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 (HfxSi1-xO2) thin film as a high-k dielectric layer. For growth of the HfxSi1-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 angstrom 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 Hf0.67Si0.33O2 dielectric layer were characterized and the results were compared to the pentacene TFTs using Al2O3 and SiO2 film as dielectric layers. The pentacene/Hf0.67Si0.33O2 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/HfxSi1-xO2 TFTs have great potential as high mobility devices with low operational voltage.