Ultimate Limits to Optical Displacement Detection in Nanoelectromechanical Systems
T. Kouh, D. Karabacak, D.H. Kim and K.L. Ekinci
Boston University, US
Keywords: nanoelectromechanical systems, optical interferometry, displacement detection
Nano-electro-mechanical Systems (NEMS) are among the most promising manifestations of the emerging field of nanotechnology. These are electromechanical systems with dimensions in the deep submicron mostly operated in their resonant modes. In this size regime, NEMS come with extremely high resonance frequencies, diminished active masses and tolerable force constants; the quality (Q) factors of resonance are in the range, significantly higher than those of electrical resonant circuits. These attributes collectively make NEMS suitable for a multitude of technological applications such as ultra-fast actuators, sensors, and high frequency signal processing components. However, there exist fundamental and technological challenges to NEMS optimization. One of the remaining challenges to developing technologies based upon NEMS is a robust, sensitive and broadband displacement detection method for sub-nanometer displacements. Most mainstay displacement sensing techniques used in the domain of Microelectromechanical Systems (MEMS) are not scaleable into the domain of NEMS necessitating the development of new techniques to realize the full potential of NEMS. Here, we explore the limits of optical-interferometry as a displacement detection scheme for NEMS displacements. For these measurements, we fabricated doubly-clamped nanomechanical beam resonators such as the ones shown in Figure 1. The structures were fabricated via a top-down fabrication approach using optical lithography, electron beam lithography and reactive ion etching (RIE). After wire bonding, the NEMS devices were transferred into an ultra-high vacuum (UHV) environment in the vicinity of a quartz window. A He-Ne laser was focused upon the structures through the window by a long working distance lens. The resonator displacements were then detected by an ac-coupled photo-detector, as the resonant modes of the structure were electrostatically excited. Through such measurements, we determined the ultimate displacement sensitivity of various optical displacement detection schemes. We will present experimental results as well as results from our theoretical sensitivity calculations.
Nanotech 2004 Conference Technical Program Abstract