Time Dependence Of Voltage Shift Research Articles

Multilevel current stress technique for investigation thin oxide layers of MOS structures

In this study, a new technique of multilevel current stress for investigation thin oxide layers of MOS structures is proposed. This technique allows to investigate the generation and relaxation of positive and negative charges, accumulating in, nano-thickness gate dielectric of MOS structures under many stressing situations. The parameters characterizing the change of charge state in the thin oxide layers of MOS structures during the stress have been monitored by means of time dependence of voltage shift applied to a sample during the injection. The method takes into account the process of the MOS capacitance charging by the constant current pulse. In comparison with the conventional techniques our method is nondestructive and enables to reduce the high-field stress time while measuring the injection current-voltage characteristics of the MOS-structure. We consider this method to provide higher accuracy and to decrease the probability of dielectric breakdown. The application of present technique was carr mied out during the investigation of charge generation and relaxation, during and after high-field tunnel injection of electrons in thin thermal film of SiO2. The thin oxide layers of MOS structures after plasma and irradiation treatments also are investigated.

MODELING OF TRAPPING INDUCED THRESHOLD VOLTAGE SHIFT DEPENDENCY ON A TIME-VARYING GATE BIAS IN THIN-FILM TRANSISTORS

The author has developed a discrete model for simulation to calculate the threshold voltage (VT) shift caused by charge trapping and detrapping in a thin film transistor (TFT) under a time-varying bias. The model divides continuous states into discrete states and simplifies tunneling among the discrete states to keep track of their occupancies. The simulation is carried out for a TFT that has traps in the gate dielectric uniformly distributed perpendicular to the semiconductor/dielectric interface and the results account for the stretched-exponential time dependence of VT shift.

Modification of metal-oxide-semiconductor devices by electron injection in high fields

The modification of metal-oxide-semiconductor (MOS) devices having Si/SiO 2/phosphosilicate glass/Al structure by Fowler–Nordheim (FN) tunnelling electron injection taking place in high fields is studied. The constant current FN electron injection from silicon substrate and metal electrode was used to modify the charge state of the MOS structure. The parameters characterizing the change of charge state in the MOS structures during the modification have been monitored by means of time dependence of voltage shift applied to a sample during the injection. It was found that the changes in the range of threshold voltage in MOS devices, which resulted from the electron injection, could reach values up to 6 V, while the range is extended with the growth of the concentration of phosphorus in the PSG layer. However, the value of the injected charge must not exceed the level of 0.1 mC/cm 2 during the adjustment of the threshold voltage, so as to provide acceptable surface state density.