An engineered substrate is a material that can be fabricated and introduced in the conventional silicon manufacturing, resulting in products that are unique and could not have been fabricated using only silicon substrate. Engineered substrates generally shall have different lattice constants. In 1992, several researchers demonstrated that controlled strain could result in up to a doubling of speed in manufacturable CMOS transistors. Mobility enhancement in Si has been demonstrated utilizing engineered substrates, for example, by straining the Si channel. Until recently, researchers have focused on biaxial strain, created by growing high-quality layers of strained material across the entire wafer. Because of the conflicting effects that strain has on n-and pMOSFETs, the whole-wafer approach of building strain into silicon typically improves the performance of one transistor type more than that of the other, which has held back the commercial use of biaxial strain. However, electron and hole mobility can be optimized separately by patterning substrates to expose different Si crystal faces for each device.