Improved performance of low-voltage pentacene OTFTs by Incorporating La to Hafinium Oxide Gate dielectric

Pentacene OTFTs with HfLaO or HfO₂ as gate dielectric were fabricated. The dielectrics were prepared by sputtering method and then annealed in NH₃ at 400 oC. The k value for the HfLaO and HfO₂ films amounted to 12.3 and 11.8 respectively. Both of the OTFTs could operate with a supply voltage of -5 V. The mobility of the OTFT with HfLaO gate dielectric was 0.688 cm²/Vs, which was much higher than that of the OTFT with HfO₂ gate dielectric. Moreover, the HfLaO-based OTFT obtained smaller sub-threshold swing, larger drive current and larger on/off current ratio than the HfO₂-baesd OTFT. The superior performance of the HfLaO-based OTFT is due to its better interfacial characteristics between the dielectric and the organic semiconductor. SEM images revealed that the pentacene film on HfLaO was more uniform and its grains were larger. C-V measurement indicated that Au-pentacene-HfLaO-Si structure displayed less hysteresis than Au-pentacene-HfO₂-Si structure.