Aluminum Nitride based Ferroelectric Memory Devices – Testing Methodologies

A material is deemed ferroelectric if it possesses an intrinsic ability to switch between two spontaneous polarization states under the influence of an external electric field. Ferroelectric materials have garnered a lot of interest over the years particularly with emerging application demands such as subthreshold transistors [1], memory devices and logic devices with reconfigurable threshold voltatges [2]. Discovery of ferroelectricity in Sc-doped Aluminum Nitride [3] paved the way for a new class of FE materials with remarkable switchable polarization (>100μC/cm2), tunable coercive fields ($2-6 \mathrm{MV} / \mathrm{cm}$) and excellent CMOS compatibility (especially with large area and low temperature deposition techniques) that can be rendered into high performance memory devices [4]. However, it is to be noted that the building block of non-centrosymmetric wurtzite structure of AlN is the origin of polarization along the c-axis in AlScN [3]. AlN, traditionally considered purely piezoelectric but not ferroelectric due to the energy required for transition from Al-polar to N-polar being too high. However, recent reports [5], [6] suggest that partial polarization reversal is possible in pure, undoped AIN. Through this work, we report ferroelectricity in undoped AIN at room temperature investigated using the dynamic hysteresis mode (DHM) and positive-up-negative-down (PUND) techniques [7].