Thermal Characterization of Ferroelectric Al1–xBxN for Nonvolatile Memory

Abstract

Boron (B)-substituted wurtzite AlN (Al_1–xB_xN) is a recently discovered wurtzite ferroelectric material that offers several advantages over ferroelectric Hf_1–xZr_xO₂ and PbZr_1–xTi_xO₃. 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 Al_1–xB_xN. It was experimentally observed that the thermal conductivity of Al_1–xB_xN 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 Al_0.93B_0.07N 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 °C in a FeRAM device based on a 5 nm thick Al_1–xB_xN 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.