Nanometer-Sized Crystalline Clusters of IGZO Films Determined from the Grazing Incidence X-ray Scattering and Anomalous X-ray Scattering Data Combined with Reverse Monte Carlo Simulations

Abstract

Grazing incidence X-ray scattering measurements have been carried out on c-axis aligned crystalline-indium gallium zinc oxide (CAAC-IGZO) film and nanocrystalline category-indium gallium zinc oxide (NC-IGZO) film and the following results were obtained: (1) the characteristic layered structure of the IGZO crystal did not hold its shape and the X-ray scattering profile showed only a relatively sharp first peak at the wave vector (Q) = 21.8 for CAAC film and 23.1 nm ¹1 for NC film, respectively, and additional weak broad peaks were observed at a higher angle. (2) In the case of the CAAC film, tiny peaks were observed at Q = 7 and 14 nm ¹1 , corresponding to the positions of the 003 and 006 reflections, respectively, of the IGZO crystal. Such tiny peaks were not detected in the case of NC film but the asymmetry of the first peak at the low angle side was clearly observed. (3) These structural features implied that more than three polyhedral units, such as InO x (x = 46), GaO y (y = 46), and ZnO z (z = 46), were likely to coexist. It is appropriate to call this structural feature as cluster-1. (4) A composite-type structure formed by combining these polyhedral units is also likely to exist and leads to middle-range ordering. This structure is called cluster-2. The size of such cluster-2 has been estimated to be 2.2 nm for CAAC film and 1.8 nm for NC film using the measured pair distribution function. To gain insights into the structural features of IGZO films, realistic atomic-scale models were obtained to fit not only the ordinary interference function of grazing incidence X-ray scattering but also the environmental interference function of the anomalous X-ray scattering (AXS) with Zn-absorption edge using reverse Monte Carlo (RMC) simulation. (5) The resultant models indicated the complex and irregular atomic arrangements of two types of IGZO films, which are well characterized by nanometer-sized crystalline clusters. This characteristic feature may be referred to as crystallineclustercomposite (triple C) structure.

Crystalline IGZO ceramics (crystalline oxide semiconductor)–based devices for artificial intelligence

“…We have confirmed the existence of an amorphous structure only in simulation . CAAC‐IGZO is a crystalline phase that has a structure in the boundary region between an amorphous structure and a crystal structure, including single crystal and polycrystal …”

“…Noboru Kimizuka, who first synthesized single‐crystalline IGZO, indicated that the crystal morphology of CAAC and nanocrystal (nc) should be classified as an intermediate state that is neither an amorphous structure nor a crystal structure. Similarly, Dr. Yoshio Waseda mentioned that CAAC and nc should be put in the category of a novel boundary region …”

“…18,19 CAAC-IGZO is a crystalline phase that has a structure in the boundary region between an amorphous structure and a crystal structure, including single crystal and polycrystal. [20][21][22][23][24][25] Dr. Noboru Kimizuka, who first synthesized single-crystalline IGZO, 1,2,26 indicated that the crystal morphology of CAAC 21 and nanocrystal (nc) [22][23][24] should be classified as an intermediate state that is neither an amorphous structure nor a crystal structure. Similarly, Dr. Yoshio Waseda mentioned that CAAC and nc should be put in the category of a novel boundary region.…”

“…Similarly, Dr. Yoshio Waseda mentioned that CAAC and nc should be put in the category of a novel boundary region. 20 Note that a single-crystalline FET is typically used in Si LSI. The single-crystalline Si FET has high mobility but requires high process temperatures, which limits available substrates.…”

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.…”