At the ultimate scaling limit, electronic memory would store bits of information by shifting atoms back and forth inside individual crystalline unit cells. Ferroelectric materials exhibit the electronic hysteresis required to realize this ideal. However, despite the perfect alignment between a material class and an economically important application, ferroelectric computer memory has almost zero commercial presence.
The materials properties that are possible in principle are not realized in practice. Strain, defects, phase competition, and inhomogenieties all confuse the experimental picture. Previously it has been difficult to look inside a ferroelectric to see what is going on. The standard high-resolution imaging techniques, piezo-force microscopy (PFM) and transmission electron microscopy (TEM), struggle to visualize the electric and polarization fields that are the hallmarks of ferroelectricity. Understanding why ferroelectric materials have not yet lived up to their potential is widely recognized open problem.
Using scanning TEM (STEM) electron beam-induced current (EBIC) imaging, we map the electric fields in a Hf0.5Zr0.5O2 capacitor, obtaining a view of the material’s ferroelectric properties that is unprecedented in its completeness. We map the whole device and inside nanoscale domains, correlating global free currents with local polarization reversals. In individual domains we isolate and measure the remanent background E-field that does not switch, and we show that this field determines the coercive E-field required to switch the domain. These measurements connect the nanoscopic crystal structure to the mesoscopic materials properties that ultimately determine device function.