Arun Anand Prabu

Comparative electrical bistable characteristics of ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer based nonvolatile memory device architectures

We report the thermal and electrical bistable characteristics of ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE) (72∕28mol%)] thin films as a function of varying memory device architectures. Rectangular-shaped capacitance-voltage (C-V) hysteresis loops obtained using 100nm P(VDF-TrFE) films with a metal-ferroelectric-insulator-semiconductor (MFIS) diode architecture were more suitable for distinguishing the data-bit state compared with the symmetrical hysteresis observed using metal-ferroelectric-metal capacitors. Poly(4-vinyl phenol) used as a dielectric insulator in the MFIS prevented shifting of the C-V hysteresis curve toward the negative bias voltage.

PVDF Nanoweb Touch Sensors Prepared Using Electro-Spinning Process for Smart Apparels Applications

Polyvinylidene fluoride (PVDF) based electrospun nanoweb fibers with outstanding piezo-, pyro- and ferroelectric behavior are being intensely studied by many researchers, especially for touch-sensor applications. In order to further improve the advantageous characteristics of PVDF nanoweb fibers, we focused our attention on studying the effect of filling PVDF solution with calculated amount of calcium chloride (CaCl2) or multi-walled carbon nanotube (MWCNT), and their electrospun nanoweb fibers were analyzed for the changes in β-crystalline phase, and its associated piezoelectric characteristics using a custom-made sensor set-up developed in our lab. FT-IR spectroscopy was used to confirm the changes in the β-crystalline content with varying content of CaCl2 and MWCNT. SEM data revealed the reducing fiber diameter with increasing CaCl2 content. PVDF nanoweb subjected to pressure showed changes in touch sensing property as analyzed using an oscilloscope integrated with Labview program. Overall, the PVDF nanoweb containing the additives used in our study exhibited greater sensitivity-in-touch for use in smart apparel applications compared to unmodified PVDF nanoweb, and the results are reported in detail here.

The effect of an external electric field on solid-state phase transition of (P(VDF/TrFE)(72/28)

The copolymers of vinylidene fluoride and trifluoroethylene (P(VDF/TrFE)) with VDF content of 50–80 mole % can be applied to the field of nonvolatile ferroelectric polymeric random access memory (FePoRAM) devices, since they exhibit stable ferroelectricβ-phase at room temperature with spontaneous polarization of the C-F dipoles towards an external electric field greater than the coercive field. Many researchers have already reported the molecular structures and dynamics of the ferroelectric (F) crystalline phase and the unique change in chain conformation between polarF phase and non-polar paraelectric (P) phase near their Curie transition temperature (Tc) which is dependent on factors such as VDF content and annealing treatment conditions. The effect of external electric field strength on theF⇔P crystalline phase transition in P(VDF/TrFE)(72/28) random copolymer samples of nanometer thickness was investigated. Capacitance of 250 nm thick sample measured as a function of heating-cooling under varying external electric field strength exhibited increasingTc’s during heating (Tc↑) and cooling (Tc↓) under an applied electric field of more than 0.03 MV/cm. Applying cyclic bias electric field (+1 to −1 MV/cm) for samples kept isothermally at just above theirTc(Tc↓) during cooling, we were able to observe the field-inducedP→F phase transition. With increasing cycles of the applied electric field for sample maintained just above (Tc↓), the bistableC-E hysteresis was observed and the phase change fromP→F is irreversible even after the electric field is removed. However, for samples kept well above (Tc↓) and nearTm (100 °C and 120°C respectively) during cooling, theF-phase initially formed through the field-induced phase transition is reversibly transformed to theP-phase when the applied electric field is removed. Drastic changes were observed in both coercive field (Ec) and remanent polarization (Pr) values during heating and cooling near theTc range due to theF⇔P phase transition and the results are reported in detail here.

Preparation and evaluation of poly(vinylidene fluoride)-sulfonated poly(1,4-phenylene sulfide) based membranes with improved hydrophilicity

AbstractPoly(vinylidene fluoride) (PVDF) based water purification membranes exhibit excellent thermal stability and chemical resistance, but also possess inherent drawbacks such as severe membrane fouling, lower separation efficiency and water flux due to its hydrophobic nature. In the present study, we attempted to enhance the hydrophilicity of PVDF membranes by treating with varying content (0 to 3 wt%) of partially sulfonated poly(1,4-phenylene sulfide) (sPPS) component using phase-inversion process. Compared to neat PVDF membrane, the PVDF/sPPS blend membranes exhibited typical asymmetric morphology with larger finger-like pores, efficient distribution of hydrophilic SO3- groups and decreasing water contact angle (WCA) upto 62° (77° for neat PVDF) as confirmed from scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and contact-angle measurements, respectively. Studies carried out for pure water flux (880 L/m2h) and blood serum albumin (BSA) solution flux (185 L/m2h) confirmed the enhanced permeability and higher fouling resistance for PVDF-sPPS (3 wt% sPPS) membranes compared to neat PVDF membrane (175 L/m2h and 63 L/m2h, respectively), though the BSA flux decreased with an increase in the filtration time due to membrane fouling. Compared to the total organic carbon (TOC) values of poly(ethylene oxide) (PEO) aqueous solutions before permeation (189.9 mg/L for Mw=100,000 and 75.68 mg/L for Mw=300,000), TOC of neat PVDF membrane decreased to 15 mg/L for Mw= 100,000 and 5 mg/L for Mw=300,000. With increasing sPPS content, the TOC values showed an increasing trend due to their increasing pore size. Overall, the incorporation of sPPS in PVDF membrane lowered the WCA, enhanced fouling resistance and improved its permeability and selectivity, which exemplifies the importance of this study.

Effect of Varying Memory Device Architectures on the Electrical Properties of P(VDF/TrFE)(72/28) Copolymer Thin Film

In this study, the dipole switching and non-volatile memory functionality of poly(vinylidene fluoride-trifluoroethylene) (PVDF/TrFE)(72/28 mol%) random copolymer ultrathin films were analyzed. PVDF/TrFE(72/28) used as ferroelectric insulator in varying memory device architectures such as metal-ferroelectric polymer-metal (MFM), MF-insulator-semiconductor (MFIS), MIS and ferroelectric field-effect transistors (FeFET) were examined using different electrical measurements. A maximum data writing speed of 1.69 MHz was calculated from the switching time measured using MFM architecture. Compared to MFM, MFIS device architecture was found to be more suitable for distinguishing the ‘0’ and ‘1’ state using the capacitance-voltage measurement. With FeFET, the measured drain current (Id) as well as its memory window increased with decreasing channel length, thereby enabling the easier identification of ‘0’ and ‘1’ state comparable to the MFIS case. The data obtained from this study will be useful in the fabrication of non-volatile random access memory (NVRAM) devices operating at lower voltage with faster data R/W/E speed and memory retention capability.

Fabrication and Electrical Studies of P(VDF/TrFE)(72/28) Copolymer based Non-Volatile Memory Devices as a Function of Varying Device Structures

Ferroelectric characteristics of poly(vinylidiene fluoride/trifluoroethylene) (P(VDF/TrFE) (72/28 mol%)) copolymer ultrathin films used as an insulator in varying memory device architectures such as metal-ferroelectric polymer-metal (MFM), MF-insulator-semiconductor (MFIS), MIS and organic field-effect transistor (OFET) were studied using different electrical measurements. A maximum data writing speed of 1.69 MHz was calculated from the switching time measured using MFM architecture. Capacitance-voltage measured using MFIS was found to be more suitable for distinguishing the ‘0’ and ‘1’ state compared to MFM device structure. In OFET, the decreasing channel length increased the measured drain current ( I d ) values as well as its memory window enabling easier identification of the ‘0’ and ‘1’ state comparable to MFIS case. The data obtained from this study will be useful in the fabrication of non-volatile random access memory (NVRAM) devices with faster data R/W/E speed and memory retention capacity.