Improved Two States Characteristics in MIS Tunnel Diodes by Oxide Local Thinning Enhanced Transient Current Behavior

The effect of oxide local thinning (OLT) on the increase in current two states in metal–insulator–semiconductor (MIS) tunnel diodes for dynamic memory usage has been demonstrated. Two orders of magnitude improvement in the read current window could be observed. The MIS sample after performing the deep depletion stress (DDS) would soft breakdown (SBD) and could be effectively considered that the oxide was locally thinned. Pulsed voltage program was used to write on fresh MIS (before SBD) and OLT MIS (after SBD). A larger magnitude of transient read current could be observed for OLT MIS, and subsequently the improved current two states characteristics. The read currents of OLT MIS were stable under the endurance test. The transient behavior of a fresh MIS could be understood by the charging and discharging of a capacitor. On the contrary, the tunneling current would be dominated in an OLT MIS. At the same time, since the electron tunneling only concentrated locally, OLT MIS would take longer to recover to the steady-state. The improvement of read current after OLT forming was reproducible, and various write programs were performed for further examination. TCAD simulations demonstrated that the electrons would leak out and the electron density would decrease under larger gate voltage for OLT MIS. This work has shown the potential of OLT MIS for the dynamic memory usage, and the idea of local thinning on the gate oxide might be beneficial for the design of the future dynamic memory.