Examination of the possibility of negative capacitance using ferroelectric materials in solid state electronic devices.

We show here, using fundamental energy storage relationships for capacitors, that there are severe constraints upon what can be realized utilizing ferroelectric materials as FET dielectrics. A basic equation governing all small signal behavior is derived, a negative capacitance quality factor is defined based upon it, and thousands of carefully measured devices are evaluated. We show that no instance of negative capacitance occurs within our huge database.

Room-temperature ferroelectricity in strained SrTiO3.

Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (T(c)) is traditionally accomplished by chemical substitution-as in Ba(x)Sr(1-x)TiO(3), the material widely investigated for microwave devices in which the dielectric constant (epsilon(r)) at GHz frequencies is tuned by applying a quasi-static electric field. Heterogeneity associated with chemical substitution in such films, however, can broaden this phase transition by hundreds of degrees, which is detrimental to tunability and microwave device performance.

Lattice-scale domain wall dynamics in ferroelectrics.

Ferroelectric domain walls are atomically thin, and consequently their dynamics are sensitive to the periodic potential of the underlying lattice. Despite their central role in domain dynamics, lattice-scale effects have never been directly observed. We investigate local domain dynamics in thin film ferroelectrics using atomic-force microscopy.

Mesoscopic microwave dispersion in ferroelectric thin films.

The microwave dielectric response of a ferroelectric thin film is measured locally using time-resolved confocal scanning optical microscopy. Measurements performed on an ensemble of nanometer-scale regions show a well-defined phase shift between the paraelectric and ferroelectric response at 2-4 GHz. Application of a static electric field produces large local variations in the phase of the ferroelectric response.