Terahertz (THz) electromagnetic spectrum draws wide attention for nondestructive and/or biocompatible sensing. In order to be widely applicable to the THz sensing, it is of prime importance to develop THz sensors that can be operated at room temperature and have high sensitivity and fast operation speed. However, conventional room-temperature THz thermal sensors fall short of expectations in these characteristics required in various applications of THz sensing, including THz cameras. Utilizing a thermomechanical transduction scheme, we have developed an uncooled, sensitive, and fast THz bolometer by using a doubly clamped GaAs microelectromechanical system (MEMS) beam resonator as a sensitive thermistor. Owing to its ultrahigh temperature sensitivity (the noise equivalent temperature difference of ∼1 μK/√Hz), the present bolometer achieves not only high sensitivity but also an operation bandwidth of several kHz, which is more than 100 times faster than other uncooled THz thermal sensors. The obtained electrical noise equivalent power is as low as ∼90 pW/√Hz, which is close to the limit set by the thermal fluctuation noise. The MEMS bolometers are fabricated by the standard semiconductor fabrication processes and are well suited for making detector arrays for realizing THz cameras.

We investigate the gate bias-stress-induced instabilities of p-type copper oxide (Cu ₂ O) thin-film transistors (TFTs). Transfer curves measured before and after the application of constant gate bias stress under air and vacuum environments show that the partial pressure of the oxygen in the environment does not much affect the transfer characteristics and bias-stress-induced instabilities of the Cu ₂ O TFTs. During the negative gate bias stresses, the transfer curves shift to the negative direction without a significant variation of the shape, which is attributed to the hole trapping in the interface or bulk dielectric layers with a negligible creation of additional interface trap states. During the positive gate bias stresses, a threshold voltage hardly moves to the positive direction because of the lack of free electron inside the p-type Cu ₂ O, but a notable degradation of the subthreshold slope is observed. From the recovery characteristics, the generated traps during the positive gate bias stress are estimated to be metastable ones in p-type Cu ₂ O TFTs.

In this study, we investigated the effects of oxygen content on the transfer characteristics and stability of high-mobility indium-gallium-tin oxide (IGTO) thin-film transistors (TFTs) during channel layer deposition. The IGTO thin films were deposited through direct current sputtering at different ambient oxygen percentages of 10%, 20%, 30%, 40%, and 50%. The experimental results indicate that the drain currents were hardly modulated by the gate-to-source voltage in the IGTO TFT prepared at 10% ambient oxygen. However, as the oxygen content increased from 20% to 50%, the transfer curves shifted to the positive direction with a decrease in field-effect mobility (μ_FE). The IGTO TFTs exhibited deteriorated positive bias stress (PBS) stability as the oxygen content increased. However, the stabilities of the IGTO TFTs under negative bias illumination stress (NBIS) improved with an increase in the ambient oxygen percentage during the channel layer deposition. Furthermore, to understand the mechanism of the observed phenomena, we performed X-ray photoelectron spectroscopy (XPS) analysis of the IGTO thin films prepared at different oxygen percentages. The XPS results demonstrate that the deteriorated PBS stability and enhanced NBIS stability of the IGTO TFTs prepared at higher oxygen percentages were mainly ascribed to the larger amount of oxygen interstitials resulting from the excess oxygen and the smaller number of oxygen vacancies within the IGTO, respectively. The obtained results suggest that the oxygen percentages of 30% in the sputtering ambient is the most suitable oxygen percentage for optimizing the electrical properties (μ_FE = 24.2 cm²/V·s, subthreshold swing = 0.43 V/dec, and threshold voltage = −2.2 V) and adequate PBS and NBIS stabilities of IGTO TFTs.

We demonstrate that the shorter channel self-aligned top-gate (SA TG) coplanar indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs), with negative voltage applied to the back-gate, exhibit superior characteristics as driving transistors in organic light-emitting diode (OLED) pixels compared to their longer channel counterparts. The shorter channel IGZO TFTs (with a channel length (L) of 3 µJm) biased with a back gate voltage of. 3.5 V showed a larger subthreshold swing (SS = 0.21 V/dec) than the longer channel ones (with L = 5 μ m, SS = 0.16 V/dec) with a similar threshold value (VTH = 0.7. 0.8 V). A large SS is beneficial for controlling grayscale levels, especially at low gray levels, when IGZO TFTs are used as driving transistors in OLED pixels. Furthermore, the negatively back-gate-biased shorter channel SA TG coplanar IGZO TFTs exhibited significantly enhanced electrical stability compared to the longer channel ones under both positive gate bias and hot carrier stresses. The findings of this study are expected to be useful in expanding the utility of IGZO TFTs in OLED displays.

Investigation of Buffer Traps in AlGaN/GaN Heterostructure Field-Effect Transistors Using a Simple Test Structure AlGaN/GaN HFET;semi-insulating GaN buffer;bulk trap;carbon-doped GaN back barrier; We propose a new method which can extract the information about the electronic traps in the semi-insulating GaN buffer of AlGaN/GaN heterostructure field-effect transistors (HFETs) using a simple test structure. The proposed method has a merit in the easiness of fabricating the test structure. Moreover, the electric fields inside the test structure are very similar to those inside the actual transistor, so that we can extract the information of bulk traps which directly affect the current collapse behaviors of AlGaN/GaN HEFTs. By applying the proposed method to the GaN buffer structures with various unintentionally doped GaN channel thicknesses, we conclude that the incorporated carbon into the GaN back barrier layer is the dominant origin of the bulk trap which affects the current collapse behaviors of AlGaN/GaN HEFTs.