U.S. patent application number 17/145770 was filed with the patent office on 2021-05-13 for crosslinkable polymeric materials for dielectric layers in electronic devices.
The applicant listed for this patent is ALTANA AG. Invention is credited to Martin Eggert, Stephan Feser, Sascha Todter-Konig.
Application Number | 20210143348 17/145770 |
Document ID | / |
Family ID | 1000005348535 |
Filed Date | 2021-05-13 |
United States Patent
Application |
20210143348 |
Kind Code |
A1 |
Eggert; Martin ; et
al. |
May 13, 2021 |
CROSSLINKABLE POLYMERIC MATERIALS FOR DIELECTRIC LAYERS IN
ELECTRONIC DEVICES
Abstract
Compositions for providing a dielectric layer in an electronic
device wherein the composition comprises a polymer which polymer
contains one or more building blocks, wherein at least 25 mol % of
the total number of building blocks in the polymer are of the
general formula having olefinic oligo-dihydrodicyclopentadienyl
functionalities.
Inventors: |
Eggert; Martin; (Hamburg,
DE) ; Feser; Stephan; (Hamburg, DE) ;
Todter-Konig; Sascha; (Hamburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALTANA AG |
Wesel |
|
DE |
|
|
Family ID: |
1000005348535 |
Appl. No.: |
17/145770 |
Filed: |
January 11, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15773881 |
May 4, 2018 |
|
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PCT/EP2016/077757 |
Nov 15, 2016 |
|
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17145770 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 51/052 20130101;
C08F 12/32 20130101; C08F 20/28 20130101; C08F 20/40 20130101; C08F
20/22 20130101; H01L 28/40 20130101; C08F 12/18 20130101; H01L
51/0043 20130101; H01L 51/004 20130101 |
International
Class: |
H01L 51/05 20060101
H01L051/05; C08F 12/18 20060101 C08F012/18; C08F 12/32 20060101
C08F012/32; C08F 20/22 20060101 C08F020/22; C08F 20/28 20060101
C08F020/28; C08F 20/40 20060101 C08F020/40; H01L 51/00 20060101
H01L051/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 18, 2015 |
DE |
102015119939.4 |
Claims
1. A composition for providing a dielectric layer in an electronic
device, the composition comprising: a polymer containing one or
more units, wherein at least 25 mol % of the total number of units
in the polymer are the following units (A) with crosslinkable side
groups, ##STR00007## in which X independently at each occurrence is
a methylene group or oxygen, R independently at each occurrence is
a methyl group or hydrogen, L.sub.1 is a divalent group which
connects the polymer chain to the side group, and L.sub.2 is a
divalent group which connects the polymer chain to the side
group.
2. The composition according to claim 1, wherein L.sub.1 is
selected from the group consisting of carbonyl, carbonyloxyethyl,
carbonyloxyisopropyl, carbonyloxyethylamide, phenyl and benzyl
groups; X is CH.sub.2; R independently is CH.sub.3 or H; n is
0.
3. The composition according to claim 1, wherein L.sub.1 is a
carbonyl or carbonyloxyethyl group; R is CH.sub.3 or H n is 0.
4. The composition according to claim 1, wherein L.sub.1,2 is a
carbonyl unit; X is CH.sub.2; R is H. n is 0.
5-6. (canceled)
7. The composition according to claim 1, wherein the polymer
further comprises a unit derived from a methacrylate having a
linear, branched or cyclic hydrocarbon group which comprises 1-18
carbon atoms.
8. The composition according to claim 1, wherein the polymer
further comprises a unit derived from any of claims 1 to 7,
characterized in that a further unit comprises styrene, ethylene,
methyl vinyl ether or octadecene.
9. The composition according to claim 1, wherein the polymer
further comprises one of the following units or combination of
units: ##STR00008## ##STR00009##
10-15. (canceled)
16. The composition according to claim 7, wherein at least some
hydrogen atoms of the hydrocarbon group are substituted with
fluorine atoms.
17. An electronic device comprising at least one dielectric layer,
wherein the at least one dielectric layer comprises: a) a
crosslinked polymer obtained by polymerizing monomers to obtain a
polymer including at least 25 mol % of the following units (A) with
crosslinkable side groups, and then crosslinking the crosslinkable
side groups: ##STR00010## in which X independently at each
occurrence is a methylene group or oxygen, R independently at each
occurrence is a methyl group or hydrogen, L.sub.1 is a divalent
group which connects the polymer chain to the side group and
L.sub.2 is a divalent group which connects the polymer chain to the
side group.
18. An electronic device comprising a thin-film capacitor including
at least one dielectric layer, wherein the at least one dielectric
layer comprises: a) a crosslinked polymer obtained by polymerizing
monomers to obtain a polymer including at least 25 mol % of the
following units (A) with crosslinkable side groups, and then
crosslinking the crosslinkable side groups: ##STR00011## in which X
independently at each occurrence is a methylene group or oxygen, R
independently at each occurrence is a methyl group or hydrogen,
L.sub.1 is a divalent group which connects the polymer chain to the
side group, and L.sub.2 is a divalent group which connects the
polymer chain to the side group.
19. The electronic device according to claim 17, further comprising
an additional polymer.
20. The electronic device according to claim 17, further comprising
one or more of a free radical photoinitiator, a stabilizer, and an
adhesion promoter.
Description
[0001] All of the documents cited in the present patent application
are incorporated by reference in their entirety into the present
disclosure.
[0002] The present invention relates to crosslinkable polymers,
dielectric layers comprising them, electronic devices, more
particularly organic field-effect transistors, comprising them.
PRIOR ART
[0003] Organic field-effect transistors (OFETs) are electronic
devices which find application in flexible displays, sensor devices
or electronic circuits.
[0004] An OFET is a multilayer device which comprises a substrate,
a source electrode and drain electrode, an organic semiconductor
layer, a dielectric layer and a gate electrode. The semiconductor
layer typically comprises an organic polymer and/or a small
molecule.
[0005] Depending on the arrangement of the layers in an OFET, a
distinction is made between a top gate and a bottom gate
configuration. In the top gate configuration, the semiconductor
layer is followed by the dielectric and lastly by the gate
electrode. In the bottom gate configuration, the layer arrangement
is in the opposite order (see FIG. 1 and FIG. 2).
[0006] OFETs are processed preferably by coating (e.g. spin coating
or slot die) or printing (e.g. ink-jet or gravure) processes from
solution, allowing large-area processing at low temperatures on
flexible polymeric substrates such as PET film, for example.
[0007] In the multilayer processing of a transistor from solution,
it is critical that the underlying layer is not partly dissolved by
the processing of the following layer. Therefore, either the
underlying layer must be converted into an insoluble state, or the
process solvent of the following layer must be orthogonal to the
underlying layer.
[0008] Crosslinkable dielectric materials which can be processed
from solution are preferred, since their layers are converted into
an insoluble state by crosslinking and, moreover, can be patterned
by photolithography.
[0009] WO 2012/059386 describes a process for producing a
transistor where the dielectric comprises a photocurable polyimide.
Polyimides do indeed have excellent dielectric properties, but
their limited solubility means that they can often only be applied
from incompatible solvents such as N-methyl-2-pyrrolidone
(NMP).
[0010] U.S. Pat. No. 8,853,820 B2 describes radically crosslinkable
polymers having acrylate side groups and alkyd resins which find
preferred use as a dielectric in OFETs.
[0011] WO 2012/028279 relates to use of polycycloolefins, primarily
as dielectrics in OFETs. The patent describes preferred polymers
which are crosslinked via sensitized photodimerization of
maleimide-functionalized side chains. Polycycloolefins, such as
polynorbornenes, for example, do have excellent dielectric
properties, but the adhesion is often limited on account of their
high glass transition temperature, especially on non-polar organic
semiconductor films. In the patent, this difficulty is resolved
through the additional use of crosslinkable adhesion promoters.
Generally speaking, however, this entails an additional process
step.
[0012] EP 2 089 442 describes polymers having cinnamate side
groups, which are crosslinked by photodimerization and are used
preferably as a dielectric in OFETs.
[0013] EP 2 368 281 (corresponds to U.S. Pat. No. 8,937,301)
describes vinyl polymers which are crosslinked by photodimerization
of coumarin side groups and find application preferably in OFETs as
a dielectric.
[0014] Under continual exposure to UV light, however, these
photodimerization reactions of cinnamates and coumarins are
considered to be reversible.
[0015] JP2011022509 describes a photosensitive composition for an
organic insulating film. These resins are used as insulating film
in electroluminescent displays and LCD-devices. The resin
compositions are alkali soluble and comprise a cationic curing
catalyst. These compositions are not suited for use as UV-cured
dielectric layers in OFET devices.
[0016] EP329441 describes UV-curable conformal coatings for use in
coating printed wire boards, to protect the printed wire board from
the environment. A mixture of monomers is applied to a substrate
and then cured using UV-radiation. The resin compositions are not
suited for use as dielectric layers in OFET devices.
[0017] US2015/0041735 describes a photosensitive composition for
use in LCD-devices. A photosensitive resin for a colour filter is
applied to a substrate and then cured using UV-radiation. The resin
compositions are not suited for use as dielectric layers in OFET
devices.
[0018] US2015/03553665 describes insulating materials for improving
the performance of organic field effect transistors. This document
does not disclose or suggest the use of polymers comprising
olefinic dihydrodicyclopentadienyl functionalities in the
preparation of dielectric layers in these devices.
[0019] The invention is based on the finding that aliphatic
polymers can be efficiently crosslinked by means of olefinic
dihydrodicyclopentadienyl (DCPD) functionalities in the side chain.
Moreover, the non-polar DCPD side groups promote wetting and
adhesion on hydrophobic semiconductor polymers, and unwanted
dipolar interactions at the semiconductor interface are minimized,
such interactions possibly influencing the device performance of
the OFET.
[0020] Problem:
[0021] A problem addressed by the present invention is that of
providing new, optionally irreversibly crosslinkable polymers which
do not have the disadvantages of the prior art. The polymers are to
be suitable as a constituent, optionally the sole constituent, of
dielectric layers, preferably for electronic devices, more
particularly for organic field-effect transistors (OFETs), are to
be soluble in compatible solvents, i.e. process solvents whose
following layer is orthogonal to an underlying layer, such as
esters and ketones, and are to adhere effectively to and be
compatible with organic semiconductor layers.
[0022] A further problem addressed by the present invention was
that of providing new dielectric substances which are an
improvement in comparison to the prior art.
[0023] An additional problem addressed by the present invention was
that of providing improved electronic devices, more particularly
OFETs.
Solution
[0024] These problems are solved by aliphatic polymers having
olefinic dihydrodicyclopentadienyl (DCPD) functionalities in this
side chain, by dielectric layers comprising or consisting of these
polymers, by electronic devices comprising these dielectric layers,
and by use of the polymers, dielectric layers and devices.
Definitions of Terms
[0025] For the purposes of the present invention, all quantity
details, unless indicated otherwise, are to be understood as weight
details.
[0026] For the purposes of the present invention, the term "room
temperature" means a temperature of 20.degree. C. Temperature
details are in degrees Celsius (.degree. C.) unless otherwise
indicated.
[0027] Unless otherwise indicated, the stated reactions or process
steps are carried out under standard/atmospheric pressure, i.e. at
1013 mbar.
[0028] For the purposes of the present invention, the formulation
"and/or" includes not only any desired combination but also all
combinations of the elements stated in the list in question.
[0029] For the purposes of the present invention, the term
"photoinitiator", unless otherwise indicated, refers both to
photosensitizers and to photoinitiators in the narrower sense.
[0030] The expression (meth)acrylic is intended for the purposes of
the present invention to encompass both methacrylic and acrylic and
also mixtures of both.
[0031] Actinic radiation, here and hereinafter, refers to
electromagnetic radiation, such as infrared, near infrared, visible
light, UV radiation or X-radiation, more particularly UV radiation,
or particulate radiation, such as electron radiation.
DETAILED DESCRIPTION
[0032] The invention is based on the finding that aliphatic
polymers can be efficiently crosslinked by means of olefinic
dihydrodicyclopentadienyl (DCPD) functionalities in the side chain.
Moreover, the non-polar DCPD side groups promote wetting and
adhesion on hydrophobic semiconductor polymers, and unwanted
dipolar interactions at the semiconductor interface are minimized,
such interactions possibly influencing the device performance of
the OFET.
[0033] A first subject of the present invention is a composition
for providing a dielectric layer in an electronic device which
composition comprises a polymer which polymer contains one or more
units, wherein at least 25 mol % of the total number of units in
the polymer are the following units (A) with pendant
oligodihydrocyclopentadienyl side groups,
##STR00001##
in which [0034] X independently at each occurrence is a methylene
group or oxygen, [0035] R independently at each occurrence is a
methyl group or hydrogen, [0036] L.sub.1 is a divalent group which
connects the polymer chain to the side group and [0037] L.sub.2 is
a divalent group which connects the polymer chain to the side
group, or is hydrogen, [0038] with the proviso that if L.sub.2 is
hydrogen, the side group in question is absent.
[0039] In one variant of the present invention, the divalent groups
L.sub.1,2 are selected independently of one another from the group
consisting of carbonyl, phenyl, benzyl, carbonyloxyethyl,
carbonyloxyisopropyl and carbonyloxyethylamide groups, and more
particularly the divalent groups L.sub.1,2 are selected
independently of one another from the group consisting of carbonyl
and carbonyloxyethyl groups.
[0040] A further subject of the present invention is an organic
field-effect transistor which comprises a dielectric layer which
has a crosslinked composition of the invention.
[0041] The invention further relates to a method for producing the
electronic device and also to the use thereof for thin-film
capacitors.
[0042] The invention further relates to a process for the
preparation of an organic field-effect transistor by using a
polymer having units with pendant oligodihydrocyclopentadienyl side
groups wherein the polymer is crosslinked using UV radiation
[0043] The polymer used in the composition of the present invention
having units of the structure (A) is prepared using preferably
monomers selected from the group consisting of the following
monomers
##STR00002## ##STR00003##
or mixtures of these monomers.
[0044] In place of these listed (meth)acrylate monomers it is also
possible for analogous vinyl and vinylbenzyl monomers to be used
for preparing a polymer in accordance with the invention.
[0045] As monomers it is additionally possible to use polymerizable
derivatives of oligodihydrocyclopentadiene, examples being esters
or diesters of the corresponding alcohol with unsaturated acids,
preferably selected from the group consisting of maleic acid,
fumaric acid, itaconic acid, sorbic acid, cinnamic acid, abietic
acid and mixtures thereof.
[0046] It is possible, moreover, to use comonomers when preparing
the polymers of the invention.
[0047] The use of comonomers makes it possible to adapt more
effectively the physicochemical properties of the polymer such as
the glass transition temperature (T.sub.G), solubility, surface
wetting, adhesion, dielectric permittivity, etc.
[0048] Monomers producing the unit of the structure (A) are
preferably copolymerized with monomers selected from the group
consisting of methyl methacrylate, ethyl methacrylate, (iso)propyl
methacrylate, n-butyl methacrylate, tert-butyl methacrylate,
ethylhexyl methacrylate, isooctyl methacrylate, tridecyl
methacrylate, cetyl methacrylate, stearyl methacrylate, lauryl
methacrylate, allyl methacrylate, cyclohexyl methacrylate,
2-isobornyl methacrylate, 4-tert-butylcyclohexyl methacrylate,
1-adamantyl methacrylate, 2-methyl-2-adamantyl methacrylate, phenyl
methacrylate, benzyl methacrylate, hexafluoroisopropyl
methacrylate, octafluoropentyl methacrylate, pentafluorophenyl
methacrylate and mixtures thereof.
[0049] With the following comonomers of high polarity it is
possible to increase the dielectric permittivity of the polymers of
the invention, which is why they are incorporated by
copolymerization in one variant of the present invention:
##STR00004##
where [0050] L is absent, -ethyloxy, -isopropyloxy or
-ethylamidoxy.
[0051] In place of the listed methacrylate comonomers it is
possible as well to use analogous acrylate, vinyl and vinylbenzyl
monomers for preparing the polymers of the invention.
[0052] In one variant of the present invention, the polymers of the
invention contain at least 35 mol % of the units (A), preferably 50
to 100 mol %, determined by means of .sup.1H-NMR spectroscopy.
[0053] In one variant of the present invention, the polymers of the
invention have no coumarin groups. In one variant of the present
invention, the polymers of the invention have no cinnamate
groups.
[0054] The polymers used in accordance with the invention may be
prepared via customary polymerization processes.
[0055] Customary polymerization processes include free radical
polymerization with radical initiators, or controlled free radical
polymerizations such as ATRP (Atom Transfer Radical
Polymerization), RAFT (Reversible Addition Fragmentation Chain
Transfer) or NMP (Nitroxide Mediated Polymerization).
[0056] The polymers used in accordance with the invention
preferably have an average molecular weight (MW) of 10 000 to 2 000
000 Daltons, more preferably of 50 000 to 500 000 Daltons,
determined by means of gel permeation chromatography (GPC).
[0057] Furthermore, the polymers used in accordance with the
invention may also be prepared by polymer-analogous reactions of
commercially available polymers with hydroxy-dicyclopentadiene
(DCPD-OH).
[0058] Polymers particularly suitable for such reactions are those
having acid or acid anhydride groups which can be esterified with
DCPD-OH.
[0059] In one variant of the present invention, this is done using
polymers selected from the group consisting of
poly(styrene-co-maleic anhydride), poly(ethylene-co-maleic
anhydride), poly(vinyl methyl ether-co-maleic anhydride),
poly(octadecene-co-maleic anhydride), polyacrylic acid,
polymethacrylic acid and mixtures thereof.
[0060] Another possibility for polymer-analogous reaction which can
be used in one variant of the present invention comes about through
nucleophilic substitution reactions of the DCPD-OH alkoxide
with--for example--polymers such as polyvinylbenzyl chloride.
[0061] Monomers used in one variant of the present invention as
monomers forming the structure (A) are dicyclopentenyloxyethyl
methacrylate or dicyclopentenyl methacrylate or
dicyclopentenyloxyethyl methacrylate and dicyclopentenyl
methacrylate and comonomers used are those selected from the group
consisting of 5-methacryloyloxy-2,6-norbornanecarbolactone, methyl
methacrylate, octafluoropentyl methacrylate, stearyl methacrylate
and mixtures thereof.
[0062] In another variant of the present invention, the polymers
used in accordance with the invention are obtained from the
reaction of styrene-co-maleic anhydride with
hydroxydicyclopentadiene and dicyclopentadiene, or from the
reaction of polyvinylbenzyl chloride with
hydroxy-dicyclopentadiene.
[0063] In the variants of the present invention in which the
polymers used in accordance with the invention not only consist of
the repeating units (A) but in which comonomers are incorporated by
polymerization, the copolymers may be, for example, alternating
copolymers, random copolymers, gradient copolymers, block
copolymers, segment copolymers, graft copolymers and/or comb
polymers.
[0064] Preferred polymers used in accordance with the invention are
the polymers 1 to 8 represented by the formulae below (polymers 3
to 8 are copolymers, in which the different repeating units have
been set apart from one another in the formula images below only
for greater legibility):
##STR00005## ##STR00006##
[0065] The polymers used in accordance with the invention may be
processed to form dielectric layers used in accordance with the
invention. This layer comprises or consists of [0066] a) one of the
above-described polymers, [0067] b) optionally a further polymer,
preferably methacrylate polymers, [0068] c) optionally further
additives, such as free radical photoinitiators, stabilizers,
optionally adhesion promoters.
[0069] For application of the dielectric layer to a substrate, the
polymer of the invention is provided in solution in a solvent.
Within the solution, the fraction of the polymer in relation to the
solvent is preferably 1-40 percent by mass, more preferably 5-15
percent by mass.
[0070] The solution may further comprise a photoinitiator, whose
fraction in relation to the polymer is preferably 0.2-15 percent by
mass, more preferably 0.5-4 percent by mass.
[0071] In one variant of the present invention, the solution may
further comprise antioxidants and radical scavengers such as
butylated hydroxytoluene, for example, in order to increase the
storage stability.
[0072] For the purposes of the present invention it is possible to
employ substantially all solvents, provided that sufficient
solubility of the polymer and other devices of the formulation is
ensured. Solvents may be used both individually and also in a
combination of two or more.
[0073] Preferred for use for the purposes of the present invention
are solvents selected from the group consisting of esters, ketones,
ethers, (cyclo)aliphatic and aromatic solvents and mixtures of
these.
[0074] In one variant of the present invention the solvents are
selected from the group consisting of ethyl acetate, isopropyl
acetate, propyl acetate, butyl acetate, isobutyl acetate, n-amyl
acetate, isoamyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate,
isopropyl isopropionate, isopropyl propionate, isobutyl
isopropionate, butyl isopropionate, amyl propionate, isopropyl
isobutyrate, isopropyl butyrate, isobutyl isobutyrate, butyl
isobutyrate, methyl lactate, ethyl lactate, ethylene glycol
diacetate, propylene glycol monomethyl ether acetate,
gamma-butyrolactone, propylene carbonate, and ethyl
3-ethoxypropionate, ShelIsol D25, tetrahydrofuran, toluene,
anisole, acetone, methyl ethyl ketone, methyl propyl ketone, methyl
isobutyl ketone, methyl amyl ketone, methyl isoamyl ketone,
cyclopentanone, cyclohexanone, diisobutyl ketone, diacetone alcohol
and mixtures thereof.
[0075] The compositions of the invention for producing dielectric
layers may in one variant comprise radical polymerization
initiators which are activated by actinic radiation such as gamma
radiation, E-beam, UV radiation, visible light or infrared
radiation.
[0076] Radical polymerization initiators in one variant of the
present invention are selected from the group consisting of
acetophenone compounds, benzophenone compounds, thioxanthone
compounds, xanthone compounds, keto-coumarin compounds, oxime ester
compounds, halomethyl-triazine compounds, hexaarylbiimidazole
compounds, phosphine compounds, ketal compounds and mixtures
thereof.
[0077] In the presence of DCPD groups, Norrish type II initiators
such as thioxanthone compounds, for example, require no additional
hydrogen donors, such as tertiary amines or thiols, for example,
since there is direct allylic hydrogen abstraction on the DCPD.
[0078] In one variant of the present invention, the photoinitiators
are selected from the group consisting of benzophenone,
2-ethylanthraquinone, thioxanthone, 2-,4-isopropylthioxanthone
(isomers), 2-chlorothioxanthone, 1-chloro-4-propoxythioxanthone,
2-trifluoromethylthioxanthone,
2,4-bis(trichloromethyl)-6-methoxystyryl-s-triazine,
(2,4,6-trimethylbenzoyl)-diphenylphosphine oxide,
bis(2,4,6-trimethylbenzoyl)-phenylphosphine,
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2-biimidazole,
4-)-4'-methylphenylthio)benzophenone, 1-hydroxycyclohexyl phenyl
ketone,
2-(4-methylbenzyl)-2-(dimethylamino)-4-morpholinobutyrophenone),
1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl)ethanone
1(O-acetyloxime) (OXE02),
2-(O-benzoyloxime)-1-[4-(phenylthio)phenyl]-1,2-octanedione
(OXE01), 3-benzoyl-7-methoxycoumarin, benzil dimethyl ketal,
2,2-dimethoxy-2-phenylacetophenone, oligomeric
1-chloro-4-propoxythioxanthone (Speedcure 7010),
5-dibenzosuberenone and mixtures thereof.
[0079] For the photocrosslinking of the polymers of the invention
it is possible in one variant of the present invention likewise to
use bifunctional photocrosslinkers based on azides, diazirines or
maleimides.
[0080] The present invention also comprises a method for producing
an electronic device which involves producing a dielectric layer,
comprising steps a) to c) or consisting thereof: [0081] a)
deposition of a formulation which comprises or consists of at least
one crosslinkable polymer with units with pendant
oligodihydrocyclopentadienyl side groups, at least one
photoinitiator and at least one organic solvent on a substrate,
[0082] b) removal of the solvent, [0083] c) photocrosslinking of
the resulting layer by actinic radiation.
[0084] In one embodiment, the crosslinkable polymer comprises at
least 5 mol % of units with pendant oligodihydrocyclopentadienyl
side groups.
[0085] In a further embodiment the crosslinkable polymer comprises
at least 10 mol % of units with pendant
oligodihydrocyclopentadienyl side groups.
[0086] In a further embodiment the crosslinkable polymer comprises
at least 20 mol % of units with pendant
oligodihydrocyclopentadienyl side groups.
[0087] In a further embodiment the crosslinkable polymer comprises
at least 25 mol % of units with pendant
oligodihydrocyclopentadienyl side groups.
[0088] The deposition of the dielectric layer produced in
accordance with the invention may take place by methods customary
in the art, preferably via spin coating, slot die coating, knife
coating, ink jet, gravure printing, flexographic printing or spray
coating.
[0089] In one variant of the present invention, the solvent is
removed by baking at temperatures preferably between 50 and
200.degree. C., more preferably between 70 and 100.degree. C.,
enabling low-temperature processing on PET substrates.
[0090] In one variant of the present invention, the dielectric
layer has a dry film layer thickness of between 100 and 2000 nm,
preferably between 300 and 1000 nm.
[0091] The photocrosslinking is induced by actinic radiation--in
one variant of the present invention, in a wavelength range between
100 and 800 nm, preferable between 250 and 600 nm, more preferably
between 300 and 500 nm.
[0092] Typical radiation sources are Hg or Hg/Fe lamps or
monochromatic radiation sources such as LEDs. The radiation dose
necessary for the photocrosslinking of the polymer is situated in
the range between 50 and 4000 mJ/cm.sup.2, preferably between 100
and 1000 mJ/cm.sup.2, more preferably 300-1000 mJ/cm.sup.2. In
principle the objective is to use radiation doses that are as low
as possible.
[0093] In one variant of the present invention, the electronic
device of the invention which comprises a dielectric layer having a
crosslinkable polymer of the invention may be an OFET, a diode or a
capacitor.
[0094] The device preferably comprises or is an OFET, consisting of
a substrate, a source electrode and drain electrode, an organic
semiconductor layer, a dielectric layer and a gate electrode.
[0095] Depending on the layer arrangement, a distinction is made
between top gate and bottom gate OFETs, with the present invention
relating to both configurations (see FIGS. 1 and 2).
[0096] A bottom gate OFET comprises a gate electrode on a
substrate, a dielectric layer applied to the gate electrode, an
organic semiconductor layer adjacent to the dielectric layer, and a
drain electrode and source electrode, which are in contact with the
semiconductor layer. Either the source and drain electrodes are
deposited on the semiconductor layer (top contact) or, conversely,
the semiconductor is applied to the source and drain electrodes
(bottom contact).
[0097] In the top gate configuration, the layer arrangement is in
reverse order. An organic semiconductor layer, which is deposited
on a substrate and is in contact with a drain electrode and source
electrode, is followed by a dielectric layer, on which a gate
electrode is deposited.
[0098] The substrate used for an electronic device of the invention
may be any of the materials commonly used for this purpose. In one
variant of the present invention, glass or plastic is used. In one
embodiment of the present invention, flexible polymeric films made
of polyethylene terephthalate (PET), polyethylene naphthalate
(PEN), polycarbonate (PC) or polyimide (PI) are the substrate
used.
[0099] The semiconductor layer for the purposes of the present
invention comprises a semiconducting organic material. The material
may be a small molecule (monomer, oligomer), polymer or else a
combination thereof. In analogy to the inorganic semiconductors, a
distinction is made between n-type and p-type semiconductors
according to the polarity of the majority charge carriers.
[0100] Examples of p-type semiconducting small molecules are
oligoacenes such as 6,13-[bis-triisopropylsilylethynyl]pentacene
(TIPS pentacene) or oligoheteroacenes such as
2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT).
Examples of p-type semiconducting polymers are polythiophenes such
as poly-3-hexylthiophene (P3HT), 2,4-dimethyl[polytriarylamine]
(PTAA), polyfluorenes, and also copolymers having repeating units
which contain isoindigo or diketopyrrolopyrrole units (DPP).
[0101] An example of a small molecule having n-type semiconducting
properties is the fullerene derivative [6,6]-phenyl-C61methyl
butyrate (PCBM). Known n-type semiconductor polymers are copolymers
which have repeating units comprising naphthalenedicarboxyimide,
such as, for example,
poly([n,n'-bis(2-octyldodecyl)-11-naphthalene-1,4,5,8-bis(dicarb-
oximide)-2,6-diyl]-alt-5,5'-(2,2'-12-bithiophene))
(P(ND12OD-T2)).
[0102] In one variant of the present invention, the electronic
device of the invention comprises electrodes which consist
preferably of metal, more particularly Au, Ag, Cu or Al, or
conductive polymer contacts (e.g. PEDOT:PSS).
BRIEF DESCRIPTION OF FIGURES
[0103] The drawings are not necessarily to scale. For reasons of
clarity and for greater ease of representation, certain features of
the invention may be shown with exaggerated size or in schematic
form, and similarly, certain details of conventional or known
elements may therefore not be shown.
[0104] FIG. 1 shows the schematic structure of a top gate
transistor (bottom contact).
[0105] FIG. 2 shows the schematic structure of a bottom gate
transistor (bottom contact).
[0106] FIG. 3 shows a micrograph of a photopatterned layer based on
a polymer of the invention.
[0107] FIG. 4 shows the transfer characteristic of a top gate OFET
with polymer 1.
[0108] FIG. 5 shows the transfer characteristic of a bottom gate
OFET with polymer 6.
[0109] FIG. 6 shows the transfer characteristic of a top gate OFET
with polymer 7.
[0110] FIG. 7 shows the transfer characteristic of a bottom gate
OFET with polymer 7.
[0111] The various embodiments of the present invention, as for
example but not exclusively those of the various dependent claims,
may be combined with one another in any desired way.
[0112] The invention is now elucidated with reference to the
non-limiting examples below.
EXAMPLES
Example A1 Preparation of Polymer 1
[0113] Using a syringe technique, 20 ml of freshly distilled
dicyclopentenyloxyethyl methacrylate (FA-512M, Hitachi Chemical)
and 20 ml of THF were transferred under argon into a two-necked
flask. Then 30 mg of 2,2'-azobisisobutyronitrile in the form of a
THF solution were added, and the mixture was heated to 60.degree.
C. with stirring. After six hours, the reaction was discontinued by
addition of 50 mg of butylated hydroxytoluene (BHT) and cooling to
room temperature. The polymerization solution was precipitated from
1000 ml of methanol, and the polymer was isolated by filtration and
dried under reduced pressure. The polymer was then dissolved again
three times in 100 ml of THF and precipitated from 800 ml of
methanol with addition of 20 mg of BHT each time.
[0114] Yield 20.2%
[0115] Mn=219 000 g/mol, Mw=520 000 g/mol
[0116] T.sub.g=61.degree. C.
Example A2 Preparation of Polymer 2
[0117] Using a syringe technique, 20 ml of freshly distilled
dicyclopentenyl methacrylate (CD535, Sartomer) and 20 ml of THF
were transferred under argon into a two-necked flask. Then 40 mg of
2,2'-azobisisobutyronitrile in the form of a THF solution were
added, and the mixture was heated to 50.degree. C. with stirring.
After ten hours, the reaction was discontinued by addition of 50 mg
of butylated hydroxytoluene (BHT) and cooling to room temperature.
The polymerization solution was precipitated from 1000 ml of
methanol, and the polymer was isolated by filtration and dried
under reduced pressure. The polymer was then dissolved again three
times in 100 ml of THF and precipitated from 800 ml of methanol
with addition of 20 mg of BHT each time.
[0118] Yield 18.5%
[0119] Mn=89 600 g/mol, Mw=237 000 g/mol
[0120] T.sub.g=178.degree. C.
Example A3 Preparation of Polymer 3
[0121] Using a syringe technique, 10 ml of freshly distilled
dicyclopentenyloxyethyl methacrylate (FA-512M, Hitachi Chemical),
10 ml of freshly distilled methyl methacrylate and 40 ml of THF
were transferred under argon into a two-necked flask. Then 30 mg of
2,2'-azobisisobutyronitrile in the form of a THF solution were
added, and the mixture was heated to 50.degree. C. with stirring.
After eight hours, the reaction was discontinued by addition of 50
mg of BHT and cooling to room temperature. The polymerization
solution was precipitated from 1000 ml of methanol, and the polymer
was isolated by filtration and dried under reduced pressure. The
polymer was then dissolved again three times in 100 ml of THF and
precipitated from 800 ml of methanol with addition of 20 mg of BHT
each time.
[0122] Yield 35%
[0123] Mn=87 700 g/mol, Mw=317 000 g/mol
[0124] T.sub.g=94.degree. C.
[0125] Repeating units in the polymer: FA-512M/MMA ratio 28:72
(determined via .sup.1H-NMR)
Example A4 Preparation of Polymer 4
[0126] 9 g of 5-methacryloyloxy-2,6-norbornanecarbolactone (NLAM,
Kuraray) and also, using a syringe technique, 10 ml of freshly
distilled dicyclopentenyloxyethyl methacrylate (FA-512M, Hitachi
Chemical), and 40 ml of THF were transferred under argon into a
two-necked flask. Then 30 mg of 2,2'-azobisisobutyronitrile in the
form of a THF solution were added, and the mixture was heated to
50.degree. C. with stirring. After eight hours, the reaction was
discontinued by addition of 50 mg of BHT and cooling to room
temperature. The polymerization solution was precipitated from 1000
ml of methanol, and the polymer was isolated by filtration and
dried under reduced pressure. The polymer was then dissolved again
three times in 100 ml of THF and precipitated from 800 ml of
methanol with addition of 20 mg of BHT each time.
[0127] Yield 15.3%
[0128] Mn=55 200 g/mol, Mw=158 000 g/mol
[0129] T.sub.g=143.degree. C.
[0130] Repeating units in the polymer: FA-512M/NLAM ratio 48:52
(determined via .sup.1H-NMR)
Example A5 Preparation of Polymer 5
[0131] Using a syringe technique, 10 ml of freshly distilled
dicyclopentenyloxyethyl methacrylate (FA-512M, Hitachi Chemical),
1.5 ml of freshly distilled octafluoropentyl methacrylate (OFPMA)
and 40 ml of THF were transferred under argon into a two-necked
flask. Then 30 mg of 2,2'-azobisisobutyronitrile in the form of a
THF solution were added, and the mixture was heated to 50.degree.
C. with stirring. After eight hours, the reaction was discontinued
by addition of 50 mg of BHT and cooling to room temperature. The
polymerization solution was precipitated from 1000 ml of methanol,
and the polymer was isolated by filtration and dried under reduced
pressure. The polymer was then dissolved again three times in 100
ml of THF and precipitated from 800 ml of methanol with addition of
20 mg of BHT each time.
[0132] Yield 19.8%
[0133] Mn=71 800 g/mol, Mw=201 000 g/mol
[0134] T.sub.g=64.degree. C.
[0135] Repeating units in the polymer: FA-512M/OFPMA ratio
80.5:19.5 (determined via .sup.1H-NMR)
Example A6 Preparation of Polymer 6
[0136] Using a syringe technique, 10 ml of freshly distilled
dicyclopentenyl methacrylate (CD535, Sartomer), 0.8 ml of freshly
distilled stearyl methacrylate (SMA) and 40 ml of THF were
transferred under argon into a two-necked flask. Then 30 mg of
2,2'-azobisisobutyronitrile in the form of a THF solution were
added, and the mixture was heated to 50.degree. C. with stirring.
After eight hours, the reaction was discontinued by addition of 50
mg of BHT and cooling to room temperature. The polymerization
solution was precipitated from 1000 ml of methanol, and the polymer
was isolated by filtration and dried under reduced pressure. The
polymer was then dissolved again three times in 100 ml of THF and
precipitated from 800 ml of methanol with addition of 20 mg of BHT
each time.
[0137] Yield 16.3%
[0138] Mn=109 000 g/mol, Mw=319 000 g/mol
[0139] T.sub.g=128.degree. C.
[0140] Repeating units in the polymer: CD535/SMA ratio 91:9
(determined via .sup.1H-NMR)
Example A7 Preparation of Polymer 7
[0141] In a single-necked flask, under nitrogen, 175 g of
styrene-co-maleic anhydride (Xiran 28110, Polyscope, 28% MAn
fraction, Mw=110 000) were dissolved in 450 ml of solvent naphtha.
Then 75.11 g of hydroxydicyclopentadiene (Texmark) and 66.0 g of
dicyclopentadiene were added and the reaction solution was stirred
at 130.degree. C. for four hours. Following addition of a further
230 ml of solvent naphtha, the reaction solution was stirred for a
further four hours under reflux at 160.degree. C. The batch was
diluted additionally with 350 ml of xylene. The polymer solution
was cooled to room temperature (RT) and 20 g of the solution was
precipitated from 475 ml of isopropanol water. Following filtration
and washing with 500 ml of isopropanol, the residue was dissolved
twice in 25 ml of methyl ethyl ketone and precipitated from 500 ml
of Shellsol D25.
[0142] Yield 86.4%
[0143] Mn=73 100 g/mol, Mw=211 000 g/mol
[0144] T.sub.g=147.degree. C.
Example A8 Preparation of Polymer 8
[0145] In a first single-necked flask, 10.4 of polyvinylbenzyl
chloride (Sigma Aldrich 182532, Mn=43 300 & Mw=79 600) were
dissolved in 250 ml of dried THF at room temperature under argon
and with stirring. In a second single-necked flask, 9.4 ml of
hydroxydicyclopentadiene were transferred under argon and 43 ml of
butyllithium (1.6 molar) in hexane were added dropwise using a
syringe technique with stirring. After a reaction time of five
hours, the solvent was removed on a rotary evaporator and 80 ml of
dried THF were added under argon. Using a syringe technique, the
solution was subsequently added dropwise to the polymer solution in
the first flask. After 48 hours the reaction was discontinued by
precipitation from 1000 ml of isopropanol. The product was isolated
by filtration and dried under reduced pressure. It was then
dissolved again twice in 300 ml of THF and precipitated from 1000
ml of isopropanol.
[0146] Yield 41%
[0147] Mn=48 300 g/mol, Mw=116 000 g/mol
[0148] T.sub.g=89.degree. C.
Example B1 Preparation of Photocrosslinked Dielectric Layers of
Polymer 1-8
[0149] A polymer solution admixed with photoinitiator was filtered
through a 0.45 .mu.m PTFE syringe filter and applied by spin
coating at 1000 rpm for 30 s to a 25.times.25 mm glass substrate.
After heating of the coated substrate on a hotplate at 90.degree.
C. for 60 s, the film was exposed with a 365 nm LED lighting unit
(LED Cube 100, Dr. Honle). The UV dose varied from 300-1000
mJ/cm.sup.2 with a constant irradiation power of 100 mW/cm.sup.2.
In order to evaluate the degree of insolubility of the
photocrosslinked film, the substrate, after exposure, was immersed
for 60 s in a solvent bath corresponding to the process solvent,
and then the film retention was ascertained. The film retention was
determined from the ratio of the layer thickness of the dry films
after and before immersion in the solvent bath. The layer thickness
was determined with the aid of a surface profilometer (Surface
Profiler 150 Veeco) by scratching the film and determining the step
height.
TABLE-US-00001 Photoinitiator content Process Polymer (weight
fraction Film Polymer solvent concentration polymer) UV dose
retention 1 MAK 120 mg/ml 2% OXE02 300 mJ/cm.sup.2 98% 1 MAK 120
mg/ml 6% ITX 500 mJ/cm.sup.2 94% 2 MAK 100 mg/ml 2% OXE02 300
mJ/cm.sup.2.sup.2 88% 2 MAK 100 mg/ml 4% SC7010 500 mJ/cm.sup.2 94%
4 CP:BuAc 1:1 90 mg/ml 4% OXE02 300 mJ/cm.sup.2 90% 5 MAK 110 mg/ml
2% OXE02 300 mJ/cm.sup.2 97% 6 MAK 110 mg/ml 2% OXE02 300
mJ/cm.sup.2 96% 7 PGMEA 90 mg/ml 8% OXE02 1000 mJ/cm.sup.2 81% 8
MAK 80 mg/ml 8% SC7010 2000 mJ/cm.sup.2 90% MAK = methyl amyl
ketone CP = cyclopentanone BuAc = n-butyl acetate OXE02 (BASF) =
1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone
1-(O-acetyloxime) ITX = isopropylthioxanthone SC7010 (Lambson) =
oligomeric 1-chloro-4-propoxythioxanthone
Example B2 Preparation of a Photopatterned Layer of Polymer 1
[0150] A 120 mg/ml solution of polymer 1 with 2% of photoinitiator
OXE02 (weight fraction polymer) in methyl amyl ketone (MAK) was
applied by spin coating to a 25.times.25 mm glass substrate. The
film was heated on a hotplate at 90.degree. C. for 60 s and was
subsequently subjected to imagewise UV exposure through a shadow
mask (LED 365 nm, 300 mJ/cm.sup.2). Following immersion of the film
for 60 s in a MAK solvent bath, the unexposed portion of the film
was removed, leaving the imagewise-exposed, crosslinked
portion.
[0151] FIG. 3 shows a micrograph in five-fold magnification of a
photopatterned layer from example B2.
Example C1 Preparation of Capacitor Devices from Polymer 1-8
[0152] The substrate used was an indium tin oxide (ITO)-coated
25.times.25 mm glass, with the ITO layer (120 nm) serving as the
back electrode. A 90-120 mg/ml polymer solution was filtered
through a 0.45 .mu.m PTFE syringe filter and applied to the
substrate by spin coating at 1000 rpm for 30 s. Thereafter the
substrate was heated on a hotplate at 90.degree. C. for ten
minutes. Finally, patterned counter-electrodes (50 nm) each with an
area of 3 mm.sup.2 were applied by thermal evaporation of gold (HHV
Auto 306) with the aid of a shadow mask.
[0153] The capacitor devices were characterized electrically using
a Cascade Microtech MS 150 Probe Station and an Agilent E4980A LCR
meter.
TABLE-US-00002 Process Polymer Layer Permittivity Loss factor
Polymer solvent concentration thickness at 20 Hz at 20 Hz 1 MAK 110
mg/ml 525 nm 3.08 0.0063 2 MAK 100 mg/ml 520 nm 2.82 0.0013 3 MAK
110 mg/ml 510 nm 3.24 0.0181 4 CP:BuAc 1:1 90 mg/ml 485 nm 3.56
0.0098 5 MAK 120 mg/ml 580 nm 3.03 0.0082 6 MAK 110 mg/ml 595 nm
2.85 0.0088 7 PGMEA 100 mg/ml 620 nm 3.25 0.0091 8 MAK 100 mg/ml
535 nm 4.56 0.0268
Example C2 Preparation of a Top Gate OFET with Polymer 1 as
Dielectric Layer
[0154] The substrate used was a PET film with prepatterned source
and drain electrodes (40 nm gold) (acquired from Fraunhofer IPM,
Freiburg). The channel length was 10 .mu.m and the channel width
was 10 mm. An 8 mg/ml solution of the semiconductor polymer
PDPP2T-TT-OD (Sigma Aldrich 791989) in xylene was filtered through
a 0.45 .mu.m PTFE syringe filter and applied to the film by spin
coating at 1000 rpm (30 s). The substrate was subsequently heated
on a hotplate at 90.degree. C. for 60 s. A 110 mg/ml solution of
polymer 1 with 2% of photoinitiator OXE02 (weight fraction polymer)
in MAK was filtered through a 0.45 .mu.m PTFE syringe filter and
applied to the film by spin coating at 1000 rpm (30 s). The coated
substrate was prebaked on a hotplate at 90.degree. C. for 60 s. The
substrate was subjected to UV exposure (LED 365 nm, 300
mJ/cm.sup.2), followed by a postbake on a hotplate at 90.degree. C.
for 60 s. Subsequently the substrate was immersed for 60 s in a MAK
bath, dried under a stream of nitrogen and heated on a hotplate at
90.degree. C. for ten minutes. A patterned gate electrode (50 nm)
was applied by thermal evaporation of gold (HHV Auto 306) using a
shadow mask.
[0155] The transistor devices were characterized electrically using
a Cascade Microtech MS 150 Probe Station and a Keithley 2612A
SMU.
[0156] FIG. 4 shows the transfer characteristic of a top gate OFET
in the saturated range (V.sub.D=-20 V). From the slope of the
characteristic, a charge carrier mobility .mu..sub.sat=0.11
cm.sup.2/Vs and an on/off ratio of 1.1*10.sup.6 is found.
Example C3 Preparation of a Bottom Gate OFET with Polymer 6 as
Dielectric Layer
[0157] The substrate used was an ITO-coated glass substrate, with
the ITO layer serving as gate electrode. A 110 mg/ml solution of
polymer 6 with 2% of OXE02 (weight fraction polymer) in MAK was
filtered through a 0.45 .mu.m PTFE syringe filter and applied to
the ITO substrate by spin coating at 1000 rpm for 30 s. The coated
substrate was prebaked on a hotplate at 90.degree. C. for 60 s.
Thereafter the substrate was subjected to UV exposure (LED 365 nm,
300 mJ/cm.sup.2), followed by a postbake on a hotplate at
90.degree. C. for 60 s. The substrate was subsequently immersed in
a MAK bath for 60 s, dried under a stream of nitrogen and heated on
a hotplate at 90.degree. C. for ten minutes. The patterned source
and drain electrodes (30 nm) were applied by thermal evaporation of
gold (HHV Auto 306) with the aid of a shadow mask. The channel
length was 100 .mu.m and the channel width was 4 mm. An 8 mg/ml
solution of the semiconductor polymer PDPP2T-TT-OD (Sigma Aldrich
791989) in xylene was filtered through a 0.45 .mu.m PTFE syringe
filter and applied to the substrate by spin coating at 1000 rpm (30
s). Lastly the substrate was heated on a hotplate at 90.degree. C.
for ten minutes.
[0158] The transistor devices were characterized electrically using
a Cascade Microtech MS 150 Probe Station and a Keithley 2612A
SMU.
[0159] FIG. 5 shows the transfer characteristic of a bottom gate
OFET in the saturated range (V.sub.D=-20 V). From the slope of the
characteristic, a charge carrier mobility .mu..sub.sat=0.07
cm.sup.2/Vs and an on/off ratio of 3.4*10.sup.4 is found.
Example C4 Preparation of a Top Gate OFET with Polymer 7 as
Dielectric Layer
[0160] The substrate used was a PET film with prepatterned source
and drain electrodes (40 nm gold) (acquired from Fraunhofer IPM,
Freiburg). The channel length was 10 .mu.m and the channel width
was 10 mm. An 8 mg/ml solution of the semiconductor polymer
PDPP2T-TT-OD (Sigma Aldrich 791989) in xylene was filtered through
a 0.45 .mu.m PTFE syringe filter and applied to the film by spin
coating at 1000 rpm (30 s). The substrate was subsequently heated
on a hotplate at 90.degree. C. for 60 s. A 110 mg/ml solution of
polymer 7 with 8% of photoinitiator OXE02 (weight fraction polymer)
in PGMEA was filtered through a 0.45 .mu.m PTFE syringe filter and
applied to the film by spin coating at 1000 rpm (30 s). The coated
substrate was prebaked on a hotplate at 90.degree. C. for 60 s. The
substrate was subjected to UV exposure (LED 365 nm, 1000
mJ/cm.sup.2), followed by a postbake on a hotplate at 90.degree. C.
for 60 s. Subsequently the substrate was immersed for 60 s in a MAK
bath, dried under a stream of nitrogen and heated on a hotplate at
90.degree. C. for ten minutes. A patterned gate electrode (50 nm)
was applied by thermal evaporation of gold (HHV Auto 306) using a
shadow mask.
[0161] The transistor devices were characterized electrically using
a Cascade Microtech MS 150 Probe Station and a Keithley 2612A
SMU.
[0162] FIG. 6 shows the transfer characteristic of a top gate OFET
in the saturated range (V.sub.D=-20 V). From the slope of the
characteristic, a charge carrier mobility .mu..sub.sat=0.096
cm.sup.2/Vs and an on/off ratio of 3.8'10.sup.4 is found.
Example C5 Preparation of a Bottom Gate OFET with Polymer 7 as
Dielectric Layer
[0163] The substrate used was an ITO-coated glass substrate, with
the ITO layer serving as gate electrode. A 110 mg/ml solution of
polymer 7 with 8% of OXE02 (weight fraction polymer) in MAK was
filtered through a 0.45 .mu.m PTFE syringe filter and applied to
the ITO substrate by spin coating at 1000 rpm for 30 s. The coated
substrate was prebaked on a hotplate at 90.degree. C. for 60 s.
Thereafter the substrate was subjected to UV exposure (LED 365 nm,
1000 mJ/cm.sup.2), followed by a postbake on a hotplate at
90.degree. C. for 60 s. The substrate was subsequently immersed in
a MAK bath for 60 s, dried under a stream of nitrogen and heated on
a hotplate at 90.degree. C. for ten minutes. The patterned source
and drain electrodes (30 nm) were applied by thermal evaporation of
gold (HHV Auto 306) with the aid of a shadow mask. The channel
length was 100 .mu.m and the channel width was 4 mm. An 8 mg/ml
solution of the semiconductor polymer PDPP2T-TT-OD (Sigma Aldrich
791989) in xylene was filtered through a 0.45 .mu.m PTFE syringe
filter and applied to the film by spin coating at 1000 rpm (30 s).
Lastly the substrate was heated on a hotplate at 90.degree. C. for
ten minutes.
[0164] The transistor devices were characterized electrically using
a Cascade Microtech MS 150 Probe Station and a Keithley 2612A
SMU.
[0165] FIG. 7 shows the transfer characteristic of a bottom gate
OFET in the saturated range (V.sub.D=-20 V). From the slope of the
characteristic, a charge carrier mobility .mu..sub.sat=0.02
cm.sup.2/Vs and an on/off ratio of 2.2*10.sup.4 is found.
* * * * *