Germanium Negative Capacitance Field Effect Transistors: Impacts of Zr Composition in Hf_1-xZr_xO₂

Germanium (Ge) negative capacitance field-effect transistors (NCFETs) with various Zr compositions in Hf_1-xZr_xO₂ (x = 0.33, 0.48, and 0.67) are fabricated and characterized. For each Zr composition, the NCFET exhibits the sudden drop in some points of subthreshold swing (SS), which is induced by the NC effect. Drive current I_DS increases with the increase of annealing temperature, which should be due to the reduced source/drain resistance and improved carrier mobility. The steep SS points are repeatable and stable through multiple DC sweeping measurement proving that they are induced by the NC effect. The values of gate voltage V_GS corresponding to steep SS are consistent and clockwise I_DS-V_GS are maintained through the multiple DC sweeps. At fixed annealing temperature, NC device with Hf_0.52Zr_0.48O₂ achieves the higher I_DS but larger hysteresis compared to the other compositions. NCFET with Hf_0.67Zr_0.33O₂ can obtain the excellent performance with hysteresis-free curves and high I_DS.