Date of Award
Doctor of Philosophy (PhD)
Mechanical Engineering & Applied Mechanics
Robert W. Carpick
Energy consumption by computers and electronics is currently 15% of worldwide energy output, and growing. Aggressive scaling of the fully-electronic transistor, which is the fundamental computational element of these devices, has led to significant and immutable energy losses. Ohmic nanoelectromechanical systems (NEMS) logic switches have been recognized as a potential transistor replacement technology with projected energy savings of one to three orders of magnitude over traditional, fully-electronic transistors. However, the use of conventional, adhesive contact materials (i.e. metals) in NEMS switches electrical contacts leads to permanent device seizure or the formation of insulating tribofilms that inhibits commercialization of this technology. Of critical need is a method to efficiently identify and interrogate low adhesion, chemically stable electrical contact material pairs under conditions and scales relevant to NEMS logic switch contacts. This thesis presents the development of two electrical contact testing methods based on atomic force microscopy (AFM) to interrogate electrical contact materials under contact forces and environments representative of NEMS logic switch operating conditions. AFM was used to mimic the interaction of Pt/Pt NEMS logic switch electrical interfaces for up to two billion contact cycles in laboratory timeframes. Contact resistance before cycling significantly exceeded theoretical predictions for clean Pt/Pt interfaces due to adsorbed contaminant films and increased up to six orders of magnitude due to cycling-induced insulating tribopolymer growth. Sliding of the contact with microscale amplitudes lead to significant recovery of conductivity through displacement of the insulating films. Based on this observation, AFM was then used to investigate the role of load, shear, electrical bias, and environment on the electrical robustness of Pt/nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) and Pt/Pt interfaces. N-UNCD was selected because similar diamond films have demonstrated low adhesion, chemical inertness, and compatibility with NEMS logic device fabrication. Pt/N-UNCD interfaces subjected to low loads during sliding demonstrated significant increases in contact resistance due to insulating film formation that was not observed at larger loads. Taken in concert, these finding demonstrate the capability of AFM to investigate nanoscale electrical contact phenomena without the need for time-consuming and expensive integration of unproven materials in NEMS logic switches.
Wabiszewski, Graham E., "Interrogation of Single Asperity Electrical Contacts Using atomic force Microscopy With Application to Nems Logic Switches" (2013). Publicly Accessible Penn Dissertations. 935.