Relation between crystallinity and constituent distribution of an IGZO thin film

Abstract

This study examines the crystallinities of indium-gallium-zinc oxide (IGZO) films deposited by sputtering at room temperature under varying conditions and a difference in composition among the films, then we assess the effect of these differences on the FET characteristics. Each sample is found to be nanocrystalline IGZO. The crystallinity and the degree of the c-axis alignment are improved with the increase of the O 2 gas flow ratio in the IGZO deposition. The composition analysis results demonstrate that the ratio of In to Ga and Zn is uneven, and the elements exist separately in all the samples with different conditions. Moreover, every sample is in a composite-like (composite-compound-like) state. An FET, including IGZO deposited with an O 2 gas flow ratio of 50%, which is the condition that improves crystallinity, exhibits a favorable reliability.

Systematic Study on the Amorphous, C-Axis-Aligned Crystalline, and Protocrystalline Phases in In–Ga–Zn Oxide Thin-Film Transistors

“…This weak signature is attributed to a-IGZO , based as well on simulated XRD . Note that previous reports have observed that such a-IGZO can present a certain compositional ordering at the nanoscale, , but this is not resolved in the present study. The increase of T sub to 100 °C triggers, on the one hand, a shift of the weak diffraction maximum (WD max) to the left, and on the other hand, an appearance of a crystalline peak at 2θ = 35°.…”

“…Substrate temperature T sub and the O 2 flow ratio in the O 2 + Ar sputtering gas mixture ( R O 2 ) are the most studied sputtering parameters for tuning of IGZO TFT performance. T sub is typically set in a range from 25 to 300 °C for IGZO sputtering. ,− R O 2 can be varied from 0 to 100% and affects the electronic defect density correlated with oxygen in IGZO films. IGZO TFT electrical properties, including bias stress, are largely influenced by the oxygen concentration and binding state in the films, − hence the optimization of R O 2 is essential for the development of IGZO TFTs with high bias stress stability.…”

“…Depending on T sub , R O 2 , and postprocessing techniques, IGZO can exhibit different phases and types of crystallinity. Examples are amorphous, polycrystalline, c -axis-aligned crystalline (CAAC), , and nanocrystalline (nc) IGZO. , As its production by reactive sputtering at room temperature is straightforward, amorphous IGZO (a-IGZO) is widely studied by many research groups. In particular, many reports describe the effect of varying R O 2 for room-temperature sputtered IGZO. ,− The formation of polycrystalline IGZO can be achieved by annealing a-IGZO thin films at temperatures above 600 °C, but it leads to severe TFT performance degradation .…”

“…CAAC IGZO and a-IGZO are thought to compete with each other, with some articles mentioning that CAAC IGZO is advantageous over a-IGZO. , However, few publications consider both CAAC and a-IGZO simultaneously to systematically show and rationalize the differences in their performance. For example, in ref ., there is a comparison of different sputtering conditions in the range of deposition temperatures between room temperature and 170 °C and R O 2 between 0 and 100% resulting in nc and CAAC IGZO, where nc-IGZO appears as amorphous in the absence of precise electron diffraction techniques. However, not much attention is paid to the exact onset between two IGZO phases.…”

A 5291‐ppi organic light‐emitting diode display using field‐effect transistors including a c‐axis aligned crystalline oxide semiconductor

“…Additionally, CAAC-OS FETs have the advantage of exhibiting an extremely low off-state current, making them suitable for display applications. Figure 2A indicates that even when the channel length of the [11][12][13][14][15][16][17][18][19][20] CAAC-OS FET employed as a driving FET is scaleddown to 200 nm, the off-state current remained lower than 1 × 10 −12 A, which is below the measurement limit. Therefore, when the display shows black, the amount of electric current that flows would be extremely small, leading to a low-power consumption.…”