Carrier Density-Tunable Work Function Buffer at the Channel/Metallization Interface for Amorphous Oxide Thin-Film Transistors

With the capability to tune the carrier density of InZnO (IZO), a thin conducting IZO buffer at the channel/metallization interface is introduced to enhance the contact behaviors for amorphous IZO thin-film transistors (TFTs). Photoelectron spectroscopic measurements reveal that the conducting IZO buffer, of which the work function (Φ) is 4.37 eV, relaxes a relatively large Φ difference between channel IZO (Φ = 4.81 eV) and Ti (Φ = 4.2–4.3 eV) metallization. The buffer is found to lower the energy barrier for charge carriers at the source to reach the effective channel region near the dielectric. In addition, the higher carrier density of the buffer and favorable chemical compatibility with the channel (compositionally the same) further contribute to a significant reduction in specific contact resistance as much as more than 2.5 orders of magnitude. The improved contact and carrier supply performance from the source to the channel lead to an enhanced field effect mobility of up to 56.49 cm2/V s and a threshold voltage of 1.18 V, compared to 13.41 cm2/V s and 7.44 V of IZO TFTs without a buffer.