(A) study on conducting polymer thin films for the microbolometer sensing material

Abstract

In this paper, Poly(3,4-ethylenedioxythiophene):Poly(Styrenesulfonate) (PEDOT:PSS) thin films for application in a bolometer, a type of uncooled infrared image sensor, are presented. In order to maximize the sensitivity of an uncooled infrared image sensor, maximization of the temperature coefficient of resistance (TCR) and minimization of the 1/f noise of the sensing materials are required. While the material’s resistivity should be large enough for higher TCR, it is widely known that large resistivity usually accompanies high 1/f noise. For this reason, traditional bolometric materials such as vanadium oxide, amorphous silicon, which respectively have a good ratio of TCR over noise (over $10^3$ [1/℃], NETD less than 70mK), have been widely used. Numerous conducting polymers have been developed and studied in recent years. The PEDOT:PSS, an aqueous composite, is one of the most attractive conducting polymers, and has found a broad range of applications including use in modified electrodes, solar cells, and electroluminescent devices. The film formation of PEDOT:PSS is easily obtained through the spin coating method. The resultant film has an amorphous crystalline structure that is known to have high TCR values. These interesting features suggest that the PEDOT:PSS film is applicable to microbolometer sensing materials. The TCR and 1/f noise dependencies of PEDOT:PSS thin films on the thermal treatment conditions are demonstrated. Thermal treatment was carried out in a temperature range of 200-300℃ with time periods ranging from 5-100 minutes under the nitrogen ambient. It was found that the resistivity, and thereby the TCR and 1/f noise factor K, of the PEDOT:PSS can be modified by specific thermal treatment conditions. It was also showed that the appropriate heat treatment can suppress the 1/f noise of the PEDOT:PSS thin film while maintaining the resistivity and TCR. A high TCR value over -4%/℃ (within 10 ohm·cm) through chemical treatment was also present...