J. Banqueri

Physical model for trap-assisted inelastic tunneling in metal-oxide- semiconductor structures

A physical model for trap-assisted inelastic tunnel current through potential barriers in semiconductor structures has been developed. The model is based on the theory of multiphonon transitions between detrapped and trapped states and the only fitting parameters are those of the traps (energy level and concentration) and the Huang–Rhys factor. Therefore, dependences of the trapping and detrapping processes on the bias, position, and temperature can be obtained with this model. The results of the model are compared with experimental data of stress induced leakage current in metal-oxide-semiconductor devices. The average energy loss has been obtained and an interpretation is given of the curves of average energy loss versus oxide voltage. This allows us to identify the entrance of the assisted tunnel current in the Fowler–Nordheim regime. In addition, the dependence of the tunnel current and average energy loss on the model parameters has been studied.

Effects of the inversion-layer centroid on the performance of double-gate MOSFETs

The role of the inversion-layer centroid in a double-gate metal-oxide-semiconductor field-effect-transistor (DGMOSFET) has been investigated. The expression obtained for the inversion charge is similar to that found in conventional MOSFETs, with the inversion-charge centroid playing an identical role. The quantitative value of this magnitude has been analyzed in volume-inversion transistors and compared with the value obtained in conventional MOSFETs. The minority-carrier distribution has been found to be even closer to the interfaces in volume-inversion transistors with very thin films, and therefore, some of the advantages assumed for these devices are ungrounded. Finally, the overall advantages and disadvantages of double-gate MOSFETs over their conventional counterparts are discussed.

Effects of the inversion layer centroid on MOSFET behavior

The effects of the average inversion-layer penetration, the inversion-layer centroid, on the inversion-charge density and the gate-to-channel capacitance have been analyzed. The quantum model has been used, and a variety of data have been obtained by self-consistently solving the Poisson and Schrodinger equations. An empirical expression for the centroid position that is valid for a wide range of electrical and technological variables has been obtained and has been applied to accurately model the inversion-layer density and capacitance.

Universality of electron mobility curves in MOSFETs: a Monte Carlo study

The universal behavior of electron mobility when plotted versus the effective field is physically studied. Due to charged centers in the silicon bulk, the oxide, and the interface, Coulomb scattering is shown to be responsible for the deviation of mobility curves. Silicon bulk-impurities have a double effect: (a) Coulomb scattering due to the charge of these impurities themselves, and (b) reduction of screening caused by the loss of inversion charge when the depletion charge is increased. The electric-field region in which mobility curves behave universally regardless of bulk-impurity concentration, substrate bias, or interface charge has been determined for state-of-the-art MOSFETs. Finally, this study shows that electron mobility must be a function of the inversion and the depletion charges rather than a simple function of the effective field. >

A model for the quantized accumulation layer in metal-insulator-semiconductor structures

Abstract A model is proposed for the quantized accumulation layer based on the union of a two-dimensional electron gas contained in several energy subbands and a three-dimensional electron-gas distributed in a continuum of energy levels. The model is valid for both low and high temperatures and is formulated to allow the incorporation of quantum effects in a simulation based on classical models. It therefore permits the study of the different operation regions of a metal-insulator-semiconductor structure with continuity between them. Equations of the model are detailed as well as the solution procedure. The validity of the model is discussed and results obtained from both the quantum and classical model are compared. Capacitance curves obtained with both models are also compared to experimental ones.

Phosphorescent sensing of carbon dioxide based on secondary inner-filter quenching

A study of different strategies to prepare phosphorescence-based sensors for gaseous CO(2) determination has been performed. It includes the characterization of different configurations tested, a discussion of the results obtained and possibilities for the future. The optical sensor for gaseous CO(2) is based on changes in the phosphorescence intensity of the platinum octaethylporphyrin (PtOEP) complex trapped both on oxygen-insensitive poly(vinylidene chloride-co-vinyl chloride) (PVCD) membranes and PVCD microparticles, due to the displacement of the alpha-naphtholphthalein acid-base equilibrium with CO(2) concentration. A secondary inner-filter mechanism was tested for the sensor and a full range linearized calibration was obtained by plotting (I(100)-I(0))/(I-I(0)) versus the inverse of the CO(2) concentration, where I(0) and I(100) are the detected luminescence intensities from a membrane exposed to 100% nitrogen and 100% CO(2), respectively, and I at a defined CO(2) concentration. The different configurations tested included the use of membranes containing luminophore and pH-sensitive dye placed on two opposite sides of a transparent support to prevent the observed degradation of the PtOEP complex in the presence of the tetraoctylammonium hydroxide (TOAOH) phase transfer agent, which produced better results regarding stability and sensitivity. The CO(2) gas sensor based on PtOEP homogeneous membranes presented better properties in terms of response time and sensitivity than that based on PtOEP microparticles. With a detection limit of 0.02%, the response time (10-90% maximum signal) is 9 s and the recovery time (90-10%) is 115 s. The lifetime of the membranes for CO(2) sensing preserved in a 94% RH atmosphere and dark conditions is longer than at least 4 months.

Influence of the oxide-charge distribution profile on electron mobility in MOSFET's

To characterize the effect of oxide-charge distribution on electron mobility in a MOSFET channel, a more precise method for obtaining the oxide-charge profile than CV measurement is needed. We have shown by Monte Carlo simulation that the effective interface-charge concentration obtained from threshold voltage measurements does not reproduce the actual effect that the oxide charge has on electron mobility. It is therefore absolutely necessary to know the real profile of the charge distribution. An analytical expression to obtain the interface-charge concentration which correctly models the effect of the actual oxide-charge distribution is calculated from Monte Carlo results. >

Influence of mobility fluctuations on random telegraph signal amplitude in n-channel metal–oxide–semiconductor field-effect transistors

The amplitude of random telegraph signals (RTS) in an n-channel metal–oxide–semiconductor field-effect transistor has been investigated. Current fluctuations originating when a single-channel electron is trapped or detrapped in the silicon dioxide have been evaluated. A simulation has been performed where the inversion-layer quantization, the dependence of the electron mobility on the transverse and longitudinal electric fields, and the influence of the oxide charges on free-carrier density and on electron mobility have been taken into account. This procedure provides the chance of studying the influence of trap depth in the oxide on the RTS amplitude. In addition, the contributions of the mobility and carrier fluctuations on the amplitude of discrete current switching have been separated, revealing the importance of each factor. Normalized mobility fluctuation has been defined and it was found that its dependence on the gate and drain voltages helped to explain the behavior of the normalized current fluc...

An analytical expression for phonon-limited electron mobility in silicon-inversion layers

A complete Monte Carlo study of phonon‐limited electron mobility in (100) silicon‐inversion layers has been carried out. It has been determined advantageous to consider more than three energy subbands for electron motion. First‐order intervalley scattering has also been shown to play an important role in ohmic transport. The results of the Monte Carlo simulation can be fitted by a simple analytical expression that coincides with the phonon‐limited mobility for the bulk in the zero transverse‐electric‐field limit.

Influence of the interface-state density on the electron mobility in silicon inversion layers

The electron inversion-layer mobility in a metal oxide semiconductor field effect transistor, as a function of the transverse electric field, has been studied in the temperature range 13–300K for different interface-state densities. Experimental data are in excellent agreement with a simple semi-empirical model. However, the term attributed by other authors to phonon scattering depends on the interface-state density, even at high temperatures, and becomes negative at low temperatures. These facts are shown to be a consequence of the dependence of coulomb scattering on the transverse electric field.