To clarify the origin of the major donor states in indium gallium zinc oxide (IGZO), we report measurement results and an analysis of several physical properties of IGZO thin films. Specifically, the concentration of H atoms and O vacancies (V O ), carrier concentration, and conductivity are investigated by hard X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, thermal desorption spectroscopy, and Hall effect measurements. The results of these experiments suggest that the origin of major donor states is H occupancy of V O sites. Furthermore, we use first-principles calculations to investigate the influence of the coexistence of V O and H in crystalline InGaO 3 (ZnO) m (m ¼ 1). The results indicate that when H is trapped in V O , a stable complex is created that serves as a shallow-level donor. V C 2014 AIP Publishing LLC.
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).
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.
In–Ga–Zn oxide (IGZO) is a next-generation semiconductor material seen as an alternative to silicon. Despite the importance of the controllability of characteristics and the reliability of devices, defects in IGZO have not been fully understood. We investigated defects in IGZO thin films using electron spin resonance (ESR) spectroscopy. In as-sputtered IGZO thin films, we observed an ESR signal which had a g-value of g = 2.010, and the signal was found to disappear under thermal treatment. Annealing in a reductive atmosphere, such as N2 atmosphere, generated an ESR signal with g = 1.932 in IGZO thin films. The temperature dependence of the latter signal suggests that the signal is induced by delocalized unpaired electrons (i.e., conduction electrons). In fact, a comparison between the conductivity and ESR signal intensity revealed that the signal's intensity is related to the number of conduction electrons in the IGZO thin film. The signal's intensity did not increase with oxygen vacancy alone but also with increases in both oxygen vacancy and hydrogen concentration. In addition, first-principle calculation suggests that the conduction electrons in IGZO may be generated by defects that occur when hydrogen atoms are inserted into oxygen vacancies.
We have fabricated a 5.5‐inch 4K2K liquid crystal display (LCD) using an oxide semiconductor. The use of an oxide semiconductor layer of a high‐mobility indium‐rich material and a top‐gate structure enables fabrication of a 4K2K LCD with a narrow bezel and an integrated demultiplexer.
The improvement in the reliability of a channel-etched fieldeffect transistor (FET) using a buried channel effect was achieved by stacking In-Ga-Zn-O (IGZO) films with different compositions.In addition, a liquid crystal display panel using an IGZO multilayer c-axis-aligned crystal FET for a backplane was fabricated.
This work presents oxide‐semiconductor FETs with submicron channel length (L) below the resolution limit of the exposure system used in their fabrication on glass substrates. The improved patterning method proposed here enables FET fabrication with L = 0.7 μm and small variation in the characteristics, leading to high on‐state current.
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