Since the first reports of charge storage in the gate dielectrics of organic semiconductors, several groups have proposed charge-storing dielectrics that become polarized through varied mechanisms, and have offered various explanations for observed charge storage phenomena. These groups were concerned either with nonvolatile memories as an application, or with controlling hysteresis in conventional OFETs. This manuscript describes measurements of surface charging and OFET threshold voltage shift for a case where charge is clearly stored in the dielectric. The magnitude and stability of the charge storage depend on the hydrophobicity of the dielectric and the charge deposition process. We focus on SiO_2 as the dielectric and use a thiophene oligomer or hexadecafluoro-copper phthalocyanine as semiconductor. In one case, the phthalocyanine was inverted from electron- to hole-carrying, enabling a complementary device to be made from a single semiconductor.
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