Strain engineering is a strategy used in semiconductor manufacturing to enhance device performance. Benefits are achieved by modulating strain in the transistor channel, which can improve electron or hole mobility and thus channel conductivity. Another example is semiconductor photocatalysts that are strain-engineered for more effective use of sunlight. The use of various strain engineering techniques has been reported by prominent microprocessor manufacturers, including AMD, IBM, and Intel, primarily in sub-130 nm technologies. One key consideration is that PMOS and NMOS respond differently to types of strain: PMOS benefits from compressive strain, while NMOS benefits from tensile strain. Many approaches induce strain locally, allowing n-channel and p-channel strain to be modulated independently. One common method uses a strain-inducing capping layer; CVD silicon nitride is often chosen because the magnitude and type of strain (tensile versus compressive) can be adjusted by changing deposition conditions, especially temperature. Standard lithography and patterning techniques can be used to selectively deposit strain-inducing capping layers—for example, to deposit a compressive film only over the PMOS. Capping layers are central to the Dual Stress Liner (DSL) approach reported by IBM and AMD: standard patterning is used to deposit a tensile silicon nitride film over the NMOS and a compressive silicon nitride film over the PMOS.

Another approach uses silicon-rich solid solutions, especially silicon–germanium (SiGe), to modulate channel strain. One method involves epitaxial growth of silicon on a relaxed SiGe underlayer; tensile strain is induced in the silicon as its lattice is stretched to match the larger SiGe lattice. Conversely, compressive strain can be induced by using a solid solution with a smaller lattice constant, such as silicon–carbon. See, e.g., U.S. Patent No. 7,023,018. A related method replaces the source and drain regions of a MOSFET with silicon–germanium. In thin films, strain can be induced by epitaxial growth or, more recently, topological growth; epitaxial strain generally arises from lattice mismatch between the film and substrate or from thermal expansion mismatch. Tuning epitaxial strain can be used to modify the properties of thin films and induce phase transitions. The misfit parameter f is given by f = (a_f − a_s)/a_s, where a_f is the lattice parameter of the epitaxial film and a_s is the lattice parameter of the substrate. After some critical film thickness, it becomes energetically favorable to relieve mismatch strain through the formation of misfit dislocations or microtwins. Misfit dislocations can be interpreted as dangling bonds at an interface between layers with different lattice constants. The critical thickness h_c was computed by Matthews and Blakeslee; it depends on the Burgers vector length b, the Poisson ratio ν, the angle λ between the Burgers vector and the misfit dislocation line, and the angle α between the Burgers vector and the vector normal to the dislocation’s glide plane. The equilibrium in-plane strain for a thin film with thickness t that exceeds h_c is reduced relative to the original misfit strain and can be expressed in terms of the dislocation density. Strain relaxation at thin-film interfaces via misfit dislocation nucleation and multiplication occurs in three stages, distinguishable by the relaxation rate. The first stage is dominated by glide of pre-existing dislocations and is characterized by a slow relaxation rate. The second stage has a faster relaxation rate, which depends on the mechanisms for dislocation nucleation in the material. Finally, the last stage represents a saturation in strain relaxation due to strain hardening. Strain engineering is well studied in complex oxide systems: epitaxial strain can strongly influence coupling among spin, charge, and orbital degrees of freedom, thereby altering electrical and magnetic properties. Epitaxial strain has been shown to induce metal–insulator transitions and to shift the Curie temperature of the antiferromagnetic-to-ferromagnetic transition in La1-xSrxMnO3. In alloy thin films, epitaxial strain affects spinodal instability and thus the driving force for phase separation. This effect is explained by coupling between the imposed epitaxial strain and the composition-dependent elastic properties of the system. More recently, researchers have achieved strains in thick oxide films larger than those possible with epitaxial growth by incorporating nanostructured topologies (Guerra and Vezenov, 2002) and by embedding nanorods or nanopillars within an oxide film matrix. Following this work, researchers worldwide have produced self-organized, phase-separated nanorod and nanopillar structures in numerous oxide films. Thulin and Guerra (2008) calculated strain-modified band structures of anatase TiO2 and found that hole mobility increases with strain. Additionally, in two-dimensional materials, strain has been shown to convert an indirect semiconductor into a direct one, allowing up to a hundred-fold increase in the light emission rate. In normal bulk materials, the maximum elastic strain typically ranges from 0.1% to 1%, which limits our ability to reversibly and quantitatively modify material properties with strain. Recent research on nanoscale materials, however, shows a much broader elastic strain range; even diamond, the hardest natural material, can exhibit up to 9.0% uniform elastic strain at the nanoscale.

Following Moore's law, semiconductor devices continue to shrink to the nanoscale, and because of the "smaller is stronger" effect, elastic strain engineering can be fully exploited there. Crystallographic direction plays a crucial role: most materials are anisotropic, so applying strain along different directions can significantly affect properties. For example, density functional theory (DFT) simulations for diamond show that strain along <110> causes a faster bandgap reduction, whereas strain along <111> yields a slower reduction but induces a transition from an indirect to a direct bandgap.