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Vinylidene fluoride-trifluoroethylene copolymer films of molar ratio 70/30 with thickness of about 1 μ m have been deposited from solution in ethyl methyl ketone to a glass substrate with an aluminum electrode by spin coating. The solution has been filtrated through a PTFE membrane filter with pore size 0.2 μ m directly before spin coating or it has been used as is (unfiltrated). After deposition of a top electrode, the samples have been polarized by hysteresis loops with an electric field amplitude of about 100 V/ μ m. In samples, annealed at temperature 145 ∘ C for 3 h, a high remanent polarization of about 7.5 μ C/cm2 has been achieved, without significant differences between samples fabricated of filtrated or unfiltrated solution. Spherulitic lamella are growing in films fabricated of filtrated solution when they are heated above the melting temperature to 159 ∘ C for 3 min before the further annealing process at 145 ∘ C. These films show substantially lower remanent polarization below 4 μ C/cm2. Pyroelectric images recorded with a pyroelectric laser scanning microscope show that the spherulites have very small pyroelectric activity, i.e., the spherulites consist of flat-on lamella. In contrast, no spherulitic lamella are growing in films fabricated of unfiltrated solution heated above the melting temperature, melted and annealed under the same conditions. An explanation for this observation is that filtrating changes the structure of the copolymer in solution from polymer coil to rod. Copolymer rods deposited on a substrate will crystallize in flat-on lamella when heated above the melting temperature, in contrast to copolymer coils which crystallize in edge-on lamella. [ABSTRACT FROM AUTHOR]

Vinylidene fluoride-trifluoroethylene copolymer films of molar ratio 70/30 with thickness of about 1 [Formula: see text]m have been deposited from solution in ethyl methyl ketone to a glass substrate with an aluminum electrode by spin coating. The solution has been filtrated through a PTFE membrane filter with pore size 0.2 [Formula: see text]m directly before spin coating or it has been used as is (unfiltrated). After deposition of a top electrode, the samples have been polarized by hysteresis loops with an electric field amplitude of about 100 V/[Formula: see text]m. In samples, annealed at temperature 145[Formula: see text]C for 3 h, a high remanent polarization of about 7.5 [Formula: see text]C/cm2 has been achieved, without significant differences between samples fabricated of filtrated or unfiltrated solution. Spherulitic lamella are growing in films fabricated of filtrated solution when they are heated above the melting temperature to 159[Formula: see text]C for 3 min before the further annealing process at 145[Formula: see text]C. These films show substantially lower remanent polarization below 4 [Formula: see text]C/cm2. Pyroelectric images recorded with a pyroelectric laser scanning microscope show that the spherulites have very small pyroelectric activity, i.e., the spherulites consist of flat-on lamella. In contrast, no spherulitic lamella are growing in films fabricated of unfiltrated solution heated above the melting temperature, melted and annealed under the same conditions. An explanation for this observation is that filtrating changes the structure of the copolymer in solution from polymer coil to rod. Copolymer rods deposited on a substrate will crystallize in flat-on lamella when heated above the melting temperature, in contrast to copolymer coils which crystallize in edge-on lamella.

Abstract Analog storage through synaptic weights using conductance in resistive neuromorphic systems and devices inevitably generates harmful heat dissipation. This thermal issue not only limits the energy efficiency but also hampers the very‐large‐scale and highly complicated hardware integration as in the human brain. Here we demonstrate that the synaptic weights can be simulated by reconfigurable non‐volatile capacitances of a ferroelectric‐based memcapacitor with ultralow‐power consumption. The as‐designed metal/ferroelectric/metal/insulator/semiconductor memcapacitor shows distinct 3‐bit capacitance states controlled by the ferroelectric domain dynamics. These robust memcapacitive states exhibit uniform maintenance of more than 104 s and well endurance of 109 cycles. In a wired memcapacitor crossbar network hardware, analog vector‐matrix multiplication is successfully implemented to classify 9‐pixel images by collecting the sum of displacement currents (I = C × dV/dt) in each column, which intrinsically consumes zero energy in memcapacitors themselves. Our work sheds light on an ultralow‐power neural hardware based on ferroelectric memcapacitors.

We investigated the effect of gate bias stress (GBS) on the electrical characteristics of ferroelectric oxide thin-film transistors (FeOxTFTs) with poly(vinylidenefluoride-trifluoroethylene). Generally, conventional oxide thin-film transistors (OxTFTs) with dielectric gate insulators exhibit a small negative shift under negative gate bias stress (NBS) and a large positive shift under positive gate bias stress (PBS) in transfer characteristic curves. In contrast, the FeOxTFTs show a small positive shift and a large negative shift under NBS and PBS, respectively. It was confirmed that sufficient changes in the electrical characteristics are obtained by 10 min NBS and PBS. The changed electrical characteristics such as threshold voltage shift, memory on- and memory off-current were maintained for more than 168 h after NBS and 24 h after PBS. It is deduced that, since the dipole alignment of the ferroelectric layer is maximized during GBS, these changes in electrical properties are caused by the remnant dipole moments still being retained during the gate sweep. The memory on- and memory off-current are controlled by GBS and the best on/off current ratio at 107 was obtained after NBS. By repeatedly alternating NBS and PBS, the electrical characteristics were reversibly changed. Our results provide the scientific and technological basis for the development of stability and performance optimization of FeOxTFTs. [ABSTRACT FROM AUTHOR]

• PVDF-TrFE and Nafion based electroactive polymer (EAP) blended films are prepared using solution casting method. • The enhancement of performance in the ferroelectric PVDF-TrFE matrix upon blending with different volume percentages of Nafion is analyzed, as evidenced by microwave reflection loss, P-E hysteresis, and electromechanical coupling studies. • The findings from these studies indicates that 10 % Nafion inclusion into the PVDF-TrFE matrix has significantly improved the microwave, ferroelectric and electromechanical response of blended polymer matrix compared to the pristine PVDF-TrFE film. This study probes the enhancement of the microwave, ferroelectric and electromechanical properties of electroactive polymer (EAP) blended films made out of P(VDF-TrFE) and Nafion. Blended films are synthesized using the solution casting method, with different Nafion volume percentage (0 % to 30 %), and the phase formation is confirmed using XRD and FTIR spectroscopy. The morphological features are studied using FESEM. The reflection loss of the blended films as a function of thickness has been studied in both X and Ku band using a VNA. The contribution of reflection and absorption to the shielding effectiveness are also explored. 10 % Nafion inclusion effectively minimizes microwave reflection. The P-E hysteresis study reveals that the blended films exhibit high performance in terms of the parameters. The electromechanical coupling factor has been enhanced for 10 % Nafion inclusion. These findings suggest that the blended films have potential applications in flexible piezoelectric sensors, capacitors, memory, and microwave devices. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper aims at improving the performance of the poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer for pyroelectric infrared detection and direct thermal to electrical energy conversion. Three different types of samples were prepared and examined: commercial, purified and porous films. Here, full characterization of the thermophysical and electrical properties relevant to pyroelectric infrared detection and energy conversion of both purified and porous P(VDF-TrFE) thin films is presented. Properties measured include (1) density, (2) ferroelectric to paraelectric phase transition temperature, (3) enthalpy of change of phase, (4) electrical resistivity and (5) ferroelectric hysteresis, as well as (6) specific heat, (7) dielectric constant, (8) loss tangent and (9) pyroelectric coefficient as a function of temperature. The figures of merit for infrared detection FV , FI and FD were improved by 47.0, 59.6 and 51.6%, respectively, for the purified films while the porous films with a porosity of 33% showed an improvement of 52.8, 66.3 and 62.6%, respectively, when compared to those of dense commercial P(VDF-TrFE) films. In addition, figures of merit for energy harvesting, FE and k^2, indicate that the purified and porous films are attractive for thermal to electrical energy conversion as well.

• C 2 HF 3 bond enrichment in P(VDF-TrFE) is realized by CF 4 plasma treatment on n+-Si BE. • P(VDF-TrFE) copolymers on CF 4 -plasma-treated n+-Si are analyzed by XPS and XRD. • Asymmetric polarization is ascribed to the β-phase increase at bottom of P(VDF-TrFE). • F-incorporated P(VDF-TrFE) MFMs show larger 2 P r and lower E c with negligible fatigue. CF 4 plasma treatment on n+-Si wafers as bottom electrodes (BEs) of poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) metal-ferroelectric-metal (MFM) capacitors has been investigated in this study. Prior to the fabrication of MFM capacitors, comprehensive material analyses are administered to identify the incorporation of fluorine atoms into P(VDF-TrFE) copolymers, revealing an enrichment in C 2 HF 3 (trifluoroethylene) bonds and an improvement in the crystallinity of the film. The P(VDF-TrFE) MFM capacitors with CF 4 -plasma-treated n+-Si wafers show a shallower charge trapping level of 0.154–0.226 eV extracted from the Frenkel–Poole (F–P) emission at 213–273 K for the BE injection compared to that for the top electrode (TE) injection, which is ascribed to the passivation of deep traps by the fluorine atoms that diffused from the n+-Si wafers. Thus, asymmetric remanent polarization and a negative internal bias field are obtained because of the significant increase in the β-phase at the bottom of the P(VDF-TrFE) films. With the CF 4 plasma treatment for 1 min, the P(VDF-TrFE) MFM capacitors demonstrate a remanent polarization (2 P r) of 6.58 µC/cm2, a coercive electric field (E c) of 0.47 MV/cm and stability for more than 3 × 104 cycles with negligible fatigue, making the fluorine-incorporated P(VDF-TrFE) copolymers suitable for future high-performance nonvolatile memory applications. [ABSTRACT FROM AUTHOR]

• Low cost solution based thin film deposition of active piezoelectric polymer layer (Poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)]) without any process complexity is demonstrated with unaltered material signature as verified by material characterization. • Adaptation of microelectronics technology on polymer layer without any appreciable compromise on the piezoelectric behavior is described that can lead to scalable mass production. • High operating frequency comparable to conventional inorganic thin film SAW devices is achieved. • Unique in-situ poling capability, enabling reversible and restorative poling of the active polymer layer is demonstrated using novel bilayer interdigitated transducer (IDT) architecture. This feature leads to the restoration of the device performance unlike any other SAW devices. • Possible application of the presented device as temperature sensor is described. Surface acoustic wave (SAW) device, which integrates the generation, propagation and detection of acoustic waves into the same device, has been known to be an essential functional unit for sensors and electromechanical systems. However, high substrate cost and process complexity of traditional inorganic SAW devices have triggered extensive research efforts to seek for alternative low cost solution, especially for disposable application. Poly(vinylidenefluoride)[P(VDF)] and its co-polymer, despite being promising materials for acoustic transducer with inexpensive processing technique, have rarely been used in SAW device due to exhibiting extremely low operating frequency (few tens of MHz) compared to the traditional SAW device (few hundreds of MHz to GHz) based on inorganic piezoelectric material. Here we demonstrate SAW device, which is entirely based on Poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)], as piezoelectric material, offering transduction and propagation of acoustic waves with a frequency around 450 MHz. The drawbacks of the previous attempts by the others are addressed and rectified systematically to obtain high operating frequency comparable to the traditional SAW. The influence of periodicity of interdigitated transducer and thickness of polymer film on device performance is thoroughly investigated. Temperature dependent variation of resonance frequency, which can be exploited as temperature sensor in integrated systems, is also demonstrated. [ABSTRACT FROM AUTHOR]

• Hf 0.5 Zr 0.5 O 2 (HZO)-stacked negative capacitance field-effect transistor (NCFET) for possible beyond-CMOS technology. • Impact of ferroelectric domain numbers on the performance of MFM stack and HZO-NCFET device-circuit co-design. • HZO-NCFET offers significant voltage amplification compared to conventional PZT-NCFET and P(VDF-TrFE)-NCFET. • This study predicts that HZO has a switching time approximately 20 times faster than traditional ferroelectric Pb(Nb 0.04 Zr 0.28 Ti 0.68)O 3. • The HZO-NCFET-RO outperforms standard CMOS-RO, showcasing its potential for advancing beyond-CMOS technologies and guiding NCFET design optimization. This paper explores the performance of Hf 0.5 Zr 0.5 O 2 (HZO)-stacked negative capacitance field-effect transistor (NCFET) for possible beyond complementary metal–oxide–semiconductor (CMOS) technology. For the first time, we investigate the impact of ferroelectric (FE) domain numbers on the negative capacitance (NC) effect, energy dissipation, NC effect voltage window, polarization ramping rate, voltage amplification (A NC), and oscillation frequency of a 5-stage HZO-NCFET inverter-based ring oscillator (HZO-NCFET-RO). The results show that HZO-NCFET is suitable for low-voltage and high-speed applications, providing a significant increase in A NC concerning the conventional PZT-NCFET and P(VDF-TrFE)-NCFET. Our study suggests that the HZO intrinsic NC effect time scale is tiny and limited by the FE switching. We show that the switching time of HZO is ∼20 times faster than the traditional FE [Pb(Nb 0.04 Zr 0.28 Ti 0.68)O 3 ]. Finally, the proposed 5-stage HZO-NCFET-RO offers superior performance with a 26% higher oscillation frequency and a 94.42% reduction in power dissipation compared to standard 5-stage CMOS inverter-based RO. These findings highlight the potential of HZO-stacked NCFET as an alternative device for the future beyond-CMOS technology. [ABSTRACT FROM AUTHOR]

The electronic device industry has recently focused its attention towards the development of organic memory devices. This research highlights the development of organic memory devices by utilizing pentacene as a semiconductor and ferroelectric polymers, such as poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] and poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], as a gate dielectric. 10 wt% solutions of P(VDF-HFP) and P(VDF-TrFE) were prepared individually and blended (50:50). The resultant solutions were coated on the gate electrode and subsequently annealed for 2 h at 90 °C. The fabricated field-effect transistors (FETs) were studied in terms of their hysteresis characteristics with particular emphasis on the memory window. The results show that the FETs fabricated using the P(VDF-HFP)/P(VDF-TrFE) blend have significantly improved memory characteristics. The enhancement in the memory characteristics is explained through the interface properties between the pentacene semiconductor and dielectric layers. This work provides a design of organic FETs with excellent memory characteristics using low-cost technology. [ABSTRACT FROM AUTHOR]

We have developed time-resolved fractal dimension analysis in ferroelectric copolymer films in order to understand the effect of polarization relaxation on domain wall roughness. Interestingly, the progressive polarization relaxation of irregular domains results from the domain back reversal at the boundaries where the antiparallel polarization encounters, and therefore has a significant influence on the fractal dimension of the irregular domains as a function of time. [ABSTRACT FROM AUTHOR]

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Different thermal treatments were used to obtain various crystal structures of hydrogenated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] films synthesized by an atom transfer radical chain transfer and controllable elimination reaction route. After analyzing the results of X-ray diffraction and differential scanning calorimeter, we found that these P(VDF-TrFE) samples possessed mixed crystal phases of \alpha , \beta , and \gamma with various compositions depending on the TrFE content and processing temperature, and this characteristic was also demonstrated by the dielectric temperature curves. After polarizing the P(VDF-TrFE) samples at different electric fields, the effect of crystal structure on their ferroelectric and piezoelectric properties was illustrated and conformed by field emission scanning electronic microscopy morphology, which was found that large TrFE content and high temperature processing were responsible for the large remnant polarization. As a result, the annealed P(VDF-TrFE) 80/20 mol% possessed a high remnant polarization of /cm2, a large piezoelectric value ( d_{33}= -25 pC/N), and a favorable electromechanical coupling factor ( k_{t}= 0.26$ ), providing a reliable method for the structure design and sample fabrication of this kind of copolymer aimed at the applications in piezoelectric sensors and actuators. [ABSTRACT FROM AUTHOR]

Regular changes in ferroelectric and pyroelectric properties of P(VDF-TrFE) polymer thin films were observed when the films have a bent-deformation caused by external force. The deformation rate dependence of the remanent polarization, relative dielectric constant and pyroelectric coefficient of the P(VDF-TrFE) thin films were studied. The results demonstrated that there was an increase of ∼12.2% in the remanent polarization of the bent films between the maximum and the minimum bent-deformation rate. Pyroelectric coefficient of the bent P(VDF-TrFE) thin films was also enhanced compared with the flat P(VDF-TrFE) films. P(VDF-TrFE) films can still maintain good performance in ferroelectric and pyroelectric properties under bent deformation, which is meaningful to the potential application in flexible devices. [ABSTRACT FROM AUTHOR]

• This paper aims to establish an accurate physical basis for the transient negative capacitance (TNC) and the relationship between the TNC and organic ferroelectric's free energy profile. • The fundamental mechanism of TNC is caused by the switching rate difference between the free charge and polarization during the two stable state switching processes. • TNC appears immediately when the change in organic ferroelectric voltage (V OFE) per unit time is negative. • Unipolar pulsing does not produce the TNC effect. • The proposed organic ferroelectric capacitor may be employed as a gate stack of any standard transistor for designing beyond CMOS transistor technology. The physical mechanism of the negative capacitance (NC) effect in an organic ferroelectric (OFE) remains unknown. Therefore, this paper presents a series circuit of a resistor and an OFE capacitor (R-OFEC) based on experimentally validated Ginzburg-Landau-Khalatnikov (GLK) theory, electrostatics, and Kirchoff's circuit rule to understand the transient NC (TNC) mechanism in TCAD environment. We show that: (i) the fundamental mechanism of TNC in an R-OFEC is caused by switching rate difference between the free charge (Q OFE) and OFE polarization (P OFE) during the two stable state switching processes; (ii) Q OFE -P OFE difference is induced by the NC region of the OFE's double-well free energy landscape and its relationship with the change in voltage transient is demonstrated analytically; (iii) a bipolar pulsing is needed for TNC appearance; (iv) TNC appears immediately when the change in voltage across the OFEC per unit time is negative. Finally, the TNC effect caused by the Q OFE -P OFE difference is justified by its dependence on R. [ABSTRACT FROM AUTHOR]

Abstract: Precursor films based on poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) and P(VDF-TrFE) blended with Pb(Zr,Ti)O3 were spin-coated on Si-substrates and subsequently annealed at 170°C. X-ray diffraction studies showed that the amorphous precursor films crystallize to the γ-phase P(VDF-TrFE) without involving the formation of other polymorphs when the P(VDF-TrFE) is blended with Pb(Zr,Ti)O3, resulting in phase mixtures composed of a crystalline γ-phase P(VDF-TrFE) and an amorphous Pb(Zr,Ti)O3. A larger memory window width and higher accumulation capacitance, as well as a lower leakage current density are induced by the blended Pb(Zr,Ti)O3 within the low operating voltage ranges from −3.0 to 3.0V and from −2.0 to 2.0V for 20wt% and 40wt% Pb(Zr,Ti)O3 blending, respectively. These improvements not only in the hysteretic capacitance–voltage characteristics but also in the leakage current density–electric field are directly correlated with the phase mixtures, their volume fraction, dipole moments, and formation of interface layer between the blended film and Si substrate. [Copyright &y& Elsevier]

Nonvolatile ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) memory based on an organic thin-film transistor with inkjet-printed dodecyl-substituted thienylenevinylene-thiophene copolymer (PC12TV12T) as the active layer is developed. The memory window is 4.5 V with a gate voltage sweep of -12.5 V to 12.5 V. The field effect mobility, on/off ratio, and gate leakage current are 0.1 cm2/Vs, 105, and 10-10 A, respectively. Although the retention behaviors should be improved and optimized, the obtained characteristics are very promising for future flexible electronics. [ABSTRACT FROM AUTHOR]

Abstract: The electroactive properties of PVDF-based ferroelectric polymers can be tailored by blending. In order to investigate the tunability of electrocaloric effect (ECE) and ferroelectric responses, blends of ferroelectric relaxor poly(vinylidene difluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer and normal ferroelectrics poly(vinylidene difluoride–co–trifluoroethylene) (P(VDF–TrFE)) copolymer are studied. At low copolymer content (<15 wt%), the coupling between the relaxor terpolymer and the nano-phase copolymer converts the copolymer into relaxor and causes an increase in the crystallinity compared with neat terpolymer. As a result, the blends exhibit an enhanced relaxor polarization response and a significant increase in the electrocaloric effect compared with those in the neat terpolymer. At high copolymer content, the blends exhibit mixed structures of the two components. By varying composition, the dielectric and ferroelectric properties of blends can be tuned in the range between the copolymer and terpolymer. This blend system provides a model system to study how random defects influence the polarization response in the normal ferroelectric copolymer, and to understand the relationship between the polarization response and ECE in the blends. The results demonstrate the promise of nanocomposite approaches in tailoring and enhancing ECE and ferroelectric properties in the ferroelectric polymers. [Copyright &y& Elsevier]

Abstract: In this report, ferroelectric behaviors were investigated as a function of temperature and poling frequency for a uniaxially stretched poly(vinylidene fluoride-co-trifluoroethylene) 50/50 (mol./mol.) film. A variety of ferroelectric behaviors, including normal ferroelectric, antiferroelectric-like, and paraelectric behaviors, were observed by varying temperature, poling frequency, and poling electric field. Especially, the ferroelectric (FE) to paraelectric (PE) transition and ferroelectric behaviors of the high temperature PE phase were studied in detail by electric displacement-electric field loop measurements. At a high poling frequency (e.g., 1000 Hz) and 100 °C (above the Curie temperature at 64 °C), a paraelectric behavior was obtained due to the nucleation of electric field-induced FE nanodomains inside the PE phase matrix. These FE nanodomains were highly reversible and they quickly depolarized upon removal of the poling field. At an intermediate poling frequency (e.g., 10 Hz) and 100 °C, an antiferroelectric-like behavior was observed, which could be attributed to the competition between depolarization and polarization fields upon reverse poling. Finally, at a low poling frequency (e.g., 1 Hz) and 100 °C, a normal ferroelectric behavior with rectangular hysteresis loops was seen because the small, reversible FE domains had enough time to grow into large irreversible ones. The presence of electric field-induced FE domains in the PE matrix was proved by field dependent Fourier transform infrared study. On the basis of this study, understanding of the paraelectric behavior in polar crystalline polymers will help us design new materials to meet the requirements for high energy density and low loss dielectric applications. [Copyright &y& Elsevier]

Abstract: In this paper we report the fabrication and detailed electrical characterization of a novel test structure based on Metal–Ferroelectric-Metal–Oxide–Semiconductor transistor with internal metal contact, aiming at extracting the surface potential and the investigation of internal voltage. This structure could possibly be used for the investigation of the differential voltage amplification expected due to negative capacitance effect. The proposed test structure is p-Fe-FET with a thin Al contact in-between the PVDF ferroelectric and a pedestal oxide, enabling access to the internal voltage potential in all the regimes of operations, from weak to strong inversion. Moreover, the capacitances of reference MOS transistor and of Fe-FET can be independently probed. The fabricated p-type Fe-FET has an excellent subthreshold slope of 75mV/decade, I on/I off >107 and I off in the pA range. Based on voltage and capacitive measurements, the Fe-FET surface potential is experimentally extracted as well as the polarization of the ferroelectric layer. We demonstrate that the internal node voltage amplitude can be controlled by the sweeping conditions of the polarization loops. We propose a first order modeling of the polarization and we report simulations of the internal potential. [Copyright &y& Elsevier]

Films of semi-crystalline P(VDF-TrFE) copolymers were deposited by spin-coating onto Si-based substrates. The ferroelectric behavior of these copolymer systems were studied by comparing (P-E) hysteresis loop, permanent polarization and pyroelectric activity as a function of TrFE content. [ABSTRACT FROM AUTHOR]

A poling process of a P(VDF-TrFE) thin film with a 70/30mol % composition is described in this work. Different parameters are studied such as the intensity of the poling field, its dwell time, or the number of voltage step during a ramp to reach the maximum field applied. The poling field appears as the most important parameter influencing the performances of the pyroelectric coefficient. However the integration of steps during a ramp to the maximum field generates a slight decrease of this coefficient. [ABSTRACT FROM AUTHOR]

Abstract: To minimize the degradation of pentacene films in the fabrication of top-gate-type MFS FETs (metal-ferroelectric-semiconductor field-effect transistors), the characteristics of four solvents which are used for overcoating organic ferroelectric films on pentacene films are investigated by dipping pentacene MOS diodes in these solvents. Then, using appropriate solvents such as 1,4-dioxane, MFS diodes composed of Au, P(VDF-TrFE) (poly(vinylidene fluoride-trifluoroethylene)), and pentacene are fabricated, and then C–V (capacitance vs. voltage) characteristics are investigated. It is concluded from comparison of C–V and data retention characteristics of the top- and bottom-gate-type MFS diodes that degradation of the pentacene film is insignificant when an appropriate solvent is used. [Copyright &y& Elsevier]

Abstract: Among the many ferroelectrics polymers, poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] has drawn a great attention with its promising memory properties such as large remanent polarization, good fatigue and retention properties. Since the ferroelectric layer plays a critical role in the operation of memory device, it is important to control the structure of ferroelectric thin film. In order to improve the performance of a ferroelectric device, in this contribution we employed P(VDF-TrFE) layers blended with various compositions of an amorphous poly(methyl methacrylate) (PMMA) from 0wt.% to 20wt.%. In metal/ferroelectric/metal capacitor structure, we observed the decrease of remanent polarization from 9.13μC/cm2 to 4.7μC/cm2 and increase of coercive voltage from 9.5V to 15.2V with PMMA. Polarization switching time of the ferroelectric blend films estimated from the switched polarization vs. time curves increases with the amount of PMMA. Furthermore, ferroelectric field-effect transistors (FeFETs) based on ferroelectric P(VDF-TrFE) and PMMA blend films with single-crystalline tri-isopropylsilylethynyl pentacene (TIPS-PEN) channels show that both ON and OFF currents of the transistors are maintained with the PMMA contents despite the reduction of remanent polarization of P(VDF-TrFE)/PMMA films. [Copyright &y& Elsevier]

Abstract: Current status of ferroelectric-gate FETs (field effect transistors) is reviewed. First, characteristics of Si FETs with MFIS (metal–ferroelectric–insulator–semiconductor) gate structures are discussed. It has been shown that the data retention characteristics of ferroelectric-gate FETs are much improved by use of HfO2-based buffer layers which are inserted between the ferroelectric-gate film and Si substrate for preventing inter-diffusion of constituent elements. Then, usefulness of organic ferroelectrics such as copolymers of vinyliden fluoride and trifluoroethylene (P(VDF–TrFE)) in fabrication of MFIS devices is demonstrated. In an Au/P(VDF–TrFE)/Ta2O5/Si MFIS diode, a memory window as wide as 2.9V has been obtained with a voltage sweep of ±4V. Finally, operation mechanisms in ferroelectric-gate CNT (carbon nano-tube) transistors are discussed, assuming Schottky barrier conduction at the source and drain contacts. [Copyright &y& Elsevier]