n-Type Thiophene Semiconductor Devices (20024
This invention demonstrates the use of n-type thiophene semiconducting films in the construction and operation of organic light-emitting diodes (OLED), thin film transistors (TFT), field effect transistors (FET) and related devices. Thiophene oligomers (nTs) and polymers (PTs) are known that operate as p-type semiconductors. However comparable electron transporting (n-type) organic materials are relatively rare as are stable n-type thiophene semiconductors. The invention of n-type thiophene conductive materials (NU 21049) provides a means to such materials. n-Type applications in FETs, stable electrode/electron transport in OLEDs, photovoltaic cells and other opto-electronic devices are feasible per this invention.
ADVANTAGES: Stable n-type organic semiconductor properties can be incorporated into the design and fabrication of a variety of transistor and electronic devices.
SUMMARY: α,α’-Conjugated thiophene oligomers (nTs) and polymers (PTs) have attracted great interest as semiconducting elements in organic thin-film transistors (TFTs). Noteworthy of this family of compounds are unsubstituted α,ω- and β,β’-dialkylsubstituted nTs (n = 4,6) and β-alkyl substituted PTs, which operate as p-type semiconductor with mobilities and Ion / Ioff ratios approaching those of amorphous silicon. The invention of an efficient preparation of n-type thiophene conductive materials (NU 21049) provides a means to meet the need for such materials in thin film deposition and related transistor and integrated circuit applications.
Thus, FET devices were constructed with 30-100 nm n-type thiophene films deposited onto n+-Si FET substrates with a 230 nm dry thermal SiO2 insulating layer, and Au source-drain contacts evaporated on the film. Transistor action was observed only for positive gate voltages indicating an accumulation of mobile electrons at the film- SiO2 gate dielectric interface. Ion / Ioff ratios ~105, 0.02 cm2/Vs mobility and 25-35 V turn on voltages were measured. (Figure A). Modification of the n-type thiophene structure and processing conditions enhance device characteristics and lifetime.
n-type thiophene films were also incorporated in n-channel junction field-effect transistors (JFET), Figure B. The JFET composed of a gate region (10) constructed from a p-type semiconductor material and a channel (12) constructed from an n-type thiophene film deposited on a suitable substrate. A voltage applied to a gate electrode (14) controls current flow through the thin/film substrate composite channel (12) between the drain (16) and source (18) electrodes.
Other transistor types including bipolar junction transistors (npn, pnp), MOSFETS (n and p), and integrated circuits can be fabricated using complementary n- and p-type thiophene materials.
Tobin J. Marks, Antonio Facchetti, Henning Sirringhaus and Richard H. Friend
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