Controlling Chain Conformations of High-k Fluoropolymer Dielectrics to Enhance Charge Mobilities in Rubrene Single-Crystal Field-Effect Transistors

An experiment was conducted to demonstrate that high-k polymer dielectrics are not incompatible with high-mobility field-effect transistors. Films of P(VDF-BTFE) were prepared by hot pressing polymer powders] Three grams of 9 mol% BTFE P(VDFBTFE) copolymer was freezer milled with 3/3 wt% each of dicumyl peroxide (DCP) and triallyl isocyanurate (TAIC) in liquid nitrogen. By placing the powder mixture in the center of a 4 in. heavily doped p-type silicon wafer, the wafer was sandwiched between two stainless steel plates and two sheets of Teflon to prevent polymer from adhering to the plates. The sample was then placed in the hot press. To melt all components before applying pressure, the temperature was increased to 100°C. Once the temperature was reached, pressure was increased by 500 psi every 5 min up to 6000 psi as the temperature was increased to 200°C. The sample was allowed to sit for 6 h where the crosslinking occurred. A thin film of crosslinked P(VDF-BTFE) was obtained. Bottom-gate, top-contact OFETs were fabricated by laminating high-quality rubrene single crystals on various dielectric films. Graphite electrodes were painted on two ends of the longer axes of crystal. Rubrene single-crystal devices based on crosslinked P(VDF-BTFE) exhibit mobilities beyond the typical limit for devices with high-k dielectrics, and achieve among the highest reported mobility for any rubrene device.