Thermal Characterization of Ferroelectric Al1-x B x N for Nonvolatile Memory

Boron (B)-substituted wurtzite AlN (Al1-x B x N) is a recently discovered wurtzite ferroelectric material that offers several advantages over ferroelectric Hf1-x Zr x O2 and PbZr1-x Ti x O3. Such benefits include a relatively low growth temperature as well as a thermally stable, and thickness-stable ferroelectric polarization; these factors are promising for the development of ferroelectric nonvolatile random-access memory (FeRAM) that are CMOS-compatible, scalable, and reliable for storing data in harsh environments. However, wurtzite ferroelectric materials may undergo exacerbated self-heating upon polarization switching relative to other ferroelectric materials; the larger energy loss is anticipated due to the higher coercive field and remanent polarization. This work provides insight into the polarization switching-induced self-heating of future FeRAM based on Al1-x B x N. It was experimentally observed that the thermal conductivity of Al1-x B x N thin films drops from 40.9 W m-1 K-1 to 4.35 W m-1 K-1 (which is 2 orders of magnitude lower than that of bulk AlN) when the B composition (x) increases from 0 to 0.18. The transient thermal response of an Al0.93B0.07N metal-ferroelectric-metal (MFM) capacitor was investigated using micro-Raman thermometry and validated via device thermal modeling. Further simulation studies reveal that the large heat generation rate and the low thermal conductivity is predicted to induce an instantaneous temperature rise that may exceed 150 degrees C in a FeRAM device based on a 5 nm thick Al1-x B x N film at GHz frequency switching. In addition, thermal crosstalk within a FeRAM cell array exacerbates the self-heating, resulting in a predicted steady-state temperature rise that is an order of magnitude higher than that of a single bit-cell.