M. A. Exarchos

Effect of space charge polarization in radio frequency microelectromechanical system capacitive switch dielectric charging

The letter presents the investigation of the temperature dependence of the charging mechanism of dielectric layer in radio frequency microelectromechanical system switch. The accumulated charge kinetics are monitored through the transient response of device capacitance when a bias greater than pull-in is applied. The capacitance transient response is shown to follow a stretched exponential law. The “time scale” of the stretched exponential process is found to be thermally activated, with an activation energy that is determined from Arrhenius plot.

Charging of Radiation Induced Defects in RF MEMS Dielectric Films

The paper investigates the charging of radiation induced defects in Si3N4 and SiO2 dielectric films, which are used in RF-MEMS switches. The radiation has been performed with 5MeV alpha particles. The assessment has been carried out in Metal-Insulator-Metal capacitors with the thermally stimulated depolarization currents and discharge current transient methods. This allowed monitoring the defects introduction as a function of radiation fluence. The defects electrical characteristics that are the activation energy and corresponding depolarization time constant were determined from the evolution of the thermally stimulated current spectra and the transient response of discharge currents at different temperatures.

Investigation of charging mechanisms in Metal-Insulator-Metal structures

In this paper we have investigated the temperature dependence of the charging effects in Metal-Insulator-Metal structures, aiming to obtain a better insight on the charging mechanism of RF-MEMS switch insulating layer. The accumulated charge kinetics have been monitored through the transient response of the depolarization current. The transient response is shown to follow rather a stretched exponential law. The time scale of the process is found to be thermally activated with activation energy determined by Arrhenius plot. The results have been compared to thermally stimulated depolarization current assessment.

An experimental study of the thermally activated processes in polycrystalline silicon thin film transistors

The thermally activated mechanisms that determine the electrical properties of polycrystalline silicon thin film transistors have been investigated. The study employed devices fabricated on long grains and different thickness polycrystalline films, which were obtained by excimer laser annealing crystallization. The transfer and the transient characteristics have been recorded and analysed in the linear operation regime. The temperature dependence of basic parameters such as leakage current, subthreshold swing and drain current overshoot transient amplitude was found to stem from the same thermally activated carriers generation mechanism. The dependence of thermally activated mechanisms on the film thickness suggests that the device operation is strongly related to polycrystalline material properties.

RF MEMS sensitivity to electromagnetic radiation

Silicon dioxide and silicon nitride as well as other insulating materials are used in micro-electro-mechanical systems. However, their tendency for electrostatic charging diminishes the device reliability. The charging effect becomes significant when these devices are subjected to ionizing radiation. The irradiation induced charging depends on the nature of irradiation, the underlying metal layers and the metal-insulator interface properties. The sensitivity of RF micro-electromechanical systems to electromagnetic ionizing radiation is presented, taking into account the simulation of charge generation and the device structure.

Switch-on overshoot transient decay mechanism in polycrystalline silicon thin-film transistors

The present work investigates the switch-on transient decay in polycrystalline thin-film transistors. The decay is found to follow the stretched exponential relaxation model independently of the polycrystalline film properties and the device bias conditions or operating temperature. The temperature dependence of the stretched exponential relaxation allows for the determination of the decay time and, furthermore, the process activation energy.

Drain current overshoot transient in polycrystalline silicon transistors : The effect of hole generation mechanism

We have investigated the overshoot effect of switch-on transients of polycrystalline silicon thin-film transistors. The investigation has been performed with devices fabricated on laterally grown polycrystalline silicon films having very long crystal domains. These films were crystallized by excimer-laser annealing and had a thickness in the range of 30–100 nm. The measurement of the switch-on transients reveals that the device transient behavior depends significantly on both temperature and illumination conditions. The temperature dependence, under dark state or under illumination, suggests that the mechanism accountable for the transient behavior of thin-film transistors cannot be attributed only to carrier trapping, but rather to a more complex mechanism involving carrier generation and recombination in the device body. This allows the estimation of the dependence of generation lifetime on the polycrystalline film thickness.

Performance and reliability of SLS ELA polysilicon TFTs fabricated with novel crystallization techniques

SLS ELA polysilicon TFTs fabricated in films crystallized with several novel techniques, yielding different film microstructure and texture, were investigated. The parameter statistics indicate that the TFT performance depends on film quality and asperities, in conjunction with the grain boundary trap density. The drain current transients, upon TFT switch from OFF to ON state, showed gate oxide polarization, related to film asperities and also confirmed the presence of extended defects in the TFTs of small mobilities. DC hot carrier stress was applied, indicating a reliability dependence on polysilicon structure and differences in degradation mechanisms for the various TFT technologies.

Investigation of defects introduced by static and dynamic hot carrier stress on SOI partially depleted body-contact MOSFETs

Abstract SOI partially depleted body-contact MOSFETs were subjected to static and dynamic hot carrier stress. Drain current was investigated by means of Deep Level Transient Spectroscopy and switch-ON transient analysis in a wide temperature range. Under static degradation regime, drain current behaviour was determined by the creation of two discrete traps most likely located in the drain vicinity; a hole trap cited in the literature and a defect of metastable nature. Under dynamic degradation regime, drain current behaviour was determined by body–Si/SiO 2 interface-state generation. Experimental data and fitting results based on stretched exponential law are in accordance.

Reliability and defectivity comparison of n- and p-channel SLS ELA polysilicon TFTs fabricated with a novel crystallization technique

SLS ELA n- and p-channel polysilicon TFTs fabricated with a novel technique were investigated, oriented both along the preferential and the non-preferential direction. The degradation mechanisms proved very different between n- and p-channel devices, while the channel orientation had a larger effect on n-channel devices than on p-ones. In order to probe the reasons causing this effect we applied DLTS analysis to both n- and p-channel devices oriented along both directions, receiving valuable information about the defectivity differences in n- and p-polysilicon films.