Ferroelectricity underpins many proposed next-generation memory technologies that are widely expected to have profound impacts on modern computing. Hf0.5Zr0.5O2 (HZO) is the leading material candidate for the ultimate commercial implementation of ferroelectric memory because it is CMOS compatible, it has a large spontaneous polarization, and it can retain its ferroelectric properties in films as thin as 1 nm. Unfortunately, the crystal phase of HZO responsible for its ferroelectricity (orthorhombic phase, space group number 29) competes with several other non-ferroelectric phases of similar free energies, making stabilization of the orthorhombic phase a challenge. Encapsulating electrodes seem to play an important role in stabilizing the ferroelectric phase, but the mechanism by which they do so remains poorly understood.
Here, we examine a ferroelectric HZO capacitor with titanium nitride (TiN) electrodes using scanning transmission electronmicroscopy (STEM) imaging in plan view. The capacitor is encircled by a lithographically-defined TiN heater that we energize in situ. Conventional STEM imaging identifies crystal grains in the TiN electrodes and in the HZO film. Simultaneously acquired STEM electron beam-induced current (EBIC) images provide electric field contrast that highlights the ferroelectric domains. At low annealing temperatures we find that the HZO’s ferroelectric domain structure is correlated with the TiN electrodes’ grain structure. Annealing at higher temperatures causes the domains to outgrow the TiN grains. Eventually the HZO domains expand to the size of the HZO grains they inhabit.