(A) flash memory cell model for circuit simulation

Abstract

In this thesis, we have proposed the flash memory cell model. The model is based on two ideas; Effective-Control-Gate (ECG) voltage method and Ideal-Current-Mirror (ICM) technique. The ECG voltage method enables the transient circuit simulation of the flash memory cell model with the DC simulation, and the ICM technique is a method for achieving an accurate floating-gate (FG) voltage, which is completely independent to the parasitic effects. Since the ECG voltage method replaces the time-dependent threshold voltage of a flash memory cell to a term of the time-dependent control-gate voltage, which can be easily obtained from a simple macro circuit model, the model is especially useful for the transient circuit simulation. The ICM technique can also be realized with a simple macro circuit model and calculates the FG voltage accurately using the drain-current of a flash memory cell, which thus becomes a useful tool for a NOR-type flash memory cell model. The chief advantage of the ICM technique is in its parasitic/structure-independent nature. Since the technique can eliminate all parasitic effect, i.e., an overlap (fringing) capacitance between the FG and drain, channel doping profile, short (narrow) channel effects, velocity saturation effect, and so on, we can always achieve the accurate FG voltage. Obtaining the accurate FG voltage has revealed a major importance in the flash memory cell model, because the gate-current of the flash memory cell is an exponential function of the FG voltage. Therefore, the ICM technique is very powerful for modeling the accurate gate-current induced by a channel-hot-electron (CHE) injection. For an accumulation region, on the other hand, we derived the simple and accurate analytical equation by applying the charge conservation law to the FG boundary. With those two ideas of the ECG voltage method and ICM technique, we could model the flash memory cell and the model was compared with the real device that is fabricated with 0.17 μm...