Thin film transistors for macroelectronics: Devices, substrates, and processes.

摘要

Recent advances in thin-film transistor technology and the rapid growth of the flat-panel display industry have stimulated interest as well as increased demand for large-area electronics. Applications are not only limited to displays, but also include sensors, RFID tags, smart cards, and disposable electronics. The list is growing. The current toolset used in the microelectronics industry, however, is designed to achieve high-resolution over small areas, and thus is ill-equipped to address the size and cost requirements for this new breed of electronics. At its core, this is a fundamentally different kind of technology which we seek, and as such, we have given it a name: Macroelectronics.; We investigate several key technologies which are essential to any macroelectronic process. To increase throughput in manufacturing, a web process utilizing a flexible yet strong substrate is required. We therefore examine the performance of TFTs fabricated on thin steel foils of various thickness, ranging from 200 mum to 1 mum, and find that the electrical performance is relatively constant, while the mechanical behavior of the substrates may vary widely throughout the fabrication process. Analysis of film stress reveals a substrate thickness dependence which is in agreement with observed substrate bending characteristics.; A direct patterning approach is also investigated. For the large-area substrates required in macroelectronic applications, this patterning method can potentially achieve much higher throughput at much lower costs than is currently possible using conventional optical steppers. We characterize the electrical performance of the devices made using electrophotographically-patterned toner masks and find that they compare well with devices made using traditional photolithographic methods.; Finally, we propose and fabricate a transistor structure which is not subject to the performance limitations characteristic of current device structures. Specifically, these devices lower the delay associated with addressing individual gate lines, which is critical as display sizes and resolutions increase. Characterization of these devices reveals performance metrics which agree well with predicted values and which are clearly superior to those of conventional devices.; We conclude by proposing future work which can be done here at Princeton in the area of macroelectronics, and summarize the key points and results presented in this work.