Multi-Probe Characterization of Ferroelectric/Dielectric Interface by C-V, P-V and Conductance Methods

Understanding the Reliability of Ferroelectric Tunnel Junction Operations using an Advanced Small-Signal Model

“…Specifically, i) to fully include the effect of the AD and, in general, of possible stray and interconnect impedance that is always present even in layouts in which the BE is directly accessible, we include a general series impedance, modelled as the parallel of and ; ii) we model each layer of the FTJ by considering their capacitance and parallel conductance, the latter being representative of the leakage through that specific layer. This is different from other works [3,4]in which the leakage was included by considering a global parallel conductance tied across the two layers, which did not allow to distinguish between the role played by each layer in charge transport; iii) we consider the well-known fact [5] that HZO does not crystallize fully in the orthorhombic (and ferroelectric) phase, but also exhibits non-orthorhombic grains with different permittivity values. So, we calculate the FE relative permittivity (…”

“…8 shows the parameters extracted on FTJs with different DE thickness: no particular trend is evidenced, not even in C it , although the G p / profiles peak at different magnitudes. This underlines even further how the typical strategy to estimate the interface trap density (i.e., proportional to the peak magnitude in the G p / profile) [3,4] can lead to misleading predictions, and that a more refined modeling approach is needed. It is worth mentioning that the C it values extracted here (20-50 μF/cm 2 ) should not be rigidly interpreted as related to traps located exclusively at the IF interface (that would lead to unrealistically high densities ≈ 1 -3•10 14 cm -2 ) but rather as an average local volumetric trap density (≈ 10 20 -10 21 cm -3 ), since defects across almost the whole stack can respond in C-f/G-f measurements, as shown by advanced multiscale simulations [12], and also play a role in compensating polarization charge.…”

“…To interpret the results, we introduce a small-signal model with significant novelties as compared to the existing ones in the literature [3,4], see Fig. 1d-e.…”

“…2d, in agreement with data from the literature that clearly show how the corner frequency may be in the range explored in this work, depending on the DE thickness and deposition process. The role of the defects located both in the DE/FE layers and at the IF interface is included, as in previous works [3,4], by means of a lumped C it -G it branch across the DE. Different attempts in positioning this branch have been done, but with ineffectual results.…”

“…These results validate the model ability to consider the contribution of the AD and, in general, of whatever series impedance may be present. This is of utter importance, since the series impedance (even when in the range of few tens of pF) strongly impacts the magnitude of the peak in the G p / profile, typically used to estimate the interface trap density [3,4]. Also, depending on the series impedance value, a second peak may appear above 1 MHz, and / profiles vary when is varied over ±2 orders of magnitude, centered on the nominal value extracted by fitting the measurements obtained by using the larger AD (blue line).…”