An active microheater matrix using polymer semiconductor diodes for thermal patterning

A novel active microheater matrix employing polymer semiconductor diodes is presented. Polymer diodes are used as heat sources instead of resistive microheaters to eliminate current leakages through unselected heater cells. In a 4 x 4 resistive microheater matrix, 44% of the applied current passes through the desired resistor, whereas in a 64 x 64 matrix, only 3% passes. Active heater matrices have been fabricated using a complementary metal oxide semiconductor (CMOS) process discrete components or amorphous silicon on glass technology, but not using organic electronics. This approach offers low cost and simplicity with a possibility of using flexible substrates. The fabricated 16 x 16 polymer diode matrix has a structure of indium tin oxide (ITO)/poly(3-hexylthiophene-2,5-diyl) (P3HT)/aluminum. They have a turn-on voltage of around 3 V. Polymer diode performance improves with temperature. A 2.7 mu A mm(-2) current density at 5 V at room temperature improves to 12.2 mu A mm(-2) at 120 degrees C due to the thermal excitation of the trap states on the boundaries of the polymer grains. The temperature of the selected heater increases with the applied current density. A current density of 3 mA mm(-2) heats the surface of the heater to 110 degrees C. Thermal patterning is achieved on thermally sensitive paper. 800 x 800 mu m(2) heater cells generate 930 x 930 mu m(2) black patterns.