Abruptly-Switching MoS₂-Channel Atomic-Threshold-Switching Field-Effect Transistor With AgTi/HfO₂-Based Threshold Switching Device.

A two-dimension (2D) atomic-threshold-switching field-effect transistor (ATS-FET) was implemented, by connecting an AgTi/HfO2-based threshold-switching (TS) device in series to the drain electrode of the 2D baseline-FET with molybdenum disulfide (MoS2) channel material. We optimized/developed the Ag/HfO2-based TS device because its characteristic is associated to the way how to achieve high performance of the 2D ATS-FET. By reducing the effective device area of the Ag/HfO2-based TS device down to 4 mu m(2), low threshold voltage (V-T similar to 0.42 V), low threshold current (I-T, drain current at the threshold voltage, similar to 3.79 x 10(11) A), and low V-T variation (similar to 0.09 V) were achieved. This is because the randomly formed filaments and electric field are better controlled with the scaled effective area. Next, the titanium (Ti)-injection barrier layer was inserted between the top electrode and the switching layer, while maintaining the optimized area in the TS device. The inserted Ti-injection barrier layer prevents the migration of Ag ions into the switching layer, enabling the stable TS operation even under the compliance current of 100 mu A. Additionally, it locally restricts the region where the filaments are created inside the switching layer, resulting in a 17% lower V-T variation and stable I-T to approximately similar to 1.5 x 10(11) A in 100 cycles. Due to the low off-state leakage current and low variation characteristic of the optimized AgTi/HfO2-based TS device, the 2D ATS-FET (vs. 2D baseline-FET) shows the reduction of off-state leakage current (by similar to 10(2) in sub-threshold region) and the stable switching characteristic. The proposed 2D ATS-FET shows stably steep switching characteristics, e.g., sub-threshold swing under forward bias (similar to 19 mV/decade) and reverse bias (similar to 26 mV/decade), because of its abruptly switching characteristics of the TS device.