Solution-Processable Low Voltage Organic Transistors of Thieno[3,2-b]thiophene-Based Conducting Polymer

Abstract

A low-operating voltage and high performance polymeric field effect transistors using octadecylphosphonic acid-treated high-k AlOx and HfO₂ hybrid dielectrics were demonstrated. High-k metal oxide hybrid dielectrics were prepared by oxygen plasma treatment of deposited Al film for AlOx and by spin coating of solution-processable HfO₂ sol-gel solution for HfO₂ in combination with phosphoric acid-based self-assembled monolayer (SAM), resulting in high capacitance (10 nF/cm² for SiO₂, 600 nF/cm² for AlOx and 580 nF/cm² for HfO₂). With phosphoric acid-based SAM on high-k metal oxide and thermal annealing of thieno[3,2-b]thiophene-based conducting polymer, the device performance was significantly enhanced. The highest mobility of the transistors using ODPA-treated AlOx as a gate dielectric is 2.3 × 10⁻² cm² V⁻¹ s⁻¹ in the saturation region with the source-drain of −2 V. In ODPA-treated HfO₂ hybrid dielectric, the saturated mobility is 1.1 × 10⁻² cm² V⁻¹ s⁻¹ and the threshold voltage was measured to be −0.31 V, which is at least one order lower than SiO₂ hybrid dielectric (−3 V).

Keywords:

• Organic transistors
• low-operating voltage
• thieno[3
• 2-b]thiophene-based polymer
• dielectrics