Technology Computer-aided Design Model Research Articles

High-Efficiency Vertical-Chip Micro-Light-Emitting Diodes via p-GaN Optimization and Surface Passivation

Micro-LEDs have found widespread applications in modular large-screen TVs, automotive displays, and high-resolution-density augmented reality glasses. However, these micron-sized LEDs experience a significant efficiency reduction due to the defects originating from the dry etching process. By controlling the current distribution via engineering the electrode size, electrons will be less concentrated in the defect region. In this work, we propose a blue InGaN/GaN compound parabolic concentrator micro-LED with a metallic sidewall to boost efficiency by combining both an optical dipole cloud model and electrical TCAD (Technology Computer-Aided Design) model. By merely modifying the p-GaN contact size, the external quantum efficiency (EQE) can be improved by 15.6%. By further optimizing the passivation layer thickness, the EQE can be boosted by 52.1%, which helps enhance the display brightness or lower power consumption.

A crossbar architecture based system (CAS) as hydrogen gas sensing platform

The development of sensing technologies and miniaturization allows for the development of smart systems with elevated sensing performance. Silicon-based hydrogen sensors have received a lot of attention due to its electrical conductivity and the mechanical endurance. With this motivation, we have proposed a two-terminal silicon-based device in a crossbar architecture as a hydrogen gas sensing platform. In this work, we have adopted a multi-layer modeling approach to analyze the performance of the proposed system. Technology computer-aided design models have been used to capture device performance. A gas sensor model based on hydrogen adsorption on the Palladium surface and a crossbar model has been adopted to understand the Palladium work function variation with gas pressure and the performance of the proposed crossbar system respectively. We have shown the impact of parameters like interconnect resistance and array size on the whole system’s performance. Finally, a comprehensive analysis has been provided for the design rule of this architecture. A fabrication process to spur future experimental works has also been added. This work will provide computational insight into the performance of a crossbar hydrogen sensor system, optimized against some critical parameters.

Investigation on floating-gate field-effect transistor for logic-in-memory application

In this paper, we present analysis results on the applicability of a previously introduced memory device, floating-gate field-effect transistor (FGFET), to a logic-in-memory (LiM) system for the first time. Device optimization and compact modeling were performed using a well-calibrated technology computer-aided design model and the results of applying LiM circuits were arranged. Device optimization in the 32 nm technology node was conducted by assessing the device performance in terms of memory window, retention time, and write speed. After device optimization, the operational characteristics were analyzed by applying the proposed compact model to a full adder (FA) circuit and a ternary content addressable memory (TCAM) circuit with LiM characteristics. Compared to FA and TCAM circuits composed of conventional FETs, the FGFET-based circuits demonstrated superior performance in terms of area and operating characteristics, implying that they offer significant potential for applications in silicon-based LiM technology.

Numerical modeling of FS-trench IGBTs by TCAD and its parameter extraction method

The electrical behavior of the IGBTs is the key factors to the application of IGBTs. Technology Computer Aided Design (TCAD) is one of the most effective methods for characterizing of electrical behavior of IGBT. However, the great difficulties in extracting the model's parameters hinder its widely applications. In the present work, a high-precision TCAD model for FS-Trench IGBT was established and verified by experiments. Firstly, the parameters necessary for TCAD models were analyzed in theoretical and experimental. The key process parameters need to be determined in a value range table. A Convolutional Neural Network (CNN) was proposed and trained to form a relationship from characteristic curves to key process parameters. Subsequently, the numerical model's parameters were established by combining the trained CNN model with experimental data. Finally, the TCAD model was established and the simulations of IGBTs were carried out and verified by experiments. Results demonstrate that the proposed TCAD model is well consistent with experiments with a Root Mean Square Error (RMSE) of about 3.7 %. This work may provide a feasible method to obtain highly precise numerical models of power semiconductor devices. It may also promote the application of Artificial Intelligence in the device modeling and optimization design.

TCAD Modeling of High-Field Electron Transport in Bulk Wurtzite GaN: The Full-Band SHE-BTE

Gallium Nitride (GaN) High-Electron Mobility Transistors (HEMTs) actually represent one of the best candidates for medium-high power and radio frequency applications. As they operate at large bias and electric fields, a comprehensive analysis of the high-field transport properties is fundamentals, as hot electrons are expected to play a relevant role for the device reliability. In this perspective, Technology Computer-Aided Design (TCAD) simulations can be a very useful tool for the understanding of the phenomena dominating hot-electron degradation mechanisms. The most-accurate modeling approaches are based on the direct solution of the Boltzmann equation, which is not actually available for the GaN material. In this work, the deterministic solution of the Boltzmann transport equation via the spherical-harmonics expansion (SHE-BTE), as incorporated in a commercial TCAD tool, has been extended to the analysis of GaN electrons. To this purpose, the details of the full-band structure has been derived from DFT calculations as in state-of-art literature works, and the electron density of states, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g(E)$ </tex-math></inline-formula> , and group velocity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$u_{g}(E)$ </tex-math></inline-formula> , have been calculated for the SHE-BTE for the first time. In addition to this, an accurate calibration of the total scattering rate accounting for nonpolar acoustic and optical carrier-phonon interaction, Coulomb scattering and impact ionization has been carried out against available Monte Carlo data and experiments. The proposed model is also shown to correctly predict the temperature dependence of the electron impact-ionization coefficient and current density up to breakdown.

Mechanisms of instability retention for ferroelectric field effect transistors with HfZrO2 gate stack scaling down

Instability threshold voltage (VT) with retention loss of read-after-write is a critical issue with fundamental physics for ferroelectric field effect transistors (FeFETs) scaling down under high-speed operation. The mechanisms including charge trapping and depolarization field (Edep) are discovered and related to surface potential and coercive field (EC). The trapped charge can be effectively detrapped by opposite polarity stimulation and validated by technology computer-aided design modeling. In addition, the Edep is revealed to be serious with ferroelectric HfZrO2 (FE-HZO) thin-down due to the unstable low-VT state at a gate voltage (VG) of 0 V. The tunable base voltage (Vbase) compensates the Edep-based polarization degradation. A stable low-VT read-after-write for a 5-nm-thick HZO FeFET is experimentally demonstrated by the opposite polarity detrapping scheme hybrid with a Vbase optimization simultaneously for a wide range of delay times from 10−7 to 102 s. This result provides the feasibility for scaling down FeFETs for nonvolatile memory applications in the future.

Study of Vertical Ga2O3 FinFET Short Circuit Ruggedness using Robust TCAD Simulation

In this paper, the short circuit ruggedness of Gallium Oxide (Ga2O3) vertical FinFET is studied using Technology Computer-Aided-Design (TCAD) simulations. Ga2O3 is an emerging ultra-wide bandgap material and Ga2O3 vertical FinFET can achieve the normally-off operation for high voltage applications. Ga2O3 has a relatively low thermal conductivity and, thus, it is critical to explore the design space of Ga2O3 vertical FinFETs to achieve an acceptable short-circuit capability for power applications. In this study, appropriate TCAD models and parameters calibrated to experimental data are used. For the first time, the breakdown voltage simulation accuracy of Ga2O3 vertical FinFETs is studied systematically. It is found that a background carrier generation rate between 105 cm−3s−1 and 1012 cm−3s−1 is required in simulation to obtain correct results. The calibrated and robust setup is then used to study the short circuit withstand time (SCWT) of an 800 V-rated Ga2O3 vertical FinFET with different inter-fin architectures. It is found that, due to the high thermal resistance in Ga2O3, to achieve an SCWT >1 μs, low gate overdrive is needed which increases Ron,sp by 66% and that Ga2O3 might melt before the occurrence of thermal runaway. These results provide important guidance for developing rugged Ga2O3 power transistors.

Role of temperature on linearity and analog/RF performance merits of a negative capacitance FinFET

Temperature plays a decisive role in semiconductor device performance and reliability analysis. The effect is more severe in a negative capacitance (NC) transistor, as the temperature modulates the ferroelectric polarization, implicitly included by the Landau coefficients (α, β, γ) in Technology Computer Aided Design (TCAD) simulations. In this paper, through TCAD simulations, the role of varying ambient temperature is investigated in the linearity and analog/radio-frequency (RF) merits of NC-FinFET. The varying temperature modulates the carrier mobility, the semiconductor bandgap, and the Landau parameter (α). We analyzed the analog/RF and linearity metrics, such as total gate capacitance (C gg), transconductance (g m), unity gain cut-off frequency (f T), the transconductance-frequency product, gain-bandwidth product, higher-order transconductance (g m2 and g m3), voltage intercept points, third-order power intercept and intermodulation points, and 1 dB CP using well-calibrated TCAD models. Our analysis reveals that these parameters are strongly dependent on temperature and the NC span (defined by using S-curve) shrinks with the rise in temperature. Finally, a source follower and three-stage ring oscillator are designed to test the frequency compatibility of the AC simulation for varying temperatures.

Investigation of Self-Heating Effects in UTBB FD-SOI MOSFETs by a Modified Thermal Conductivity Model

In this article, an analytical thermal conductivity model considering the degradation caused by the different phonon scattering mechanisms is presented for studying the self-heating effects (SHEs) in ultrathin body and buried oxide (UTBB) silicon-on-insulator (SOI) MOSFETs. By allowing for phonon-boundary and phonon–electron scattering, as well as tuning the surface roughness, the model enables accurate predictions for silicon films of different thicknesses over a wide temperature range. In order to apply the temperature-dependent self-built thermal conductivity model to the technology computer-aided design (TCAD) electrothermal simulation, a piecewise fitting, and equivalent strategy is developed by using the zero points (ZPs) and extreme points (EPs) of the first- and second-order discrete differentials of the model. The results show that the modified model is closer to the experimental data from literature studies than the default TCAD model in predicting the thermal conductivity distribution of the SOI-structure. Furthermore, the TCAD simulation results with our modified model show the same trend as that with its default model in predicting the performance degradation of UTBB SOI devices due to SHEs, such as the degradation of carrier mobility in the channel and the increase of subthreshold swing (SS).

TCAD numerical modeling of negative capacitance ferroelectric devices for radiation detection applications

In this work advanced TCAD (Technology Computer Aided Design) modeling will be used aiming at investigating the potentiality of Negative Capacitance (NC) devices in non-conventional application domains (e.g., radiation detection). A device-level approach to simulate the electrical characteristics of ferroelectric Hf0.5Zr0.5O2 (HZO) has been developed. The validation of the models and of the adopted numerical methods relies on the comparison between simulations and measurements of Metal-Ferroelectric-Metal and Metal-Ferroelectric-Insulator-Metal capacitors. By introducing the experimentally observed dielectric/ferroelectric interfacial trapped charges, our simulations are in a strong agreement with experimental measurements. These charges compensate the bound ferroelectric polarization charge when no external electric field is applied. The ferroelectric/dielectric interface could be therefore studied before and after X-ray irradiation. The goal will be to investigate the suitability of innovative NC devices to be used in High Energy Physics experiments detection systems, featuring self-amplified segmented, high granularity detectors.

Assessing the analog/RF and linearity performances of FinFET using high threshold voltage techniques

One of the severe issues of the downscaling of semiconductor devices is the threshold voltage reduction which significantly increases the leakage current. Thus, high threshold voltage (HVT) techniques are required to bring down the leakage hike for improved performances. In this paper, for the first time, we investigate the analog/radio frequency (RF) and linearity performances of silicon (Si) FinFET by employing HVT techniques. Using well-calibrated technology computer aided design models, to mitigate the leakage current, we analyzed the following approach to get HVT: (a) increasing channel doping (N ch′); (b) making drain-side underlap (L dsu); (c) increasing gate length (L g′). Two flavors of fin field effect transistors (FinFETs) viz bulk and silicon-on-insulator (SOI) are suitably compared over their baseline counterpart, i.e. without HVTs. A thorough investigation of analog/RF metrics such as transconductance, output resistance, gate capacitance, cut-off frequency, gain-bandwidth, and transconductance-frequency product proves the eminence of bulk-FinFET over its peer SOI-FinFET. In contrast, SOI-FinFET shows merits in intrinsic gain and linearity such as g m2, g m3, VIP2, VIP3, IIP3, IMD3, and 1 dB compression point. Thus, HVT techniques are worth analyzing for a FinFET architecture employed in analog/RF applications.

Modeling the impact of defects on the charge collection efficiency of a Cadmium Telluride detector

Cadmium telluride is a favorable material for X-ray detection as it has an outstanding characteristic for room temperature operation. It is a high-Z material with excellent photon radiation absorption properties. However, CdTe single crystals may include a large number of extended crystallographic defects, such as grain boundaries, twins, and tellurium (Te) inclusions, which can have an impact on detector performance. A Technology Computer Aided Design (TCAD) local defect model has been developed to investigate the effects of local defects on charge collection efficiency (CCE). We studied a 1 mm thick Schottky-type CdTe radiation detector with transient-current technique by using a red laser at room temperature. By raster scanning the detector surface we were able to study signal shaping within the bulk, and to locate surface defects by observing their impact on the CCE. In this paper we present our TCAD model with localized defect, and compare the simulation results to TCT measurements. In the model an inclusion with a diameter of 10 μm was assumed. The center of the defect was positioned at 6 μm distance from the surface. We show that the defect has a notable effect on current transients, which in turn affect the CCE of the CdTe detector. The simulated charge collection at the position of the defect decreases by 80 % in comparison to the defect-free case. The simulations show that the defects give a characteristic shape to TCT signal. This can further be used to detect defects in CdTe detectors and to estimate the overall defect density in the material.

Performance prediction of InP/GaAsSb double heterojunction bipolar transistors for THz applications

The intrinsic performance of “type-II” InP/GaAsSb double heterojunction bipolar transistors (DHBTs) toward and beyond THz is predicted and analyzed based on a multi-scale technology computer aided design modeling platform calibrated against experimental measurements. Two-dimensional hydrodynamic simulations are combined with 1D full-band, atomistic quantum transport calculations to shed light on future DHBT generations whose dimensions are decreased step-by-step, starting from the current device configuration. Simulations predict that a peak transit frequency fT,peak of around 1.6 THz could be reached in aggressively scaled type-II DHBTs with a total thickness of 256 nm and an emitter width WE of 37.5 nm. The corresponding breakdown voltage BVCEO is estimated to be 2.2 V. The investigations are put in perspective with two DHBT performance limiting factors, self-heating, and breakdown characteristics.

A Complete Analytical Model for MOS-HEMT Biosensors: Capturing the Effect of Stern Layer and Charge Screening on Sensor Performance

This letter presents analytical and technology computer aided design models for analyzing the performance of biohigh-electron-mobility transistor (HEMT) sensors. Unlike existing models for these sensors in the literature, where the biolayer is modeled as semiconductor or insulator layer with analyte-induced interface charge (i.e., surface potential), the model presented in this letter provides a better design insights by taking into consideration charge screening effect and impact of electric double layer (Stern layer) on device performance. The simulation case study is focused on prostate cancer detection using prostate-specific antigen (PSA) present in human serum as the target biomarker. Application specific validation of the model has been presented through demonstration of a MOS-HEMT PSA sensor design with sensitivity large enough to detect clinically relevant concentration of PSA in human serum (1ng/ml-4ng/ml).

Assessment of Junction Termination Extension Structures For Ultrahigh-Voltage Silicon Carbide Pin-Diodes; A Simulation Study

The junction termination extension (JTE) structures for ultrahigh-voltage (UHV) devices consumes a considerable part of the semiconductor chip area. The JTE area is closely related to chip performance, process yield and ultimately device cost. The JTE lengths for UHV devices (i.e., > 30 kV) are still unknown, not visible in the scientific literature and have therefore been predicted in this study by means of two-dimensional numerical simulations using the Sentaurus based technology computer-aided design (TCAD) tool. A previously reported space-modulated, two-zone JTE (SM-JTE) structure has been used as an input to set up a suitable TCAD model, which is further scaled to JTE lengths required for 40 kV class and 50 kV class SiC PiN diodes. The simulation results indicate that the SM-JTE requires an 1800 μm one-sided JTE length with 27 guard rings for a 40 kV theoretical PiN diode and 2700 μm with 36 guard rings for a 50 kV device, resulting in breakdown voltages of 41.4 kV and 51.7 kV, respectively. Moreover, the design considerations of different JTE categories are discussed with focus on the adaptability of the termination structures in ultrahigh-voltage devices, e.g., VB > 30 kV, which results in a comparison of the SM-JTE structure with other high-voltage JTE designs.

Wide-Range Prediction of Ultra-High Voltage SiC IGBT Static Performance Using Calibrated TCAD Model

In this paper, a technology computer-aided design (TCAD) model of a silicon carbide (SiC) insulated-gate bipolar transistor (IGBT) has been calibrated against previously reported experimental data. The calibrated TCAD model has been used to predict the static performance of theoretical SiC IGBTs with ultra-high blocking voltage capabilities in the range of 20-50 kV. The simulation results of transfer characteristics, IC-VGE, forward characteristics, IC-VCE, and blocking voltage characteristics are studied. The threshold voltage is approximately 5 V, and the forward voltage drop is ranging from VF = 4.2-10.0 V at IC = 20 A, using a charge carrier lifetime of τA = 20 μs. Furthermore, the forward voltage drop impact for different process dependent parameters (i.e., carrier lifetimes, mobility/scattering and trap related defects) and junction temperature are investigated in a parametric sensitivity analysis. The wide-range simulation results may be used as an input to facilitate high power converter design and evaluation. In this case, the TCAD simulated static characteristics of SiC IGBTs is compared to silicon (Si) IGBTs in a modular multilevel converter in a general high-power application. The results indicate several benefits and lower conduction energy losses using ultra-high voltage SiC IGBTs compared to Si IGBTs.

A genetic algorithm to optimize the performance of the tunneling field-effect transistor

The double-gate tunneling field-effect transistor (DGTFET) is investigated with two channel lengths (50 and 20 nm), along with the effect of the variation of the device design on its overall direct-current (DC) and radiofrequency (RF) performance. The studied design parameters are the drain doping abruptness (or spread) and its shift relative to the gate electrode. Additionally, the gate work function, and the dielectric material and its thickness are investigated. The studied performance parameters are the ON/OFF ratio, the maximum cutoff frequency, the subthreshold swing, and the ambipolar current. The device’s figure of merit (FOM) is expressed as a weighted-sum objective function for optimization by a genetic algorithm (GA). The results are validated against multifactorial experimentation to study the effect of changing each parameter on the FOM. It is shown that the genetic optimization can enhance the performance of the 20-nm-channel device to become comparable to that of a device with a long channel of 50 nm. The GA is run multiple times using parallel processing, MATLAB, and a technology computer-aided design (TCAD) model to validate its efficiency for the optimization of electronic devices when a TCAD model can be built without a great need to define a mathematical model in closed form.

TCAD Model for TeraFET Detectors Operating in a Large Dynamic Range

We present technology computer-aided design (TCAD) models for AlGaAs/InGaAs and AlGaN/GaN and silicon TeraFETs, plasmonic field effect transistors (FETs), for terahertz (THz) detection validated over a wide dynamic range. The modeling results are in good agreement with the experimental data for the AlGaAs/InGaAs heterostructure FETs (HFETs) and, to the low end of the dynamic range, with the analytical theory of the TeraFET detectors. The models incorporate the response saturation effect at high intensities of the THz radiation observed in experiments and reveal the physics of the response saturation associated with different mechanisms for different material systems. These mechanisms include the gate leakage, the velocity saturation and the avalanche effect.

A Defects-Based Model on the Barrier Height Behavior in 3C-SiC-on-Si Schottky Barrier Diodes

3C-silicon carbide (3C-SiC) Schottky barrier diodes (SBDs) on silicon (Si) substrates (3C-SiC-on-Si) have been found to suffer from excessive subthreshold current, despite the superior electrical properties of 3C-SiC. In turn, that is one of the factors deterring the commercialization of this technology. The forward current–voltage ( $I$ – $V$ ) characteristics in these devices carry considerable information about the material quality. In this context, an advanced technology computer-aided design (TCAD) model is proposed and validated with measurements obtained from a fabricated and characterized platinum/3C-SiC-on-Si SBD with scope to shed light on the physical carrier transport mechanisms, the impact of traps, and their characteristics on the actual device performance. The model includes defects originating from both the Schottky contact and the heterointerface of 3C-SiC with Si, which allows the investigation of their impact on the magnification of the subthreshold current. Furthermore, the simulation results and measured data allowed for the identification of additional distributions of interfacial states, the effect of which is linked to the observed nonuniformities of the Barrier height value. A comprehensive characterization of the defects affecting the carrier transport mechanisms of the investigated 3C-SiC-on-Si power diode is thus achieved, and the proposed TCAD model is able to accurately predict the device current both during forward and reverse bias conditions.

Characterization of an “Edgeless” Dosimeter for Angular Independent Measurements in Advanced Radiotherapy Treatments

In this paper, the performance of an “edgeless” device is evaluated for use as an angular independent detector for dosimetric quality assurance in radiotherapy. The edgeless diodes were tested in terms of current–voltage (IV) and capacitance–voltage (CV) characteristics, charge collection efficiency and radiation hardness. A model of the edgeless device was developed to simulate the distribution of the electric field for different geometries using technology computer aided design (TCAD). IV and CV characteristics of the diodes indicate the appropriate operational conditions and provide a means to assess the consistency/quality of the edgeless diode technology. TCAD model shows good agreement with experimental results demonstrating the accuracy of the model in simulating the behavior of the edgeless diodes. The charge collection efficiency is evaluated for two of the edgeless configurations PP and NP. The angular dependence measurements of edgeless devices before and after 2 Mrad irradiation shows negligible effect of radiation damage on response as a function of the angle. The experimental data are supported by the results of the TCAD simulation study, which indicates negligible impact of radiation damage from a clinical use perspective. Both the experimental and simulated results derived from the radiation damage study show minimal degradation (within 4%) of the diodes sensitivity.