Negative Capacitance Effect Research Articles

Size Effect of Negative Capacitance State and Subthreshold Swing in Van der Waals Ferrielectric Field‐Effect Transistors

AbstractAnalytical calculations corroborated by the finite element modeling show that thin films of Van der Waals ferrielectrics covered by a 2D‐semiconductor are promising candidates for the controllable reduction of the dielectric layer capacitance due to the negative capacitance (NC) effect emerging in the thin films. The NC state is conditioned by energy‐degenerated poly‐domain states of the ferrielectric polarization induced in the films under incomplete screening conditions in the presence of a dielectric layer. Calculations performed for the FET‐type heterostructure “ferrielectric CuInP2S6 film—2D‐MoS2 single‐layer—SiO2 dielectric layer” reveal the pronounced size effect of the multilayer capacitance. Derived analytical expressions for the electric polarization and multilayer capacitance allow to predict the thickness range of the dielectric layer and ferrielectric film for which the NC effect is the most pronounced in various Van der Waals ferrielectrics, and the corresponding subthreshold swing becomes much less than the Boltzmann's limit. Obtained results can be useful for the size and temperature control of the NC effect in the steep‐slope ferrielectric FETs.

Revealing Fast Negative Capacitance in PbZr0.2Ti0.8O3 Thin Film with Acicular Ferroelastic Domains.

Negative capacitance effects with fast response times hold great potential for reducing the power consumption in high-frequency nanoelectronics. Nevertheless, the negative capacitance effect faces considerable complexity arising from the dynamic interplay among electrostatic, nucleation energies, and domain evolution. This intricate balance poses a formidable challenge to achieving fast negative capacitance. Herein, we have achieved a fast negative capacitance time of ∼16.23 ns in PbZr0.2Ti0.8O3 (PZT) thin film, and our investigation confirms the presence of acicular ferroelastic domains within the PZT thin film. Under reversal electric fields, these acicular ferroelastic domains undergo a unique flipping process, transitioning through domain expansion and contraction. This distinct domain flipping manner accelerates the nucleation and growth of ferroelectric domains, thereby facilitating the observed fast negative capacitance. The realization of fast negative capacitance holds substantial promise for reducing operational time and power consumption, offering prospects for the design of nanoelectronics with significantly lower power requirements.

An Ultrasensitive Programmable 2D Photoelectric Synaptic Transistor

AbstractThe burgeoning advancement of information technology has engendered a discernible surge in the examination of neuromorphic devices, notably drawing broader attention to artificial vision systems endowed with sensory recognition capabilities. Current photoelectric synapse devices employed in artificial vision systems are generally well‐suited for well‐illuminated conditions, yet exhibit diminished sensitivity in weak‐light scenarios, resulting in a pronounced deterioration of recognition accuracy. Here, an ultrasensitive photoelectric synaptic transistor based on negative quantum capacitance effect resulted from the 2D semi‐metallic graphene layer that partially enclosed within the gate dielectric layer, which manifests a noteworthy reduction in device control voltage and exhibits perception and storage capabilities for weak light of 39.4 nW cm−2 with detectivity above 1016 cm Hz1/2 W−1 is demonstrated. The voltage amplification effect and the concomitant formation of an equivalent local electrostatic field induced by the negative quantum capacitance effect engenders a robust programmable synaptic plasticity for extremely weak light by modifying the control gate. These results represent the inaugural integration of the negative quantum capacitance effect into optoelectronic devices and furnish a robust hardware foundation for developing vision systems in weak‐light environments.

Emergence and transformation of polar skyrmion lattices via flexoelectricity

As analogies to magnetic skyrmions, polar skyrmions in ferroelectric superlattices and multilayers have garnered widespread attention for their non-trivial topology and novel properties like negative capacitance and nonlinear optical effect. So far, they have only been theoretically predicted to be able to assemble ordered hexagonal skyrmion lattices (SkLs) in ferroelectric thin films. Here, based on phase-field simulations, we report the critical roles of flexoelectricity playing in the stabilization and transformation of polar SkLs. Different polar SkL patterns can emerge in the ferroelectric thin films, including tetragonal-SkL, and hexagonal-SkLs with diverse orientations, as summarized by phase diagrams. These emergent SkL states are attributed to the material anisotropy modified by the flexoelectric effect. Interestingly, we further found that the hexagonal-SkLs can be rotated by applying strain gradient or in-plane electric field to the films. Moreover, a nonreciprocal bending response of tetragonal-SkL is also induced by the flexoelectric effect. Our results provide useful guidelines for the implementation of polar skyrmion lattices in experiments.

Au/Nb2O5 terahertz-gigahertz electro-optical filters designed for high frequency applications

Herein enhanced broad band filters are fabricated by deposing thin films of Nb2O5 onto glass and semitransparent Au nanosheets using the ion coating technique. Remarkable enhancement in the surface roughness of the films and in the visible and infrared light absorption by more than 270% and 750%, respectively, is achieved by coating the films onto Au nanosheets. Au nanosheets redshifted the energy band gap and initiated the free carrier absorption in the Nb2O5 films. As terahertz band filters, Au/Nb2O5 interfaces exhibited higher dielectric constant, higher optical conductivity and higher terahertz cutoff frequency values. Au/Nb2O5 optical filters showed terahertz resonator characteristics displaying six resonance modes two, three and one of which are dominant in the infrared, visible and ultraviolet ranges, respectively. On the other hand the impedance spectroscopy analyses for Au/Nb2O5/Au (ANA) filter showed microwave resonator characteristics with cutoff frequency values reaching 700 GHz for signal carriers of driving frequency of 1.65 GHz. ANA devices exhibited negative capacitance effect in a wide range of driving frequency domain. The features of the Au/Nb2O5 films demonstrate their potential for use as gigahertz-terahertz broad band electro-optical resonators suitable for high frequency applications.

Compact modeling of short-channel effects in back-gated 2D negative capacitance (NC) FETs

The negative capacitance field-effect transistor with 2D channel material (2D NC-FET) holds significant promise for low-power applications owing to its remarkable resilience against short-channel effects (SCEs) and favorable noise characteristics. In this study, we establish a compact current–voltage (I–V) model for short-channel back-gated 2D NC-FETs with metal-ferroelectric-metal–insulator–semiconductor structure by self-consistently solving the two-dimensional Poisson, drift–diffusion and Landau–Khalatnikov equations. The proposed model is valid and continuous throughout the entire operating regime, including the fully-depleted region, partly-depleted region, and accumulation region. Furthermore, we derive analytical equations for the threshold voltage ( VTH ) and subthreshold swing ( SS ) of back-gated 2D NC-FETs based on the developed I–V model. Lastly, we elucidate the influence mechanisms of various device parameters and voltage bias on the subthreshold characteristics of short-channel back-gated 2D NC-FETs using the proposed I–V model in conjunction with analytical expressions of VTH and SS . Our findings reveal that back-gated 2D NC-FETs shows unconventional degradation behavior in VTH and SS, resulting from the competition between traditional SCEs and novel negative capacitance effects.

Negative slope polarization in ferroelectric hysteresis loop engineered by defect dipoles

The power dissipation in conventional microelectronic devices is facing a fundamental barrier of Boltzmann Tyranny. The negative capacitance (NC) effect in ferroelectric materials provides possible solution to overcome this impending problem and gets a lot of attention. Here we report a novel method to design negative capacitance in ferroelectrics by the introduction of defect-dipole engineering. In the molecular dynamics simulations of a first principles-based effective Hamiltonian, an abnormal polarization with negative slope and corresponding differential capacitance are observed in the polarization-electric field (P-E) hysteresis loops when the applied electric field is perpendicular to the direction of the defect dipoles in acceptor-doped BaTiO3 single crystals. This phenomenon is attributed to the fact that the polarization overshoots, oscillates and finally gradually switches to the direction of defect dipoles by their restoring forces during the polarization switching near the coercive field. The P-E loop exhibits abnormal NC response only at a certain range of defect levels, and there are double loops at high level and typical square-shaped loops at low level. Moreover, in the experiments of poled 1 mol.% Mn-doped BaTiO3 ceramics, the abnormal negative slope polarization in P-E loops is confirmed, which are in good agreement with the simulation results.

N-DIBL optimization of NC-GAAFET NW for low power fast switching applications

Gate-all-around field effect transistors (GAAFETs), exhibit improved SCEs, are proposed to replace conventional FinFET in scaled nanodevices owing to excellent gate control. The voltage scaling concept is embodied in negative capacitance (NC) which provides same on current at reduced voltage. The proposed NC-GAAFET yields 5.31 times larger ION and IOFF is significantly reduced by ⁓105 orders, which is due NC effect, compared to baseline NW. SSavg for the NC-GAAFET is 33mV/dec which surpasses Boltzmann tyranny and manifests steep subthreshold behavior. Effect of FE thickness (tfe) variations on DIBL has been explored and found to be negative, which improves SCEs. The negative-DIBL for device has been found to be −20 mV/V at tfe = 6 nm. Furthermore, a CMOS inverter circuit employing the NC-GAAFET has been presented that provides an average propagation delay of 174 fS which is 47 % lesser as compared to that of baseline device. The NC-GAAFET NW findings fulfill the quest of low power fast switching device for digital applications.

3D Ferroelectric Phase Field Simulations of Polycrystalline Multi‐Phase Hafnia and Zirconia Based Ultra‐Thin Films

AbstractHfO2– and ZrO2–based ferroelectric thin films have emerged as promising candidates for the gate oxides of next‐generation electronic devices. Recent work has experimentally demonstrated that a tetragonal/orthorhombic (t/o‐) phase mixture with partially in‐plane polarization can lead to negative capacitance (NC) stabilization. However, there is a discrepancy between experiments and the theoretical understanding of domain formation and domain wall motion in these multi‐phase, polycrystalline materials. Furthermore, the effect of anisotropic domain wall coupling on NC has not been studied so far. Here, 3D phase field simulations of HfO2– and ZrO2–based mixed‐phase ultra‐thin films on silicon are applied to understand the necessary and beneficial conditions for NC stabilization. It is found that smaller ferroelectric grains and a larger angle of the polar axis with respect to the out‐of‐plane direction enhances the NC effect. Furthermore, it is shown that theoretically predicted negative domain wall coupling even along only one axis prevents NC stabilization. Therefore, it is concluded that topological domain walls play a critical role in experimentally observed NC phenomena in HfO2– and ZrO2–based ferroelectrics.

P‐140: The Miniaturization of InGaN/GaN Micro‐LEDs for Micro‐Displays – Size Effects, Frequency Dispersion and Compact Modeling

InGaN/GaN green micro‐light‐emitting diode (micro‐LED, μLED) arrays with varying device sizes down to 4 μm are fabricated and characterized. The size effects on current‐voltage and capacitance‐voltage characteristics are analyzed showing minimal sidewall effects only at low bias. The influence of pulse modulation frequency on luminance is also characterized and the effect of diode negative capacitance is discussed. Subsequently, a universal and comprehensive compact model for μLEDs are built based on these findings, which covers the capacitance frequency dispersion and size scaling effects. This work reveals the significance of frequency in the display driving strategy and provides design enablement for μLED micro‐display applications including augmented/mixed reality (AR/MR).

22‐3: Negative Capacitance ZAO/ZnO Ferroelectric Thin‐Film Transistor for Neuromorphic Computing

We report complementary metal‐oxide semiconductor (CMOS)‐compatible, negative capacitance (NC) ferroelectric (FE) zirconium‐aluminum oxide (ZAO)/ZnO thin‐film transistors (TFTs) at a low thermal budget of 360 °C. The NC‐FE‐TFTs demonstrate uniform device‐to‐device performances, featuring a high memory window of 6.7 ± 0.1 V and steep subthreshold swing of 43 ± 4 mV dec–1 . The observation of negative differential resistance at room temperature confirms the NC effect in FE‐ZAO/ZnO TFTs. In addition, a learning accuracy of ≈92% is achieved, highlighting the potential for high precision neuromorphic computing application.

Influence of chemical strains on the electrocaloric response, polarization morphology, tetragonality, and negative-capacitance effect of ferroelectric core-shell nanorods and nanowires

Using Landau-Ginzburg-Devonshire (LGD) approach, we proposed the analytical description of the influence of chemical strains on spontaneous polarization and the electrocaloric response in ferroelectric core-shell nanorods. We postulate that the nanorod core presents a defect-free single-crystalline ferroelectric material, and elastic defects are accumulated in the ultrathin shell, where they can induce tensile or compressive chemical strains. Finite-element modeling (FEM) based on the LGD approach reveals transitions of domain-structure morphology induced by chemical strains in the BaTiO3 nanorods. Namely, tensile chemical strains induce and support the single-domain state in the central part of the nanorod, while the curled domain structures appear near the unscreened or partially screened ends of the rod. The vortexlike domains propagate toward the central part of the rod and fill it entirely, when the rod is covered by a shell with compressive chemical strains above some critical value. The critical value depends on the nanorod sizes, aspect ratio, and screening conditions at its ends. Both analytical theory and FEM predict that the tensile chemical strains in the shell increase the nanorod polarization, lattice tetragonality, and electrocaloric response well above the values corresponding to the bulk material. The physical reason for the increase is strong electrostriction coupling between the mismatch-type elastic strains induced in the core by chemical strains in the shell. Comparison with earlier XRD data confirmed an increase of the tetragonality ratio in tensile BaTiO3 nanorods compared to the bulk material. Obtained analytical expressions, which are suitable for the description of strain-induced changes in a wide range of multiaxial ferroelectric core-shell nanorods and nanowires, can be useful for strain engineering of advanced ferroelectric nanomaterials for energy storage, harvesting, electrocaloric applications, and negative capacitance elements. Published by the American Physical Society 2024

High-Detectivity and Broadband MoS2 Phototransistor Array by Coupling Negative Capacitance and Local Surface Plasmon Resonance Effects

High-Detectivity and Broadband MoS₂ Phototransistor Array by Coupling Negative Capacitance and Local Surface Plasmon Resonance Effects

Performance investigation of ferroelectric L-shaped tunnel FET with suppressed corner tunneling for low power applications

In this work, a ferroelectric L-shaped tunnel FET (FE-LSTFET) is introduced to offer improvement in various DC and analog/high-frequency parameters. In this design, the incorporated FE layer enhances the vertical electric field at the source-channel interface, which improves the tunneling rate of charge carriers during the ON-state. The effect of negative capacitance (NC) and L-shaped N+ pocket causes dominance of vertical tunneling over corner tunneling (mainly at low gate voltages), which in turn reduces the transition voltage and current from 0.85 to 0.25 V and 1.2 × 10-8 to 5.67 × 10-11 A/µm respectively, thereby improving parameters such as ION, IOFF, and SSavg. Further, optimization of the thickness and doping concentration helps to keep the N+ pocket in fully depleted mode and consequently, ION/IOFF is increased from 0.3 × 1012 to 1.2 × 1014 and SSavg is reduced from 52 to 30 mV/decade. Subsequently, NC parameters such as remanent polarization (Pr) and coercive electric field (Ec) are optimized to increase the memory window, which further improves the read margin of FE-LSTFET as a memory device. Furthermore, TCAD-based simulation results show that optimizing the FE thickness improves ION and IOFF in the order of ∼ 1 and ∼ 2, respectively compared to those of C-LSTFET. With an optimum drain-overlap length, IOFF is shown to reduce from 6.6 × 10-17 to 5.43 × 10-19 A/µm due to a reduction in the SRH generation rate of the charge carriers. Despite the degradation in Cgg due to drain-overlap by the stack of FE and SiO2 layers, a significant increase in e-BTBT helps in achieving a transconductance of 2.48 × 10-4 S/µm, thus leading to a large cut-off frequency of 34.12 GHz. Next, analysis of the FE-LSTFET-based inverter shows significant improvements in several parameters including propagation delay and full swing. Moreover, FE-LSTFET shows more reluctance to self-heating effects than C-LSTFET as ION/IOFF is increased by an order of ∼ 3 at 500 K. Lastly, the performance of FE-LSTFET is benchmarked with existing TFET designs indicating that FE-LSTFET is suitable as a high-speed and low-power memory device.

Novel strategies for low-voltage NAND flash memory with negative capacitance effect

Here, we present a novel approach to employing a negative capacitance (NC) phenomenon in the blocking oxide of charge trap flash (CTF) memory. To achieve this, we developed an inversible mono-domain like ferroelectric (IMFE) film through high-pressure post-deposition annealing in a forming gas at 200 atm (FG-HPPDA). The FG-HPPDA process enables to form a uniform alignment of domains and facilitates invertible domain switching behavior in ferroelectrics, generating an internal field by the flexo-electric effect as well as interface-pinned polarization by chemical reaction. Subsequently, to stabilize the NC effect, we fabricated the IMFE/Al2O3 heterostructure, which exhibits an outstanding capacitance-boosting feature. Finally, we successfully demonstrate unprecedented CTF memory with the NC effect in a blocking oxide. Our unique CTF device shows the improved performance (maximum incremental-step-pulse-programming (ISPP) slope ∼1.05) and a large MW (>8 V), attributed to the capacitance boosting by NC phenomenon.

ZnPc based multifunctional devices designed as fast capacitors, rectifiers, infrared detectors and microwave resonators adequate for 6 G technology applications

Herein Zinc phthalocyanine (ZnPc) based multifunctional devices are fabricated and characterized. The device fabrication included formation of an Au nanosheets onto n-Si wafers and coating these nanosheets with 500 nm thick ZnPc layer. Silver and platinum were used to form a Schottky and an ohmic contacts with n-Si and ZnPc, respectively. The device hybrid structure (Ag/n-Si/Au/p-ZnPc/Pt; abbreviated as ASZ) is composed of Ag/n-Si Schottky arm and p- and n- layers forming pn junction separated by Au nanosheets. Electrical and photoelectrical measurements on the ASZ devices have shown their ability to perform as conventional metal-oxide-semiconductor capacitors (CMOS). These CMOS devices showed light and frequency controlled charge accumulation, depletion and inversion mechanisms within the range of 1.0–50 MHz. The flat band and threshold voltages of the ASZ capacitors are engineered by the imposed ac signal frequency and by infrared (IR) light. In addition, ASZ devices performed as biasing controlled IR photosensors and as current rectifiers. A rectification ratio of 103, IR light sensitivity of 39, specific detectivity of .96 ×109 Jones and current responsivity exceeding 9.0 mA W−1 are recorded at biasing voltage of 4.5 V. Moreover ASZ devices displayed microwave resonator characteristics presented by negative capacitance effect, resonance –antiresonance phenomena and high microwave cutoff frequency. The latter is larger than 10 GHz nominating the device for 6 G technology applications.

Unveiling the mechanism behind the negative capacitance effect in Hf0.5Zr0.5O2-Based ferroelectric gate stacks and introducing a Circuit-Compatible hybrid compact model for Leakage-Aware NCFETs

This paper addresses the lack of understanding of the origin of negative capacitance (NC) effect in the hafnium zirconium oxide (HZO) ferroelectric (FE) gate stack and proposes a new circuit-compatible hybrid compact model for NC field-effect transistors (NCFETs). The model supports Landau and Preisach FE models, encompassing multiple FE domains, FE leakage, and FE damping. The proposed model is experimentally validated, and the intrinsic switching speed of HZO is predicted. It is revealed that the NC effect in HZO stems from a mismatch in free charge and polarization switching rates. Performance evaluation of the model reveals that HZO-NCFET achieves ∼1.18x and ∼9.17x higher amplification at low and high frequencies compared to its PZT-NCFET counterpart. Our study demonstrates the superior ON-current (2.74 mA/µm) of the Engineered Leaky-HZO NCFET, surpassing FinFET and Germanium-source L-shaped TFET by ∼7.89x and ∼4.81x, respectively. This study briefly examines the direct causes of the negative drain-induced barrier lowering effect and negative differential resistance effect in Landau NCFETs. Furthermore, we emphasize the crucial role of FE thickness in determining the magnitude of the NC effect, offering valuable insights for the design and optimization of NC-based devices and circuits. Analysis of the Miller effect in NCFET-based inverters demonstrates significant improvements owing to high ON-current and voltage amplification, making them suitable for high-speed NCFET-based circuitry. Landau and Preisach NCFET-based inverters exhibit (50.70%, 51.34%) lower overshoots and (28.45%, 28.61%) reduced propagation delay compared to the NC nanowire FET-based inverter. Moreover, NCFET-based 2:1 fork circuits significantly reduce (46.69%, 51.37%) critical clock skew compared to CMOS FET-based circuits, showcasing the potential of NCFET technology in addressing timing violations in random logic paths. Furthermore, the Landau and Preisach NCFET-based ring oscillators (ROs) achieve (39.97%, 49.38%) and (52.65%, 62.92%) higher oscillation frequencies (fOSC) compared to state-of-the-art graphene FET-RO and CMOS-RO, respectively. The 15-stage Leaky-HZO and Engineered Leaky-HZO NCFET-ROs outperform the double gate-FET-RO by ∼2.19x and ∼16.69x in terms of fOSC, highlighting their superior performance in frequency-domain metrics. These findings demonstrate the potential of NCFET-based digital and mixed-signal circuits for high-performance integrated circuit designs.

Effectively Suppressed Short-Channel Effects in Small-Size MoS2 Transistors by Introducing Negative-Capacitance Effect Resulted From Ferroelectric HfZrO2 Film

Effectively Suppressed Short-Channel Effects in Small-Size MoS₂ Transistors by Introducing Negative-Capacitance Effect Resulted From Ferroelectric HfZrO₂ Film

Assessment of the Biosensing Capabilities of SiGe Heterojunction Negative Capacitance-Vertical Tunnel Field-Effect Transistor.

In this study, a comparison of the negative capacitance vertical tunnel field-effect transistor (NC-VTFET) and VTFET for biosensing applications was conducted. Dielectrically modulated TFET demonstrates better sensitivity than the traditional metal oxide field effect transistor as a biosensor in label-free biosensing applications. The TFET biosensor, however, has much room for advancement by enhancing its DC characteristics. This research addresses the impact of ferroelectric gate oxide for integration of negative capacitance (NC) effect with the SiGe heterojunction pocket at the source-channel junction to enhance performance for biosensor applications. By putting the NC layer over SiO2, the channel voltage increases with decreased subthreshold slope and OFF current, thereby creating an NC effect. Because SiGe has a narrow band gap, pocket doping of SiGe near the source channel junction will increase the concentration of charge carriers, improving the band-to-band tunneling. In order to aid in the integration of biomolecules and to modulate band-to-band tunneling based on charge density (qf), dielectric constant (k), temperature, and cavity length, a cavity is additionally inserted above the source channel junction and underneath the NC layer, near to SiO2. These values were compared with and without the incorporation of NC layer with respect to various electrical properties such as drain current (Id), sensitivity, and electric field (E). According to the findings, labeled and label-free biosensors' sensitivity may be increased by incorporating the NC effect into VTFET biosensors.

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 Hf0.5Zr0.5O2 and antiferroelectric ZrO2 films with single-phase structure and observe the capacitance enhancement effect of Hf0.5Zr0.5O2/Al2O3 and ZrO2/Al2O3 capacitors compared to that of the isolated Al2O3 capacitor, verifying the stabilized NC effect. The capacitance of Hf0.5Zr0.5O2 and ZrO2 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.