Improvement of Nondestructive Readout of Ferroelectric Gate FET Memory with an Intermediate Electrode by using New Data Writing and Reading Methods

The nondestructive readout characteristics of the ferroelectric gate field-effect transistor (F-FET) memory with an intermediate electrode for data writing (IF-FET) was investigated by using the conventional and the new writing and reading methods. Normally, for the conventional writing, we use two positive or negative square pulses to induce the positive (Pr⁺) or the negative (Pr^-) remnant polarizations, respectively. For the conventional reading, unipolar square pulses were applied. Although the difference in output voltages between Pr⁺ and Pr^- is large, the nondestructive readout characteristic for the Pr^- is poor because the Pr^- memory state is quickly degraded after each reading due to non-reswitched or nonreturned domains. Therefore, for the new writing, we proposed a new memory state, Pr₀, instead of Pr^-. The Pr⁰ was induced by a combined pulse with a positive part (V_w ⁺) and a negative part (V_w ^-). For the new reading, a negative voltage (V_R ^-) was applied, following a positive voltage (V_R ⁺) to recover the memory state to the initial one. By optimizing the V_w ^- and the V_R ^- in the new method, the nondestructive readout is further improved, compared with the conventional method.