Ferroelectric FETs with Separated Capacitor in the Back-End-of-Line: Role of the Capacitance Ratio

Hafnium oxide based ferroelectric (FE) memory concepts like FE field effect transistors (FeFETs) will become increasingly important. They are highly scalable, provide high operation speed, and consume low power. Just recently, an 1T1C FeFET concept with one transistor (1T) and one separated FE capacitor (1C) was demonstrated. This alternative approach is promising to overcome the drawbacks usually observed for the classic 1T concept like limited endurance, reduced retention, and high device-to-device variability. Electrically, the 1T1C FeFET consists of a series connection of the FE capacitor and the gate oxide capacitance. To operate at low voltages, a large fraction of the applied voltage must drop across the FE, which can be achieved by optimizing the capacitance ratio. Herein, 1T1C FeFETs with various capacitance ratios are fabricated and its impact on the electrical performance is discussed. Furthermore, the observed endurance of up to 108 field cycles illustrates the great potential of the new concept.