Dielectric properties and resistive switching characteristics of lead zirconate titanate/hafnia heterostructures

Abstract

We report the dielectric response and resistive switching properties of bilayers of PbZr0.40Ti0.60O3 [PZT (40:60)] and HfO2 of varying thickness on platinized Si substrates. PZT (40:60) and HfO2 films were grown using chemical solution deposition and atomic layer deposition, respectively. We show here that the addition of an interposed linear dielectric layer with a high permittivity between the ferroelectric film and the top electrode modifies the polarization and resistive switching characteristics of the multilayer stack. We observe an increase in the coercive field by 45% for PZT films of 250 nm thickness with a 20 nm HfO2 layer compared to 250 nm thick PZT films grown under identical conditions. Simultaneously, the dielectric constant decreases by 43% from 409 to 175 for a 250 nm PZT film with 20 nm HfO2, accompanied by a significant improvement in the leakage current density from 5.6 × 10−4 A/cm2 to 8.7 × 10−8 A/cm2. Our resistance measurements show that there are two separate resistance states that are accessible with at least an order of magnitude in resistance difference from 5 × 108 to 5 × 109 Ω. We show that the dielectric response and the coercivity of the bilayer system can be explained by a capacitors-in-series model. This indicates that the PZT and the HfO2 layer could effectively be considered decoupled, presumably due to bound/trapped charges at the interlayer interface. This charged ferroelectric/dielectric interface could be the reason for the intermediate resistance states which could be used as multistate resistive memories in neuromorphic computing applications.