A New Excimer-Laser-Annealing Method for Manufacturing Large OLED Displays
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A New Excimer-Laser-Annealing Method for Manufacturing Large OLED Displays James S. Im Applied Physics and Applied Mathematics, School of Engineering and Applied Sciences, Columbia University, New York, NY ABSTRACT In this paper, we present an example of a new generation of laser-crystallization approaches that can crystallize Si films for large active-matrix displays at drastically increased effective crystallization rates. The particular scheme presented in this paper is referred to as the advanced excimer-laser-annealing (AELA) method, and it can be readily configured for manufacturing large OLED TVs using various available and field-proven technical components. As in ELA, it is mostly a partial-/near-complete-melting-regime-based crystallization approach; AELA can, however, eventually achieve greater than one order of magnitude increase in the effective rate of crystallization over that of the conventional ELA technique utilizing the same laser source. We discuss in this paper how and why such a dramatic increase can be attained, and some strategical and technological benefits and options that can be entertained regarding, and as a result of the availability of, the AELA technique. INTRODUCTION Organic light-emitting diode (OLED) TVs represent a substantial category of new products for the flat-panel display industry [1]. This opportunity, as it happens, also calls for reexamining and evaluating various backplane technologies. The long-established and presently dominant a-Si:H TFTs are viewed as being not entirely suitable for the application due to the issues stemming from poor device stability and limited field-effect mobility values. As a result, more OLED-optimal TFTs with better stability and higher mobilities are being sought and scrutinized for the application. The excimer-laser-crystallization-based [2, 3] low-temperature polycrystalline-Si (LTPS) TFT technology [4], particularly in the form of the manufacturing-pervasive ELA method [5], can be identified as an obvious candidate for the task. In actuality, the conventional ELA method – as well as other laser-based crystallization techniques – has been dismissed for various reasons over the years as being ill-suited for OLED displays, in general, and large OLED TVs, in particular. To this end, the metal-oxide TFTs [6] and solid-phase-based crystallization [7, 8] techniques have been (and continue to be) actively pursued as alternative and promising “nonlaser” backplane technology candidates. As it presently stands, however, many of the technical issues and problems that have been previously pointed out with respect to the use of ELA for OLED displays can be identified as being largely eliminated. That this is so can be concluded, partially but forcefully, from the demonstrated success of the ELA technology in high-yield volume manufacturing of highresolution OLED screens for mobile phones and tablets. In fact, one could argue that the sole remaining issue of substance for the ELA technology may pertain to the effective rate of crystallization, the rate of
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