Design optimization of a silicon-germanium heterojunction negative capacitance gate-all-around tunneling field effect transistor based on a simulation study

The steep sub-threshold swing of a tunneling field-effect transistor(TFET)makes it one of the best candidates for lowpower nanometer devices.However,the low driving capability of TFETs prevents their application in integrated circuits.In this study,an innovative gate-all-around(GAA)TFET,which represents a negative capacitance GAA gate-to-source overlap TFET(NCGAA-SOL-TFET),is proposed to increase the driving current.The proposed NCGAA-SOL-TFET is developed based on technology computer-aided design(TCAD)simulations.The proposed structure can solve the problem of the insufficient driving capability of conventional TFETs and is suitable for sub-3-nm nodes.In addition,due to the negative capacitance effect,the surface potential of the channel can be amplified,thus enhancing the driving current.The gateto-source overlap(SOL)technique is used for the first time in an NCGAA-TFET to increase the band-to-band tunneling rate and tunneling area at the silicon-germanium heterojunction.By optimizing the design of the proposed structure via adjusting the SOL length and the ferroelectric layer thickness,a sufficiently large on-state current of 17.20μA can be achieved and the threshold voltage can be reduced to 0.31 V with a sub-threshold swing of 44.98 mV/decade.Finally,the proposed NCGAA-SOL-TFET can overcome the Boltzmann limit-related problem,achieving a driving current that is comparable to that of the traditional complementary metal-oxide semiconductor devices.

Band gap control of phononic beam with negative capacitance piezoelectric shunt

Periodic arrays of negative capacitance shunted piezoelectric patches are employed to control the band gaps of phononic beams. The location and the extent of induced band gap depend on the mismatch in impedance generated by each patch. The total impedance mismatch is determined by the added mass and stiffness of each patch as well as the shunting electrical impedance. Therefore, the band gap of the shunted phononic beam can be actively tuned by appropriately selecting the value of negative capacitance. The control of the band gap of phononic beam with negative capacitive shunt is demonstrated numerically by employing transfer matrix method. The result reveals that using negative capacitive shunt to tune the band gap is effective.

Analytical model for the effects of the variation of ferrolectric material parameters on the minimum subthreshold swing in negative capacitance capacitor

In this paper,we analytically study the relationship between the coercive field,remnant polarization and the thickness of a ferroelectric material,required for the minimum subthreshold swing in a negative capacitance capacitor.The interdependence of the ferroelectric material properties shown in this study is defined by the capacitance matching conditions in the subthreshold region in an NC capacitor.In this paper,we propose an analytical model to find the optimal ferroelectric thickness and channel doping to achieve a minimum subthreshold swing,due to a particular ferroelectric material.Our results have been validated against the numerical and experimental results already available in the literature.Furthermore,we obtain the minimum possible subthreshold swing for different ferroelectric materials used in the gate stack of an NC-FET in the context of a manufacturable semiconductor technology.Our results are presented in the form of a table,which shows the calculated channel doping,ferroelectric thickness and minimum subthreshold for five different ferroelectric materials.

Singular variation property of elastic constants of piezoelectric ceramics shunted to negative capacitance

Piezoelectric shunt damping has been widely used in vibration suppression, sound absorption, noise elimination, etc. In such applications, the variant elastic constants of piezoelectric materials are the essential parameters that determine the performances of the systems, when piezoelectric materials are shunted to normal electrical elements, i.e., resistance, inductance and capacitance, as well as their combinations. In recent years, many researches have demonstrated that the wideband sound absorption or vibration suppression can be realized with piezoelectric materials shunted to negative capacitance. However, most systems using the negative-capacitance shunt circuits show their instabilities in the optimal condition, which are essentially caused by the singular variation properties of elastic constants of piezoelectric materials when shunted to negative capacitance. This paper aims at investigating the effects of negative-capacitance shunt circuits on elastic constants of a piezoelectric ceramic plate through theoretical analyses and experiments, which gives an rational explanation for why negative capacitance shunt circuit is prone to make structure instable. First, the relationships between the elastic constants c11, c33, c55 of the piezoelectric ceramic and the shunt negative capacitance are derived with the piezoelectric constitutive law theoretically. Then, an experimental setup is established to verify the theoretical results through observing the change of elastic constant c55 of the shunted piezoelectric plate with the variation of negative capacitance. The experimental results are in good agreement with the theoretical analyses, which reveals that the instability of the shunt damping system is essentially caused by the singular variation property of the elastic constants of piezoelectric material shunted to negative capacitance.

Negative capacitance in doped bi-layer organic light-emitting devices

This paper reports that the doped bi-layer organic light-emitting devices are fabricated by doping in different regions of the light-emitting layer, the admittance and luminance spectra to characterize the capacitance and luminance of the device are measured. Negative capacitance （NC） appeared at low frequencies when the doped devices are biased with high voltages. The measured phase difference between AC voltage applied across the device and AC current flowing through the device show that the device is inductive when NC appears.

A Possible Minimum Toy Model with Negative Differential Capacitance for Self-sustained Current Oscillation

We generalize a simple model for superlattices to include the effect of differential capacitance. It is shown that the model always has a stable steady-state solution （SSS） if all differential capacitances are positive. On the other hand, when negative differential capacitance is included, the model can have no stable SSS and be in a self-sustained current oscillation behavior. Therefore, we find a possible minimum toy model with both negative differential resistance and negative differential capacitance which can include the phenomena of both self-sustained current oscillation and I-V oscillation of stable SSSs.

Charge recombination mechanism to explain the negative capacitance in dye-sensitized solar cells

Negative capacitance （NC） in dye-sensitized solar cells （DSCs） has been confirmed experimentally. In this work, the recombination behavior of carriers in DSC with semiconductor interface as a carder＇s transport layer is explored theoreti- cally in detail. Analytical results indicate that the recombination behavior of carriers could contribute to the NC of DSCs under small signal perturbation. Using this recombination capacitance we propose a novel equivalent circuit to completely explain the negative terminal capacitance. Further analysis based on the recombination complex impedance show that the NC is inversely proportional to frequency. In addition, analytical recombination resistance is composed by the alternating current （AC） recombination resistance （Rrac） and the direct current （DC） recombination resistance （Rrdc）, which are caused by small-signal perturbation and the DC bias voltage, respectively. Both of two parts will decrease with increasing bias voltage.

Insight into influence of thermodynamic coefficients on transient negative capacitance in Zr-doped HfO_(2) ferroelectric capacitors

We study the influence of the thermodynamic coefficients on transient negative capacitance for the Zr-doped HfO_(2)(HZO)ferroelectric capacitors by the theoretical simulation based on the Landau-Khalatnikov(L-K)theory and experimental measurement of electrical properties in the resistor-ferroelectric capacitor(R-FEC)circuit.Our results show that the thermodynamic coefficientsα,βandγalso play a key role for the transient NC effect besides the viscosity coefficient and series resistor.Moreover,the smaller coefficientsαandβ,the more significant the transient NC effect.In addition,we also find that the thermodynamic process of transient NC does not obey the generally accepted viewpoint of Gibbs free energy minimization.

Study the Effect of Ruthenium Dye Layer on Negative Capacitance in Solar Cells Based on the Nc-TiO₂Semiconducting Polymer Heterojunction

We report the effect of ruthenium dye on negative capacitance of nanocrystalline titanium dioxide/poly(3-hexyl thiophene), nc-TiO2/P3HT, heterojunction solar cells. It has been found that the low frequency capacitance reaches a high positive value and then drop to the negative region. In P3HT/Ru-Dye/nc-TiO2 solar cells, the negative capacitance is observed under very low forward bias condition unlike the negative capacitance in P3HT/ncTiO2 solar cells. That is attributed to the difference of the concentration of dipole and presence of depletion region at interface between the P3HT and nc-TiO2.

Observing suppressed polarization in flexible ferroelectric negative capacitance field effect transistors

Negative capacitance(NC)has the potential to enable low power microelectronics beyond the fundamental thermionic limit,and it has been theorized that the thermodynamically unstable NC of ferroelectrics can be stabilized by linear dielectric,making negative capacitance ferroelectric field effect transistors(NC-FeFET)possible.Nevertheless,the validity of NC as a physical concept for ferroelectrics remain contentious despite numerous theoretical and experimental investigations,and the intrinsic ferroelectric NC with suppressed polarization has not been demonstrated except locally at vortex core.While NC-FeFET with subthreshold swing(SS)lower than 60 mV/dec limit has been reported,such device characteristics has not been directly connected to suppressed polarization at materials’level,and alternative mechanisms other than NC have also been proposed.Here we demonstrate stable sub-60 mV/dec SS with hysteresis free Isingle bondV in NC-FeFET based on SrTiO_(3)/Pb(Zr_(0.1)Ti_(0.9))O_(3)/SrTiO_(3) heterostructure,and observe its suppressed polarization at both macroscopic and microscopic scales.The intrinsic ferroelectric NC thus is experimentally confirmed and directly connected to NC-FeFET performance,and the mica-based device is also highly flexible and robust under cyclic bending as well as extended heating.

Observation of stabilized negative capacitance effect in hafnium-based ferroic films

A negative capacitance(NC)effect has been proposed as a critical pathway to overcome the‘Boltzmann tyranny’of electrons,achieve the steep slope operation of transistors and reduce the power dissipation of current semiconductor devices.In particular,the ferroic property in hafnium-based films with fluorite structure provides an opportunity for the application of the NC effect in electronic devices.However,to date,only a transient NC effect has been confirmed in hafnium-based ferroic materials,which is usually accompanied by hysteresis and is detrimental to low-power transistor operations.The stabilized NC effect enables hysteresis-free and low-power transistors but is difficult to observe and demonstrate in hafnium-based films.This difficulty is closely related to the polycrystalline and multi-phase structure of hafnium-based films fabricated by atomic layer deposition or chemical solution deposition.Here,we prepare epitaxial ferroelectric Hf_(0.5)Zr_(0.5)O_(2) and antiferroelectric ZrO_(2) films with single-phase structure and observe the capacitance enhancement effect of Hf_(0.5)Zr_(0.5)O_(2)/Al_(2)O_(3) and ZrO_(2)/Al_(2)O_(3) capacitors compared to that of the isolated Al_(2)O_(3) capacitor,verifying the stabilized NC effect.The capacitance of Hf_(0.5)Zr_(0.5)O_(2) and ZrO_(2) is evaluated as−17.41 and−27.64 pF,respectively.The observation of the stabilized NC effect in hafnium-based films sheds light on NC studies and paves the way for low-power transistors.

Sensing with extended gate negative capacitance ferroelectric field-effect transistors

With major signal analytical elements situated away from the measurement environment,extended gate(EG)ion-sensitive fieldeffect transistors(ISFETs)offer prospects for whole chip circuit design and system integration of chemical sensors.In this work,a highly sensitive and power-efficient ISFET was proposed based on a metal-ferroelectric-insulator gate stack with negative capacitance–induced super-steep subthreshold swing and ferroelectric memory function.Along with a remotely connected EG electrode,the architecture facilitates diverse sensing functions for future establishment of smart biochemical sensor platforms.

Transient performance estimation of charge plasma based negative capacitance junctionless tunnel FET

We investigate the transient behavior of an n-type double gate negative capacitance junctionless tun- nel field effect transistor （NC-JLTFET）. The structure is realized by using the work-function engineering of metal electrodes over a heavily doped n＋ silicon channel and a ferroelectric gate stack to get negative capacitance be- havior. The positive feedback in the electric dipoles of ferroelectric materials results in applied gate bias boosting. Various device transient parameters viz. transconductance, output resistance, output conductance, intrinsic gain, intrinsic gate delay, transconductance generation factor and unity gain frequency are analyzed using ac analysis of the device. To study the impact of the work-function variation of control and source gate on device performance, sensitivity analysis of the device has been carried out by varying these parameters. Simulation study reveals that it preserves inherent advantages of charge-plasma junctionless structure and exhibits improved transient behavior as well.

Theoretical modification of the negative Miller capacitance during the switching transients of IGBTs

The insulated gate bipolar transistor （1GBT） has negative Miller capacitance during switching transients. It has conventionally been attributed to the voltage dependency of the Miller capacitance. However this explanation has physical ambiguity, yet, it lacks a discussion of the conditions for the occurrence of negative Miller capacitance as well. We argue that it is the current dependence to the Miller capacitance that results in the negative case. In this paper, we provide a modification to the theoretical analysis of this phenomenon. The occurrence condition for it and the device parameters about it are discussed. It is discovered that the negative Miller capacitance must occur during the turn-off process for any IGBT, while it is relatively difficult during the turn-on process. At the device design level, the current gain of the PNP transistor in the IGBT is an important factor for the negative Miller capacitance.

(p)nc-Si∶H/(n)c-Si异质结变容二极管

采用等离子体增强化学气相沉积技术和电子束蒸发技术制备了一种新型的线性缓变异质结变容二极管———Au/Cr合金(电极)/multi-layer(p)nc-Si∶H/(n)c-Si/(电极)Au/Ge合金结构.I V,C V,C f以及DLTS的测试结果表明:其电容变化系数远大于单晶硅线性缓变异质结的电容变化系数,正向导电机制符合隧穿辅助辐射复合模型,这是nc-Si∶H层中nc-Si晶粒的量子效应所致;反向电流主要由异质结中空间电荷区的产生电流决定,且反向漏电流小,反向击穿电压高,表现出较好的整流特性.

Nc-Si∶H薄膜器件的研究

介绍了氢化纳米硅(nc-Si∶H)薄膜在电子学器件和光电转换器件(如隧道二极管、异质结二极管、变容二极管、单电子晶体管、太阳能电池、发光二极管)等方面的研究进展,分析了这些器件的性能与nc-Si∶H薄膜结构之间的关系,阐述了新型器件的优点。

A 58-dBΩ20-Gb/s inverter-based cascode transimpedance amplifier for optical communications

This work presents a high-gain broadband inverter-based cascode transimpedance amplifier fabricated in a 65-nm CMOS process.Multiple bandwidth enhancement techniques,including input bonding wire,input series on-chip inductive peak-ing and negative capacitance compensation,are adopted to overcome the large off-chip photodiode capacitive loading and the miller capacitance of the input device,achieving an overall bandwidth enhancement ratio of 8.5.The electrical measure-ment shows TIA achieves 58 dBΩup to 12.7 GHz with a 180-fF off-chip photodetector.The optical measurement demonstrates a clear open eye of 20 Gb/s.The TIA dissipates 4 mW from a 1.2-V supply voltage.

NC-FinFET器件的仿真研究

通过结合BSIMCMG模型与负电容(NC)模型,构建了NC-FinFET模型。基于所建立的NC-FinFET模型,推导分析了其等效电容模型。利用Hspice对NC-FinFET的器件特性进行了系统仿真与分析。结果表明,与FinFET相比,NC-FinFET在电学特性上有更加明显的优势,亚阈值摆幅更低。此外,分析了铁电材料的厚度对亚阈值摆幅及栅压放大倍数的影响,以及衬偏电压对NC-FinFET性能的影响,为在NC-FinFET中降低功耗和抑制寄生效应提供了理论依据和解决思路。

Evaluation of the differential capacitance for ferroelectric materials using either charge-based or energy-based expressions

Differential capacitance is derived based upon energy,charge or current considerations,and determined when it may go negative or positive.These alternative views of differential capacitances are analyzed,and the relationships between them are shown.Because of recent interest in obtaining negative capacitance for reducing the subthreshold voltage swing in field effect type of devices,using ferroelectric materials characterized by permittivity,these concepts are now of paramount interest to the research community.For completeness,differential capacitance is related to the static capacitance,and conditions when the differential capacitance may go negative in relation to the static capacitance are shown.

Solid State Physics View of Liquid State Chemistry Ⅱ. Electrical Capacitance of Pure and Impure Water

More than 80 years of theories and experiments on water suggested to us, described in our first water-physics report, that pure water＇s ＂abnormally＂ high electrical conductivity is due to transport of positive and negative quasi-protons, p＋ and p-, between the neutral proton traps V （H20） in the extended water, [（H20）N]＋, converting it respectively to positively and negatively charged proton traps, V＋ = （H30）1＋ and V- = （HO）1-. In this second report, we present the theoretical charge control capacitances of pure and impure water as a function of the DC electric potential applied to water.