Thin Film Microelectromechanical Systems
- PDF / 220,974 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 212 Views
Thin Film Microelectromechanical Systems V. Chu1, J. Gaspar1,2, J.P. Conde2 1 INESC Microsistemas and Nanotecnologias, Rua Alves Redol 9, 1000-029 Lisbon, Portugal 2 Departament of Materials Engineering, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
ABSTRACT This paper presents the fabrication and characterization of MEMS structures on glass substrates using thin film silicon technology and surface micromachining. The technology developed to process bridge and cantilever structures as well as the electromechanical characterization of these structures is discussed. This technology can enable the expansion of MEMS to applications requiring large area and/or flexible substrates. The main results for the characterization of the movement of the structures are as follows: (1) in the quasi-DC regime and at low applied voltages, the response is linear with the applied dc voltage. Using an electromechanical model which takes into account the constituent materials and geometry of the bilayer, it is possible to extract the deflection of the structures. This estimate suggests that it is possible to control the actuation of these structures to deflections on the sub-nanometric scale; (2) resonance frequencies of up to 20 MHz have been measured on hydrogenated amorphous silicon (a-Si:H) bridge structures with quality factors (Q) of 70-100 in air. The frequency depends inversely on the square of the structure length, as predicted by the mechanical model; and (3) using an integrated permanent magnet/magnetic sensor system, it is possible to measure the structure movement on-chip and to obtain an absolute calibration of the deflection of the structures.
INTRODUCTION Microelectromechanical systems or MEMS are a class of devices consisting of threedimensional structures capable of mechanical or electro-mechanical functionality [1]. The fabrication of MEMS utilizes processes based largely on planar silicon microelectronics technology, modified to allow the formation of released 3-D mechanical structures. MEMS devices can usually be put into 3 classes: (1) sensors; (2) actuators; or (3) passive structures. Examples of commercial products that incorporate MEMS are the inkjet print head nozzle [2], acceleration sensors for airbag deployment in automobiles [3], pressure sensors [4], infrared imagers [5] and the Digital Micromirror DeviceTM [6,7]. In almost all of the applications mentioned above, the technology is based on the use of a crystalline silicon wafer and high temperature polysilicon. The main fabrication techniques are bulk micromachining, surface micromachining, silicon fusion bonding and a process called LIGA. In bulk micromachining, the selective etching of the silicon wafer creates mechanical structures. The use of anisotropic etching allows a 100:1 ratio of etch rate in the orientation relative to the orientation. Heavy doping also slows the etch rate allowing for the use of doped layers as etch stops. Surface micromachining involves the use of a sacrificial material, usually silicon dioxide, whi
Data Loading...
