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

Abstract

Ferroelectric technology is becoming ever more appealing for a variety of applications, especially analog neuromorphic computing. In this respect, elucidating the physical mechanisms occurring during device operation is of key importance to improve the reliability of ferroelectric devices. In this work, we investigate ferroelectric tunnel junctions (FTJs) consisting of a ferroelectric hafnium zirconium oxide (HZO) layer and an alumina (Al2O3) layer by means of C-f and G-f measurements performed at multiple voltages and temperatures. For a dependable interpretation of the results, a new small signal model is introduced that goes beyond the state of the art by i) separating the role of the leakage in the two layers; ii) including the significant impact of the series impedance (that depends on the samples layout); iii) including the frequency dependence of the dielectric permittivity; iv) accounting for the fact that likely not the whole HZO volume crystallizes in the orthorhombic ferroelectric phase. The model correctly reproduces measurements taken on different devices in different conditions. Results highlight that the typical estimation method for interface trap density may be misleading.

Impedance Investigation of MIFM Ferroelectric Tunnel Junction Using a Comprehensive Small-Signal Model

“…The paper extends our previous conference paper [5] by providing a more detailed explanation on the model parameter's extraction methodology, together with the sensitivity analysis that encompasses all the parameters in the model and other modeling attempts comparison.…”

Linking the Intrinsic Electrical Response of Ferroelectric Devices to Material Properties by Means of Impedance Spectroscopy

“…In this research, we extend our conference paper [35] and expand upon our previous findings on the validation of the small-signal model for ferroelectric tunnel junctions (FTJs) [33], [34], also used to investigate aging mechanisms [36], and examine the electrical response of FTJs with a metaldielectric-ferroelectric-metal (MDFM) stack at various voltages through multi-voltage capacitancefrequency/conductance-frequency (C-f/G-f) measurements.…”

“…(CSER//GSER) to model the parasitic impedance of the access metal lines, which cannot be removed with open-circuit and/or short-circuit compensation [33], [34], which are however performed before the measurements. A Cit-Git branch is also inserted between the TiN electrodes (for MFM and MDM) to model to the first order the presence of interface defects at the parasitic TiON / TiAlO layers caused by post-deposition annealing [28], [38].…”

“…2b), the MFM and FTJ results are hereafter reported, for simplicity, only for positive polarization (i.e., +3(+4) V  -3(-4) V). Notice that 𝜖 represents an effective permittivity, accounting for both orthorhombic (i.e., ferroelectric) and non-ferroelectric phases present in the FE [33], [34], [41].…”

“…This technique allows for a detailed analysis of the electrical response of ferroelectric devices. However, especially when investigating lab-level samples, test devices may be strongly affected by the parasitic impedance of the metal lines (or broken access device [33], [34]) contacting the electrodes of the device, which is not always negligible and may strongly alter the measured response, with consequences on the interpretation of the results.…”