Technology Computer-aided Design Research Articles

Simulation of synaptic properties of ferroelectric memory capacitors and neural network applications

In this work, the electrical properties and synaptic characteristics of hafnium oxide-based ferroelectric memory capacitor with metal - ferroelectric layer - metal (MFM) structure were simulated using TCAD (technology computer aided design) software. Based on the synaptic potentiation/depression characteristics of the simulated memory capacitor, a multilayer perceptron (MLP) network was constructed, and the recognition accuracy and convergence speed of the MLP network in the MNIST recognition task were simulated, and the feasibility of the ferroelectric memory capacitor synaptic device for real neural network operation was analyzed. The results show that the recognition accuracy of the MLP network reaches 93% and stabilizes after 50 iterations of training, and the recognition accuracy of the MLP network is already at a high usable level after a smaller number of training times of 20, which suggests that the synaptic plasticity of the ferroelectric memory capacitor has a good potential for the practical application of the weight updating of the MLP network.

High-density 3D-NAND flash with dual-string select line (D-SSL)

In this study, high-density 3D-NAND flash memory is proposed. Using D-SSL, lateral shrink of cell area can be achieved by distinguishing two strings in a word-line (WL). We verify erase/program and read characteristics using technology computer-aided design (TCAD) simulations with rigorous calibrated condition. The proposed high density NAND flash has normally-on state SSLs through additional process and electrical treatment. In the conventional reference NAND flash, the cell string connected to the bit-line (BL) is distinguished by WL cut (WLC). On the other hand, in the proposed high density NAND flash, the cell string is selected by utilizing the normally-on state SSLs using trapped hole and doped arsenic at the intersection of SSL1 and SSL2. Compared with the conventional scheme, the proposed D-SSL exhibits almost same erase/program and read characteristics. Consequently, the proposed D-SSL scheme can increase memory density with reduced number of WLCs by distinguishing strings using D-SSL.

Aggravated NBTI reliability due to hard-to-detect open defects

FinFET technology has become an attractive candidate for high-performance and power-efficient applications. In the other hand, the behavior of FinFET devices is influenced by self-heating effect (SHE) due to its 3D structure, low thermal coupling and quantum confinement effect, among others. SHE degrades the device’s performance and could worsen reliability mechanisms like NBTI. In addition, some hard-to-detect open defects in FinFET based-circuits using logic gates designed with multi-fin and multi-finger techniques may escape the test and present abnormal static currents, which may increase the impact of self-heating effect and make the NBTI degradation more severe. Hence, it is crucial to accurately determine the temperature profiles of those chips passing the test and presenting abnormal static currents. This paper investigates the reliability of chips passing the test with abnormal static currents using Sentaurus Technology Computer-Aided Design (TCAD). FinFET transistors are calibrated with Intel 14-nm FinFET technology. Our TCAD simulation framework determines accurately the temperature and NBTI degradation. Using the TCAD information, the device degradation over time can be predicted. Moreover, the delay penalization of a critical logic path of an ISCAS benchmark circuit is investigated. The delay penalization of logic paths, attributed to the defect and NBTI, is analyzed with varying logic depths, emphasizing the importance of addressing critical paths with different logic depths. Our study leads to new considerations for improving the prediction of circuit reliability and taking countermeasures.

Multi-objective optimization and inverse design of complementary field-effect transistor using combined approach of machine learning and non-dominated sorting genetic algorithms for next-generation semiconductor devices

Complementary field-effect transistors (CFETs), which are structures in which different types of transistors are vertically stacked with a shared control gate, are being focused on for continuing to satisfy Moore's law by overcoming the limitations in pitch scaling. The structures of semiconductor devices become more complex as technology node shrinks, and interrelated multivariate parameters increase. In addition, predicting problems and proposing solutions by identifying complex patterns within extensive data collected for emerging semiconductor designs pose significant computational challenges and are inherently difficult. As a breakthrough in design technology co-optimization for advanced devices, this study developed a novel optimization framework integrating technology computer-aided design simulations, machine learning, and non-dominated sorting genetic algorithms. The developed framework provides unbiased optimal solutions, even in a high-dimensional objective space, while considering the tradeoff relationships between multiple variables. In addition, it enables inverse design to identify the design parameters of devices that satisfy specific electrical performance criteria using only a forward model, while achieving an error rate of less than 2%. Using this framework, we analyzed the operational mechanism of CFETs by comparing the inverse designs of various devices. This novel approach is particularly important when the design space is complex and extensive and is well suited for developing devices that emerge with technological advancements in the semiconductor industry.

Measurements and TCAD simulations of guard-ring structures of thin silicon sensors before and after irradiation

The developing of high performing silicon detectors for particle tracking in the next generation of high-energy physics experiments at future colliders (e.g., HL-LHC, FCC) able to operate efficiently up to very high fluence (∼1⋅10171MeVneq/cm2) is of the utmost importance. In order to sustain high voltage values with minimum leakage current injection into the core region of the sensor, the design and optimization of the Guard-Ring (GR) protection structure is crucial, especially when small substrate thicknesses are used. In a recent R&D batch produced at Fondazione Bruno Kessler (FBK) in the framework of the “eXFlu” project - INFN CSN5 grant for Young Researchers, different optimisation studies of GR structures for thin substrates (45, 30, 20 and 15μm) up to high fluence (2.5⋅10151MeVneq/cm2) have been addressed. These have been enabled thanks to ad-hoc advanced Technology CAD (TCAD) modelling of different GR design strategies, accounting for the comprehensive bulk and surface radiation-induced damage effects, and an extensive test campaign on such GR structures, both before and after irradiation. In this paper the validation of the development framework of the various GR design options before and after irradiation is presented.

TCAD approach for negative capacitance ferroelectric devices for radiation detection applications

Negative capacitance (NC) emerges as a promising technology for low-power, high-performance transistors. The HiEnD project intends to analyze and design high-energy efficient electronic devices based on innovative ferroelectric materials. It explores NC technology for high-resolution tracking detectors in future high-energy physics experiments. It aims to create ultra-thin, radiation-resistant devices for superior signal detection in harsh environments. This paper presents detailed modeling, simulation results, and a comparison with experimental data, highlighting the potential of the developed methodology but also of the technology for the realization of compact, high-performance detectors. Advanced Technology CAD modeling has been employed to investigate the potentiality of NC devices in unconventional application domains, such as high-energy physics experiments. Numerical simulations, capable of verifying experimental results, enhance predictive power, reducing time and cost in detector design and testing.

Influence of annealing treatment on performance of 4H–SiC SBD irradiated by heavy ions under room temperature and low temperature

The influence of the annealing treatment on the performance of commercial 4H–SiC Schottky barrier diodes (SBDs) subjected to heavy ion irradiation under room temperature (RT) and low temperature (LT) are presented. Experimental results confirm that annealing treatment effectively eliminates defects and interface states caused by heavy ion irradiation, particularly for 4H–SiC SBD under LT irradiation. Increasing the annealing temperature leads to the slight improvement in forward current, leakage current and breakdown voltage. However, the annealing process may result in the formation of Ti and Si compounds at the interface between the Schottky metal and SiC, as well as a significant number of vacancies. Combined with Technology Computer Aided Design (TCAD) simulations, it is concluded that the interface trap charge concentrations exceeding 1 × 1012 cm−2 significantly impact the breakdown characteristics of 4H–SiC SBDs.

Optimizing TCAD Model and Temperature-Dependent Analysis of Pt/AlN Schottky Barrier Diodes for High-Power and High-Temperature Applications

This research presents a comprehensive investigation and optimization of the Pt/AlN Schottky Barrier diode (SBD) using technology computer-aided design (TCAD) modeling. The study explores the electrical characteristics of AlN SBDs with various metal contacts, including Aluminum (Al), Silver (Ag), Tungsten (W), Gold (Au), Nickel (Ni), and Platinum (Pt). Through the comparative analyses of different metal/AlN Schottky contacts, the Pt/AlN structure emerges as the most promising due to its superior barrier height and lower leakage current. At [Formula: see text]K, the diode demonstrates a barrier height of 2.72[Formula: see text]V, a nearly ideal leakage current of 0.046[Formula: see text]pA, and a breakdown voltage of 363[Formula: see text]V. The research extends to examining the temperature-dependent electrical behavior of Pt/AlN Schottky diodes, particularly for high-power and high-temperature applications. Analysis carried out across temperatures ranging from [Formula: see text]K to [Formula: see text]K reveals a trend of increasing ON resistance and consistently lower leakage current with rising temperature. Importantly, the study indicates that the impact of temperature on the barrier height and breakdown voltage of the diode is negligible, thus rendering it suitable for high-temperature operation. Leveraging the unique properties of AlN as an ultra-wide bandgap material within the III-V compound semiconductor family, this research provides valuable insights into the potential applications of Pt/AlN Schottky contact. The study highlights that the Pt/AlN Schottky contact is effective not only for high-power, high-temperature SBDs but also as superior metal/semiconductor gate contacts for field-effect transistors (FETs). Their suitability is attributed to their ability to handle high voltages, minimize reverse leakage current, and demonstrate improved thermal stability.

Delay characteristics of quasi-nonvolatile memory devices operating in positive feedback mechanism.

This study examines the memory and read delay characteristics of quasi-nonvolatile memory (QNVM) devices operating in a positive feedback mechanism through technology computer-aided design simulation. The QNVM devices exhibit a rapid operation speed of 5 ns, a significant sensing margin of approximately 8.0 μA, and a retention time of around 1 s without any external bias. These devices showcase an exceptionally brief read delay of 0.12 ns. The energy band diagrams during the memory operation are analysed to clarify the factors influencing the read delay. The write and standby conditions modulate the potential barrier height during the standby operation, thereby affecting the read delay. Moreover, the shorter rising time causes the reduction of the read delay. This study demonstrates that the QNVM device has the potential to resolve energy consumption and speed issues in nonvolatile memory devices.

Statistical analysis of vertically stacked nanosheet complementary FET based on polycrystalline silicon with multiple grain boundaries

In this study, a complementary field-effect transistor (CFET) based on a polycrystalline silicon (poly-Si) stacked-nanosheet (NS) structure with a grain boundary (GB) is designed and analyzed using a technology computer-aided design (TCAD) simulation. The advantage of the CFET using a poly-Si is that the active cell region can be reduced by 50 % because the p-type transistors are vertically stacked on the n-type transistors. In addition, it is possible to replace the conventional CMOS process and fabricate a three-dimensional vertically stacked structure at a low cost. To consider the effect of the GB in poly-Si, we assumed that there is a single GB at the center of the body region. By optimizing the geometrical parameters of the proposed CFET, the transfer characteristics of the NMOS and PMOS transistors, such as the threshold voltage (Vth), on current (Ion), off current (Ioff), and subthreshold swing (SS), are symmetrical. The proposed CFET demonstrated a superior logic performance of NML = 0.299 V and NMH = 0.297 V at an operation voltage of VDD = 0.65 V. To consider random GBs in the poly-Si, we assumed that five GBs existed in the proposed CFET, and the variation in CMOS logic inverter characteristics are statistically analyzed. As a result, the RSDs for Vm of the NMOS and PMOS transistors are 2.067 % and 0.293 %, and the RSDs of the pull-down delay time (tpHL) and pull-up delay time (tpLH) are 5.320 % and 3.244 %, respectively. An acceptor-like traps with high trap density are dominant in the proposed CFET, and this trend is similar across the 1024 samples. Nevertheless, most of the differences are within 5 % and the proposed CFET exhibited stability against GBs and the potential to replace the conventional CMOS logic inverters.

Tunable Band‐to‐Band Tunneling and Conducting Path Transition in Local‐Control‐Gate Heterostructure Transistor

AbstractTransition metal dichalcogenide (TMD) material‐based heterostructures have exhibited great potential for building advanced architectures in novel logic devices. A local‐control‐gate (LCG) transistor based on MoTe2/MoS2 heterostructure is fabricated and analyzed, illustrating its tunable electrical characteristics and achieving band‐to‐band tunneling (BTBT) enhancement with an improved peak‐to‐valley current ratio (PVCR) value of 3.04. Compared to the basic dual‐gate tunnel field‐effect transistor (TFET) structure, adding LCG at the bottom not only isolates defect‐induced doping effects from the deposition of top gate dielectrics, but also paves the way for broader applications in multivalued logic and artificial intelligence. Aiming to further verify the operating mechanism of conducting path transition and electrical characteristic trends, commercial technology computer‐aided design (TCAD) is systematically employed assisted by density functional theory (DFT). So that the transition of conducting paths in the heterostructure channel including interlayer quantum effects can be visibly demonstrated while applying various voltages to the LCG. In summary, this work highlights the feasibility of a new LCG structure with tunable electrical characteristics and presents DFT‐assisted TCAD simulations for effective verifications.

Energy-Performance Assessment of Oscillatory Neural Networks Based on VO2 Devices for Future Edge AI Computing.

Oscillatory neural network (ONN) is an emerging neuromorphic architecture composed of oscillators that implement neurons and are coupled by synapses. ONNs exhibit rich dynamics and associative properties, which can be used to solve problems in the analog domain according to the paradigm let physics compute. For example, compact oscillators made of VO2 material are good candidates for building low-power ONN architectures dedicated to AI applications at the edge, like pattern recognition. However, little is known about the ONN scalability and its performance when implemented in hardware. Before deploying ONN, it is necessary to assess its computation time, energy consumption, performance, and accuracy for a given application. Here, we consider a VO2-oscillator as an ONN building block and perform circuit-level simulations to evaluate the ONN performances at the architecture level. Notably, we investigate how the ONN computation time, energy, and memory capacity scale with the number of oscillators. It appears that the ONN energy grows linearly when scaling up the network, making it suitable for large-scale integration at the edge. Furthermore, we investigate the design knobs for minimizing the ONN energy. Assisted by technology computer-aided design (TCAD) simulations, we report on scaling down the dimensions of VO2 devices in crossbar (CB) geometry to decrease the oscillator voltage and energy. We benchmark ONN versus state-of-the-art architectures and observe that the ONN paradigm is a competitive energy-efficient solution for scaled VO2 devices oscillating above 100 MHz. Finally, we present how ONN can efficiently detect edges in images captured on low-power edge devices and compare the results with Sobel and Canny edge detectors.

Projected performance of Si- and 2D-material-based SRAM circuits ranging from 16 nm to 1 nm technology nodes.

Researchers have been developing 2D materials (2DM) for electronics, which are widely considered a possible replacement for silicon in future technology. Two-dimensional transition metal dichalcogenides are the most promising among the different materials due to their electronic performance and relatively advanced development. Although field-effect transistors (FETs) based on 2D transition metal dichalcogenides have been found to outperform Si in ultrascaled devices, the comparison of 2DM-based and Si-based technologies at the circuit level is still missing. Here we compare 2DM- and Si FET-based static random-access memory (SRAM) circuits across various technology nodes from 16 nm to 1 nm and reveal that the 2DM-based SRAM exhibits superior performance in terms of stability, operating speed and energy efficiency when compared with Si SRAM. This study utilized technology computer-aided design to conduct device and circuit simulations, employing calibrated MoS2 nFETs and WSe2 pFETs. It incorporated layout design rules across various technology nodes to comprehensively analyse their SRAM functionality. The results show that, compared with three-dimensional structure Si transistors at 1 nm node, the planar 2DMFETs exhibited lower capacitance, leading to reduced cell read access time (-16%), reduced time to write (-72%) and lowered dynamic power (-60%). The study highlights the provisional benefits of using planar 2DM transistors to mitigate the performance degradation caused by reduced metal pitch and increased wire resistance in advanced nodes, potentially opening up exciting possibilities for high-performance and low-power circuit applications.

Enhancement of Electrical Safe Operation Area of 60 V nLDMOS by Engineering of Reduced Surface Electrical Field in the Drift Region.

To enhance the electrical safe operation area (eSOA) of laterally diffused metal oxide semiconductor (LDMOS) transistors, a novel reduced surface electric field (Resurf) structure in the n-drift region is proposed, which was fabricated by ion implantation at the surface of the LDMOS drift region and by drift region dimension optimization. Technology computer-aided design (TCAD) simulations show that the optimal value of Resurf ion implantation dose 1 × 1012 cm-2 can reduce the surface electric field in the n-drift region effectively, thereby improving the ON-state breakdown voltage of the device (BVon). In addition, the extended n-drift region length of the Ld design also improves device BVon significantly, and is aimed at reducing the current density and the electric field, and eventually suppressing the n-drift region impact ionization. The results show that the novel 60 V nLDMOS has a competitive BVon performance of 106.9 V, which is about 20% higher than that of the conventional one. Meanwhile, the OFF-state breakdown voltage of the device (BVoff) of 88.4 V and the specific ON-resistance (RON,sp) of 129.7 mΩ⋅mm2 exhibit only a slight sacrifice.

Investigation of the forward gate leakage current in pGaN/AlGaN/GaN HEMTs through TCAD simulations

In this study, we examined the gate leakage characteristics of normally off pGaN/AlGaN/GaN HEMTs through a simulation study. The Fowler Nordheim Tunneling (FNT) mechanism mainly contributes to the gate leakage process as indicated by the Technology Computer-Aided Design (TCAD) simulation. However, at low bias, the FNT undercalculates the leakage current since the electric field is low in this region. This extra leakage current component at this low bias region can be attributed to the presence of surface traps. Trap-assisted tunneling current along with the FNT current can explain forward leakage characteristics of the pGaN HEMTs. Our TCAD simulations were matched with the experimental data for five devices from four different research groups to support this claim. Using TCAD simulations, we have been able to analyze several device parameters including the various potential drops inside the gate stack structure. We were able to identify some of the trap levels and compare them to the dominant defects expected to be present in the pGaN cap layer. Furthermore, we studied the effects of different device parameters on the gate leakage process in the pGaN HEMT.

Thermal-induced bandgap broadening phenomenon in copolymer organic semiconductors

This study elucidates the thermal-induced bandgap broadening (TBB) phenomenon in copolymer organic semiconductors (OSCs). From the perspective of device physics, the diketopyrrolopyrrole-based copolymer was employed as the semiconductor layer to fabricate a back-to-back Schottky junction structure. Characterization through the analysis of I–V curves enables the qualitative exploration of the correlation between bandgap and temperature in copolymer OSCs. Then, technology computer-aided design was utilized to explore the influence of thermal-induced bandgap broadening on the back-to-back Schottky I–V curves. Subsequently, the variable temperature UV-VIS-NIR absorption spectra of the copolymer OSCs were analyzed, providing quantitative evidence of the thermal-induced bandgap broadening phenomenon and confirming its recoverability. Through the research of the Schottky junction and absorption spectra, we verified the consistency of the TBB phenomenon in both the electrical and optical bandgaps. From the scanning electron microscope images of the copolymer OSC films, it is found that the thermal-induced bandgap broadening phenomenon is mainly caused by thermal expansion and increased disorder of copolymer molecules. This study highlights a physical phenomenon of copolymer OSCs that is different from most inorganic semiconductors, and such insight offers a theoretical perspective for the application and thermal stability investigation of copolymer devices under high temperature conditions.

Simulation of 2D ReS2/WSe2 based complementary field-effect transistors towards 1 nm technology node

Advanced Integrated Circuit technology demands high-performance channel materials and innovative device architectures to sustain the scaling of field-effect transistors. In this study, we simulate the electrical performance of rhenium disulfide and tungsten diselenide nanosheet FETs (NSFETs) with gate lengths ranging from 12 nm to 8 nm using Technology Computer-Aided Design method. The simulated high performance including 393 μA/μm on-state current and over 105 on/off ratio can meet the criteria for integrated circuit applications in the 1 nm technology node. Complementary FET (CFET) simulations are conducted through the vertical stacking of ReS2 and WSe2 NSFETs, exhibiting a small parasitic capacitance of 1.0 fF/μm, and notable noise margin (>235 mV) at different process corners. The construction and performance simulation of Static Random-Access Memory (SRAM) is realized through CFET interconnection, involving the calculation of read current and read/write noise margin. This research offers a forward-looking analysis of performance metrics for future 2D materials-based NSFETs, CFETs, and SRAMs.

3.3 kV-class NiO/β-Ga2O3 heterojunction diode and its off-state leakage mechanism

This Letter demonstrates a high-performance 3.3 kV-class β-Ga2O3 vertical heterojunction diode (HJD) along with an investigation into its off-state leakage mechanism. The vertical β-Ga2O3 HJD with field plate assisted deep mesa (FPDM) termination was fabricated using a self-aligned technique to etch the deep mesa to a depth of 9 μm, thereby reducing electric field crowding at the anode edge. In addition, a thick dielectric is deposited to fill the trench, facilitating the utilization of a field plate to further reduce the electric field at the anode edge. TCAD (Technology Computer Aided Design) simulations show significant suppression of electric field crowding at the anode edge. The fabricated HJD exhibits a high current swing of ∼1010 over a temperature range from 25 °C to 175 °C. The specific on-resistance (Ron,sp) is extracted to be 3.9 mΩ cm2, and the breakdown voltage is 3.42 kV with the FPDM termination. These conduction and blocking characteristics lead to a high power figure of merit of 3 GW/cm2, which is one of the highest among multi-kilovolt β-Ga2O3 diodes. Furthermore, the off-state current leakage mechanism of the HJD under a reverse bias up to 2000 V was investigated. The fitted results reveal that the leakage current is primarily dominated by Poole–Frenkel (PF) emission, with the trap level of PF extracted to be 0.36 eV below the conduction band of NiO.

Electron-Induced Single-Event Effect in 28 nm SRAM-Based FPGA

As the feature size of integrated circuit decreases, the critical charge of single-event effect decreases as well, making nano-scale devices more susceptible to the high-energy charged particles during their application in space. Here, we study the electron-induced single-event effect in 28 nm static random-access memory (SRAM)-based field programmable gate array (FPGA) utilizing high-energy electrons with energy of 1 MeV~5 MeV. The experimental results demonstrate that the 3 MeV electrons can cause single-event functional interrupts (SEFIs) in FPGA, while the electrons with other energies cannot. To further explore the mechanism of electron-induced SEFIs in this nanoscale FPGA, we combined Monte Carlo, Technology Computer-Aided Design (TCAD), and Simulation Program with Integrated Circuit Emphasis (SPICE) simulations. It is revealed that the SEFI was mainly caused by the direct ionization effect of high-energy electrons, and the SEFI was related to the interactions between multiple sensitive nodes.

Understanding of multiway heat extraction using peripheral diamond in an AlGaN/GaN high electron mobility transistor by electrothermal simulations

High-power operation of high electron mobility transistors (HEMTs) is limited due to a variety of thermal resistances in HEMT devices that cause self-heating effects (SHEs). To reduce SHEs, diamond heat spreaders integrated in the device have proven efficient in extracting heat from the device. In this report, we use electrothermal technology computer-aided design simulations to demonstrate a qualitative understanding of multiway heat extraction utilizing diamond heat spreaders to improve HEMT thermal performance at high DC output power densities (∼40 W mm−1). The impact of each heat extraction pathway is understood while considering the thermal boundary resistance between the diamond/GaN heterointerface and optimization of the GaN buffer layer thickness. Using these findings, we simulate an AlGaN/GaN HEMT device operating at 40 W mm−1 DC output power and demonstrate significant reduction in the temperature.