Physics of the ferroelectric nonvolatile memory field effect transistor

The operation of the ferroelectric nonvolatile memory field effect transistor is theoretically examined extensively for the first time. The ferroelectric transistor device properties are derived by combining the silicon charge-sheet model of metal-oxide-semiconductor field-effect transistor device operation with Maxwell’s first equation which describes the properties of the ferroelectric film. The model we present describes ferroelectric transistor I-V and C-V behavior when time-dependent voltages are applied which result in hysteresis due to ferroelectric switching. The theoretical results provide unique insight into the effects of geometrical and material parameters on the electrical properties of the transistor. These parameters include the ferroelectric spontaneous and remanent polarization, the coercive field, and dielectric layer thicknesses. We have found that the conventional concept of threshold voltage is no longer useful, and that increasing the spontaneous polarization has only a minor impact on memory operation due to reverse dipole switching of the ferroelectric layer. The application of the model to optimize design and fabrication parameters is illustrated with a virtual prototyping example. The model is also used to develop a practical testing methodology for this unique device.