MEMS/NEMS based on mono-, nano-, and ultrananocrystalline diamond fi lms

© 2014 Materials Research Society MRS BULLETIN • VOLUME 39 • JUNE 2014 • www.mrs.org/bulletin Introduction Chemical vapor deposition (CVD) diamond fi lm technology has experienced modest growth in the last two decades in terms of scientifi c and technological advances in the fi eld, which has, ultimately, positively affected progress in diamondbased microelectromechanical/nanoelectromechanical systems (MEMS/NEMS). In the early 1990s, soon after realizing excellent mechanical, chemical, electrical, and optical properties of polycrystalline diamond fi lms, which attracted attention from the MEMS community, the initial challenges ranged from mostly dealing with the rough microcrystalline morphology and developing surface micromachining processing techniques to the fabrication of basic MEMS structures (e.g., cantilever, bridges, comb-drive) 1 , 2 and characterization of mechanical properties such as Young’s modulus, intrinsic stress, and fracture strength. Soon after the introduction of nanocrystalline (NCD) and ultrananocrystalline diamond (UNCD) thin-fi lm technology in the late 1990s, demonstrating mechanical and tribological properties close to that of single crystal diamond (SCD), 3 interest peaked in this area. Multiple groups worked from all over the world, leading to rapid progress in this fi eld in recent years. Although in terms of optimizing residual stress (stress management), diamond thin-fi lms are still not there yet as compared to silicon, it is now possible to control the residual stress in diamond fi lms to a certain extent to fabricate “all diamond” moving MEMS devices with reasonable complexity. 4 Surface micromachining technology in diamond is now well matured, and advanced NEMS devices even in SCD have been demonstrated. 5 , 6 Integration of diamond with piezoelectric materials such as PZT 7 and AlN 8 added another boost, enabling fabrication of high-performance piezoelectric-driven MEMS/NEMS. The fi rst demonstration of complementary metal oxide semiconductor (CMOS) compatibility of UNCD 9 and thereafter fabrication of a radio frequency MEMS switch using UNCD as a dielectric layer driven by on-chip CMOS at wafer-scale 10 was a major step forward in diamond MEMS technology, paving the entry of diamond MEMS in communications electronics. Researchers are now successful in locating and manipulating electron spin associated with nitrogen-vacancy (NV) centers in diamond (substituted nitrogen atom in the diamond lattice paired with a nearest-neighbor vacancy) by applying external stimuli such as an electric fi eld, magnetic fi eld, microwave radiation or light, or a combination. This could be utilized to develop ultrasensitive NEMS sensors that can detect very weak magnetic fi elds ( ∼ few nano tesla) 11 useful for biomedical imaging. 12 The NV centers are also considered a basic MEMS/NEMS based on mono-, nano-, and ultrananocrystalline diamond fi lms