Nanofluidics is a promising area where the fields of Chemistry, Biology, and Engineering all play a role. As the name implies, nanofluidics involves nano-scale channels used to transport fluids. By scaling down the size of the channels only a tiny amount of fluid is required to fill them, an important quality when dealing with expensive reagents. Scaled channels also enable concepts such as ?Lab on a Chip?, where nano channels transport reactants and analytes to a number of pico-liter sized reaction chambers so that a number of tests can be carried out quickly in a very small package. This proposal presents a methodology to interface electronics to nanofluidics. The electronics portion will provide ultra-sensitive electrometers placed in one wall of the nanochannel. An electrometer senses charge, so it can be used to detect charge change at the wall of the nanochannel or in the fluid near the wall. The surface of the electrometer could be functionalized to provide specific binding of reaction products, and the electrometer signal would then represent the density of the bound product. The goal is to achieve single ion detection in the channel. The intellectual merit of this proposal is that it addresses the lack of a suitable electrical transducing element. Most fluidic experiments done today use optical transduction based on fluorescence. Electrical transduction would enable a simple interface to standard electronics, leading to reduction in system size and cost. Singleelectron transistor electrometers are the most sensitive known, but have yet to be applied to nanofluidics. The proposed research is transformative in a number of ways. It will develop a process that should be scalable and manufacturable, and it will extend CMP processing into nanoscale dimensions. The integration of room temperature electrometers with nanofluidic channels will enable a number of applications, perhaps even the rapid sequencing of DNA. A key feature is the easy integration of these devices with CMOS will form an excellent bridge between nanoelectronics and the enormous base of CMOS infrastructure. The broader impact of the proposed project will be in both scientific and educational impact. The scientific impact will come from the research developing the theory and devices for silicon-based QCA. This project will also make a significant outreach to middle school students in the South Bend, Indiana area. South Bend public schools have a diverse student population with a large number of students from groups underrepresented in the areas of science and technology. The outreach program proposed will target middle school students through classroom activities involving faculty and graduate students, and field trips to bring students to the Notre Dame labs. Middle school aged children are an excellent group for outreach since they are advanced enough to understand science, but are still making choices about their areas of interests. The outreach will benefit the middle schoolers by giving them a first-hand taste of science in both the classroom and lab.
Single Electron Transistors (SET) have tremendous promise in applications such as electrometers for nanofluidic systems. The main drawback of SETs is that they usually operate only at very low temperatures, below 4 K. SETs operating at room temperature have been made, but these are often "happy accidents" rather than reproducible manufacturable devices. The key to making high-temperature SETs is to make them small, about 5-8 nm for the smallest dimensions, but controllable fabrication below 10 nm is extremely difficult. In this project we were able to make significant progress toward this goal, producing devices with dimensions between 10 and 15 nm. We were able to explore several fabrication variations in the course of this project. We introduced chemical mechanical polishing (CMP) as a tool in nanofabrication. CMP is a process used to planarize surfaces, much like a sanding step in woodworking is used to remove high spots and smooth the surface. Using CMP we were able to pattern the very small features, in metal and silicon, and produce a very smooth surface. The devices that we produced were able to operate at temperatures above 77 K. While this is still short of room temperature operation, it is a significant advance in SET technology. An interesting part of the work of project grew out of undergraduate research. Anyone who uses a mobile electronic device is familiar with the issues of power dissipation: laptops that too hot for your lap, and that drain batteries in too short a time. As electronics scale down the issues of how energy is used in computation become more important. This is an area of some controversy, a controversy that can be traced back over 100 years. The most important question involved in this controversy is: "When must energy be dissipated to heat when doing a computation?" Some say that energy must be dissipated when a measurement, or decision, is made, while Rolf Landauer in the 1960s argued that energy must be dissipated only when information is destroyed. If Landauer is correct, then lower-power computers can be made by not destroying information, and there are ways to accomplish that. For nearly 50 years no one was able to experimentally test whether Landauer was correct, because the energies involved were so small. However, we were able to make experimental measurements that show that Landauer was correct. This could lead to computers with much lower dissipation, a laptop that doesn’t burn your lap with a battery that lasts much longer. Intellectual Merit. This project has advanced the state of the art in SET fabrication, moving closer to manufacturable room-temperature devices. Our work also showed, for the first time, that Landauer was correct in his assertion that dissipation in computation must occur only when information is destroyed. This result demonstrates a path to ultra-low power computing. Broader Impact. In the course of this project grad students and faculty visited classrooms in two high schools and a middle school, contacting over 600 students. In addition, over 200 students were able to visit Notre Dame on field trips to do hands-on experiments.
