The strength of indium phosphide based microstructures

Micro opto electro mechanical systems with InP based micromechanics are proposed for devices with wide tuning ranges in the optical wavelengths where InP optoelectronics are normally used. To evaluate if these InP based micromechanical structures may be strong enough the mechanical strengths of surface micromachined epitaxial InP micro beams are evaluated. Reactive ion etching (RIE) with CH4:H-2:Ar is used to structure the beams. A sacrificial InGaAs layer is below the InP microstructures and selectively etched by HCl:H2O2:H2O in ratios 1:1:10 to release the InP beams. Sublimation of tert-butanol is used to dry the micro structures. The RIE conditions are shown to be of large importance, since the induced surface defects are here the dominant reasons for fracture. Bending strength values up to 3.1 GPa were measured, i.e. much higher than for the strongest construction steel. Weibull statistics show that it is possible to make micromechanics for typical MOEMS applications with acceptable loss in yield due to fracture probability, i.e. with a fracture probability of 0.0001 far 100 MPa maximum bending stress.