Ferroelectric polymers

Last updated

Ferroelectric polymers [1] [2] are a group of crystalline polar polymers that are also ferroelectric, meaning that they maintain a permanent electric polarization that can be reversed, or switched, in an external electric field.

Electric field Vector field representing the Coulomb force per unit charge that would be exerted on a test charge at each point due to other electric charges

An electric field surrounds an electric charge, and exerts force on other charges in the field, attracting or repelling them. Electric field is sometimes abbreviated as E-field. The electric field is defined mathematically as a vector field that associates to each point in space the force per unit of charge exerted on an infinitesimal positive test charge at rest at that point. The SI unit for electric field strength is volt per meter (V/m). Newtons per coulomb (N/C) is also used as a unit of electric field strength. Electric fields are created by electric charges, or by time-varying magnetic fields. Electric fields are important in many areas of physics, and are exploited practically in electrical technology. On an atomic scale, the electric field is responsible for the attractive force between the atomic nucleus and electrons that holds atoms together, and the forces between atoms that cause chemical bonding. Electric fields and magnetic fields are both manifestations of the electromagnetic force, one of the four fundamental forces of nature.

Contents

Ferroelectric polymers, such as polyvinylidene fluoride (PVDF), are used in acoustic transducers and electromechanical actuators because of their inherent piezoelectric response, and as heat sensors because of their inherent pyroelectric response. [3]

Polyvinylidene fluoride polymer

Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride.

Figure 1: Structure of poly(vinylidene fluoride) Polyvinylidene fluoride.png
Figure 1: Structure of poly(vinylidene fluoride)

Background

First reported in 1971, ferroelectric polymers are polymer chains that must exhibit ferroelectric behavior, [4] hence piezoelectric [3] and pyroelectric behavior. [3]

A ferroelectric polymer must contain permanent electrical polarization that can be reversed repeatedly, by an opposing electric field. [4] In the polymer, dipoles can be randomly oriented, but application of an electric field will align the dipoles, leading to ferroelectric behavior. In order for this effect to happen, the material must be below its Curie Temperature. [5] Above the Curie Temperature, the polymer exhibits paraelectric behavior, which does not allow for ferroelectric behavior because the electric fields do not align.

Figure 2: Structure of polytrifluoroethylene Polytrifluoroethylene.png
Figure 2: Structure of polytrifluoroethylene

A consequence of ferroelectric behavior leads to piezoelectric behavior, where the polymer will generate an electric field when stress is applied, or change shape upon application of an electric field. This is viewed as shrinking, or changes in conformation of the polymer in an electric field; or by stretching and compressing the polymer, measure generated electric fields. Pyroelectric behavior stems from the change in temperature causing electric behavior of the material. While only ferroelectric behavior is required for a ferroelectric polymer, current ferroelectric polymers exhibit pyroelectric and piezoelectric behavior. [3]

In order to have an electric polarization that can be reversed, ferroelectric polymers are often crystalline, much like other ferroelectric materials. [5] Ferroelectric properties are derived from electrets, which are defined as a dielectric body that polarizes when an electric field and heat is applied. Ferroelectric polymers differ in that the entire body undergoes polarization, and the requirement of heat is not necessary. Although they differ from electrets, they are referred to as electrets often. [2] Ferroelectric polymers fall into a category of ferroelectric materials known as a 'order-disorder' [4] material. This material undergoes a change from randomly oriented dipoles which are paraelectric, to ordered dipoles which become ferroelectric.

After the discovery of PVDF, many other polymers have been sought after that contain ferroelectric, piezoelectric, and pyroelectric properties. Initially different blends and copolymers of PVDF were discovered, such as a polyvinylidene fluoride with poly(methyl methacrylate). [2]

Other structures were discovered to possess ferroelectric properties, such as polytrifluoroethylene [6] and odd-numbered nylon. [2] [7] [8]

History

Figure 3: Brief timeline describing important events that have occurred in piezoelectricity and ferroelectric polymer history New Timeline Ferroelectric.png
Figure 3: Brief timeline describing important events that have occurred in piezoelectricity and ferroelectric polymer history

The concept of ferroelectricity was first discovered in 1921. This phenomenon began to play a much larger role in electronic applications during the 1950s after the increased use of BaTiO3. This ferroelectric material is part of the corner-sharing oxygen octahedral structure, but ferroelectrics can also be grouped into three other categories. These categories include organic polymers, ceramic polymer composites, and compounds containing hydrogen-bonded radicals. It wasn't until 1969 that Kawai first observed the piezoelectric effect in a polymer polyvinylidene fluoride. Two years later, the ferroelectric properties of the same polymer were reported. Throughout the 1970s and 1980s, these polymers were applied to data storage and retrieval. Subsequently, there has been tremendous growth during the past decade in exploring the materials science, physics, and technology of poly(vinylidenefluoride) and other fluorinated polymers. Copolymer PVDF with trifluoroethylene and odd-numbered nylons were additional polymers that were discovered to be ferroelectric. This propelled a number of developing applications on piezoelectricity and pyroelectricity.

Polyvinylidene fluoride

Synthesis of polyvinylidene fluoride (PVDF)

The easiest way of synthesizing PVDF is the radical polymerization of vinylidene fluoride (VF2), however, the polymerization is not completely regiospecific. The asymmetric structure of VF2 leads to the orientation isomers during the polymerization. The configuration of the monomer in the chain can be either "head to head" or "head to tail".

Figure 4: Three orientation isomers of polyvinylidene fluoride Ferroelectric-wiki-w1.png
Figure 4: Three orientation isomers of polyvinylidene fluoride

To get more control on the regiospecific polymer synthesis, copolymerization was proposed. One of these methods is introducing the precursor polymer made from copolymerization of VF2 with either 1-chloro-2,2-difluoroethylene (CVF2) or 1-bromo-2,2-difluoroethylene( BVF2). The chlorinated or brominated monomers are attacked at their CF2 carbon by growing –CH2CF2∙ radical. After reductive dechlorination or debromination with tri-n-butyltin hydride they become a reversed VF2 unit in the final polymer.Therefore, a regioisomer of PVDF is formed. [9]

Figure 5: Scheme of regiospecific polymer synthesis Ferroelectric-wiki-w2.png
Figure 5: Scheme of regiospecific polymer synthesis
Figure 6: Schematic description of two most common conformations of PVDF, the left one is tg tg and the right one is all trans, the yellow sphere represents fluorine atom, the white sphere represents hydrogen atom and the grey sphere represents the carbon atom. Ferroelectric-wiki-w3.png
Figure 6: Schematic description of two most common conformations of PVDF, the left one is tg tg and the right one is all trans, the yellow sphere represents fluorine atom, the white sphere represents hydrogen atom and the grey sphere represents the carbon atom.

Study of the structure of PVDF

To minimize the potential energy of the chains arising from internal steric and electrostatic interactions, the rotation about single bonds happens in the chain of PVDF. There are two most favorable torsional bond arrangements: trans ( t ) and gauche± ( g± ). In the case of “ t”, the substituents are at 180° to each other. In the case of “g±”, the substituents are at ±60° to each other. PVDF molecules contain two hydrogen and two fluorine atoms per repeat unit, so they have a choice of multiple conformations. However, rotational barriers are relatively high, the chains can be stabilized into favorable conformations other than that of lowest energy. The three known conformations of PVDF are all-trans, tg+tg−, and tttg+tttg−. The first two conformations are the most common ones and are sketched out in the figure on right. In the tg+tg− conformation, the inclination of dipoles to the chain axis leads to the polar components of both perpendicular (4.0 × 10−30 C-m per repeat) and parallel to the chain (3.4 × 10−30 C-m per repeat). In the all trans structure, the alignment of all its dipoles are in the same direction normal to the chain axis. In this way, it can be expected that the all trans is the most highly polar conformation in PVDF (7.× 10−30 C-m per repeat). These polar conformations are the crucial factors that lead to the ferroelectric properties. [3]

Current Research

Ferroelectric polymers and other materials have been incorporated into many applications, but there is still cutting edge research that is currently being done. For example, there is research being conducted on novel ferroelectric polymer composites with high dielectric constants. Ferroelectric polymers, such as polyvinylidene fluoride and poly[(vinylidenefluoride-co-trifluoroethylene] [P(VDF-TrFE)], are very attractive for many applications because they exhibit good piezoelectric and pyroelectric responses and low acoustic impedance, which matches water and human skin. More importantly, they can be tailored to meet various requirements. A common approach for enhancing the dielectric constant is to disperse a high-dielectric-constant ceramic powder into the polymers. Popular ceramic powders are lead-based complexes such as PbTiO3 and Pb(Zr,Ti)O3. This can be disadvantageous because lead can be potentially harmful and at high particulate loading, the polymers lose their flexibility and a low quality composite is obtained. Current advances use a blending procedure to make composites that are based on the simple combination of PVDF and cheap metal powders. Specifically, Ni powders were used to make up the composites. The dielectric constants were enhanced from values there were less than 10 to approximately 400. This large enhancement is explained by the percolation theory. [10]

These ferroelectric materials have also been used as sensors. More specifically, these types of polymers have been used for high pressure and shock compression sensors. [11] It has been discovered that ferroelectric polymers exhibit piezoluminescence upon the application of stress. Piezoluminescence has been looked for in materials that are piezoelectric. [12]

Figure 7: Stress-strain curve showing the different regions. Light seen at fracture is known as triboluminescence and light emitted in the elastic regime is known as piezoluminescence. StressStrain.png
Figure 7: Stress–strain curve showing the different regions. Light seen at fracture is known as triboluminescence and light emitted in the elastic regime is known as piezoluminescence.

It is useful to distinguish among the several regimes in a typical stress–strain curve for a solid material. The three regimes of the stress–strain curve include elastic, plastic, and fracture. Light emitted in the elastic regime is known piezoluminescence. Fig. 7 shows a general stress–strain curve.

These types of polymers have played a role in biomedical and robotic applications and liquid crystalline polymers. In 1974, R.B. Meyer predicted ferroelectricity in chiral smectic liquid crystals by pure symmetry conditions. Shortly after, Clark and Lagerwall had done work on the fast electrooptic effect in a surface-stabilized ferroelectric liquid crystal (SSFLC) structure. This opened up promising possibility of technical applications of ferroelectric liquid crystals in high-information display devices. Through applied research, it was shown that SSFLC structure has faster switching times and bistability behavior in comparison with commonly used nematic liquid crystal displays. In the same time period, the first side-chain liquid crystalline polymers (SCLCP) were synthesized. These comb-like polymers has mesogenic side chains that are covalently bonded (via flexible spacer units) to the polymer backbone. The most important feature of the SCLCP's is their glassy state. In other words, these polymers have a "frozen" ordered state along one axis when cooled below their glass transition temperature. This is advantageous for research in the area of nonlinear optical and optical data storage devices. The disadvantage is that these SCLCP's suffered from their slow switching times due to their high rotational viscosity.

Applications

Nonvolatile memory

The ferroelectric property exhibits polarization–electric-field-hysteresis loop, which is related to "memory". One application is integrating ferroelectric polymer Langmuir–Blodgett (LB) films with semiconductor technology to produce nonvolatile ferroelectric random-access memory(NV-FRAM or NV-FeRAM) and data-storage devices. Recent research with LB films and more conventional solvent formed films shows that the VDF copolymers(consisting of 70% vinylidene fluoride (VDF) and 30% trifluoroethylene (TrFE)) are promising materials for nonvolatile memory applications. The device is built in the form of the metal–ferroelectric–insulator–semiconductor (MFIS) capacitance memory. The results demonstrated that LB films can provide devices with low-voltage operation. [13]

Thin Film Electronics successfully demonstrated roll-to-roll printed non-volatile memories based on ferroelectric polymers in 2009. [14] [15] [16] [17]

Transducers

The ferroelectric effect always relates the various force to electric properties, which can be applied in transducers. The flexibility and low cost of polymers facilitates the application of ferroelectric polymers in transducers. The device configuration is simple, it usually consists of a piece of ferroelectric film with an electrode on the top and bottom surfaces. Contacts to the two electrodes complete the design. [18]

Sensors

When the device functions as a sensor, a mechanical or acoustic force applied to one of the surfaces causes a compression of the material. Via the direct piezoelectric effect, a voltage is generated between the electrodes.

Actuators

In actuators, a voltage applied between the electrodes causes a strain on the film through the inverse piezoelectric effect.

Soft transducers in the form of ferroelectric polymer foams have been proved to have great potential. [19]

See also

Related Research Articles

Piezoelectricity the electric charge that accumulates in certain solid materials in response to applied mechanical stress

Piezoelectricity is the electric charge that accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure and latent heat. It is derived from the Greek word πιέζειν; piezein, which means to squeeze or press, and ἤλεκτρον ēlektron, which means amber, an ancient source of electric charge. French physicists Jacques and Pierre Curie discovered piezoelectricity in 1880.

Dielectric electrically poorly conducting or non-conducting, non-metallic substance of which charge carriers are generally not free to move

A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the opposite direction. This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axes align to the field.

Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are pyroelectric, with the additional property that their natural electrical polarization is reversible. The term is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment. Ferromagnetism was already known when ferroelectricity was discovered in 1920 in Rochelle salt by Valasek. Thus, the prefix ferro, meaning iron, was used to describe the property despite the fact that most ferroelectric materials do not contain iron. Materials that are both ferroelectric and ferromagnetic are known as multiferroics.

Pyroelectricity property of certain crystals which are naturally electrically polarized and contain large electric fields

Pyroelectricity is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal. If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current.

An electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet. Although Oliver Heaviside coined this term in 1885, materials with electret properties were already known to science and had been studied since the early 1700s. One particular example is the electrophorus, a device consisting of a slab with electret properties and a separate metal plate. The electrophorus was originally invented by Johan Carl Wilcke in Sweden and again by Alessandro Volta in Italy.

Lead zirconate titanate intermetallic inorganic chemical compound

Lead zirconate titanate is an inorganic compound with the chemical formula Pb[ZrxTi1−x]O3 (0≤x≤1). Also called PZT, it is a ceramic perovskite material that shows a marked piezoelectric effect, meaning that the compound changes shape when an electric field is applied. It is used in a number of practical applications such as ultrasonic transducers and piezoelectric resonators. It is a white to off-white solid.

Electrostriction is a property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field.

Energy harvesting is the process by which energy is derived from external sources, captured, and stored for small, wireless autonomous devices, like those used in wearable electronics and wireless sensor networks.

Electroactive polymers

Electroactive polymers, or EAPs, are polymers that exhibit a change in size or shape when stimulated by an electric field. The most common applications of this type of material are in actuators and sensors. A typical characteristic property of an EAP is that they will undergo a large amount of deformation while sustaining large forces.

Multiferroics are defined as materials that exhibit more than one of the primary ferroic properties:

Barium titanate chemical compound

Barium titanate is an inorganic compound with chemical formula BaTiO3. Barium titanate appears white as a powder and is transparent when prepared as large crystals. It is a ferroelectric ceramic material that exhibits the photorefractive effect and piezoelectric properties. It is used in capacitors, electromechanical transducers and nonlinear optics.

Ferroelectrets also known as piezoelectrets, are thin films of polymer foams, exhibiting piezoelectric and pyroelectric properties after electric charging. Ferroelectret foams usually consist of a cellular polymer structure filled with air. Polymer-air composites are elastically soft due to their high air content as well as due to the size and shape of the polymer walls. Their elastically soft composite structure is one essential key for the working principle of ferroelectrets, besides the permanent trapping of electric charges inside the polymer voids. The elastic properties allow large deformations of the electrically charged voids. However, the composite structure can also possibly limit the stability and consequently the range of applications.

A polymer blend, or polymer mixture, is a member of a class of materials analogous to metal alloys, in which at least two polymers are blended together to create a new material with different physical properties.

Electron-beam processing process which involves using electrons, usually of high energy, to treat an object for a variety of purposes

Electron-beam processing or electron irradiation (EBI) is a process that involves using electrons, usually of high energy, to treat an object for a variety of purposes. This may take place under elevated temperatures and nitrogen atmosphere. Possible uses for electron irradiation include sterilization and cross-linking of polymers.

Qiming Zhang is a distinguished professor of Electrical Engineering and Materials Science and Engineering at Pennsylvania State University. He is also the vice President & CTO at Strategic Polymer Sciences, Inc.

A Nanogenerator is a type of technology that converts mechanical/thermal energy as produced by small-scale physical change into electricity. A Nanogenerator has three typical approaches: piezoelectric, triboelectric, and pyroelectric nanogenerators. Both the piezoelectric and triboelectric nanogenerators can convert mechanical energy into electricity. However, pyroelectric nanogenerators can be used to harvest thermal energy from a time-dependent temperature fluctuation.

A biotransducer is the recognition-transduction component of a biosensor system. It consists of two intimately coupled parts; a bio-recognition layer and a physicochemical transducer, which acting together converts a biochemical signal to an electronic or optical signal. The bio-recognition layer typically contains an enzyme or another binding protein such as antibody. However, oligonucleotide sequences, sub-cellular fragments such as organelles and receptor carrying fragments, single whole cells, small numbers of cells on synthetic scaffolds, or thin slices of animal or plant tissues, may also comprise the bio-recognition layer. It gives the biosensor selectivity and specificity. The physicochemical transducer is typically in intimate and controlled contact with the recognition layer. As a result of the presence and biochemical action of the analyte, a physico-chemical change is produced within the biorecognition layer that is measured by the physicochemical transducer producing a signal that is proportionate to the concentration of the analyte. The physicochemical transducer may be electrochemical, optical, electronic, gravimetric, pyroelectric or piezoelectric. Based on the type of biotransducer, biosensors can be classified as shown to the right.

Piezoelectric Micromachined Ultrasonic Transducers (PMUT) are MEMS-based piezoelectric ultrasonic transducers. Unlike bulk piezoelectric transducers which use the thickness-mode motion of a plate of piezoelectric ceramic such as PZT or single-crystal PMN-PT, PMUT are based on the flexural motion of a thin membrane coupled with a thin piezoelectric film, such as PVDF. In comparison with bulk piezoelectric ultrasound transducers, PMUT can offer advantages such as increased bandwidth, flexible geometries, natural acoustic impedance match with water, reduced voltage requirements, mixing of different resonant frequencies and potential for integration with supporting electronic circuits especially for miniaturized high frequency applications.

A polar metal, metallic ferroeletric, or ferroelectric metal is a metal that contains an electric dipole moment. Its components have an ordered electric dipole. Such metals should be unexpected, because the charge should conduct by way of the free electrons in the metal and neutralize the polarized charge. However they do exist. Probably the first report of a polar metal was in single crystals of the cuprate superconductors YBa2Cu3O7-δ,. A polarization was observed along one (001) axis by pyroelectric effect measurements, and the sign of the polarization was shown to be reversible, while its magnitude could be increased by poling by an electric field. The polarization was found to disappear in the superconducting state.. The lattice distortions responsible were considered to be a result of oxygen ion displacements induced by doped charges that break inversion symmetry. The effect was utilized for fabrication of pyroelectric detectors for space applications, having the advantage of large pyroelectric coefficient and low intrinsic resistance. Another substance family that can produce a polar metal is the nickelate perovskites. One example interpreted to show polar metallic behavior is lanthanum nickelate, LaNiO3. A thin film of LaNiO3 grown on the (111) crystal face of lanthanum aluminate, (LaAlO3) was interpreted to be both conductor and a polar material at room temperature. The resistivity of this system, however, shows an upturn with decreasing temperature, hence does not strictly adhere to the definition of a metal. Also, when grown 3 or 4 unit cells thick (1-2 nm) on the (100) crystal face of LaAlO3, the LaNiO3 can be a polar insulator or polar metal depending on the atomic termination of the surface. Lithium osmate, LiOsO3 also undergoes a ferrorelectric transition when it is cooled below 140K. The point group changes from R3c to R3c losing its centrosymmetry. At room temperature and below, lithium osmate is an electric conductor, in single crystal, polycrystalline or powder forms, and the ferroelectric form only appears below 140K. Above 140K the material behaves like a normal metal.

References

  1. ↑ "Ferroelectric Properties of Vinylidene Fluoride Copolymers," by T. Furukawa, in Phase Transitions, Vol. 18, pp. 143–211 (1989).
  2. 1 2 3 4 Nalwa, H. (1995). Ferroelectric Polymers (First ed.). New York: Marcel Dekker, INC. ISBN   0-8247-9468-0.
  3. 1 2 3 4 5 Lovinger, A.J. (1983). "Ferroelectric polymers". Science. 220 (4602): 1115–1121. Bibcode:1983Sci...220.1115L. doi:10.1126/science.220.4602.1115. PMID   17818472.
  4. 1 2 3 Poulsen, M.; Ducharme, S.. (2010). "Why Ferroelectric Polyvinylidene Fluoride is Special". IEEE Transactions on Dielectrics and Electrical Insulation. 17 (4): 1028–1035. doi:10.1109/TDEI.2010.5539671.
  5. 1 2 Atkins, P. (2006). "23". Inorganic Chemistry. Overton, Rourke, Weller, Armstrong (Fourth ed.). New York: W.H. Freeman and Company. pp. 609–610. ISBN   0-7167-4878-9.
  6. ↑ Tashiro, K.; Takano, K.; Kobayashi, M.; Chatani, Y.; Tadokoro, H. (2011). "Structural study on ferroelectric phase transition of vinylidene fluoride-trifluoroethylene copolymers (III) dependence of transitional behavior on VDF molar content". Ferroelectrics. 57 (1): 297–326. doi:10.1080/00150198408012770. ISSN   0015-0193.
  7. ↑ Nalwa, H.S. (1991). "Recent development in ferroelectric polymers". J. Macromol. Sci. Rev. Macromol. Chem. Phys. 29 (4): 341. doi:10.1080/15321799108021957.
  8. ↑ Kepler, R.G.; Anderson, R.A. (1992). "Ferroelectric polymers" (PDF). Advances in Physics. 41 (1): 1–57. Bibcode:1992AdPhy..41....1K. doi:10.1080/00018739200101463. ISSN   0001-8732.
  9. ↑ Cais, R.E.; Kometani, J.M. (1985). "Synthesis and two-dimensional NMR of highly aregic poly(vinylidene fluoride)". Macromolecules. 18 (6): 1354–1357. Bibcode:1985MaMol..18.1354C. doi:10.1021/ma00148a057.
  10. ↑ Dang, Zhi-Ming; Ce-Wen Nan (2003). "Novel Ferroelectric Polymer Composites with High Dielectric Constants". Advanced Materials. Tsinghua University: Communications. 15 (19): 1625–1628. doi:10.1002/adma.200304911.
  11. ↑ Bauer, Francois (2002). "Ferroelectric Polymers for High Pressure and Shock Compression Sensors". Mat. Res. Soc. Symposium. Materials Research Society. 698.
  12. ↑ Reynolds, George (1997). "Piezoluminescence from a ferroelectric polymer and quartz". Journal of Luminescence . Princeton. 75 (4): 295–299. Bibcode:1997JLum...75..295R. doi:10.1016/S0022-2313(97)00134-8.
  13. ↑ Ducharme, D.; Reece, T.J.; Othon, C.M; Rannow, R.K. (2005). "Ferroelectric polymer Langmuir-Blodgett films for nonvolatile memory applications". IEEE Transactions on Device and Materials Reliability. 5 (4): 720–733. doi:10.1109/TDMR.2005.860818.
  14. ↑ Thinfilm and InkTec awarded IDTechEx' Technical Development Manufacturing Award IDTechEx, 15 April 2009
  15. ↑ PolyIC, ThinFilm announce pilot of volume printed plastic memories EETimes, 22 September 2009
  16. ↑ All set for high-volume production of printed memories Printed Electronics World, 12 April 2010
  17. ↑ Thin Film Electronics Plans to Provide ‘Memory Everywhere’ Printed Electronics Now, May 2010
  18. ↑ Kressmann, R. (2001). "New piezoelectric polymer for air-borne and water-borne sound transducers". J. Acoust. Soc. Am. 109 (4): 1412–6. Bibcode:2001ASAJ..109.1412K. doi:10.1121/1.1354989. PMID   11325112.
  19. ↑ Bauer, Siegfried; Gerhard-Multhaupt, Reimund; Sessler, Gerhard M. (2004). "Ferroelectrets: Soft Electroactive Foams for Transducers". Physics Today. 57 (2): 37–43. Bibcode:2004PhT....57b..37B. doi:10.1063/1.1688068. ISSN   0031-9228.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.