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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Experimental Demonstration of Ferroelectric Spiking Neurons for Unsupervised Clustering

© 2018 IEEE. We report the first experimental demonstration of ferroelectric field-effect transistor (FEFET) based spiking neurons. A unique feature of the ferroelectric (FE) neuron demonstrated herein is the availability of both excitatory and inhibitory input connections in the compact 1T-1FEFET structure, which is also reported for the first time for any neuron implementations. Such dual neuron functionality is a key requirement for bio-mimetic neural networks and represents a breakthrough for implementation of the third generation spiking neural networks (SNNs) - also reported herein for unsupervised learning and clustering on real world data for the first time. The key to our demonstration is the careful design of two important device level features: (1) abrupt hysteretic transitions of the FEFET with no stable states therein, and (2) the dynamic tunability of the FEFET hysteresis by bias conditions which allows for the inhibition functionality. Experimentally calibrated, multi-domain Preisach based FEFET models were used to accurately simulate the FE neurons and project their performance at scaled nodes. We also implement an SNN for unsupervised clustering and benchmark the network performance across analog CMOS and emerging technologies and observe (1) unification of excitatory and inhibitory neural connections, (2) STDP based learning, (3) lowest reported power (3.6nW) during classification, and (4) a classification accuracy of 93%.

Wang, Z↗
DOE OSTI2024

On the Origin of Holes During Polarization Reset in Floating Body Ferroelectric FETs Towards Improving Switching Efficiency

In this article, we performed a comprehensive combined experimental and modeling study on the polarization reset mechanisms of floating body (i.e., channel) ferroelectric FETs, an important class of device with growing interests due to added functionalities and improved reliabilities. Using fully-depleted silicon-on-insulator (FDSOI) FeFET as a classical example, we demonstrate that: 1) without hole generation mechanisms, floating body FeFETs during reset is simply a capacitor divider, with negligible ferroelectric voltage drop for switching; ii) Band-to-band-tunneling (BTBT) around gate-to-S/D overlap even with zero drain bias generates holes to facilitate the reset in FDSOI FeFET, though at a slower speed and hold the reset state; iii) With scaling, S/D inner fringe field can enable fast reset, thus offering a potential efficiency boost approach; iv) a compact FDSOI FeFET model is developed that can capture the BTBT effect and reproduce the observed behaviors; v) the reset mechanism is also validated in a NAND string composed of FDSOI FeFETs, demonstrating its relevant applications. These insights show the strategies in improving reset efficiency, i.e., enhanced BTBT and inner fringe field.

42 ENGINEERING↗
DOE OSTI2024

First Demonstration of Vertical 2T-nC FeRAM Hybrid Cell and its Scalability for High-Density 3D Ferroelectric Capacitor Memory

In this article, we perform a comprehensive experimental and modeling study into the scaling of vertical 2T-nC ferroelectric random-access memory (FeRAM) hybrid cell to demonstrate a high performance and high-density 3D capacitor memory. We demonstrate: i) first time successful integration of the vertical 2T-3C FeRAM cell by stacking the vertical metal-ferroelectricmetal (MFM) stack on top of Si CMOS transistors; ii) successful experimental operation of the memory cell, including the quasi-nondestructive read out (QNRO) of the polarization without write back after 106 read cycles; iii) the write bit line (WBL) heavily screens the coupling between neighboring strings, making it a minor concern; V ) aggressive stacking of the WBLs, i.e., number of MFMs in a string, could facilitate the self-boosting during write operation due to ferroelectric linear capacitance (CFE), which allows self-boosted inhibition for Vw/2 scheme and worsens the Vw/3 scheme as disturb increases to intolerable 2Vw/3; v) aggressive horizontal scaling significantly increases the read disturb to cells on neighboring planes due to capacitance between two WBLs (Cz).

42 ENGINEERING↗
DOE OSTI2021

Design Space Exploration of Ferroelectric Tunnel Junction Toward Crossbar Memories

We perform a simulation-based analysis on the potential of emerging ferroelectric tunnel junctions (FTJs) as a memory device for crossbar arrays. Though FTJs are promising due to their low power switching characteristics compared to other emerging technologies, the greatest challenge for FTJs is the tradeoff between integration density and read performance. Our analysis highlights the need to co-optimize the ferroelectric thickness of the FTJ and read/write voltages to achieve proper functionality at large array sizes. Our analysis shows that FTJ-based crossbar achieves 93% higher sense margin at isoread power of 116 nW (per bit), but this FTJ design comes at a cost of 9.28× higher write power at isowrite time of 250 ns. In response, we study the potential tradeoffs of design points outside the feasible region to understand what device characteristics are desired to overcome such challenges.

Jao, Nicholas↗
DOE OSTI2021

Negative Capacitance MgZnO-Channel Thin-Film Transistor With Ferroelectric NiMgZnO in the Gate Stack

We demonstrate the negative capacitance thin-film transistor (NC-TFT) on glass substrate using the multifunctional MgZnO (MZO). The Mg 0.03 Zn 0.97 O semiconductor layer acts as the TFT channel for stable operation while the Ni-doped MZO, i.e. Ni 0.02 Mg 0.15 Zn 0.83 O (NMZO) serves as the ferroelectric layer in the NMZO/SiO 2 stacking gate dielectric structure. The subthreshold swing (SS) value is significantly reduced over the reference TFT without ferroelectric layer. The minimum SS value of the NC-TFT reaches 52 mV/dec while the on/off ratio of drain current ID reaches 10 9 .

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Synthesis of Ferroelectric Lead Titanate Nanohoneycomb Arrays via Lead Supplement Process

In this paper, we demonstrate a novel process to convert TiO 2 nanotubes into ferroelectric nanohoneycombs, comprised of vertically aligned PbTiO 3 nanotubes. Tube bottom opening process enabled effective infiltration of lead acetate precursor into the nanotubes. Finally, nanohoneycombs, which were converted via additional lead supplement process, showed uniform conversion and well-defined ferroelectric properties with the effective piezoelectric coefficient of approximately 20 pm/V, which was measured by piezoresponse force microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Strain effects on domain structures in ferroelectric thin films from phase‐field simulations

Abstract Strain and applied external electric fields are known to influence domain evolution and associated ferroelectric responses in ferroelectric thin films. Here, phase‐field simulations are used to predict equilibrium domain structures and polarization‐field ( P ‐ E ) hysteresis loops of lead zirconate titanate (PZT) thin films under a series of mismatch strains, ranging from strongly tensile to strongly compressive. In particular, the evolution of domains and the P ‐ E curves under different applied strains reveal the mesoscale mechanism, the appearance of in‐plane polarization during domain switching, that is responsible for a relatively small coercive field and remnant polarization. A Landau energy distribution is analyzed to better understand the domain evolution under various strain conditions. The results provide guidance for choice of mismatched strains to yield the desired P ‐ E hysteresis loops and the domain structures.

Lin, Fang‐Yin↗
DOE OSTI2017

Tunable electroresistance and electro-optic effects of transparent molecular ferroelectrics

Recent progress in molecular ferroelectrics (MOFEs) has been overshadowed by the lack of high-quality thin films for device integration. We report a water-based air-processable technique to prepare large-area MOFE thin films, controlled by supersaturation growth at the liquid-air interface under a temperature gradient and external water partial pressure. We used this technique to fabricate ImClO4 thin films and found a large, tunable room temperature electroresistance: a 20-fold resistance variation upon polarization switching. The as-grown films are transparent and consist of a bamboo-like structure of ($2,\overline{1},0$) and ($1,0,\overline{2}$) structural variants of R3m symmetry with a reversible polarization of 6.7 μC/cm 2 . The resulting ferroelectric domain structure leads to a reversible electromechanical response of d 33 = 38.8 pm/V. Polarization switching results in a change of the refractive index, n, of single domains, $\frac{Δn}{n}$ = 0.3. The remarkable combination of these characteristics renders MOFEs a prime candidate material for new nanoelectronic devices. The information that we present in this work will open a new area of MOFE thin-film technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atomic-scale polarization switching in wurtzite ferroelectrics

Ferroelectric wurtzites have the potential to revolutionize modern microelectronics because they are easily integrated with multiple mainstream semiconductor platforms. However, the electric fields required to reverse their polarization direction and unlock electronic and optical functions need substantial reduction for operational compatibility with complementary metal-oxide semiconductor (CMOS) electronics. To understand this process, we observed and quantified real-time polarization switching of a representative ferroelectric wurtzite (Al 0.94 B 0.06 N) at the atomic scale with scanning transmission electron microscopy. The analysis revealed a polarization reversal model in which puckered aluminum/boron nitride rings in the wurtzite basal planes gradually flatten and adopt a transient nonpolar geometry. Independent first-principles simulations reveal the details and energetics of the reversal process through an antipolar phase. Furthermore, this model and local mechanistic understanding are a critical initial step for property engineering efforts in this emerging material class.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Heterogeneous field response of hierarchical polar laminates in relaxor ferroelectrics

Understanding the microscopic origin of the superior electromechanical response in relaxor ferroelectrics requires knowledge not only of the atomic-scale formation of polar nanodomains (PNDs) but also the rules governing the arrangements and stimulated response of PNDs over longer distances. Using x-ray coherent nanodiffraction, we show the staggered self-assembly of PNDs into unidirectional mesostructures that we refer to as polar laminates in the relaxor ferroelectric 0.68PbMg 1/3 Nb 2/3 O 3 -0.32PbTiO 3 (PMN-0.32PT). Here, we reveal the highly heterogeneous electric-field–driven responses of intra- and interlaminate PNDs and establish their correlation with the local strain and the nature of the PND walls. Our observations highlight the critical role of hierarchical lattice organizations on macroscopic material properties and provide guiding principles for the understanding and design of relaxors and a wide range of quantum and functional materials.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Features of the low-frequency polarization response in the region of the ferroelectric phase transition in multiferroic TbMnO 3

The unusual behavior of the low-frequency (10 Hz–1 MHz) permittivity in single crystals of ferroelectric multiferroic TbMnO3 has been experimentally and theoretically studied in detail in the region of the narrow temperature peak of the permittivity, associated with the ferroelectric phase transition (T C ~ 27.4 K). It has been found that the ε c (ω, T) maximum sharply decreases with increasing measured field frequency, while the temperature position of the maximum is independent of frequency. It has been shown that the observed features of the polarization response can be satisfactorily described within the Landau–Khalatnikov polarization relaxation theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Enhancement of second-order optical nonlinearities and nanoscale periodic domain patterning in ferroelectric boron-substituted aluminum nitride thin films

The discovery and development of CMOS-compatible, nonlinear optical materials is essential to produce integrated photonic devices with advanced functionalities. AlN is a strong candidate for on-chip device demonstration due to its intrinsic second-order optical nonlinearities, large bandgap, and well-established fabrication techniques. However, AlN is not easily phase matched for the largest coefficient d 33 ; the coefficients that could potentially be dispersion phase-matched, d 31 and d 15 , have weak nonlinearities. This work investigates ferroelectric Al 1-x B x N (x = 0 to 0.11) for viability as a large bandgap nonlinear optical material with unique suitability towards ultraviolet light generation using second harmonic generation. The linear and nonlinear optical properties are characterized accounting for material anisotropy. With increasing B concentration, a large enhancement from near negligible values to d 31 = 0.9 ± 0.1 pm/V and d 15 = 1.2 ± 0.1 pm/V is observed. This compares favorably to other large bandgap materials like β-Ba(BO 2 ) 2 , where the largest nonlinear coefficient is d 22 ~ 2.3 pm/V at 800 nm. This is accompanied by a change in the bandgap from 6.1 eV to 5.8 eV as B substitution goes from 0 to 11%. A periodically poled, quasi-phase-matched ferroelectric domain pattern with 400 nm domain size and a wall roughness of <16 nm is demonstrated.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Simulation studies of nucleation of ferroelectric polarization reversal.

Electric field-induced reversal of spontaneous polarization is the defining characteristic of a ferroelectric material, but the process(es) and mechanism(s) associated with the initial nucleation of reverse-polarity domains are poorly understood. This report describes studies carried out using phase field modeling of LiTaO 3 , a relatively simple prototype ferroelectric material, in order to explore the effects of either mechanical deformation or optically-induced free charges on nucleation and resulting domain configuration during field-induced polarization reversal. Conditions were selected to approximate as closely as feasible those of accompanying experimental work in order to provide not only support for the experimental work but also ensure that additional experimental validation of the simulations could be carried out in the future. Phase field simulations strongly support surface mechanical damage/deformation as effective for dramatically reducing the overall coercive field (Ec) via local field enhancements. Further, optically-nucleated polarization reversal appears to occur via stabilization of latent nuclei via the charge screening effects of free charges.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Fundamental Physics of Ferroelectrics 2019

The workshop “Fundamental Physics of Ferroelectrics 2019” took place in January 2019 at USF and hosted around 80 participants (from both US and overseas) 32 of whom were early career professionals (PostDocs and graduate students). This was a 2.5 day workshop with 8 invited presentations, 39 oral presentations, and 27 posters. It brought together experts in the area of ferroelectrics and related materials and allowed for interactions, collaborations and exchange of ideas and progress. The invited speakers were Jorge Iniguez (University of Luxembourg), Manila Songvilay (University of Edinburgh), James Scott (St. Andrews), David Singh (University of Missouri), Philippe Ghosez (Université de Liège), Marin Alexe (University of Warwick), Takeshi Egami (University of Tennessee), Sergey Vakhrushev (Ioffe Physical Technical Institute), and Karin Rabe (Rutgers University). The DOE funding was used (i) to provide awards for junior participants (graduate students and PostDocs): best oral presentations (1st, 2nd and 3rd places) and best poster presentations (1st, 2nd and 3rd places). First places in both categories $\$ $300, second places in both categories $\$ $250 and third places in both categories $\$ $200. Information about the awardees available at the conference website.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electrothermal Phenomena in Ferroelectrics

Physical properties of lead-zirconate-titanate (PZT) ceramics change according to the initial electric poling process and electrical boundary conditions. This paper reports the electrothermal, piezothermal, and piezoelectric coupling phenomena in ferroelectrics from thermodynamics viewpoints, in particular, thermal property differences between unpoled and poled PZT’s in the poling direction for open circuit and short circuit conditions. We propose a new terminology, “secondary electrothermal” coupling factor kλ, which is analogous to the electromechanical coupling factor k, relating the elastic compliances under short- and open-circuit conditions, in order to explain the fact that the short-circuit condition exhibited the larger thermal diffusivity than the open-circuit condition. On the other hand, the unpoled specimen exhibits the lowest thermal diffusivity. This tutorial paper was authored for providing comprehensive knowledge on equilibrium and time-dependent thermodynamics in ferroelectrics.

Uchino, Kenji (ORCID:0000000316517912)↗
NASA NTRS1981

Raman study of the improper ferroelectric phase transition in iron iodine boracite

The reduction in the dielectric anomaly near the phase transition temperature in improper ferroelectrics suggests that this behavior may be exploited to significantly enhance the figure-of-merit for pyroelectric infrared detection. This reduction is associated with a decoupling of the thermal and dielectric responses which, in turn, reflects the unusual nature of the lattice instability at the phase transition. In order to elucidate the characteristics of the phonon behavior connected with the lattice instability, Raman scattering of Fe3B7O13I has been examined in both the paraelectric and ferroelectric phases. The results of this study as well as results from earlier measurements on other boracites, provides insight into the nature of the mode softening.

Kim, Q.↗
NASA NTRS1982

Photovoltaic properties of ferroelectric BaTiO3 thin films RF sputter deposited on silicon

Ferroelectric thin films of BaTiO3 have been successfully deposited on n-type silicon substrates at temperatures above 500 C by RF sputtering in an O2/Ar atmosphere. Analysis by X-ray diffraction patterns show that films deposited at room temperature are amorphous. At temperatures above 500 C, crystalline BaTiO3 films with a tetragonal structure are obtained. The polarization-electric field (P-E) hysteresis loops and a broad peak in the dielectric constant versus temperature curve at Curie point indicate that the RF sputtered BaTiO3 films are ferroelectric. An anomalous photovoltaic effect is observed in these thin films which is related to the remanent polarization of the material. The results on open-circuit and short-circuit measurements provide an important basis for a better understanding of the role of photovoltaic field, photovoltaic current, and the pyroelectric properties in photoferroelectric domain switching.

Dharmadhikari, V. S.↗