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A phase-change memory (PCM) model for robust and efficient simulations of circuits including neuromorphic ones is reported in this work. The features of a hysteretic dynamic resistance in the voltage domain, and the incubation in the crystallization, are covered in the model. The Landau–Khalatnikov (LK)-type equation for ferroelectric is used to develop the PCM hysteresis module. A voltage-controlled relaxation oscillation is successfully simulated for the Ge2Sb2Te5 (GST) PCM. A technique of direct evaluation (DE) is then developed to reformulate the PCM model without any internal node. A significant enhancement of simulation efficiency is achieved compared with the traditional approach without sacrificing the accuracy. The functional correctness of the PCM device model and the acceleration effect in circuit simulations are verified.

The negative holding voltage of high-voltage (HV) dual-directional silicon-controlled rectifier (DDSCR) is usually attenuated to a very low level due to the grounded guard ring, which has been ignored by many researchers nowadays. In this brief, a novel symmetrical DDSCR (SDDSCR) is proposed to suppress the deterioration of DDSCR’s negative holding voltage. By introducing a diffusion resistor into the p-type guard ring (PGR), experimental results indicated that the reverse parasitic SCR path associated with PGR is suppressed effectively. Thus, a symmetric high holding voltage characteristic is implemented for SDDSCR without increasing any silicon footprint. Moreover, the PGR resistor technology presented in this brief can be extended to various existing HV DDSCRs, which could improve their negative holding voltage deteriorated by guard ring.

A dynamic current model for the double gate negative capacitance field-effect transistor (NCFET) of the metal–ferroelectric–insulator–semiconductor (MFIS) structure is presented in this work. With a damping parameter $\rho $ in the Landau–Khalatnikov (LK) theory for general ferroelectric (FE) materials, the gate control equation of NCFET is intrinsically dynamic which is solved directly as a basis of NCFET modeling. With the time-dependent charge densities at the source and drain sides, a dynamic current model is formulated analytically for the first time, considering the dynamic terms in a self-consistent way. The model has been verified with numerical TCAD simulations. It accurately reproduces the static negative capacitance (NC) effect in enhancing the driving current, as well as the dynamic NC effect, in the conduction delay and hysteresis for a wide range of NCFET parameters. The dynamic model after implementations is successfully applied to circuit simulations such as ring oscillators without convergence issues.

The existing gate-stack small-signal models of metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) were analyzed, and a new model that could fit the measured admittance characteristics in the whole bias regime after learning about their shortcomings was presented. The capacitance and conductance frequency characteristics were fitted simultaneously, and the extracted fitting parameters showed reasonable values and trends. These parameters were then used in the determination of interface traps as well as the quantitative analysis of two C-V slopes for MIS-HEMTs. It was proven that the intrinsic barrier resistance was also a critical factor for the second slope. Thus, this resistance could not be neglected by the capacitance method that determined the interface trap densities directly by the frequency dispersion of the second slope. This article extracted the energy distribution of the interface trap density, which could be fitted by a Gaussian distribution with a maximum value of $\sim 3\times 10^{{12}}$ cm−2 eV−1. Although this method was a suitable alternative because the capacitance and conductance were correlated by the admittance characteristics, the detected shallow-level traps may not account for the threshold voltage drift or other reliability problems of MIS-HEMTs.

This paper presents a comprehensive study on the statistical variability in charge plasma junctionless FinFET (CP-JLF) and junctionless accumulation-mode FinFET (JAM) compared with conventional junctionless FinFET (JLF). The variability in key figures of merits induced by line edge roughness (LER), random dopant fluctuation (RDF), and work function variation is analyzed. Results indicate that JAM and CP-JLF are more immune to LER and RDF than conventional JLF. Furthermore, elevating doping concentration in source while remaining relatively lower in drain is beneficial in reducing RDF-induced current variability in JAM. Besides, the impact of gate length on current variability becomes less significant or even negligible as source doping concentration increases, which helps alleviate more serious RDF upon scaling. Moreover, it is essential for JAM and CP-JLF to control geometry and doping variation in the source side that have major influence on LER and RDF. Overall, JAM and CP-JLF with improved current driving and reduced statistical variability mitigate two main obstacles that hinder conventional JLF.

Thin-film transistors (TFTs) have been widely used in the increasingly advanced field of displays. However, it remains a challenge for TFTs to overcome the poor subthreshold swing in the fast switching and high-speed applications. Here, we provide a solution to the above-mentioned challenge via supercritical dehydroxylation, which combines a low temperature, environmentally friendly supercritical fluid technology with a CaCl2 treatment. An embedded structure of amorphous indium gallium zinc oxide (a-IGZO) TFTs with double-layer high-k dielectric containing Ta2O5 and SiO2 layers was first manufactured. The subthreshold swing of the fabricated TFTs treated with supercritical dehydroxylation was optimized to an ultra-low value of 72.7 mV dec-1. Moreover, other key figures of merits including threshold voltage, on/off ratio and field effect mobility all improved after the supercritical dehydroxylation. The bandgap of the gate dielectric material increased due to the supercritical dehydroxylation verified by the current conduction mechanism. Besides, numerous material analyses further confirmed that owing to the supercritical dehydroxylation the dominant dehydration reactions can effectively repair the defects introduced in the device manufacture. The ultra-low subthreshold swing with optimized electrical performances can be achieved via the low-temperature supercritical dehydroxylation treatment, enabling its promising potential in realizing ultra-fast and low power electronics.

To describe both Arrhenius and non-Arrhenius temperature-dependent drain currents for the organic thin-film transistors, the effective trapped carrier concentration expression is presented. Based on the expression, following the Shur and Hack’s trap limited carrier conduction theory, the analytical drain current model is developed. The temperature-dependent trap states’ density is presented to explain the origin of the effective trapped carrier concentration expression.

Analytical drain current and capacitance model is developed for the amorphous InGaZnO (a-IGZO) thin-film transistor (TFT). The numerical Pao–Sah model is presented to describe the temperature characteristics considering the deep and tail trap states in the energy gap of the a-IGZO thin film. The numerical model is successful for the TFT in both the subthreshold regime and the above-threshold regime. In the subthreshold regime, considering that the trapped electron concentration in the deep trap states dominates the Poisson’s equation, the surface-potential-based analytical model is presented. In the above-threshold regime, the threshold-voltage-based analytical model is presented. Applying the smooth function to connect the subthreshold model and the above-threshold model, the analytical compact model is obtained. The compact model is verified by the numerical Pao–Sah model and the available experimental data from 253 to 393 K. Furthermore, the temperature characteristics of the field-effect mobility are discussed.

A robust simulation framework was developed for nanoscale phase change memory (PCM) cells. Starting from the reaction rate theory, the dynamic nucleation was simulated to capture the evolution of the cluster population. To accommodate the non-uniform critical sizes of nuclei due to the non-isothermal conditions during PCM cell programming, an improved crystallization model was proposed that goes beyond the classical nucleation and growth model. With the above, the incubation period in which the cluster distributions reached their equilibrium was captured beyond the capability of simulations with a steady-state nucleation rate. The implications of the developed simulation method are discussed regarding PCM fast SET programming and retention. This work provides the possibility for further improvement of PCM and integration with CMOS technology.

As a key component responsible for information processing in the brain, the development of a bionic synapse possessing digital and analog bifunctionality is vital for the hardware implementation of a neuro-system. Here, inspired by the key role of sodium and potassium in synaptic transmission, the alkali metal element lithium (Li) belonging to the same family is adopted in designing a bifunctional artificial synapse. The incorporation of Li endows the electronic devices with versatile synaptic functions. An artificial neural network based on experimental data exhibits a high performance approaching near-ideal accuracy. In addition, the regenerative ability allows synaptic functional recovery through low-frequency stimuli to be emulated, facilitating the prevention of permanent damage due to intensive neural activities and ensuring the long-term stability of the entire neural system. What is more striking for an Li-based bionic synapse is that it can not only emulate a biological synapse at a behavioral level but realize mechanism emulation based on artificial voltage-gated “ion channels”. Concurrent digital and analog features lead to versatile synaptic functions in Li-doped artificial synapses, which operate in a mode similar to the human brain with its two hemispheres excelling at processing imaginative and analytical information, respectively.

A phase change memory (PCM) model suitable for neuromorphic circuit simulations is developed. A crystallization ratio module is used to track the memory state in the SET process, and an active region radius module is developed to track the continuously varying amorphous region in the RESET process. To converge the simulations with bi-stable memory states, a predictive filament module is proposed using a previous state in iterations of nonlinear circuit matrix under a voltage-driven mode. Both DC and transient analysis are successfully converged in circuits with voltage sources. The spiking-time-dependent-plasticity (STDP) characteristics essential for synaptic PCM are successfully reproduced with SPICE simulations verifying the model’s promising applications in neuromorphic circuit designs. Further on, the developed PCM model is applied to propose a neuron circuit topology with lateral inhibitions which is more bionic and capable of distinguishing fuzzy memories. Finally, unsupervised learning of handwritten digits on neuromorphic circuits is simulated to verify the integrity of models in a large-scale-integration circuits. For the first time in literature an emerging memory model is developed and applied successfully in neuromorphic circuit designs, and the model is applicable to flexible designs of neuron circuits for further performance improvements.

Emerging resistive random access memory has attracted extensive research enthusiasm. In this study, an indirect way to improve resistive random access memory (RRAM) comprehensive performance through electrode material re-design without intensive switching layer engineering is presented by adopting a hafnium-indium-tin-oxide composite. Working parameters of the device can be effectively improved: not only are low operation power consumption and high working stability achieved, but the memory window is significantly enlarged, accompanied by an automatic self-current-compliance function. The correlation between hafnium incorporation and performance improvements and the corresponding current conduction mechanisms have been thoroughly investigated to clarify the resistive switching behavior and to explain the oxygen absorption buffer effect. The hafnium atom, with large atomic radius, is surrounded by soft electron clouds and has high chemical activity to attract oxygen ions. It facilitates the accumulation of more oxygen ions around the interface of the top electrode and the resistive switching layer, leading to lower current and Schottky conduction. This study presents an important strategy for designing and developing electrode materials to improve the characteristics of RRAM and offers an indirect method to modify device working behaviors, also unveiling a promising prospect for its potential future application in low-power information storage and calculation technology.

A SPICE model for phase change memories (PCM) without relying on macro modules is developed in this work. The crystal fraction, physical geometry, and the conduction path of the amorphous region are treated as dynamic state variables to keep track of the memory cell status during SET and RESET. The memory cell resistance is calculated based on a detail 3-D resistance model to capture its transitional behavior during switching. The detail physical formulation correctly reproduced a recent observation of oscillation during the SET operation. The model has been implemented in SPICE, and the convergence of the model is demonstrated by simulations of a complete PCM array. The use of dynamic state variables also significantly reduces the number of internal nodes to one, which helps convergence and reduces the simulation time.

This study investigates the physical and chemical mechanisms during the resistive switching process by means of obtaining the activation energy in the reaction procedure. From the electrochemical and electrical measurement analysis results of HfO2-based resistive random access memory (RRAM), it can be observed that the chemical reaction during the reset process is consistent with the first-order reaction law. The activation energy, Ea, is determined from the reaction rate constant k under a varying-temperature environment in the reset process. The whole reset chemical reaction process can be divided into five phases involving N-O bond breaking, O-O bond breaking and triple-step oxygen ion migration. The methodology of the activation energy determination carried out in this study showcases a distinct approach to elucidate the resistive switching mechanism of RRAM and offers insight into RRAM design for future potential application.

In this work, we report the theoretical maximum bending angle of MoS2 devices using the creative non-collinear electrodes method based on the first principles theory. The results show that the device with 1T-phase MoS2 electrodes sandwiching N-type MoS2 in a zigzag direction has a better conducting behavior as compared with P-type in an armchair direction. The conductance decreases less than 15% when the angle between the two electrodes is less than 45° in both the equilibrium state and non-equilibrium state because of the continuous resonant response between the two electrodes and the little deformed band structure. This work provides guidance and a physical mechanism for achieving flexible MoS2 transistors that are reliable at a sub-nm bending radius.

Polymethyl methacrylate (PMMA) has been widely applied in the semiconductor field due to its excellent specialties of transparency and durability, but impurities in the polymerization process result in electric leakage and are tough to remove even during high-temperature baking. In this study, a near-room-temperature supercritical CO2 fluid (NRT-SCF) treatment method is adopted to purify PMMA and improve its insulating properties. Residual solvent and initiators in PMMA films can be easily taken away by supercritical CO2 fluid at near-room-temperature to enhance the electric characteristics. An Al/PMMA/Mo metal–insulator–metal device is fabricated to investigate the improvement in PMMA quality. The leakage current of the device can be decreased more than 10-fold and its capacitance can also become more stable after NRT-SCF treatment. The current conduction mechanism is transformed from Hopping conduction to Schottky emission. Fourier transform infrared spectroscopy test results confirmed that defects like butyl acetate and benzoyl peroxide in PMMA films have been reduced a lot based on material analysis. The findings of this study lead to the hopeful prospect that supercritical CO2 fluid technology can greatly promote the insulating properties of PMMA and offer more potential applications for PMMA in wider fields.

Complementary resistive switching (CRS) is a core requirement in memristor crossbar array construction for neuromorphic computing in view of its capability to avoid the sneak path current. However, previous approaches for implementing CRS are generally based on a complex device structure design and fabrication process or a meticulous current-limiting measurement procedure. In this study, a supercritical fluid-assisted ammoniation (SFA) process is reported to achieve CRS in a single device by endowing the original ordinary switching materials with dual-ion operation. In addition to self-compliant CRS behavior, a multi-bit storage function has also been achieved through the SFA process accompanied by superior retention and reliability. These substantial evolved resistive phenomena are elucidated attentively by our chemical reaction model and physical mechanism model corroborated by the material analysis and current conduction fitting analysis results. The findings in this research present the most efficient way to achieve CRS through only one chemical procedure with significantly improved device performance. Moreover, the supercritical fluid approach envisions tremendous possibilities for further development of materials and electric devices by a low-temperature process, with semiconductor fabrication compatibility and environmental friendliness.

Thin-film transistors (TFTs) have drawn widespread applications in the increasingly sophisticated display field. Despite the mature process of fabricating enhancement-mode TFTs, lack of facile methods to realize depletion-mode TFTs restrains the implementation of complementary-type circuits, which in turn leads to relatively high power. Here, the supercritical fluid technique is introduced to elaborately design and tune the interface, providing the opportunity for function-mode transformation of TFTs. By harnessing supercritical-assisted ammoniation (SCA) treatment, interfacial polarization induces negative shift of threshold voltage (from 0.2 to -9.8 V), which allows TFTs to remain normally on-state in the absence of complex capacitor-integrated circuits. This convenient technique, without an additional manufacturing process to achieve function-mode transformation, can thus enable the fabrication of comprehensive-mode TFTs under the same process. Furthermore, comprehensive optimizations in the mobility (increases from 2.08 to 17.12 cm2 V-1 s-1), leakage current (reduces from 1.33 × 10-11 to 2.22 × 10-12 A), hysteresis (reduces from 11.2 to 0.2 V), and on/off current ratio (increases from 9.65 × 104 to 7.98 × 106) are achieved simultaneously. Based on conjoint analysis of electrical and material characterization, a reaction model is established for a clearer understanding of the interfacial polarization process. Overall, this low-temperature SCA treatment offers an environmentally benign strategy to modulate the function mode of electronic devices via interfacial engineering and optimize device performance at the same time, exhibiting promise in promoting the implementation of complementary, low-power circuit.

A low temperature supercritical fluid (SCCF) technology was employed to repair the dangling bonds existed in the amorphous-silicon thin-film transistors (a-Si TFTs) fabricated on the flexible polyimide substrate. The electrical characteristics of manufactured a-Si TFTs gained improvements in the on-state current, threshold voltage, as well as subthreshold swing after the SCCF treatment. The inner mechanisms accounting for those optimizations were verified by the material analysis with reduced dangling bonds. Furthermore, a reaction model was proposed to describe the defects removal process in the a-Si flexible TFTs due to SCCF technology.

In this work, the electrical performance of the negative capacitance gate-all-around nanosheet junctionless transistors (NS-NCJLT) at advanced technology node is studied. The NS-NCJLT shows better performance than NS-JLT such as the higher driving current and steeper subthreshold slope (SS). Besides, the NS-NCJLT is proved has the best performance after benchmarked against its counterparts based on FinFET and nanowire structures. Then it is found that the smaller-size NS-NCJLT benefits more from NC effect, which indicate it could be applied more appropriately to the 7-nm device and beyond. Finally, we have investigated the influence of self-heating effect on NS-NCJLT. The results show that although the introduction of ferroelectric layer increases the heat conduction path, the electrical properties of NS-NCJLT still be enhanced.

In this work, a design of X-band solid-state power amplifier (SSPA) is proposed. Its operating frequency is from 7.7 GHz to 8.5 GHz, and the matching circuit is designed as a band-pass filter circuit. The results show that the power added efficiency of the single-stage power amplifier designed by GaN HEMT can reach 55%, the saturated output power is 51.5 dBm, and the maximum power gain can reach about 12 dB.

We present a systematic investigation on growth parameters (the ratio of reactive gases and total flow rate) of silicon nitride (StNx) films by Low-Pressure Chemical Vapor Deposition (LPCVD). The post-growth annealing condition would influence the bonds and electrical properties of the SiN x. When the concentration of SiH 2 Cl2 and NH3 is 20sccm/250sccm and with post-growth annealing in O 2 at 650°C, the electrical performance of SiN x film is the best, which is evaluated by capacitance-voltage, dielectric breakdown and reliability test. Increasing the total flow rate of gas source can improve the reliability of device.

In this paper, a comparison study between different drain current models including velocity saturation effect for gate-all-around (GAA) MOSFET is performed from the aspect of accuracy and symmetry. A charge-based drain current model with velocity saturation effects by the Caughey- Thomas model with an exponent factor n=2 is developed. Its relationships with the industry standard BSIM-CMG model which assumes an exponent factor n=1 are discussed. 3-D TCAD simulations are performed to benchmark the models' accuracy. It is shown that similar accuracy is achieved with both models while applying an even number in the velocity saturation formula helps improving the model's performance under Gummel symmetry tests.

In this paper, a charge-plasma based negative capacitance junctionless transistor (NC-CPJLT) is proposed and studied through several simulations. By adopting the ferroelectric material on the CPJLT, the new device can effectively achieve much steeper subthreshold slope (SS) and higher I on /I off ratio. It is found that the improvement of driving current of the NC-CPJLT becomes more remarkable with the increase of channel doping level while the SS of the proposed device still performs well. Besides, smaller device shares better SS optimization effect in the NC-CPJLT. This work indicates that the NC-CPJLT shows great application potential for low power dissipation circuits.