1T1C FeFETs with Separated MFM Capacitor in the BEoL – The Role of the Capacitance Ratio

Hafnium oxide based ferroelectric memory concepts like the FeFET will become increasingly important. They are good scalable, provide high operation speed, and consume low power. Just recently, an 1T1C FeFET concept with one transistor (1T) and one separated ferroelectric capacitor (1C) was demonstrated. This alternative approach is expected 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 ferroelectric capacitor and the gate oxide capacitance. To operate at low voltages, a large fraction of the applied voltage must drop across the ferroelectric, which can be archived 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.