Germanium (Ge) negative capacitance field-effect transistors (NCFETs) with various Zr compositions in Hf1-xZrxO2 (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 IDS 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 VGS corresponding to steep SS are consistent and clockwise IDS-VGS are maintained through the multiple DC sweeps. At fixed annealing temperature, NC device with Hf0.52Zr0.48O2 achieves the higher IDS but larger hysteresis compared to the other compositions. NCFET with Hf0.67Zr0.33O2 can obtain the excellent performance with hysteresis-free curves and high IDS.
Keywords: FET; Ferroelectric; Hysteresis; Negative capacitance; Subthreshold swing.