An ultrawideband absorptive common-mode filter (A-CMF) with a newly developed defected ground structure (DGS) is proposed in this article. The DGS miniaturized to a subwavelength size is able to ...totally suppress the common-mode noise while maintaining the signal integrity of the differential mode. In addition, the reflection and radiation of the common-mode noise are negligible in the stopband. For quick design, a simplified equivalent circuit model is also proposed. This model can be employed to estimate the resistances of the lumped resistors embedded in the DGS to obtain a very wide absorption band. In the demonstrated example, the fractional bandwidth determined by a 90% absorption efficiency can achieve as large as 104% around 3.55 GHz for an A-CMF realized on a simple two-layer printed circuit board. Such a widely absorptive bandwidth is never achieved before to our knowledge. The design methodology is validated by full-wave simulation. Finally, real measurement of the design is also carried out to confirm the design and analysis.
This article presents an analytical method for parameter extraction in oxide semiconductor field-effect transistors (OS FETs), including threshold voltage (<inline-formula> <tex-math ...notation="LaTeX">{V}_{\text {T}} </tex-math></inline-formula>), effective channel length (<inline-formula> <tex-math notation="LaTeX">{L}_{\text {eff}} </tex-math></inline-formula>), source-drain series resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{\text {SD}} </tex-math></inline-formula>), and intrinsic effective mobility (<inline-formula> <tex-math notation="LaTeX">\mu _{\text {int}} </tex-math></inline-formula>). An analytical expression of effective mobility (<inline-formula> <tex-math notation="LaTeX">\mu _{\text {eff}} </tex-math></inline-formula>) is implemented with the consideration of percolation conduction and <inline-formula> <tex-math notation="LaTeX">{R}_{\text {SD}} </tex-math></inline-formula> effects. This method relies on the concept of <inline-formula> <tex-math notation="LaTeX">{Y} </tex-math></inline-formula>-function method and the channel length dependent measurement. The extraction results are compared to those from the combination of transfer length method (TLM). It has been shown that a better accuracy of the extracted parameters is achieved with the proposed method. Furthermore, transfer characteristics are resimulated based on the extracted parameters, in which a good match between measurement and simulation is obtained.
This letter investigates degradation after negative bias temperature instability (NBTI) stress applied to LTPS TFTs with different polycrystalline-silicon grain sizes. The initial characteristics of ...the LTPS TFTs are similar regardless of grain size; however, we observed a different degree of degradation after NBTI depending on grain size. In general, after NBTI, both grain boundary traps and interface traps were generated. We found that the degree of NBTI degradation is dominated by the concentration of grain boundary traps, which themselves are a result of the different grain sizes that occur due to excimer laser annealing energy. At initial, dangling bonds in the grain boundaries and at the interface are passivated by hydrogen atoms, hence the initial characteristics are similar. Since the large grain of poly-Si initially generates more dangling bonds in the grain boundaries, after NBTI, hydrogen depassivation generates more grain boundary traps and causes much more serious degradation in device performance.
In this study, the impact of moisture on the electrical characteristics of an amorphous In–Ga–Zn–O thin-film transistor (a-IGZO TFT) was investigated. In commercial applications of such TFTs, high ...stability and quality performance in humid environments are essential. During TFT operation under ambient moisture, the electrolysis of water molecules occurs via the tip electric field effect. Hydrogen diffuses from the etch-stop layer or back-channel into the main channel under a negative electric field. The hydrogen atoms act as shallow donors (which causes the carrier concentration in the channel to rise), causing the threshold voltage (VTH) to shift in the negative direction. Hydrogen diffusion from the overlap of the source/drain and gate electrodes to the channel center caused by the tip electric field induces a significant barrier lowering and VTH shifts in a short-channel device. However, under negative bias stress (NBS) in ambient moisture, the negative VTH shift is more obvious in short- than in long-channel devices, indicating suppressed hydrogen diffusion in long-channel devices. This is attributed to the electrolysis of water by the tip electric field at the source, drain, and gate electrodes, which causes hydrogen to diffuse to the center of the channel. Here, a novel physical model of the capacitance–voltage (C–V) electrical property changes under ambient moisture is proposed, based on the early appearance of abnormalities in the C–V measurements. The electrolysis of water caused by the tip electric field and electrical abnormalities caused by hydrogen diffusion into the a-IGZO active layer are explained by this model. A secondary-ion mass spectrometry analysis shows that hydrogen content in the channel generally increases under NBS in ambient moisture. The degradation behavior due to moisture in a-IGZO is clarified. Thus, inhibiting the tip electric field may benefit future flexible-display and gas-sensing applications.
This paper analyzes the abnormal degradation induced by hydrogen annealing. Although device performance is enhanced after hydrogen annealing, an abnormal hump is observed in transfer characteristics ...(<inline-formula> <tex-math notation="LaTeX">{I}_{D} - {V}_{G} </tex-math></inline-formula>) under positive bias temperature stress (PBTS). Threshold voltage shift (<inline-formula> <tex-math notation="LaTeX">\Delta \text{V}_{\text {TH2}} </tex-math></inline-formula>) in this hump region increases with increasing stress voltage and temperature. Additionally, <inline-formula> <tex-math notation="LaTeX">\Delta \text{V}_{\text {TH2}} </tex-math></inline-formula> is independent of the channel width. A novel hydrogen rupture-diffusion model is proposed to explain the degradation. COMSOL simulation and <inline-formula> <tex-math notation="LaTeX">{C} - {V} </tex-math></inline-formula> measurement are utilized to clarify the precise degradation position. Moreover, variable S/D spacing (<inline-formula> <tex-math notation="LaTeX">\text{L}_{\text {SD}} </tex-math></inline-formula>) devices are designed to support the mechanism. Finally, ISE-TCAD software is carried out to verify the proposed model. Our results from electrical measurement suggest that hydrogen can cause additional instability, which shares a similar conclusion for those by using material analyzation and first-principle simulation.
In this study, an abnormal two-stage degradation of low-temperature polycrystalline-silicon (LTPS) thin-film transistors (TFTs) on a polyimide flexible substrate after hot carrier stress was ...investigated. The degradation mechanism was divided into two stages. In the first stage, the increases in capacitance in the off region and transconductance are caused by impact ionization induced electron trapping into the gate insulator (GI) at the drain edge. Furthermore, the threshold voltage (<inline-formula> <tex-math notation="LaTeX">\text{V}_{\text {th}} </tex-math></inline-formula>) shift in the positive direction is caused by electrons flowing back to the source side and trapping into the buffer that induces source barrier lowing. The second stage of degradation, including a <inline-formula> <tex-math notation="LaTeX">\text{V}_{\text {th}} </tex-math></inline-formula> shift in the negative direction and a decrease in the transconductance is caused by Joule heating induced negative bias temperature instability (NBTI). Furthermore, NBTI hardly occurs behind the pinch off in the channel and fixed oxide charge does not compensate the trapped electron at drain side which is induced in the first stage.
This study investigates an abnormal degradation induced in a moist environment. Although devices maintain optimal performance under bias stress operation in a vacuum, an abnormal hump is observed in ...capacitance-voltage (<inline-formula> <tex-math notation="LaTeX">{C} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">{V} </tex-math></inline-formula>) electrical characteristics under negative bias stress (NBS) operation in a moist environment. Electrolysis of the H 2 O model is proposed to explain the degradation. An asymmetric stress condition, with <inline-formula> <tex-math notation="LaTeX">{V} _{\text {GD}} = {0} </tex-math></inline-formula> V, is designed to confirm that a vertical electric field causes the electrolysis of H 2 O, which is the reason for the hump phenomenon in the <inline-formula> <tex-math notation="LaTeX">{C} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">{V} </tex-math></inline-formula> curve. Moreover, COMSOL simulation and <inline-formula> <tex-math notation="LaTeX">{C} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">{V} </tex-math></inline-formula> measurement of the source and drain parasitic capacitances are utilized to clarify the precise degradation position and support the mechanism. The results from electrical measurement suggest that a vertical electric field can cause instability in a moist environment.
This work studies the effect of the location of the light shielding (LS) layer on negative bias illumination stress (NBIS) instability in self-aligned top-gate amorphous indium-gallium-zinc oxide ...thin-film transistors (SA-TG a-InGaZnO TFTs). Although the NBIS instability can be mitigated by introducing a fully covered LS layer, it causes an unwanted parasitic capacitance, as evidenced by capacitance-voltage (<inline-formula> <tex-math notation="LaTeX">{C} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">{V} </tex-math></inline-formula>) measurements. An alternative solution, in which the device that is partially covered by the LS layer at the source side, is proposed to optimize the tradeoff. This study suggests that an LS layer could be adopted in the SA-TG configuration, as it is versatile in different structural designs, depending on the requirement of targeted applications.
This letter investigates variations in polycrystalline silicon thin film transistor (TFT) performance under illumination and negative bias temperature instability (NBTI) tests due to different ...dehydrogenation annealing temperatures during the fabrication process. The depth of the density of state (DOS) in polysilicon can be indirectly determined by the TFT response to light illumination, since dangling bonds act as recombination centers. The electrical characteristics of TFTs after undergoing NBTI can also be indicative of the bonding type of silicon atoms. By analyzing the results of these reliability tests, the type of DOS can be clarified, which is beneficial for realizing the relationship between performance and reliability.
This letter analyzes performance and reliability of inverted staggered type amorphous indium-gallium-zinc oxide devices in a moist environment with H 2 O molecules in the passivation layer. There is ...a negative threshold voltage shift (Δ Vth) in the saturation region (VD = 10 V), which increases with decreasing channel length. We propose that this is explained by the drain-induced barrier lowering that is due to the H 2 O molecules. Moreover, a hydrogen bonding model under bias stress is also proposed, in contrast to the conventional H 2 O doping model. Recovery behavior after bias stress and ac operation were utilized to distinguish the difference between these models.
