Ferroelectric charge transfer device using polarization-assisted tunneling for single transistor nonvolatile memories

In this work we announce a ferroelectric charge transfer device that uses a high-k buffer layer underneath the ferroelectric layer as a tunnel oxide, where the high electric field required for Fowler-Nordheim charge tunneling through the buffer layer is provided by the polarized ferroelectric. This device exhibits data retention of 10 years at room temperature while retaining the properties of fast write and low voltage operation. Since the electric field across a buffer layer due to the ferroelectric polarization surface charge is similar to E = (Pr)/(epsilon 0 epsilon ox) then with P-r on the order of 10 mu C/cm(2) and epsilon(ox) for a high k dielectric is similar to 20, we have an electric field of 5.6 MV/cm which is sufficient to generate significant tunnel currents across a high-k buffer layer. Charges tunneling from the Si substrate are trapped in the interface between the high-k buffer and the ferroelectric and only detrap thermally; this leads to the long data retention observed on these devices. Despite the fact that charge transfer is accomplished by tunneling, a relatively slow process, this device can be programmed or erased in only the time it takes to switch the ferroelectric, which is of the order of nanoseconds.