Nondestructive Readout of Ferroelectric-Gate Field-Effect Transistor Memory With an Intermediate Electrode by Using an Improved Operation Method

We investigated the reading and writing of ferroelectric-gate field-effect transistor memory with an intermediate electrode (IF-FET) to achieve perfect nondestructive readouts. In the previous operation method, although the difference in output voltage ΔV_O between positive P_r^+ and negative P_r^- remanent polarization memory states was adequate for the first reading time, the nondestructive readout for the P_r^- state was seriously degraded due to the generation of nonreturning domains. In order to solve this issue, a P_r^0 memory state was used instead of the previous P_r^- memory state. The P_r}^0 state was induced by applying a pulse combined with a positive voltage V_W^+ and a negative voltage (V_W^-). V_W^+ was to reset the previously written memory states, and V_W^- was to control the amount of remanent polarization. In addition, in order to extinguish perfectly the nonreturning domains, a negative voltage V_R^- was applied for data reading, following a positive voltage V_R^+, where V_R^+ was determined for clear decoding. The appropriate heights of the writing and reading voltages were determined individually from the viewpoint of good nondestructive readout and large ΔV_O. As a result, it was verified experimentally that the reading endurance reached more than 10^8 cycles and that the retention time of IF-FET at 150 ℃ was possible to exceed ten years