Achievement of a high-mobility FET with a cloud-aligned composite oxide semiconductor

Abstract

We have recently discovered that films of a widely used In–Ga–Zn oxide (IGZO) with have different material composition states when sputter-deposited under different conditions using the same polycrystalline IGZO target. Significant improvements in on-state current and mobility (as high as 40 cm2·V−1·s−1) are obtained. The results of local composition analysis indicate that the deposited film is not composed of any known homogeneous IGZO compound and that the components of this film are separated into two types of nanoparticle regions: one type is composed mainly of GaO x and GaZnO x , which contribute to on/off (switching) characteristics, and the other is composed mainly of InO x and InZnO x , which contribute to on-state characteristics. These regions constitute a new type of oxide semiconductor (OS) film. The nanoparticles with a blurry boundary extend like a cloud, probably complementing one another. We consider that this OS film has a novel composition, which can be described as a “cloud-aligned composite OS” (CAC-OS).

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 …”

“…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.…”

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.…”

23‐2: 2351‐ppi OLED Display with Stacked OS‐FETs with L = 0.36 µm

“…The OS-FETs in both the layers have normally-off characteristics and their off-state currents are below the measurement limit. Novel boundary region [14] Amorphous [12,13] Crystalline Crystal [2,3,11] completely ・ CAAC [6] (2009) ・ single crystal amorphous ・ nc [7][8][9] (2013) ・ poly crystal ・ CAC [10] (2016) excluding single crystal and poly crystal "Intermediate state" [ 3…”

“…Figure 1 shows classification of IGZO crystal structures. We have discovered c-axis aligned crystalline IGZO (CAAC-IGZO) [6], nanocrystalline IGZO (nc-IGZO) [7][8][9], and cloud-aligned composite IGZO (CAC-IGZO) [10], which, according to Kimizuka, have a structure with an "intermediate state" between an amorphous structure and a crystal structure [15]. We thus classify CAAC-IGZO, nc-IGZO, and CAC-IGZO as crystalline IGZO.…”