U.S. patent application number 11/493050 was filed with the patent office on 2007-01-04 for lamination of organic semiconductors.
Invention is credited to Irina Malajovich.
Application Number | 20070004229 11/493050 |
Document ID | / |
Family ID | 34107798 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070004229 |
Kind Code |
A1 |
Malajovich; Irina |
January 4, 2007 |
Lamination of organic semiconductors
Abstract
Low temperature, ambient pressure processes are desired for
fabrication of transistors on flexible polymer substrates.
Lamination of semiconductors is such a process. The semiconductor
is deposited on a donor substrate. The donor is positioned over a
receiver substrate, which may be patterned with additional
transistor elements. The semiconductor is transferred from the
donor to the receiver by lamination.
Inventors: |
Malajovich; Irina;
(Swarthmore, PA) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
34107798 |
Appl. No.: |
11/493050 |
Filed: |
July 26, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10895599 |
Jul 21, 2004 |
7105462 |
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11493050 |
Jul 26, 2006 |
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60489330 |
Jul 22, 2003 |
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60501687 |
Sep 10, 2003 |
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Current U.S.
Class: |
438/780 |
Current CPC
Class: |
H01L 51/0062 20130101;
H01L 51/0052 20130101; H01L 51/0036 20130101; H01L 51/0008
20130101; H01L 51/0013 20130101; H01L 51/0024 20130101; Y10T
156/1705 20150115; H01L 51/0545 20130101 |
Class at
Publication: |
438/780 |
International
Class: |
H01L 21/31 20060101
H01L021/31 |
Claims
1. (canceled)
2. (canceled)
3. An electronic device comprising an organic semiconductor
laminated on a receiver substrate.
4. The electronic device of claim 3 where the device is a
transistor.
5. The electronic device of claim 3 where the receiver substrate is
a flexible polymer.
6. The electronic device of claim 4 where the receiver substrate is
a flexible polymer.
7. An electronic device comprising at least one drop of a dried
solution of an organic semiconductor wherein the drop was laminated
on a receiver substrate.
8. The electronic device of claim 7 wherein the receiver substrate
is a flexible polymer.
9. The electronic device of claim 7 wherein the organic
semiconductor is selected from pentacene, alpha,
alpha'-bis-4(n-hexyl)phenyl bitiophene and polythiophene.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for the
fabrication of thin film electronic devices in which the
semiconductor portion of the device is deposited by lamination from
a donor substrate on to a receiver substrate. The donor or the
substrate may include other elements of the device, such as
conductors or dielectrics. This dry lamination process is useful
for fabricating devices such as transistors or light-emitting
devices on flexible, polymer substrates, which require low
temperature fabrication processes.
TECHNICAL BACKGROUND
[0002] Most active electronics today is done using silicon
integrated circuit (IC) technology on crystalline or on other hard
surfaces. In recent years, lower cost paths than silicon IC
processes have been emerging. Thin film transistors can be
fabricated with low-cost flexible plastics as a substrate using low
temperature processes. Combining flexible substrates with low cost
continuous printing methods is a goal that would allow for the
production of inexpensive or large applications that IC silicon
technology cannot deliver. Examples of products that would benefit
with low cost flexible electronics are disposable tags, sensors or
flexible displays. The use of polymer substrates dictates that the
thin film transistor fabrication processes operate at low
temperature. Additionally, it is desired that transistor
fabrication processes operate at ambient pressure so that large
areas of polymer substrate can be processed without introduction
into a vacuum chamber.
[0003] Japanese Patent 2002236286 discloses a colored organic film
used as a layer insulation membrane, which is laminated. U.S. Pat.
No. 6,197,663 discloses a thin film transistor formed by laminating
two substrates together. An interconnect structure is transferred
during the lamination. An organic semiconductor is not transferred.
In contrast, the present invention describes a process where the
semiconductor of a thin film device is transferred to a substrate
by lamination as defined herein.
SUMMARY OF THE INVENTION
[0004] The present invention concerns a process comprising: [0005]
a) depositing an organic semiconductor on a donor substrate; [0006]
b) laminating the organic semiconductor on the donor substrate with
a receiver substrate; and [0007] c) removing the donor
substrate.
[0008] The present invention also includes the above process where
the receiver substrate is a flexible polymer.
[0009] The present invention further describes an electronic device
comprising a semiconductor laminated on a receiver substrate.
[0010] The present invention further describes an electronic device
comprising a semiconductor laminated on a receiver substrate where
the electronic device is a transistor.
[0011] The present invention also includes the transistor described
above where the substrate is a flexible polymer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates an organic polymer semiconductor
deposited on a donor sheet.
[0013] FIG. 2 depicts the donor sheet oriented for lamination with
a substrate containing transistor elements.
[0014] FIG. 3 shows a micrograph of a laminated organic polymer
semiconductor on a substrate.
[0015] FIG. 4 shows the transistor characteristics of a transistor
with a laminated organic semiconductor of
.alpha.,.alpha.'-bis-4-(n-hexyl) phenyl bitiophene (6PTTP6).
[0016] FIG. 5 shows the transistor characteristics of a transistor
with a laminated organic polymer semiconductor of
polythiophene.
[0017] FIG. 6 compares the transistor characteristics of laminated
and evaporated pentacene.
[0018] FIG. 7 further compares the transistor characteristics of
laminated and evaporated pentacene.
DETAILED DESCRIPTION
[0019] A thin film field effect transistor herein consists of a
semiconductor material between a source and a drain electrode. The
source and the drain electrodes and the semiconductor are
electrically insulated from a third, gate, electrode by a
dielectric layer. Numerous low temperature printing processes have
been developed to apply the conductive electrodes to polymer
substrates. These include lithography, laser printing, micro
contact printing and ink jet printing. The objective of the present
invention is to provide a low temperature, ambient pressure method
of depositing a semiconductor during the fabrication of a thin film
transistor.
[0020] In the present invention, organic semiconductors such as
pentacene, alpha, alpha'-bis-4(n-hexyl)phenyl bitiophene or
polythiophene can be deposited on a flexible donor substrate. The
donor substrate is the material on which the semiconductor is
initially deposited prior to lamination with the desired receiver
substrate. The receiver substrate is frequently patterned with
other elements of an electronic device such as sources and drains
of a field effect transistor. Deposition can be accomplished
through evaporation, spin casting or drop casting. Evaporation of
the semiconductor on to the donor substrate may be performed in a
vacuum chamber. Spin casting or drop casting involve the
dissolution of the semiconductor in a solvent, application of the
resulting solution to the donor substrate, and evaporation of the
solvent, leaving a film of semiconductor on the donor substrate.
The donor substrate may be sheets of Teflon, Mylar, Kapton, or
similar materials. Some donor substrates may contain additional
intermediate layers to facilitate the semiconductor film formation
or release, or to improve the conformal coverage of the receiver
substrate.
[0021] After semiconductor deposition on the donor substrate, the
donor substrate is positioned relative to the flexible polymer
substrate with the semiconductor deposit situated between the
flexible polymer substrate and the transfer substrate. At this
point, the receiver substrate may be already patterned with other
elements of the thin film transistor. Two arrangements are
particularly convenient. In the first arrangement, the gate
electrode may be deposited directly on the flexible polymer
substrate and then covered with a dielectric layer. The organic
polymer semiconductor is then laminated over the dielectric. By
lamination, it is meant that a layer of transferable material
deposited on a donor substrate will be pressed against a receiver
substrate at a desired temperature such that the transferable
material adheres to the receiver substrate. There is no motion of
the donor substrate in the plane of contact with the receiver
substrate. Finally, the source and drain electrodes are deposited
on the semiconductor layer. Alternatively, the source and drain may
be deposited directly on the donor substrate. The semiconductor is
then laminated over the source and drain. A dielectric layer is
then deposited over the semiconductor and a gate electrode is
deposited over the dielectric.
[0022] The semiconductor deposition via lamination presents several
advantages over the direct deposition onto a substrate. In the case
of solution deposition, applying the solvent on to a donor sheet
first resolves all the chemical compatibility issues between
different layers of the transistor, since by the time the
semiconductor is ready for lamination, all the solvents have
evaporated. This technique also allows for a preparation of a
smaller size donor sheet that can be partitioned to cover a large
area electronic panel. The latter feature of lamination can be
critical when semiconductors need to be evaporated in a vacuum
chamber: the size of the vacuum chamber does not limit the size of
the electronic panel. Spin coating of large areas can also be
challenging, and lamination again decouples the size of the donor
and the size of the electronic circuits being built. It may also be
possible to have a donor sheet that can withstand higher
temperatures than the substrate, and thus semiconductor lamination
opens up opportunities in flexible electronics to materials that
require high temperature annealing, such as amorphous Si. Finally,
the intermediate step of preparing a donor sheet allows for
preparation of semiconductors in a different facility and at a
different time than the final device, which can be a feature if
solvents or vacuum chambers have different requirements than the
semiconductor assembly facility.
EXAMPLES
Example 1
[0023] This example describes how to laminate a semiconductor by
coating a donor with a drop of organic semiconductor solution.
[0024] A sheet of Teflon paper 11 was placed on a 120.degree. C.
hot plate inside a glove box. A few drops of
.alpha.,.alpha.'-bis-4-(n-hexyl) phenyl bitiophene (6PTTP6)
semiconductor in chloroform were placed on the Teflon. The drops
were allowed to dry on the hotplate for a few minutes, resulting in
circular patterns of semiconductor with thicker edges where most of
the solution agglomerated. After about 5 minutes the donor was
removed from the hotplate and left at room temperature for 30
minutes. The drop of 6PTTP6 dried unevenly, leaving a ring pattern
10 as depicted in FIG. 1. The donor sheet 11 was then pressed in a
laminator onto a Si wafer patterned with a gate electrode 15,
dielectric 12, and source 13/drain 14 pair. The laminator press
(not shown) consist of two iron plates which were warmed to
85.degree. C. and pressed together with a force of 1 to 10
kilopounds. FIG. 2 illustrates the orientation of the donor
substrate and the dried semiconductor relative to the electrode
elements of a transister. The donor was then peeled-off. The
semiconductor remained on the Si-wafer thereby completeing the
transistor. A Micrograph of the device achieved using a "laminated
semiconductor" is shown in FIG. 3.
[0025] The area surrounding the transistor was scratched to reduce
the leakage. The sample current-voltage characteristic obtained
from this device is shown as FIG. 4, where the gate voltage was
swept from 0 to -60V. The resulting mobilities are .about.10.sup.-7
cm.sup.2/Vs.
Example 2
[0026] This example describes the lamination of a semiconductor by
spin-coating the semiconductor onto the donor sheet. A sample of
polythiophene (Aldrich) dissolved in toluene was spin-coated onto a
Mylar/Elvax/Cronar/Latex donor. The coating was done inside a
glove-box, at room temperature and a speed of 1000 rpm for 1
minute. The coated donor was then laminated onto a Si-based
gate/dielectric/source-drain structure, completing the transistor
by the transfer of a semiconductor. The lamination was performed at
2 klb pressure at 85.degree. C. During lamination, only the
semiconductor was transferred from the donor sheet to the Si-chip.
The resulting transistor had mobilities as high as 10.sup.-3
cm.sup.2/Vs: The current voltage characteristics are shown in FIG.
5.
Example 3
[0027] This is an example of lamination of a semiconductor where
the semiconductor donor was prepared by evaporation. A
Mylar/Elvax/Latex donor sheet was placed in a thermal evaporator.
Pentacene was evaporated at a pressure of 10.sup.-7 Torr at a rate
of .about.0.02 nm/sec. As a control, a Si-chip containing a
gate/dielectic/source-drain structure was placed together with the
donor sheet. Approximately 1200 nm of pentacene was deposited at
room temperature. The donor sheet was laminated onto a Si-chip
identical to the control sample, at 85.degree. C. and 2 klb. The
pentacene was transferred onto the chip but the dielectric (latex)
was not. The results of the laminated pentacene as compared to the
evaporated pentacene are shown as FIG. 6. The mobilities decreased
with lamination as compared to evaporation. The threshold voltage
increased, but the on/off ratios of the transistors remained the
same or improved, as shown in FIG. 7. In FIG. 7, the evaporated
pentacene is the upper curve. The on/off current ratio is
2.times.10.sup.3. The lower curve of FIG. 7 is laminated pentacene.
The on/off ration is 10.sup.5.
* * * * *