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 DeltaV _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 DeltaV _O . As a result, it was verified experimentally that the reading endurance reached more than 10⁸ cycles and that the retention time of IF-FET at 150^degC was possible to exceed ten years.