Electrical characterization of high-k based MIS capacitors using flat-band voltage transients

In this work, we show the existence of flat-band voltage transients in MIS capacitors with ultrathin high-k dielectric films. The transients are obtained when recording the gate voltage while keeping the capacitance constant at the value of flat-band condition (C_FB). Gadolinium oxide and hafnium oxide are studied in this work. Transient time constant seems to be temperature independent, whereas the amplitude of the transient is thermally activated with energies in the range of soft-optical phonons usually reported for high-k dielectrics. So, the dependencies of transient time constant and amplitude on dielectric thickness and temperature, suggest that there are tunnelling assisted processes involved. Moreover, dependency of the flat-band voltage transient on the bias history, and on the sign of the capacitance-voltage curves is demonstrated.