U.S. patent application number 11/823859 was filed with the patent office on 2008-07-03 for crosslinked polymeric dielectric materials and methods of manufacturing and use thereof.
Invention is credited to Hyuk-Jin Choi, Antonio Facchetti, Tobin J. Marks, Zhiming Wang.
Application Number | 20080161464 11/823859 |
Document ID | / |
Family ID | 38660573 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080161464 |
Kind Code |
A1 |
Marks; Tobin J. ; et
al. |
July 3, 2008 |
Crosslinked polymeric dielectric materials and methods of
manufacturing and use thereof
Abstract
Solution-processable dielectric materials are provided, along
with precursor compositions and processes for preparing the same.
Composites and electronic devices including the dielectric
materials also are provided.
Inventors: |
Marks; Tobin J.; (Evanston,
IL) ; Facchetti; Antonio; (Chicago, IL) ;
Wang; Zhiming; (Chicago, IL) ; Choi; Hyuk-Jin;
(Evanston, IL) |
Correspondence
Address: |
Kirkpatrick & Lockhart Preston Gates Ellis LLP;(FORMERLY KIRKPATRICK &
LOCKHART NICHOLSON GRAHAM)
STATE STREET FINANCIAL CENTER, One Lincoln Street
BOSTON
MA
02111-2950
US
|
Family ID: |
38660573 |
Appl. No.: |
11/823859 |
Filed: |
June 28, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60816952 |
Jun 28, 2006 |
|
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|
Current U.S.
Class: |
524/401 ;
257/347; 257/40; 257/E29.273; 257/E51.007; 526/279; 528/10; 528/25;
528/26; 528/29; 528/33 |
Current CPC
Class: |
C08K 5/544 20130101;
H01B 3/30 20130101; H01L 51/052 20130101; C08K 5/5415 20130101 |
Class at
Publication: |
524/401 ; 528/33;
528/10; 528/25; 528/29; 528/26; 526/279; 257/40; 257/347;
257/E29.273; 257/E51.007 |
International
Class: |
C08G 77/04 20060101
C08G077/04; C08G 77/00 20060101 C08G077/00; H01L 29/786 20060101
H01L029/786; H01L 51/05 20060101 H01L051/05 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] The United States government has certain rights to the
invention(s) pursuant to Grant Nos. N00014-02-1-0909
(0650-300-F445), DMR-0076097 (MRC), and NCC2-1363 from,
respectively, the Office of Naval Research, the National Science
Foundation, and the National Aeronautics and Space Administration,
all to Northwestern University.
Claims
1. A crosslinked polymeric material comprising a thermally cured
product of a precursor composition, the precursor composition
comprising at least one of (i) a polymeric component and a
crosslinker component, the crosslinker component comprising a
thermally curable crosslinker having the formula:
(X).sub.3-m(Y).sub.mSi-Z-Si(Y).sub.m(X).sub.3-m, and (ii) a
polymeric crosslinker comprising a pendant group, the pendant group
comprising a thermally curable crosslinking moiety having the
formula: -Q-Si(Y).sub.m(X).sub.3-m, wherein: m, at each occurrence,
is independently selected from 0, 1, and 2; X, at each occurrence,
is independently selected from a halogen, --NR.sup.1R.sup.2,
--OR.sup.3, and --OC(O)R.sup.3; Y, at each occurrence, is
independently selected from H, a C.sub.1-6 alkyl group, and a
C.sub.1-6 haloalkyl group; Z is Q-W-Q; and Q, at each occurrence,
is independently selected from -L-, --O--, --O-L-, -L-O--,
--NR.sup.4--, --NR.sup.4-L-, -L-NR.sup.4--, and a covalent bond;
wherein: L, at each occurrence, is independently a divalent
C.sub.1-10 alkyl group or a divalent C.sub.1-10 haloalkyl group,
each of which is optionally substituted with 1-4 R.sup.4 groups; W
is selected from --SiXX--, --SiXY--, --SiYY--, --SiXX--O--,
--O--SiXX--, --SiXY--O--, --O--SiXY--, --SiYY--O--, --O--SiYY--,
--O--{[(CR.sup.4.sub.2).sub.t--O].sub.p--[(CR.sup.5.sub.2).sub.t--O].sub.-
q}--, a divalent C.sub.6-14 aryl group, a divalent 5-14 membered
heteroaryl group, and a covalent bond, wherein each of the divalent
C.sub.6-14 aryl group and the divalent 5-14 membered heteroaryl
group is optionally substituted with 1-4 R.sup.4 groups; R.sup.1
and R.sup.2 are independently selected from H, a C.sub.1-6 alkyl
group, a C.sub.6-14 aryl group, a 5-14 membered heteroaryl group, a
--C.sub.1-6 alkyl-C.sub.6-14 aryl group, and a --C.sub.1-6
alkyl-5-14 membered heteroaryl group; R.sup.3 is selected from H, a
C.sub.1-6 alkyl group, a C.sub.1-6 haloalkyl group, a C.sub.2-6
alkenyl group, a C.sub.2-6 alkynyl group, a C.sub.6-14 aryl group,
a 5-14 membered heteroaryl group, a --C.sub.1-6 alkyl-C.sub.6-14
aryl group, and a --C.sub.1-6 alkyl-5-14 membered heteroaryl group;
R.sup.4 and R.sup.5, at each occurrence, are independently selected
from H, a halogen, a C.sub.1-6 alkyl group, a C.sub.1-6 haloalkyl
group, a C.sub.6-14 aryl group, a 5-14 membered heteroaryl group, a
--C.sub.1-6 alkyl-C.sub.6-14 aryl group, a --C.sub.1-6 alkyl-5-14
membered heteroaryl group, and -Q-Si(Y).sub.m(X).sub.3-m; t, at
each occurrence, is independently 1, 2, 3, 4, 5 or 6; p is 0, 1, 2,
3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19; and
q is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,
19 or 20, provided that p+q.ltoreq.20; and provided that Z is not
--O--, a divalent C.sub.1-20 alkyl group, or a covalent bond.
2. The crosslinked polymeric material of claim 1, wherein the
polymeric component comprises one or more polymers selected from a
polyalkylene, a substituted polyalkylene, a siloxane polymer, and a
copolymer thereof.
3. The crosslinked polymeric material of claim 1, wherein the
polymeric component comprises one or more polymers selected from
polyethylene, polypropylene, polyvinylalcohol, polystyrene, a
ring-functionalized derivative of polystyrene, polyacrylate, a
siloxane polymer, and copolymers thereof.
4. The crosslinked polymeric material of claim 1, wherein Q, at
each occurrence, is independently selected from --O--,
--CH.sub.2).sub.t--, --(CF.sub.2).sub.t--, and a covalent bond; and
W is selected from --O--[(CH.sub.2).sub.2--O].sub.t--,
--O--[(CF.sub.2).sub.2--O].sub.t--, a divalent phenyl group, and a
covalent bond; wherein t is as defined in claim 1.
5. The crosslinked polymeric material of claim 1, wherein X, at
each occurrence, is independently selected from Cl, --OCH.sub.3,
--OCH.sub.2CH.sub.3, --N(CH.sub.3).sub.2--,
--N(CH.sub.2CH.sub.3).sub.2--, --OC(O)CH.sub.3, and
--OC(O)CH.sub.2CH.sub.3; and Y, at each occurrence, is
independently selected from H, CF.sub.3, a methyl group, and an
ethyl group.
6. The crosslinked polymeric material of claim 1, wherein the
crosslinker component comprises a crosslinker selected from
[CH.sub.3C(O)O].sub.3Si--(CH.sub.2).sub.3--O--(CH.sub.2).sub.2--O--(CH.su-
b.2).sub.3--Si[CH.sub.3C(O)O].sub.3,
Cl.sub.3Si--(CH.sub.2).sub.3--O--(CH.sub.2).sub.2--O--(CH.sub.2).sub.3--S-
iCl.sub.3,
(CH.sub.3O).sub.3Si--(CH.sub.2).sub.2-phenyl-(CH.sub.2).sub.2---
Si(OCH.sub.3).sub.3,
Cl.sub.3Si--(CH.sub.2).sub.2--(CF.sub.2).sub.2--(CH.sub.2).sub.2--SiCl.su-
b.3, and
[CH.sub.3C(O)O].sub.3Si--CH.sub.2).sub.2(CF.sub.2).sub.2(CH.sub.2-
).sub.2--Si[CH.sub.3C(O)O].sub.3.
7. The crosslinked polymeric material of claim 1, wherein the
polymeric crosslinker has the formula: ##STR00017## wherein:
R.sup.6, at each occurrence, is independently H, a halogen, or a
C.sub.1-6 alkyl group; R.sup.7 is selected from H, OH, a halogen,
C(O)O--R.sup.3, a C.sub.1-6 alkyl group, a C.sub.1-6 haloalkyl
group, a C.sub.6-14 aryl group, a 5-14 membered heteroaryl group, a
3-14 membered cycloheteroalkyl group, a --C.sub.1-6
alkyl-C.sub.6-14 aryl group, a --C.sub.1-6 alkyl-5-14 membered
heteroaryl group, and a --C.sub.1-6 alkyl-3-14 membered
cycloheteroalkyl group, wherein each of the C.sub.6-14 aryl groups,
the 5-14 membered heteroaryl groups, and the 3-14 membered
cycloheteroalkyl groups is optionally substituted with 1-5
substituents independently selected from a halogen, an oxo group,
OH, CN, NO.sub.2, C(O)O--C.sub.1-6 alkyl, a C.sub.1-6 alkyl group,
a C.sub.1-6 alkoxy group, and a C.sub.1-6 haloalkyl group; R.sup.8
is selected from --O--, --C(O)O--, a divalent C.sub.1-6 alkyl
group, and a divalent phenyl group; x and y are independently a
real number, wherein 0<x<1, 0<y<1, and x+y=1; and Q, X,
Y and m are as defined in claim 1.
8. The crosslinked polymeric material of claim 1, wherein the
precursor composition further comprises at least one of (iii) a
crosslinker component comprising a photochemically curable
crosslinker and (iv) a photochemically curable polymeric
crosslinker.
9. A dielectric material comprising the crosslinked polymeric
material of claim 1.
10. The dielectric material of claim 9 comprising a plurality of
metal oxide particles, the metal oxide particles comprising a metal
component selected from a Group I metal, a Group II metal, a Group
III metal, a Group IV metal, a transition metal, and combinations
thereof.
11. The dielectric material of claim 9 having a thickness of less
than about 50 nm.
12. A thin film transistor comprising the dielectric material of
claim 9 and an organic semiconductor material.
13. A thin film transistor comprising the dielectric material of
claim 9 and an inorganic semiconductor material.
14. A method for preparing a dielectric material, the method
comprising applying a precursor composition onto a substrate and
curing thermally the precursor composition to provide a dielectric
material, the precursor composition comprising at least one of (i)
a polymeric component and a crosslinker component and (ii) a
polymeric crosslinker dissolved in one or more solvents, wherein
the crosslinker component comprises a thermally curable crosslinker
having the formula:
(X).sub.3-m(Y).sub.mSi-Z-Si(Y).sub.m(X).sub.3-m, and the polymeric
crosslinker comprises a pendant group comprising a thermally
curable crosslinking moiety having the formula:
-Q-Si(Y).sub.m(X).sub.3-m, wherein: m, at each occurrence, is
independently selected from 0, 1, and 2; X, at each occurrence, is
independently selected from a halogen, --NR.sup.1R.sup.2,
--OR.sup.3, and --OC(O)R.sup.3; Y, at each occurrence, is
independently selected from H, a C.sub.1-6 alkyl group, and a
C.sub.1-6 haloalkyl group; Z is Q-W-Q; and Q, at each occurrence,
is independently selected from -L-, --O--, --O-L-, -L-O--,
--NR.sup.4--, --NR.sup.4-L-, -L-NR.sup.4--, and a covalent bond;
wherein: L, at each occurrence, is independently a divalent
C.sub.1-10 alkyl group or a divalent C.sub.1-10 haloalkyl group,
each of which is optionally substituted with 1-4 R.sup.4 groups; W
is selected from --SiXX--, --SiXY--, --SiYY--, --SiXX--O--,
--O--SiXX--, --SiXY--O--, --O--SiXY--, --SiYY--O--, --O--SiYY--,
--O--{[(CR.sup.4.sub.2).sub.t--O].sub.p--[(CR.sup.5.sub.2).sub.t--O].sub.-
q}--, a divalent C.sub.6-14 aryl group, a divalent 5-14 membered
heteroaryl group, and a covalent bond, wherein each of the divalent
C.sub.6-14 aryl group and the divalent 5-14 membered heteroaryl
group is optionally substituted with 1-4 R.sup.4 groups; R.sup.1
and R.sup.2 are independently selected from H, a C.sub.1-6 alkyl
group, a C.sub.6-14 aryl group, a 5-14 membered heteroaryl group, a
--C.sub.1-6 alkyl-C.sub.6-14 aryl group, and a --C.sub.1-6
alkyl-5-14 membered heteroaryl group; R.sup.3 is selected from H, a
C.sub.1-6 alkyl group, a C.sub.1-6 haloalkyl group, a C.sub.2-6
alkenyl group, a C.sub.2-6 alkynyl group, a C.sub.6-14 aryl group,
a 5-14 membered heteroaryl group, a --C.sub.1-6 alkyl-C.sub.6-14
aryl group, and a --C.sub.1-6 alkyl-5-14 membered heteroaryl group;
R.sup.4 and R.sup.5, at each occurrence, are independently selected
from H, a halogen, a C.sub.1-6 alkyl group, a C.sub.1-6 haloalkyl
group, a C.sub.6-14 aryl group, a 5-14 membered heteroaryl group, a
--C.sub.1-6 alkyl-C.sub.6-14 aryl group, a --C.sub.1-6 alkyl-5-14
membered heteroaryl group, and -Q-Si(Y).sub.m(X).sub.3-m; t, at
each occurrence, is independently 1, 2, 3, 4, 5 or 6; p is 0, 1, 2,
3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19; and
q is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,
19 or 20, provided that p+q.ltoreq.20; and provided that Z is not
--O--, a divalent C.sub.1-20 alkyl group, or a covalent bond.
15. The method of claim 14, wherein the one or more solvents are
selected from ethyl acetate, dioxane, bis(2-methoxyethyl)ether, and
tetrahydrofuran.
16. The method of claim 14 comprising spin-coating the precursor
composition onto the substrate.
17. The method of claim 14 comprising printing the precursor
composition onto the substrate.
18. The method of claim 14 comprising heating the precursor
composition at a temperature within a range of about 70.degree. C.
and about 150.degree. C. in a high humidity atmosphere.
19. The method of claim 14, wherein the precursor composition
further comprises at least one of (iii) a crosslinker component
comprising a photochemically curable crosslinker and (iv) a
photochemically curable polymeric crosslinker, the method further
comprising curing photochemically the precursor composition.
20. The method of claim 19 comprising exposing the precursor
composition to ultraviolet light.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Provisional Patent Application Ser. No. 60/816,952, filed on Jun.
28, 2006, the disclosure of which is incorporated by reference in
its entirety.
BACKGROUND
[0003] The development of polymeric dielectric materials has been
fundamental for the progress of both traditional and organic
electronic devices. In particular, emerging display and labeling
technologies based on organic thin-film transistors (OTFTs), such
as electronic paper and radiofrequency identification (RFID) cards,
require fabrication of OTFTs on flexible plastic substrates over
very large areas and via high throughput processes. Therefore,
there has been considerable effort in developing new materials for
OTFT components (semiconductor, dielectric, and contacts) that can
be deposited via solution-processing methods such as spin-coating,
casting, and printing.
[0004] Many organic semiconductors are readily deposited from
solution either directly or as molecular/polymeric soluble
precursors which are then converted into the insoluble form. Doped
conjugated polymers and nanoparticle-based conductive inks allow
solution fabrication of sufficiently low resistivity lines for
source/drain and gate contact applications.
[0005] Although various polymers have been employed as dielectrics
for OTFTs, two major limitations with current-generation polymeric
dielectric-based OTFTs exist. First, OTFTs function at relatively
large operating voltages due to the intrinsically low (compared to
crystalline semiconductors) semiconductor charge carrier
mobilities. Second, because very few polymeric dielectric materials
can perform optimally with a wide range of both hole-transporting
(p-type) and electron-transporting (n-type) organic semiconductors,
there has been limited complementary circuit application. These
problems are exacerbated when printed dielectric/circuits are
fabricated.
[0006] In a typical organic field effect transistor (OFET), the
conductance of the source-drain channel region is modulated by the
source-gate electric field (E.sub.G). When the device is in the
off-state (E.sub.G=0), the channel conductance is very low
(typically>10.sup.12 .OMEGA.). When the device is in the
on-state (E.sub.G.noteq.0), a sharp increase in conductance is
observed (<10.sup.6 .OMEGA.), and the output current flow (in
saturation) between the source and the drain (I.sub.DS) is defined
by:
I DS = W 2 L .mu. C i [ V G - V T ] 2 ( Eq . 1 ) ##EQU00001##
where W is the width of the channel, L is the length of the
channel, .mu. is the semiconductor charge carrier mobility, C.sub.i
is the dielectric capacitance per unit area, V.sub.G is the
source-gate voltage, and V.sub.T is the threshold voltage. It can
be seen that for a given device geometry and semiconductor,
equivalent current gains (I.sub.DS) can be achieved at lower
operating biases by increasing C.sub.i.
[0007] Because
C i = 0 k d , ( Eq . 2 ) ##EQU00002##
where k is the dielectric constant, .epsilon..sub.0 is the vacuum
permittivity, and d is the thickness of the dielectric material,
C.sub.i is increased when k increases and/or d decreases. However,
k of most insulating polymers is low (.about.3-6). Additionally,
most insulating polymers need to be quite thick (usually .about.1
.mu.m) to avoid considerable current leakage through the gate
electrode.
[0008] To reduce current leakage for thinner films, polymeric
dielectrics such as crosslinked melamine/Cr.sup.6+
salts-polyvinylphenol (PVP) and crosslinked benzocyclobutene (BCB)
have been introduced. However, these polymer films require high
annealing temperatures and C.sub.i values are typically <<20
nF cm.sup.-2.
[0009] Furthermore, the choice of dielectric material can affect
.mu., which is an important device parameter. In particular, the
gate dielectric permits the creation of the gate field and the
establishment of the two-dimensional channel charge sheet. Upon
application of a source-drain bias, the accumulated charges move
very close to the dielectric-semiconductor interface from the
source electrode to the drain electrode. Therefore, the nature of
the dielectric-semiconductor interface, more particularly, the
dielectric surface morphology prior to the deposition of the
semiconductor material, can greatly affect how these charges move
within the semiconductor, i.e., the carrier mobility. Moreover, the
surface morphology of the dielectric material and variations in its
surface energies (e.g., surface treatment via self-assembled
monolayers) have been shown to modify the growth, morphology, and
microstructure of the vapor/solution-deposited semiconductor, each
of these being a factor affecting .mu. and I.sub.on:I.sub.off, the
latter being the drain-source current ratio between the "on" and
"off" states, another important device parameter. The properties of
the dielectric material can also affect the density of state
distribution for both amorphous and single-crystal
semiconductors.
[0010] It is also desirable to have dielectric materials that
adhere well to diverse substrates, i.e., the dielectric materials
do not delaminate easily, to ensure device integrity under
operating conditions, and to have dielectric materials that are
hydrophobic such that device performance is not affected by
humidity.
[0011] Accordingly, there is a desire in the art for polymeric
dielectric materials that can exhibit relatively high capacitance
and low current leakage, that can be prepared from commercially
available polymer/molecular precursors via solution processes at
low temperatures and atmospheric pressures, that can be compatible
with diverse gate materials and semiconductors, that can adhere
well to various substrates, and that can be resistant to the
absorption of ambient moisture.
SUMMARY
[0012] In light of the foregoing, the present teachings provide
dielectric materials and related precursor compositions and/or
associated devices that address various deficiencies and
shortcomings of the prior art, including some of those outlined
above.
[0013] In one aspect, the present teachings provide a precursor
composition that includes in solution at least one of (i) a
polymeric component and a crosslinker component, and (ii) a
polymeric crosslinker that includes a pendant group having a
thermally curable crosslinking moiety. The composition is adapted
to form a dielectric material after crosslinking (e.g., by
thermally curing) the precursor composition. The crosslinker
component can include a thermally curable crosslinker having the
formula:
(X).sub.3-m(Y).sub.mSi-Z-Si(Y).sub.m(X).sub.3-m,
and the polymeric crosslinker can include a thermally curable
crosslinking moiety having the formula:
-Q-Si(Y).sub.m(X).sub.3-m,
wherein Q, X, Y, Z, and m are as defined herein.
[0014] For example, thermally curable crosslinkers of the present
teachings can include
[CH.sub.3C(O)O].sub.3Si--(CH.sub.2).sub.3--O--(CH.sub.2).sub.2--O(CH.sub.-
2).sub.3--Si[CH.sub.3C(O)O].sub.3,
Cl.sub.3Si--(CH.sub.2).sub.3--O--(CH.sub.2).sub.2--O--(CH.sub.2).sub.3--S-
iCl.sub.3,
(CH.sub.3O).sub.3Si--(CH.sub.2).sub.2-phenyl-(CH.sub.2).sub.2---
Si(OCH.sub.3).sub.3,
Cl.sub.3Si--(CH.sub.2).sub.2--(CF.sub.2).sub.2--(CH.sub.2).sub.2--SiCl.su-
b.3, and
[CH.sub.3C(O)O].sub.3Si--(CH.sub.2).sub.2(CF.sub.2).sub.2(CH.sub.-
2).sub.2--Si[CH.sub.3C(O)O].sub.3.
[0015] An exemplary polymeric crosslinker having a thermally
curable crosslinking moiety according to the present teachings can
have the formula:
##STR00001##
wherein R.sup.6, R.sup.7, R.sup.8, Q, X, Y, and m are as defined
herein.
[0016] In certain embodiments, the precursor composition can
further include at least one of (iii) a crosslinker component
comprising a photochemically curable crosslinker and (iv) a
photochemically curable polymeric crosslinker. Such photochemically
curable crosslinkers typically include an alkenyl group (i.e., one
or more double bonds), for example, an allyl group, a phenylethenyl
group, or a cinnamoyl group.
[0017] In some embodiments, the polymeric component of the
composition can include a polymer selected from a polyalkylene, a
substituted polyalkylene, a siloxane polymer and a copolymer
thereof. Examples of polyalkylenes and substituted polyalkylenes
include, but are not limited to, polyethylenes, polypropylenes,
polyvinylalcohols, polystyrenes, ring-functionalized derivatives of
polystyrenes (e.g. polyvinylphenol (PVP)), and polyacrylates (e.g.,
polymethylmethacrylates (PMMA)).
[0018] At least one of the polymeric component and the crosslinker
component typically is dissolved in an anhydrous solvent. The
anhydrous solvent can be selected from ethyl acetate, dioxane,
bis(2-methoxyethyl) ether (diglyme), tetrahydrofuran, toluene,
xylene, various alcohols including methanol and ethanol, and
various ketones including acetone, cyclopentanone (CP),
methylethylketone, and the like.
[0019] In some embodiments, the precursor composition can further
include a metal oxide component, for example, to increase the
dielectric constant (k) of a dielectric formed from the
composition. The metal oxide component can be in particulate form
and can be blended, mixed and/or incorporated in the composition.
The metal oxide component can include a metal component selected
from a Group I metal, a Group II metal, a Group III metal, a Group
IV metal, a transition metal, and combinations thereof.
[0020] In another aspect, the present teachings provide dielectric
materials that include a crosslinked polymeric material that is a
thermally cured product and/or a photochemically cured product of
any of the precursor compositions described above. Also embraced
with the scope of the present teachings are various compositions,
composites (e.g., structures) and articles of manufacture (e.g.,
electronic devices) that incorporate the dielectric materials
disclosed herein. Examples of electronic devices that can
incorporate one or more dielectric materials of the present
teachings include, but are not limited to, organic thin film
transistors (OTFTs) (e.g., organic field effect transistors
(OFETs)) and capacitors. In addition to a dielectric component,
these devices can include, for example, a substrate component, a
semiconductor component, and/or one or more metallic contact
components.
[0021] In a further aspect, the present teachings provide various
methods for preparing a dielectric material. The methods can
include applying a precursor composition of the present teachings
onto a substrate, and thermally curing the precursor composition
(i.e., the coated substrate) to provide a dielectric material. The
applying step can be performed by, for example, spin-coating,
printing, spraying, or casting. In some embodiments, the curing
step can include heating at a temperature within a range of about
70.degree. C. to about 150.degree. C. in a high humidity
atmosphere. In embodiments in which the precursor composition
includes a photochemically curable crosslinker, the curing step can
include exposing the precursor composition (i.e., the coated
substrate) to ultraviolet light, e.g., by irradiation at a
wavelength of about 245 nm. For a dielectric precursor composition
that includes both a thermally curable crosslinker and a
photochemically curable crosslinker, the curing step can include
first heating at a temperature within a range of about 70.degree.
C. and about 150.degree. C. in a high humidity atmosphere, followed
by irradiation with a wavelength of about 245 nm, or vice versa. In
some embodiments, the crosslinking reaction can be achieved by
electron beam irradiation.
[0022] The foregoing as well as other features and advantages of
the present teachings, will be more fully understood from the
following figures, description, and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] It should be understood that the drawings described below
are for illustration purposes only and are not necessarily to
scale. The drawings are not intended to limit the scope of the
present teachings in any way.
[0024] FIG. 1 is a schematic representation of different
crosslinking strategies that can be employed using dielectric
precursor compositions of the present teachings.
[0025] FIG. 2 is a schematic representation of a
crosslinking-patterning process, illustrating in order: depositing
a dielectric precursor composition onto a substrate,
photochemically curing the coated substrate, washing the
dielectric/substrate composite, and heating the dielectric material
to induce further crosslinking/patterning.
[0026] FIG. 3 shows representative leakage current plots for
several embodiments of dielectric films of the present teachings.
Specifically, the films have a thickness between about 40 nm and 50
nm and were fabricated on doped silicon (Si) substrates using the
polymer-crosslinker ratios listed in Table 1.
[0027] FIG. 4 shows representative leakage current plots for the
same embodiments of dielectric films as FIG. 3, except that they
were fabricated on aluminium-polyethylene naphthalate (Al-PEN) and
indium tin oxide (ITO)-glass substrates.
[0028] FIG. 5 shows current-voltage (I-V) plots for several
embodiments of dielectric films of the present teachings fabricated
in capacitor structures.
[0029] FIG. 6 shows the transfer plots of several embodiments of
OFETs of the present teachings (the present dielectric material on
a silicon substrate (CPB-Si) and the present dielectric material on
an aluminum substrate (CPB-Al)) and a comparative OFET having
SiO.sub.2 as the dielectric material.
[0030] FIG. 7 shows leakage current density vs voltage (J-V) plots
(A) and leakage current density vs electric field (J-E) plots for
thin dielectric films according to the present teachings prepared
from precursor compositions including PVP and one of the following
crosslinkers: C.sub.6Cl, C.sub.6OAc, EGOAc, and
C.sub.6NMe.sub.2.
[0031] FIG. 8 shows the transfer plots of several embodiments of
OFETs of the present teachings. The OFETs were fabricated with an
ultra-thin dielectric film prepared from a precursor composition
that includes PVP and one of the following crosslinkers: C.sub.6Cl,
C.sub.6OAc, EGOAc, and C.sub.6NMe.sub.2, and either a pentacene
semiconductor layer (A) or a DFHCO-4T semiconductor layer (B).
[0032] FIG. 9 is a plot of leakage current density versus applied
bias for two embodiments of dielectric precursor compositions of
the present teachings.
[0033] FIG. 10 shows a transfer plot (A) and an output plot (B) for
a pentacene-OFET that includes a dielectric material of the present
teachings.
[0034] FIG. 11 shows output plots for an OFET including a
dielectric layer of the present teachings and an organic
semiconductor layer prepared with N,N'-bis(n-octyl)-(1,7 and
1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN.sub.2)
(A), and an OFET including a dielectric layer of the present
teachings and an organic semiconductor layer prepared with
bis(n-hexylphenyl)dithiophene (DH-PTTP) (B).
[0035] FIG. 12 shows wide angle x-ray diffraction (WAXRD) spectra
of composites including a 50 nm-thick semiconductor film
(pentancene, PDI-8CN.sub.2, and DH-6T) vapor-deposited on a
dielectric film of the present teachings.
[0036] FIG. 13 provides the transfer plots of two pentacene OFETs
including gate dielectrics of the present teachings.
DETAILED DESCRIPTION
[0037] The present teachings relate to dielectric materials and
precursor compositions for preparing the same, as well as to
electronic devices that include such dielectric materials.
[0038] The present teachings provide crosslinked polymeric
dielectric materials that can exhibit good insulating properties
(e.g., with leakage currents in the order of
.about.10.sup.-6-10.sup.-7 A/cm.sup.2) and can be fabricated using
low-temperature solution processes (e.g., spin-coating and
printing). Solution-processed thin films (<300 nm) of the
present dielectric materials can exhibit high mechanical
flexibility and have very smooth surfaces. The dielectric materials
disclosed herein were found to adhere well to different substrates
(e.g., gate materials such as doped silicon, aluminum, and indium
tin oxide) and can be compatible with a wide range of p-type and
n-type organic and inorganic semiconductors, making them attractive
materials for fabricating various organic electronic devices. For
example, organic thin film transistors (OTFTs) incorporating
dielectric materials of the present teachings can operate at low
biases, hence minimizing power consumption, particularly when the
dielectric materials of the present teachings are in the form of
ultra-thin films (<about 50 nm), which can exhibit capacitance
as high as .about.300 nF cm.sup.-2.
[0039] More specifically, the present teachings provide dielectric
materials that include crosslinked polymeric matrices in which
polymeric chains can be either covalently crosslinked by one or
more thermally curable and/or photochemically curable crosslinkers,
or embedded within or otherwise incorporated (e.g., mixed or
blended) in a crosslinked matrix formed by the thermally curable
and/or photochemically curable crosslinkers. These crosslinked
polymeric matrices can be structurally robust and can exhibit good
insulating properties. The present teachings also provide precursor
compositions that can enable high-throughput fabrication (e.g., via
fast and quantitative reactions under mild conditions) of such
dielectric materials.
[0040] Throughout the description, where compositions are described
as having, including, or comprising specific components, or where
processes are described as having, including, or comprising
specific process steps, it is contemplated that compositions of the
present teachings also consist essentially of, or consist of, the
recited components, and that the processes of the present teachings
also consist essentially of, or consist of, the recited processing
steps.
[0041] In the application, where an element or component is said to
be included in and/or selected from a list of recited elements or
components, it should be understood that the element or component
can be any one of the recited elements or components and can be
selected from a group consisting of two or more of the recited
elements or components. Further, it should be understood that
elements and/or features of a composition, an apparatus, or a
method described herein can be combined in a variety of ways
without departing from the spirit and scope of the present
teachings, whether explicit or implicit herein.
[0042] The use of the terms "include," "includes", "including,"
"have," "has," or "having" should be generally understood as
open-ended and non-limiting unless specifically stated
otherwise.
[0043] The use of the singular herein includes the plural (and vice
versa) unless specifically stated otherwise. In addition, where the
use of the term "about" is before a quantitative value, the present
teachings also include the specific quantitative value itself,
unless specifically stated otherwise.
[0044] It should be understood that the order of steps or order for
performing certain actions is immaterial so long as the present
teachings remain operable. Moreover, two or more steps or actions
may be conducted simultaneously.
[0045] As used herein, "polymer" or "polymeric compound" refers to
a molecule including at least three or more repeating units
connected by covalent chemical bonds. The polymer or polymeric
compound can have only one type of repeating unit as well as two or
more types of different repeating units. In the latter case, the
term "copolymer" or "copolymeric compound" can be used herein
instead, especially when the polymer includes chemically
significantly different repeating units. Unless specified
otherwise, the assembly of the repeating units in the copolymer can
be head-to-tail, head-to-head, or tail-to-tail. In addition, unless
specified otherwise, the copolymer can be a random copolymer, an
alternating copolymer, or a block copolymer. The polymer can
include one or more pendant groups. As used herein, a "pendant
group" refers to a moiety that is substituted on the backbone of a
polymer.
[0046] As used herein, "solution-processable" refers to compounds,
materials, or compositions that can be used in various
solution-phase processes including spin-coating, printing (e.g.,
inkjet printing), spray coating, electrospray coating, drop
casting, dip coating, and blade coating.
[0047] As used herein, "halo" or "halogen" refers to fluoro,
chloro, bromo, and iodo.
[0048] As used herein, "alkoxy" refers to --O-alkyl group. Examples
of alkoxy groups include, but are not limited to, methoxy, ethoxy,
propoxy (e.g., n-propoxy and isopropoxy), t-butoxy groups, and the
like.
[0049] As used herein, "alkyl" refers to a straight-chain or
branched saturated hydrocarbon group. Examples of alkyl groups
include methyl (Me), ethyl (Et), propyl (e.g., n-propyl and
isopropyl), butyl (e.g., n-butyl, isobutyl, s-butyl, t-butyl),
pentyl groups (e.g., n-pentyl, isopentyl, neopentyl), and the like.
A lower alkyl group typically has up to 4 carbon atoms. Examples of
lower alkyl groups include methyl, ethyl, propyl (e.g., n-propyl
and isopropyl), and butyl groups (e.g., n-butyl, isobutyl, s-butyl,
t-butyl).
[0050] As used herein, "haloalkyl" refers to an alkyl group having
one or more halogen substituents. Examples of haloalkyl groups
include CF.sub.3, C.sub.2F.sub.5, CHF.sub.2, CH.sub.2F, CCl.sub.3,
CHCl.sub.2, CH.sub.2Cl, C.sub.2Cl.sub.5, and the like. Perhaloalkyl
groups, i.e., alkyl groups wherein all of the hydrogen atoms are
replaced with halogen atoms (e.g., CF.sub.3 and C.sub.2F.sub.5),
are included within the definition of "haloalkyl." For example, a
C.sub.1-20 haloalkyl group can have the formula
--C.sub.aX.sub.2a+1-- or --C.sub.aH.sub.2a+1-bX.sub.b--, wherein X
is F, Cl, Br, or I, a is an integer in the range of 1 to 20, and b
is an integer in the range of 0 to 40, provided that
b.ltoreq.2a+1.
[0051] As used herein, "arylalkyl" refers to an -alkyl-aryl group,
wherein the arylalkyl group is covalently linked to the defined
chemical structure via the alkyl group. An arylalkyl group is
within the definition of an -L-C.sub.6-14 aryl group, wherein L is
as defined herein. An example of an arylalkyl group is a benzyl
group (--CH.sub.2--C.sub.6H.sub.5). An arylalkyl group can be
optionally substituted, i.e., the aryl group and/or the alkyl group
can be substituted as disclosed herein.
[0052] As used herein, "alkenyl" refers to a straight-chain or
branched alkyl group having one or more carbon-carbon double bonds.
Examples of alkenyl groups include, but are not limited to,
ethenyl, propenyl, butenyl, pentenyl, hexenyl, butadienyl,
pentadienyl, hexadienyl groups, and the like. The one or more
carbon-carbon double bonds can be internal (such as in 2-butene) or
terminal (such as in 1-butene).
[0053] As used herein, "cycloalkyl" refers to a non-aromatic
carbocyclic group including cyclized alkyl, alkenyl, and alkynyl
groups. A cycloalkyl group can be monocyclic (e.g., cyclohexyl) or
polycyclic (e.g., containing fused, bridged, and/or spiro ring
systems), wherein the carbon atoms are located inside or outside of
the ring system. Any suitable ring position of the cycloalkyl group
can be covalently linked to the defined chemical structure.
Examples of cycloalkyl groups include, but are not limited to,
cyclopropyl, cyclopropylmethyl, cyclobutyl, cyclopentyl,
cyclohexyl, cyclohexylmethyl, cyclohexylethyl, cycloheptyl,
cyclopentenyl, cyclohexenyl, cyclohexadienyl, cycloheptatrienyl,
norbornyl, norpinyl, norcaryl, adamantyl, and spiro[4.5]decanyl
groups, as well as their homologs, isomers, and the like. In some
embodiments, cycloalkyl groups can be substituted as disclosed
herein.
[0054] As used herein, "heteroatom" refers to an atom of any
element other than carbon or hydrogen and includes, for example,
nitrogen, oxygen, sulfur, phosphorus, and selenium.
[0055] As used herein, "cycloheteroalkyl" refers to a non-aromatic
cycloalkyl group that contains at least one ring heteroatom
selected from O, N and S, and optionally contains one or more
double or triple bonds. One or more N or S atoms in a
cycloheteroalkyl ring may be oxidized (e.g., morpholine N-oxide,
thiomorpholine S-oxide, thiomorpholine S,S-dioxide). In some
embodiments, nitrogen atoms of cycloheteroalkyl groups can bear a
substituent, for example, a hydrogen atom, an alkyl group, or other
substituents as described herein. Cycloheteroalkyl groups can also
contain one or more oxo groups, such as piperidone, oxazolidinone,
pyrimidine-2,4(1H,3H)-dione, pyridin-2(1H)-one, and the like.
Examples of cycloheteroalkyl groups include, among others,
morpholine, thiomorpholine, pyran, imidazolidine, imidazoline,
oxazolidine, pyrazolidine, pyrazoline, pyrrolidine, pyrroline,
tetrahydrofuran, tetrahydrothiophene, piperidine, piperazine, and
the like. In some embodiments, cycloheteroalkyl groups can be
substituted as disclosed herein.
[0056] As used herein, "aryl" refers to an aromatic monocyclic
hydrocarbon ring system or a polycyclic ring system in which two or
more aromatic hydrocarbon rings are fused (i.e., having a bond in
common with) together or at least one aromatic monocyclic
hydrocarbon ring is fused to one or more cycloalkyl and/or
cycloheteroalkyl rings. An aryl group can have from 6 to 14 carbon
atoms in its ring system, which can include multiple fused rings.
In some embodiments, a polycyclic aryl group can have from 8 to 14
carbon atoms. Any suitable ring position of the aryl group can be
covalently linked to the defined chemical structure. Examples of
aryl groups having only aromatic carbocyclic ring(s) include, but
are not limited to, phenyl, 1-naphthyl (bicyclic), 2-naphthyl
(bicyclic), anthracenyl (tricyclic), phenanthrenyl (tricyclic) and
like groups. Examples of polycyclic ring systems in which at least
one aromatic carbocyclic ring is fused to one or more cycloalkyl
and/or cycloheteroalkyl rings include, among others, benzo
derivatives of cyclopentane (i.e., an indanyl group, which is a
5,6-bicyclic cycloalkyl/aromatic ring system), cyclohexane (i.e., a
tetrahydronaphthyl group, which is a 6,6-bicyclic
cycloalkyl/aromatic ring system), imidazoline (i.e., a
benzimidazolinyl group, which is a 5,6-bicyclic
cycloheteroalkyl/aromatic ring system), and pyran (i.e., a
chromenyl group, which is a 6,6-bicyclic cycloheteroalkyl/aromatic
ring system). Other examples of aryl groups include, but are not
limited to, benzodioxanyl, benzodioxolyl, chromanyl, indolinyl
groups, and the like. In some embodiments, aryl groups can be
substituted as disclosed herein.
[0057] As used herein, "heteroaryl" refers to an aromatic
monocyclic ring system containing at least 1 ring heteroatom
selected from oxygen (O), nitrogen (N) and sulfur (S) or a
polycyclic ring system where at least one of the rings present in
the ring system is aromatic and contains at least 1 ring
heteroatom. Polycyclic heteroaryl groups include two or more
heteroaryl rings fused together and monocyclic heteroaryl rings
fused to one or more aromatic carbocyclic rings, non-aromatic
carbocyclic rings, and/or non-aromatic cycloheteroalkyl rings. A
heteroaryl group, as a whole, can have, for example, from 5 to 14
ring atoms and contain 1-5 ring heteroatoms. The heteroaryl group
can be attached to the defined chemical structure at any heteroatom
or carbon atom that results in a stable structure. Generally,
heteroaryl rings do not contain O--O, S--S, or S--O bonds. However,
one or more N or S atoms in a heteroaryl group can be oxidized
(e.g., pyridine N-oxide, thiophene S-oxide, thiophene S,S-dioxide).
Examples of heteroaryl groups include, for example, the 5-membered
monocyclic and 5-6 bicyclic ring systems shown below:
##STR00002##
where T is O, S, NH, N-alkyl, N-aryl, or N-(arylalkyl) (e.g.,
N-benzyl). Examples of such heteroaryl rings include, but are not
limited to, pyrrole, furan, thiophene, pyridine, pyrimidine,
pyridazine, pyrazine, triazole, tetrazole, pyrazole, imidazole,
isothiazole, thiazole, thiadiazole, isoxazole, oxazole, oxadiazole,
indole, isoindole, benzofuran, benzothiophene, quinoline,
2-methylquinoline, isoquinoline, quinoxaline, quinazoline,
benzotriazole, benzimidazole, benzothiazole, benzisothiazole,
benzisoxazole, benzoxadiazole, benzoxazole, cinnoline, 1H-indazole,
2H-indazole, indolizine, isobenzofuran, naphthyridine, phthalazine,
pteridine, purine, oxazolopyridine, thiazolopyridine,
imidazopyridine, furopyridine, thienopyridine, pyridopyrimidine,
pyridopyrazine, pyridopyridazine, thienothiazole, thienoxazole, and
thienoimidazole. Further examples of heteroaryl groups include, but
are not limited to, 4,5,6,7-tetrahydroindole, tetrahydroquinoline,
benzothienopyridine, benzofuropyridine, and the like. In some
embodiments, heteroaryl groups can be substituted as disclosed
herein.
[0058] At various places in the present specification, substituents
of compounds are disclosed in groups or in ranges. It is
specifically intended that the description include each and every
individual subcombination of the members of such groups and ranges.
For example, the term "C.sub.1-6 alkyl" is specifically intended to
individually disclose C.sub.1, C.sub.2, C.sub.3, C.sub.4, C.sub.5,
C.sub.6, C.sub.1-C.sub.6, C.sub.1-C.sub.5, C.sub.1-C.sub.4,
C.sub.1-C.sub.3, C.sub.1-C.sub.2, C.sub.2-C.sub.6, C.sub.2-C.sub.5,
C.sub.2-C.sub.4, C.sub.2-C.sub.3, C.sub.3-C.sub.6, C.sub.3-C.sub.5,
C.sub.3-C.sub.4, C.sub.4-C.sub.6, C.sub.4-C.sub.5, and
C.sub.5-C.sub.6 alkyl. By way of other examples, an integer in the
range of 0 to 40 is specifically intended to individually disclose
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,
19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
36, 37, 38, 39, and 40, and an integer in the range of 1 to 20 is
specifically intended to individually disclose 1, 2, 3, 4, 5, 6, 7,
8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. Additional
examples include that the phrase "optionally substituted with 1-5
substituents" is specifically intended to individually disclose a
chemical group that can include 0, 1, 2, 3, 4, 5, 0-5, 0-4, 0-3,
0-2, 0-1, 1-5, 1-4, 1-3, 1-2, 2-5, 2-4, 2-3, 3-5, 3-4, and 4-5
substituents.
[0059] Throughout the specification, structures may or may not be
presented with chemical names. Where any question arises as to
nomenclature, the structure prevails.
[0060] The present teachings provide precursor compositions
including one or more polymers (i.e., a polymeric component) and
one or more crosslinking moieties or crosslinkers (i.e., a
crosslinker component) which, upon crosslinking (e.g., by thermally
curing or photochemically curing), can provide crosslinked
polymeric materials that are suitable for use as dielectric
materials. In some embodiments, the precursor composition can
include the polymeric component and the crosslinker component as
separate chemical moieties. For example, the crosslinker component
can include one or more crosslinkers that are small molecule
compounds having one or more crosslinking groups. In other
embodiments, the polymeric component and the crosslinker component
can be chemically combined in the form of a polymeric crosslinker,
specifically, a polymer having one or more pendant crosslinking
groups on its backbone. The precursor composition can include one
or more solvents in which at least one of the polymeric component
and the crosslinker component is substantially soluble.
[0061] In some embodiments, the crosslinker component of the
precursor composition can include thermally curable crosslinkers
that include two or more silyl groups. These silyl groups can
include one or more (e.g., one, two, or three) hydrolyzable
moieties such as halo groups, amino groups, alkoxy groups, and
carboxylate groups that can react with OH groups and induce
crosslinking. For example, the thermally curable crosslinkers can
have the formula:
(X).sub.3-m(Y).sub.mSi-Z-Si(Y).sub.m(X).sub.3-m,
and (ii) a polymeric crosslinker comprising a pendant group, the
pendant group comprising a thermally curable crosslinking moiety
having the formula:
-Q-Si(Y).sub.m(X).sub.3-m,
[0062] wherein: [0063] m, at each occurrence, is independently
selected from 0, 1, and 2; [0064] X, at each occurrence, is
independently selected from a halogen, --NR.sup.1R.sup.2,
--OR.sup.3, and --OC(O)R.sup.3; [0065] Y, at each occurrence, is
independently selected from H, a C.sub.1-6 alkyl group, and a
C.sub.1-6 haloalkyl group; [0066] Z is Q-W-Q; and [0067] Q, at each
occurrence, is independently selected from -L-, --O--, --O-L-,
-L-O--, --NR.sup.4--, --NR.sup.4-L-, -L-NR.sup.4--, and a covalent
bond; [0068] wherein: [0069]
[0070] L, at each occurrence, is independently a divalent
C.sub.1-10 alkyl group or a divalent C.sub.1-10 haloalkyl group,
each of which is optionally substituted with 1-4 R.sup.4 groups;
[0071] W is selected from --SiXX--, --SiXY--, --SiYY--,
--SiXX--O--, --O--SiXX--, --SiXY--O--, --O--SiXY--, --SiYY--O--,
--O--SiYY--,
--O--{[(CR.sup.4.sub.2).sub.t--O].sub.p--[(CR.sup.5.sub.2).sub.t--O].sub.-
q}--, a divalent C.sub.6-14 aryl group, a divalent 5-14 membered
heteroaryl group, and a covalent bond, wherein each of the divalent
C.sub.6-14 aryl group and the divalent 5-14 membered heteroaryl
group is optionally substituted with 1-4 R.sup.4 groups; [0072]
R.sup.1 and R.sup.2 are independently selected from H, a C.sub.1-6
alkyl group, a C.sub.6-14 aryl group, a 5-14 membered heteroaryl
group, a --C.sub.1-6 alkyl-C.sub.6-14 aryl group, and a --C.sub.1-6
alkyl-5-14 membered heteroaryl group; [0073] R.sup.3 is selected
from H, a C.sub.1-6 alkyl group, a C.sub.1-6 haloalkyl group, a
C.sub.2-6 alkenyl group, a C.sub.2-6 alkynyl group, a C.sub.6-14
aryl group, a 5-14 membered heteroaryl group, a --C.sub.1-6
alkyl-C.sub.6-14 aryl group, and a --C.sub.1-6 alkyl-5-14 membered
heteroaryl group; [0074] R.sup.4 and R.sup.5, at each occurrence,
are independently selected from H, a halogen, a C.sub.1-6 alkyl
group, a C.sub.1-6 haloalkyl group, a C.sub.6-14 aryl group, a 5-14
membered heteroaryl group, a --C.sub.1-6 alkyl-C.sub.6-14 aryl
group, a --C.sub.1-6 alkyl-5-14 membered heteroaryl group, and
-Q-Si(Y).sub.m(X).sub.3-m; [0075] t, at each occurrence, is
independently 1, 2, 3, 4, 5 or 6; [0076] p is 0, 1, 2, 3, 4, 5, 6,
7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19; and [0077] q is
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19
or 20, provided that p+q.ltoreq.20.
[0078] In certain embodiments, X, at each occurrence, can be
independently selected from Cl, OCH.sub.3, OCH.sub.2CH.sub.3,
--N(CH.sub.3).sub.2--, --N(CH.sub.2CH.sub.3).sub.2--,
--OC(O)CH.sub.3, and --OC(O)CH.sub.2CH.sub.3; and Y, at each
occurrence, can be independently selected from H, CF.sub.3, a
methyl group, and an ethyl group. For example, the thermally
curable crosslinkers can be .alpha.,.omega.-bisfunctionalized with
SiX.sub.3 groups, wherein X is selected from Cl, OCH.sub.3,
OCH.sub.2CH.sub.3, --N(CH.sub.3).sub.2--,
--N(CH.sub.2CH.sub.3).sub.2--, --OC(O)CH.sub.3, and
--OC(O)CH.sub.2CH.sub.3.
[0079] It should be understood that the linker Z, as defined above,
can exclude certain combinations of Q-W-Q. For example, it should
be understood that Z cannot be --O--, a divalent C.sub.1-20 alkyl
group, or a covalent bond.
[0080] In some embodiments, Z can be a divalent linker that can be
symmetrical or asymmetrical. In certain embodiments, Q, at each
occurrence, can be independently selected from --O--, a divalent
C.sub.1-10 alkyl group (e.g., --(CH.sub.2).sub.t--), a divalent
C.sub.1-10 haloalkyl group (e.g., --(CF.sub.2).sub.t--), and a
covalent bond; and W can be selected from
--O--[(CR.sup.4.sub.2).sub.t--O].sub.p--[(CR.sup.5.sub.2).sub.t--O].sub.q-
-- (e.g., --O--[(CH.sub.2).sub.2--O].sub.t-- and
--O--[(CF.sub.2).sub.2--O].sub.t--), a divalent phenyl group, and a
covalent bond, wherein R.sup.4 and R.sup.5 can be independently H
or F, and p, q, and t are as defined herein. In particular
embodiments, Z can be an alkylene glycol linker. For example, Z can
be Q-W-Q, wherein Q, at each occurrence, is independently a
divalent C.sub.1-6 alkyl group or a covalent bond, and W is
--O--{[(CH.sub.2).sub.3--O].sub.p--[(CH.sub.2).sub.2--O].sub.q}--,
wherein p is 0, 1, 2, 3, 4, 5 or 6, and q is 1, 2, 3, 4, 5 or
6.
[0081] Crosslinkers according to the formula given above include,
but are not limited to,
##STR00003##
[0082] In certain embodiments, Z can include one or more
-Q-Si(Y).sub.m(X).sub.3-m substituents to provide additional groups
for crosslinking. For example, Z can be Q-W-Q, wherein Q, at each
occurrence, can be independently a divalent C.sub.1-10 alkyl group
or a divalent C.sub.1-10 haloalkyl group, and W can be selected
from
--O--[(CR.sup.4.sub.2).sub.t--O].sub.p--[(CR.sup.5.sub.2).sub.t--O].sub.q-
-- and a divalent phenyl group, wherein the divalent C.sub.1-10
alkyl group, the divalent C.sub.1-10 haloalkyl group, and the
divalent phenyl group can be substituted with 1-4
-Q-Si(Y).sub.m(X).sub.3-m groups (thereby creating a higher order
valency group, e.g., a trivalent or tetravalent phenyl group),
R.sup.4 and R.sup.5 can be independently H, F, or
-Q-Si(Y).sub.m(X).sub.3-m, and Q, X, Y, m, p, q, and t are as
defined herein. A non-limiting example of these embodiments is a
crosslinker having the formula:
##STR00004##
[0083] As aforementioned, the precursor composition can include a
polymeric crosslinker, i.e., a polymer having one or more
crosslinking pendant groups. For example, the pendant group can
include a thermally curable crosslinking moiety having the
formula:
-Q-Si(Y).sub.m(X).sub.3-m,
wherein Q, X, Y, and m are as defined herein. In certain
embodiments, the thermally curable polymeric crosslinker can have
the formula:
##STR00005##
wherein: [0084] R.sup.6, at each occurrence, is independently H, a
halogen, or a C.sub.1-6 alkyl group; [0085] R.sup.7 is selected
from H, OH, a halogen, C(O)O--R.sup.3, a C.sub.1-6 alkyl group, a
C.sub.1-6 haloalkyl group, a C.sub.6-14 aryl group, a 5-14 membered
heteroaryl group, a 3-14 membered cycloheteroalkyl group, a
--C.sub.1-6 alkyl-C.sub.6-14 aryl group, a --C.sub.1-6 alkyl-5-14
membered heteroaryl group, and a --C.sub.1-6 alkyl-3-14 membered
cycloheteroalkyl group, wherein each of the C.sub.6-14 aryl groups,
the 5-14 membered heteroaryl groups, and the 3-14 membered
cycloheteroalkyl groups is optionally substituted with 1-5
substituents independently selected from a halogen, an oxo group,
OH, CN, NO.sub.2, C(O)O--C.sub.1-6 alkyl, a C.sub.1-6 alkyl group,
a C.sub.1-6 alkoxy group, and a C.sub.1-6 haloalkyl group; [0086]
R.sup.8 is selected from --O--, --C(O)O--, a divalent C.sub.1-6
alkyl group, and a divalent phenyl group; [0087] x and y are
independently a real number, wherein 0<x<1, 0<y<1, and
x+y=1; and [0088] Q, X, Y and m are as defined herein.
[0089] In some embodiments of the polymeric crosslinker having the
formula described above, R.sup.6, at each occurrence, can be H or a
methyl group; R.sup.7 can be selected from H, OH, a methyl group,
C(O)O--C.sub.1-6 alkyl, and a phenyl group optionally substituted
with OH or --O--C.sub.1-6 alkyl; R.sup.8 can be selected from
--O--, --C(O)O--, a divalent C.sub.1-4 alkyl group, and a divalent
phenyl group; and Q can be selected from -L-, --O-L-, and a
covalent bond, wherein L is as defined herein. A non-limiting
example of such a thermally curable polymeric crosslinker is
##STR00006##
wherein Ac is an acetyl group (i.e., CH.sub.3C(O)--), and x and y
are as defined herein.
[0090] Without wishing to be bound to any particular theory,
crosslinking reactions with these thermally curable crosslinkers
typically rely on the fast and quantitative coupling reactions of
the functional groups (e.g., the one or more halo groups, alkoxy
groups, amino groups, and carboxylate groups) on the silicon with
water and/or the hydroxyl group(s) of a OH-functionalized molecule
or polymer to produce a robust siloxane network.
[0091] To enable efficient patterning and enhance the robustness of
the polymeric network even further, one or more photochemically
curable crosslinkers can be utilized alone or in conjunction with
one or more thermally curable crosslinkers. Such photochemically
curable crosslinkers are well known in the art and typically
include an alkenyl group (i.e., one or more double bonds), for
example, an allyl group, a phenylethenyl group, or a cinnamoyl
group.
[0092] In some embodiments, these photochemically curable
crosslinkers are polymers that include one or more photochemically
curable crosslinking groups. For example, a photochemically curable
polymeric crosslinker can have the formula:
##STR00007##
wherein R.sup.6, R.sup.7, R.sup.8, Q, x and y are as defined
herein.
[0093] Without wishing to be bound to any particular theory, the
crosslinking chemistry involving these photochemically curable
crosslinkers can consist of a 2+2 photo-stimulated cycloaddition
that provides stable cyclobutane moieties. The crosslinking
chemistry can also involve free radical additions.
[0094] The polymeric component of the precursor compositions
described above can include various electrically non-conducting
polymers, including those that have been used as dielectric
materials. Examples include, but are not limited to, polyalkylenes,
substituted polyalkylenes, siloxane polymers, and copolymers of
polyalkylenes, substituted polyalkylenes, and/or siloxane
polymers.
[0095] More specifically, polyalkylenes and substituted
polyalkylenes can include, but are not limited to, polyethylenes
(PE), polypropylenes (PP), polyvinylalcohols (PVA), polystyrenes
(PS), ring-functionalized derivatives of polystyrenes (e.g.,
polyvinylphenols (PVP)), and polyacrylates (e.g.,
polymethylmethacrylates (PMMA)).
[0096] Siloxane polymers can have a repeating unit of the
formula:
##STR00008##
wherein R.sup.9, at each occurrence, is independently selected from
H, a C.sub.1-6 alkyl group, a C.sub.1-6 haloalkyl group, a
C.sub.6-14 aryl group, a 5-14 membered heteroaryl group, wherein
each of the C.sub.1-6 alkyl group, the C.sub.6-14 aryl group, the
5-14 membered heteroaryl group can be optionally substituted with
1-5 substituents independently selected from a halogen, CN, OH, and
a C.sub.1-6 haloalkyl group. For example, the siloxane polymer can
have the formula:
##STR00009##
wherein x and y are as defined herein.
[0097] The precursor compositions described above also can include
a metal oxide component. The metal oxide component typically has a
high dielectric constant (k). Therefore, the incorporation of such
a metal oxide component into a precursor composition can help
increase the dielectric constant of the resulting dielectric
material. The metal oxide component can be in particulate form and
can be blended, mixed and/or otherwise incorporated in the
composition. The metal oxide component can include a metal
component selected from a Group I metal, a Group II metal, a Group
III metal, a Group IV metal, a transition metal, and combinations
thereof.
[0098] To provide desirable processing advantages, the various
crosslinkers and polymers described above typically are somewhat
soluble, and preferably highly soluble, in various solvents (e.g.,
various anhydrous solvents). The crosslinker component and the
polymeric component can be dissolved in the same solvent or in
different solvents before combining with each other to provide the
precursor compositions of the present teachings. As used herein, a
compound can be considered soluble in a solvent when at least 1 mg
of the compound is soluble in 1 mL of the solvent. Examples of
common solvents include petroleum ethers; acetonitrile; aromatic
hydrocarbons such as benzene, toluene, xylene, and mesitylene;
ketones such as acetone, cyclopentanone (CP), methyl ethyl ketone,
and 2-butanone; ethers such as tetrahydrofuran (THF), dioxane,
bis(2-methoxyethyl)ether(diglyme), diethyl ether, di-isopropyl
ether, and t-butyl methyl ether; alcohols such as methanol,
ethanol, butanol, and isopropyl alcohol; aliphatic hydrocarbons
such as hexanes; acetates such as methyl acetate, ethyl acetate
(EtOAc), methyl formate, ethyl formate, isopropyl acetate; and
halogenated aliphatic and aromatic hydrocarbons such as
dichloromethane, chloroform, ethylene chloride, chlorobenzene,
dichlorobenzene, and trichlorobenzene.
[0099] The precursor compositions are adapted to form dielectric
materials that can exhibit a wide range of desirable properties and
characteristics. For example, the dielectric materials prepared
from the precursor compositions described above can be very thin
and pinhole-free, can have a high breakdown voltage and good
long-term stability, can exhibit high capacitance and low current
leakage, can show good adhesion to various substrates, and can be
patterned using conventional techniques without delamination. The
present dielectric materials also can demonstrate other
advantageous characteristics such as, but not limited to,
solution-processability, fabricability at low temperatures and/or
atmospheric pressures, and compatibility with a diverse range of
materials used in fabricating various electronic devices (e.g.,
thin film transistors, field-effect devices, organic light emitting
diodes (OLEDs), organic photovoltaics, photodetectors, capacitors,
and sensors).
[0100] To prepare a dielectric material in the form of a film using
the precursor compositions of the present teachings, various film
deposition techniques can be used. These techniques include casting
(e.g., drop-casting), dip coating, blade coating, spraying,
printing, and spin-coating. Spin-coating involves applying an
excess amount of a precursor composition (e.g., a solution of a
polymeric component and a crosslinker component) onto a substrate,
then rotating the substrate at high speed to spread the fluid by
centrifugal force. The thickness and the surface morphology of the
resulting dielectric film prepared by this technique is dependent
on the spin-coating rate, the concentration of the solution, as
well as the solvent used. Printing can be performed, for example,
with a rotogravure printing press, a flexo printing press, or an
inkjet printer. The thickness of the dielectric film in these cases
will similarly be dependent on the concentration of the solution,
the choice of solvent, and the number of printing repetitions. Much
of the printed electronics technology has focused on inkjet
printing, primarily because this technique offers greater control
over feature position and multilayer registration. Inkjet printing
is a noncontact process, which offers the benefits of not requiring
a preformed master (compared to contact printing techniques), as
well as digital control of ink ejection, thereby providing
drop-on-demand printing. However, contact printing techniques have
the key advantage of being well-suited for very fast roll-to-roll
processing. Exemplary contact printing techniques include
screen-printing, gravure, offset, and microcontact printing.
[0101] The thickness of the dielectric materials of the present
teachings can be controlled, and can be made as thin as 10 nm to
several microns as established by profilometry and/or atomic force
microscopy (AFM). For example, dielectric films prepared according
to the present teachings can have a thickness range from about 10
nm to about 20 nm and up to 10 .mu.m or more. Films of greater
thicknesses, if desired or required, can be obtained by 1) multiple
spin-on depositions/printing repetitions before curing, as the
dielectric materials of the present teachings can be stable to and
not adversely affected by precursor or processing solutions; or 2)
adjusting and/or increasing the polymer precursor concentration(s).
Generally, dielectric films of the present teachings are relatively
thin (e.g., less than about 300 nm), and in some embodiments,
ultra-thin (e.g., less than about 50 nm or less than about 30
nm).
[0102] Various curing or crosslinking strategies can be employed to
form a crosslinked polymeric material from the precursor
compositions described above. The crosslinked polymeric material
can be a thermally cured product and/or a photochemically cured
product of the precursor composition. For example, four different
crosslinking strategies can be employed depending on the type and
the order of the crosslinking chemistry. Referring to FIG. 1, these
processes include: i) thermal/high-humidity curing; ii)
photochemical curing; iii) thermal/high-humidity curing followed by
photochemical curing; and iv) photochemical curing followed by
thermal/high-humidity curing. The thermal curing step can include
annealing at an elevated temperature range in a high-humidity
environment (.about.70%-90% humidity) for a short period of time
(e.g., 5-10 minutes), followed by dry curing (e.g., in a vacuum
oven) at a similar temperature range for a longer period of time
(e.g., 1-3 hours). The elevated temperature range can be from about
70.degree. C. to about 150.degree. C., from about 90.degree. C. to
about 140.degree. C., and from about 100.degree. C. to about
130.degree. C. The photocuring step can include exposure to
ultraviolet light (e.g., irradiation with a wavelength of about 245
nm) for about 5-15 minutes depending on the thickness of the film.
In some embodiments, crosslinking also can be achieved by electron
beam irradiation alone or in conjunction with one or both of the
techniques discussed above. Crosslinked polymeric dielectric
materials with different and/or complementary properties can be
obtained using one or more of these processes. The use of
photochemically curable crosslinkers can facilitate patterning, for
example, as illustrated in the process in FIG. 2.
[0103] Accordingly, fabrication of a dielectric material can be
performed in air (e.g., in a simple fume hood) in a controllable
manner. Silane hydrolysis, condensation, and/or crosslinking
typically occurs within seconds after deposition under ambient
conditions. The process can be optimized by using
controlled-atomosphere conditions during film deposition and
annealing.
[0104] The structural integrity of the resulting dielectric
material can be evident by its insolubility in the mother solution.
The curing temperatures, typically lower than 130.degree. C., are
compatible with common plastic substrates employed in organic
electronics such as polyethylene terephthalate (PET) and
polyethylene naphthalate (PEN). In addition, the crosslinking
chemistry according to the present teachings can ensure strong
adhesion to a substrate, for example, a bottom gate electrode, thus
preventing delamination upon successive deposition and/or
patterning of subsequent device layers, as well as during device
operation.
[0105] The present teachings further provide an article of
manufacture, for example, a composite, that comprises a dielectric
material of the present teachings and a substrate component and/or
a semiconductor component. The substrate component can be selected
from, but is not limited to, a doped silicon, an indium tin oxide
(ITO), ITO-coated glass, ITO-coated mylar, aluminum, a doped
polythiophene, and the like. The composite can include a
semiconductor component. The semiconductor component can be
selected from, but is not limited to, various fused heterocycles,
polythiophenes, fused aromatics, and other such semiconductor
compounds or materials, whether p-type or n-type, otherwise known
or found useful in the art. The semiconductor component also can
include inorganic semiconductor materials such as silicon,
germanium, gallium arsenide, and the like. One or more of the
composites described above can be embodied within an organic
electronic device such as an OTFT, specifically, an OFET. Such an
OFET can operate at low biases due to the high capacitance of the
dielectric materials of the present teachings.
[0106] In the following examples, dielectric materials according to
the present teachings were prepared and characterized by AFM,
metal-insulator-metal (MIM) device and
metal-insulator-semiconductor (MIS) device leakage and impedance
spectroscopy measurements, to demonstrate, among other things,
their compatibility with various p-type and n-type organic
semiconductors. Organic electronic devices, e.g., organic thin film
transistors (OTFTs), specifically, organic field effect transistors
(OFETs), based on these dielectric films also have been fabricated
and characterized, data of which are provided below.
[0107] The following examples are provided to illustrate further
and to facilitate the understanding of the present teachings and
are not in any way intended to limit the invention.
EXAMPLE 1
Preparation of
1-trichlorosilanyl-3-[2-(3-trichlorosilanyl-propoxy)-ethoxy]-propane
(EGCl) and
1-triacetoxysilanyl-3-[2-(3-triacetoxysilanyl-propoxy)-ethoxy]-propane
(EGOAc)
[0108] Scheme 1 below depicts an exemplary synthetic route for the
preparation of
1-trichlorosilanyl-3-[2-(3-trichlorosilanyl-propoxy)-ethoxy]-propane
(EGCl) and
1-triacetoxysilanyl-3-[2-(3-triacetoxysilanyl-propoxy)-ethoxy]-propane
(EGOAc).
##STR00010##
[0109] Step 1: Preparation of 3-(2-allyloxy-ethoxy)-propene
[0110] Sodium hydride (NaH, 5.0 g, 0.208 mol) was slowly added to a
solution of 2-allyloxy-ethanol (20 mL, 0.187 mol) while stirring.
Allyl bromide (32 mL, 0.370 mol) was added and the mixture was
stirred at 60.degree. C. for 10 hours. After cooling, the reaction
mixture was filtered and a dark oil was obtained after solvent
evaporation. The oil was fractionally distilled to give 22 grams of
3-(2-allyloxy-ethoxy)-propene (0.155 mol, yield 83%) as a colorless
oil. .sup.1H NMR (400 Mz, CDCl.sub.3): .delta. 3.6 (t, 2H), 4.0 (d,
2H), 5.1 (d 1H), 5.3 (d 1H), 5.9 (q, 1H).
[0111] Step 2: Preparation of
1-trichlorosilanyl-3-[2-(3-trichlorosilanyl-propoxy)-ethoxy]-propane
(EGCl)
[0112] 3-(2-Allyloxy-ethoxy)-propene (20 g, 0.141 mol) and 40 mg of
hydrogen hexachloroplatinate (IV) hydrate were added to a 250-mL
air-free flask with a condenser. Trichlorosilane (40 mL, 0.396 mol)
was added dropwise to the stirred solution which was subsequently
heated in an oil bath of 80.degree. C. The reaction mixture was
heated at reflux for 4 hours and then distilled in vacuum. The
fraction containing di(3-trichlorosilyl)propyl ethylene ether (39
g, 0.0944 mol) at 90.degree. C. and 20 mtorr was collected with a
yield of 70% based on 3-(2-allyloxy-ethoxy)-propene. .sup.1H NMR
(400 Mz, CDCl.sub.3): .delta. 1.5 (t, 2H), 1.8 (m, 2H), 3.4 (t,
2H), 3.6 (t, 2H). .sup.29Si NMR (79.6 Mz, CDCl.sub.3): 13.4
(s).
[0113] Step 3: Preparation of
1-triacetoxysilanyl-3-[2-(3-triacetoxysilanyl-propoxy)-ethoxy]-propane
(EGOAc)
[0114] Di(3-trichlorosilyl)propyl ethylene ether (10 g, 0.0242 mol)
and acetic anhydride (27 mL, 0.048 mol) were slowly added to a 100
mL air-free flask. The reaction solution was stirred at 80.degree.
C. for 5 hours. Acetyl chloride was removed by distillation
occasionally during the reaction. After all the volatiles were
removed (120.degree. C. at 5 mtorr), 13.4 g (0.0241 mol) of
di(3-triacetoxysilyl)propyl ethylene ether (EGOAc) were obtained
with a yield of 99.6%. .sup.1H NMR (400 Mz, CDCl.sub.3): .delta.
1.1 (t, 2H), 1.7 (m, 2H), 2.0 (s, 9H), 3.3 (t, 2H), 3.5 (t, 2H).
.sup.29Si NMR (79.6 Mz, CDCl.sub.3): -44.9 (s). Anal. Calcd for
C.sub.20H.sub.34O.sub.14Si2: C, 43.31; H, 6.18. Found: C, 42.79; H,
6.16.
EXAMPLE 2
Preparation of 1,6-bis(tri(dimethylamino)silyl)hexane
(C.sub.6NMe.sub.2)
[0115] A solution of 1,6-bis(trichlorosilyl)hexane (2 mL, 7.518
mmol) in 25 mL of tetrahydrofuran (THF) was placed in a 100 mL
air-free flask under nitrogen atmosphere. The solution was then
cooled in an ice bath and a solution of dimethylamine (2M, 90.2
mmol) in 50 mL of THF was added dropwise while stirring. After the
addition of dimethylamine, the mixture was allowed to slowly warm
up to 50.degree. C., kept overnight then filtered with an air-free
grit. The solvent was removed under vacuum and 3.0 g of
1,6-bis(tri(dimethylamino)silyl)hexane was obtained with a yield of
98%. .sup.1H NMR (400 Mz, CDCl.sub.3): .delta. 0.65 (t, 4H), 1.35
(m, 8H), 2.42 (s, 36H). .sup.29Si NMR (79.6 Mz, CDCl.sub.3): -16.6
(s). Anal. Calcd for C.sub.18H.sub.48N.sub.6Si.sub.2: C, 53.41; H,
11.95; N, 20.76. Found: C, 51.07; H, 11.39; N, 18.11.
EXAMPLE 3
Preparation of 1,6-bis(trichlorosilyl)-3,3,4,4-tetrafluorohexane
(F.sub.4C.sub.6Cl) and
1,6-bis(triacetoxysilyl)-3,3,4,4-tetrafluorohexane
(F.sub.4C.sub.6OAc)
[0116] Scheme 2 below depicts an exemplary synthetic route for the
preparation of 1,6-bis(trichlorosilyl)-3,3,4,4-tetrafluorohexane
(F.sub.4C.sub.6Cl) and
1,6-bis(triacetoxysilyl)-3,3,4,4-tetrafluorohexane
(F.sub.4C.sub.6OAc).
##STR00011##
[0117] Step 1: Preparation of
1,6-bis(trichlorosilyl)-3,3,4,4-tetrafluorohexane
(F.sub.4C.sub.6Cl)
[0118] 1,2-Diethenyltetrafluoroethane (1 g, 6.5 mmol) and 4 mg of
hydrogen hexachloroplatinate (IV) hydrate were dissolved in dried
CH.sub.2Cl.sub.2 (15 mL). Trichlorosilane (10 mL, 9.9 mmol) was
added dropwise to the stirred solution. The reaction mixture was
heated at 40.degree. C. overnight, followed by removal of excess
HSiCl.sub.3 and solvent by vacuum evaporation. The crude product
was recovered in a yield of greater than about 96% (2.6 g). .sup.1H
NMR (400 Mz, CDCl.sub.3): .delta. 2.4 (m, 4H), 1.4 (m, 4H).
.sup.29Si NMR (CDCl.sub.3): 14.1 (s). .sup.19F NMR (CDCl.sub.3):
-115.1 (t, J=12 Hz, 4F).
[0119] Step 2: Preparation of
1,6-bis(triacetoxysilyl)-3,3,4,4-tetrafluorohexane
(F.sub.4C.sub.6OAc)
[0120] 1,6-Bis(trichlorosilyl)-3,3,4,4-tetrafluorohexane (1 g, 2.35
mmol) and acetic anhydride (4 mL) were added to a 10 mL air-free
flask. The reaction solution was stirred at 80.degree. C. for 5
hours. After all the volatiles were removed (120.degree. C. at 5
mtorr), 1.24 g (2.20 mol) of the product were obtained with a yield
of 99.6%. .sup.1H NMR (400 Mz, CDCl.sub.3): .delta. 2.4 (m, 4H),
1.3 (m, 4H). .sup.29Si NMR (79.6 Mz, CDCl.sub.3): -45.3 (s).
.sup.19F NMR (CDCl.sub.3): -114.6 (t, J=13 Hz, 4F).
EXAMPLE 4
Preparation of poly[4-methoxystyrene-co-4-(3-triacetoxysilyl
propoxystyrene)]
[0121] Scheme 3 below depicts an exemplary synthetic route for the
preparation of
poly[4-methoxystyrene-co-4-(3-triacetoxysilylpropoxystyrene)].
##STR00012##
[0122] Step 1: Preparation of
poly[4-methoxystyrene-co-4-allyloxystyrene]
[0123] Poly(4-vinyl phenol) (1.0 g, Mw=8,000 g/mol or 20,000 g/mol)
was dissolved in 30 mL of dried THF, followed by the addition of
6.7 g of sodium carbonate, 0.25 mL (4.2 mmol) of iodomethane and 6
mL (69 mmol) of allyl bromide. The reaction mixture was heated at
reflux in an oil bath of 70.degree. C. for 24 hours and
subsequently slowly poured into 500 mL of deionized water. The
precipitated viscous solid was dried in vacuum. Based on .sup.1H
NMR spectra, the composition of the resulting
poly[4-methoxystyrene-co-4-allyloxystyrene was determined to be
10:90 (mol. %) 4-methoxystyrene:4-allyloxystyrene. .sup.1H NMR (400
Mz, CDCl.sub.3): .delta. 1.1-2.5 (b), 3.7 (s), 4.5 (d), 5.2 (d),
5.4 (d), 5.9 (d), 6.2-7.3 (b).
[0124] Step 2: Preparation of
poly[4-methoxystyrene-co-4-(3-triacetoxysilyl propoxystyrene)]
[0125] Poly(4-methoxystyrene-co-4-allyloxystyrene) from Step 1 (1.0
gram), 3 mg of hydrogen hexachloroplatinate (IV) hydrate, and 30 mL
dried THF were added to a 250-mL air-free flask with a condenser.
Trichlorosilane (2 mL, 0.0198 mol) was added dropwise to the
solution and the solution was subsequently heated in an oil bath of
80.degree. C. The reaction mixture was heated at reflux for 4
hours, followed by filtration and condensation of the filtrate. The
resulting yellowish viscous solid (1.9 g) was dissolved in 20 mL of
dried THF. Distilled acetic anhydride (5 mL) was added to the
solution which was subsequently heated to 80.degree. C. for 10
hours. After all the volatile fractions had been removed by
distillation at 120.degree. C. and 5 mtorr, 1.9 g of the viscous
residue
poly[4-methoxystyrene-co-4-(3-triacetoxysilylpropoxystyrene) was
obtained. .sup.1H NMR (400 Mz, CDCl.sub.3): .delta. 0.9 (t),
1.1-2.0 (b), 2.0 (b), 3.5 (s), 3.7 (t), 6.2-7.0 (b).
EXAMPLE 5
Preparation of poly(vinylphenol-co-4-cinnamoylstyrene)
[0126] Scheme 4 below depicts an exemplary synthetic route for the
preparation of poly(vinylphenol-co-4-cinnamoylstyrene).
##STR00013##
[0127] Poly(4-vinylphenol) (1.0 g, Mw=8,000 g/mol or 20,000 g/mol,
hydroxyl group: 8.33 mmol) was dissolved in 20 mL of THF. Cinnamoyl
chloride (0.70 g, 4.2 mmol) and triethylamine (1.0 mL, 8.33 mmol)
were slowly added to the solution which was subsequently heated to
50.degree. C. for 4 hours. The reaction mixture was poured into 500
mL of deionized water. The precipitated solid was filtered, washed
with 100 mL of methanol three times and dried in vacuum. .sup.1H
NMR verified 50% cinnamation of the poly(vinylphenol). .sup.1 H NMR
(400 Mz, CDCl.sub.3): .delta. 1.1-2.6 (b), 6.4 (d), 6.5-7.6 (b),
7.7 (d).
EXAMPLE 6
Surface Morphology and Dielectric Properties of Spin-Coated
Ultrathin Dielectric Films Prepared from Precursor Compositions
Containing Bifunctionalized-Silane Crosslinkers
[0128] To assess how the surface morphology and various dielectric
characteristics of a CPB dielectric film can be affected by the
choice of the polymeric component and the crosslinker component of
the precursor composition, precursor compositions were prepared
from different combinations of various polymers, thermally curable
crosslinkers, and solvents. These precursor compositions were
subsequently spin-coated onto silicon substrates to provide
ultrathin (<50 nm) dielectric films.
[0129] The following polymers were used:
##STR00014##
[0130] Poly(4-vinyl phenol) (PVP, M.sub.w=8-20K), poly(styrene)
(PS, M.sub.w=1M), poly(vinyl alcohol) (PVA), and
poly(methylmethacrylate) (PMMA) were purchased from Sigma-Aldrich
(St. Louis, Mo.) and used without further purification.
Poly(4-vinyl phenol-co-styrene) [P(VP.sub.x-S.sub.y)] was
synthesized according to the procedures described in Lei et al.
(2003), Macromolecules, 23: 5071-5074.
[0131] The following crosslinkers (cxn) were used:
##STR00015##
[0132] Hexachlorodisiloxane (C.sub.0Cl) and
1,6-bis(trichlorosilyl)hexane (C.sub.6Cl) were purchased from Acros
Organics (Geel, Belgium) and Gelest, Inc. (Morrisville, Pa.),
respectively, and purified by distillation.
1,12-Bis(trichlorosilyl)dodecane (C.sub.12Cl) was synthesized by
hydrosilylation of commercially available 1,11-dodecadiene.
1,6-Bis(trimethoxysilyl)hexane (C.sub.6OMe) and
1,6-bis(triacetoxysilyl)hexane (C.sub.6OAc) were synthesized from
the chloro precursors C.sub.6Cl.
1,4-Bis(trimethoxysilylethyl)benzene (PhOMe) was synthesized
according to procedures described in Kabeta et al., J. Polym. Sci.
A. Polym. Chem., 34(14): 2991-2998 (1996).
1,6-Bis(tri(dimethylamino)silyl)hexane (C.sub.6NMe.sub.2),
1,6-bis(trichlorosilyl)-3,3,4,4-tetrafluorohexane
(F.sub.4C.sub.6Cl), and
1,6-bis(triacethoxysilyl)-3,3,4,4-tetrafluorohexane
(F.sub.4C.sub.6OAc) were prepared as described in Examples 2 and
3.
[0133] The solvents used were tetrahydrofuran (THF), dioxane, and
ethyl acetate (AcOEt).
[0134] The silicon substrates were highly n-doped silicon wafers
obtained from Montco Silicon Tech, Inc. (Spring City, Pa.) and
cleaned according to standard procedures, e.g., sonication in
organic solvent, Pirahna solution, and oxygen plasma treatment,
before use.
[0135] To prepare the precursor composition, solutions of the
polymer and the crosslinker were prepared with the selected solvent
and the solutions combined in a specific volume ratio. The
precursor composition was then spin-coated onto freshly oxygen
plasma-treated silicon substrates. The thickness of the film
samples was partially controlled by adjusting the spin coating rate
between about 1500 rpm and about 5000 rpm (acceleration 60). After
the spin-coating step, the resulting dielectric films were annealed
(thermally cured) in a high humidity atmosphere (70-90%) at about
100.degree. C. to about 130.degree. C. for 5-10 minutes and then
for 1-3 hours in a vacuum oven (dry curing) at the same
temperature. Film thickness and surface smoothness (represented by
root mean square (RMS)) were determined by profilometry and AFM.
MIS capacitor structures were fabricated using the resulting
dielectric films, and the capacitance of the dielectric films was
measured. The results are summarized in Table 1 below.
TABLE-US-00001 TABLE 1 Ratio Thickness RMS C.sub.i Entry Polymer
Crosslinker Solvent Polymer:Cxn (nm) (nm) (nF cm.sup.-2) 1 PVP
C.sub.0Cl THF 4:4 18-40 6-8 150-305 2 PVP C.sub.6Cl THF 4:4 18-40
1-3 150-300 3 PVP C.sub.12Cl THF 4:4 20-40 4-6 150-290 4 PVP
C.sub.6OMe Dioxane 4:8 17-40 0.5-1.sup. 160-250 5 PVP PhOMe Dioxane
4:8 18-40 0.5-1.sup. 170-320 6 PVP C.sub.6OAc AcOEt 4:8 17-40
0.4-0.5 150-250 7 PVP C.sub.6OAc AcOEt 4:6 13-35 0.2-0.3 160-300 8
PVP C.sub.6OAc AcOEt 4:4 12-25 0.2-0.3 170-325 9 PVP C.sub.6OAc
AcOEt 4:2 10-20 0.2-0.3 180-340 10 PVP C.sub.6NMe.sub.2 AcOEt 4:6
15-25 0.5-0.9 170-320 11 PVP F.sub.4C.sub.6Cl AcOEt 4:4 13-20
0.4-0.5 180-350 12 PVP F.sub.4C.sub.6OAc AcOEt 4:4 12-18 0.2-0.3
200-360 13 PS C.sub.0Cl THF 4:4 12-25 8-10 120-220 14 PS C.sub.6Cl
THF 4:4 10-20 1-2 120-220 15 PS C.sub.12Cl THF 4:4 13-30 4-5
100-200 16 cPVPS C.sub.6OAc Dioxane 4:4 22-45 0.5-1.sup. 130-280 17
PVA C.sub.6OAc Dioxane 4:4 10-20 0.5-2.sup. 400-600 18 PMMA
C.sub.6OAc Dioxane 4:4 19-40 1-2 160-320
EXAMPLE 7
Insulating Properties of of Spin-Coated Ultrathin Dielectric Films
Prepared from Precursor Compositions Containing
Bifunctionalized-Silane Crosslinkers
[0136] All of the dielectric films prepared in Example 6 exhibit
very low leakage currents, ranging between 10.sup.-6 and 10.sup.-7
A/cm.sup.2 at 2-4 MV/cm. Representative leakage current-voltage
plots are shown in FIG. 3.
[0137] Comparable leakage current densities were obtained using
other gate substrates, specifically, Al-PEN and ITO-glass
substrates. Al-PEN substrates were prepared according to literature
reports; e.g., by sputtering aluminum (about 20-100 nm in
thickness) on an O.sub.2-plasma treated commercially-available PEN
substrate. ITO-glass substrates were cleaned with an oxygen plasma
before use. Representative leakage current-voltage plots are
provided in FIG. 4.
EXAMPLE 8
Surface Morphology and Dielectric Characteristics of Spin-Coated
Dielectric Films Prepared from Precursor Compositions Containing
Bifunctionalized-Silane Ethylene Glycol Crosslinkers
[0138] Spin-coated dielectric films were prepared using thermally
curable precursor compositions containing bifunctionalized
triacetoxylated-silane ethylene glycol crosslinkers (EGOAc)
following procedures described in Examples 1 and 6. The
compositions of the precursor compositions were summarized in Table
2, along with the thickness and the capacitance values of the
resulting dielectric films and the substrate used. Both ultrathin
(<50 nm) and thin dielectric films (about 50-400 nm) were
prepared.
TABLE-US-00002 TABLE 2 Ratio Thickness C.sub.i Entry Gate PVP:EGOAc
(nm) (nF cm-2) 1 Si 80:80 325 15.25 2 Si 60:60 220 21.0 3 Si 40:40
145 29.5 4 Si 30:30 80 52.7 5 Si 20:20 40 85.0 6 Al 80:80 320-330
16.25 7 Al 60:60 210-230 22.5 8 Al 40:40 140-150 36.0 9 Al 30:30 80
55.75 10 Al 20:20 40 80.75 11 ITO 80:80 320-330 18.5 12 ITO 60:60
210-230 23.0 13 ITO 40:40 140-150 38.5 14 ITO 30:30 80 56.0 15 ITO
20:20 40 82.7
[0139] Dielectric films prepared with bifunctionalized-silane
ethylene glycol crosslinkers exhibited excellent surface
smoothness, with an RMS roughness of about 0.3 nm to about 0.7
nm.
EXAMPLE 9
Insulating Properties of Spin-Coated Dielectric Films Prepared from
Precursor Compositions Containing Bifunctionalized-Silane Ethylene
Glycol Crosslinkers
[0140] The dielectric films from Example 8 were used to fabricate
capacitor structures and were found to exhibit very large
dielectric strength as demonstrated by the current-voltage plots
shown in FIG. 5.
EXAMPLE 10
Device Performance of OFETs Fabricated with Spin-Coated Dielectric
Films Prepared from Precursor Compositions Containing
Bifunctionalized-Silane Ethylene Glycol Crosslinkers
[0141] Pentacene OFETs were fabricated with dielectric films of
Example 8 on both silicon and aluminium gate materials.
Specifically, the silicon substrates were highly n-doped silicon
wafers obtained from Montco Silicon Tech, Inc. (Spring City, Pa.)
and cleaned according to standard procedures, e.g., sonication in
organic solvent, Pirahna solution, and oxygen plasma treatment,
before use. The aluminium substrates were cut from commercially
available aluminium foil (Reynolds Wrap.RTM.). Pentacene was
purchased from Sigma-Aldrich (St. Louis, Mo.) and vacuum-deposited
at about 2.times.10.sup.-6 Torr (500 .ANG., 0.2 .ANG./s) while
maintaining the substrate temperature at about 50.degree. C. to
about 70.degree. C. Gold electrodes were vacuum-deposited through
shadow masks at 3-4.times.10.sup.-6 Torr (1000 .ANG., 0.5 .ANG./s).
The channel length is 100 .mu.m, and the channel width is 2000
.mu.m.
[0142] These OFETs were found to perform very well at variable
operating voltages, indicating a high capacitance of the dielectric
materials. Representative OFET transfer plots are shown in FIG. 6.
The use of thinner dielectric films (20:20) compared to thicker
ones (e.g., 60:60) were shown to achieve similar output current.
However, the thinner films allowed much lower operating voltages
due to their higher capacitance (see Eq. 2). The carrier mobilities
of these devices are about 0.5 cm.sup.2/Vs to about 3 cm.sup.2/Vs,
which are typical for pentacene films grown at 50.degree. C.
Current modulations (I.sub.on:I.sub.off ratios) were measured to be
>10.sup.6.
[0143] A comparative pentacene OFET device was fabricated using
silicon oxide (SiO.sub.2) as the dielectric material. The silicon
oxide film has a thickness of 300 nm. The carrier mobilities of
this comparative device was found to be about 0.1 cm.sup.2/Vs to
about 0.3 cm.sup.2/Vs at larger operating voltages.
EXAMPLE 11
Surface Morphology and Dielectric Properties of Spin-Coated Thin
Dielectric Films Prepared from Precursor Compositions Containing
Bifunctionalized-Silane Crosslinkers
[0144] Thin dielectric films (about 50-300 nm) were prepared using
precursor compositions employing PVP as the polymer and C.sub.6Cl,
C.sub.6OAc, EGOAc, C.sub.6NMe.sub.2 and F.sub.4C.sub.6Cl,
respectively as the crosslinker component. The precursor
compositions were spin-coated on Si and flexible AUPEN substrates
following procedures described in Example 6. Table 3 summarizes the
compositions of the precursor compositions, as well as the
electrical and physical properties of the resulting dielectric
films on Si substrates.
TABLE-US-00003 TABLE 3 Ratio Thickness RMS C.sub.i Entry Polymer
Crosslinker Solvent Polymer:Cxn (nm) (nm) (nF cm.sup.-2) 1 PVP
C.sub.6Cl THF 40:40 155 0.3-0.4 32 2 PVP C.sub.6OAc Dioxane 20:20
50 0.2-0.3 91 3 PVP C.sub.6OAc Dioxane 40:40 130 0.2-0.3 33 4 PVP
C.sub.6OAc Dioxane 60:60 205 0.2-0.3 22 5 PVP C.sub.6OAc Dioxane
80:80 305 0.2-0.3 12 6 PVP C.sub.6NMe.sub.2 AcOEt 40:40 90 2-3 56 7
PVP F.sub.4C.sub.6Cl AcOEt 40:40 115 0.6-0.9 47
[0145] Thin dielectric films fabricated with crosslinkers C.sub.6Cl
and C.sub.6NMe.sub.2 afford .about.10 times higher leakage current
densities (.about.1.times.10.sup.-6 A/cm.sup.2) compared to those
fabricated with EGOAc and F.sub.4C.sub.6Cl
(.about.1.times.10.sup.-7 A/cm.sup.2) at an electric field of 2
MV/cm. EGOAc-based dielectric films also afford smoother film
morphology (RMS .about.0.2-0.3 nm) than C.sub.6Cl-based
(.about.0.3-0.4 nm) or C.sub.6NMe.sub.2-based (.about.2-3 nm)
films. While dielectric films fabricated with C.sub.6Cl show
relatively smooth film morphology at a small area, the overall film
morphology is not as smooth as EGOAc-based films. Compared to films
fabricated on Si substrates, dielectric films fabricated on Al/PEN
substrates afford relatively rough surface morphologies (RMS
.about.0.5-0.6 nm) and higher leakage current densities
(.about.1.times.10.sup.-6 A/cm.sup.2) at an electric field of 2
MV/cm. Representative leakage current-voltage plots are shown in
FIG. 7.
EXAMPLE 12
Fabrication and Performance of Thin Film Transistors Using
Ultra-Thin and Thin Spin-Coated Dielectric Films
[0146] Top-contact OFETs were fabricated with ultra-thin (<50
nm) and thin (about 50-300 nm) spin-coated dielectric films
prepared with PVP and a crosslinker selected from C.sub.6Cl,
C.sub.6OAc, EGOAc, C.sub.6NMe.sub.2 and F.sub.4C.sub.6Cl. Si and
Al/PEN substrates were used, along with pentacene (P5) and
5,5'''-diperfluorohexylcarbonyl-2,2':5',2'':5'',2'''-quaterthiophene
(DFHCO-4T) as the p-type and n-type semiconductor, respectively. P5
was purchased from Sigma-Aldrich (St. Louis, Mo.) and
vacuum-deposited at about 2.times.10.sup.-6 Torr (500 .ANG., 0.2
.ANG./s) while maintaining the substrate temperature at about
50.degree. C. to about 70.degree. C. DFHCO-4T were prepared and
deposited as described in U.S. Patent Application Publication No.
2006/0186401, the disclosure of which is incorporated by reference
in its entirety. Gold electrodes were vacuum-deposited through
shadow masks at 3-4.times.10.sup.-6 Torr (1000 .ANG., 0.5 .ANG./s).
The channel length is 100 .mu.m, and the channel width is 2000
.mu.m.
[0147] Transfer characteristics of the devices were measured in the
saturation regime and transfer plots for 50-nm thick film FETs are
shown in FIG. 8. Table 4 summarizes the OFET performance
parameters, carrier mobility (.mu..sub.sat) and current on/off
ratio (I.sub.on:I.sub.off). The charge carrier mobility shows
strong correlation with the thickness of the dielectric films. Thin
(<50 nm) dielectric films show relatively low mobility of
0.02-0.16 cm.sup.2/Vs for both P5 and DFHCO-4T devices, compared to
thicker films (.about.50-300 nm) fabricated with EGOAc
(.about.0.30-0.50 cm.sup.2/Vs). For all dielectric films,
I.sub.on:I.sub.off shows comparable values between
.about.10.sup.5-10.sup.6.
TABLE-US-00004 TABLE 4 P5 DFHCO-4T Crosslinker Ratio
.mu..sub.sat.sup.a I.sub.on/I.sub.off .mu..sub.sat
I.sub.on/I.sub.off C.sub.6Cl 6:6 0.07 10.sup.5 0.12 10.sup.5
C.sub.6OAc 4:6 0.12 10.sup.5 0.12 10.sup.5 4:6 0.15 10.sup.5 0.16
10.sup.6 20:20 0.40 10.sup.5 0.44 10.sup.6 EGOAc 40:40 0.31
10.sup.6 0.43 10.sup.6 60:60 0.38 10.sup.6 0.47 10.sup.5 80:80 0.47
10.sup.6 0.52 10.sup.5 C.sub.6NMe.sub.2 4:6 0.03 10.sup.5 0.02
10.sup.5 F4C.sub.6Cl 4:4 0.04 10.sup.5 0.09 10.sup.5
.sup.aCalculated for the charge carrier concentration (n.sub.Q =
C.sub.i V.sub.G/e = 5 - 6 .times. 10.sup.12 cm.sup.-2).
[0148] The trend in mobility values is consistent with the
aforementioned dielectric film morphologies. For thin dielectric
films, the P5 FET device fabricated with EGOAc, with the smoothest
film morphology, afford the highest carrier mobility of 0.15
cm.sup.2/Vs among all crosslinkers, followed by C.sub.6OAc (0.12 cm
.sup.2/Vs), C.sub.6Cl (0.07 cm.sup.2/Vs), F.sub.4C.sub.6Cl (0.04
cm.sup.2/Vs), and C.sub.6NMe.sub.2 (0.03 cm.sup.2/Vs). Similar
trend in charge carrier mobility for n-type semiconductor DFHCO-4T
was observed. Because charge transport in OTFT is confined to the
small region at the semiconductor/dielectric interface, the
smoothness of the dielectric film is a prerequisite for improved
OTFT performance. It has been reported with pentacene film FETs
that rough gate dielectric surfaces afford smaller pentacene grains
compared to very smooth substrates, leading to poorer FET
performance. Grain boundaries between semiconductor crystallites
are considered to be one type of interfacial charge trapping sites,
which disrupt charge transport. Pentacene films grown on relatively
smooth dielectric films fabricated with C.sub.6OAc and EGOAc afford
large, dendritic grains (>3 .mu.m), while very small (<0.3
.mu.m) pentacene grains are grown on C.sub.6Cl-based and
C.sub.6NMe.sub.2-based dielectric films.
EXAMPLE 13
Printability of Dielectric Precursor Compositions Containing
Thermally Curable Bifunctionalized-Silane Ethylene Glycol
Crosslinkers
[0149] Using acetoxy-bisfunctionalized crosslinkers such as
C.sub.6OAc from Example 6 and EGOAc from Example 8, printable
dielectric materials were fabricated. Experiments were performed to
identify the best printing solvent for a certain
polymer-crosslinker precursor composition. For instance, in the
case of PVP and C.sub.6OAc or EGOAc, the solvents tested are shown
in Table 5 below. The experiments were performed using an IGT
Reprotest F1 printing press (IGT, Amsterdam, Netherlands) in
gravure mode with the following parameters: Anilox force 100 N,
printing speed 0.4 m/s, anilox cylinder 402.206 (copper
engraved-chromium plated, stylus 120.degree., screen angle 45,
volume 7.5 mL/m.sup.2). Similar to the procedures described in
Example 6, the polymer and the crosslinker were individually
dissolved in solvent and combined at a specific volume ratio. The
resulting formulation was gravure-printed (also can be flexo
printed) onto freshly oxygen plasma-treated ITO-mylar or Al-PEN
substrates.
TABLE-US-00005 TABLE 5 Crosslinker Solvent Entry PVP (mg) (mg) (0.4
mL) Quality C.sub.6OAc 1 100 50 THF Good 2 100 50 Dioxane Poor 3
100 50 AcOEt Excellent 4 100 50 CP Poor 5 100 50 EtOH Good 6 100 50
MeOH Poor 7 100 40 AcOEt Excellent EGOAc 8 100 50 THF Excellent 9
100 50 Dioxane Good 10 100 50 AcOEt Excellent 11 100 50 CP Poor 12
100 50 EtOH Excellent 13 100 50 MeOH Excellent 14 100 40 AcOEt
Excellent
[0150] Similarly, experiments were performed to determine the best
polymer-crosslinker concentration ratios using the same printing
press and printing parameters as provided above. The tested
concentration ratios are summarized in Table 6 below.
TABLE-US-00006 TABLE 6 Crosslinker Solvent Entry PVP (mg) (mg) (0.4
mL) Quality C.sub.6OAc 1 100 50 AcOEt excellent 2 100 60 AcOEt good
3 100 40 AcOEt good 4 100 30 AcOEt poor 5 100 20 AcOEt poor 6 100
10 AcOEt excellent 7 100 70 AcOEt good EGOAc 8 100 50 AcOEt
excellent 9 100 60 AcOEt excellent 10 100 40 AcOEt excellent 11 100
30 AcOEt good 12 100 20 AcOEt poor 13 100 50 AcOEt excellent 14 100
70 AcOEt good
[0151] In Tables 5 and 6, the dielectric quality was rated from
excellent to poor based on the dielectric performance (leakage
current, breakdown characteristics) as well as film morphological
(roughness) and mechanical (robustness/solubility)
characteristics.
EXAMPLE 14
Surface Morphology of Dielectric Films Printed from Precursor
Compositions Containing Bifunctionalized-Silane Ethylene Glycol
Crosslinkers
[0152] AFM micrographs of dielectric films printed from optimized
precursor compositions containing bifunctionalized-silane ethylene
glycol crosslinkers were obtained (see Tables 5 and 6). These
micrographs show that the optimized printed dielectric films
exhibit a very smooth surface which is a prerequisite for good OFET
charge transport.
[0153] Identifying the optimal composition of the dielectric
precursor formulations (type of polymer, crosslinker, solvent, as
well as polymer:crosslinker concentration ratio) is critical to
achieve pinhole-free defect-free dielectric films. The quality of
gravure-printed dielectric films fabricated using unoptimized and
optimized formulations are significantly different, with films made
from the optimized formulations being extremely smooth and
defect-free, and films from the unoptimized formulations exhibiting
a large number of defects and cracks.
EXAMPLE 15
Dielectric Data of Dielectric Films Printed from Precursor
Compositions Containing Bifunctionalized-Silane Ethylene Glycol
Crosslinkers
[0154] Table 7 summarizes representative dielectric data (film
roughness, capacitance (C.sub.i) and breakdown voltage (BV)) of
dielectric films printed from precursor compositions containing PVP
and C.sub.6OAc or EGOAc, following procedures described in Examples
6, 8 and 13. Use of the ethylene glycol-based crosslinkers was
shown to reduce film roughness and improve dielectric strength.
TABLE-US-00007 TABLE 7 PVP(mg):C.sub.6OAc(mg) Roughness C.sub.i BV
Entry (0.4 mL AcOEt) (nm) (nF/cm.sup.2) (V) 1 100:50 0.3-0.5 5-7
>100 2 100:40 0.3-0.4 5-7 >100 3 100:30 0.4-0.6 4-6 >80 4
50:25 0.4-0.6 13-16 >90 5 50:20 0.3-0.8 13-16 >80 6 50:15
0.6-1.0 13-16 >50 PVP(mg):EGOAc(mg) Roughness C.sub.i BV Entry
(0.4 mL AcOEt) (nm) (nF/cm.sup.2) (V) 7 100:50 0.3-0.4 5-7 >120
8 100:40 0.3-0.4 5-7 >100 9 100:30 0.3-0.5 5-7 >80 10 50:25
0.4-0.5 13-16 >90 11 50:20 0.3-0.8 13-16 >80 12 50:15 0.5-0.9
13-16 >60
EXAMPLE 16
Insulating Properties of Dielectric Films Printed from Precursor
Compositions Containing Thermally Curable Bifunctionalized-Silane
Ethylene Glycol Crosslinkers
[0155] The leakge current at various operating voltages was
measured for the dielectric films of Example 16. FIG. 9 is a
representative plot, using dielectric films of Entries 7 and 10
from Example 16. These films were shown to have good insulating
properties.
EXAMPLE 17
Device Performance of OFET Fabricated with Dielectric Films Printed
from Precursor Compositions Containing Thermally Curable
Bifunctionalized-Silane Ethylene Glycol Crosslinkers
[0156] Pentacene transistors fabricated on the printed dielectric
films from Example 15 were found to exhibit excellent device
performance. FIGS. 10A and 10B are representative transfer and
output plots for one of the printed PVP-EGOAc formulations (Entry
7, Table 7). All OTFT measurements described herein were carried
out in air using a Keithly 6430 subfemtoammeter and a Keithly 2400
source meter, operated by a local Labview program and GPIB
communication. Triaxial and/or coaxial shielding was incorporated
into Signaton probe stations to minimize the noise level. A digital
capacitance meter (Model 3000, GLK Instruments) and an HP4192A
Impedance Analyzer were used for capacitance measurements.
[0157] Compatibility with various p-type and n-type semiconductors
was also demonstrated. FIGS. 11A and 11B provide output plots for
OFETs fabricated with the printed PVP-EGOAc formulation of Entry 7
in Table 5 as the dielectric component and, as the semiconductor
component N,N'-bis(n-octyl)-(1,7 and
1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN.sub.2)
and 5,5'-di-(p-hexylphenyl)-2,2'-bithiophene (DH-PTTP),
respectively. PDI-8CN.sub.2 was prepared according to the
procedures described in U.S. Patent Application Publication No. US
2005/0176970, the disclosure of which is incorporated by reference
herein.
[0158] It was also found that very high carrier mobilities (.mu.)
and current on-off ratios (I.sub.on:I.sub.off) could be achieved by
OFETs fabricated with the dielectric films of the present
teachings, implying very low charge trapping states and good
semiconductor film crystallinity. Table 8 summarizes data (carrier
mobilities, current on-off ratios) related to OFET performance for
different semiconductors (pentacene, PDI-8CN.sub.2, DFHCO-4T, and
dihexylsexithiophene (DH-6T)) on a variety of dielectric films of
the present teachings. DH-6T was prepared according to the
procedures described in U.S. Pat. No. 6,585,914, the disclosure of
which is incorporated by reference herein. In all cases, the
transistors were active and the reported carrier mobilities were
among the highest obtained for these semiconductor materials.
TABLE-US-00008 TABLE 8 PVP(mg):C.sub.6OAc(mg) Semi- Entry (0.4 mL
AcOEt) conductor .mu. (cm.sup.2/Vs) I.sub.on:I.sub.off 1 Not Not
Not Not measured measured measured measured 2 100:50 (ITO)
Pentacene 10-90 4-6 .times. 10{circumflex over ( )}4 3 100:40 (ITO)
Pentacene 5-20 2-3 .times. 10{circumflex over ( )}4 4 100:30 (ITO)
Pentacene 4-15 1-2 .times. 10{circumflex over ( )}4 5 100:50 (Al)
Pentacene 4-30 1-2 .times. 10{circumflex over ( )}4 6 50:25 (Al)
Pentacene 10-20 4-6 .times. 10{circumflex over ( )}4 7 100:50 (ITO)
DH-6T 0.006-0.008 1-5 .times. 10{circumflex over ( )}2 8 100:50
(ITO) PDI-8CN.sub.2 0.08 1-5 .times. 10{circumflex over ( )}2 10
100:40 (ITO) PDI-8CN.sub.2 0.06 1-5 .times. 10{circumflex over (
)}2 11 100:30 (ITO) PDI-8CN.sub.2 0.05 1-5 .times. 10{circumflex
over ( )}2 12 100:30 (ITO) DFHCO-4T 0.05 1-5 .times. 10{circumflex
over ( )}3 PVP(mg):EGOAc(mg) Semi- Entry (0.4 mL AcOEt) conductor
.mu. (cm.sup.2/Vs) I.sub.on:I.sub.off 13 100:50 (Al) Pentacene 5-10
1-2 .times. 10{circumflex over ( )}6 14 100:40 (Al) Pentacene 5-7
2-3 .times. 10{circumflex over ( )}6 15 50:25 (Al) Pentacene 5-7
1-2 .times. 10{circumflex over ( )}6 16 100:50 (ITO) Pentacene
10-15 4-6 .times. 10{circumflex over ( )}5 Carrier mobility has
been calculated in saturation.
[0159] WAXRD (wide angle x-ray diffraction) spectra of pentacene as
well as PDI-8CN.sub.2 and DH-6T on dielectric films of the present
teachings (FIG. 12) exhibit sharp multiple reflections
demonstrating a great degree of texture.
[0160] Printed OFETs can be mechanically flexible.
EXAMPLE 18
Dielectric Properties of Dielectric Films Prepared from Precursor
Compositions Containing Polymeric Crosslinkers
[0161] Tables 9 and 10 summarize the properties of various
dielectric films obtained from different polymer-crosslinkable
copolymer precursor formulations having the formula:
##STR00016##
[0162] Table 9 shows that relatively high capacitance films can be
fabricated both by spin-coating and printing various precursor
formulations employing a thermally curable polymeric crosslinker
having the formula:
TABLE-US-00009 TABLE 9 Ink Composition CPB Film PVP
PVAn.sub.0.1Cxn.sub.0.9 Deposition C.sub.i BV Entry (mg) (mg)
Solvent Method Quality (nF/cm.sup.2) (V) 1 60 10 Dioxane (2 mL) SC
63-64 >60 2 60 20 Dioxane (2 mL) SC excellent 54-55 >60 3 60
40 Dioxane (2 mL) SC good 34-35 >60 4 60 40 Dioxane (2 mL) SC
good 32-33 >60 5 120 40 AcOEt (0.6 mL) Print 12-13 >60 6 120
40 AcOEt (0.6 mL) Print excellent 17-18 >60 7 120 40 AcOEt (1.0
mL) Print excellent 18-19 >60
[0163] Table 10 shows that relatively high capacitance films can be
fabricated both by spin-coating and printing various
photochemically curable polymer-crosslinkable copolymer precursor
formulations.
TABLE-US-00010 TABLE 10 Ink Composition CPB Film PVP
PVP.sub.xCxn.sub.y EGOAc Method C.sub.i BV Entry (mg) (mg) (mg)
Solvent (Curing) Quality (nF/cm2) (V) 1 100 0 50 AcOEt (0.4 mL)
Print (i) 2 80 0 80 Dioxane (2 mL) SC (i) excellent 14-16 >80 3
40 0 40 Dioxane (2 mL) SC (i) excellent 28-32 >70 4 20 0 20 THF
(2 mL) SC (i) good 80-90 >60 5 100 0 30 AcOEt (0.4 mL) Print (i)
excellent 5-7 >80 6 50 0 25 AcOEt (0.4 mL) Print (i) good 13-16
>90 7 0 40 30 Dioxane (2 mL) SC (iv) excellent 38-39 >90 8 0
40 20 Dioxane (2 mL) SC (iv) excellent 41-42 >90 10 0 40 10
Dioxane (2 mL) SC (iv) excellent 43-45 >90 11 0 40 0 Dioxane (2
mL) SC (iv) good 42-43 >90 12 0 40 30 Dioxane (2 mL) SC (iii)
excellent 37-39 >90 13 0 40 20 Dioxane (2 mL) SC (iii) excellent
41-43 >90 14 0 40 10 Dioxane (2 mL) SC (iii) good 43-45 >90
14 0 40 0 Dioxane (2 mL) SC (iii) good 42-43 >90 15 0 100 50
AcOEt (0.4 mL) Print (iv) poor 8-20 >60 16 0 200 100 AcOEt (0.3
mL) Print (iv) poor 8-16 >60 17 0 200 0 AcOEt (0.3 mL) Print
(iv) excellent 12-13 >60 18 200 50 AcOEt (0.3 mL) Print (iv)
excellent 12-13 >90 19 100 100 50 AcOEt (0.3 mL) Print (iv)
excellent 12-13 >90 20 100 50 50 AcOEt (0.3 mL) Print (iv)
excellent 15-16 >90
[0164] As shown in Table 10, crosslinked polymeric dielectric films
of excellent quality were fabricated by spin-coating or printing
various precursor formulations including a conventional polymer
such as PVP, a thermally curable crosslinker such as EGOAc, and
optionally a photochemically curable polymeric crosslinker such as
PVP.sub.xCxn.sub.y. Referring back to FIG. 1, different
crosslinking strategies (ii-iv) were employed (using the same
numbering schemes).
[0165] Using these thermally and/or photochemically curable
dielectric materials, high-performance OFETs were fabricated on
patterned dielectrics. FIG. 13 shows the transfer plots for
pentacene transistors exhibiting carrier mobilities close to 30
cm.sup.2/Vs and current on-off ratios greater than 10.sup.5,
demonstrating the great potential of the compositions and processes
of the present teachings.
[0166] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The foregoing embodiments are therefore to be considered
in all respects illustrative rather than limiting on the present
teachings described herein. Scope of the invention is thus
indicated by the appended claims rather than by the foregoing
description, and all changes that come within the meaning and range
of equivalency of the claims are intended to be embraced
therein.
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