Quantifying electromechanics: Electrostatics, “Blind spots” and beyond Moore’s law ferroelectric materials

Motivated in many cases by the need for ever smaller dimensions in micro- and nano-electronics, there has been a rapid expansion of research on thin film ferroelectric materials. Ideally, materials that go into these beyond Moore’s law devices should be compatible with currently used CMOS technologies, leading, for example to Hafnia based materials and layered van der Waals ferroelectrics. These materials commonly have inverse piezo coefficients that are small, often less than 1pm/volt. A similar challenge is being faced by researchers They also often have small switching voltages, required for low power device performance but that also limits the range of the excitation potential. This year marks the 30th anniversary since piezoresponse force microscopy (PFM) was demonstrated on ferroelectric polymers by Guthner and Dransfield. Since then, it has emerged as the preeminent nanoscale approach to characterizing electromechanical response and is commonly used as a verification for ferroelectricity on the nanoscale. The recent advent of weaker, beyond Moore’s law materials has accelerated the reporting of “strange ferroelectrics” – synonymous with materials that are mistakenly interpreted as ferroelectric. In this talk, I will discuss some recent results that demonstrate quantitative PFM measurements at noise floors as low as 100fm/Volt. I will also report on a large series of systematic studies exploring so called blind spots where the measured amplitude and phase are independent of electrostatic crosstalk. These exhaustive measurements were simultaneously made with both a standard optical beam (beam bounce) detector and a quantitative interferometric detector. The results are in good agreement with Euler-Bernoulli beam theory and allow a quantitative comparison of various strategies for quantifying electromechanical response and for eliminating crosstalk. Careful application of these results will enable artifact free, quantitative measurements of the electromechanical response.