Two-Dimensional Oxyhalide Transistors Compatible with Back-End-of-the-Line Processing

Energy consumption is one of the most pressing challenges for semiconductor technologies. This is a result of applications like artificial intelligence (AI) leading to exponential growth in energy consumption. At this rate, energy demand from computing may outpace energy production within a few decades. In addition to making transistors more energy efficient, it is also necessary to integrate them in new ways. The greatest advancements are expected when transistors are directly processed in the back-end-of-the-line (BEOL). In comparison to the stacking of chips, BEOL processing minimizes energy consumption through short and fine interconnects. However, BEOL processing requires semiconductors that can be grown below approximately 450 ºC to prevent damage to the underlying chip. This is a fundamental challenge for traditional semiconductors and other two-dimensional (2D) semiconductors like transition metal dichalcogenides (TMDs). This project is developing a new kind of 2D semiconductor compatible with BEOL processing. By combining theoretical and experimental approaches, it is overcoming key hurdles for new 2D semiconductors like (1) controlled doping and (2) low electrical contact resistance. The project is also integrating workforce development for the United States semiconductor industry by collaborating with the North Texas Semiconductor Institute to create programs that address the regional shortage of skilled workers, accelerating the transition from technician to operator roles. This project is developing a new class of 2D oxyhalides for BEOL-compatible electronic devices. It is investigating the low-temperature growth of these oxyhalides and correlating relationships between low-temperature growth kinetics and electronic properties of these thin films. This project is also bridging major gaps in the present knowledge of how to fabricate 2D oxyhalides into transistors. Any new 2D material will likely face challenges to control the chemical doping and form the electrical contacts. These properties can be difficult to compute as they are often set by the rich structural and chemical complexity of their interfaces. For example, manipulating 2D semiconductor-metal interfaces for low electrical contact resistance has taken a decade for 2D transition metal dichalcogenides (TMDs). This project will significantly advance our control over chemical doping by identifying extrinsic dopants and those that can be controllably introduced during growth. It will also decode important relationships between contact metals, the oxyhalide-metal interface chemistry, and the electrical contact resistance, which are critical for short-channel transistors. Beyond their applications as classical electron devices, these 2D oxyhalides also present possibilities for quantum devices. Their tunable bandgaps and novel charge transport behaviors that can be applied to quantum tunneling devices, excitonic devices, and even platforms for quantum information processing. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.