Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2002-01-15
2003-09-16
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S099000, C438S164000, C438S455000
Reexamination Certificate
active
06620657
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to semiconductor technology and device designs, and more particularly to an organic-based thin-film transistor device and a method for producing the same.
2. Description of the Related Art
Thin-film transistors (TFTs) with active organic layers and polymer-based electronic components are emerging as an inexpensive alternative to silicon-based TFTs for some applications. The use of organic and polymeric materials provides two main advantages: First, organic-based devices can be produced using a simpler and less expensive fabrication process in contrast to the expensive equipment and processing associated with silicon processing. Second, it is possible to fabricate the devices on flexible plastic substrates due to the ability to process organic materials at lower temperatures, and due to the greater mechanical flexibility of organic-based components relative to inorganic materials such as silicon and conductive metals. However, despite considerable research and development effort, organic-based TFTs have not yet reached commercialization, at least, in part, due to relatively poor device characteristics of prior art organic TFTs.
Fabrication of an all-organic TFT requires various organic or organic/inorganic hybrid materials: semiconductors, insulators, and conductors. The conductor may be selected from conducting polymers such as polyaniline and poly(ethylene dioxide thiophene), and metal or graphite colloid particle-based inks. There are a variety of polymeric organic insulators that may be used, such as polyimide or PMMA for the semiconductor. Organic p-type (hole transporting) and n-type (electron transporting) materials are both known in the art and have been tested as the semiconductive channel in TFTs. Two relatively simple device structures which have been used are the top contact and bottom contact, as shown in
FIGS. 1 and 2
, respectively. Generally, these devices comprise a source
1
and drain
2
. In the top contact (FIG.
1
), the source
1
and drain
2
are on top of an organic semiconductor
3
, whereas in the bottom contact (FIG.
2
), the source
1
and drain
2
are embedded in the organic semiconductor
3
. Below the organic semiconductor
3
is an insulator
4
in both the top and bottom contact devices. Embedded within the insulator
4
is a gate
5
. The entire device (both the top and bottom contact devices) is disposed on a substrate
6
.
FET mobilities are generally assessed in the top-contact geometry because applying the electrode materials on top of the semiconductor layer ensures intimate contact. It is desirable to use the bottom-contact configuration for some applications, but in this geometry, the contact between the electrode and semiconductor may be limited to a fraction of the vertical wall area of the electrode. This results in increased contact resistance. Problems with bottom-contact devices are well-known to those skilled in the art. A method to improve the bottom-contact geometry is to planarize the source and drain electrodes, which increases the area of contact to the organic semiconductor. A planar substrate allows for improved semiconductor films deposited by spin-coating or printing. However, topography of the bottom source and drain contacts in the prior art causes problems with printing the organic semiconductor, which would be remedied by using a planar substrate.
As mentioned, organic p-type (hole transporting) and n-type (electron transporting) materials are known in the art and have been tested as the semiconducting channel in TFTs. P-type materials include conjugated polymers and linear, conjugated molecules. Examples of p-type conjugated polymers include derivatives of regioregular polythiophene described in Bao and Lovinger, “Soluble Regioregular Polythiophene Derivatives as Semiconducting Materials for Field-Effect Transistors,” Chem. Mater., Vol. 11, pp. 2607-2612 (1999), the complete disclosure of which is herein incorporated by reference.
Examples of p-type conjugated molecules include pentacene, which has been extensively studied in TFTs, and further disclosed in U.S. Pat. Nos. 5,946,551; 5,981,970; and 6,207,472 B1; benzodithiophene dimers (Laquindanum et al., “Benzodithiophene Rings As Semiconductor Building Blocks,” Adv. Mater., Vol. 9, pp. 36 (1997); phthalocyanines (Bao et al., “Organic Field-Effect Transistors with High Mobility Based On Copper Phthalocyanine,” Appl. Phys. Lett., Vol. 69, pp. 3066-3068 (1996)); anthradithophenes (U.S. Pat. No. 5,936,259); and substituted and unsubstituted oligothiophenes, originally proposed in Gamier et al., in “Structural Basis For High Carrier Mobility In Conjugated Oligomers,” Synth. Met., Vol. 45, pp. 163 (1991); the complete disclosures of which are herein incorporated by reference.
There are comparatively fewer n-type organic semiconductors. Examples include 3,4,9,10-perylene tetracarboxylic dilmides described in Struijk et al., “Liquid Crystalline Perylene Dilmides: Architecture and Charge Carrier Mobilities,” J. Am. Chem. Soc., Vol. 122, pp. 11057-11066 (2000); 1,4,5,8-naphthalene tetracarboxylic dianhydride (Laquindanum et al., “n-Channel Organic Transistor Materials Based on Naphthalene Frameworks,” J. Am. Chem. Soc., Vol. 118, pp. 11331-11332 (1996)); 1,4,5,8-naphthalenetetracarboxylic dumide derivatives (Katz et al., “Naphthalenetetracarboxylic Dilmide-Based n-Channel Transistor Semiconductors: Structural Variation and Thiol-Enhanced Gold Contacts,” J. Am. Chem. Soc., Vol. 122, pp. 7787-7792 (2000)); and metallophthalocyanines substituted with various electron-withdrawing groups (Bao et al., “New Air-Stable n-Channel Organic Thin-film Transistors,” J. Am. Chem. Soc., Vol. 120, pp. 27-208 (1998); the complete disclosures of which are herein incorporated by reference.
In general, circuitry using organic transistors has the potential of reduced power consumption and simplicity in the design. However, complementary circuitry using both organic N and P channel transistors are not common, for example, U.S. Pat. No. 5,625,199, the complete disclosure of which is herein incorporated by reference, teaches a technique to fabricate complementary circuits with inorganic n-channel and organic p-channel thin-film transistors. Additionally, U.S. Pat. No. 5,936,259, the complete disclosure of which is herein incorporated by reference, describes a switch based on a thin-film transistor design (TFT) using a fused ring organic compound as a semiconductor. Furthermore, U.S. Pat. No. 5,804,836, the complete disclosure of which is herein incorporated by reference, describes an image processor design which operates on an array of polymer grid triodes. Similarly, prior art disclosures also teach a 5-stage ring oscillator using copper hexadecafluorophthalocyanide as the n-channel material and oligothiophenel oligothiophene derivative as the p-channel material.
Two popular structures of an existing polymer thin-film transistor are shown in FIGS.
3
(
a
) and
3
(
b
). These structures have two major disadvantages. First, the comer thinning problem due to topography, and second, the most sensitive portion of the body element is exposed to process-induced contamination. The resulting devices have poor performance and inconsistent properties. Shown in FIG.
3
(
a
) is the first typical structure of the polymer transistor. The source
11
and drain
12
are first patterned. Then, the body material
13
is deposited and patterned. The body
13
is a semiconductive polymer or oligomer, and it is applied to the surface of the source
11
and drain
12
islands by evaporation, spin-coating, dip-coating or printing, depending on the organic semiconductor used. The body material
13
is patterned in one of three ways: the most common method is by evaporation of the semiconductive material through a shadow mask.
The other two methods are printing (i.e., screen printing or inkjet printing) and using conventional lithography by first applying a protective coating over the semiconductor, then applying the photore
Breen Tricia L.
Clevenger Lawrence A.
Hsu Louis L.
Wang Li-Kong
Wong Kwong Hon
Roman Angel
Underweiser, Esq. Marian
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