Introduction to the Focus Issue on Oxide Thin Film Transistors

Abstract

The thin film transistor (TFT) operates on the same basic principle as the metal–oxide–semiconductor field-effect transistor (MOSFET). TFT-based liquid crystal displays (LCDs) and MOSFET-based integrated circuits (ICs) are two of the largest semiconductor products currently in production. They have a similar history of market growth, as shown in Fig. 1. The main advantages of the TFT over the MOSFET are a low fabrication temperature and the sizeand wafer-independent substrate. In addition to LCDs, TFTs have been used in a large number of products, including organic light-emitting diodes (OLEDs), other types of flat panel displays, X-ray imagers, radio-frequency identification, finger printers, sensors, etc. In spite of the successful demonstration of functional TFTs since the 1960s, the mass production of TFT products, e.g., large-area LCDs, has never been realized. The breakthrough in the field came from the report of the first functional amorphous silicon (a-Si:H) TFT with a silicon nitride gate dielectric layer in 1979. Today’s TFT LCDs are dominated by this technology, specifically large area displays. A small portion of the business, such as small mobile displays, is based on the polycrystalline silicon (poly-Si) TFT technology. The a-Si:H TFT suffers from low mobility. The poly-Si TFT is hindered by the large area, high throughput production problem. The dream of having a TFT technology that can be easily fabricated on a large-area, low-temperature substrate with a high throughput has never died. In recent years, metal oxide TFTs that can be prepared by sputter deposition at room temperature have been reported. This kind of TFT can have a mobility one order of magnitude larger than that of the a-Si:H TFT or similar to that of the poly-Si TFT. The oxide TFTs may also be useful for transparent electronics. This result attracted immediate attention from many academic and industry researchers. Many papers on oxide TFTs have been published in various types of journals and presented at conferences, such as the ECS Journal of Solid State Science and Technology, ECS Solid State Letters, and ECS Transactions volumes. The ECS TFT symposium series, which have been held regularly for more than 24 years, are popular platforms for presenting new results. Because we are still in the early production stage for oxide TFTs, there are many unsolved issue that remain under intensive study. For that reason, it was felt that a focus issue covering up-to-date research efforts would be valuable for those working in these areas. This issue of the ECS Journal of Solid State Science and Technology is devoted to the publication of scientific and technological papers