3.2.4 Approach to Simulate the Charge-Pumping Experiments



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3.2.4 Approach to Simulate the Charge-Pumping Experiments

 

The simulation procedure is analogous to the experimental procedure. Transient pulses are applied to the device terminals. After the simulation, lasting a few signal periods, the time averages of the interface effective generation of electrons and holes , and of the electron and hole components in the terminal currents , , , , and are calculated. The averaging is performed in the period for which the periodic-steady-state condition is fulfilled:

 

where is the charge-pumping current. Note that we simulate an aperiodic signal. Therefore, the steady-state solution at the chosen starting bias, which is set as an initial condition for the transient simulation, is not equal to the periodic-steady-state condition at this bias point. For the large-signal techniques the simulation of to periods is sufficient to perform a proper averaging in time. However, in some problems the simulation of several signal periods is necessary to obtain the periodic-steady-state solution, as e.g. for the front-back interface coupling in SOI devices [357], the charge pumping in LDD devices [168] (gate-corner/LDD-region electric-field fringing analyzed in Section 3.5.3 and Appendix E) and for the small-rectangular-pulse technique [495][494]. The averaging in time must be consistent with the discretization of the continuity equations 3.1 and 3.2, because of the time-discretization errorgif. Comparing the calculated DC electron and hole components in the terminal currents and the interface net generation rates with each other, the deviations from the `ideal charge-pumping theory' can be extracted for some particular problem. For example, the differences between the total and indicate the presence of the geometric current component (Section 3.4). The transient currents are of order , while the charge-pumping currents are of order . It is evident that very accurate terminal current calculation becomes indispensible for the presented approach. The method of weighting functions is used to accurately calculate the terminal currents in transient cases [324]. Because of the error in the current calculation, the gate current ranges after an averaging in time (in the periodic-steady-state condition). Details on the current calculation are given in [191].



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Next: 3.3 Analytical Modeling of Up: 3.2 Physical Model and Previous: 3.2.3 Solution of the



Martin Stiftinger
Sat Oct 15 22:05:10 MET 1994