Xiaolei Tong

Ferroelectric aluminum scandium nitride (Al₁-_xSc_xN, AlScN) offers CMOS-compatible integration but suffers from high coercive fields and leakage currents that hinder thickness scaling. Further reduction in thickness is essential for low-voltage embedded nonvolatile memory applications. Boron incorporation into AlScN (AlBScN) suppresses leakage current in films down to 40 nm, yet its ferroelectric characteristics in ultrathin films remain unexplored. This letter demonstrates robust ferroelectric switching in 10 nm sputtered AlBScN capacitors with a low coercive field and approximately two orders of magnitude lower leakage than AlScN. Notably, The coercive field (E_c) extracted from capacitance-voltage measurements was 2.3 MV/cm, and the onset of symmetric polarization reversal was observed near 4.6 MV/cm in positive-up-negative-down (PUND) measurements using 2 μs pulses. Moreover, the breakdown field (E_BD) was determined to be 10.0 MV/cm for 10 μm diameter capacitors, suggesting a substantial margin between E_BD and E_c for reliable operation. These findings demonstrate AlBScN as a promising candidate for CMOS back-end-of-line (BEOL) compatible ferroelectric applications with improved energy consumption and reduced leakage current.

In this work, we demonstrate a high-performance surface acoustic wave (SAW) delay line based on a Scandium alloyed aluminum nitride (AlScN)-on-sapphire platform operating at 5.9 GHz with an exceptionally high acoustic propagation Q-factor. An 800 nm AlScN thin film with 40% scandium alloying concentration was deposited on a thick sapphire substrate to achieve strong acoustic energy confinement and large electromechanical coupling, thereby minimizing the insertion loss (IL) and propagation loss (PL) of the acoustic delay line (ADL). The proposed ADL was designed to operate in the Sezawa mode using a Single-Phase Unidirectional Transducer (SPUDT) electrode configuration for better unidirectionality. The fabricated ADLs with different delay lengths, after conjugate matching, exhibited delay times spanning 13 to 214 ns and IL ranging from 7.6 to 18.3 dB. The extracted PL reached as low as 9.2 dB/mm at 5.9 GHz, with a group velocity (v_g) of around 5,779 m/s. Based on these results, the proposed ADLs exhibit a high acoustic propagation Q-factor of 3,044. These findings highlight the potential of AlScN-on-sapphire platforms for high operational frequency, low-loss SAW ADL devices in advanced RF applications.

This letter presents Sezawa mode surface acoustic wave (SAW) resonators based on 500 nm boron-doped aluminum scandium nitride (Al ${}_{\mathbf {1-x-y}}$ B ${}_{\mathbf {x}}$ Sc ${}_{\mathbf {y}}$ N), AlBScN thin films co-sputtered from AlB and Sc targets onto sapphire and silicon carbide (SiC) substrates. The devices exhibit series resonance frequencies ranging from 4.3 GHz to 7.6 GHz. Atomic Force Microscopy (AFM) revealed smooth film surfaces, with root mean square roughness values of 0.65 and 0.54 nm on sapphire and SiC, respectively. X-ray diffraction (XRD) $\omega $ -scans around the wurtzite (002) reflection confirmed a highly c-axis oriented film exhibiting a full width at half maximum of 0.96° on sapphire. Electrical measurements revealed a maximum Sezawa mode velocity of 6748 m/s on SiC, while the sapphire-based device achieved a peak parallel resonance quality factor ( $Q$ ${}_{\mathbf {p}}$ ) of 1400. These results demonstrate the suitability of AlBScN for high-frequency, high-performance resonator applications.[2025-0143]

This letter presents high-temperature ferroelectric characterization of 40 nm ${\mathrm {Al}}_{\text {1-x-y}}$ BxScyN (AlBScN) thin film capacitors grown by co-sputtering Al0.89B0.11 and Sc targets onto Pt(111)/Ti(002)/Si(100) substrates. Structural analysis confirmed a c-axis-oriented wurtzite structure with a low surface roughness of 1.37 nm. Ferroelectric switching, characterized by positive-up-negative-down (PUND) measurements up to 600° C, exhibited a linear decrease in coercive fields from 6.2 MV/cm at room temperature to 4.2 MV/cm at 600°C, while remanent polarization remained stable with temperature. Direct current I–V measurements highlight a significant suppression of leakage currents, over two orders of magnitude lower compared to AlScN capacitors fabricated under similar conditions. These results position AlBScN thin films as strong candidates for ferroelectric applications in extreme environments.