Photonic curing of sol-gel derived HfO2 dielectrics for organic field-effect transistors

An efficient way to reduce the supply voltages of organic field-effect transistors is the use of high-k inorganic materials. In order to allow high throughput during fabrication, solution-based processes for realizing inorganic dielectrics by using sol-gel procedures have become attractive in recent years. However, this procedure typically involves extended high-temperature annealing steps to achieve high-quality insulating layers which hampers fast fabrication and is incompatible to be carried out on low-temperature organic substrates. In this work, the use of a photonic curing technique is presented for the annealing of sol-gel derived hafnium oxide (HfO2) dielectrics within a few seconds. The investigations demonstrate the reduction of the leakage current density of more than 3 orders of magnitude after the photonic curing process reaching only slightly higher values as obtained with dielectric films formed from highly sophisticated atomic layer deposition. Moreover, capacitance measurements reveal a dielectric constant of 26 indicating bulk-like properties. Furthermore, organic transistors based on photonically cured HfO2 sol-gel dielectrics are fabricated and characterized operating at low voltages (<2 V), low subthreshold swing (110 mV/decade) and charge carrier mobilities of 1 cm2/Vs using a semiconducting liquid-crystal polymer.