Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
2001-05-29
2003-03-04
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
C257S368000, C438S099000
Reexamination Certificate
active
06528816
ABSTRACT:
The invention concerns an integrated inorganic/organic complementary thin-film transistor circuit comprising a first and a second transistor which are operatively connected and provided on a common substrate, wherein the first transistor is an inorganic thin-film transistor and the second transistor an organic thin-film transistor, wherein the separate gate electrodes are provided for each of the transistors, and wherein the complementary thin-film transistor circuit forms a multilayer thin-film structure.
The present invention also concerns a method for fabricating an integrated inorganic/organic complementary thin-film transistor circuit comprising a first and a second transistor which are operatively connected and provided on a common substrate, wherein the first transistor is an inorganic thin-film transistor and the second transistor a organic thin-film transistor, and wherein the complementary thin-film transistor circuit forms a multilayer thin-film structure with successively deposited and patterned thin-film layers, and wherein the method comprises depositing separate gate electrodes for respectively the first and the second transistor on a common substrate, and depositing material for the source electrode and the drain electrode of the organic thin-film transistor on the same level in the thin-film structure of the organic thin-film transistor.
Finally the present invention concerns a method for fabricating an integrated inorganic/organic complementary thin-film transistor circuit, comprising a first and a second transistor which are operatively connected and provided on a common substrate, wherein the first transistor is an inorganic thin-film transistor and the second transistor an organic thin-film transistor, and wherein the complementary thin-film transistor circuit forms a multilayer thin-film structure with successively deposited and patterned thin-film layers.
Integrated circuits of silicon realized as complementary metal-oxide semiconductors dominate the markets for a number of microelectronic applications such as microprocessors. But complementary circuits may also be of interest for more general application, e.g. in portable battery-operated electronic products, as they can provide very low static power dissipation for digital circuits. It has, however, turned out to be difficult to realize complementary integrated thin-film circuits with sufficient performance for commercial applications.
Hydrogenated thin-film transistors of silicon (a-Si:H TFT) have found a new application in thin-film components, particularly in liquid crystal displays with active matrix. However, complementary a-Si:H circuits are problematic, as the hole transport mobility typically is much lower than the electron transport mobility. Recently TFTs with organic active layers have been fabricated and with performance comparable to that which can be obtained with amorphous silicon devices (a-Si:H devices).
For instance there is in U.S. Pat. No. 5,347,144 (Garnier & al.) disclosed a thin-film field-effect transistor with an MIS structure which includes a thin semiconductor layer between the source and drain electrode. The thin semiconductor layer contacts a surface of a thin-film made of isolating material which at its second surface contacts a conducting grid. The semiconductor is made of at least one polyconjugated organic compound with a determined molecular weight. As organic semiconductor material Garnier & al. among others mention different various aromatic polycyclic hydrocarbons and among these polyacenes. The transistor of Garnier & al. is stated to be particularly suited as a switching or amplifying device.
Also simple organic complementary thin-film transistor circuits have been discussed in the literature, but have not shown the desired performance properties. Further attempts have been made building complementary circuits with combinations of inorganic and organic devices on separate substrates and with external connection.
In U.S. Pat. No. 5,625,199 (Baumbach & al.) there is, however, disclosed a complementary circuit with an inorganic n-channel thin-film transistor and an organic p-channel thin-film transistor. The n-channel thin-film transistor employs hydrogenated amorphous silicon as active material and the p-channel of the organic thin-film transistor employs &agr;-hexathienylene (&agr;-6T) as active semiconductor material. The complementary thin-film transistor circuit according to Baumbach & al. can be used for implementing an integrated complementary inverter or other complementary circuits.
The integrated complementary inorganic/organic thin-film transistor according to Baumbach & al. is, however, encumbered with a number of disadvantages both from a processual point of view as well as with regard to general application in more comprehensive transistor circuits. Thus Baumbach & al. propose to provide respectively the source and drain electrodes on both sides of the organic semiconductor layer, something which firstly is not necessary and additionally comports a number of disadvantages in the fabrication. Further the source and drain contacts of the organic thin-film transistor must be formed in different steps and it will also be difficult to pattern contacts on the top of the organic semiconductor unless shadow masks are used.
Nor has the complementary thin-film transistor according to Baumbach an isolated organic semiconductor material in the organic thin film transistor. As it will be desirable to be able to turn the inorganic transistor on and to turn the organic transistor off or vice versa using potential with the same sign, this may be problematic. In the complementary thin-film transistor according to Baumbach & al. it is probable that an undesirable large leakage will be problematic if the complementary thin-film transistor shall be used in complex circuits. An inverter realized according to Baumbach & al. switches as stated in the cited U.S. patent at about 5 V at a supply voltage of 7.2 V. Another disadvantage of the complementary thin-film transistor according to Baumbach & al. is that a common gate electrode is used both for the n-channel and the p-channel transistor. More complex transistor circuits built from complementary devices shall require that common electrodes are not used in these. Even in simple inverters a common gate electrode will give increased stray capacitance. Further it shall be remarked that the complementary thin-film transistor according to Baumbach & al. uses the inorganic transistor as n-channel transistor and the organic transistor as p-channel transistor, something which is understandable in light of the materials proposed. It is, however, evident from Baumbach & al. that the use of organic materials which may be used for forming active semiconductors of the n-type demands relatively complicated and costly fabricating processes and hence is not easy to realize for the time being.
In U.S. Pat. No. 5,162,228 (Shieh & al.) there is disclosed a method of fabricating a thin-film transistor with separate gate electrodes. The inorganic and organic thin-film transistors are of the n type and p type respectively and are shown integrated into a complementary circuit with the source and drain electrodes in both transistors being on the same respective levels. The organic thin-film transistor is shown patterned with an active semiconductor material of the p type and it is evident that the problem with stray capacitance essentially may be avoided. Shieh & al. relies on low-temperature processes in the deposition of the active semiconductor materials, but does not consider the problem inherent in the conventional patterning methods applied to an organic semiconducting material. Neither is the device as disclosed by Shieh & al. amenable to embodiments with n-type organic materials, particularly as the metal electrodes are deposited on the top of the n-type transistor's active and patterned semiconductor material.
A first object of the present invention is hence to overcome the disadvantages which are connected with prior art and particu
Bonse Mathias
Gundlach David J.
Jackson Thomas
Klauk Hagen
Thomasson Daniel B.
Birch & Stewart Kolasch & Birch, LLP
Meier Stephen D.
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