U.S. patent application number 13/988392 was filed with the patent office on 2013-09-05 for semiconductor structure and method for its production.
This patent application is currently assigned to BASF SE. The applicant listed for this patent is Tomi Hassinen, Tero Mustonen, Roger Pretot. Invention is credited to Tomi Hassinen, Tero Mustonen, Roger Pretot.
Application Number | 20130228771 13/988392 |
Document ID | / |
Family ID | 44010085 |
Filed Date | 2013-09-05 |
United States Patent
Application |
20130228771 |
Kind Code |
A1 |
Mustonen; Tero ; et
al. |
September 5, 2013 |
SEMICONDUCTOR STRUCTURE AND METHOD FOR ITS PRODUCTION
Abstract
The present invention relates to a semiconductor structure and a
method for its production, the semiconductor structure comprising
at least one conductor region 9 and at least two semiconductor
regions (30,40), which semiconductor regions are partly separated
by the at least one conductor region. The at least one conductor
region comprises openings (22) extending between the semiconductor
regions which are partly separated by the respective conductor
region. The semiconductor regions comprise at least one organic
semiconductor material having a specific HOMO energy level, in
particular a DPP polymer. The conductor region comprises a
conductive material having a specific work function, said
combination of specific energy level and work function allowing for
a simple preparation of the conductive region. The invention
further relates to a method for providing such a semiconductor
structure.
Inventors: |
Mustonen; Tero; (Binningen,
CH) ; Pretot; Roger; (Basel, CH) ; Hassinen;
Tomi; (Vantaa, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mustonen; Tero
Pretot; Roger
Hassinen; Tomi |
Binningen
Basel
Vantaa |
|
CH
CH
FI |
|
|
Assignee: |
BASF SE
Ludwigshafen
DE
|
Family ID: |
44010085 |
Appl. No.: |
13/988392 |
Filed: |
December 19, 2011 |
PCT Filed: |
December 19, 2011 |
PCT NO: |
PCT/EP11/73159 |
371 Date: |
May 20, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61425777 |
Dec 22, 2010 |
|
|
|
Current U.S.
Class: |
257/40 ;
438/99 |
Current CPC
Class: |
C09B 57/004 20130101;
H01L 51/057 20130101; H01L 51/0036 20130101; H01L 51/0043 20130101;
C09B 69/109 20130101; H01L 51/0508 20130101 |
Class at
Publication: |
257/40 ;
438/99 |
International
Class: |
H01L 51/05 20060101
H01L051/05 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2010 |
EP |
10196429.4 |
Claims
1. A semiconductor structure, comprising: at least one conductor
regions; and at least two semiconductor regions, which are partly
separated by the at least one conductor region, wherein: the at
least one conductor region comprises openings extending between
semiconductor regions which are partly separated by a respective
conductor region; at least one semiconductor region comprises a
diketopyrrolopyrrole polymer as a semiconductor material; the
semiconductor regions comprise at least one organic semiconductor
material having a highest occupied molecular orbital energy level
E.sub.H, E.sub.H being defined by: 5.0
eV.ltoreq.|E.sub.H|.ltoreq.5.8 eV; and the conductor region
comprises a conductive material having a work function E.sub.C by:
|E.sub.H|-1.5 eV.ltoreq.|E.sub.C|.ltoreq.|E.sub.H|-0.4 eV.
2. The semiconductor structure of claim 1, wherein the organic
semiconductor material has a bulk concentration of positive charge
carrier equivalents N.sub.p with N.sub.p.ltoreq.1.times.10.sup.16
cm.sup.-3, N.sub.p.ltoreq.8.times.10.sup.15 cm.sup.-3,
N.sub.p.ltoreq.6.times.10.sup.15 cm.sup.-3,
N.sub.p.ltoreq.5.times.10.sup.15 cm.sup.-3,
N.sub.p.ltoreq.10.sup.16 cm.sup.-3,
N.sub.p.ltoreq.4.times.10.sup.15 cm.sup.-3,
N.sub.p.ltoreq.2.times.10.sup.15 cm.sup.-3 , or
N.sub.p.ltoreq.1.times.10.sup.15 cm.sup.-3.
3. The semiconductor structure of claim 2, wherein E.sub.H,
E.sub.C, and N.sub.p are adapted to yield a depletion width I.sub.d
of more than 100 nm within the semiconductor region.
4. The semiconductor structure of claim 1, wherein the at least one
organic semiconductor material comprises a diketopyrrolopyrrole
(DPP) polymer having one or more DPP skeletons represented by the
following formula: ##STR00023## in the repeating unit, wherein:
R.sup.1 and R.sup.2 are the same or different from each other and
are selected from the group consisting of hydrogen; a
C.sub.1-C.sub.100 alkyl group; --COOR.sup.3; a C.sub.1-C.sub.100
alkyl group which is substituted by one or more halogen atoms,
hydroxyl groups, nitro groups, --CN, or C.sub.6-C.sub.18 aryl
groups and/or interrupted by --O--, --COO--, --OCO--, or --S--; a
C.sub.7-C.sub.100 arylalkyl group; a carbamoyl group; a
C.sub.5-C.sub.12 cycloalkyl group which can be substituted one to
three times with a C.sub.1-C.sub.8 alkyl group and/or a
C.sub.1-C.sub.8 alkoxy group; a C.sub.6-C.sub.24 aryl group, and
pentafluorophenyl; and R.sup.3 represents a C.sub.1-C.sub.50 alkyl
group.
5. The semiconductor structure of claim 4, wherein the DPP polymer
is selected from the group consisting of a polymer of formula (Ia):
* A .sub.n* (Ia), a copolymer of formula (Ib): * A-D .sub.n* (Ib),
a copolymer of formula (Ic): * A-D .sub.x B-D .sub.y .sub.n* (Ic),
and and a copolymer of formula (Id): * A-D .sub.r B-D .sub.s A-E
.sub.t B-E .sub.u .sub.n* (Id), wherein: x=0.995 to 0.005; y=0.005
to 0.995, with the proviso that x+y=1; r=0.985 to 0.005; s=0.005 to
0.985; t=0.005 to 0.985; u=0.005 to 0.985, with the proviso that
r+s+t+u=1; n=4 to 1000; A is a group of formula (X): ##STR00024##
wherein a'=1, 2, or 3; a''=0, 1, 2, or 3; b=0, 1, 2, or 3; b'=0, 1,
2, or 3; c=0, 1, 2, or 3; c'=0, 1, 2, or 3; d=0, 1, 2, or 3; d'=0,
1, 2, or 3; with the proviso that b' is not 0 if a'' is 0;
Ar.sup.1, Ar.sup.1', Ar.sup.2, Ar.sup.2', Ar.sup.3, Ar.sup.3',
Ar.sup.4 and Ar.sup.4' are independently of each other
heteroaromatic or aromatic rings, which optionally can be condensed
and/or substituted; D is --CO--, --COO--, --S--, --O--, or
--NR.sup.112--; E is C.sub.1-C.sub.8 thioalkoxy, C.sub.1-C.sub.8
alkoxy, CN, --NR.sup.112R.sup.113, --CONR.sup.112R.sup.113, or
halogen, R.sup.112 and R.sup.113 are independently of each other H;
C.sub.6-C.sub.18 aryl; C.sub.6-C.sub.18 aryl which is substituted
by C.sub.1-C.sub.18 alkyl, or C.sub.1-C.sub.18 alkoxy;
C.sub.1-C.sub.18 alkyl; or C.sub.1-C.sub.18 alkyl which is
interrupted by --O--; B, D and E are independently of each other a
group of formula: * Ar.sup.4 .sub.k.sup. Ar.sup.5 .sub.l Ar.sup.6
.sub.r Ar.sup.7 .sub.z*, or formula (X), with the proviso that in
case B, D and E are a group of formula (X), they are different from
A, wherein k=1; l=0 or 1; r=0 or 1; z=0 or 1; Ar.sup.4, Ar.sup.5,
Ar.sup.6 and Ar.sup.7 are independently of each other a group of
formula: ##STR00025## wherein one of X.sup.5 and X.sup.6 is N and
the other is CR.sup.14; and R.sup.14, R.sup.14', R.sup.17 and
R.sup.17' are independently of each other H, or a C.sub.1-C.sub.25
alkyl group, which may optionally be interrupted by one or more
oxygen atoms.
6. The semiconductor structure of claim 5, wherein the DPP polymer
is a polymer according to formula (Ib-1), (Ib-9), (Ib-10):
##STR00026## wherein: R.sup.1 and R.sup.2 are independently from
each other a C.sub.8-C.sub.36 alkyl group; and n=4 to 1000.
7. The semiconductor material of claim 1, wherein the organic
semiconductor material has a polydispersity in the range of from
1.01 to 10.
8. The semiconductor structure of claim 1, wherein the openings
comprised in the conductor region have an inner width of more than
200 nm.
9. The semiconductor structure of claim 1, wherein the conductive
material of the conductor region comprises a metal, an alloy, or a
conductive polymer.
10. The semiconductor structure of claim 1, further comprising at
least two electrodes at end faces of the semiconductor regions,
wherein the electrodes as well as the conductor region each
comprise a contact region or are provided with a conductor adapted
for external contact.
11. The semiconductor structure of claim 1, wherein: the
semiconductor regions which are partly separated by the respective
conductor region are in direct contact with each other through the
openings of said conductor region; and the semiconductor regions
are separated by the respective conductor region by sections of the
respective conductor region, which sections are lateral to the
openings.
12. The semiconductor structure of claim 1, comprising a conductor
region partly separating two semiconductor regions, wherein: the
conductor region and the two semiconductor regions provide a
vertical transistor structure; and the conductor region provides a
gate adapted for conductivity control between the semiconductor
regions.
13. A semiconductor structure, comprising: at least one conductor
region:, and at least two semiconductor regions, which are partly
separated by the at least one conductor region, wherein: the at
least one conductor region comprises openings extending between the
semiconductor regions which are partly separated by the respective
conductor region; the semiconductor regions comprise at least one
organic semiconductor material which is at least one DPP polymer;
and the conductor region comprises a metal selected from the group
consisting of Al, Cr, Cu, Fe, In, Sb, Si, Sn, and Zn.
14. A method for producing the semiconductor structure of claim 1,
the method comprising partly contacting the at least two
semiconductor regions through the openings of the at least one
conductor region.
15. The method of claim 14, further comprising embossing,
mechanically cutting, or laser cutting the openings with an inner
width of more than 200 nm through a continuous layer, wherein the
at least one conductor region is the continuous layer of the
conductive material.
Description
[0001] The present invention relates to the field of organic
semiconductor structures, in particular to the field of vertical
semiconductor structures based on diketopyrrolopyrrole (DPP)
polymers. In particular, the present invention relates to a
semiconductor structure and a method for its production, the
semiconductor structure comprising at least one conductor region
and at least two semiconductor regions, which semiconductor regions
are partly separated by the at least one conductor region, wherein
the at least one conductor region comprises openings extending
between the semiconductor regions which are partly separated by the
respective conductor region, wherein the semiconductor regions
comprise at least one organic semiconductor material having a
specific HOMO (highest occupied molecular orbital) energy level, in
particular a DPP (diketopyrrolopyrrole) polymer, and wherein the
conductor region comprises a conductive material having a specific
work function.
[0002] In WO 2010/049321 and in WO 2008/000664, organic
semiconductor structures are described wherein the semiconductor
materials are diketopyrrolopyrrole (DPP) polymers. Further, the use
of a gate insulated by a gate dielectric within the structure is
generally disclosed. However, these prior art documents are silent
as regards form or structure of the gates.
[0003] In US 2006/0086933 A1, an organic semiconductor structure is
described having a comb-like electrode or a meshed electrode. The
gate electrode is patterned based on photolithography.
[0004] In US 2009/0001362 A1, an organic semiconductor structure is
described having a comb-like electrode patterned by electron-beam
direct lithography.
[0005] These patterning methods of the prior art require a
substantial amount of time and are not adapted for high throughput
processing.
[0006] Further, in Yu-Chiang Chao et. al., "High-performance
solution-processed polymer space-charge-limited transistor",
Organic Electronics 9 (2008), pp. 310-316, it is described to use a
conductive Al-layer with openings having a diameter of 200 nm. Due
to their size, openings are formed by depositing Al and polystyrene
spheres which are subsequently removed. As semiconductors,
materials like poly(3-hexylthiophene) are employed. As to this
technique, it is noted that the removal of the polystyrene spheres
cannot be reliably realized in an automated high-throughput
process. In addition, the resulting pattern is based on
statistically arranged spheres. In particular, a clogging of
spheres results in opening sizes depending on the number of spheres
per clogged cluster, which can vary to a large extent. Therefore,
the pattern cannot be determined reliably and inappropriately large
opening sizes cannot be not excluded.
[0007] US-2009/0181513 A1 as well as Chao et al., Applied Physics
Letters 88 (2006) 223510, introduce openings to the conductive
Al-layer at size of 200 nm and 500 nm. Large openings of 200 nm and
especially 500 nm show large off-current in the transistors,
because the small depletion width between Al and
poly(hexyl-thiophene) is insufficient to prevent charge
transporting, thus resulting in large off-current and poor
transistor performance.
[0008] In Yasuyuki Watanabe et. al., "Characteristics of organic
inverters using vertical- and lateral-type organic transistors",
Thin Solid Films 516 (2008), pp. 2731-2734, a transistor structure
based on pentacene as semiconductor is shown, in which a gate
within the pentacene is in form of slits. However, slits provide a
periodic sequence of gate material and space in between only in one
direction, i.e. perpendicular to the slits. Along the slits, gate
material and the space in between are not provided in an
alternating manner such that a high gate voltage sensitivity due to
the gate material and a high source-drain current due to the space
in between cannot be provided at the same area. This results in
poor electrical properties of the transistor.
[0009] In US 2005/0196895 A1 as well as in US 2009/0042142 A1, an
organic semiconductor device is shown having a perforated
intermediate layer of conductive material denoted as grid. The
openings of the grid are provided by a patterning die with raised
portions of 50-200 nm. The grid is isolated with regard to the
organic semiconductor material. As p-type semiconductor material,
organic semiconductor materials like PTCDA, CuPc and a-NPD are
proposed. The patterning die mechanically transfers the pattern to
the semiconductor material. However, the raised portions in these
sizes, 50-200 nm, cannot be provided in reliable manner due to
significant tolerances of the pattering die and due to wearing and
deformations of the raised portions. Thus, also electrical
properties of the semiconductor device resulting from the opening
size (gain, drain-source current, etc.) cannot be reproduced in
reliable manner.
[0010] Therefore, it is an object of the invention to provide a
semiconductor structure and a method for producing such
semiconductor structure enabling reliable electrical properties and
a high throughput.
[0011] Surprisingly, it was found that said object can be solved by
semiconductor structure comprising at least one conductor region
and at least two semiconductor regions, which semiconductor regions
are partly separated by the at least one conductor region, wherein
the at least one conductor region comprises openings extending
between the semiconductor regions which are partly separated by the
respective conductor region, wherein the semiconductor regions
comprise at least one organic semiconductor material having a HOMO
(highest occupied molecular orbital) energy level E.sub.H, E.sub.H
being defined by 5.0 eV.ltoreq.|E.sub.H|.ltoreq.5.8 eV as
determined by cyclic voltammetry (see further below), and wherein
the conductor region comprises a conductive material having a work
function E.sub.C being defined by |E.sub.H|-1.5
eV.ltoreq.|E.sub.C|.ltoreq.|E.sub.H|-0.4 eV.
[0012] Alternative ranges for the energy level E.sub.H are: 5.1
eV.ltoreq.|E.sub.H|.ltoreq.5.8 eV or 5.0
eV.ltoreq.|E.sub.H|.ltoreq.5.7 eV or, preferably, 5.1
eV.ltoreq.|E.sub.H|.ltoreq.5.7 eV.
[0013] Each of the at least one conductor regions separates two of
the at least two semiconductor regions. On each side of each
conductor region, one of the semiconductor regions contacts the
conductor region. The contacts between each of the conductor
regions and each of the semiconductor regions are Schottky
contacts.
[0014] The current of free charge carriers between the
semiconductor regions separated by the at least one conductor
region, can be controlled by the conductor region comprising the
openings through which the free charge carriers can pass from one
semiconductor region to the semiconductor region following the
conductor region. Thus, the conductor region can be regarded as
gate or basis of a vertical transistor formed by the semiconductor
regions and the at least one conductor region. Further, the
conductor region can be regarded as grid of a solid equivalent of
an electron tube structure. The at least one conductor region is
adapted to impose an electrical field within at least one of the
semiconductor regions by which the current of free charge carriers
can be controlled. Such a current of free charge carriers between
at least two of the semiconductor regions is the result of a
voltage applied to the semiconductor regions in the sense of a
source-drain voltage, wherein the current is controlled by the
voltage of the conductor region, which has the function of a gate.
The gate voltage at the conducting region controls the width of the
depletion region which extends to the grid opening. The width of
the depletion region in turn controls the current through the
opening. Particular electrical properties of the inventive
semiconductor structure are the maximum bulk current density of the
current through the conductor region as well as the gain defined by
the dependency of the current on a control voltage or control
current applied to the at least one conductive layer. It has been
found that the inventive semiconductor structure exhibits
significantly improved electrical properties.
[0015] Further, the improved electrical properties are achieved
also in case that the structural elements of the conductive layer
are provided in larger dimensions. According to the present
invention, the semiconductor structure can be produced with a
higher precision since the absolute influence of tolerances or
deformations is reduced due to the larger gate structures. Further,
a plurality of patterning mechanisms can be used, in particular
patterning mechanisms adapted for larger structure dimensions only.
In addition, a large depletion width can be provided by the
inventive combination of materials. Due to the larger openings, the
influence of tolerances is decreased, and the precision can be
improved. Thus, the electrical properties linked with the structure
can be defined with higher precision. As a consequence, the scrap
rate of the manufactured semiconductor structures is significantly
decreased.
[0016] According to the invention, the at least one conductor
region is one conductor region or more than one conductor regions
made of a conductive material. As conductive material, materials
are denoted which have a specific electrical resistance of less
than 10.sup.4, less than 10.sup.3, less than 10.sup.2, or of less
than 10 .OMEGA.m. Preferably, the conductive material has a
specific electrical resistance of less than 10.sup.-3, less than
10.sup.-5, or less than 10.sup.-6 .OMEGA.m. Most preferably, the
specific electrical resistance of the conductive material is less
than 5.times.10.sup.-7 .OMEGA.m or is less than 1.times.10.sup.-7
.OMEGA.m, particularly in the range of the specific electrical
resistance of aluminum.
[0017] The conductor region is an integral region and, for each
semiconductor region, all subregions of the semiconductor region
are electrically connected. Further, a semiconductor region
separating two conductor regions coextends with these semiconductor
regions or coextends with parts of these semiconductor regions. In
particular, the at least one conductor region and the at least two
semiconductor regions can be stacked or be provided in a laminated
structure. Within the context of the invention, the semiconductor
regions are partly separated by the at least one conductor region,
wherein the semiconductor regions are connected via the openings of
the intermediate conductor regions. Further, the conductive
material outside the openings, i.e. lateral to the openings,
physically separates the respective semiconductor regions.
[0018] The openings within the at least one conductor region are
preferably of the same shape and are in particular of the same
cross-section. Further, the openings have preferably the same
cross-sectional area. The openings are through-holes. This allows
to connect semiconductor regions abutting from both sides to the
conductor region. The openings extend along a direction inclined to
or substantially perpendicular to a direction, along which the
conductor region extends.
[0019] The semiconductor regions comprise at least one organic
semiconductor material. The at least one organic semiconductor
material is a p-type semiconductor and provides free positive
charges. Further, the semiconductor material preferably extends
through the complete width of the respective semiconductor regions.
Therefore, the semiconductor regions form an integral
semiconducting region. The semiconductor regions enable currents to
flow through the complete width of each semiconductor region. The
semiconductor regions can be provided between conductor regions or
between an electrode and a conductor region. Further, the
semiconductor material of at least of the semiconductor regions
extends along the openings such that physical contact is given
between semiconductor regions separated by a conductor region by
the openings within the conductor region. This preferably applies
to all conductor regions and semiconductor regions of the
semiconductor structure.
[0020] The at least one conductor region and the at least two
semiconductor regions preferably extend parallel to each other in a
stacked fashion providing a stacked or laminated structure.
Additionally, also electrodes can be provided, which also extend
parallel to the semiconductor regions and the at least one
conductor region. The at least one conductor region and the at
least two semiconductor regions are preferably provided as layers.
Further, the conductor region extends from one of the semiconductor
regions to another one of the semiconductor regions. Preferably,
each of the at least one conductor region and the at least two
semiconductor regions are provided with a constant thickness,
wherein the thickness is given in a direction perpendicular to a
direction, in which one of the regions extends.
[0021] The organic semiconductor material of the semiconductor
regions has a particular energy level E.sub.H corresponding to the
energy level of the highest occupied molecular orbital, which is
also denoted as HOMO. The HOMO level E.sub.H reflects the affinity
of the organic semiconductor material to provide free charge
carriers. In particular, the HOMO level reflects the energy
necessary to provide free charge carriers from the organic
semiconductor material and can be compared to an excitation energy.
According to the invention, the absolute value of E.sub.H is at
least 5.0 eV or at least 5.1 and does not exceed 5.7 eV or 5.8 eV.
Further, the absolute value of the LUMO level, ie. the level of the
lowest unoccupied molecular orbital, is preferably 3.3-4.1.
[0022] The conductive material of the conductor region according to
the present invention is adapted to the energy level E.sub.H of the
semiconductor material in order to provide the beneficial
electrical and mechanical properties of the inventive semiconductor
structure. The conductive material has a work function E.sub.C, the
absolute value of which is equal to or higher than the absolute
value of E.sub.H diminished by 1.5 eV. The absolute value of the
work function E.sub.C does not exceed the absolute value of E.sub.H
diminished by 0.4 eV. Therefore, the absolute value of the work
function E.sub.C is less than the absolute value of E.sub.H. In
particular, the absolute value of the work function E.sub.C differs
from the absolute value of E.sub.H by at least 0.4 eV. Further, the
absolute value of the work function E.sub.C does not differ from
the absolute value of E.sub.H by more than 1.5 eV.
[0023] In a preferred embodiment, the organic semiconductor
material has a bulk concentration of positive charge carrier
equivalents N.sub.p with N.sub.p.ltoreq.1.times.10.sup.16
cm.sup.-3, N.sub.p.ltoreq.8.times.10.sup.15 cm.sup.-3,
N.sub.p.ltoreq.6.times.10.sup.15 cm.sup.-3,
N.sub.p.ltoreq.5.times.10.sup.15 cm.sup.-3,
N.sub.p.ltoreq.10.sup.16 cm.sup.-3,
N.sub.p.ltoreq.4.times.10.sup.15 cm.sup.-3,
N.sub.p.ltoreq.2.times.10.sup.15 cm.sup.-3, or
N.sub.p.ltoreq.1.times.10.sup.15 cm.sup.-3. Positive charge carrier
equivalents are positive charge distributions within the organic
semiconductor material which have the electrical effect of free
positive charge carriers, for example holes. A positive charge
carrier equivalent corresponds to a charge unit if the
electrostatic effect of the positive charge carrier equivalent
corresponds to the electrostatic effect of a positive free charge
carrier being charged with one charge unit.
[0024] Different bulk concentrations within an organic
semiconductor material can be provided by distinct physical
structures of the organic semiconductor material due to the
dependency of the bulk concentration of charge carrier equivalents
within the organic semiconductor material on its structure. In
particular, this applies to organic semiconductor material which is
deposited as a solution, wherein at least one of the concentration
of the solution, the kind of solvent, the process temperature, a
mechanical pressure exerted on the semiconductor material, e.g. a
centrifugal force, the process duration and the time elapsed since
the preparation of the solution defines the charge carrier
equivalents.
[0025] According to a more preferred embodiment, the semiconductor
structure is adapted to provide a depletion width I.sub.d of at
least 100 nm, preferably of at least 125 nm, and most preferably of
at least 250 nm within the semiconductor region. The depletion
width applies to a condition, in which no external voltage is
applied to the conductor region. Further, the semiconductor
structure is adapted to provide a depletion width I.sub.d of at
least 75 nm, at least 100 nm, at least 150 nm, at least 200 nm, at
least 300 nm, at least 400 nm, at least 500 nm, at least 600 nm, at
least 700 nm, at least 800 nm, at least 900 nm, or at least 1
.mu.m. The depletion width can be provided or adapted by at least
one of the energy level E.sub.H of the highest occupied molecular
orbital of the at least one organic semiconductor material, the
work function E.sub.C of the conductive material and the bulk
concentration of positive charge carrier equivalents N.sub.p at an
appropriate level. The depletion width is the width of the
depletion zone at the condition that no external voltage is applied
to the conductor region.
[0026] As far as the materials of the semiconductor regions are
concerned, no specific restrictions exist provided that
above-described embodiments of the present invention can be
realized.
[0027] According to a preferred embodiment, at least one of the
semiconductor regions of the inventive semiconductor structure
contains at least one suitable diketopyrrolopyrrole (DPP) polymer
as semiconductor material. Preferably, at least one of the
semiconductor regions comprises, as semiconductor material, at
least one suitable DPP polymer. More preferably, each of the at
least one of the semiconductor regions comprises, as semiconducting
material, at least one suitable DPP polymer wherein the at least
one DPP polymer comprised in a given semiconductor region is the
same as or different from the at least one DPP polymer in another
semiconductor region.
[0028] Generally, a DPP polymer of the present invention is a
polymer having one or more DPP
[0029] skeletons represented by the following formula
##STR00001##
in the repeating unit. Examples of DPP polymers and their synthesis
are, for example, described in U.S. Pat. No. 6,451,459B1,
WO05/049695, WO2008/000664, WO2010/049321, WO2010/049323,
WO2010/108873, WO2010/115767, WO2010/136353, PCT/EP2011/060283 and
WO2010/136352.
[0030] According to a preferred embodiment, the at least one
organic semiconductor material comprises a diketopyrrolopyrrole
(DPP) polymer having one or more DPP skeletons represented by the
following formula
##STR00002##
[0031] in the repeating unit,
[0032] wherein R.sup.1 and R.sup.2 are the same or different from
each other and are selected from the group consisting of hydrogen;
a C.sub.1-C.sub.100 alkyl group; --COOR.sup.106; a
C.sub.1-C.sub.100 alkyl group which is substituted by one or more
halogen atoms, hydroxyl groups, nitro groups, --CN, or
C.sub.6-C.sub.18 aryl groups and/or interrupted by --O--, --COO--,
--OCO--, or --S--; a C.sub.7-C.sub.100 arylalkyl group; a carbamoyl
group; a C.sub.5-C.sub.12 cycloalkyl group which can be substituted
one to three times with a C.sub.1-C.sub.8 alkyl group and/or a
C.sub.1-C.sub.8 alkoxy group; a C.sub.6-C.sub.24 aryl group, in
particular phenyl or 1- or 2-naphthyl which can be substituted one
to three times with a C.sub.1-C.sub.8 alkyl group, a
C.sub.1-C.sub.25 thioalkoxy group, and/or a C.sub.1-C.sub.25 alkoxy
group; and pentafluorophenyl;
[0033] with R.sup.106 being a C.sub.1-C.sub.50 alkyl group,
preferably a C.sub.4-C.sub.25 alkyl group.
[0034] Still more preferably, the DPP polymer comprised in the at
least one semiconductor region of the semiconductor structure of
the present invention is selected from a group consisting of a
polymer of formula (Ia)
* A .sub.n* (Ia)
[0035] a copolymer of formula (Ib)
* A-D .sub.n* (Ib)
[0036] a copolymer of formula (Ic)
* A-D .sub.x B-D .sub.y .sub.n* (Ic)
[0037] and a copolymer of formula (Id),
* A-D .sub.r B-D .sub.s A-E .sub.t B-E .sub.u .sub.n* (Id)
[0038] wherein x=0.995 to 0.005, y=0.005 to 0.995, preferably x=0.2
to 0.8, y=0.8 to 0.2, with the proviso that x+y=1;
[0039] r=0.985 to 0.005, s=0.005 to 0.985, t=0.005 to 0.985,
u=0.005 to 0.985, with the proviso that r+s+t+u=1;
[0040] n=4 to 1000, preferably 4 to 200, more preferably 5 to
100,
[0041] A is a group of formula
##STR00003##
[0042] wherein a'=1, 2, or 3, a''=0, 1, 2, or 3; b=0, 1, 2, or 3;
b'=0, 1, 2, or 3; c=0, 1, 2, or 3; c'=0, 1, 2, or 3; d=0, 1, 2, or
3; d'=0, 1, 2, or 3; with the proviso that b' is not 0 if a'' is
0;
[0043] Ar.sup.1, Ar.sup.1', Ar.sup.2, Ar.sup.2', Ar.sup.3,
Ar.sup.3', Ar.sup.4 and Ar.sup.4' are independently of each other
heteroaromatic or aromatic rings, which optionally can be condensed
and/or substituted, preferably
##STR00004##
[0044] wherein one of X.sup.3 and X.sup.4 is N and the other is
CR.sup.99;
[0045] R.sup.99, R.sup.104, R.sup.104', R.sup.123 and R.sup.123'
are independently of each other hydrogen, halogen, especially F, or
a C.sub.1-C.sub.25 alkyl group, especially a C.sub.4-C.sub.25
alkyl, which may optionally be interrupted by one or more oxygen or
sulphur atoms, C.sub.7-C.sub.25 arylalkyl, or a C.sub.1-C.sub.25
alkoxy group;
[0046] R.sup.105, R.sup.105', R.sup.106 and R.sup.106' are
independently of each other hydrogen, halogen, C.sub.1-C.sub.25
alkyl, which may optionally be interrupted by one or more oxygen or
sulphur atoms; C.sub.7-C.sub.25 arylalkyl, or C.sub.1-C.sub.18
alkoxy;
[0047] R.sup.107 is C.sub.25 arylalkyl, C.sub.6-C.sub.18 aryl;
C.sub.6-C.sub.18 aryl which is substituted by C.sub.1-C.sub.18
alkyl, C.sub.1-C.sub.18 perfluoroalkyl, or C.sub.1-C.sub.18 alkoxy;
C.sub.1-C.sub.18 alkyl; C.sub.1-C.sub.18 alkyl which is interrupted
by --O--, or --S--; or --COOR.sup.124;
[0048] R.sup.124 is C.sub.1-C.sub.25 alkyl group, especially a
C.sub.4-C.sub.25 alkyl, which may optionally be interrupted by one
or more oxygen or sulphur atoms, C.sub.7-C.sub.25 arylalkyl;
[0049] R.sup.108 and R.sup.109 are independently of each other H,
C.sub.1-C.sub.25 alkyl, C.sub.1-C.sub.25 alkyl which is substituted
by E and/or interrupted by D, C.sub.7-C.sub.25 arylalkyl,
C.sub.6-C.sub.24 aryl, C.sub.6-C.sub.24 aryl which is substituted
by G, C.sub.2-C.sub.20 heteroaryl, C.sub.2-C.sub.20 heteroaryl
which is substituted by G, C.sub.2-C.sub.18 alkenyl,
C.sub.2-C.sub.18 alkynyl, C.sub.1-C.sub.18 alkoxy, C.sub.1-C.sub.18
alkoxy which is substituted by E and/or interrupted by D, or
C.sub.7-C.sub.25 aralkyl; or
[0050] R.sup.108 and R.sup.109 together form a group of formula
.ident.CR.sup.110R.sup.111, wherein
[0051] R.sup.110 and R.sup.111 are independently of each other H,
C.sub.1-C.sub.18 alkyl, C.sub.1-C.sub.18 alkyl which is substituted
by E and/or interrupted by D, C.sub.6-C.sub.24 aryl,
C.sub.6-C.sub.24 aryl which is substituted by G, or
C.sub.2-C.sub.20 heteroaryl, or C.sub.2-C.sub.20 heteroaryl which
is substituted by G; or
[0052] R.sup.108 and R.sup.109 together form a five or six-membered
ring, which optionally can be substituted by C.sub.1-C.sub.18
alkyl, C.sub.1-C.sub.18alkyl which is substituted by E and/or
interrupted by D, C.sub.6-C.sub.24 aryl, C.sub.6-C.sub.24 aryl
which is substituted by G, C.sub.2-C.sub.20 heteroaryl,
C.sub.2-C.sub.20 heteroaryl which is substituted by G,
C.sub.2-C.sub.18 alkenyl, C.sub.2-C.sub.18 alkynyl,
C.sub.1-C.sub.18 alkoxy, C.sub.1-C.sub.18 alkoxy which is
substituted by E and/or interrupted by D, or C.sub.7-C.sub.26
aralkyl;
[0053] D is --CO--, --COO--, --S--, --O--, or NR.sup.112--;
[0054] E is C.sub.1-C.sub.8 thioalkoxy, C.sub.1-C.sub.8 alkoxy, CN,
--NR.sup.112R.sup.113, --CONR.sup.112R.sup.113, or halogen,
[0055] G is E, or C.sub.1-C.sub.18 alkyl, and
[0056] R.sup.112 and R.sup.113 are independently of each other H;
C.sub.6-C.sub.18 aryl; C.sub.6-C.sub.18 aryl which is substituted
by C.sub.1-C.sub.18 alkyl, or C.sub.1-C.sub.18 alkoxy;
C.sub.1-C.sub.18 alkyl; or C.sub.1-C.sub.18 alkyl which is
interrupted by --O-- and
[0057] B, D and E are independently of each other a group of
formula
* Ar.sup.4 .sub.k.sup. Ar.sup.5 .sub.l Ar.sup.6 .sub.r Ar.sup.7
.sub.z*
[0058] or formula (X), with the proviso that in case B, D and E are
a group of formula (X), they are different from A, wherein k=1; l=0
or 1; r=0 or 1; z=0 or 1; and
[0059] Ar.sup.4, Ar.sup.5, Ar.sup.6 and Ar.sup.7 are independently
of each other a group of formula
##STR00005##
[0060] wherein one of X.sup.5 and X.sup.6 is N and the other is
CR.sup.14,
[0061] c is an integer of 1, 2, or 3,
[0062] d is an integer of 1, 2, or 3,
[0063] Ar.sup.8 and Ar.sup.8' are independently of each other a
group of formula
##STR00006##
[0064] X.sup.1 and X.sup.2 are as defined above,
[0065] R.sup.1'' and R.sup.2'' may be the same or different and are
selected from hydrogen, a C.sub.1-C.sub.36 alkyl group, especially
a C.sub.6-C.sub.24 alkyl group, a C.sub.6-C.sub.24 aryl, in
particular phenyl or 1- or 2-naphthyl which can be substituted one
to three times with C.sub.1-C.sub.8 alkyl, C.sub.1-C.sub.8
thioalkoxy, and/or C.sub.1-C.sub.8 alkoxy, or
pentafluorophenyl,
[0066] R.sup.14, R.sup.14', R.sup.17 and R.sup.17' are
independently of each other H, or a C.sub.1-C.sub.25 alkyl group,
especially a C.sub.6-C.sub.26 alkyl, which may optionally be
interrupted by one or more oxygen atoms.
[0067] Ar.sup.1 and Ar.sup.1' are preferably
##STR00007##
more preferably
##STR00008##
is most preferred.
[0068] Ar.sup.2, Ar.sup.2', Ar.sup.3, Ar.sup.3', Ar.sup.4 and
Ar.sup.4' are preferably
##STR00009##
more preferably
##STR00010##
[0069] The group of formula * Ar.sup.4 .sub.k Ar.sup.5 .sub.l
Ar.sup.6 .sub.r Ar.sup.7 .sub.z* is preferably
##STR00011##
more preferably
##STR00012##
most preferred
##STR00013##
[0070] R.sup.1 and R.sup.2 may be the same or different and are
preferably selected from hydrogen, a C.sub.1-C.sub.100alkyl group,
especially a C.sub.8-C.sub.36alkyl group.
[0071] The group A is preferably selected from
##STR00014##
[0072] The group of formula * Ar.sup.4 .sub.k Ar.sup.5 .sub.l
Ar.sup.6 .sub.r Ar.sup.7 .sub.z* is preferably a group of
formula
##STR00015##
[0073] Examples of preferred DPP polymers of formula Ia are, for
example:
##STR00016##
[0074] Examples of preferred DPP polymers of formula Ib are, for
example:
##STR00017##
[0075] Examples of preferred DPP polymers of formula Ic are, for
example:
##STR00018##
[0076] In particular in above-described preferred DPP polymers of
structures (Ia), (Ib), and (Ic), the groups R.sup.1 and R.sup.2
are, independently from each other, a C.sub.1-C.sub.36alkyl group,
especially a C.sub.8-C.sub.36alkyl group. n is preferably 4 to
1000, especially 4 to 200, very especially 5 to 100. R.sup.3 is
preferably a C.sub.1-C.sub.18alkyl group. R.sup.15 is preferably a
C.sub.4-C.sub.18alkyl group. As far as the indices are concerned, x
is preferably in the range from 0.995 to 0.005, and y is preferably
in the range from 0.005 to 0.995. More preferably, x=0.4 to 0.9,
and y=0.6 to 0.1, with x+y=1.
[0077] According to an especially preferred embodiment of the
present invention, the at least one DPP polymer comprised in the at
least one semiconductor region is a DPP polymer of structure (Ib),
even more preferably of structure (Ib-1), (Ib-9), (Ib-10).
Therefore, the present invention relates to above-described
semiconductor structure, wherein the DPP polymer is, for example, a
polymer according to formula (Ib-1)
##STR00019##
[0078] wherein R.sup.1 and R.sup.2 are independently from each
other a C.sub.8-C.sub.36 alkyl group,
[0079] with n=4 to 1000, preferably 4 to 200, more preferably 5 to
100. One especially preferred DPP polymer according to structure
(Ib-1) is, for example,
##STR00020##
[0080] with Mw=39,500, and a polydispersity=2.2 (measured by
HT-GPC)). Reference is made, for example, to Example 1 of
WO2010/049321.
[0081] Halogen is fluoro, chloro, bromo, iodo, especially
fluoro.
[0082] C.sub.1-C.sub.25alkyl (C.sub.1-C.sub.18alkyl) is typically
linear or branched, where possible. Examples are methyl, ethyl,
n-propyl, isopropyl, n-butyl, sec.-butyl, isobutyl, tert.-butyl,
n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl,
1,1,3,3-tetramethylpentyl, n-hexyl, 1-methylhexyl,
1,1,3,3,5,5-hexamethylhexyl, n-heptyl, isoheptyl,
1,1,3,3-tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n-octyl,
1,1,3,3-tetramethylbutyl and 2-ethylhexyl, n-nonyl, decyl, undecyl,
dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl,
octadecyl, eicosyl, heneicosyl, docosyl, tetracosyl or pentacosyl.
C.sub.1-C.sub.8alkyl is typically methyl, ethyl, n-propyl,
isopropyl, n-butyl, sec.-butyl, isobutyl, tert.-butyl, n-pentyl,
2-pentyl, 3-pentyl, 2,2-dimethyl-propyl, n-hexyl, n-heptyl,
n-octyl, 1,1,3,3-tetramethylbutyl and 2-ethylhexyl.
C.sub.1-C.sub.4alkyl is typically methyl, ethyl, n-propyl,
isopropyl, n-butyl, sec.-butyl, isobutyl, tert.-butyl.
[0083] C.sub.1-C.sub.25alkoxy (C.sub.1-C.sub.18alkoxy) groups are
straight-chain or branched alkoxy groups, e.g. methoxy, ethoxy,
n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, amyloxy,
isoamyloxy or tert-amyloxy, heptyloxy, octyloxy, isooctyloxy,
nonyloxy, decyloxy, undecyloxy, dodecyloxy, tetradecyloxy,
pentadecyloxy, hexadecyloxy, heptadecyloxy and octadecyloxy.
Examples of C.sub.1-C.sub.8alkoxy are methoxy, ethoxy, n-propoxy,
isopropoxy, n-butoxy, sec.-butoxy, isobutoxy, tert.-butoxy,
n-pentoxy, 2-pentoxy, 3-pentoxy, 2,2-dimethylpropoxy, n-hexoxy,
n-heptoxy, n-octoxy, 1,1,3,3-tetramethylbutoxy and 2-ethylhexoxy,
preferably C.sub.1-C.sub.4alkoxy such as typically methoxy, ethoxy,
n-propoxy, isopropoxy, n-butoxy, sec.-butoxy, isobutoxy,
tert.-butoxy. The term "alkylthio group" means the same groups as
the alkoxy groups, except that the oxygen atom of the ether linkage
is replaced by a sulfur atom.
[0084] C.sub.2-C.sub.25alkenyl (C.sub.2-C.sub.18alkenyl) groups are
straight-chain or branched alkenyl groups, such as e.g. vinyl,
allyl, methallyl, isopropenyl, 2-butenyl, 3-butenyl, isobutenyl,
n-penta-2,4-dienyl, 3-methyl-but-2-enyl, n-oct-2-enyl,
n-dodec-2-enyl, isododecenyl, n-dodec-2-enyl or
n-octadec-4-enyl.
[0085] C.sub.2-24alkynyl (C.sub.2-18alkynyl) is straight-chain or
branched and preferably C.sub.2-8alkynyl, which may be
unsubstituted or substituted, such as, for example, ethynyl,
1-propyn-3-yl, 1-butyn-4-yl, 1-pentyn-5-yl, 2-methyl-3-butyn-2-yl,
1,4-pentadiyn-3-yl, 1,3-pentadiyn-5-yl, 1-hexyn-6-yl,
cis-3-methyl-2-penten-4-yn-1-yl, trans-3-methyl-2-penten-4-yn-1-yl,
1,3-hexadiyn-5-yl, 1-octyn-8-yl, 1-nonyn-9-yl, 1-decyn-10-yl, or
1-tetracosyn-24-yl.
[0086] C.sub.5-C.sub.12cycloalkyl is typically cyclopentyl,
cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl,
cycloundecyl, cyclododecyl, preferably cyclopentyl, cyclohexyl,
cycloheptyl, or cyclooctyl, which may be unsubstituted or
substituted. The cycloalkyl group, in particular a cyclohexyl
group, can be condensed one or two times by phenyl which can be
substituted one to three times with C.sub.1-C.sub.4-alkyl, halogen
and cyano. Examples of such condensed
[0087] cyclohexyl groups are:
##STR00021##
[0088] in particular
##STR00022##
wherein R.sup.151, R.sup.152, R.sup.153, R.sup.154, R.sup.155 and
R.sup.156 are independently of each other C.sub.1-C.sub.8-alkyl,
C.sub.1-C.sub.8-alkoxy, halogen and cyano, in particular
hydrogen.
[0089] C.sub.8-C.sub.24aryl (C.sub.8-C.sub.18aryl) is typically
phenyl, indenyl, azulenyl, naphthyl, biphenyl, as-indacenyl,
s-indacenyl, acenaphthylenyl, fluorenyl, phenanthryl,
fluoranthenyl, triphenlenyl, chrysenyl, naphthacen, picenyl,
perylenyl, pentaphenyl, hexacenyl, pyrenyl, or anthracenyl,
preferably phenyl, 1-naphthyl, 2-naphthyl, 4-biphenyl,
9-phenanthryl, 2- or 9-fluorenyl, 3- or 4-biphenyl, which may be
unsubstituted or substituted. Examples of C.sub.8-C.sub.12aryl are
phenyl, 1-naphthyl, 2-naphthyl, 3- or 4-biphenyl, 2- or 9-fluorenyl
or 9-phenanthryl, which may be unsubstituted or substituted.
[0090] C.sub.7-C.sub.25aralkyl is typically benzyl,
2-benzyl-2-propyl, .beta.-phenyl-ethyl,
.alpha.,.alpha.-dimethylbenzyl, .omega.-phenyl-butyl,
.omega.,.omega.-dimethyl-.omega.-phenyl-butyl,
.omega.-phenyl-dodecyl, .omega.-phenyl-octadecyl,
.omega.-phenyl-eicosyl or .omega.-phenyl-docosyl, preferably
C.sub.7-C.sub.18aralkyl such as benzyl, 2-benzyl-2-propyl,
.beta.-phenyl-ethyl, .alpha.,.alpha.-dimethylbenzyl,
.omega.-phenyl-butyl,
.omega.,.omega.-dimethyl-.omega.-phenyl-butyl,
.omega.-phenyl-dodecyl or .omega.-phenyl-octadecyl, and
particularly preferred C.sub.7-C.sub.12aralkyl such as benzyl,
2-benzyl-2-propyl, .beta.-phenyl-ethyl,
.alpha.,.alpha.-dimethylbenzyl, .omega.-phenyl-butyl, or
.omega.,.omega.-dimethyl-.omega.-phenyl-butyl, in which both the
aliphatic hydrocarbon group and aromatic hydrocarbon group may be
unsubstituted or substituted. Preferred examples are benzyl,
2-phenylethyl, 3-phenylpropyl, naphthylethyl, naphthylmethyl, and
cumyl.
[0091] The term "carbamoyl group" typically stands for a
C.sub.1-18carbamoyl radical, preferably C.sub.1-8carbamoyl radical,
which may be unsubstituted or substituted, such as, for example,
carbamoyl, methylcarbamoyl, ethylcarbamoyl, n-butylcarbamoyl,
tert-butylcarbamoyl, dimethylcarbamoyloxy, morpholinocarbamoyl or
pyrrolidinocarbamoyl.
[0092] Heteroaryl is typically C.sub.2-C.sub.28heteroaryl
(C.sub.2-C.sub.20heteroaryl), i.e. a ring with five to seven ring
atoms or a condensed ring system, wherein nitrogen, oxygen or
sulfur are the possible hetero atoms, and is typically an
unsaturated heterocyclic group with five to 30 atoms having at
least six conjugated .pi.-electrons such as thienyl,
benzo[b]thienyl, dibenzo[b,d]thienyl, thianthrenyl, furyl,
furfuryl, 2H-pyranyl, benzofuranyl, isobenzofuranyl,
dibenzofuranyl, phenoxythienyl, pyrrolyl, imidazolyl, pyrazolyl,
pyridyl, bipyridyl, triazinyl, pyrimidinyl, pyrazinyl, pyridazinyl,
indolizinyl, isoindolyl, indolyl, indazolyl, purinyl, quinolizinyl,
chinolyl, isochinolyl, phthalazinyl, naphthyridinyl, chinoxalinyl,
chinazolinyl, cinnolinyl, pteridinyl, carbazolyl, carbolinyl,
benzotriazolyl, benzoxazolyl, phenanthridinyl, acridinyl,
pyrimidinyl, phenanthrolinyl, phenazinyl, isothiazolyl,
phenothiazinyl, isoxazolyl, furazanyl or phenoxazinyl, which can be
unsubstituted or substituted.
[0093] Possible substituents of the above-mentioned groups are
C.sub.1-C.sub.8alkyl, a hydroxyl group, a mercapto group,
C.sub.1-C.sub.8alkoxy, C.sub.1-C.sub.8alkylthio, halogen,
halo-C.sub.1-C.sub.8alkyl, a cyano group, a carbamoyl group, a
nitro group or a silyl group, especially C.sub.1-C.sub.8alkyl,
C.sub.1-C.sub.8alkoxy, C.sub.1-C.sub.8alkylthio, halogen,
halo-C.sub.1-C.sub.8alkyl, or a cyano group.
[0094] If, according to a conceivable embodiment, the inventive
semiconductor structure has two semiconductor regions which are
partly separated by the one conductor regions, it is preferred that
each of the two semiconductor regions comprises at least one DPP
polymer of structure (Ib), more preferably at least one DPP polymer
of structure (Ib-1), even more preferably at least one DPP polymer
of structure (Ib-1) wherein R.sup.1 and R.sup.2 are independently
from each other a C.sub.8-C.sub.36 alkyl group, with n=4 to 1000,
preferably 4 to 200, more preferably 5 to 100. According to an even
more preferred embodiment of the present invention, both
semiconductor regions contain the same DPP polymers, even more
preferably exactly one DPP polymer.
[0095] In particular, the polydispersity of the polymer comprised
by the at least one organic semiconductor material, preferably the
at least one DPP polymer, has a polydispersity in the range of from
1.01 to 10, preferably from 1.1 to 3.0 and more preferably from 1.5
to 2.5.
[0096] The openings within the at least one conductor region have
an inner width of at least 200 nm, preferably at least 250 nm and
most preferably at least 500 nm. Further, the inner width of the
openings can be at least 150 nm, at least 200 nm, at least 300 nm,
at least 400 nm, at least 600 nm, at least 800 nm, at least 1000
nm, at least 1200 nm, at least 1400 nm, at least 1600 nm, at least
1800 nm, or at least 2 .mu.m. A variety of simple approaches can be
used for providing such openings. In particular due to the large
inner size of the openings, the openings can be easily provided
with mechanical methods. Particular method steps for providing such
openings are given below in the context of the inventive method.
The openings have a substantially circular inner cross section.
[0097] According to an embodiment of the present invention, the
openings within the at least one conductor region are embossed
openings, mechanically cut openings or laser-cut openings. In
particular, the openings can be embossed openings, which are formed
by pressing into a layer of conductive material. A patterned matrix
can be used, which is pressed into the conductive layer such that
the resulting openings are formed by mechanical removal of the
conductive material. Thus, the openings can be formed by the
formation using a patterned matrix. Further, the openings can be
formed by cutting, wherein two cutting matrices are used which are
pressed into a layer of the conductive material from both sides of
the layer thereby cutting conductive material from the location of
the openings. In particular, such matrices used for providing the
openings can have the shape of rollers. In case that embossed
openings are provided, the layer of conducting material can be an
individual layer or a layer supported by a substrate, e.g.
supported by a semiconductor region. Further, the openings can be
laser-cut openings formed by evaporation of conducting material
within a layer at the locations of the openings. In the case of
laser-cut openings, the openings can be formed within an individual
layer of conductive material forming the conductor region or can be
formed by a layer supported by substrate, e.g. by a semiconductor
region. The conductor region comprising the openings can be
provided by a foil, a sheet or a deposited layer of conductive
material.
[0098] The conductive material of the conductor region comprises or
preferably consists of a metal, of an alloy or of a conductive
polymer, preferably a metal, more preferably a metal selected from
the group consisting of Al, Cr, Cu, Fe, In, Sb, Si, Sn, and Zn,
wherein the metal is in particular Al. The alloy is preferably an
alloy comprising at least two of these metals. The conductive
material can be provided as a homogenous structure of the metal,
the alloy or the conductive polymer, or can be a compound
comprising at least two of the metal, the alloy or the conductive
polymer. In a particular embodiment, the conductive material is
provided by nanotubes, which can be provided within a matrix of the
metal, the alloy or the conductive polymer. In another embodiment,
the conductive material is provided by a semiconducting material,
which is highly doped. Since highly doped semiconductor materials
provide high electrical conductivity, such highly doped
semiconductor materials are regarded as conductive materials in the
sense of the invention as far as they exhibit a specific electrical
resistance of the conductor material. In addition, instead of the
metal or the alloy, an electrically conducting compound thereof can
be used. In particular, indium tin oxide can be used as conductive
material. In particular, the highly doped semiconductor material is
a semiconductor material doped with a p-dopant or, preferably, an
n-dopant at a high concentration leading to high electrical
conductivity. The conductive material and in particular the highly
doped semiconductor material has a specific electrical resistivity
of less than 1.times.10.sup.2, less than 1.times.10.sup.1, or less
than 1 .OMEGA.m.
[0099] The present invention thus includes a semiconductor
structure comprising at least one conductor region and at least two
semiconductor regions, which semiconductor regions are partly
separated by the at least one conductor region, wherein the at
least one conductor region comprises openings extending between the
semiconductor regions which are partly separated by the respective
conductor region, wherein the semiconductor regions comprise at
least one organic semiconductor material selected from DPP polymers
described above, and wherein the conductor region comprises a metal
selected from the group consisting of Al, Cr, Cu, Fe, In, Sb, Si,
Sn, and Zn, the metal in particular being Al.
[0100] An embodiment of the inventive semiconductor structure
comprises at least two electrodes at end faces of the semiconductor
regions, preferably one electrode at each of both end faces of the
semiconductor regions. The electrodes as well as the conductor
region each comprise a contact region or are provided with a
conductor adapted for external contact. The electrodes are provided
at faces of the semiconductor region, which are not covered by a
conductor region. Preferably, all conductor regions are located
between two semiconductor regions and, consequently, are located
between two electrodes. The electrodes coextend with the
semiconductor regions and the at least one conductor region.
Electrodes are provided by conductive material, preferably by a
conductive material having a work function E.sub.E with
|E.sub.E|.gtoreq.|E.sub.H|-0.3 eV. Further, the absolute value of
the work function E.sub.E of the electrode material is preferably
less than or equal to |E.sub.H|+0.9 eV. The electrodes are an
integral layer, which is preferably continuous. As an example, the
electrodes substantially consist of Au or Ag. However, also other
conducting materials can be used, e.g. indium tin oxide or zinc
oxide or a material comprises at least one conducting polymer. If
the conductor is provided for external contact, the conductor at
least partly extends laterally to the electrode. In addition, each
of the electrodes can have a multilayered substructure, wherein the
electrode material having a work function of E.sub.E is provided by
a coating of the substructure abutting to the semiconductor region
or semiconductor regions, and wherein this coating is provided on
an electrically conductive substrate with the work function of
E.sub.E. The semiconductor regions which are partly separated by
the respective conductor region are in direct contact with each
other through the openings of said conductor region. The
semiconductor regions are separated by the respective conductor
region by sections of the respective conductor region lateral to
the openings. The semiconductor regions are separated by the
material of the conductor region within the sections lateral to the
openings. These sections are provided for applying an electrical
field to at least one of the semiconductor regions. The
semiconductor regions on both sides of the respective conductor
region are physically connected to each other via the openings.
Preferably, semiconductor material extending through openings forms
a continuous inner opening section. The semiconductor regions are
on both sides of the respective conductor region and are
continuously and physically connected with each other, preferably
via the inner opening section of the semiconductor material. In
this way, the inventive semiconductor structure is adapted to
provide transfer of free charge carriers between semiconductor
regions partly separated by the conductor region.
[0101] The inventive semiconductor structure comprises or,
preferably, substantially consists of a conductor region partly
separating two semiconductor regions. The conductor region and the
two semiconductor regions provide a vertical transistor structure,
wherein the conductor region provides a gate, a basis or a grid
adapted for conductivity control between the semiconductor regions.
A particular embodiment of such a semiconductor structure comprises
one conductor region separating two semiconductor regions, as well
as two electrodes. The end faces of each of the semiconductor
regions opposite to the conductor region each carry one of the
electrodes. The resulting vertical transistor structure is adapted
to controllably provide current between the electrodes, wherein the
current is controlled by a voltage or a current between the gate,
i.e. the conductor region on one side and one of the electrodes on
the other side. In such a structure, preferably each of the two
semiconductor regions comprises the same organic semiconductor
material, preferably the same DPP polymer. In particular, each of
the two semiconductor regions consists of the same organic
semiconductor material, preferably the same DPP polymer.
[0102] The organic semiconductor material of at least one of the
semiconductor regions is most preferably a cast material, in
particular a spin-cast material, coated material or printed
material. A cast material is provided by a solution of the organic
semiconductor material within at least one solvent, and by removing
such a solvent, e.g. by evaporation. The electrical properties of
the semiconductor material can be set by a microstructure of the
organic semiconductor material, wherein the microstructure is
mainly defined by the deposition method of the cast material.
Further, the material can be printed in form of dissolved
semiconductor material. In particular, the semiconductor material
can be inkjet-printed material. Inkjet-printed material can be
provided in a desired pattern in order to pattern the semiconductor
structure in a direction along which the semiconductor structure
extends.
[0103] According to a further aspect of the invention, a method for
producing an inventive semiconductor structure is provided. The
method comprises the following steps: [0104] (a) providing at least
two semiconductor regions comprising at least one organic
semiconductor material; [0105] (b) providing at least one conductor
region between the at least two semiconductor regions; [0106] (c)
providing openings in the at least one conductor region extending
through the entire conductor region; and [0107] (d) partly
contacting the at least two semiconductor regions through the
openings of the at least one conductor region.
[0108] In a preferred method, step (b) comprises providing the at
least one conductor region as a continuous layer of the conductive
material and step (c) comprises embossing, mechanically cutting or
laser cutting the openings with an inner width of the openings of
more than 200 nm, preferably more than 250 nm, more preferably more
than 500 nm, through the continuous layer. In this preferred method
step (b), at least one of the conductor regions usually is provided
as an individual continuous sheet, and step (c) is carried out
before (b) is completed and before, during or after the conductor
region is joined with one of the at least two semiconductor
regions. The individual continuous sheet preferably is a
prefabricated sheet.
[0109] Alternatively, said preferred method may be carried out in
that in step (b), at least one of the conductor regions is
deposited onto one of the at least two semiconductor regions
provided in (a), preferably by vapor deposition, and step (c) is
carried out before (b) is completed and during or after the
conductor region is deposited.
[0110] Also preferred is a method, wherein, for each of the
semiconductor regions, (a) comprises applying the organic
semiconductor material onto a substrate or onto the at least one
conductor region in one or more steps, wherein the organic
semiconductor material is applied in free-flowing form as a
solution, suspension, or emulsion comprising the organic
semiconductor material, preferably by casting, spraying or
printing, or wherein the organic semiconductor material is applied
in solid form, and wherein (d) comprises applying the organic
semiconductor material of at least one of these semiconductor
regions into the openings, in particular by casting, and preferably
in the course of (a). According to this method, the organic
semiconductor material often is provided as a solution or
dispersion of the material in at least one organic solvent, the
solution preferably having a content of 0.5 to 20 weight-% of the
organic semiconductor material, relative to the total weight of the
solution or dispersion. The solution or dispersion may be spin cast
on the substrate.
[0111] In a preferred method, the above process is carried out
performing the following steps: [0112] (i) providing at least one
semiconductor region comprising at least one organic semiconductor
material; [0113] (ii) providing at least one conductor region in
contact to the semiconductor region; [0114] (iii) providing
openings in the at least one conductor region extending through the
entire conductor region; [0115] (iv) providing at least one
semiconductor region comprising at least one organic semiconductor
material in contact with the conductor region in way that conductor
region is between at least two semiconductor regions; and [0116]
(v) partly contacting the at least two semiconductor regions 5
through the openings of the at least one conductor region.
[0117] One embodiment of steps (ii) and (iii) of said method is
applying a conductor having pre-formed openings (ii), another
embodiment thereof comprises the forming the openings after
applying to the 1st semiconductor (iii), i.e.
[0118] (a) providing at least one conductor region with openings in
the at least one conductor region extending through the entire
conductor region in contact to the semiconductor region ; or
[0119] (b) providing at least one conductor region in contact to
the semiconductor region, and subsequently providing openings in
the at least one conductor region extending through the entire
conductor region.
[0120] When the 2nd semiconductor region is provided (step iv),
contact with the 1st semiconductor layer through openings (step v)
may be formed as a separate step or preferably immediately.
[0121] Furthermore preferred is a method, wherein at least two
electrodes are applied to end faces of the semiconductor regions by
depositing an electrode material onto at least one of the end
faces, or by providing the electrode material, onto which at least
one of the semiconductor regions is applied, wherein the electrode
material is preferably Au, Ag, Pt, Pd or an alloy of at least two
of these materials.
[0122] The organic semiconductor material of step (a) has a HOMO
(highest occupied molecular orbital) energy level E.sub.H, E.sub.H
being defined by 5.0 eV.ltoreq.|E.sub.H|.ltoreq.5.8 eV. The at
least one conductor region provided in step (b) comprises a
conductive material having a work function E.sub.C being defined by
|E.sub.H|=1.5 eV.ltoreq.|E.sub.C|.ltoreq.|E.sub.H|-0.4 eV.
[0123] Alternatives for the range of the energy level E.sub.H are:
5.1 eV.ltoreq.|E.sub.H|.ltoreq.5.8 eV, 5.0
eV.ltoreq.|E.sub.H|.ltoreq.5.7 eV or preferably 5.1
eV.ltoreq.|E.sub.H|.ltoreq.5.7 eV.
[0124] HOMO/LUMO values are obtained experimentally using cyclic
voltammetry (Autolab PGSTAT30.RTM. Potentiostat), using Pt working
electrode, Ag counter electrode and AgCl coated Ag as
pseudo-reference electrode; electrolyte is 0.1M tetrabutylammonium
hexafluorophosphate in o-dichlorobenzene; internal reference is
ferrocene.
[0125] In particular, the semiconductor regions, the organic
semiconductor material, the at least one conductor region and/or
the conductive material are provided according to the definitions
provided above with regard to the inventive semiconductor
structure.
[0126] Preferably, step (b) comprises providing at least one
conductor region as a continuous layer of the conductive material.
Further, step (c) comprises embossing, mechanically cutting or
laser-cutting the openings with an inner width of the openings of
more than 200 nm, preferably more than 250 nm, more preferably more
than 500 nm, through the continuous layer. In particular, the
openings provided by step (c) are provided with an inner width of
at least 150 nm, 200 nm, 300 nm, 400 nm or 600 nm. In addition, the
inner width can be at least 800 nm, at least 1000 nm, at least 1200
nm, at least 1400 nm, at least 1600 nm, at least 1800 nm or at
least 2 .mu.m. The conductor region can be coated and the openings
can be provided after having applied the continuous layer as a
coating. Alternatively, the conductor region can be applied by
patterning such that the openings are formed when the conductor
region is provided.
[0127] The conductor region can be provided by coating or
patterning the conductive material, in particular by coating or
patterning the conductive material dissolved in a solvent. The
conductive material can be spray-coated, printed, in particular
inkjet-printed, deposited, e.g. by chemical vapor deposition, or by
other suitable coating or patterning methods. Generally,
subtractive or additive methods for providing the conductor region
can be used. In particular, these methods are role-to-role
techniques. The additive methods include deposition, in particular
by evaporation, sputtering, coating or printing of the conductive
material. The pattern is formed by removal or modification of the
conductive material. In particular, removal includes lithographical
methods combined with etching, lift-off, delamination or laser
ablation/laser cutting of the conductive material. Modification
includes embossing, oxidation, light exposure or chemical treatment
of the conductive material. The subtractive methods include
printing, e.g. gravure, screen printing, flexo printing or
p-contact printing. Further, the subtractive methods include the
application of the shadow mask before adding the conductive
material, wherein the conductive material is added by evaporation
or sputtering. In addition, the subtractive methods include
transfer of conductive material, in particular by stamping, by
lamination or by thermal transfer.
[0128] These methods can also be used to provide electrodes at end
faces of the semiconducting material, wherein electrode material
takes the place of the conductive material.
[0129] Advantageously, at least one of the conductor regions is
provided as an individual continuous sheet. Further, step (c) of
providing the openings is carried out before step (b) of providing
the at least one conductive region is completed. The openings can
be provided in the at least one conductor region by using an
individual continuous sheet, perforating this individual continuous
sheet by embossing, mechanically cutting or laser-cutting and by
applying the perforated continuous sheet onto the semiconductor
region, in particular by lamination. Further, the openings can be
provided by joining the continuous sheet with one of the
semiconductor regions as one step, e.g. by rolling the continuous
sheet onto the semiconductor region using a roller comprising an
outer structure adapted for pressing or cutting the openings into
the sheet. Therefore, the roller presses the sheet onto the
semiconductor region in order to join the conductor region and the
semiconductor region and, at the same time, embosses or cuts the
openings into the sheet. Further, the openings can be provided
after the conductor region is joined with the semiconductor region
by laser-cutting, by mechanically cutting or by embossing. In this
way, the conductor region is joined with the semiconductor region
as a first step, e.g. by lamination or by vapor deposition, and, as
a subsequent second step, openings are cut or embossed into the
sheet, which is already joined with the semiconductor region.
Preferably, embossing is provided by nano imprinting using stamps
having a structure complementary to the structure of the
openings.
[0130] In an exemplifying embodiment, the individual continuous
sheet is a prefabricated sheet. The individual continuous sheet is
already provided with all structural features before joining the
sheet with the semiconductor region. The prefabricated sheet and
the conductor region within the semiconductor structure provide the
same structural features including the openings.
[0131] In another embodiment, the at least one conductor region is
deposited onto one of the at least two semiconductor regions
provided in step (a). The at least one conductor region is
preferably deposited by vapor deposition. Step (c) of providing the
openings is carried out before step (b) of providing the at least
one conductor region is completed and during or after the the
conductor region is deposited. Therefore, the openings are provided
according to step (c) during or after the conductor region is
joined with one of the at least two semiconductor regions.
Therefore, the openings are embossed, mechanically cut or laser-cut
into the conductor region, which is already joined with the
adjacent semiconductor region.
[0132] For each of the semiconductor regions, step (a) comprises
applying the organic semiconductor material onto a substrate or
onto the at least one conductor region in one or more steps. The
organic semiconductor material is applied in free-flowing form as a
solution, suspension or emulsion comprising the organic
semiconductor material, preferably by casting, spraying or
printing. Alternatively, the organic semiconductor material is
applied in solid form, wherein step (d) comprises applying the
organic semiconductor material of at least one of these
semiconductor regions into the openings, in particular by casting,
and preferably in the course of step (a) of providing the
semiconductor regions. The organic semiconductor material is
applied in free-flowing form, in particular by spray-coating,
knife-coating or other appropriate deposition techniques.
[0133] Suitable coating methods for applying the semiconductor
material include spin-coating, slot-die coating (also called
extrusion coating), curtain coating, reverse gravure coating, blade
coating, spray coating and dip coating.
[0134] Suitable printing methods for applying the semiconductor
material include inkjet printing, flexography printing, gravure
printing, in particular forward gravure printing, screen printing,
pad printing, offset printing and reverse offset printing.
[0135] Spin coating and inkjet printing are the preferred methods.
Generally, the same or distinct methods for applying the at least
two semiconductor regions. In particular, one of the at least two
semiconductor regions can be provided by spin coating and another
one of these at least two semiconductor regions can be provided by
inkjet printing.
[0136] Further, the organic semiconductor material can be applied
in solid form, in particular as a solid layer of semiconductor
material, which is applied by laminating.
[0137] The organic semiconductor material of at least one of these
semiconductor regions is applied into the openings, in particular
by casting the semiconductor material in liquid form, in particular
as a solution. In this way, the openings are filled with
semiconductor material in order to provide a physical contact
between two semiconductor regions separated by a conductor region
comprising the openings. The application of the semiconductor
material into the openings can be supported by pressing
semiconductor material towards the openings, e.g. by spin-coating
or by pressing a surface onto the semiconductor material towards
the openings.
[0138] When applying the organic semiconductor material in
free-flowing form, the semiconductor material is provided as a
solution or dispersion of the material in at least one organic
solvent. The solution preferably has a content of 0.1 to 20 wt.-%
of the organic semiconductor material. Particularly, the content is
0.1 to 8 wt.-%, for example 1 to 8 wt.-%, more particularly 0.5 to
4 wt.-% or 1 to 2 wt.-% of the organic semiconductor material;
further advantageous ranges of the semiconductor material are 2 to
6 wt.-%, or 3 to 5 wt.-%. Advantageously, the content of organic
semiconductor material does not exceed 10 wt.-% or 8 wt.-%, or even
5 wt.-%, and is at least 0.5 wt.-%, preferably at least 1 wt.-%,
more preferably at least 2 wt.-%. The organic solvent may be a
single solvent or a binary solvent (i.e. mixture of two or more
solvents); it can be used with or without additives. In particular,
a dichlorobenzene can be used, preferably 1,2-dichlorobenzene or
1,3-dichlorobenzene. Further, toluene can be used as solvent.
[0139] Suitable solvents preparing the formulations according to
the present application are organic solvents, in which the DPP
polymer and possible additives have satisfactory solubility.
Examples of further suitable organic solvents include, but are not
limited to,
[0140] petroleum ethers, aromatic hydrocarbons such as benzene,
chlorobenzene, dichlorobenzene, trichlorobenzene,
cyclohexylbenzene, toluene, anisole, xylene, naphthalene,
chloronaphtalene, tetraline, indene, indane, cyclooctadiene,
styrene, decaline and mesitylene; halogenated aliphatic
hydrocarbons such as dichloromethane, chloroform and
ethylenechloride; ethers such as dioxane and dioxolane; ketones
such as cyclopentanone and cyclohexanone; aliphatic hydrocarbons
such as hexanes and cyclohexanes; and mixtures of two or more of
said solvents.
[0141] Preferred solvents are dichlorobenzene, toluene, xylene,
tetraline, chloroform, mesitylene and mixtures of two or more
thereof.
[0142] Preferably, the organic semiconductor material is applied in
free-flowing form, as a solution, in particular as a solution of
the semiconductor material in at least one organic solvent, wherein
the solution is spin-cast on the substrate, onto which the organic
semiconductor material is applied. The substrate and/or the
solution can be heated at a temperature of at least 45.degree. C.,
at least 60.degree. C., and preferably at least 70.degree. C.
during the application of the semiconductor material. Further, the
temperature of the substrate or the organic semiconductor material
during its application does not exceed 150.degree. C., 140.degree.
C. or preferably 120.degree. C. In particular, during the
application of the semiconductor material, the temperature of the
solution and/or the substrate does not exceed the boiling point of
the at least one organic solvent. However, the semiconductor
material (as well as the substrate, if applicable) is preferably at
room temperature during its application.
[0143] In order to remove the at least one solvent, the substrate
and/or the solution are heated in order to force the evaporation of
the at least one solvent. The solvent is removed after the
application of the semiconductor material in dissolved form. The
heating can be carried out by applying a hot air stream, by
directing infrared radiation onto the substrate and/or the solution
or by placing the substrate and/or the solution onto a hot plate or
into a drying oven.
[0144] For preferred embodiments, the semiconductor material is
applied at room temperature (20.degree. C.). The semiconductor
material is dried at a higher temperature, however preferably below
the boiling of the solvent. The semiconductor material is
preferably dried at a temperature of at least 45.degree. C., at
least 60.degree. C., and advantageously at least 70.degree. C.
Preferably, the semiconductor material is dried at temperature
which does not exceed 150.degree. C., 140.degree. C. or preferably
120.degree. C.
[0145] A further embodiment of the inventive method concerns the
application of electrodes. In this embodiment, at least two
electrodes are applied to end faces of the semiconductor regions by
depositing an electrode material onto at least one of the end faces
or by providing the electrode material, onto which at least one of
the semiconductor materials is applied. The electrode material used
therefore is preferably Au, Ag, Pt, Pd, an alloy or a compound of
at least two of these metals, or any other conductive material used
for the electrodes. The electrode material can be a metal, an alloy
of at least two metals, at least one conductive polymer or an at
least electrically conducting metal compound. In particular, indium
tin oxide (ITO) or other electrically conductive metal compounds
can be used. Further, conductive polymers can be used as electrode
material, such as PEDOT:PSS or polyaniline. The electrode material
can be applied by vapor deposition or can be laminated onto the end
faces of the semiconductor regions. Further, the electrode material
can be attached to the at least one of the end faces using a
conductive adhesive.
[0146] In addition, the electrodes can be provided with a contact
region facing away from the semiconductor material or can be
provided with a conductor attached thereto, which is adapted for
providing external contact.
[0147] Preferably, the ratio between the inner width of the
openings and the thickness of the semiconductor region in which the
openings are provided is at least 2, 4, 5, 10 or 20.
[0148] The present invention is illustrated by the following
examples. Room temperature denotes a temperature from the range
18-23.degree. C., the term "work function" denotes the vacuum work
function, and percentages are given by weight (often abbr. wt.-%,
or % b.w.), unless otherwise indicated.
EXAMPLES
Example 1
[0149] A glass substrate has been provided, onto which a gold
electrode with a thickness of 40 nm has been evaporated. Next, a
DPP polymer according to Example 1 of WO2010/049321 (HOMO as
determined by cyclic voltammetry/Autolab PGSTAT.RTM. 30:
|E.sub.H|=5.35 eV) is applied in form of a solution of 5% of DPP in
toluene. The solution containing 5% DPP is spin-cast at 1000 rpm
and dried at 90.degree. C. The spin-cast DPP forms a first
semiconductor region. In particular, the solution can be dried at a
temperature of less than 50.degree. C., or at room temperature
(20.degree. C.).
[0150] After having applied this first semiconductor region, a
conductor region is applied onto the semiconductor region in form
of evaporated aluminium with a thickness of 40 nm (work function
|E.sub.C|=4.3 eV). The evaporated aluminium is provided with
openings by nanoimprint lithography. The openings have a diameter
of 300-500 nm. The openings are arranged in a grid, wherein the
openings have a center to center distance of 2 .mu.m. The ratio of
the cross-section area of the openings to the area of the conductor
region is 0.196%.The thickness of the first semiconductor region is
1 .mu.m. The conductor layer has been applied by an evaporation
technique, in particular by sputtering.
[0151] The openings are provided by a nano imprint stamp comprising
a silicon wafer. The silicon wafer has a diameter of 100 mm. The
stamp comprises projections with a height of ca. 135 nm and a
diameter of 350 nm. The projections have a approximately circular
cross section. The stamp has been pressed onto the conductor region
with a force of 20-80 N, in particular with a force of 20-40 N.
This force has been applied to the area of the 100 mm silicon
wafer. The resulting depressions within the conductor layer (and
the underlying semiconductor layer) have a depth of ca. 100 nm and
a width of 300-500 nm. The stamp is pressed into the conductor
region at room temperature (20.degree. C.). Preferably, the stamp
is pressed into the conductor region at temperatures below
100.degree. C., and in particular below 50.degree. C.
[0152] The stamp has been formed by UV lithography, wherein a
resist is removed by oxygen plasma. The resulting structure is
formed by isotrope dry etching.
[0153] After having applied the conductor region in form of a layer
of 40 nm aluminium, a solution of 4% of DPP in dichlorobenzene is
applied by inkjet-printing. The solution is deposited and dried at
75.degree. C. The resulting semiconductor region had an average
thickness of 1 .mu.m.
[0154] After having applied the second semiconductor region, an
electrode of gold with a thickness of 40 nm was applied by
evaporation.
[0155] A current of 100 .mu.A was achieved at a gate voltage of 3
V. Further, the mobility was 0.05 cm.sup.2/Vs. The bulk charge
carrier concentration was 2.times.10.sup.15 cm.sup.-3 and the bulk
conductivity was 500 .OMEGA.m. The thickness of the first
semiconductor region was measured using a capacitance method. The
mobility was measured with the resulting semiconductor structure in
a FET configuration and the bulk charge carrier concentration was
measured with a capacity/voltage method in the Schottky contact
formed by the conductor region and the first semiconductor region.
The transistor had a cross-sectional area of 0.1 mm.sup.2 and the
total number of openings within the conductor region was 24000.
[0156] With a semiconductor structure comprising DPP as
semiconductor material and aluminium as conductor material,
Schottky contacts could be formed with a bulk charge carrier
density of 1-2.times.10.sup.15 cm.sup.-3 and a forward bias voltage
drop of 0.8-0.4 V. Further, a depletion width of 0.3-0.8 .mu.m
could be yielded. These results refer to a semiconductor structure
with a semiconductor region provided by spin-casting a solution of
4 or 5% of DPP and a conductor region of 33 or 40 nm aluminium. The
conductor region was formed of aluminium with openings of 200-500
nm in diameter.
Example 2
[0157] In a second example, the conductor region was formed of an
evaporated aluminium layer of 40 nm with an inner width of the
opening of 200 nm. The openings were arranged in grid with a center
to center distance of 500 nm. The semiconductor regions have been
produced according to Example 1. In contrast to example 1, the
openings in example 2 resulted resulted in a ratio of
cross-sectional area of the openings to the area of the conductor
region of 0.126. As with Example 1, Example 2 yielded a bulk
current density at 3 V of 0.53 A/cm.sup.2. The total number of
openings in Example 2 was 600000 for an area of 0.16 mm.sup.2. As
with Example 1, a current of 100 .mu.A at 3 V has been yielded at a
thickness of the semiconductor regions of 1 .mu.m measured with a
capacitance method. As regards bulk charge carrier concentration,
conductivity and mobility, the same results as in Example 1 have
been yielded.
[0158] In further examples of the invention using DPP as
semiconductor material and aluminium as conductor material, charge
carrier concentrations of 1.3.times.10.sup.15 cm.sup.-3 as well as
a depletion width of 760 nm have been yielded. Further, charge
carrier concentrations of 2.3.times.10.sup.15 cm.sup.-3 and a
depletion width of 450 nm could be yielded with DPP as
semiconductor material and aluminium as conductor material.
BRIEF DESCRIPTION OF THE DRAWING
[0159] FIG. 1 shows an inventive semiconductor structure in form of
a schematic drawing.
DETAILED DESCRIPTION OF THE FIGURE
[0160] In FIG. 1, an embodiment of the inventive semiconductor
structure is shown in a sectional side view. The depiction is not
drawn to scale, in particular with respect to the widths of the
structure elements. The semiconductor structure comprises an
electrode 10 with an electrical connection 12. Electrode 10 is made
of conducting material. Further, the structure comprises a
conductor region 20, which is provided with openings 22. The
openings 22 extend perpendicular to the direction along which the
conductor region 20 extends. Between the first electrode 10 and the
conductor region 20, a first semiconductor region 30 is provided,
which extends from the first electrode 10 to the conductor region
20. On the side of the conductor region 20, opposed to the
semiconductor region 30, a second semiconductor region 40 is
located. Further, a second electrode 50 is provided, together with
an electrical connection 52. The second electrode 50 is arranged on
the side of the second semiconductor region 40, which is opposed to
the conductor region 20 as well as to the first semiconductor
region 30. Therefore, the first electrode 10 as well as the second
electrode 50 are located at opposed end faces of the semiconductor
structure. In particular, the electrodes 10 and 50 are located at
end faces of the semiconductor regions 30 and 40, which are opposed
to the conductor region 20.
[0161] The structure shown in FIG. 1 is a layered structure such
that the electrodes 10 and 50, the conductor region 20 as well as
the first and the second semiconductor regions 30 and 40 are
provided as layers with a constant thickness. The openings 22 are
filled with semiconductor material such that the first
semiconductor region 30 and the second semiconductor region 40 are
physically connected with each other by the semiconductor material
within the openings 22. The conductor region 20 can be provided
with an electrical connector in order to impose a certain voltage
onto the conductor region 20.
[0162] For example, if a certain voltage is applied between the
second electrode 50 and the conductor region 20, the semiconductor
region 40 in-between, i.e. the second semiconductor region, is
modified as regards its electrical properties. In particular, the
voltage between the conductor region 20 and the second electrode 50
imposes an electrical field within the second semiconductor region
40 which increases the bulk concentration of free charge carriers
or their equivalents within the second semiconductor region 40.
Thus, if an additional voltage is applied at the electrodes 50 and
10, a current is generated based on the free charge carriers within
the semiconductor regions 30, 40, the bulk concentration of which
is controlled via the voltage applied at the conductor region 20.
In this way, a gain can be produced and the voltage at the
conductor region 20 controls a current between the electrical
connections 12 and 52 of the first and second electrode 10, 50. In
particular, by applying voltage difference between the electrodes
10 and 50, the charge carrier movement is controlled by applying a
voltage to the conductor region 20. This voltage varies a depletion
range located at the conductor region 20 and the semiconductor
region 30. In addition, a depletion range located at the conductor
region 20 and the semiconductor region 40 can be varied. In this
way, a channel for charge carriers is opened, which travel from the
semiconductor region 30 to the semiconductor region 40 through the
openings 22. If not voltage is applied to conductor region 20, the
depletion range covers the area of 22, and charges do not travel
through openings resulting in a transport current between the
semiconductor regions 30 and 40 of zero.
[0163] According to an exemplifying embodiment, the electrodes 10
and 50 can be formed of a layer of evaporated gold and the first
and the second semiconductor region 30, 40 can be provided by
layers of DPP, which are preferably produced by casting the organic
semiconductor material dissolved in a solvent. Of course, after
dissolved organic semiconductor material is applied, the solvent
has to be removed before another structural element is applied to
the respective semiconductor region 30, 40. The conductor region 20
can be formed of a layer of aluminium, preferably with a thickness
of less than 100 nm or less than 50 nm. The openings 22 in the
conductor region 20 are provided by nanoimprinting lithography into
a layer of aluminium, which provides the conductor region 20 and
which is formed by evaporation of aluminium onto one of the
semiconductor regions 30 or 40. The openings 22 have an inner width
of e.g. 500 nm.
REFERENCE SIGNS
[0164] 10 first electrode
[0165] 12 electrical connection
[0166] 20 conductor region
[0167] 22 openings
[0168] 30 first semiconductor region
[0169] 40 second semiconductor region
[0170] 50 second electrode
[0171] 52 electrical connection
CITED DOCUMENTS
[0172] WO 2010/049321 [0173] WO 2008/000664 [0174] US 2006/0086933
A1 [0175] US 2009/0001362 A1 [0176] Yu-Chiang Chao et. al.,
"High-performance solution-processed polymer space-charge-limited
transistor", Organic Electronics 9 (2008), pp. 310-316 [0177]
Yasuyuki Watanabe et. al., "Characteristics of organic inverters
using vertical- and lateral-type organic transistors", Thin Solid
Films 516 (2008), pp. 2731-2734 [0178] US 2005/0196895 A1 [0179] US
2009/0042142 A1 [0180] U.S. Pat. No. 6,451,459 B1 [0181] WO
05/049695 [0182] WO 2010/049323 [0183] PCT/EP2010/053655 [0184]
PCT/EP2010/054152 [0185] PCT/EP2010/056778 [0186] PCT/E
P2010/056776
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