| Description |
This dissertation describes the design, fabrication, testing, reliability, and harsh environment performance of single-device Micro-electro-mechanical-system (MEMS)- based digital logic gates, such as XOR and AND, for applications in ultra-low-power computation in unforgiving settings such as high ionizing radiation and high temperatures. Within the scope of this dissertation are several significant contributions. First, this work was the first ever to report the evolution in logic design architecture from a CMOS-paradigm to a MEMS architecture utilizing a single functional device per logic, as opposed to multiple relays per logic. This novel approach reduces the number of devices needed to implement a logic function by approximately 10X, leading to better reliability, yield, speed, and overall better characteristics (subthreshold characteristics, smaller turn-on/off voltage variations, etc.) and it simplifies implementation of MEMSbased circuits. The logic gates illustrate ~1.5V turn-on voltage at 5MHz with >109 cycles of reliable operations and low operational power consumption (leakage current and power <10-9A, <1^W). Second, this work is the first ever to report an intensive study on the cycle-bycycle evolution of contact resistance (Rc) up to 100,000 cycles, on materials such as, Ir, Pt, W, Ni, Cr, Ti, Cu, Al, and graphite, which are materials commonly used in MEMS switches. Adhesion forces between contacts were also studied using a contact-modeAFM, force vs. displacement, experiment. Results show that materials with high Young's modulus, high melting temperatures, and high density show low initial contact resistances and low adhesion forces (such as Ir, Pt, and W). Third, the devices were interrogated separately in harsh environments where they were exposed to high doses of ionizing radiation (90kW) in a nuclear reactor for a prolonged time (120 min) and, separately, at high temperatures (409K). Here, results show that solid-state devices begin to deteriorate almost immediately to a point where their gate can no longer control the drain-to-source current, whereas MEMS switches survive such ionizing radiation and temperatures portraying clear ON and OFF states for far longer. In terms of the applications empowered and the breadth of topics covered to accomplish these results, the work presented here demonstrates significant contributions to an important and developing branch of engineering. |
