Polarization switching and interface charges in BEOL compatible Ferroelectric Tunnel Junctions

Abstract

We here report a joint experimental and theoretical analysis of polarization switching in ferroelectric tunnel junctions. Our results show that the injection and trapping of charge into the ferroelectric-dielectric stack has a large influence on the polarization switching. Our results are relevant to the physical understanding and to the design of the devices, and for both memory and memristor applications.

Investigating charge trapping in ferroelectric thin films through transient measurements

“…In both of these devices, an intentional dielectric (DE) layer is added to a metal-ferroelectric-metal (MFM) stack, which will modulate the impact of charge trapping due to the additional FE-DE interface. Assuming fixed and trapped charge densities is necessary in order to fully model the switching behavior of ferroelectric devices with DE layers (Fontanini et al, 2021;Hoffmann et al, 2022). Nonetheless, charge trapping is also involved in the switching of HfO 2 ferroelectrics without any intentional interfacial layer (IL) (Mehta et al, 1973;Islamov et al, 2019), due to the unavoidable presence of non-switching "dead layers" at the FE-electrode interfaces (Stengel and Spaldin, 2006).…”

“…Even in the common case when ferroelectric HfO 2 is sandwiched between two TiN electrodes with no intentionally grown dielectric layers, TiO x and TiON can form at the ferroelectricmetal interfaces which will impact the depolarization field and interface trap states Hamouda et al (2020). In the presence of a DE layer, a significant leakage current (Si et al, 2019) and high density of interface traps (Fontanini et al, 2021) need to be considered to fully compensate charges arising from polarization switching. The degree to which polarization charges are compensated can be controlled via the switching pulse parameters, and thereby the charge injected during switching (Park et al, 2021).…”

Limitations to Electrical Probing of Spontaneous Polarization in Ferroelectric-Dielectric Heterostructures

“…Thanks to the discovery of a robust ferroelectricity in hafnium oxide thin films [1], several intriguing applications of ferroelectricity in CMOS electron devices have been proposed and are being presently scrutinized. Device concepts include nanoscale CMOS FETs exploitating the effective negative capacitance to improve the subthreshold swing [2]- [7], as well as Ferroelectric Tunnelling Junctions (FTJs) [8], [9], and ferroelectric FETs [10], [11], which may be used as non-volatile memories or as memristors for neuromorphic computing applications [12].…”

Investigating charge trapping in ferroelectric thin films through transient measurements

“…In both of these devices, an intentional dielectric (DE) layer is added to a metal-ferroelectric-metal (MFM) stack, which will modulate the impact of charge trapping due to the additional FE-DE interface. Assuming fixed and trapped charge densities is necessary in order to fully model the switching behavior of ferroelectric devices with DE layers [8,14]. Nonetheless, charge trapping is also involved in the switching of HfO 2 ferroelectrics without any intentional interfacial layer (IL) [25,16], due to the unavoidable presence of non-switching 'dead layers' at the FE-electrode interfaces [36].…”

“…Even in the common case when ferroelectric HfO 2 is sandwiched between two TiN electrodes with no intentionally grown dielectric layers, TiO x and TiON can form at the ferroelectric-metal interfaces which will impact the depolarization field and interface trap states [13]. In the presence of a DE layer, a significant leakage current [34] and high density of interface traps [8] need to be considered to fully compensate charges arising from polarization switching. The degree to which polarization charges are compensated can be controlled via the switching pulse parameters, and thereby the charge injected during switching [31].…”