Fabrication on Flexible Substrates and Curved Surfaces

Conventional microfabrication technologies apply only to flat and rigid substrates and materials. In recent years, advances in technologies allow 

The first one essentially reinvents the microfabrication processes by replacing the rigid solid materials with flexible polymer counterparts in semiconductors, conductors, and insulators. The second approach is to thin the films used to make the devices, followed by transfer onto flexible substrates. For example, nanometer-thick Si is flexible enough to allow transfer onto polymer substrates such as PDMS while maintaining its superb properties as a semiconductor [19]. 

The third approach takes full advantage of established microfabrication techniques [20,21]. The devices and systems are still fabricated onto traditional substrates but divided into smaller parts that reside on individual small islands. These islands are connected mechanically, electrically, or both ways by thin flexible pol5uner substrates. The complete structure may then be transferred onto other flexible structures or curved surfaces. Most of the mechanical stress suffered from such transfers will be absorbed by the thin polymer substrates the small islands and the devices on them experience much less stress. 

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In addition to the three basic microfabrication steps discussed above, other fabrication techniques are quite useful. We will briefly discuss a few of them, namely lift-off, annealing, liquid phase photopolymerization, micromolding, soft lithography, electroplating, sacrificial processes, bonding, surface modification, laser-assisted processes, planarization, and fabrication on flexible substrates and curved surfaces. Some of these techniques do not necessarily belong to the traditional repertoire of microfabrication of ICs. However, they have proved very useful for the creation of other types of microdevices and systems such as MEMS, microfluidics, and labs on chips. 

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