Design and Modeling of Scandium-Alloyed Wurtzite III-Nitrides Based Ferroelectric Heterostructure for Power Efficient Applications

<b>Introduction:</b> The transient negative capacitance (TNC) effect observed in ferroelectric materials offers a promising approach to reducing energy consumption in field-effect transistors by enabling a subthreshold slope (SS) below the conventional limit (e.g. 60 mV/dec at 300K) [1]. Scandium-alloyed wurtzite III-nitrides based ferroelectric high electron mobility transistor (FerroHEMT) which combines the high piezoelectric coefficients and low coercive field ferroelectricity in AlScN with the TNC effects, enables both high on-current and high-speed characteristics [2]. While the static charge-voltage (Q-V) characteristics of AlScN/AlN/GaN heterostructures has been carefully modeled in Ref. [3]. The TNC effects related to ferroelectricity in AlScN and related phenomena such as reverse DIBL and negative differential resistance (NDR) are not analyzed and included in the model [4]. To effectively utilize the advantages in the FerroHEMTs structure for circuit design, in this work, we identify the design constraints that must be met and develop model to capture the Q-V relation within AlScN/AlN/GaN heterostructures with TNC effects. We also extend the study and analysis from room temperature down to cryogenic level.<br/><b>Methodology:</b> The TNC origins from the difference between responding time of build-in polarization and screening charge at the materials interfaces. It can be observed when polarization switching current (dP/dt) exceeds free carrier displacement current (dQ/dt). When dP/dt largely increases, dQ/dt through a small depletion layer capacitance in the subthreshold region cannot fully balance. Then the voltage across the ferroelectric layer is reduced, which results in depolarization effect. We start with calibrating the static Q-V characteristics under different combinations of Sc composition, AlScN and AlN thicknesses in Sentaurus TCAD with 1D Schrodinger-Poisson solver at room temperature [5]. Then we carry out transient simulation in Sentaurus TCAD for the 1-D AlScN/AlN/GaN heterostructures. To observe the TNC effects, we carried out transient TCAD simulation on metal (M) / ferroelectric (F) / insulator (I) / semiconductor (S) structure, in which time dependent Landau-Khalatnikov (L-K) equation can be considered. To incorporate transient negative capacitance (TNC) effects into compact models for circuit design and simulation, we have modified the virtual source-based Q-V model for GaN HEMTs by integrating the dynamic L-K theory. This theory provides a time-dependent relationship between ferroelectric polarization and the electric field, as described in references [6, 7]. Additionally, we employed a 1D Schrödinger-Poisson solver to estimate the low-temperature characteristics.<br/><b>Summary:</b> We investigate and identify the optimal material and geometrical parameters of AlScN/AlN/GaN heterostructures that exhibit transient negative capacitance (TNC) effects, aiming to maximize carrier concentration at the heterointerface and achieve subthreshold slopes below the Boltzmann limit. We propose an analytical compact model that incorporates TNC effects to accurately describe the Q-V relationship within AlScN/AlN/GaN heterostructures.<br/><br/><b>References</b><br/>[1] Chang, Sou-Chi, et al. Physical Review Applied 9.1 (2018): 014010.<br/>[2] Casamento, J., et al. 2022 International Electron Devices Meeting (IEDM). IEEE, 2022.<br/>[3] Wu, Bohao, and Shaloo Rakheja. 2022 Device Research Conference (DRC). IEEE, 2022.<br/>[4] Kobayashi, Masaharu, Chengji Jin, and Toshiro Hiramoto. 2019 IEEE 13th International Conference on ASIC (ASICON). IEEE, 2019.<br/>[5] Birner, Stefan, et al. IEEE Transactions on Electron Devices 54.9 (2007): 2137-2142.<br/>[6] Li, Kexin, and Shaloo Rakheja. Gallium Nitride Materials and Devices XII. Vol. 10104. SPIE, 2017.<br/>[7] Pahwa, Girish, et al. IEEE Transactions on Electron Devices 63.12 (2016): 4986-4992.