The influence of 8 MeV electrons on the threshold voltage (VTH), transconductance (gm) and mobility (?) of n-channel depletion metal?oxide semiconductor field-effect transistors (MOSFETs) irradiated at gate bias, VGS = +2, 0 and ?2 V, has been studied in the dose range of 0.5?31 kGy. The measurements performed after irradiation showed considerable decrease in VTH, gm and ?. The densities of interface trapped charge (?Nit) and oxide trapped charge (?Not) for irradiated devices have been estimated from the subthreshold measurements. It has been found that ?Not is higher than ?Nit. The mobility of carriers (?) in the n-channel was estimated from the peak transconductance (gmPeak) and it was found that ? decreased by around 68.5?73.5% after exposure to the total dose of 31 kGy. Mobility degradation coefficients due to interface traps (?it) and oxide trapped charge (?ot) were estimated and it was found that the mobility degradation was mainly due to ?Nit and the effect of ?Not was negligible.

https://iopscience.iop.org/article/10.1088/0268-1242/18/12/307/pdf

High-energy radiation effects on subthreshold characteristics, transconductance and mobility of n-channel MOSFETs

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

The effects of the presence of charged centers of different sign on the electron mobility in n‐channel metal‐oxide‐semiconductor transistors are studied by a Monte Carlo simulation. By solving the Poisson equation for the potential fluctuations, an expression for the Coulomb‐scattering rate when there are charged centers of different sign is provided. In addition, it is shown that, when charges of different sign exist in the structure, local band‐bending fluctuations are greater, thus resulting in lower electron mobility. In contrast, since in this case the potential mean value is lower, the influence of the charged centers on the threshold voltage is lesser. The electron mobility in compensated substrates is also analyzed.

Influence of negatively and positively charged scattering centers on electron mobility in semiconductor inversion layers: A Monte Carlo study

N-channel MOSFETs were irradiated by 48 MeV Li3+ ions, 100 MeV F8+ ions and Co-60 gamma radiation with doses ranging from 100krad to 100Mrad. The threshold voltage (V-TH), voltage shift due to interface trapped charge (Delta V-Nit), voltage shift due to oxide trapped charge (Delta V-Not), density of interface trapped charge (Delta N-it), density of oxide trapped charge (Delta N-ot), transconductance (g(m)), mobility (mu) of electrons in the channel and drain saturation current (I-D (Sat)) were studied as a function of dose. Considerable increase in Delta N-it and Delta N-ot, and decrease in V-TH, g(m) and I-D S-at were observed in all the irradiated devices. We correlated the degradation of mu with the Delta N-it and the effect of Delta N-ot is found to be negligible for degrading the mu. The maximum degradation was observed for the devices irradiated with Co-60 gamma radiation when compared with those irradiated with ions, since gamma radiation can generate more trapped charge in field oxide when compared to the high energy ions. (C) 2009 Elsevier B.V. All rights reserved.

A comparison of 48 MeV Li3+ ion, 100 MeV F8+ ion and Co-60 gamma irradiation effect on N-channel MOSFETs

N-channel depletion MOSFETs were irradiated with different swift heavy ions viz., 175 MeV Ni13+ ions, 140 MeV Si10+ ions, 100 MeV F8+ ions, 95 MeV O7+ ions and 48 MeV Li3+ ions in the same dose range of 100 krad–100 Mrad. The different electrical characteristics of MOSFETs were studied before and after irradiation and after annealing. The degradation and recovery mechanisms were studied systematically. It was found that around 80 % degradation in transconductance and mobility and almost 100 % recoveries in the electrical characteristics of irradiated MOSFETs after annealing.

Swift heavy ion irradiation and annealing studies on the I – V characteristics of N -channel depletion Metal–oxide–semiconductor field-effect transistors

Radiation causes oxide charge buildup which can degrade carrier mobility in the inversion layer of a metal‐oxide‐semiconductor field‐effect transistor (MOSFET). An expression for the carrier mobility in MOSFETs due to oxide charge scattering has been derived. The model predicts the mobility degradation given any specified charge density profile in the oxide. It accounts for screening of oxide charges by channel carriers. To validate the proposed model we performed an experiment to place a measured quantity of charge at a definite position in the gate oxide and then measured the mobility degradation. The experimental results are in good agreement with the predictions of the model.

D. Sharma

Papers

Carrier mobility degradation in metal‐oxide‐semiconductor field‐effect transistors due to oxide charge