AVS 49th International Symposium
    Microelectromechanical Systems (MEMS) Thursday Sessions
       Session MM+TF-ThM

Paper MM+TF-ThM5
Micro-Mechanical Characterization of Indium Phosphide (InP) for Active Optical MEMS Applications

Thursday, November 7, 2002, 9:40 am, Room C-210

Session: Development and Characterization of MEMS Materials
Presenter: M.W. Pruessner, University of Maryland
Authors: M.W. Pruessner, University of Maryland
T. King, NASA Goddard Space Flight Center
D. Kelly, University of Maryland
R. Ghodssi, University of Maryland
Correspondent: Click to Email
Monolithic integration of InP-based optoelectronics with MEMS actuators will enable wavelength division multiplexed (WDM) lossless switches, tunable lasers, and optical filters at the 1550 nm communications wavelength. Before InP-based MEMS can be realized, however, the mechanical properties of thin-film InP need to be determined. Three methods are presented. In nanoindentation, the applied load vs. displacement of thin films or bulk substrates is measured, and Youngs modulus (E) and film hardness (H) can be extracted. In the bending test, load-displacement data of microbeams is used to extract E. Finally, M-Test takes advantage of the pull-in instability of electrostatically actuated microbeams. Measurement of the pull-in voltage enables E and residual stress to be extracted. A surface micromachining fabrication process for InP-based MEMS actuators was developed. The devices consist of 1.7 µm thick InP beams oriented in the [011] direction with 1.7 µm In@sub 0.53@Ga@sub 0.47@As sacrificial layer on a (100) InP substrate. Fabrication utilizes methane-hydrogen-argon RIE of InP followed by sacrificial etching of the InGaAs layer and supercritical CO@sub 2@ drying. After release the longer cantilevers curved out of plane indicating a stress gradient. Furthermore, the longer fixed-fixed beams buckled indicating compressive stress. Both are likely the result of arsenic (As) contamination of the InP beam layer during MBE sample growth. An optimization of growth parameters should alleviate this effect. Bulk nanoindentation experiments resulted in E=103 GPa and H=6.3 GPa. Bending tests on short fixed-fixed beams resulted in E=80 GPa. InP beam-type electrostatic actuators were also demonstrated. However, M-Test could not be performed reliably on the existing samples due to out-of-plane curvature of the longer beams. Short beams were flat but required excessive actuation voltage. Device design and experimental results are presented.