Compact Modeling and Design Exploration of Non-Destructive Read-Out 1T1C FeRAM

Abstract

Capacitive memory window-based non-destructive read-out (NDRO) is a promising operating mode in improving the read endurance of ferroelectric random-access memories (FeRAMs). This work presents the first successful attempt toward a unified, capacitance-enabled compact model for ferroelectric capacitors (FeCAPs) and explores the attainable sensing margin (SM) in the NDRO operation of 1T1C FeRAM. Using a Preisach multidomain, quasi-static Landau free energy-based approach, the model captures measured P-V and C-V characteristics on hafnium zirconate FeCAPs with one unified polarization, including both non-switching oscillatory behaviors in small-signal (SS) C-V and switching behaviors in large-signal (LS) P-V. Based on it, we predict that the key figure of merit permittivity window (Delta epsilon(r ))can be enhanced by increasing the remnant polarization of the FE layer. Device exploration based on the model however suggests that the theoretical maximum charge window depends additionally on the coercive field of the FE layer, which requires tradeoff with Delta epsilon(r ). At the bitcell level, we identify that the bitline (BL) SM of a 1T1C FeRAM is constrained by the: 1) voltage-dividing and 2) charge-sharing effects between the FeCAP and the BL capacitance, which as a result limits itself to < 100 mV with a sub-unity BL-to-FeCAP loading ratio. The article thus highlights the quest for novel FeCAP materials/device structures and/or disruptive sensing schemes in order to best exploit the signal-limited capacitive NDRO-FeRAM.