POLYMER DIODE

Abstract

The present invention provides flexible polymer diodes in the form of a printable polymer sandwich configuration similar to that found in electroactive polymer transducers. The inventive flexible polymer diodes comprise a dielectric layer sandwiched between a pair of electrodes. With appropriate optional additives introduced in the electrode formulation and the proper electrical properties in the electrode, a device may be constructed which allows current to pass through for only one polarity of applied voltage.

Description

FIELD OF THE INVENTION

The present invention is directed in general to polymer-based electronic devices and in particular to polymer diodes for use in flexible electronic devices.

BACKGROUND OF THE INVENTION

There has been a desire in recent years for flexible electronic devices which in turn has driven a need for flexible electronic components that can be applied to flexible (polymer) substrates at low temperatures. Although polymer and organic light emitting diodes are generally available, reliable, easy to process polymer diodes are not readily available for flexible electronics applications. Some work has been done with wet electrolytic systems. Both solutions require good sealing for long lifetimes. There has been a movement to use high speed. printing and other deposition methods rather than subtractive lithographic methods.

Approaches have generally centered on solution processable semiconductors such as those used in polymer light emitting diodes (PLEDs) sandwiched between electrodes that can be deposited, and optionally sintered, at low temperatures. Many of the semiconducting materials are difficult to process and can have lifetime issues. Some may chemically de-dope and become inactive. In addition, such materials can be sensitive to atmospheric moisture and need to be sealed. Multilayer structures may be difficult to fabricate. Many of these electrode systems require sintering temperatures that can cause damage to the polymer substrate and need to be tailored to have the correct work function for diode operation. Some methods have introduced pressure-annealing or lamination steps to improve the performance of the devices.

For example, Yoshida et al., in Jpn. Appl. Phys. 50 (2011) 04DK16 describe a pressure-annealing method for fabricating printed low-work-function metal patterns and printed metal alloy patterns. The pressure-annealed metal electrodes of Yoshida et al., are used as bottom electrodes of printed polymer diodes.

Reports on the development of solution-state polymer diodes with nanogap electrodes that support intra-chain-dominant conduction are provided at http://nanotechweb.org/cws/article/lab/50114.

In all these cases, the diode mechanism has moving charges—electrons and holes—which flow through an electrically (semi-)conductive layer with similar mobilities (relative to the mobilities of any of the molecular species in the layer between the electrodes). Ionic diodes are known in the art but typically these require fluidic electrolytes to enable ionic mobility.

Lee et al., in U.S. Published Patent Application Nos. 2007/0221926 and 20120025174 describe the production of solution-processed titanium oxide layer containing polymer diodes.

There continues to be a need in the art for polymer diodes that are suitable for use in flexible electronics applications.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides such flexible polymer diodes in the form of a printable polymer sandwich configuration similar to that found in electroactive polymer transducers. The inventive flexible polymer diodes comprise a dielectric layer sandwiched between a pair of electrodes. With appropriate optional additives introduced in the electrode formulation and the proper electrical properties in the electrode, a device may be constructed which allows current to pass through for only one polarity of applied voltage.

These and other advantages and benefits of the present invention will be apparent from the Detailed Description of the invention herein below.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will now be described for purposes of illustration and not limitation in conjunction with the figures, wherein:

FIG. 1 is a plot showing current vs. time vs. cycle with alternating polarity;

FIG. 2 is a plot showing displacement vs. time vs. cycle with alternating polarity;

FIGS. 3A, 3B and 3C show a possible mechanism for the present invention;

FIG. 4 provides a plot of current vs. time vs. cycle for a standard electrode material with alternating polarity for 10 cycles;

FIG. 5 shows a plot of displacement vs, time vs. cycle for 10 cycles;

FIG. 6 is a plot of current vs. time at voltage;

FIG. 7 converts the data from FIG. 6 to a plot of resistance vs. time;

FIG. 8 shows the response to positive polarity pulses with a plot of current vs. time vs. cycles;

FIG. 9 shows the response to positive polarity pulses with a plot of displacement vs. time vs. cycle;

FIG. 10 illustrates response to negative polarity pulses with a plot of current vs. time vs. cycles;

FIG. 11 illustrates response to negative polarity pulses with a plot of displacement vs. time vs. cycle;

FIG. 12 shows response to cyclic negative polarity with a plot of current vs. time vs. cycles;

FIG. 13 shows response to cyclic negative polarity with a plot of displacement vs. time vs. cycle;

FIG. 14 illustrates pulse response to cyclic negative polarity with a plot of current vs. time vs. cycles;

FIG. 15 illustrates pulse response to cyclic negative polarity with a plot of displacement vs. time vs. cycle;

FIG. 16 shows response to cyclic positive polarity with a plot of current vs. time vs. cycles;

FIG. 17 shows response to cyclic positive polarity with a plot of displacement vs. time vs. cycle;

FIG. 18 illustrates pulse response to cyclic positive polarity with a plot of current vs. time vs. cycles; and

FIG. 19 illustrates pulse response to cyclic positive polarity with a plot of displacement vs. time vs. cycle.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described for purposes of illustration and not limitation.

Examples of electroactive polymer devices and their applications are described, for example, in U.S. Pat. Nos. 6,343,129; 6,376,971; 6,543,110; 6,545,384; 6,583,533; 6,586,859; 6,628,040; 6,664,718; 6,707,236; 6,768,246; 6,781,284; 6,806,621; 6,809,462; 6,812,624; 6,876,135; 6,882,086; 6,891,317; 6,911,764; 6,940,221; 7,034,432; 7,049,732; 7,052,594; 7,062,055; 7,064,472; 7,166,953; 7,199,501; 7,199,501; 7,211,937; 7,224,106; 7,233,097; 7,259,503; 7,320,457; 7,362,032; 7,368,862; 7,378,783; 7,394,282; 7,436,099; 7,492,076; 7,521,840; 7,521,847; 7,567,681; 7,595,580; 7,608,989; 7,626,319; 7,750,532; 7,761,981; 7,911,761.; 7,915,789; 7,952,261; 8,183,739; 8,222,799; 8,248,750; and in U.S. Patent Application Publication Nos.; 2007/0200457; 2007/0230222; 2011/0128239; and 2012/0126959, the entireties of which are incorporated herein by reference.

The present inventors have surprisingly discovered that a polymer diode may be constructed from a simple, printed electroactive polymer material stack as such stacks show consistent difference in measured current based on the polarity of the applied voltage.

This current difference may be enhanced by the inclusion of additives. Mobile, electrically active additives added to the electrode formulation can significantly improve the performance of electroactive polymer material stack. Such additives do not need to be ionic. Although not wishing to be bound to any particular theory, the present inventors speculate that a portion of these electrically active additives diffuse into the dielectric layer. These diffusants may chemically interact with the functional groups of the dielectric layer material, particularly after photo- or thermal exposure.

Chemical modifications of the dielectric film to increase interaction between the polymer matrix and the electrically active additives may enhance performance and long-term stability. The diffusivity of the electrically active additives and their fragments may relate to molecular size and also to their charge or induced charge. The electrically active additives and their fragments may have functional groups that can react or interact with the dielectric matrix to limit their diffusivity. This can enable the creation of permanent concentration gradients in the dielectric layer which may enhance performance.

Additives containing iodonium salts, sulfonium salts and phthalocyanines are preferred as electrically active additives in the present invention. As iodonium salts, the following may be mentioned, phenyl iodonium hexafiuorophosphate, diphenyl iodonium hexafluoroantimonate, diphenyl iodonium tetrafluoroborate, diphenyl iodonium tetrakis(pentafluorophenyl)borate, bis(dodecylphenyl)iodonium hexafluorophosphate, bis-(dodecylphenyl)iodonium hexafluoroantimonate, bis(dodecylphenyl)iodonium tetrafluoroborate, bis(dodecylphenyl)iodonium tetrakis(pentafluorophenyl)borate, 4-methylphenyl-4-(1-methyl-ethyl)phenyl iodonium hexafluorophosphate, 4-methylphenyl-4-(1-methylethyl)phenyl iodonium hexafluoroantimonate, 4-methylphenyl-4-(1-methylethyl)phenyl iodonium tetrafluoroborate, and 4-methylphenyl-4-(1-methylethyl)phenyl iodonium tetrakis(pentafluorophenyl)borate.

As a sulfonium salt, examples include, but are not limited to, bis[4-(diphenylsulfonio)phenyl]sulfide bishexafluorophosphate, bis[4-(diphenylsulfonio)phenyl]sultide bishexafluoroantimonate, bis[4-(diphenylsulfonio)phenyl]sulfidebistetralluoroborate, bis[4-(diphenylsulfonio)phenyl]sulfide tetrakis(pentafluorophenyl)borate, diphenyl-4-(phenylthio)phenylsulfonium hexafluorophosphate, diphenyl-4-(phenylthio)phenylsulfonium hexafluoroantimonate, diphenyl-4-(phenylthio)phenylsulfonium tetrafluoroborate, diphenyl-4-(phenylthio)phenylsulfonium tetrakis(pentafluorophenyl)borate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrafluoroborate, triphenylsulfonium tetrakis(pentafluorophenyl)borate, bis[4-(di-(4-(2-hydroxyethoxy))phenylsulfonio)phenyl]sulfide hishexafluorophosphate, bis[4-(di-(4-(2-hydroxyethoxy))phenylsulfonio)phenyl]sulfide bishexafluoroantimonate, bis[4-(di-(4-(2-hydroxyethoxy))phenylsulfonio)phenyl]sulfidebistetrafluoroborate, and bis[4-(di-(4-(2-hydroxyethoxy))phenylsulfonio)phenyl]sulfide tetrakis(pentafluoro-phenyl)horate, tris({4-[(4-acetylphenyl)sulfanyl]phenyl})sulfanium hexafluorophosphate (commercially available from BASF as IRGACURE PAG270), tris({4-[(4-acetylphenyl)sulfanyl]phenyl})sulfanium tetrakis(pentafluorophenyl)borate (commercially available from BASF as IRGACURE PAG290).

In some embodiments, mixtures of electrically active additives may be used to balance performance, time response, and long-term stability as needed for a particular application. Also, many of these compounds are photo- and thermally labile, and in some embodiments, the polymer film may be photo- or thermally treated to release fragments that are more effective as electrically active additives or that may react with functional groups in the dielectric matrix material. In some embodiments, the photo- or thermal treatment may be used to create permanent compositional gradients within the dielectric layer to reduce diffusional effects.

A particularly preferred additive in the present invention is sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (Formula I);

As can be appreciated by reference to FIG. 1, a plot showing current vs. time vs. cycle with alternating polarity for 10 cycles illustrates the current measured when a positive voltage is applied across the diode (odd cycles) or when a negative voltage is applied across the diode (even cycles). During the odd cycles, it is evident that current changes with time while the voltage is applied indicating that electrical charges are being transferred during the cycle. During the even cycles with negative polarity, the current is constant and the diode behaves as a resistor.

FIG. 2, a plot depicting displacement vs. time vs. cycle with alternating polarity for 10 cycles, shows that displacement is observed only during the odd (positive polarity) cycles. Little or no displacement is observed during the even (negative polarity) cycles.

FIGS. 3A, 3B and 3C illustrate a possible mechanism of the present invention. There are orders of magnitude difference in the diffusivities of the anions and cations. The polarity effect is not seen with anion/cation pairs that are more comparable in size and diffusivities

As shown in FIG. 3A, with no voltage flowing, anions 30 and cations 32, are associated with each other. One electrode is grounded 36; the other is active 34 and has high resistance. Charging is current limited—it takes a finite amount of time to transfer charge (electrons) onto the high resistance electrodes.

As shown in FIG. 3B, when imposing a negative voltage, electrons are transferred to the active electrode 34 (rather than to the grounded electrode 36). The cations 32 can diffuse almost instantaneously and are in sufficient quantity to balance the incoming electrons. The rest of the material in the capacitor stack does not experience an electric field.

When imposing a positive voltage as depicted in FIG. 3C, electrons are removed from the active electrode 34 faster than the large anions 30 can diffuse, enabling the imposition of an electric field across the pair of electrodes (34, 36).

The opposite polarity effect should occur when the anions 30 diffuse more easily than the cations 32.

FIG. 4 provides a plot of current vs. time vs. cycle for a standard electrode material with alternating polarity and FIG. 5 shows a plot of displacement vs. time vs. cycle for 10 cycles. As can be appreciated by reference to FIGS. 4 and 5, the lines for the first through 10^th cycles essentially overlay each other. The same response to either positive or negative polarity was observed.

FIGS. 6 and 7 show plots of current vs. time and resistance vs. time for samples conditioned at different voltages for 80 seconds. As can be appreciated by reference to FIGS. 6 and 7, there seems to be charge transfer.

FIGS. 8 and 9 show the response to positive polarity pulses with FIG. 8 showing a plot of current vs. time vs. cycles with the first pulse 80 being uppermost, the second 82 below that, etc. FIG. 9 provides a plot of displacement vs. time vs. cycle with the first pulse 90 being the lowermost line, the second pulse 92 being directly above that, etc. As can be appreciated by reference to FIGS. 8 and 9, the material converts from a resistor to a capacitor.

FIGS. 10 and 11 illustrate response to negative polarity pulses. FIG. 10 is a plot of current vs. time vs. cycles and FIG. 11 is a plot of displacement vs. time vs, cycle. As can be appreciated by reference to FIGS. 10 and 11, the material remains a resistor, there is no displacement.

FIGS. 12 and 13 show response to cyclic negative polarity. FIG. 12 is a plot of current vs. time vs. cycles and FIG. 13 is a plot of displacement vs. time vs. cycle. The conditions were 75 Hz for 15 sec; negative polarity; data taken at 1 sec., 7 sec. and 14 sec. As can be appreciated from FIGS. 12 and 13 the material appears to condition quickly.

FIGS. 14 and 15 illustrate pulse response to cyclic negative polarity, 10 pulses with negative polarity. The material immediately reverts back to a resistor. FIG. 14 is a plot of current vs. time vs. cycles and FIG. 15 is a plot of displacement vs. time vs. cycle.

FIGS. 16 and 17 show response to cyclic positive polarity. Conditions were: 75 Hz for 15 sec; positive polarity; data taken at 1 sec., 7 sec. and 14 sec. FIG. 16 is a plot of current vs. time vs. cycles and FIG. 17 is a plot of displacement vs. time vs. cycle. As can be appreciated by reference to FIGS. 16 and 17, the material appeared to condition quickly.

FIGS. 18 and 19 illustrate pulse response to cyclic positive polarity. 10 pulses with positive polarity. FIG. 18 is a plot of current vs. time vs. cycles and FIG. 19 is a plot of displacement vs. time vs. cycle. As can be appreciated by reference to FIGS. 16 and 17, the material remained conditioned.

An exemplary application of the present invention is as a component in an electrical circuit. A positive voltage applied across the polymer diode results in a displacement of a portion of the diode which mechanically closes a switch or relay elsewhere in the circuit. If the voltage has a negative polarity, no displacement of the polymer diode occurs and there is no change in the state of the circuit.

Various aspects of the subject matter described herein are set o in the thllowing numbered clauses in any combination thereof:

1. A flexible polymer diode comprising: a dielectric elastomer material; a first electrode material on a first side of the dielectric elastomer material; and a second electrode material on a second side of the dielectric elastomer material.

2. The flexible polymer diode according to claim 1 further including an electrically active additive.

3. The flexible polymer diode according to claim 2, wherein the electrically active additive comprises one or more compounds selected from the group consisting of ionic salts, iodonium salts and sulthnium salts.

4. The flexible polymer diode according to claim 2, wherein the electrically active additive comprises one or more compounds selected from the group consisting of (4-tert-Butylphenyl) diphenyl sulfonium triflate, Tris(pentafluorophenyl)boron, 4-isopropyl-4′-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate, Sodium tetraphenylborate, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, bis(4-tert-butylphenyl)iodonium triflate, tris({4-[(4-acetylphenyl)sulfanyl]phenyl})sulfanium tetrakis(penta-fluorophenyl)borate, sodium chloride and a phthalocyanine.

The foregoing examples of the present invention are offered for the purpose of illustration and not limitation. It will be apparent to those skilled in the art that the embodiments described herein may be modified or revised in various ways without departing from the spirit and scope of the invention. The scope of the invention is to be measured by the appended claims.

Claims

1. A flexible polymer diode comprising: a dielectric elastomer material;a first electrode material on a first side of the dielectric elastomer material; anda second electrode material on a second side of the dielectric elastomer material.

2. The flexible polymer diode according to claim 1, further comprising an electrically active additive.

3. The flexible polymer diode according to claim 2, wherein the electrically active additive comprises one or more compounds selected from the group consisting of ionic salts, iodonium salts and sulfonium salts.

4. The flexible polymer diode according to claim 2, wherein the electrically active additive comprises one or more compounds selected from the group consisting of (4-tert-Butylphenyl)diphenyl sulfonium triflate, Tris(pentafluorophenyl) boron, 4-isopropyl-4′-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate, Sodium tetraphenylborate, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, bis(4-tert-butylphenyl)iodonium triflate, tris({4-[(4-acetylphenyl)sulfanyl]phenyl})sulfanium tetrakis(penta-fluorophenyl)borate, sodium chloride and a phthalocyanine.

5. The flexible polymer diode according to claim 2, wherein the first electrode material and the second electrode material are configured such that a current may be pass from one of the first electrode material or the second electrode material to the other of the first electrode material or the second electrode material for only one polarity of voltage applied to either the first electrode material or the second electrode material.

6. The flexible polymer diode according to claim 2, wherein one of the first electrode material or the second electrode material comprises the electrically active additive.

7. The flexible polymer diode according to claim 6, wherein the electrically active additive comprises one or more compounds selected from the group consisting of ionic salts, iodonium salts and sulfonium salts.

8. The flexible polymer diode according to claim 6, wherein the electrically active additive comprises one or more compounds selected from the group consisting of (4-tert-Butylphenyl)diphenyl sulfonium triflate, Tris(pentafluorophenyl) boron, 4-isopropyl-4′-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate, Sodium tetraphenylborate, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, bis(4-tert-butylphenyl)iodonium triflate, tris({4-[(4-acetylphenyl)sulfanyl]phenyl})sulfanium tetrakis(penta-fluorophenyl)borate, sodium chloride and a phthalocyanine.

9. The flexible polymer diode according to claim 2, wherein the electrically active additive comprises a functional group that reacts with the dielectric elastomer material to limit a diffusivity of the electrically active additive.

10. The flexible polymer diode according to claim 2, wherein the electrically active additive is a compound that is photo labile or thermally labile.

11. The flexible polymer diode according to claim 1, wherein the dielectric elastomer material is photo treated or thermally treated.

12. The flexible polymer diode according to claim 11, wherein the photo treatment or the thermal treatment is configured to release fragments of the dielectric elastomer material that comprises an electrically active additive.

13. The flexible polymer diode according to claim 11, wherein the photo treatment or the thermal treatment is configured to release fragments of the dielectric elastomer material that reacts with a functional group in the dielectric matrix material.

14. The flexible polymer diode according to claim 2, wherein the electrically active additive comprises sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate.

15. The flexible polymer diode according to claim 2, wherein one of the first electrode material or the second electrode material is grounded.

16. The flexible polymer diode according to claim 15, wherein the one of the first electrode material or the second electrode material that is grounded is a grounded electrode material, and wherein a negative voltage is applied to one of the first electrode material or the second electrode material that is not grounded.

17. The flexible polymer diode according to claim 15, wherein the one of the first electrode material or the second electrode material that is grounded is a grounded electrode material, and wherein a positive voltage is applied to one of the first electrode material or the second electrode material that is not grounded.

18. The flexible polymer diode according to claim 2, wherein a voltage with alternating polarity is applied to one of the first electrode material or the second electrode material.

19. The flexible polymer diode according to claim 1, wherein the dielectric elastomer material comprises a permanent compositional gradient.

20. The flexible polymer diode according to claim 1, wherein at least one of the first electrode material and the second electrode material are coupled to an electrical circuit.