Pentacene organic thin-film transistors (OTFTs) have demonstrated the highest performance among TFTs with an organic semiconductor channel. High operating voltages (20-100 V), stemming from poor capacitive coupling between gate electrode and channel, are a major limitation, particularly for portable battery-powered device applications. OTFTs fabricated on flexible polymer substrates, often characterized by rough surfaces, benefit from the use of high-K dielectrics given the ability to accommodate thicker films which ensure the pinhole-free and good coverage without need to increase operating voltage. As we demonstrate, pyrochlore structured thin films can provide the requisite high dielectric constant coupled with excellent leakage current characteristics, while remaining compatible with the processing requirements of flexible OTFTs. The introduction of an extremely thin parylene film between the BZN dielectric and the pentacene semiconductor markedly shifts the threshold voltage, making it possible to fabricate both enhancement (E) and depletion (D) TFTs. We report the successful fabrication of low-voltage (< 2 V) organic transistors and depletion-load inverter using a 200-nm-thick pyrochlore gate dielectric, Bi1.5Zn1.0Nb1.5O7 (BZN), prepared by a room temperature process. The inverters with depletion load were successfully operated under 5 V with excellent noise margin.