The integration of 4 nm thick amorphous indium tungsten oxide (a-IWO) and a hafnium oxide (HfO2) high-κ gate dielectric has been demonstrated previously as one of promising amorphous oxide semiconductor (AOS) thin-film transistors (TFTs). In this study, the more positive threshold voltage shift (∆VTH) and reduced ION were observed when increasing the oxygen ratio during a-IWO deposition. Through simple material measurements and Technology Computer Aided Design (TCAD) analysis, the distinct correlation between different chemical species and the corresponding bulk and interface density of states (DOS) parameters were systematically deduced, validating the proposed physical mechanisms with a quantum model for a-IWO nanosheet TFT. The effects of oxygen flow on oxygen interstitial (Oi) defects were numerically proved for modulating bulk dopant concentration Nd and interface density of Gaussian acceptor trap NGA at the front channel, significantly dominating the transfer characteristics of a-IWO TFT. Furthermore, based on the studies of density functional theory (DFT) for the correlation between formation energy Ef of Oi defect and Fermi level (EF) position, we propose a numerical methodology for monitoring the possible concentration distribution of Oi as a function of a bias condition for AOS TFTs.
Fluorine ͑F͒-implanted polycrystalline silicon thin-film transistor ͑poly-Si TFT͒ are proposed for the enhancement of device performance. A significant improvement in electrical characteristics, such as I ON /I OFF ratio, and field effect mobility, can be realized in the new thin-film transistor. The field effect mobility for F-implanted poly-Si TFTs is 53.82 cm 2 /V-s, and higher than 19.74 cm 2 /V-s in conventional SPC poly-Si TFTs. Furthermore, the F-implanted poly-Si TFT exhibits high immunity against hot carrier effect and improved electrical reliability. The manufacturing processes are simple and without additional thermal annealing steps, thereby compatible with the conventional TFT fabrication processes.In recent years polycrystalline silicon thin-film transistors ͑Poly-Si TFTs͒ have been widely used in active matrix liquid crystal displays ͑AMLCDs͒. 1,2 The poly-Si TFTs offer great potential for AMLCDs technology, due to their higher field effect mobility, which gives superior electrical characteristics over those of amorphous Si thin film transistors ͑a-Si TFTs͒. The major attraction of applying poly-Si TFTs in AMLCDs lies in the ability to integrate the pixel switching elements, the panel array, and the peripheral driving circuit on the same substrates. 3-5 However, the poly-Si TFTs usually suffer from undesirable leakage current resulted from the trap states at grain boundaries. The typical manufacture process of poly-Si film uses long-term solid phase crystallization ͑SPC͒ to transform the low-pressure chemical vapor deposited ͑LPCVD͒ amorphous silicon ͑a-Si͒ film into the polycrystalline silicon. The SPC process, requiring 24-48 h, is a time consuming procedure, which obviously affects the throughput and thermal budget of fabrication processes. Furthermore, the resultant lower field effect mobility will limit the development for SPC poly-Si TFTs. To eliminate the undesirable leakage current from the trap states, the hydrogen plasma treatment was applied to passivate the dangling bonds. 6 However, it was difficult to control the hydrogen concentration in poly-Si TFTs. In addition, the formed Si-H bonds were not strong enough to avoid the hot carrier generation. To obtain the moderate characteristics of SPC poly-Si TFTs, fluorine ͑F͒ ions implantation to poly-Si was applied to improve the device characteristics. 7,8 It was reported that the bonding energy of Si-F bond was greater than Si-H bond. 9 Hence, the thermal reliability for Si-F bond was superior to Si-H bond. By piling up at poly-Si/SiO 2 interfaces during the thermal annealing step, the fluorine ions can form stronger Si-F bond at the polySi/SiO 2 interfaces. 7 The electrical characteristics of F ions incorporated poly-Si TFTs were superior to conventional poly-Si TFTs, such as field effect mobility and threshold voltage. Although the electrical characteristics of F-implanted poly-Si TFTs will be improved, the previous research needed additional thermal annealing step and pad oxide deposition.In this work, the poly-Si TFTs with F ions implan...
Variable temperature electrical measurement is well-established and used for determining the conduction mechanism in semiconductors. There is a Meyer-Neldel relationship between the activation energy and the prefactor with a Meyer -Neldel energy of 30.03 meV, which corresponds well with the isokinetic temperature of about 350 K. Therefore, the multiple trapping and release model is properly used to explain the thermally activated phenomenon. By the method, an exponential distribution of traps is assumed to be a better representation of trap states in band tail. Samples with higher temperature during measurement are observed to show better mobility, higher on-current and lower resistance, which agree well with the multiple trapping and release model proposed to explain the conduction mechanism in pentacene-based OTFTs.
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