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

Abstract

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 Å 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.