Distributed Microsensor Packaging Based on Self-Assembly after Sensing

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

In this proposal, a post-operation packaging process is proposed where distributed microsensors that are too small to include data transmission electronics can be packaged and read using self-assembly after they have performed their sensing operations. There are many systems in use today where fluids move through extremely small channels. Examples include flow cytometry, fuel injection, and chemical processing. Good information about the physical state of the flow in such systems can be difficult to obtain because sensors set into the flow can be difficult to position and may interfere with the very processes that they are supposed to measure. One possible solution would be to collect data using mobile microsensors that actually travel with the flow. This is extremely appealing because sensing could be performed continuously and in-situ, but it has some basic technical difficulties since power supplies and data transmission electronics would be difficult to include due to size and cost restrictions. In addition, if an extremely large number of sensors were used, coordinating transmission protocols for all of them would be impractical. The PI proposes to solve these problems by using fluidic self-assembly (FSA) to package and read-out information from the devices after they have sensed. Since sensing operations typically consume much less power than data transmission operations, ambient energy from the environment such as light or RF could be used to drive the sensors and all interfacing for data transfer would be provided by the self-assembly process. The program has both practical engineering and fundamental scientific goals. Among the engineering goals is the development of a fluid test apparatus to investigate post-operation packaging. Power transfer to microsensors will be examined with emphasis given to the use of ambient light, laser, and RF power. Since these power sources may be intermittent, nonvolatile data storage is extremely important. Nonvolatile memory technologies that write with very little power using tunnel processes will be examined. Electronic interfacing to the self-assembled microsensors is perhaps the most critical engineering issue. Metallic bonding, micro-electro-mechanical switching, and capacitive coupling are considered. Micro-electro-mechanical switches are singled out as particularly versatile because they require no special circuitry on the microsensor and can release microsensors back into the flow after their data has been read. Scientific goals include studying the self-assembly capture process, that is, how free microsensors move into the sphere of influence of the assembly site. A study of electrostatic "fine-tuning" of the fluidic self-assembly process will also be performed, where micron-scale misalignments might be eliminated using capacitive coupling to guide the final stage of assembly. Studies will also be performed on device lifetimes in a flow. These will attempt to ascertain if flow dynamics can be modified or protective coatings used to minimize mechanical damage to devices that have circulated repeatedly through a flow system. The program has been designed with educational objectives in mind. Certain projects, such as the lifetime studies and parts of the self-assembly capture studies have been identified as shorter-term projects suitable for introducing undergraduates to research. Some of this work could be performed as part of the University of Minnesota's Undergraduate Research Opportunities Program (UROP) or Research Experience for Undergraduates (REU) program for underrepresented students or those from small universities. Both the graduate and undergraduate level work is extremely multidisciplinary, allowing students to explore experimental as well as theoretical aspects of physics, chemistry and engineering. Finally, the technological impact of the project is broad, with potential applications in medicine, remote sensing, and industrial process control, among others. This project, since its philosophy is to include only those functions that are truly necessary on a microdevice and then package the rest later, may also be a first step in a long sought goal to create smart micro- or nanodevices with only simple initial capabilities, but the potential to self-organize new functions in response to their environment.