1. Field of the Present Invention
The present invention relates to an organic inverter and a method of manufacturing the same, and more particularly, to an organic inverter including a surface-treated insulating layer, and a method of manufacturing the same. The present invention has been produced from the work supported by the IT R&D program of MIC (Ministry of Information and Communication)/IITA (Institute for Information Technology Advancement) [2005-S070-02, Flexible Display] in Korea.
2. Discussion of Related Art
An organic field-effect transistor is spotlighted as the next-generation electronic device because it has a simple process and may be manufactured on a flexible plastic substrate at low temperature compared to conventional silicon transistors. The organic field-effect transistor is used as a switching device in a flexible display, or used to manufacture a circuit such as organic radio frequency identification (RFID). When the organic field-effect transistor is used as a pixel driving switch of a display, it may be a transistor with a single polarity (i.e., a p-type transistor), but when it is used as a circuit, a CMOS transistor that is a combination of p- and n-type transistors is the most preferable for reducing power consumption or raising speed.
However, since organic semiconductors have not stable characteristics and reliability with respect to n-type devices so far, an inverter is generally formed of only a p-type transistor.
FIGS. 1A and 1B illustrate structures of D- and E-inverters which are formed of only a conventional p-type transistor. FIG. 1A illustrates a depletion-mode inverter in which a depletion transistor 1 is formed as a load, and an enhancement transistor 2 is formed as a driver. FIG. 1B illustrates an enhancement inverter having an enhancement transistor, which is used as both load and driver transistors 3 and 4. The former is commonly known as a D-inverter or a zero-driver load logic inverter, and the latter as an E-inverter or a diode-connected load logic inverter. The D-inverter illustrated in FIG. 1A provides better results in power consumption, gain and swing width than the E-inverter.
However, unlike the conventional silicon semiconductor, the organic semiconductor made of an organic material cannot control a threshold voltage by doping, and thus it is difficult to manufacture devices, which have different threshold voltage characteristics depending on positions on the same substrate. Until now, the variation of transistor dimension W/L (channel width/length) was an established solution for fabricating the load transistor of depletion mode and the driver transistor of enhancement mode in the same substrate for D-inverter. As the channel length is reduced, the shift from enhancement mode to depletion mode is observed. Thus, it is not easy to use the depletion load transistor with a relatively high W/L ratio in manufacturing a highly-integrated organic circuit with high resolution, and all the characteristics according to a size ratio have to be obtained for circuit design, since voltage transfer characteristics such as a speed or swing width depend on the size ratio between the depletion load transistor and the enhancement driver transistor.
In other words, in manufacturing a conventional organic inverter, a transistor with a high W/L ratio is generally used as a depletion load transistor due to a large current at a gate voltage (VG) of 0V, and a transistor with a small W/L ratio is generally used as an enhancement driver transistor due to a relatively small current at a gate voltage (VG) of 0V. Thus, prior to the design and manufacture of the inverter, all characteristics of the transistors depending on W/L ratios have to be ensured to obtain optimal conditions.