U.S. patent application number 12/659194 was filed with the patent office on 2010-09-16 for circuitry and method.
Invention is credited to Marten Armgarth, Rolf M. Berggren, Miaioxiang M. Chen, Robert Forchheimer, Thomas Kugler, David A. Nilsson, Tommi M. Remonen.
Application Number | 20100230731 12/659194 |
Document ID | / |
Family ID | 27354669 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100230731 |
Kind Code |
A1 |
Armgarth; Marten ; et
al. |
September 16, 2010 |
Circuitry and method
Abstract
An electrochemical transistor device is provided, comprising a
source contact, a drain contact, at least one gate electrode, an
electrochemically active element arranged between, and in direct
electrical contact with, the source and drain contacts, which
electrochemically active element comprises a transistor channel and
is of a material comprising an organic material having the ability
of electrochemically altering its conductivity through change of
redox state thereof, and a solidified electrolyte in direct
electrical contact with the electrochemically active element and
said at least one gate electrode and interposed between them in
such a way that electron flow between the electrochemically active
element and said gate electrode(s) is prevented. In the device,
flow of electrons between source contact and drain contact is
controllable by means of a voltage applied to said gate
electrode(s). Also provided are displays incorporating such
electrochemical transistor devices and processes for the production
of such devices.
Inventors: |
Armgarth; Marten;
(Linkoping, SE) ; Chen; Miaioxiang M.; (Kista,
SE) ; Nilsson; David A.; (Mantorp, SE) ;
Berggren; Rolf M.; (Vreta Kloster, SE) ; Kugler;
Thomas; (Cambridge, GB) ; Remonen; Tommi M.;
(Nykoping, SE) ; Forchheimer; Robert; (Linkoping,
SE) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Family ID: |
27354669 |
Appl. No.: |
12/659194 |
Filed: |
February 26, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11980359 |
Oct 31, 2007 |
7705410 |
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12659194 |
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11327438 |
Jan 9, 2006 |
7582895 |
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11980359 |
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10819306 |
Apr 7, 2004 |
7012306 |
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11327438 |
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10091419 |
Mar 7, 2002 |
6806511 |
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10819306 |
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60276218 |
Mar 16, 2001 |
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Current U.S.
Class: |
257/253 ;
257/E21.04; 257/E29.226; 438/49 |
Current CPC
Class: |
G02F 2001/1635 20130101;
H01L 21/31604 20130101; H01L 2924/0002 20130101; C09K 9/02
20130101; G11C 2213/15 20130101; H01L 27/283 20130101; H01L 28/56
20130101; H01L 51/0508 20130101; G11C 13/0014 20130101; H01L
2924/0002 20130101; B82Y 10/00 20130101; G02F 1/163 20130101; G11C
13/0009 20130101; H01L 51/0037 20130101; H01L 51/052 20130101; G11C
13/0016 20130101; G02F 2202/022 20130101; H01L 2924/00 20130101;
H01L 51/0097 20130101 |
Class at
Publication: |
257/253 ; 438/49;
257/E21.04; 257/E29.226 |
International
Class: |
H01L 29/76 20060101
H01L029/76; H01L 21/04 20060101 H01L021/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2001 |
SE |
0100748-3 |
Claims
1. A supported or self-supporting electrochemical transistor device
comprising: a source contact, a drain contact, at least one gate
electrode, an electrochemically active element arranged between,
and in direct electrical contact with, the source and drain
contacts, which electrochemically active element comprises a
transistor channel and is of a material comprising an organic
material having the ability of electrochemically altering its
conductivity through change of redox state thereof, and a
solidified electrolyte in direct electrical contact with the
electrochemically active element and said at least one gate
electrode and interposed between them in such a way that electron
flow between the electrochemically active element and said gate
electrode(s) is prevented, whereby flow of electrons between source
contact and drain contact is controllable by means of a voltage
applied to said gate electrode(s).
2. An electrochemical transistor device according to claim 1, in
which said source and drain contacts, gate electrode(s) and
electrochemically active element are arranged in one common
plane.
3. An electrochemical transistor device according to claim 2, in
which a continuous or interrupted layer of said solidified
electrolyte covers the electrochemically active element and covers
at least partially said gate 35 electrode(s).
4. An electrochemical transistor device according to claim 1 in
which at least one of said source and drain contacts and gate
electrode(s) is formed from the same material as the
electrochemically active element.
5. An electrochemical transistor device according to claim 4, in
which all of said source and drain contacts and gate electrode(s)
are formed from the same material as the electrochemically active
element.
6. An electrochemical transistor device according to claim 4, in
which the source and drain contacts and the electrochemically
active element are formed from a continuous piece of said material
comprising an organic material.
7. An electrochemical transistor device according to claim 1, in
which said transistor channel retains its redox state upon removal
of the gate voltage.
8. An electrochemical transistor device according to claim 1, in
which said transistor channel spontaneously returns to its initial
redox-state upon removal of the gate voltage.
9. An electrochemical transistor device according to claim 8, in
which the electrochemically active element further comprises a
redox sink volume adjacent to the transistor channel, the device
comprising at least two gate electrodes arranged on opposite sides
of the electrochemically active element so that one gate electrode
is closer to the transistor channel and one gate electrode is
closer to the redox sink volume.
10. An electrochemical transistor device according to claim 1, in
which said organic material is a polymer.
11. An electrochemical transistor device according to claim 10, in
which said polymer material is selected from the group consisting
of polythiophenes, polypyrroles, polyanilines,
polyisothianaphtalenes, polyphenylene vinylenes and copolymers
thereof.
12. An electrochemical transistor device according to claim 11, in
which said polymer material is a polymer or copolymer of a
3,4-dialkoxythiophene, in which said two alkoxy groups may be the
same or different or together represent an optionally substituted
oxy-alkylene-oxy bridge.
13. An electrochemical transistor device according to claim 12, in
which said polymer or copolymer of a 3,4-dialkoxythiophene is
selected form the group consisting of
poly(3,4-methylenedioxythiophene), poly(3,4-methlyene
dioxythiophene) derivatives, poly(3,4-ethylenedioxythiophene),
poly(3,4-ethylenedioxythiophene) derivatives,
poly(3,4-propylenedioxythiophene),
poly(3,4-propylenedioxythiophene) derivatives,
poly(3,4-butylenedioxythiophene), poly(3,4-butylenedioxythiophene)
derivatives, and copolymers therewith.
14. An electrochemical transistor device according to claim 1, in
which said organic material further comprising a polyanion
compound.
15. An electrochemical transistor device according to claim 14, in
which said polyanion compound is poly(styrene sulphonic acid) or a
salt thereof.
16. An electrochemical transistor device according claim 1, in
which said solidified electrolyte comprises a binder.
17. An electrochemical transistor device according to claim 16, in
which said binder is a gelling agent selected from the group
consisting of gelatine, a gelatine derivative, polyacrylic acid,
polymethacrylic acid, poly(vinylpyrrolidone), polysaccharides,
polyacrylamides, polyurethanes, polypropylene oxides, polyethylene
oxides, poly(styrene sulphonic acid) and poly(vinyl alcohol), and
salts and copolymers thereof.
18. An electrochemical transistor device according to claim 1, in
which said solidified electrolyte comprises an ionic salt.
19. An electrochemical transistor device according to claim 1,
which is self-supporting.
20. An electrochemical transistor device according to claim 1,
which is arranged on a support.
21. An electrochemical transistor device according to claim 20, in
which said support is selected from the group consisting of
polyethylene terephthalate, polyethylene naphthalene dicarboxylate,
polyethylene, polypropylene, polycarbonate, paper, coated paper,
resin-coated paper, paper laminates, paperboard, corrugated board
and glass.
22. A process for the production of a supported electrochemical
transistor device comprising: a source contact, a drain contact, at
least one gate electrode, an electrochemically active element
arranged between, and in direct electrical contact with, the source
and drain contacts, which electrochemically active element
comprises a transistor channel and is of a material comprising an
organic material having the ability of electrochemically altering
its conductivity through change of redox state thereof, and a
solidified electrolyte in direct electrical contact with the
electrochemically active element and said at least one gate
electrode and interposed between them in such a way that electron
flow between the electrochemically active element and said gate
electrode(s) is prevented, which process comprises deposition of
said contacts, electrode(s), electrochemically active element and
electrolyte onto a support.
23. A process according to claim 22, wherein said contacts,
electrode(s), electrochemically active element and/or electrolyte
are deposited by means of printing techniques.
24. A process according to claim 22, wherein said contacts,
electrode(s), electrochemically active element and electrolyte are
deposited by means of coating techniques.
25. A process according to claim 22, in which device said organic
material comprises a polymer, which process comprises deposition of
said polymer on a support through in situ polymerisation.
26. A process according to claim 22, comprising patterning of any
one of said contacts, electrode(s) and electrochemically active
element using a subtractive method.
27. A process according to claim 26, in which said patterning is
performed through chemical etching.
28. A process according to claim 26, in which said patterning is
performed through gas-etching.
29. A process according to claim 26, in which said patterning is
performed by mechanical means, comprising scratching, scoring,
scraping and milling.
30. A process according to claim 22, using said supported
electrochemical transistor device.
Description
PRIORITY STATEMENT
[0001] This application is a continuation application of U.S. Ser.
No. 11/980,359, filed Oct. 31, 2007, now allowed, which is a
divisional application of parent U.S. patent application Ser. No.
11/327,438, filed Jan. 9, 2006 (now U.S. Pat. No. 7,582,895), which
is a continuation of U.S. patent application Ser. No. 10/819,306,
filed Apr. 7, 2004 (now U.S. Pat. No. 7,012,306), which in turn is
a continuation-in-part of U.S. Ser. No. 10/091,419 filed Mar. 7,
2002 (now U.S. Pat. No. 6,806,511), claiming the benefit under 35
U.S.C. .sctn.119(a)-(d) of Swedish Application No. 0100748-3, filed
Mar. 7, 2001 and under 35 U.S.C. .sctn.119(e) of U.S. Provisional
Application No. 60/276,218, filed Mar. 16, 2001, the contents of
each of which are hereby incorporated herein by reference in their
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to electrochemical devices, in
particular to printable, electrochemical transistor devices based
on conducting organic materials.
BACKGROUND OF THE INVENTION
[0003] Semiconducting and conducting organic materials, both
polymers and molecules, have successfully been included in a large
range of electronic devices, e.g. electrochemical devices, for
instance as dynamic colorants in smart windows and in polymer
batteries. Reversible doping and de-doping involving mobile ions
switches the material between different redox states.
[0004] Use has been made of semiconducting polymers for the
realisation of field effect transistor (FET) devices. The
transistor channel of these devices comprises the semiconducting
polymer in question, and their function is based on changes in
charge carrier characteristics in the semiconducting polymer,
caused by an externally applied electric field. In such
transistors, the polymer is used as a traditional semiconductor, in
that the electric field merely redistributes charges within the
polymer material. One such transistor has been realised, which is
adapted for miniaturisation and can be used for the production of
integrated circuits consisting entirely of polymer material (PCT
publication WO99/10939). A stack of sandwiched layers is described,
with either a top-gate or a bottom-gate structure. A transistor
device with a similar architecture, also using a polymer as
semiconducting material in the channel of the transistor, is
described in the European patent application EP1041653.
[0005] Another type of transistor device based on organic materials
utilises electrochemical redox reactions in the organic material.
These devices comprise an electrolyte and a conducting polymer that
can be switched between an oxidised and a reduced state. One of
these oxidation states then corresponds to low, preferably zero,
conductivity in the material, whereas the other oxidation state
corresponds to a high conductivity relative to the first state.
Electrochemical transistor devices have been used as sensors, e.g.
for detection of oxidant in a solution (see, for review, Baughman
and Shacklette, Proceedings of the Sixth Europhysics Industrial
Workshop (1990), p 47-61). Furthermore, a transistor of the
electrochemical type is reported in Rani et al, J Solid State
Electrochem (1998), vol 2, p 99-101. The gate electrode
architecture in this prior art transistor is shown in FIG. 1 of
this reference.
[0006] Problems with electrochemical transistor devices of the
prior art include the fact that they are difficult and expensive to
manufacture. In particular, no electrochemical transistor devices
have been disclosed which are capable of being mass produced.
Furthermore, the practical use of prior art electrochemical
transistor devices has been hampered by their comparatively high
power consumption. Furthermore, materials used in prior art devices
suffer from a lack of environmental friendliness, processability
and economic production possibilities. There is therefore a need
for new and improved electrochemical chemical transistor
devices.
SUMMARY OF THE INVENTION
[0007] One of the objects of the present invention is then to meet
this demand, by developing the art of electrochemical transistor
devices, and by providing a device with handling, production,
disposal and other characteristics superior to those of the prior
art.
[0008] Another object of the present invention is to provide vide
an electrochemical transistor device which can be deposited on a
large range of different rigid or flexible substrates by
conventional printing methods.
[0009] Yet another object of the present invention is to provide an
environmentally safe electrochemical transistor device, so that the
disposal of the device, along with any support onto which it has
been deposited, doesn't give rise to handling problems, and so that
no safety restrictions have to be imposed on the use of the
device.
[0010] Still another object of the present invention is to make
possible new applications of conducting organic materials, using
several different properties of such materials in combination.
[0011] A further object of the invention is to provide processes
for the production of such devices, which processes utilise
conventional printing' methods or other deposition techniques that
are well known, relatively un-expensive and easily scaled up.
[0012] The aforementioned objects are met by an electrochemical
transistor device as defined in the independent claims. Specific
embodiments of the invention are defined in the dependent claims.
In addition, the present invention has other advantages and
features apparent from the detailed description below.
[0013] Thus, a supported or self-supporting electrochemical
transistor device is provided, which comprises: [0014] a source
contact, [0015] a drain contact, [0016] at least one gate
electrode, [0017] an electrochemically active element arranged
between, and in direct electrical contact with, the source and
drain contacts, which electrochemically active element comprises a
transistor channel and is of a material comprising an organic
material having the ability of electrochemically altering its
conductivity through change of redox state thereof, and [0018] a
solidified electrolyte in direct electrical contact with the
electrochemically active element and said at least one gate
electrode and interposed between them in such a way that electron
flow between the electrochemically active element and said gate
electrode(s) is prevented, whereby flow of electrons between source
contact and drain contact is controllable by means of a voltage
applied to said gate electrode(s).
[0019] The architecture of the electrochemical transistor device
according to the invention is advantageous in that it makes
possible the realisation of a layered transistor device with only a
few layers, having for example one patterned layer of material
comprising a conducting organic material, which layer comprises
source and drain contacts and gate electrode(s), as well as the
electrochemically active element. The source and drain contacts and
the electrochemically active element are then preferably formed by
one continuous piece of said material. The source and drain
contacts could alternatively be formed from another electrically
conducting material in direct electrical contact with the
electrochemically active element, The gate electrode(s) may also be
of another electrically conducting material. To provide for the
necessary electrochemical reactions, whereby the conductivity in
the active element is changed, a solidified electrolyte is arranged
so that it is in direct electrical contact with both the active
element and the gate electrode(s).
[0020] In a preferred embodiment, the source and drain contacts and
gate electrode(s), as well as the active element, are all arranged
to lie in a common plane, further simplifying production of the
device by ordinary printing methods. Thus, the electrochemical
device according to this embodiment of the invention uses a lateral
device architecture. A layer of solidified electrolyte can
advantageously be deposited so that it covers, at least partly, the
gate electrode(s) as well as covering the electrochemically active
element. This layer of solidified electrolyte may be continuous or
interrupted, depending partly on which of two main types of
transistor architectures is to be realised (see below).
[0021] The electrochemical transistor device according to the
invention allows for control of electron flow between source and
drain contacts. The conductivity of the transistor channel of the
electrochemically active element can be modified, through altering
of the redox state of the organic material therein. This is
achieved by application of a voltage to the gate electrode(s),
which generates an electric field in the electrolyte. In the
contact area between electrolyte and electrochemically active
element, electrochemical redox reactions take place, which change
the conductivity of the organic material. Either the organic
material in the transistor channel is modified from a conducting
state to a non-conducting state as a result of said redox
reactions, or it is modified from a non-conducting to a conducting
state.
[0022] As is readily appreciated by the skilled person, and in
analogy to conventional field effect transistors, the
electrochemical transistor device of the invention may readily be
made to function as a diode device through short-circuiting of the
gate electrode and source contact, or of the gate electrode and
drain contact. One non-limiting example of this is described in the
description below. However, any configuration of the
electrochemical transistor device may naturally be used as a diode
in this fashion.
[0023] Depending on the precise patterning of the conducting
organic material and the electrolyte, the electrochemical
transistor device of the invention can either be of a bi-stable or
a dynamic type. In the bi-stable transistor embodiment, a voltage
applied to the gate electrode(s) leads to a change in conductivity
in the transistor channel that is maintained when the external
circuit is broken, i.e. when the applied voltage is removed. The
electrochemical reactions induced by the applied voltage can not be
reversed, since the electrochemically active element and the gate
electrode(s) are not in direct electrical contact with each other,
but separated by electrolyte. In this embodiment, the transistor
channel can be switched between non-conducting and conducting
states using only small, transient gate voltages. The bi-stable
transistor can be kept in an induced redox state for days, and, in
the most preferred, ideal case, indefinitely.
[0024] Thus, the bi-stable transistor embodiment of the present
invention offers a memory function, in that it is possible to
switch it on or off using only a short voltage pulse applied to the
gate electrode. The transistor stays in the conducting or
non-conducting redox state even after the applied voltage has been
removed. A further advantage with such bi-stable transistors is
that close to zero-power operation is made possible, since the
short voltage pulses applied to the gate need not be larger than a
fraction of the gate voltages needed for operation of a
corresponding dynamic device.
[0025] In the dynamic transistor embodiment, the change in the
redox state of the material is reversed spontaneously upon
withdrawal of the gate voltage. This reversal is obtained through
the provision of a redox sink volume adjacent to the transistor
channel in the electrochemically active element. Also, a second
gate electrode is provided, and arranged so that the two gate
electrodes are positioned on either side of the electrochemically
active element, one closer to the transistor channel, and the other
closer to the redox sink volume. Both gate electrodes are separated
from the electrochemically active element by electrolyte.
Application of a voltage between the two gate electrodes results in
the electrochemically active element being polarised, whereby redox
reactions take place in which the organic material in the
transistor channel is reduced while the organic material in the
redox sink volume is oxidised, or vice versa. Since the transistor
channel and the redox sink volume are in direct electrical contact
with each other, withdrawal of gate voltage leads to a spontaneous
reversal of the redox reactions, so that the initial conductivity
of the transistor channel is re-established. It is to be stressed
that in contrast to electrochemical transistors of the prior art,
dynamic transistors according to this embodiment of the present
invention revert spontaneously to the initial conductivity state
without the need for a reversing bias.
[0026] The electrochemical transistor device according to the
invention is also particularly advantageous in that it can be
easily realised on a support, such as polymer film or paper. Thus,
the different components can be deposited on the support by means
of conventional printing techniques such as screen printing, offset
printing, ink-jet printing and flexographic printing, or coating
techniques such as knife coating, doctor blade coating, extrusion
coating and curtain coating, such as described in "Modern Coating
and Drying Technology" (1992), eds E D Cohen and E B Gutoff, VCH
Publishers Inc, New York, N.Y., USA. In those embodiments of the
invention that utilise a conducting polymer as the organic material
(see below for materials specifications), this material can also be
deposited through in situ polymerisation by methods such as
electropolymerisation, UV-polymerisation, thermal polymerisation
and chemical polymerisation. As an alternative to these additive
techniques for patterning of the components, it is also possible to
use subtractive techniques, such as local destruction of material
through chemical or gas etching, by mechanical means such as
scratching, scoring, scraping or milling, or by any other
subtractive methods known in the art. An aspect of the invention
provides such processes for the manufacture of an electrochemical
transistor device from the materials specified herein.
[0027] However, the invention is not limited to supported devices,
as the contacts and electrode(s), electrochemically active element
and electrolyte can be arranged in such a way that they support
each other. An embodiment of the invention thus provides for a
self-supporting device.
[0028] According to a preferred embodiment of the invention, the
electrochemical transistor device is encapsulated, in part or
entirely, for protection of the device. The encapsulation retains
any solvent needed for e.g. the solidified electrolyte to function,
and also keeps oxygen from disturbing the electrochemical reactions
in the device. Encapsulation can be achieved through liquid phase
processes. Thus, a liquid phase polymer or organic monomer can be
deposited on the device using methods such as spray-coating,
dip-coating or any of the conventional printing techniques listed
above. After deposition, the encapsulant can be hardened for
example by ultraviolet or infrared irradiation, by solvent
evaporation, by cooling or through the use of a two-component
system, such as an epoxy glue, where the components are mixed
together directly prior to deposition. Alternatively, the
encapsulation is achieved through lamination of a solid film onto
the electrochemical transistor device. In preferred embodiments of
the invention, in which the components of the electrochemical
transistor device are arranged on a support, this support can
function as the bottom encapsulant. In this case encapsulation is
made more convenient in that only the top of the sheet needs to be
covered with liquid phase encapsulant or laminated with solid
film.
[0029] The invention will now be further described with reference
to specific embodiments thereof and to specific materials. This
detailed description is intended for purposes of exemplification,
not for limitation in any way of the scope of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1. Schematic structure of one embodiment of a bi-stable
transistor according to the invention, showing (A) a top view, (B)
a cross-section along I-I in A, and (C) a top view with a different
position for application of V.sub.g.
[0031] FIG. 2. Schematic structure of a dynamic transistor
according to the invention, showing (A) a top view and (B) a
cross-section along I-I in A.
[0032] FIG. 3. Schematic structure of another embodiment of a
bi-stable transistor according to the invention, showing (A) a top
view and (B) a cross-section along I-I in A.
[0033] FIG. 4. I.sub.ds vs V.sub.ds characteristics at various gate
voltages for experiments carried out on a bi-stable PE-DOT-PSS
transistor as shown in FIG. 1. The inset shows I.sub.ds vs V.sub.g
at constant V.sub.ds (V.sub.ds=2.0 V).
[0034] FIG. 5. I.sub.ds vs V.sub.ds characteristics at various gate
voltages for experiments carried out on a dynamic transistor. The
inset shows Id vs V.sub.g at constant V.sub.ds (V.sub.ds=2.0
V).
[0035] FIG. 6. I.sub.ds vs V.sub.ds characteristics at various gate
voltages for experiments carried out on a bi-stable polyaniline
transistor as shown in FIG. 1. The polyaniline was supplied in
toluene solution. (A) General characteristics. (B) Y-axis expansion
of a part of the diagram shown in A.
[0036] FIG. 7. I.sub.ds vs V.sub.ds characteristics at various gate
voltages for experiments carried out on a bi-stable polyaniline
transistor as shown in FIG. 1. The polyaniline was supplied in
m-cresol solution.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Definitions
[0037] Bi-stable electrochemical transistor: an electrochemical
transistor device in which the transistor channel retains its redox
state (and hence its conductivity characteristics) when the gate
voltage is removed.
[0038] Dynamic electrochemical transistor: an electrochemical
transistor device in which the transistor channel spontaneously
returns to its initial redox state (and hence its initial
conductivity characteristics) when the gate voltage is removed.
[0039] Source contact: an electrical contact which provides charge
carriers to a transistor channel.
[0040] Drain contact: an electrical contact which accepts charge
carriers from a transistor channel.
[0041] Gate electrode: an electrical contact of which any fraction
of the surface area is in direct electrical contact with solidified
electrolyte, and therefore in ionic contact with the
electrochemically active element.
[0042] Electrochemically active element: an "electrochemically
active element" according to the present invention, is a piece of a
material comprising an organic material having a conductivity that
can be electrochemically altered through changing of the redox
state of said organic material. The electrochemically active
element is in ionic contact with at least one gate electrode via a
solidified electrolyte. The electrochemically active element may
furthermore be integrated with each of the source and drain
contacts individually or with both of them, being composed of the
same or different materials. The electrochemically active element
in the electrochemical transistor devices of the invention
comprises a transistor or channel, and may furthermore comprise a
redox sink volume.
[0043] Transistor channel: the "transistor channel" of the
electrochemically active element establishes electrical contact
between source and drain contacts.
[0044] Redox sink volume: in certain embodiments of the invention,
the electrochemically active element further comprises a "redox
sink volume". This is a part of the electrochemically active
element adjacent to and in direct electrical contact with the
transistor channel, which can provide or accept electrons to or
from the transistor channel. Thus, any redox reactions within the
transistor channel are complemented by opposing reactions within
the redox sink volume.
[0045] Redox state: when reference is made to changes in the "redox
state" of the electrochemically active element, this is intended to
include cases where the organic material in the electrochemically
active element is either oxidised or reduced, as well as cases
where there is a redistribution of charges within the
electrochemically active element, so that one end. (e.g. the
transistor channel) is reduced and the other end (e.g. the redox
sink volume) is oxidised. In the latter case, the electrochemically
active element as a whole, retains its overall redox state, but its
redox state has nevertheless been changed according to the
definition used herein, due to the internal redistribution of
charge carriers.
[0046] Direct electrical contact: Direct physical contact (common
interface) between two phases (for example electrode and
electrolyte) that allows for the exchange of charges through the
interface. Charge exchange through the interface can comprise
transfer of electrons between electrically conducting phases,
transfer of ions between ionically conducting phases, or conversion
between electronic current and ionic current by means of
electrochemistry at an interface between for example electrode and
electrolyte or electrolyte and electrochemically active element, or
by occurrence of capacitive currents due to the charging of the
Helmholtz layer at such an interface.
[0047] Solidified electrolyte: for the purposes of the invention,
"solidified electrolyte" means an electrolyte, which at the
temperatures at which it is used is sufficiently rigid that
particles/flakes in the bulk therein are substantially immobilised
by the high viscosity/rigidity of the electrolyte and that it
doesn't flow or leak. In the preferred case, such an electrolyte
has the proper Theological properties to allow for the ready
application of this material on a support in an integral sheet or
in a pattern, for example by conventional printing methods. After
deposition, the electrolyte formulation should solidify upon
evaporation of solvent or because of a chemical cross-linking
reaction, brought about by additional chemical reagents or by
physical effect, such as irradiation by ultraviolet, infrared or
microwave radiation, cooling or any other such. The solidified
electrolyte preferably comprises an aqueous or organic
solvent-containing gel, such as gelatine or a polymeric gel.
However, solid polymeric electrolytes are also contemplated and
fall within the scope of the present invention. Furthermore, the
definition also encompasses liquid electrolyte solutions soaked
into, or in any other way hosted by, an appropriate matrix
material, such as a paper, a fabric or a porous polymer. In some
embodiments of the invention, this material is in fact the support
upon which the electrochemical transistor device is arranged, so
that the support forms an integral part of the operation of the
device.
Materials
[0048] Preferably, the solidified electrolyte comprises a binder.
It is preferred that this binder have gelling properties. The
binder is preferably selected from the group consisting of
gelatine, a gelatine derivative, polyacrylic acid, polymethacrylic
acid, poly(vinyl-pyrrolidone), polysaccharides, polyacrylamides,
polyurethanes, polypropylene oxides, polyethylene oxides,
poly-(styrene sulphonic acid) and poly(vinyl alcohol) and salts and
copolymers thereof; and may optionally be cross-linked. The
solidified electrolyte preferably further comprises an ionic salt,
preferably magnesium sulphate if the binder employed is gelatine.
The solidified electrolyte preferably further contains a
hygroscopic salt such as magnesium chloride to maintain the water
content therein.
[0049] The organic material for use in the present invention
preferably comprises a polymer which is electrically conducting in
at least one oxidation state and optionally further comprises a
polyanion compound. Organic materials comprising combinations of
more than one polymer material, such as polymer blends, or several
layers of polymer materials, wherein the different layers consist
of the same polymer or different polymers, are also contemplated.
Conductive polymers for use in the electrochemical transistor
device of the invention are preferably selected from the group
consisting of polythiophenes, polypyrroles, polyanilines,
polyisothianaphthalenes, polyphenylene vinylenes and copolymers
thereof such as described by J C Gustafsson et al in Solid State
Ionics, 69, 145-152 (1994); Handbook of Oligo- and Polythiophenes,
Ch 10.8, Ed D Fichou, Wiley-VCH, Weinhem (1999); by P Schottland et
al in Macromolecules, 33, 7051-7061 (2000); Technology Map
Conductive Polymers, SRI Consulting (1999); by M Onoda in Journal
of the Electrochemical Society, 141, 338-341 (1994); by M
Chandrasekar in Conducting Polymers, Fundamentals and Applications,
a Practical Approach, Kluwer Academic Publishers, Boston (1999);
and by A J Epstein et al in Macromol Chem, Macromol Symp, 51,
217-234 (1991). In an especially preferred embodiment, the organic
material is a polymer or copolymer mer of a 3,4-dialkoxythiophene,
in which said two alkoxy groups may be the same or different or
together represent an optionally substituted oxy-alkylene-oxy
bridge. In the most preferred embodiment, the polymer is a polymer
or copolymer of a 3,4-dialkoxythiophene selected from the group
consisting of poly(3,4-methylenedioxythiophene),
poly(3,4-methylenedioxythiophene) derivatives,
poly(3,4-ethylenedioxythiophene), poly(3,4-ethylenedioxythiophene)
derivatives, poly(3,4-propyleneoxy thiophene),
poly(3,4-propylenedioxythiophene) derivatives,
poly(3,4-butylenedioxythiophene) poly(3,4-butylenediloxythiophene)
derivatives, and copolymers therewith. The polyanion compound is
then preferably poly(styrene sulphonate).
[0050] The support in some embodiments of the electrochemical
transistor device of the present invention is preferably selected
from the group consisting of polyethylene terephthalate;
polyethylene naphthalene dicarboxylate; polyethylene;
polypropylene; paper; coated paper, e.g. coated with resins,
polyethylene, or polypropylene; paper laminates; paperboard;
corrugated board; glass and polycarbonate.
Principal Device Architectures
[0051] By patterning of the organic material of the
electrochemically active element and of the contacts, electrode(s)
and electrolyte in different ways, two main types of
electrochemical transistor devices can be realised. These main
types, bi-stable and dynamic electrochemical transistor devices,
will now be exemplified along with reference to figures thereof and
an outline of their working principles.
[0052] Bi-stable transistor (type 1): FIGS. 1A and 1B schematically
show one embodiment of a bi-stable transistor. The transistor
comprises a source contact 1, a drain contact 2 and an
electrochemically active element 3, which have all been formed from
a continuous piece of organic material. Both the source and drain
contacts are in electrical contact with an external power source,
which allows the application of a voltage V.sub.ds between them.
The transistor further comprises a gate electrode 4, which can be
formed from the same organic material as the source and drain
contacts and the electrochemically active element. The gate
electrode 4 is in electrical contact with an external power source,
which allows applying a voltage V.sub.g between the gate electrode
and the electrochemically active element. This can be realised by
applying V.sub.g between the gate 4 and the source 1 or the drain
2, or directly between the gate 4 and the electrochemically active
element 3. All of these organic material components have been
deposited in one layer on a support 6. On top of this layer,
covering part of the gate electrode 4 and the active element 3, is
a layer of gel electrolyte 5. Furthermore, the gel electrolyte
layer 5 is covered with an encapsulating layer 7 for prevention of
solvent evaporation.
[0053] Working principle for the polarity of V.sub.g shown in FIG.
1, and in the case of an organic material which is conducting in
its oxidised state and non-conducting when reduced to its neutral
state: when a gate voltage V.sub.g is applied between the gate
electrode 4 and the electrochemically chemically active element 3,
the gate electrode is polarised positive (anode), and the
electrochemically active element is polarised negative (cathode).
This leads to onset of electrochemistry in the electrochemically
active element and at the gate electrode; the organic material in
the transistor channel is reduced at the same time as an oxidation
reaction takes place at the gate electrode. The reduced material in
the transistor channel displays a drastically diminished electrical
conductivity, which results in the closure of the transistor
channel and an effective reduction of the current between source
and drain for a given source-drain voltage V.sub.ds, i.e. the
transistor is in an "off" mode. When the external circuit supplying
voltage to the gate electrode and the electrochemically active
element is broken, the oxidation state of the transistor channel is
maintained. No reversal of the electrochemical reactions is
possible because of the interruption by electrolyte 5 of electron
flow between gate electrode 4 and electrochemically active element
3.
[0054] Thus, the bi-stable transistor has a memory-function: It is
possible to switch on or off the transistor channel with short
pulses of gate voltage, V.sub.g, applied to the gate. The
respective conductivity states remain when gate voltage is removed
(a zero-power device). Further adjustments of conduction
characteristics in the electrochemically active element, or
resetting thereof to the initial, high conductivity modes can be
performed by applying different voltages to the gate electrode.
[0055] As explained above in the summary, the transistor device of
the invention may easily be made to function as a diode. This is
achieved for example through a transistor device architecture as
shown schematically in FIG. 1C. In comparison to the device
discussed above in relation to FIG. 1A, the gate voltage is instead
applied between the gate electrode 4 and the source contact 1.
There is no difference in potential between the positions for the
negative polarity of the V.sub.g voltage, but the change of this
position makes it possible to short-circuit the gate electrode and
source contact through replacing V.sub.g with a conductor. Such a
short-circuit results in that, when a positive voltage is applied
to the source contact 1, the gate electrode 4 will polarised
positively also. Accordingly, and as described above, resistance
will mount within the transistor channel upon reduction or
oxidation in the electrochemically active element 3, which
resistance will hinder charge transport therethrough. As the
resistance in the channel mounts, the current supplied to the
"common" source and gate will increasingly be led to the gate
electrode, further feeding the electrochemical reaction and thus
raising the resistance in the transistor channel even more. If the
polarity of the source-drain voltage is reversed, the opposite
situation will arise, so that the electrochemically active element
is instead rendered conducting. Thus, the device, when the source
and gate are connected in this way, will allow current in one
direction and not in the other, and in practice functions as a
diode.
[0056] Dynamic transistor: FIGS. 2A and 2B schematically show a
dynamic transistor. The transistor comprises a source contact 1, a
drain contact 2 and an electrochemically active element 3, which
have all been formed from a continuous piece of organic material.
The electrochemically active element 3 comprises a transistor
channel 3a and a redox sink volume 3b. Both the source and drain
contacts are in electrical contact with an external power source,
which allows the application of a voltage V.sub.ds between them.
The transistor further comprises two gate electrodes 4a and 4b
arranged on either side of the electrochemically active element 3.
The gate electrodes can be formed from the same organic material as
the source and drain contacts and the electrochemically active
element, The gate electrodes are in electrical contact with an
external power source, which allows application of a voltage
V.sub.g between them. All of these organic material components have
been deposited in one layer on a support 6. On top of this layer,
covering parts of the gate electrodes 4a and 4b and the active
element 3, is a layer of gel electrolyte 5. Furthermore, the gel
electrolyte layer 5 is covered with an encapsulating layer 7 for
prevention of solvent evaporation.
[0057] Working principle for the polarity of V.sub.g shown in FIG.
2, and in the case of an organic material which is conducting in
its oxidised state and non-conducting when reduced to its neutral
state: when a gate voltage V.sub.g is applied between the gate
electrodes 4a and 4b, gate electrode 4a is polarised positive
(anode), and gate electrode 4b is polarised negative (cathode).
This leads to onset of electrochemistry in the electrochemically
active element; the organic material in the transistor channel 3a
(adjacent to gate electrode 4a) is reduced, while the organic
material in the redox sink volume 3b (adjacent to gate electrode
4b) is oxidised. These electrochemical reactions require an
internal transfer of electrons within the electrochemically active
element. Electrons that are released in the oxidation reaction in
the redox sink volume migrate to the transistor channel, where they
replenish the electrons consumed in the reduction of organic
material occurring in this segment of the electrochemically active
element. The reduced volume in the transistor channel displays a
drastically diminished electrical conductivity, which results in
the closure of the transistor channel and an effective reduction of
the source drain current for a given source drain voltage V.sub.ds,
i.e. the transistor is "off". When the external circuit applying
voltage to the gate electrodes 4a and 4b is broken, a spontaneous
discharge occurs, in that electrons flow from the reduced material
in the transistor channel to the oxidised material in the redox
sink volume, until the original redox state is re-established
within the electrochemically active element. For maintenance of
overall charge neutrality, this flow of electrons within the
electrochemically active element is accompanied by an ion flow
within the solidified electrolyte.
[0058] Bi-stable transistor (type 2): FIGS. 3A and 3B schematically
show another embodiment of a bi-stable transistor, the architecture
of which is based on the dynamic transistor architecture described
immediately above. With reference to FIGS. 3A, and 3B, this
embodiment of a bi-stable transistor has the same components as
said dynamic transistor, the difference being that the layer of
solidified electrolyte 5 is patterned, forming two separate
segments of electrolyte 5a and 5b. This patterning has the effect
of interrupting ion flow within the electrolyte, which interruption
in turn means that no spontaneous reversal of electrochemical
reactions can occur between transistor channel 3a and redox sink
volume 3b. In similarity to the case of the first bi-stable
transistor device described above, the oxidation state of the
transistor channel is maintained when the external circuit, here
supplying voltage to the gate electrodes, is broken.
Experiment 1
Materials and Methods
[0059] Bi-stable (type 1) and dynamic transistors were realised by
patterning films of partially oxidised
poly(3,4-ethylenedioxythiophene) with poly(styrene sulphonate) as
counterions (frequently referred to as PEDOT:PSS in the present
text) into a T-shaped structure. The design followed the schematic
drawings of the bi-stable and dynamic transistors presented in
FIGS. 1 and 2, respectively. In its pristine, partially oxidised
state, PEDOT:PSS films are conductive, providing the opportunity of
modulating the current in the transistor channel by reduction of
the PEDOT:PSS electrochemically. All processing and material
handling was done in ambient atmosphere.
[0060] Patterning through screen-printing: PEDOT:PSS was applied as
a thin film on a polyester carrier, Orgacon.TM. EL-300
.OMEGA./square, as provided by AGFA, Conducting patterns were
generated using a screen-printed deactivation paste:
Orgacon-Strupas gel, as provided by AGFA, was mixed with an aqueous
sodium hypochlorite solution, resulting in a concentration of the
active degradation agent of approximately 1.2%. Printing was
performed using a manual screen printing board (Movivis, purchased
from Schnaidler) using a screen with 77 lines/cm mesh. After 1
minute, the deactivation agent was removed from the PEDOT:PSS film
by washing thoroughly with copious amounts of water.
[0061] Deposition of source and drain contacts and gate
electrode(s): After patterning of the PEDOT:PSS film, silver paste
(DU PONT 5000 Conductor) was printed on top of the PEDOT:PSS areas
that form the drain and source contacts and gate electrode(s).
Alternatively, the transistors can be entirely made of organic
materials by locally increasing the layer thickness of the
PEDOT:PSS in the gate, source and drain areas by drying-in of a
PEDOT-PSS solution (Baytron p.TM. from Bayer) onto these areas.
Such all-organic transistors were successfully realised on
polyester foils.
[0062] Deposition of gelled electrolyte: Calcium chloride (2%),
iso-propanol (35%), and gelatine (10%) (Extraco gelatine powder
719-30) were dissolved in de-ionised water at approximately
50.degree. C. (weight percentages of the resulting gel in
parenthesis). Structures of gelled electrolyte on patterned
PEDOT:PSS film were formed by printing the gel on top of the
PEDOT:PSS film. The thickness of the gelled electrolyte ranged from
20 to 100 .mu.m. Gelled electrolyte structures were realised at
line widths down to 300 .mu.m. Screen-printing of gelled
electrolyte was performed using a 32 mesh screen. The distance
between the drain and source contacts was typically 1 to 2 mm.
[0063] Encapsulation: The gelled electrolyte was coated with a
waterproof coating, such as plastic paint or foils, encapsulating
the device. Shelf lifetimes of several months were achieved.
[0064] Electrical characterisation: All testing was performed in
ambient atmosphere at room temperature. Current-voltage (I-V)
transistor curves were measured with a HP Parameter Analyzer 4155
B, in combination with an external HP E3631A power supply.
Experiment 1
Results
[0065] Bi-stable transistor: A bi-stable transistor such as that
shown schematically in FIGS. 1A and 1B was realised.
[0066] The bi-stable transistor had a transistor channel width of
600 .mu.m and a gel width of 800 .mu.m, with a transistor channel
of 0.48 cm.sup.2. However, smaller dimensions were also
successfully tested using photolithographic photoresist patterning
in combination with reactive ion plasma etching. These devices
exhibited channel widths ranging from 5 to 20 .mu.m and a gel width
of 20 .mu.m.
[0067] Typically, the gate voltages V.sub.g applied to the gate
electrode were in the interval between 0 V and 0.7 V. Drain-source
characteristics were determined by sweeping the source-drain
voltage from 0 V to 2 V. The resulting I-V curves are displayed in
FIG. 4.
[0068] Characteristic switching times for the conductivity
modulation were determined by applying a square shaped modulation
voltage (alternating between 0 V and 1 V) and measuring the
resulting current changes. Typical rise and decline times (defined
as the time required for a 90% increase crease respectively
decrease of the current level) were determined as 0.1 s and 0.2 s,
respectively.
[0069] On/Off ratios (defined as the current ratio
I.sub.ds,max/I.sub.ds,min at a source-drain voltage V.sub.ds of 2 V
for V.sub.g=0 V (on) and V.sub.g=0.7 V (off)) reached 15000. FIG. 4
displays the output characteristics of the bi-stable transistor,
I.sub.ds vs V.sub.ds for different gate voltages.
[0070] The inset in FIG. 4 shows the source-drain current I.sub.ds
as a function of the gate voltage V.sub.g for a constant
source-drain voltage V.sub.ds (V.sub.ds=2 V). From these curves, an
important parameter, the trans-conductance g.sub.m, can be
evaluated. g.sub.m is defined as:
g m = .delta. I ds .delta. V g ( V ds = constant ) ##EQU00001##
[0071] The value of the trans-conductance of the bi-stable
transistor device was found to be -1.2 mA/V.
[0072] Dynamic transistor: A dynamic transistor such as that shown
schematically in FIGS. 2A and 2B was realised. The dynamic
transistor had a channel width of 250 .mu.m and a gel width of 900
.mu.m, with a transistor channel of 0.23 cm.sup.2. However, smaller
dimensions of PEDOT and gel patterns down to 4 .mu.m were
successfully reached using photolitographic patterning. These
devices exhibited channel widths ranging from 4 to 20 .mu.m and a
gel width of 20 .mu.m.
[0073] Typically, the gate voltages V.sub.g applied to the gate
electrodes spanned an interval of 0 V to 3 V. On/Off ratios
(defined as the current ratio I.sub.ds,max/I.sub.ds,min at a
source-drain voltage V.sub.ds of 2 V for V.sub.g=0 V (on) and
V.sub.g=3 V (off)) reached 1000. FIG. 5 displays the output
characteristics of the dynamic transistor, I.sub.ds vs V.sub.ds for
different gate voltages.
[0074] The inset in FIG. 5 shows the source-drain current I.sub.ds
as a function of the gate voltage V.sub.g for a constant
source-drain voltage V.sub.ds (V.sub.ds=2 V). From these curves,
the value of the trans-conductance of the dynamic transistor device
was found to be -0.10 mA/V.
Experiment 2
Materials and Methods
[0075] Bi-stable (type 1) transistors were realised by patterning
films of polyaniline. The design followed the schematic drawing of
the bi-stable transistor presented in FIGS. 1A and 1B.
[0076] Patterning through evaporation and doctor blade: Panipol.TM.
F (commercial polyaniline) was provided in solution in toluene or
in m-cresol, at a concentration of 10 mg/ml in both cases. One
transistor was made starting from each of the two solutions of
polyaniline. The solvent was evaporated, and the polyaniline formed
a thin film on a plastic carrier (conventional transparency films).
Conducting patterns were made using a doctor blade.
[0077] Deposition of source and drain contacts and gate electrode:
After patterning of the polyaniline film, silver paste (DU PONT
5000 Conductor) was printed on top of those polyaniline areas that
formed the drain and source contacts. To ensure good contact with
the power source, a silver paste (DU PONT 5000 Conductor) was
printed on to the areas not covered with electrolyte on the gate
electrode. Alternatively, the transistors can be entirely made of
organic materials by locally increasing the thickness of the layer
of polyaniline in the gate, source and drain areas, by drying-in of
a polyaniline solution (e.g. Panipol.TM.) onto these areas.
[0078] Deposition of gelled electrolyte: In the transistor
employing polyaniline originally dissolved in toluene, gelatine
(Extraco gelatine powder 719-30) was dissolved in de-ionised water
at approximately 50.degree. C., in an amount resulting in a gel
having 10% by weight of gelatine, which was used as electrolyte. In
the transistor employing polyaniline originally dissolved in
m-cresol, Blagel.TM. (purchased from Apoteksbolaget, Sweden) was
used as gelled electrolyte. Structures of gilled electrolyte on the
respective patterned polyaniline films were formed by painting the
gel on top of the polyaniline films with a brush. The thickness of
the gelled electrolyte ranged from 100 to 300 .mu.m. The distance
between the drain and source contacts was typically from 1 to 2
cm.
[0079] Electrical characterisation: All testing was performed in
ambient atmosphere at room temperature. Current-voltage (I-V)
transistor curves were measured with a HP Parameter Analyzer 4155 B
in combination with an external HP E3631A power supply.
Experiment 2
Results
[0080] Bi-stable transistors such as that shown schematically in
FIGS. 1A and 1B were realised. The bi-stable transistors had a
transistor channel width of 3 mm and a gel width of 4 mm, with a
transistor channel of 12 mm.sup.2. Typically, the gate voltages
V.sub.g applied to the gate electrode were in the interval between
-15 V and 15 V. Drain-source characteristics were determined by
sweeping the source-drain voltage from 0 V to 10 V. The resulting
I-V curves are displayed in FIG. 6 (polyaniline supplied in toluene
solution) and FIG. 7 (polyaniline supplied in m-cresol
solution).
[0081] On/Off ratios (defined as the current ratio
I.sub.ds,max/I.sub.ds,min at a source-drain voltage V.sub.ds of 2 V
for V.sub.g=0 V (on) and V.sub.g=4 V or -4 V (off)) reached 100 for
both negative and positive gate voltages.
* * * * *