Two-State Current Behavior in MIS Tunnel Diode with Ultra-thin Surrounding Gate Metal Electrode

In this thesis, a Metal-Insulator-Semiconductor (MIS) tunnel diode with an ultrathin oxide and with a metal gate electrode surrounded by ultrathin metal was fabricated. The pattern of the device in this work is a circle with thicker metal encircled by a circular electrode with ultrathin metal, which has a high-resistance property. In chapter 3, the declined saturated gate current under inversion region was demonstrated compared to that of a traditional MIS tunnel diode whose saturated gate inversion current is influenced by the fringing field effect in an Al / ultrathin SiO2 / p-Si MIS structure. The current reduction phenomenon is attributed to the fact that the ultrathin metal structure plays a role like a resistance which suppresses the fringing field effect at the gate edge. Also, the C-V curves show the analogous experimental results that the effective gate area of ultrathin metal is more subtle than practically physical area of gate metal owing to the big difference in accumulation capacitance. In chapter 4, the two-state current phenomenon with opposite read current sign was observed after applying voltage pulses. It is quite different from the traditional DRAM with charged and discharged states which can be represented as “0” state and “1” state. With the help of surrounding ultrathin metal, the potential distribution of gate electrode is no longer equivalent everywhere, and the two state currents are magnified compared to those of a traditional MIS tunnel diode. Further, the retention time constant of the device reaches a value of 650ms, which matches the 64ms requirement of ITRS. In summary, the device discussed in this thesis is the promising candidate to be applied into memory application on account of its advantages of distinguishable two state currents and simple processes for semiconductor industry to fabricate.