Analog Integrated Circuits and Signal Processing, 37, 45–56, 2003 c  2003 Kluwer Academic Publishers. Manufactured in The Netherlands. Experimental Determination of Micromachined Discrete and Continuous Device Spring Constants Using Nanoindentation Method M.L. CHAN, 1 FRANCIS E.H. TAY, 1, ∗ V.J. LOGEESWARAN, 1 K.Y. ZENG, 2 LU SHEN 2 AND F.S. CHAU 1 1 Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Tel: 065-68746818, Fax: 065-67791459 2 Institute of Materials Research & Engineering, 3 Research Link, Singapore 117602 E-mail: mpetayeh@nus.edu.sg Received May 31, 2002; Revised September 13, 2002; Accepted December 31, 2002 Abstract. A rapid and accurate static and quasi-static method for determining the out-of-plane spring constants of cantilevers and a micromachined vibratory sensor is presented. In the past much of the effort in nanoindentation application was to investigate the thin-film mechanical properties. In this paper, we have utilized the nanoindentation method to measure directly some micromachined device (e.g. microgyroscope) spring constants. The cantilevers and devices tested were fabricated using the MUMPS process and an SOI process (patent pending). Spring constants are determined using a commercial nanoindentation apparatus UMIS-2000 configured with both Berkovich and spherical indenter tip that can be placed onto the device with high accuracy. Typical load resolution is: 20 μN to 0.5 N and a displacement resolution of 0.05 nm. Information was deduced from the penetration depth versus load curves during both loading and unloading. Key Words: nanoindentation, spring constant, bending test, microgyroscope, cantilever 1. Introduction Recent technological trends have caused an increase in the use of MicroElectroMechanical Systems (MEMS). As a result, the modelling need has arisen for the ca- pability to determine static and dynamic responses of micromachined devices or structures with analytical and computational methods. A prerequisite for predic- tion of these responses is the availability of accurate information regarding material properties; and where applicable device functional parameters for example, the spring constants. Conventional material property measurement methods are generally not adequate to provide the information concerning the material prop- erties of the micromachined devices. Hence, nanoin- dentation, a measurement method which has evolved from traditional hardness measuring techniques, is par- ticularly suitable to measure the properties of MEMS scale test samples [1]. The test procedure is similar to a macroscopic bending test where an external load is ap- plied to a beam and its bending measured. The spring ∗ Corresponding author. constant was determined from the load-displacement curve traced by the applied load on the indenter tip and the corresponding displacement. The advantage of this method is that load, displacement and time is continu- ously monitored and recorded. Sub-micron indentation or nanoindentation test us- ing either spherical, Berkovich or Vickers indenters is now widely accepted as an important tool for measur- ing the mechanical properties of thin films and small volumes of material [2, 3]. With the advent of inden- tation instruments that allows depth of penetration to be measured with nanometer resolution of around 1 or 2 nm, elastic properties such as modulus, plastic properties such as hardness and time-dependent prop- erties such as creep can be measured with minimal influences from the presence of the substrate [4]. Usu- ally, the principal objective of such indentation test is to extract the elastic modulus and hardness of the thin film from the experimental data of the indenter load and depth of penetration. Such indentations re- quire the use of the either sharp indenters, Vickers or Berkovich, where penetration into the material is required.