BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIGS. 1A˜1C are cross-sectional views illustrating the manufacturing flow of an active layer of a thin film transistor according to the first embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating the method of fabricating an active layer of a thin film transistor according to the second embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating the structure of a liquid crystal display according to the third embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
FIGS. 1A˜1C are cross-sectional views illustrating the manufacturing flow of an active layer of a thin film transistor according to the first embodiment of the present invention.
Referring to FIG. 1A, a substrate 100 having a gate 102 and a source/drain 104 formed thereon is provided, and an insulating layer 106 which separates the gate 102 and the source/drain 104 is further deposited on the substrate 100. For the application to low cost and large size product, the substrate 100 may be a Si wafer, a glass substrate, a ceramic substrate, a metal substrate, a paper substrate, or a plastic substrate. The gate 102 and the source/drain 104 may be comprised of metal material, transparent conductive material, and organic conductive material, wherein the metal material may be Al, Cu, Mo, Ag, or Au, the transparent conductive material may be indium tin oxide (ITO) or antimony tin oxide (ATO), and the organic conductive material may be poly (3,4-ethylene dioxy-thiophene) (PEDOT). The insulating layer 106 may include organic insulating material such as poly (vinyl pyrrolidone) (PVP), polyvinyl alcohol (PVA), poly (methyl methacrylate) (PMMA), and polyimide (PI), or inorganic insulating material such as SiOx, SiNx, LiF, and Al2O3. Even though only a bottom-gate thin film transistor is illustrated in the figures of the first embodiment, the present invention may also be applied to other types of thin film transistors, such as a top-gate thin film transistor.
Referring to FIG. 1B, a semiconductor precursor solution is then prepared through a liquid process which may be sol-gel, chemical bath deposition, photo-chemical deposition, or evenly distributing suitable semiconductor nano particles into a solvent. After that, the semiconductor precursor solution is provided on the substrate 100 to form a semiconductor precursor thin film 108, and the method used herein may be spin-coating, inkjet printing, drop-printing, casting, micro-contact, micro-stamp, or dipping. The material of the semiconductor precursor thin film 108 may be II-VI compound semiconductor precursor, and other II-VI compound semiconductor precursors may also be used besides ZnO adopted in following embodiments. Here a soft baking step is performed selectively to remove organics in the semiconductor precursor solution.
Referring to FIG. 1B again, a light source 114 is used to irradiate the semiconductor precursor thin film 108 to remove residual solvent in the semiconductor precursor thin film 108 and transform the semiconductor precursor thin film 108 into a semiconductor layer having semiconductor property. In this embodiment, the light source 114 has a wavelength between 5 nm and 750 nm and an energy density between 0.01 mj/cm2 and 1200 mj/cm2. For example, the light source 114 may be KrF excimer laser of 248 nm, H-20 UV (referring to Journal of CRYSTAL GROWTH 256 (2003) pages 73-77, titled as “Photoconductive UV detectors on sol-gel-synthesized ZnO films”) between 300 nm and 750 nm, Nd:YAG laser (referring to IEEE Photonics Technology Letters, Vol. 16, No. 11 (November, 2004) pages 2418-2420, titled as “Sol-Gel ZnO-SiO2 Composite Waveguide Ultraviolet Lasers”) of 355 nm, or other light sources of suitable wavelengths. Besides, to accomplish patterned effect, a mask 110 composed of a non-transmissive region 112a and a transmissive region 112b may be provided as a mask before irradiating the semiconductor precursor thin film 108 with the light source 114.
Referring to FIG. 1C, the semiconductor precursor thin film 108 irradiated by the light source (the light source 114 in FIG. 1B) then transforms into a semiconductor active layer 116. In an embodiment of the present invention, the semiconductor precursor thin film 108 that is not irradiated by the light source can be removed selectively and the solvent used for preparing the semiconductor precursor solution can be used directly so that no photolithography process is required.
The actual procedure of the first embodiment will be described in following example.
EXAMPLE
In this example, the zinc oxide (ZnO) sol-gel solution is prepared with sol-gel. First, 100 ml 2-methoxyethanol and 3.62 ml monoethanol amine (MEA) are mixed into a mixture solution, and then 13.2 g zinc acetate is dissolved into the mixture solution. The mixture solution is stirred for 30 minutes at 60° C. to be confectioned into a ZnO precursor solution.
After that, the foregoing ZnO precursor solution is formed on a glass substrate through spin-coating having an ITO gate (˜1 kÅ) and a source/drain (˜1 kÅ) a layer of SiO2 has been deposited between the gate and the source/drain serving as an insulating layer (˜3 kÅ) formed thereon. Next, a step of soft baking is performed at 200° C. to transform the ZnO precursor solution into a ZnO thin film. Eventually, a KrF excimer laser having a wavelength of 248 nm is used for irradiating the ZnO thin film over the device channel (the area between the source and the drain) through a mask to remove organic bonding in the ZnO thin film and to transform the ZnO from insulative into semiconductive, so as to obtain the desired thin film transistor.
When the voltage at the gate of the thin film transistor is 100V and the voltage at the drain thereof is also 100V, the current on/off ratio of the ZnO thin film transistor is 103, and the carrier mobility thereof is 1.81×10−4 cm2/Vs.
FIG. 2 is a cross-sectional view illustrating the fabrication process of an active layer of a thin film transistor according to the second embodiment of the present invention, wherein the same reference numerals as those in the first embodiment are used.
Referring to FIG. 2, the difference of FIG. 2 from the first embodiment is that the semiconductor precursor thin film 200 with a desired pattern may be formed using, such as inkjet printing, drop-printing, casting, micro-contact, or micro-stamp. Accordingly, no mask is required for irradiating the semiconductor precursor thin film 200 with the light source 114.
FIG. 3 is a cross-sectional view illustrating the structure of a liquid crystal display according to the third embodiment of the present invention.
Referring to FIG. 3, in the present embodiment, the liquid crystal display includes a display substrate 302, a counter substrate 304, and a liquid crystal layer 306 between the display substrate 302 and the counter substrate 304. The display substrate 302 includes a first substrate 308, a first electrode layer 310 formed on the first substrate 308, a thin film transistor 312 deposited on the first substrate 308 and electrically connected to the first electrode layer 310, and a first alignment film 314 deposited on the first electrode layer 310. Wherein the thin film transistor 312 is a thin film transistor formed in the first embodiment and which includes a gate 102, a source/drain 104, an insulating layer 106, and a semiconductor active layer 116. The semiconductor active layer 116 connecting the source/drain 104 may be a ZnO II-VI compound semiconductor layer, and the materials of the other layers can be referred to the first embodiment. Besides, the thin film transistor 312 also includes a semiconductor precursor thin film 108 connected to the semiconductor active layer 116; however, the semiconductor precursor thin film 108 may also be removed.
Referring to FIG. 3 again, a passivation layer 316 may be further deposited between the first electrode layer 310 and the thin film transistor 312. The counter substrate 304 includes a second substrate 318, a second electrode layer 320 formed on the second substrate 318, and a second alignment film 322 deposited on the second electrode layer 320. The first and the second alignment layers 314 and 322 may be rubbing alignment layers, photo alignment layers, or ion alignment layers.
Besides being applied to the active-matrix liquid crystal display in the third embodiment, the thin film transistor in the present invention may also be applied to other types of displays or equipments such as smart card, price tag, inventory tag, solar cell, and large-area sensor array.
In summary, a liquid process is adopted along with a light source of suitable wavelength and energy in the present invention to replace the conventional thermal process. Thus, the process of the present invention can be performed in atmospheric air where only partial heating is required. Accordingly, the process is suitable for manufacturing low-cost, large-size product. Alternatively, a desired pattern may be formed, and therefore no additional photolithography or etching process is required, accordingly the process can be simplified and the fabrication cost can be effectively reduced.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Patent Application
20080057631
