2.1.2 Direct Monitoring of

To improve the measurement resolution of , Reisinger et al. developed a fast -method [11], which is depicted in Fig. 2.2. It distinguishes two modes of operation: During the measurement-mode a constant and device-specific drain current serves as “threshold current” -criterium.² This is achieved by a feedback loop using an operating amplifier. Simultaneously, the resulting corresponding threshold voltage of the device is recorded. (The initial reference has to be measured in advance.) When switching to the stress-mode all contacts but the gate are grounded, the latter being set to .

Figure 2.2: Fast--method after Reisinger et al. [11]. When switched to the measurement-mode ‘m’ the drain current of the device under test (DUT) is forced to a constant () by the feedback loop of the operating amplifier. At the same time the threshold voltage is measured. When switched to the stress-mode ‘s’, source and drain are grounded and only the gate is set to . The switching between the two modes is done by fast electronic switches.

With the fast--method a measurement delay of has been achieved, equivalent to the settling time of the feedback loop. Compared to the studies of Rangan et al. [14], who only use off-the-shelf equipment, this results in a three decades faster read-out speed.