Fully Transparent Epitaxial Oxide Thin-Film Transistor Fabricated at Back-End-of-Line Temperature by Suboxide Molecular-Beam Epitaxy

Transparent oxide thin film transistors (TFTs) are an important ingredient of transparent electronics. Their fabrication at the back-end-of-line (BEOL) opens the door to novel strategies to more closely integrate logic with memory for data-intensive computing architectures that overcome the scaling challenges of today's integrated circuits. A recently developed variant of molecular-beam epitaxy (MBE) called suboxide MBE (S-MBE) is demonstrated to be capable of growing epitaxial In2O3 at BEOL temperatures with unmatched crystal quality. The fullwidth at halfmaximum of the rocking curve is 0.015 degrees and, thus, approximate to 5x narrower than any reports at any temperature to date and limited by the substrate quality. The key to achieving these results is the provision of an In2O beam by S-MBE, which enables growth in adsorption control and is kinetically favorable. To benchmark this deposition method for TFTs, rudimentary devices were fabricated. Suboxide MBE is utilized to grow In2O3 films of unprecedented structural quality at BEOL compatible temperatures. Utilizing these films proof-of-concept fully transparent thin film transistors are fabricated. image