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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Physics of ferroelectric differential capacitance based upon free energy, and implications for use in electronic devices

In this paper,it is shown that for stable,steady state operation of devices typical of microwave and millimeter wave electronics,no negative differential capacitance is possible with conventional thinking.However,it may be possible,with strain engineering of materials,to obtain some if not all elements of the differential capacitance tensor which are negative.Rigorous derivations are provided based upon analyzing the physics using thermodynamic phenomenological free energy.It should be emphasized that,even with strain engineering,and possible discovery of some negative capacitive elements,stable operation will not be obtained because the thermodynamics precludes it.

PT-symmetric electronic dimer without gain material

In this paper,a way of building an electronic Parity Time(PT)-symmetric dimer without gain material is presented.This is achieved by capacitively coupling a pair of LZC circuits,each combining an inductance L,an imaginary resistance Z and a positive/negative capacitance C.We derive the effective Hamiltonian of the system,which commutes with the joint PT operator.The eigenspectrum displays spontaneous breaking points,where the system undergoes a transition from real to complex values.The transition points are imposed by the range value of the coupling thanks to the use of a negative capacitance.Temporal charge solutions and energy propagation are also analytically and numerically investigated,and the results are compatible.In the exact phase,these quantities oscillate,whereas in the broken phase,oscillations disappear,giving place to amplification.Our results pave the way to innovative PT-symmetric circuits.Applications could include,among others,optics,metamaterials,photonics and sensitive detection.

A 40 Gbit/s fully integrated optical receiver analog front-end in 90 nm CMOS

A fully integrated 40 Gbit/s optical receiver analog front-end （AFE） including a transimpedance amplifier （TIA） and a limiting amplifier （LA） for short distance communication is described in this paper. The proposed TIA employs a modified regulated cascode （RGC） configuration as input stage, and adopts a third order interleaving active feedback gain stage. The LA utilizes nested active feedback, negative capacitance, and inductor peaking technology to achieve high voltage gain and wide bandwidth. The tiny photo current received by the receiver AFE is amplified to a single-ended voltage swing of 200 mV（p-p）. Simulation results show that the receiver AFE provides conversion gain of up to 83 dBΩ and bandwidth of 34.7 GHz, and the equivalent input noise current integrated from 1 MHz to 30 GHz is about 6.6 μA（rms）.

An inductorless CMOS programmable-gain amplifier with a>3 GHz bandwidth for60 GHz wireless transceivers

An inductorless wideband programmable-gain amplifier （PGA） for 60 GHz wireless transceivers is presented. To attain wideband characteristics, a modified Cherry-Hooper amplifier with a negative capacitive neu- tralization technique is employed as the gain cell while a novel circuit technique for gain adjustment is adopted; this technique can be universally applicable in wideband PGA design and greatly simplifying the design of wideband PGA. By cascading two gain cells and an output buffer stage, the PGA achieves the highest gain of 30 dB with the bandwidth much wider than 3 GHz. The PGA has been integrated into one whole 60 GHz wireless transceiver and implemented in the TSMC 65 nm CMOS process. The measurements on the receiver front-end show that the re- ceiver front-end achieves an 18 dB variable gain range with a 〉 3 GHz bandwidth, which proves the proposed PGA achieves an 18 dB variable gain range with a bandwidth much wider than 3 GHz. The PGA consumes 10.7 mW of power from a 1.2-V supply voltage with a core area of only 0.025 mm2.