Abstract
Flexible thin-film transistors with high current-driven capability are of great significance for the next-generation new display technology. The effect of a Cu-Cr-Zr (CCZ) copper alloy source/drain (S/D) electrode on flexible amorphous neodymium-doped indium-zinc-oxide thin-film transistors (NdIZO-TFTs) was investigated. Compared with pure copper (Cu) and aluminum (Al) S/D electrodes, the CCZ S/D electrode changes the TFT working mode from depletion mode to enhancement mode, which is ascribed to the alloy-assisted interface layer besides work function matching. X-ray photoelectron spectroscopy (XPS) depth profile analysis was conducted to examine the chemical states of the contact interface, and the result suggested that chromium (Cr) oxide and zirconium (Zr) oxide aggregate at the interface between the S/D electrode and the active layer, acting as a potential barrier against residual free electron carriers. The optimal NdIZO-TFT exhibited a desired performance with a saturation mobility (μsat) of 40.3 cm2·V−1·s−1, an Ion/Ioff ratio of 1.24 × 108, a subthreshold swing (SS) value of 0.12 V·decade−1, and a threshold voltage (Vth) of 0.83 V. This work is anticipated to provide a novel approach to the realization of high-performance flexible NdIZO-TFTs working in enhancement mode.
Highlights
Today, Cu interconnection metallization, including bus lines and device electrodes, plays an important role in high refresh rate, ultra-high definition, and large size of flexible displays, owing to its low resistivity and good mechanical performance [1]
Pure Cu has the advantages in terms of low resistivity [2, 3], it is difficult to be directly used as an electrode for a thin-film transistor (TFT) device due to its poor adhesion strength to a flexible substrate and copper atom diffusion issue
The results show that both the RC of TFTCCZ and TFTs with the pure Cu (TFT-Cu) will be modulated with the variation of VG: low VG corresponding to high RC and high VG corresponding to low RC
Summary
Cu interconnection metallization, including bus lines and device electrodes, plays an important role in high refresh rate, ultra-high definition, and large size of flexible displays, owing to its low resistivity and good mechanical performance [1]. Pure Cu has the advantages in terms of low resistivity [2, 3], it is difficult to be directly used as an electrode for a thin-film transistor (TFT) device due to its poor adhesion strength to a flexible substrate and copper atom diffusion issue. In view of this matter, copper alloying is a very promising copper metallization strategy without introducing a heterogeneous adhesion-barrier layer that leads to variety of etching problems in the subsequent photolithography process [4, 5]. Low-resistivity Cu-Cr-Zr (CCZ) ternary alloy following the “microquantity and multielement” guideline was developed for a flexible PI substrate, which is proposed in our previous work [16]
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