Conduction mechanisms of ferroelectric tunnel junction (FTJ) using metal-ferroelectric-insulator-semiconductor (MFIS) on n- and p-type semiconductor is clarified by a new developed model, which is verified by the experimental results. In the model, electron tunneling from conduction band and valence band, and hole tunneling from valence band are included to calculate the read current in ON/OFF-state of MFIS-FTJ. The model explains the unexpected polarization polarity of ON/OFF-state in p-type and the difference of tunneling electroresistance (TER) ratio between n- and p-type MFIS-FTJ, which cannot be understood just by the depletion/accumulation for majority carriers in semiconductor.

Tunneling processes of ferroelectric tunnel junction (FTJ) based on metal-ferroelectric-insulator-semiconductor (MFIS) stack are studied for both n- and p-type semiconductor electrodes using experimentally calibrated model. In the model, the calculation of ON- ( J _{mathrm ON} ) and OFF-current ( J _{mathrm OFF} ) in MFIS-FTJ considers the electron tunneling from both conduction (CBE) and valence band (VBE), and hole tunneling from the valence band (VBH). Depending on metal work function, doping concentration and remnant polarization, the conduction modes in both n- and p-type MFIS can respectively be classified according to the contribution of minority carriers in semiconductor. The optimal tunneling electroresistance (TER) ( ≈ J _{mathrm ON} /J _{mathrm OFF} ) for the n-type device is achieved, when semiconductor works under depletion/accumulation state driven by polarization reversal. With respect to its p-type counterpart, the accumulation/strong inversion state is preferable. The underlying physics are revealed, that if semiconductor goes into the strong inversion, the tunneling of VBH will increase the J _{mathrm OFF} and decrease the TER ratio in n-type device, whereas the tunneling of CBE will increase the J _{mathrm ON} and thus TER ratio in p-type device. Guided by the model, the band structure engineering of MFIS structure is provided to design and optimization of FTJ performance.

The HfO2-based ferroelectric (FE) tunnel junction (FTJ) and its crossbar array are promising for energy-efficient computing. However, its limited ON- current (JON) and ON/OFF tunneling electroresistance (TER) ratio become a bottleneck for large array circuits. We theoretically propose using a low-barrier Ta2O5 dielectric to enhance the device asymmetry, instead of SiO2 or Al2O3. Through resonant band engineering by inserting Ta2O5 between two FE HfO2 barriers, both JON and TER ratio are enhanced by several orders of magnitude, while a good retention is maintained benefiting from high permittivity of Ta2O5; besides, high current rectification ratio and negative differential resistance are observed. These abundant physical effects in HfO2/Ta2O5/HfO2 based MFIFM resonant FTJ may enable selector-less crossbar.

Dynamical hysteresis in thin film ferroelectrics (FE) is modeled by the multi-domain time-dependent Landau–Khalatnikov theory based on nucleation limited switching. Thin film ferroelectrics are treated as an ensemble of elementary regions characterized by independent coercive voltage and permanent polarization assumed to be Gaussian distributions, due to the intrinsic randomness of the material. Simulation of multi-domain based ferroelectrics reveals the effects of domain number and inhomogeneity of material on the polarization behaviors. Particularly a direct extraction for ferroelectric parameters as well as their distributions is proposed by comparison with experiment, which is very important to assess the performance limit of ferroelectric-based devices. Based on this approach, the frequency-dependent hysteresis loops in thin film HZO FE capacitors measured by triangular waveforms are successfully reproduced. The presented model provides a physical insight into understanding and analyzing the polarization dynamics in ferroelectric-based devices.

This work focuses on the effect of remote phonon arising from the substrate and high-κ gate dielectric on electron mobility in two-dimensional (2D) InSe field-effect transistors (FETs). The electrostatic characteristic under quantum confinement is derived by self-consistently solving the Poisson and Schrödinger equations using the effective mass approximation. Then mobility is calculated by the Kubo–Greenwood formula accounting for the remote phonon scattering (RPS) as well as the intrinsic phonon scatterings, including the acoustic phonon, homopolar phonon, optical phonon scatterings, and Fröhlich interaction. Using the above method, the mobility degradation due to remote phonon is comprehensively explored in single- and dual-gate InSe FETs utilizing SiO₂, Al₂O₃, and HfO₂ as gate dielectric respectively. We unveil the origin of temperature, inversion density, and thickness dependence of carrier mobility. Simulations indicate that remote phonon and Fröhlich interaction plays a comparatively major role in determining the electron transport in InSe. Mobility is more severely degraded by remote phonon of HfO₂ dielectric than Al₂O₃ and SiO₂ dielectric, which can be effectively insulated by introducing a SiO₂ interfacial layer between the high-κ dielectric and InSe. Due to its smaller in-plane and quantization effective masses, mobility begins to increase at higher density as carriers become degenerate, and mobility degradation with a reduced layer number is much stronger in InSe compared with MoS₂.