In this study, the negative bias temperature instability (NBTI) under mechanical strain conditions of low-temperature polycrystalline silicon thin-film transistors (LTPS TFTs) with a stress-release ...structure was investigated. With both electrical and mechanical stresses simultaneously applied, more significant degradation behaviors will be observed in standard TFT devices because mechanical stress makes it easier to generate strain in Si-H bonds, thus benefiting the process of electrochemical reaction. By employing a stress-release shape in the poly channel, mechanical stress, which mainly accumulates at the width edge of the poly-Si/SiO 2 interface, is moved away from the main channel; thus, fewer strained Si-H bonds can participate in the electrochemical reaction compared to the standard structure. Therefore, the degradation of devices under strained NBTI is effectively mitigated, such that the reliability of the devices is enhanced. These observations were obtained using electrical characteristics and extraction of the trap state distribution.
In this study, the electrical characteristics of top-gate amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) under positive bias stress (PBS) are investigated. Abnormal two-step degradation and ...hump effects are observed under PBS. When the self-aligned process is applied during the interlayer dielectric (ILD) deposition, <inline-formula> <tex-math notation="LaTeX">\text{n}^{+} </tex-math></inline-formula> IGZO is formed by hydrogen doping to define the source and drain, which is accompanied by hydrogen diffusion not only into the channel to influence the initial electrical performance but also into the gate insulator (GI), which leads to the degradation under PBS. The diffusion distance in the length and width directions is calculated. Also, the differences in the diffusion distance in the width and length directions can be ascribed to the geometric structure of the top-gate a-IGZO TFTs. The hump occurs after PBS because of the impact of hydrogen diffusion in the width direction. The two-step degradation and its sequences can be ascribed to two mechanisms, including electron trapping and hydrogen diffusion.
In this study, abnormal on-current (I on ) degradation in n-type lateral double-diffused metal-oxide-semiconductor transistor (LDMOS) after non-conductive stress (NCS) is investigated. The ...degradation is caused by electron injection into the insulator layer (IL) during stress. Moreover, I on degradation reaches saturation within a short time after stress. Experimental data and technology computer aided design (TACD) simulations show that, after NCS, the contact field plate (CFP) induces carriers to inject into the IL above the drift region. It increases the overall on-resistance (R on ) and results in I on degradation during turn-on.
In this study, the electrical characteristics and hot-carrier reliability are investigated in via-contact type amorphous indium-gallium-zinc oxide thin-film transistors (TFTs) with different ...field-plate structures, generally used as a light-shielding layer. Compared to a conventional symmetric structure, the output current characteristics of the asymmetric structures with a source-connected (drain-connected) field plate are more saturated (unsaturated). The source-connected field plate (SCFP) structure exhibits a good channel control ability, which can effectively suppress the drain-induced barrier-lowering effect and improve the IR-drop phenomena to achieve uniform brightness in each pixel over a large-area display. In addition, this structure demonstrates a good hot-carrier stress (HCS) stability confirmed by simulations and energy bands analysis. Based on the results of this study, it is proposed that the SCFP structure with stably saturated output current characteristics and HCS reliability is suitable for driving TFTs in active-matrix organic light-emitting diode (AM-OLED) applications.
This work investigates the abnormal phenomena that are observed in electrical characteristics under negative bias stress (NBS) in flexible p-channel low-temperature polycrystalline silicon thin-film ...transistors (p-channel LTPS TFTs) after TFTs being lifted off from a rigid substrate. During the lift-off process, mechanical strain accumulates in the buffer layer due to the unilateral force, thus resulting in the generation of defects in the buffer layer. Therefore, abnormal degradation behaviors in electrical characteristics of the lifted-off TFTs were observed during negative gate bias stress. A study on physical mechanisms is introduced to describe such abnormal phenomena, and it is confirmed that defects are produced in the buffer layer when the LTPS TFTs are lifted off. In addition, different device dimensions were discussed to support our proposed model. The findings in this work are supported by the discussion of electrical characteristics, trap state extraction, and COMSOL simulation.
The effect of hydrogen diffusion in the bilayer bottom gate insulator (BGI) in dual-gate InGaZnO (IGZO) thin-film transistors (TFT) is investigated. It is discovered that hydrogen diffuses from the ...first deposited GI, migrates toward the second one, and forms a weak chemical bond with a dangling bond at the interface between the GI and the active layer. The stress condition with a positive gate bias at various temperatures makes the weakly bonded hydrogen break, thereby forming defects that can induce electron trapping in the interface and bulk, causing the threshold voltage to increase. With the rising temperature of positive bias temperature stress (PBTS), more broken bonds appear at the interface, which results in more trapped electrons. Through a charge trapping model and data fitting, the parameter that indicates the quality of the film can be extracted and compared. The trend of degradation between threshold voltage, bond breaking, and defect generation is examined.
In this work, the suppression of hydrogen diffusion in top-gate InGaZnO thin film transistors (TFTs) was observed. Under positive-bias temperature stress, the threshold voltage in short-channel ...devices was negatively shifted; this shift was attributed to hydrogen diffusion. To inhibit hydrogen migration, low-temperature high-pressure (LTHP) fluorine treatment was subsequently utilized. Under supercritical fluid states, fluorine, the most electronegative species of all elements, acted as a reactant and reduced mobile hydrogen. It was confirmed that the treatment benefited the characteristic properties of InGaZnO TFTs with varied channel lengths, especially in devices with short channels. The reliability of devices under stress improved through the LTHP treatment; the effects of suppression of hydrogen diffusion were illustrated by the energy band and capacitance-voltage curves of devices. Energy-dispersive X-ray spectroscopy of the specimen treated with LTHP indicated the presence of fluorine, which ensured the contribution of the treatment. Thus, LTHP treatment enables the realization of small-sized high-performance top-gate InGaZnO TFTs.
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.
This study investigates the properties of a onetransistor- one-capacitor (1T1C) device that includes a transistor and ferroelectric random access memory (FeRAM) at the nanoscale. The hysteresis ...characteristics are presented. A simultaneous measurement of writing and reading was used. A difference was observed between the forward and reverse transconductance (gm) −V G curves, and the reason can be explained by the relationship between the operating voltage and coercive voltages. According to the relationship between gm and polarization, the polarization signal can be obtained using gm at the nano-scale. The remnant polarization of the 1T1C device per unit ferroelectric-layer area was confirmed by the polarization value of FeRAM via the Positive Up Negative Down method. Finally, the P-V loops obtained using gm values with different measurement ranges are also reported.
