Atomistic Modeling of Ferroelectric Materials in Devices

The polarization, switching dynamics and dielectric properties of ferroelectric materials are usually measured experimentally through a device structure in which ferroelectric component is often sandwiched by two metal electrodes. Such a device can be electrically stimulated, and its dielectric response can be used to infer the ferroelectric properties. However, molecular-level simulations generally focus on ferroelectric materials alone, with idealized stimuli and readily available atomic characteristics such as coordinates. Here we report a new molecular dynamics simulation protocol to describe the archetypal two-terminal ferroelectric device: a parallel plate capacitor with ferroelectric thin film serving as the dielectric layer. The key enabler is a device-level charge equilibration method capable of prescribing electrical connectivity onto atoms. Thus, voltage difference, electric field, charge, or current can be either imposed as stimuli or measured as responses. Using this device, we demonstrated the measurement of ferroelectric, piezoelectric and pyroelectric properties of aluminum nitride (AlN). In addition, we show the structure-property relation in AlN by comparing single-crystalline, polycrystalline, and amorphous AlN in terms of the aforementioned properties. This work will help close the gap between experimental and computational investigations of ferroelectric materials and extending device-level modeling with atomic-level characteristics.