| Thin film transfer techniques enable the fabrication of microstructures that are difficult to make with conventional microfabrication techniques. Approaches such as temporary wafer bonding and microtransfer printing have been developed, however, there remains room for improvement in the area of adhesiveless transfer of thin semiconductor membranes. This dissertation examines the mechanics of these transfer processes via theoretical analyses and experimental measurements, and suggests routes to improve the effectiveness and versatility of the transfer processes.;To examine control of adhesion in transfer processes using patterning, the effect of interface patterning on fracture loads is studied using double cantilever beam specimens made of direct bonded silicon wafers. Analytical and finite element modeling both predict that the fracture load will increase as the height-to-width ratio of the pillar at the interface increases. This also agrees with experimental results. The behavior is the result of the pillar geometry affecting the interface stiffness and hence the stress distribution at the interface.;The remainder of this dissertation investigates microtransfer printing with elastomeric stamps. Firstly, shear-enhanced transfer printing is analyzed with finite element modeling. It examines the adhesion between stamps and substrates, and explains the reduced pull-off force of stamps that is observed when shear displacement is applied during printing. Next, advanced models with two interfaces (stamp-ink, ink-substrate) are introduced, and the crack path selection between those interfaces is predicted under a range of conditions. The results suggest that smaller interface toughness between the stamp and ink, as well as thicker ink layers are beneficial for printing. Furthermore, the model predictions agree with experimental measurements. Lastly, post stamps with asymmetric cross-sections, such as triangular and chevron shapes, are introduced and investigated for improving transfer printing processes. The pull-off forces of stamps under shear displacements are larger and the printing yield is higher when the crack propagates from the sharp side, rather than from the flat side, of the stamp. The difference in pull-off forces for two opposite crack propagation directions becomes larger as the angle of the sharp side of stamp becomes more acute. Using this difference, asymmetric stamps can be used to improve printing efficiency. |
