Spin-On Glass as low temperature gate insulator
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Spin-On Glass as low temperature gate insulator Miguel A. Domínguez1, Pedro Rosales1, Alfonso Torres1, Joel Molina1, Mario Moreno1, Francisco J. De la Hidalga1, Carlos Zuñiga1 and Wilfrido Calleja1 1 National Institute for Astrophysics, Optics and Electronics (INAOE), Electronics Department, Luis Enrique Erro No. 1, Puebla, C.P. 72840, Mexico. ABSTRACT In this work, we report the characterization of Spin-On Glass (SOG) as low temperature gate insulator. Our SOG film was deposited at temperature of 200°C, which is compatible to use on flexible substrates. The optical and electrical characterization showed that the refractive index and dielectric constant are very close to those of thermally grown SiO2. Also, analysis of surface roughness by AFM is presented. We demonstrated the use of SOG as gate insulator, fabricating and characterizing inverted staggered a-SiGe:H TFTs. The observed results are promising and suggest that SOG films deposited at 200°C in the Laboratory of Microelectronics of INAOE could be an alternative to improve electrical characteristics of TFTs on low temperature flexible substrates. INTRODUCTION At present, Thin Film Transistors (TFT) research field is of high interest because of development of low cost products, such as circuits arrays and LCDs. Low temperature deposition processes are required in order to use flexible substrates. Nevertheless, the performance of the gate insulators at temperatures below 300 °C is not as good as in CMOS technology [1]. Thus, physical and electrical properties of semiconductor and insulator materials deposited at these low temperatures must be improved. Spin-on-Glass (SOG) is an interlevel insulator that is supplied in liquid form. It consists of alkoxylanes which form an arrangement of silicate polymers with a Si-O structure, these polymers are in an alcohol solvent system. The advantages of SOG include filling the gaps and smoothing of the surface with multiple coatings, good uniformity, low cost per die, lower defect density, no need for hazardous gases required in chemical-vapor-deposition (CVD) process, and planarization. The datasheet of SOG suggest an annealing in the range of 400 – 900°C to obtain a SiO2 thin film. However, typically a-Si TFTs are deposited below of 300 °C, therefore is necessary use temperatures of cured and annealing lower than this temperature. The characterization of SOG at 200°C has not been reported in literature, the lower temperature reported for SOG as gate insulator is at 425°C by J. H. Cheon et al [2, 3]. They fabricated Inverted staggered low-temperature polycrystalline silicon thin film transistors (ISLTPS-TFT) and coplanar Poly-Si TFTs using SOG as gate insulator. The best p-channel TFT exhibited a threshold voltage of -4.3 V and a subtreshold slope of 0.8 V/DEC. In this work, we report the use of SOG as gate insulator cured at 200° C made on Inverted staggered a-SiGe:H TFTs. The n-channel a-SiGe:H TFT exhibit a threshold voltage approximately of 2.1 V and a subtreshold slope of 0.32 V/DEC.
EXPERIMENT The gate insulator n
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