Showing papers by "Bruce E. Gnade published in 2011"

Ferroelectric Properties and Polarization Switching Kinetic of Poly (vinylidene fluoride-trifluoroethylene) Copolymer

Abstract: The discovery of the piezoelectric properties of poly(vinylidene fluoride) (PVDF) by Kawai [Kawai, 1969], and the study of its pyroelectric and nonlinear optical properties [Bergman et al, 1971; Glass, 1971] led to the discovery of its ferroelectric properties in the early 1970s Since that time, considerable development and progress have been made on both materials and devices based on PVDF This work helped establish the field of ferroelectric polymer science and engineering [Nalwa, 1995a] There are many novel ferroelectric polymers, such as poly(vinylidene fluoride) (PVDF) copolymers, poly(vinylidene cyanide) copolymers, odd-numbered nylons, polyureas, ferroelectric liquid crystal polymers and polymer composites of organic and inorganic piezoelectric ceramics [Nalwa, 1991 and Kepler & Anderson, 1992 as cited in Nalwa, 1995b; Nalwa, 1995a] Among them, PVDF, and its copolymers are the most developed and promising ferroelectric polymers because of their high spontaneous polarization and chemical stability Ferroelectricity is caused by the dipoles in crystalline or polycrystalline materials that spontaneously polarize and align with an external electric field The polarization of the dipoles can be switched to the opposite direction with the reversal of the electric field Similar to inorganic ferroelectric materials such as PbZr05Ti05O3 (PZT) and SrBi2Ta2O9 (SBT), organic ferroelectric materials exhibit ferroelectric characteristics such as Curie temperature (the transition temperature from ferroelectrics to paraelectrics), coercive field (the minimum electric field to reverse the spontaneous polarization) and remanent polarization (the restored polarization after removing the electric field) However, the low temperature and low fabrication cost of organic ferroelectric materials enable them to be used in a large number of applications, such as flexible electronics In this chapter, the discussion is focused on poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], one of the most promising PVDF ferroelectric copolymers The main objective of this chapter is to describe the ferroelectric properties of P(VDF-TrFE) copolymer and review the current research status of ferroelectric devices based on this material The chapter is divided in six sections The first section introduces the topic of organic ferroelectrics The second section describes the material properties of the ferroelectric phase of P(VDF-TrFE) including phase structures, surface morphology, crystallinity and molecule chain orientation Next, the electrical properties such as polarization, switching current, etc

PMMA-SiO2 organic–inorganic hybrid films: determination of dielectric characteristics

Abstract: Organic–inorganic hybrid thin films have been prepared by a modified sol–gel route using tetraethyl orthosilicate as the inorganic (silica) source, methyl methacrylate (MMA) as the organic source, and 3-trimetoxysilylpropyl methacrylate as the coupling agent. The films were prepared by spin coating on Si (100) p-type substrates and subsequently heat-treated at 90 °C. Fourier transform infrared results reveal a set of absorption bands associated with the formation of both PMMA and SiO2 phases in the hybrid films. Capacitance–voltage (C–V) characterization was carried out on metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) structures, with the hybrid films as the insulator layer to evaluate the electrical properties. We present a detailed comparative analysis of the dielectric constant obtained from C–V characterization in the frequency range of 1 kHz–1 MHz. For the PMMA-SiO2 hybrid material the dielectric constant values obtained were around 9.5 at 1 MHz which is superior to the values reported for thermally grown SiO2 and pure PMMA materials. The interface state density for PMMA-SiO2 on Si was approximately 1010 cm−2, which is comparable to the standard SiO2/Si structures. Due to the electrical behavior and low processing temperatures this hybrid dielectric is a very promising candidate for flexible electronic devices and its subsequent implementation does not require complex equipment.

Low-Temperature Hybrid CMOS Circuits Based on Chalcogenides and Organic TFTs

Abstract: In this letter, we demonstrate a fully integrated approach to fabricate cadmium sulfide (CdS)-pentacene complementary metal-oxide-semiconductor (CMOS) digital circuits compatible with flexible electronics. Low-cost and low-temperature chemical bath deposition is used to deposit CdS at 70°C with mobility values >; 10 cm2/V·s and threshold voltages around 5 V for fully integrated devices. p-MOS thin-film transistors were fabricated using thermally evaporated pentacene as semiconductor with mobility and threshold voltages in the range of 3×10-2 cm2/V·s and -3 V, respectively. The CMOS integration approach includes six mask levels with a maximum processing temperature of 100°C.

Effect of Sputtered ZnO Layers on Behavior of Thin-Film Transistors Deposited at Room Temperature in a Nonreactive Atmosphere

Abstract: In this work we present the electrical characterization of ZnO-based thin-film transistors fabricated at room temperature. The ZnO films were deposited by radiofrequency magnetron sputtering at variable argon pressure (3 mTorr to 10 mTorr) at room temperature. The sputtered ZnO films were polycrystalline with hexagonal structure and electrical resistivity ranging from 101 Ω cm to 108 Ω cm for films deposited from 3 mTorr to 10 mTorr. The trend in the electrical behavior of the devices was found to be due to the variation of the electron concentration of the ZnO films. The devices with better performance showed a field-effect mobility of 2.9 cm2/Vs, threshold voltage of 20 V, Ion/Ioff ≈ 106, and electrical resistivity of ~108 Ω cm. In addition, linear behavior of Ion/Ioff with deposition pressure was observed. The lowest Ion/Ioff ratio (~2) was calculated for devices with ZnO layers deposited at 3 mTorr, and the highest ratio (~106) for devices processed at 10 mTorr. Hall-effect measurements were performed on ZnO films showing the lowest resistivity. The layer grown at 3 mTorr showed a Hall mobility of μH = 8.9 cm2/Vs and carrier concentration of n = 4.2 × 1016 cm−3 with resistivity of ρ = 31.8 Ω cm. For films deposited at 5 mTorr, the Hall mobility, carrier concentration, and resistivity were μH = 7.9 cm2/Vs, n = 3.4 × 1016 cm−3, and ρ = 38.4 Ω cm, respectively. Films deposited at 8 mTorr and 10 mTorr could not be measured due to their high resistance.

CMOS TFT Op-Amps: Performance and Limitations

Abstract: In this letter, we demonstrate the feasibility of building thin-film transistor (TFT) complementary metal-oxide-semiconductor (CMOS) operational amplifiers (op-amps) at low temperature (180°C) for large-area sensor applications. The classic two-stage Miller-compensated CMOS design is built using a-Si:H and pentacene TFTs. In addition, we have studied the impact of electrical stress-induced aging of TFTs on op-amp performance using two different kinds of biasing circuits.

Permeation studies on transparent multiple hybrid SiO2-PMMA coatings-Al2O3 barriers on PEN substrates

Abstract: In this work we report the performance of permeation barriers based on organic/inorganic multilayer stacks. We have used PMMA-SiO2 (poly methyl methacrylate-silica) hybrid films synthesized through a sol–gel route as organic–inorganic components, whereas Al2O3 thin films were used as the inorganic component. The hybrid layers were deposited by dip coating and the Al2O3 by atomic layer deposition (ALD), films were prepared on polyethylene naphthalene (PEN) substrates. The permeability of the films and stacks is evaluated using helium as the diffusion gas in a custom made ultra-high vacuum system. The results show that permeability for PEN is reduced from 5 × 10−3 g/m2-day to about 9 × 10−5 g/m2-day for the best multiple barrier evaluated. Increased barrier properties are due to the increasing in the path and hence the lag-time of the permeating gas. In particular, we report the surface roughness of the different layers and its impact on the barrier performance. The hybrid layers reduced notably the roughness of the bare PEN substrate improving the quality of the Al2O3 layer in the barrier. The optical transmittance of the barriers in the visible region is higher than 80% in all the studied cases.

Novel stone-magnetizing microparticles: in vitro toxicity and biologic functionality analysis.

Abstract: Background and Purpose: We have developed novel iron-based microparticles (Fe-MP) that bind to calcium oxalate stone fragments, rendering them paramagnetic. Previously, we demonstrated enhanced efficiency of stone extraction in an inanimate model using magnetic instrumentation. Before in vivo stone extraction studies, we sought to further characterize Fe-MP with regard to cellular toxicity and to assess the influence of biologic fluids on binding performance. Materials and Methods: Toxicity: Monolayers of murine fibroblasts, human urothelium, and human transitional-cell carcinoma cells were exposed to 1 mg/mL of Fe-MP or saline via an agarose overlay. Cellular viability was assessed using neutral red staining and densitometry. Biologic functionality: Human calcium oxalate stone fragments were incubated with a solution of 1 mg/mL of Fe-MP containing varying concentrations of urine (10%–50%) or blood (0.5%–2%) for 10 minutes. Fragments were then extracted using an 8F magnetic tool. Assays of 10 sto...

Fabrication and electrical characteristics of TFTs based on chemically deposited CdS films, using glycine as a complexing agent

Abstract: In this work, we report on the fabrication and electrical characteristics of thin film transistors (TFTs) using chemically deposited cadmium sulfide (CdS) thin films as the semiconductor active layer in back-gated devices. The CdS thin films were deposited by the chemical bath deposition (CBD) technique using glycine as the complexing agent. The CdS layers were deposited on SiO2/Si-n substrates and lift-off was used to define the source and drain contacts (Au) on top of these layers. The Si-n wafer with a chromium-gold back contact served as the common gate for the transistors. Several devices with different channel lengths ranging from 10 to 80 μm were fabricated by this process. We studied the properties of the CdS layers deposited by this glycine-based CBD process and the electrical behavior of the transistors as a function of the channel length. The experimental results show that as-deposited CdS are n-type in character and devices exhibit typical pinch-off in drain current versus source–drain voltage (IDS–VDS) curves for several gate voltages. The values of the threshold voltage of the devices were in the range from 8.5 to 8.9 V, depending on the channel length. Channel mobility was between 4.3 and 5.2 cm 2 V −1 s −1 . This research implies that CdS TFTs produced by a simple and low-cost technique could be applicable to electronic devices. (Some figures in this article are in colour only in the electronic version)

Optimization of Pb(Zr0.53,Ti0.47)O3 films for micropower generation using integrated cantilevers

Abstract: Lead zirconate titanate, Pb(Zr 0.53 ,Ti 0.47 )O 3 or PZT, thin films and integrated cantilevers have been fabricated for energy harvesting applications. The PZT films were deposited on PECVD SiO 2 /Si substrates with a sol–gel derived ZrO 2 buffer layer. It is found that lead content in the starting solution and ramp rate during film crystallization are critical to achieving large-grained films on the ZrO 2 surface. The electrical properties of the PZT films were measured using metal–ferroelectric–metal and inter-digital electrode structures, and revealed substantial improvement in film properties by controlling the process conditions. Functional cantilevers are demonstrated using the optimized films with output of 1.4 V peak-to-peak at 1 kHz and 2.5 g.

Impact of semiconductor/metal interfaces on contact resistance and operating speed of organic thin film transistors

Abstract: The contact resistance of field effect transistors based on pentacene and parylene has been investigated by experimental and numerical analysis. The device simulation was performed using finite element two-dimensional drift-diffusion simulation taking into account field-dependent mobility, interface/bulk trap states and fixed charge density at the organic/insulator interface. The width-normalized contact resistance extracted from simulation which included an interface dipole layer between the gold source/drain electrodes and pentacene was 91 k?cm. However, contact resistance extracted from the simulation, without consideration of interface dipole was 52.4 k?cm, which is about half of the experimentally extracted 108 k?cm. This indicates that interface dipoles are critical effects which degrade performances of organic field effect transistors by increasing the contact resistance. Using numerical calculations and circuit simulations, we have predicted a 1 MHz switching frequency for a 1 μm channel length transistor without dipole interface between gold and pentacene. The transistor with dipole interface is predicted, via the same methods, to exhibit an operating frequency of less than 0.5 MHz.

First principles study of electronic structures of dopants in Mg 2 Si

Abstract: We investigate the impact of various dopants (Na, Ag, Cd, Zn, Al, Ga, In, Tl, Ge, and Sn) on the electronic structure of Mg 2 Si by first principles calculations using a hybrid functional that does not need a band gap correction. We find that for Na and Ge in Mg 2 Si, the impurity-induced states do not affect the density of states at both edges of the valence band and the conduction band. Ag- and Sn affect slightly the density of states at the valence band edge, while Cd and Zn affect slightly the density of state at the conduction band edge. Al and In could modify significantly the density of states at the conduction band edge. Ga introduces states just at the bottom of the conduction band. Tl introduces states in the band gap. This study provides useful information on optimizing the thermoelectric efficiency of Mg 2 Si.

Fabrication and Characterization of Pb(Zr 0.53 ,Ti 0.47 )O 3 -Pb(Nb 1/3 ,Zn 2/3 )O 3 Thin Films on Cantilever Stacks

Abstract: 0.9Pb(Zr0.53,Ti0.47)O3-0.1Pb(Zn1/3,Nb2/3)O3 (PZT–PZN) thin films and integrated cantilevers have been fabricated. The PZT–PZN films were deposited on SiO2/Si or SiO2/Si3N4/SiO2/poly-Si/Si membranes capped with a sol–gel-derived ZrO2 buffer layer. It is found that the membrane layer stack, lead content, existence of a template layer of PbTiO3 (PT), and ramp rate during film crystallization are critical for obtaining large-grained, single-phase PZT–PZN films on the ZrO2 surface. By controlling these parameters, the electrical properties of the PZT–PZN films, their microstructure, and phase purity were significantly improved. PZT–PZN films with a dielectric constant of 700 to 920 were obtained, depending on the underlying stack structure.

Vicinity sensor system and related systems and methods

Abstract: Embodiments of vicinity sensor systems are described herein. Other embodiments and related methods are also disclosed herein.