Mechanical property measurement of InP-based MEMS for optical communications

We investigate mechanical properties of indium phosphide (InP) for optical micro-electro-mechanical systems (MEMS) applications. A material system and fabrication process for InP-based beam-type electrostatic actuators is presented. Strain gradient, intrinsic stress, Young's modulus, and hardness are evaluated by beam profile measurements, nanoindentation, beam bending, and electrostatic testing methods. We measured an average strain gradient of deltaepsilon(0)/delta(t) = 4.37 x 10(-5) mum(-1), with an average intrinsic stress of sigma(0) = -5.4 MPa for [011] beams. The intrinsic stress results from arsenic contamination during molecular beam epitaxy and (MBE) can be minimized by careful MBE growth and through the use of stress compensating layers. Nanoindentation of (100) InP resulted in E = 106.5 GPa and H = 6.2 GPa, while beam bending of [011] doubly clamped beams resulted in E = 80.4 GPa and sigma(0) = -5.6 MPa. We discuss the discrepancy in Young's modulus between the two measurements. In addition, we present a method for simultaneously measuring Young's modulus and residual stress using beam bending. Electrostatic actuation in excess of 20 V is demonstrated without breakdown. (C) 2003 Elsevier Science B.V. All rights reserved.