small, deformation bands are formed. Orientational analysis of the contact point of deformation bands reveals alternating microbands, each with slight different orientation, which are separated by small-angle boundaries. In the rolling of a (110)[001] single crystal with lubrication (reduced friction), twinning is observed even with slight deformation. The twinning is evidently due to the reduced contribution of surface energy to the total energy of twin nucleation. Throughout the whole deformation process, either the twins of both systems retain the strict Σ3 crystallographic relation with the matrix or else, on account of the local lattice reorientation, Σ3 disorientations are converted to similar special Σ17b and Σ43c disorientations. On the basis of experimental data, a dislocation model is proposed for the formation of deformational mesostructures in the cold rolling of a (110)[001] single crystal. This model includes the formation of microbands in the initial stage of deformationband generation; the formation of transition bands parallel to the rolling plane with the dynamic retention of the initial orientation; and the formation of transition bands inclined to the rolling plane with a habitus parallel to the {112} matrix plane. These inclined planes are equivalent to shear bands whose habitus is inclined at ~17° to the rolling plane.     

The Effect of Electroactive Defects in the Gate Oxide on the Threshold Voltage of a Submicron MOS Transistor

A new mechanism underlying the effect of the gate oxide geometry on the threshold voltage and other electrical properties of an MOS transistor (MOST) is proposed. This mechanism includes a relationship between the ionized center concentration in the gate oxide and its length. The dependence of the charge on these centers on the gate oxide configuration is associated with hydrogen redistribution between the gate and side oxide layers, as well as with the superposition of the ionized center distributions in the oxide layer along its horizontal and vertical boundaries in the peripheral drain and source contact windows. The revealed strong dependence of the charge density of the ionized centers in the oxide layer on the gate configuration (up to charge polarity reversal) specifies the strong dependence of the threshold voltage on the configuration of the gate and side oxide layers.     

Radical Modification of Gate Oxide by Lateral Gettering of Electroactive Centers

An approach to radically modifying gate dielectric by laterally gettering electroactive defects (centers) is suggested. Gettering of the ionized centers is accomplished through intentionally creating structure defects in the surface layers of the side oxide that are adjacent to the periphery of the gate oxide. The process was carried out at low temperatures, e.g., during postmetallization annealing in a hydrogen-free atmosphere. The structure defects in the side oxide capture excessive hydrogen, which otherwise produces ionized donors in the gate oxide layer. If the gate size is comparable to the hydrogen diffusion length (5–10 m), ionized acceptor centers of concentration no more than 10¹¹ cm^–2 dominate in the gate oxide after annealing. This is apparently related to the minimization of excessive hydrogen content in the gate oxide of structures with small lateral dimensions.     

Electroactive Centers at the Outer Interface of an Ultrathin Oxide Layer and Their Effect on the Electrical Performance of Single-Crystal Silicon/Noncrystalline Oxide/Polysilicon Structures

Single-crystal silicon/noncrystalline ultrathin oxide multilayer structures were investigated. The oxide was formed by (100)Si thermal oxidation. An undoped polysilicon layer with an aluminum contact was used as a gate. The distribution of ionized electroactive centers (defects) in the ultrathin oxide and the energy spectrum of the centers at the oxide interfaces and near the polysilicon surface were considered. It was found that the centers at the outer interface of the oxide affect the electrical performance of the multilayer structures.