UHF Nickelmicromechanical Spoke-Supported Ring Resonators

A review of MEMS oscillators for frequency reference and timing applications

“…The use of SiGe as the capping layer for packaging of MEMS is discussed and demonstrated in [46,47] been maintained over a period of at least several months by sealing the SiGe cap with PVD Al [47]. Ni is another material that can be deposited at low temperatures using electroplating techniques and has been used for the processing of resonators [48]. Piezoelectric resonators comprising sputtered AlN thin films can be processed below 450 • C and therefore allow for the processing on top of CMOS.…”

“…For almost all capacitive transduced resonators, Si is used for the resonator body and in many cases the resonator is processed on a silicon-on-insulator (SOI) substrate. In some cases, especially when the resonator needs to be deposited at low temperature, capacitive transduced resonators are made from alternative materials, such as electroplated Ni [48], PECVD SiGe [45] or polycrystalline diamond [78]. Very high Q-factor can be obtained with capacitive transduced resonators, since no lossy metallic electrodes need to be deposited on top of the resonator as is the case for piezoelectric transduced resonators, see also section 4.2.…”

A novel multi-level IC-compatible surface microfabrication technology for MEMS with independently controlled lateral and vertical submicron transduction gaps

“…Reported technologies predominantly use either thermally-grown SiO 2 or low-pressure chemical vapor deposited (LPCVD)-based glass (e.g. phosphosilicate, borosilicate) sacrificial layers because of their high conformality [7,10,13,14]. However, these deposition methods require temperatures that are generally not considered IC-compatible (>400 °C).…”

“…In addition to the same temperature and HF release limitations as the previous technologies, bulk processing presents an additional hurdle to above-IC integration, since semiconductor devices are highly sensitive to any stress variation caused by the unavoidable removal of parts of the substrate. In [14], two layers of electroplated nickel are separated by a permanent thin nitride solid gap. Although the technology fully complies with above-IC requirements, it does not allow the implementation of released air gaps, and limits the applicability of the technology in other applications such as inertial sensors or out-of-plane structures.…”