Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
2001-11-05
2003-09-09
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
C257S411000, C438S099000, C438S281000
Reexamination Certificate
active
06617609
ABSTRACT:
TECHNICAL FIELD
This invention relates to organic thin film transistors having improved performance. More particularly, the invention relates to organic thin film transistors having a siloxane polymeric layer between the semiconductor and gate dielectric and methods of making such transistors.
BACKGROUND
Organic semiconductors are of great interest for a variety of applications involving low-cost electronics. It is believed that organics can be synthesized to incorporate the necessary electronic properties for a wide variety of devices, and also can be constructed to allow low-cost, reel-to-reel processing that is not currently possible for crystalline silicon microelectronics.
One area of concern in organic electronic devices is the quality of the interface formed between the organic semiconductor and another device layer. Prior work on the interface between the semiconductor and the gate dielectric has included using silazane or silane coupling agents on silicon oxide surfaces. Silane coupling agents can require complex deposition processes.
EP 1041652 A2 describes the use of several surface treatments to enhance the crystalline domain size of solution-cast oligothiophenes on SiO
x
for thin film transistors (TFTs), although measured charge carrier mobility values were generally lower than the untreated controls. Other work involving surface treatments in TFTs involved poly(vinyl alcohol) layers, which may be relatively thick. In rare instances, previous work has shown minor improvements in mobility. The predominant effects shown in the previous work have been no improvement and/or detrimental effects on mobility, without regard for other important aspects of device performance.
SUMMARY
The present inventors discovered materials for and methods of improving the properties of organic thin film transistors by controlling the interface between the organic semiconductor and the dielectric material. The organic thin film transistors of the invention also are suitable for low-cost manufacturing processes.
The present invention provides a substantially nonfluorinated polymeric layer having a thickness less than about 400 Å interposed between a gate dielectric and an organic semiconductor layer in an OTFT. The polymeric layer comprises a polymer having interpolymerized units according to the formula:
In this formula, each R comprises, independently, a group selected from hydrogen, C
1
-C
20
aliphatic, C
4
-C
20
alicyclic, arylalkyl, or aryl, and a combination thereof which may contain one or more heteroatom(s) and/or one or more functional group(s).
In another aspect, the present invention provides a method of making an OTFT comprising providing a substrate, forming a gate electrode on the substrate, forming a gate dielectric on the gate electrode, applying a substantially nonfluorinated polymeric layer having a thickness less than about 400 Å interposed between the gate dielectric and an organic semiconductor layer, depositing an organic semiconductor layer adjacent to the polymeric layer, and depositing a source electrode and a drain electrode contiguous to the organic semiconductor layer. An integrated circuit comprising OTFTs is also provided.
Any known thin film transistor construction option is possible with the invention. For example, the source and drain electrodes may be adjacent to the gate dielectric with the organic semiconductor layer over the source and drain electrodes, or the organic semiconductor layer may be interposed between the source and drain electrodes and the gate dielectric. In each option, the invention provides a siloxane polymeric layer between the organic semiconductor layer and the gate dielectric.
The present invention provides organic thin film transistors with one or more improvements over known devices. With the present invention, improvements in properties such as threshold voltage, subthreshold slope, on/off ratio, and charge-carrier mobility can be achieved. In addition, large improvements in at least one property, such as charge-carrier mobility, can be achieved with the invention, while maintaining other OTFT properties within desirable ranges. The improvements in device performance provided by the present invention enable the production by simpler processing conditions of complex circuits having higher operating speeds than an OTFT made without the polymer layer. This invention also enables the production of larger circuit elements having comparable performance to devices with very small features. Devices with larger feature sizes can be less expensive as they do not require expensive precision patterning methods.
As used herein, “a” or “an” or “the” are used interchangeably with “at least one”, to mean “one or more” of the element being modified.
Other features and advantages of the invention will be apparent from the following detailed description of the invention and the claims. The above summary of principles of the disclosure is not intended to describe each illustrated embodiment or every implementation of the present disclosure. The detailed description that follows more particularly exemplifies certain preferred embodiments utilizing the principles disclosed herein.
DETAILED DESCRIPTION
Generally, a thin film transistor includes a gate electrode, a gate dielectric on the gate electrode, a source electrode and a drain electrode adjacent to the gate dielectric, and a semiconductor layer adjacent to the gate dielectric and adjacent to the source and drain electrodes. More specifically, an organic thin film transistor (OTFT) has an organic semiconductor layer. Such OTFTs are known in the art as shown, for example, in copending application U.S. Ser. No. 09/947,845, filed on Sep. 6, 2001, now U.S. Pat. No. 6,433,359, which is herein incorporated by reference.
The organic thin film transistor of the present invention further includes a siloxane polymeric layer interposed between the gate dielectric and the organic semiconductor layer.
Substrate
A substrate can be used to support the OTFT, e.g., during manufacturing, testing, storage, use, or any combination thereof. The gate electrode and/or gate dielectric may provide sufficient support for the intended use of the resultant OTFT and another substrate is not required. For example, doped silicon can function as the gate electrode and support the OTFT. In another example, one substrate may be selected for testing or screening various embodiments while another substrate is selected for commercial embodiments. In another embodiment, a support may be detachably adhered or mechanically affixed to a substrate, such as when the support is desired for a temporary purpose. For example, a flexible polymeric substrate may be adhered to a rigid glass support, which support could be removed. In some embodiments, the substrate does not provide any necessary electrical function for the OTFT. This type of substrate is termed a “non-participating substrate” in this document.
Useful substrate materials can include organic and/or inorganic materials. For example, the substrate may comprise inorganic glasses, ceramic foils, polymeric materials, filled polymeric materials, coated metallic foils, acrylics, epoxies, polyamides, polycarbonates, polyimides, polyketones, poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) (sometimes referred to as poly(ether ether ketone) or PEEK), polynorbomenes, polyphenyleneoxides, poly(ethylene naphthalenedicarboxylate) (PEN), poly(ethylene terephthalate) (PET), poly(phenylene sulfide) (PPS), and fiber-reinforced plastics (FRP).
A flexible substrate is used in some embodiments of the present invention. This allows for roll processing, which may be continuous, providing economy of scale and economy of manufacturing over some flat and/or rigid substrates. The flexible substrate chosen preferably is capable of wrapping around the circumference of a cylinder of less than about 50 cm diameter without distorting or breaking. The substrate chosen more preferably is capable of wrapping around the circumference of a cylinder of less than about 25 cm diameter with
Boardman Larry D.
Dunbar Timothy D.
Jones Todd D.
Kelley Tommie W.
Muyres Dawn V.
3M Innovative Properties Company
Crane Sara
Kokko Kent S.
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