On Numerical Modelling of Industrial Powder Compaction Processes for Large Deformation of Endochronic Plasticity at Finite Strains

Compaction processes are one the most important par ts of powder forming technology. The main applications are focused on pieces for a utomotive, aeronautic, electric and electronic industries. The main goals of the compaction processes are to obtain a compact with the geometrical requirements, without cracks, and with a uniform distribution of density. Design of such proc esses consist, essentially, in determine the sequence and relative displacements of die and punches in order to achieve such goals. A.B. Khoei presented a gener al framework for the finite element simulation of powder forming processes based on the following aspects; a large displacement formulation, centred on a total and updated Lagrangian formulation; an adaptive finite element strategy based on error estimates and automatic remeshing techniques; a cap model based on a hard ening rule in modelling of the highly non-linear behaviour of material; and the use of an efficient contact algorithm in the context of an interface element fo rmulation. In these references, the non-linear behaviour of powder was adequately desc ribed by the cap plasticity model. However, it suffers from a serious deficiency when the stress-point reaches a yield surface. In the flow theory of plasticit y, the transition from an elastic state to an elasto-plastic state appears more or less abruptly. For powder material it is very difficult to define the locati on of yield surface, because there is no distinct transition from elastic to ela stic-plastic behaviour. Results of experimental test on some hard met al powder show that the plastic effects were begun immediately upon loading. In such mater ials the domain of the yield surface would collapse to a point, so making the di rection of plastic increment indeterminate, because all directions are normal to a point. Thus, the classical plasticity theory cannot deal with such materials and an advanced constitutive theory is necessary. In the present paper, the constitutive equations of powder materials will be discussed via an endochronic theory of plasticity. This theory provides a unifi ed point of view to describe the elastic-plastic behaviour of material since it places no requirement for a yield surface and a ’loading function’ to disting uish between loading an unloading. Endochronic theory of plasticity has been app lied to a number of metallic materials, concrete and sand, but to the knowledge of authors, no numerical scheme of the model has been applied to powder material . In the present paper, a new approach is developed based on an endochronic rate independent, density-dependent plasticity model for describing the isothermal deformation behavior of metal powder at low homologous temperature. Although the concept of yield surface has not been explicitly assumed in endochronic theory, it is shown that the cone-cap plasticity yield surface (Fig.1), which is the m ost commonly used plasticity models for describing the behavior of powder materi al can be easily derived as a special case of the proposed endochronic theory. Fig.1 Trace of cone-cap yield function on the meridian pl ane for different relative density As large deformation is observed in powder compaction process, a hypoelastic-pl astic formulation is developed in the context of finite deformation plasticity. Constitutive equations are stated in unrotated frame of reference that greatly s implifies endochronic constitutive relation in finite plasticity. Constitutive e quations of the endochronic theory and their numerical integration are establish ed and procedures for determining material parameters of the model are demonstra ted. Finally, the numerical schemes are examined for efficiency in the model ling of a tip shaped component, as shown in Fig.2. Fig.2 A shaped tip component. a) Geometry, boundary conditio n and finite element mesh; b) density distribution at final stage of

Clastic compaction unit classification based on clay content and integrated compaction recovery using well and seismic data

Compaction correction is a key part of paleogeomorphic recovery methods. Yet, the influence of lithology on the porosity evolution is not usually taken into account. Present methods merely classify the lithologies as sandstone and mudstone to undertake separate porositydepth compaction modeling. However, using just two lithologies is an oversimplification that cannot represent the compaction history. In such schemes, the precision of the compaction recovery is inadequate. To improve the precision of compaction recovery, a depth compaction model has been proposed that involves both porosity and clay content. A clastic lithological compaction unit classification method, based on clay content, has been designed to identify lithological boundaries and establish sets of compaction units. Also, on the basis of the clastic compaction unit classification, two methods of compaction recovery that integrate well and seismic data are employed to extrapolate well-based compaction information outward along seismic lines and recover the paleo-topography of the clastic strata in the region. The examples presented here show that a better understanding of paleo-geomorphology can be gained by applying the proposed compaction recovery technology.

Finite element modeling of consolidation of composite laminates

Advanced fiber reinforced polymer composites have been increasingly applied to various structural components. One of the important processes to fabricate high performance laminated composites is an autoclave assisted prepreg lay-up. Since the quality of laminated composites is largely affected by the cure cycle, selection of an appropriate cure cycle for each application is important and must be optimized. Thus, some fundamental model of the consolidation and cure processes is necessary for selecting suitable parameters for a specific application. This article is concerned with the ＂flow-compaction＂ model during the autoclave processing of composite materials. By using a weighted residual method, two-dimensional finite element formulation for the consolidation process of thick thermosetting composites is presented and the corresponding finite element code is developed. Numerical examples, including comparison of the present numerical results with one-dimensional and twodimensional analytical solutions, are given to illustrate the accuracy and effectiveness of the proposed finite element formulation. In addition, a consolidation simulation of AS4/3501-6 graphite/epoxy laminate is carded out and compared with the experimental results available in the literature.

New Method of Total Ionizing Dose Compact Modeling in Partially Depleted Silicon-on-Insulator MOSFETs

On the basis of a detailed discussion of the development of total ionizing dose （TID） effect model, a new commercial-model-independent TID modeling approach for partially depleted silicon-on-insulator metal-oxide- semiconductor field effect transistors is developed. An exponential approximation is proposed to simplify the trap charge calculation. Irradiation experiments with 60Co gamma rays for IO and core devices are performed to validate the simulation results. An excellent agreement of measurement with the simulation results is observed.

A review for compact model of graphene field-effect transistors

Graphene has attracted enormous interests due to its unique physical, mechanical, and electrical properties. Specially, graphene-based field-effect transistors （FETs） have evolved rapidly and are now considered as an option for conventional silicon devices. As a critical step in the design cycle of modem IC products, compact model refers to the development of models for integrated semiconductor devices for use in circuit simulations. The purpose of this review is to provide a theoretical description of current compact model of graphene field-effect transistors. Special attention is devoted to the charge sheet model, drift-diffusion model, Boltzmann equation, density of states （DOS）, and surface-potential-based compact model. Finally, an outlook of this field is briefly discussed.

Performance and analytical modelling of halo-doped surrounding gate MOSFETs

Halo structure is added to sub-100 nm surrounding-gate metal-oxide-semiconductor fieldeffect-transistors （MOS- FETs） to suppress short channel effect. This paper develops the analytical surface potential and threshold voltage models based on the solution of Poisson＇s equation in fully depleted condition for symmetric halo-doped cylindrical surrounding gate MOSFETs. The performance of the halo-doped device is studied and the validity of the analytical models is verified by comparing the analytical results with the simulated data by three dimensional numerical device simulator Davinci. It shows that the halo doping profile exhibits better performance in suppressing threshold voltage roll-off and drain-induced barrier lowering, and increasing carrier transport efficiency. The derived analytical models are in good agreement with Davinci.

BSIM-CMG Compact Model for IC CAD: from FinFET to Gate-All-Around FET Technology

We discuss the BSIM-CMG compact model for SPICE simulations of any common multi-gate(CMG)device.This is an industry standard model which has been used extensively for FinFETs IC design and simulation,and has now been extended to accurately model gate-allaround FET(GAAFET).We present the core framework of BSIM-CMG and discuss the latest updates that capture various physical phenomena originating from the quantum confinement of electrons by the small cross section of the GAAFET channel.Special attention is paid to providing suitable model parameters that can be adjusted using software tools to match the model with manufactured transistors very accurately.Furthermore,the model’s speed allows the use of Monte Carlo circuit simulation to account for random device variations encountered in manufacturing.This model is the industry standard compact model for GAAFETs and will help bridge the wide divide between GAA IC manufacturing and design,starting at 3nm/2nm technologies.

An improvement to computational efficiency of the drain current model for double-gate MOSFET

As a connection between the process and the circuit design, the device model is greatly desired for emerging devices, such as the double-gate MOSFET. Time efficiency is one of the most important requirements for device modeling. In this paper, an improvement to the computational efficiency of the drain current model for double-gate MOSFETs is extended, and different calculation methods are compared and discussed. The results show that the calculation speed of the improved model is substantially enhanced. A two-dimensional device simulation is performed to verify the improved model. Furthermore, the model is implemented into the HSPICE circuit simulator in Verilog-A for practical application.

A review of compact modeling for phase change memory

Phase change memory(PCM)attracts wide attention for the memory-centric computing and neuromorphic comput-ing.For circuit and system designs,PCM compact models are mandatory and their status are reviewed in this work.Macro mod-els and physics-based models have been proposed in different stages of the PCM technology developments.Compact model-ing of PCM is indeed more complex than the transistor modeling due to their multi-physics nature including electrical,thermal and phase transition dynamics as well as their interactions.Realizations of the PCM operations including threshold switching,set and reset programming in these models are diverse,which also differs from the perspective of circuit simulations.For the purpose of efficient and reliable designs of the PCM technology,open issues and challenges of the compact modeling are also discussed.

A unified charge-based model for SOI MOSFETs applicable from intrinsic to heavily doped channel

A unified charge-based model for fully depleted silicon-on-insulator （SOI） metal oxide semiconductor field-effect transistors （MOSFETs） is presented. The proposed model is accurate and applicable from intrinsic to heavily doped channels with various structure parameters. The framework starts from the one-dimensional Poisson Boltzmann equa- tion, and based on the full depletion approximation, an accurate inversion charge density equation is obtained. With the inversion charge density solution, the unified drain current expression is derived, and a unified terminal charge and intrinsic capacitance model is also derived in the quasi-static case. The validity and accuracy of the presented analytic model is proved by numerical simulations.

Overpressure origin and its effects on petroleum accumulation in the conglomerate oil province in Mahu Sag, Junggar Basin, NW China

The origin of overpressure and its effect on petroleum accumulation in the large Permian/Triassic conglomerate oil province in the Mahu Sag,Junggar Basin have been investigated based on comprehensive analysis of log curve combinations,loading-unloading curves,sonic velocity-density cross-plot,and porosity comparison data.The study results show that there are two kinds of normal compaction models in the study area,namely,two-stage linear model and exponent model;overpressure in the large conglomerate reservoirs including Lower Triassic Baikouquan Formation and Permian Upper and Lower Wu’erhe Formations is the result of pressure transfer,and the source of overpressure is the overpressure caused by hydrocarbon generation of Permian Fengcheng Formation major source rock.The petroleum migrated through faults under the driving of hydrocarbon generation overpressure into the reservoirs to accumulate,forming the Permian and Triassic overpressure oil and gas reservoirs.The occurrence and distribution of overpressure are controlled by the source rock maturity and strike-slip faults connecting the source rock and conglomerate reservoirs formed from Indosinian Movement to Himalayan Movement.As overpressure is the driving force for petroleum migration in the large Mahu oil province,the formation and distribution of petroleum reservoirs above the source rock in this area may have a close relationship with the occurrence of overpressure.

Continuous analyticⅠ-Ⅴmodel for GS DG MOSFETs including hot-carrier degradation effects

We have studied the influence of hot-carrier degradation effects on the drain current of a gate-stack double-gate （GS DG） MOSFET device. Our analysis is carried out by using an accurate continuous current-voltage （I-V） model, derived based on both Poisson＇s and continuity equations without the need of charge-sheet approxi- mation. The developed model offers the possibility to describe the entire range of different regions （subthreshold, linear and saturation） through a unique continuous expression. Therefore, the proposed approach can bring consid- erable enhancement at the level of multi-gate compact modeling including hot-carrier degradation effects.

A simplified compact model of miniaturized cross-shaped CMOS integrated Hall devices

A simplified compact model for a miniaturized cross-shaped CMOS integrated Hall device is presented. The model has a simple circuit structure,only consisting of a passive network with eight non-linear resistors and four current-controlled voltage sources.It completely considers the following effects：non-linear conductivity,geometry dependence of sensitivity,temperature drift,lateral diffusion,and junction field effect.The model has been implemented in Verilog-A hardware description language and was successfully performed in a Cadence Spectre simulator.The simulation results are in good accordance with the classic experimental results reported in the literature.

Statistically modeling I-V characteristics of CNT-FET with LASSO

With the advent ofinternet of things （lOT）, the need for studying new material and devices for various applications is increasing. Traditionally we build compact models for transistors on the basis of physics. But physi- cal models are expensive and need a very long time to adjust for non-ideal effects. As the vision for the application of many novel devices is not certain or the manufacture process is not mature, deriving generalized accurate physi- cal models for such devices is very strenuous, whereas statistical modeling is becoming a potential method because of its data oriented property and fast implementation. In this paper, one classical statistical regression method, LASSO, is used to model the I-V characteristics of CNT-FET and a pseudo-PMOS inverter simulation based on the trained model is implemented in Cadence. The normalized relative mean square prediction error of the trained model versus experiment sample data and the simulation results show that the model is acceptable for digital circuit static simulation. And such modeling methodology can extend to general devices.

Ambipolar Transport Compact Models for Two-Dimensional Materials Based Field-Effect Transistors

Three main ambipolar compact models for Two-Dimensional(2D)materials based Field-Effect Transistors(2D-FETs)are reviewed:(1)Landauer model,(2)2D Pao-Sah model,and(3)virtual Source Emission-Diffusion(VSED)model.For the Landauer model,the Gauss quadrature method is applied,and it summarizes all kinds of variants,exhibiting its state-of-art.For the 2D Pao-Sah model,the aspects of its theoretical fundamentals are rederived,and the electrostatic potentials of electrons and holes are clarified.A brief development history is compiled for the VSED model.In summary,the Landauer model is naturally appropriate for the ballistic transport of short channels,and the 2D Pao-Sah model is applicable to long-channel devices.By contrast,the VSED model offers a smooth transition between ultimate cases.These three models cover a fairly completed channel length range,which enables researchers to choose the appropriate compact model for their works.

A semi-empirical analytic model for threshold voltage instability in MOSFETs with high-k gate stacks

A semi-empirical analytic model for the threshold voltage instability of a MOSFET is derived from Shockley-Read-Hall （SRH） statistics to account for the transient charging effects in a MOSFET high-k gate stack. Starting from the single energy level and single trap assumption, an analytical expression for the filled trap density in terms of dynamic time is derived from SRH statistics. The semi-empirical analytic model for the threshold voltage instability is developed based on MOSFET device physics between the threshold voltage and the induced trap density. The obtained model is also verified by extensive experimental data of trapping and de-trapping stress from different high-k gate configurations.

BSIM--making the first international standard MOSFET model

BSIM （Berkeley Short-Channel IGFET） became the first international industry standard model for simulation of MOS integrated circuits in 1997. The cumulative sales of ICs that have been designed with the aid of BSIM and produced for computing, communication, consumer, and industrial applications is estimated to be around 400 billion US dollars. From 0.35μm CMOS to multi-gate FinFET, BSIM serves a wide range of technologies. Many China educated researchers have contributed to its success.

A novel compact model for on-chip stacked transformers in RF-CMOS technology

A novel compact model for on-chip stacked transformers is presented.The proposed model topology gives a clear distinction to the eddy current,resistive and capacitive losses of the primary and secondary coils in the substrate.A method to analytically determine the non-ideal parasitics between the primary coil and substrate is provided.The model is further verified by the excellent match between the measured and simulated S-parameters on the extracted parameters for a 1：1 stacked transformer manufactured in a commercial RF-CMOS technology.

A SPICE model for a phase-change memory cell based on the analytical conductivity model

By way of periphery circuit design of the phase-change memory,it is necessary to present an accurate compact model of a phase-change memory cell for the circuit simulation.Compared with the present model,the model presented in this work includes an analytical conductivity model,which is deduced by means of the carrier transport theory instead of the fitting model based on the measurement.In addition,this model includes an analytical temperature model based on the 1D heat-transfer equation and the phase-transition dynamic model based on the JMA equation to simulate the phase-change process.The above models for phase-change memory are integrated by using Verilog-A language,and results show that this model is able to simulate theⅠ-Ⅴcharacteristics and the programming characteristics accurately.

Benchmark tests on symmetry and continuity characteristics between BSIM4 and ULTRA-BULK

This paper presents the benchmark test results on the symmetry and continuity characteristics between BSIM4 from Berkeley and ULTRA-BULK from Peking University. It is shown that the industry standard model BSIM4 has a series of the shortcomings of the continuity and symmetry, such as the charge, high-order current derivatives, and the trans-capacitances while the latest advanced surface-potential based MOSFET compact model, ULTRA-BULK, demonstrates all necessary continuity and symmetry characteristics, which are very important for analog and RF circuit design.