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° and, thus, ≈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.