Atomic layer deposition of hafnium silicate film for high mobility pentacene thin film transistor applications

The performance of pentacene thin film transistors (TFTs) was improved using a hafnium silicate (Hf_xSi_1-xO₂) thin film as a high-k dielectric layer. For growth of the Hf_xSi _1-xO₂ thin films, an atomic layer chemical vapor deposition (ALCVD) process was optimized using silicon alkoxide and hafnium amido as precursors. The self-limiting surface reactions of each precursor were observed, indicating the ALCVD growth characteristics. The film thickness linearly increased depending on the number of process cycles, with a remarkably high growth rate of 2.3 per cycle. The chemical binding states, thermal stability and electrical characteristics of the films grown were investigated using XPS, XRD and capacitance-voltage and leakage current-voltage analysis. The pentacene TFTs fabricated with the ALCVD-grown Hf_0.67Si _0.33O₂ dielectric layer were characterized and the results were compared to the pentacene TFTs using Al₂O₃ and SiO₂ film as dielectric layers. The pentacene/Hf _0.67Si_0.33O₂ TFT showed a three-fold and five-fold higher mobility than a pentacene/Al₂O₃ TFT and a pentacene/SiO₂ TFT, respectively. With additional treatments to enhance the characteristics of the OTFT, pentacene/Hf_xSi _1-xO₂ TFTs have great potential as high mobility devices with low operational voltage.