The feasibility of using Cu/CuMg as a gate electrode for a-Si:H thin-film transistors ͑TFTs͒ has been investigated in this work. The issue of adhesion between the Cu film and glass substrates has been overcome by introducing the Cu/CuMg alloy. Furthermore, a wet-etching process of Cu-based gate metal has been proposed by using the copper etchant in the conventional printed circuit boards. The experimental result showed superior performance of a-Si:H TFT with desired electrode taper angle and minimal loss of critical dimension. The a-Si:H TFT exhibited mobility of 0.37 cm 2 /V s, subthreshold slope of 0.83 V/dec, and V th of 2.02 V.
The effect of mechanical strain on the performance of a-Si:H thin-film transistors ͑TFTs͒ with different channel lengths was studied under uniaxial compressive and tensile strain applied parallel to the TFT source-drain current path. The source-drain parasitic resistance and channel sheet conductance were extracted to explain the device performance under mechanical strain. These results indicate that the compressive bending leads to a significant decrease ͑ϳ16%͒ in the source-drain parasitic resistance. The channel sheet conductance has shown a 6% variation under mechanical bending. The variation under mechanical bending strain originates from the evolution of defect state density in a-Si:H channel material.Amorphous silicon thin-film transistors ͑a-Si:H TFTs͒ have been widely used as switching devices in active matrix liquid crystal displays ͑AMLCDs͒. Electronic paper, smart labels, displays for vehicles, and portable electronic devices are fields of rapidly growing interest. 1 For these applications, the glass substrate must be replaced with flexible and lightweight substrate. 2 Many organic polymer substrates are inexpensive and transparent in the visible part of the visible light spectrum. However, a new group of substrate characteristics becomes important in TFT fabrication. These requirements for suitable flexible substrates include chemical stability, high softening, high glass transition temperature, low coefficient of thermal expansion ͑comparable to that of the materials used in TFTs͒, negligible shrinkage during fabrication, low water and oxygen permeability, and small surface roughness. There have been many efforts toward the development of plastic substrates process in the last years. In additional to plastic substrates, stainless steel foils are also candidates for the flexible display panel application 3-6 if one seeks to use the full temperature range of TFT fabrication process without much change to conventional manufacturing. 7 Furthermore, for flexible display application, display panels are required to sustain a certain degree of bending. Bending would induce strain in the electronic circuits and might affect TFT device characteristics. According to previous studies, 8-10 the change in the resistance ͑conduc-tance͒ of a-Si:H was found as a function of strain. However, the lack of long-range order should attenuate any piezoresistive effect. As a result, the transport mechanisms specific to a-Si:H would not apply to single-crystal silicon. 11-13 Won et al. 14 reported that both the threshold voltage ͑V th ͒ and the mobility increase under tensile stress, while V th increases and mobility decreases under compressive stress. Gleskova also concluded that the decrease in the mobility under compressive strain is caused by the broadening of the band tail states near both the valence and conduction band of the a-Si:H channel material. 15 The effect of the source-drain parasitic resistance, and channel sheet conductance under mechanical bending strain, however, has not been reported yet. In this study, ...
The instability of amorphous Si thin film transistors under uniaxial strain has been studied. Compared to the effect of tensile bias stress, larger threshold voltage shift is observed under compressive bias stress. These results are related to the damage of weak Si-Si bonds during the ac bias stress. However, the V th shift of devices on the re-flattened substrate is larger after tensile strain than that of compressive strain. In addition, the defeat diminished effect of tensile situation is decreased after re-flattening the device. Therefore, after re-flattening the substrate the V th shift resulting from tensile bias stress is larger than that of the compressive one.The amorphous Si thin film transistor ͑a-Si:H TFT͒ has been widely used as a switching device of AM-LCD. Recently, a portable communication system is spotlighted such as electronic paper, smart labels, displays for vehicles and portable electron devices. 1 For these applications, the traditional glass substrate of large-area electronics must be replaced with a flexible and lightweight substrate. 2 Except for the substrates, the electrical instability is also a critical issue for a-Si:H TFTs, as it can degrade the electrical characteristics and affects the lifetime of devices. Many reports indicated that the electrical instability is composed of charge trapping and state creation. 3,4 The charge trapping in the slow state, which is dominant at higher voltage and long stress time, relates to trap sites in the gate insulator. 5 Conversely, the state creation in the fast state, which is dominant at lower voltage, is associated with the breaking of Si-Si weak bonds in the a-Si:H layer or at the interface between the gate insulator and a-Si:H layer. 6,7 The charge trapping shows logarithmic and weak temperature dependence while the state creation shows power-law time and thermally activated temperature dependence. 8 The charge trapping leads to the threshold voltage shift, and less degradation of subthreshold swing. 9 On the other hand, the state creation can lead to positive shifts of threshold voltage, and degrade the subthreshold swing. Furthermore, the defeat pool model has been proposed to explain the instability mechanisms of a-Si:H TFTs. 10 For flexible display application, display panels are required to suffer a certain degree of bending. Bending operation will induce strain in the electronic circuits and would influence the TFT device characteristics. Another consideration for TFT device characteristics is the device operation modes. The dc and ac operation has been extensively studied, but not for flexible display applications in which the real operation mode is under the mechanical strain with ac operation. Therefore, the knowledge of the electrical performance of TFTs under the mechanical strain with the ac operation becomes more important for flexible display application. There are many studies on the relationship between mechanical strain and a-Si:H TFT characteristics. 11-17 The simple stress for a-Si:H TFT has already been reported by Won ...
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