Wen-Zhang Zhu

It is usually difficult to realize high mobility together with a low threshold voltage and good stability for amorphous oxide thin-film transistors (TFTs). In addition, a low fabrication temperature is preferred in terms of enhancing compatibility with the back end of line of the device. In this study, α-IGZO TFTs were prepared by high-power impulse magnetron sputtering (HiPIMS) at room temperature. The channel was prepared under a two-step deposition pressure process to modulate its electrical properties. X-ray photoelectron spectra revealed that the front-channel has a lower Ga content and a higher oxygen vacancy concentration than the back-channel. This process has the advantage of balancing high mobility and a low threshold voltage of the TFT when compared with a conventional homogeneous channel. It also has a simpler fabrication process than that of a dual active layer comprising heterogeneous materials. The HiPIMS process has the advantage of being a low temperature process for oxide TFTs.

In this article, the tunable Zn-doped Ga $_{\text{2}}$ O $_{\text{3}}$ films were obtained by introducing ZnO intercalation during the film deposition using plasma-enhanced atomic layer deposition (PEALD). The effect of the ZnO cycle ratio on the performance of solar-blind photodetectors (PDs) was first analyzed. Compared to the pure Ga $_{\text{2}}$ O $_{\text{3}}$ , an obviously enhanced performance of Zn-doped Ga $_{\text{2}}$ O $_{\text{3}}$ films PDs was observed by the introduction of Zn dopants, especially photocurrent or responsivity, even if the light intensity is low. A high sensitivity of Zn-doped Ga $_{\text{2}}$ O $_{\text{3}}$ PD has been achieved with superior photoelectric characteristics for an extremely low dark current of 2.22 $\times$ 10 $^{-\text{13}}$ A, an ultrahigh light ON/OFF current ratio of 2.89 $\times$ 10 $^{\text{6}}$ , and a satisfactory responsivity of 104 mA/W when the ZnO cycle ratio is 5%. The above excellent results imply that the Zn-doped Ga $_{\text{2}}$ O $_{\text{3}}$ PD can be greatly beneficial to the application in deep-ultraviolet (DUV) detection.

In this work, aluminum oxide (Al2O3) films are grown using atomic layer deposition (ALD) with trimethylaluminum (TMA) and water, and inserted into blue mini-light-emitting diodes (mini-LEDs) as a moisture barrier layer to provide chip-level encapsulation. The effect of the inserted Al2O3 layer on the stability of the mini-LED performance is investigated. The experimental results show that the optimized substrate temperature for preparing the Al2O3 films under self-limiting surface reaction conditions and linear growth is in the range of 200 °C–250 °C. The highest film density, lowest impurity content, and lowest water vapor transmission rate (WVTR) can be obtained at 250 °C. The performance of the mini-LEDs with the Al2O3 layer does not degrade after 1000 h in 85% relative humidity (RH) and 85 °C temperature aging conditions, while the device without the moisture layer completely fails after 500 h. The degradation is found to be related to the increased series resistance and ideality factor of the devices. Moreover, it is found that the addition of the Al2O3 moisture layer improves the light intensity of mini-LEDs. The inserted Al2O3 layer with a simple process and thin thickness is therefore capable of providing excellent resistance against high humidity and high temperature environment for mini-LEDs.

Transparent indium–gallium–zinc oxide thin film transistor (IGZO-TFT) prepared by all plasma enhanced atomic layer deposition (PEALD) has been firstly investigated. As the chemical composition has a considerable impact on the performance of IGZO TFTs, the properties of IGZO film and IGZO-TFT based on different In2O3 cycle ratios are investigated. The IGZO film prepared by PEALD shows amorphous state with excellent conformity and uniformity. Moreover, the a-IGZO films with different In2O3 cycle ratios are applied to TFT fabrication. When the a-IGZO thin film with 35% In2O3 cycle ratios, the transistor presents satisfactory electrical performance with a threshold voltage ( $\text{V}_{\text {th}}$ ) of 1.7 V, a saturation mobility ( $\mu _{\text {sat}}$ ) of 8.8 cm2/Vs, a subthreshold swing (SS) of 0.2 V/decade and an $\text{I}_{ON}/\text{I}_{OFF}$ of $2.2\times 10^{{8}}$ . This work provides a new way to achieve transparent TFT which better for practical commercial applications.

In recent years, the application of (In, Al, Ga)N materials in photovoltaic devices has attracted much attention. Like InGaN, it is a direct band gap material with high absorption at the band edge, suitable for high efficiency photovoltaic devices. Nonetheless, it is important to deposit high-quality GaN material as a foundation. Plasma-enhanced atomic layer deposition (PEALD) combines the advantages of the ALD process with the use of plasma and is often used to deposit thin films with different needs. However, residual oxygen during growth has always been an unavoidable issue affecting the quality of the resulting film, especially in growing gallium nitride (GaN) films. In this study, the NH₃-containing plasma was used to capture the oxygen absorbed on the growing surface to improve the quality of GaN films. By diagnosing the plasma, NH₂, NH, and H radicals controlled by the plasma power has a strong influence not only on the oxygen content in growing GaN films but also on the growth rate, crystallinity, and surface roughness. The NH and NH₂ radicals contribute to the growth of GaN films while the H radicals selectively dissociate Ga-OH bonds on the film surface and etch the grown films. At high plasma power, the GaN film with the lowest Ga-O bond ratio has a saturated growth rate, a better crystallinity, a rougher surface, and a lower bandgap. In addition, the deposition mechanism of GaN thin films prepared with a trimethylgallium metal source and NH₃/Ar plasma PEALD involving oxygen participation or not is also discussed in the study.

Gallium nitride (GaN) is a wide bandgap semiconductor with remarkable chemical and thermal stability, making it a competitive candidate for a variety of optoelectronic applications. In this study, GaN films are grown using a plasma-enhanced atomic layer deposition (PEALD) with trimethylgallium (TMG) and NH₃ plasma. The effect of substrate temperature on growth mechanism and properties of the PEALD GaN films is systematically studied. The experimental results show that the self-limiting surface chemical reactions occur in the substrate temperature range of 250–350 °C. The substrate temperature strongly affects the crystalline structure, which is nearly amorphous at below 250 °C, with (100) as the major phase at below 400 °C, and (002) dominated at higher temperatures. The X-ray photoelectron spectroscopy spectra reveals the unintentional oxygen incorporation into the films in the forms of Ga₂O₃ and Ga-OH. The amount of Ga-O component decreases, whereas the Ga-Ga component rapidly increases at 400 and 450 °C, due to the decomposition of TMG. The substrate temperature of 350 °C with the highest amount of Ga-N bonds is, therefore, considered the optimum substrate temperature. This study is helpful for improving the quality of PEALD GaN films.

Accurate implementation of action classification for the elderly on lightweight convolutional neural networks benefits resource-limited embedded and mobile devices in the healthcare industry. The study proposes a lightweight convolutional neural network model called mD-MobileNet. The micro-Doppler feature spectrograms of 106 elderly people were studied as a dataset. Transfer learning methods were used to train the proposed model, and three lightweight convolutional neural networks (MobileNetV3-Small, ShuffleNetV2, and EfficientNet-B0) were compared using the same training method. All of these models were able to correctly classify various actions. By comparison, mD-MobileNet gave the best classification results. mD-MobileNet’s Top-1 Accuracy reached 96.1% while Marco F1 was 96.30. By comparing the results with Grad-CAM’s visualization and analyzing them in conjunction with its network structure features, it was determined that mD-MobileNet has the best local perception with the least number of model parameters and the highest accuracy rate compared to other models.

Hafnium oxide (HfO₂) thin film has remarkable physical and chemical properties, which makes it useful for a variety of applications. In this work, HfO₂ films were prepared on silicon through plasma enhanced atomic layer deposition (PEALD) at various substrate temperatures. The growth per cycle, structural, morphology and crystalline properties of HfO₂ films were measured by spectroscopic ellipsometer, grazing-incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR), field-emission scanning electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy. The substrate temperature dependent electrical properties of PEALD–HfO₂ films were obtained by capacitance–voltage and current–voltage measurements. GIXRD patterns and XRR investigations show that increasing the substrate temperature improved the crystallinity and density of HfO₂ films. The crystallinity of HfO₂ films has a major effect on electrical properties of the films. HfO₂ thin film deposited at 300 °C possesses the highest dielectric constant and breakdown electric field.

The promising functional tin oxide (SnO_x) has attracted tremendous attention due to its transparent and conductive properties. The stoichiometric composition of SnO_x can be described as common n-type SnO₂ and p-type Sn₃O₄. In this study, the functional SnO_x films were prepared successfully by plasma-enhanced atomic layer deposition (PEALD) at different substrate temperatures from 100 to 400 °C. The experimental results involving optical, structural, chemical, and electrical properties and morphologies are discussed. The SnO₂ and oxygen-deficient Sn₃O₄ phases coexisting in PEALD SnO_x films were found. The PEALD SnO_x films are composed of intrinsic oxygen vacancies with O-Sn⁴⁺ bonds and then transformed into a crystalline SnO₂ phase with increased substrate temperature, revealing a direct 3.5–4.0 eV band gap and 1.9–2.1 refractive index. Lower (300 °C) substrate temperatures can cause precursor condensation and desorption, respectively, resulting in reduced film qualities. The proper composition ratio of O to Sn in PEALD SnO_x films near an estimated 1.74 suggests the highest mobility of 12.89 cm² V⁻¹ s⁻¹ at 300 °C.