SMALL-SCALE MICRO / NANO-MANIPULATORS IN PRECISION ALIGNMENT AND POSITIONING

摘要

Micro-electro-mechanical systems (MEMS) are small-scale machines which are generally a few millimeters to a few microns in size. They are of interest to precision engineers because of their favorable dynamic characteristics (potential for tens to 100s of kHz bandwidth), favorable thermal characteristics (small size and high thermal diffusivity materials can be used to limit thermal strain errors) and potential for low cost and small packaging that follow when machines are miniaturized. Although the technology required to make simple MEMS devices has existed for several decades; the rate at which the technology has developed solutions for small-scale, precision machines has been slow. This is due in part to the challenges that the small-scale machine designer faces: (1) Design using materials with non-isotropic material properties and which experience non-isotropic material removal rates in MEMS fabrication processes, (2) Many MEMS process rely on chemical processes with rates that may form micron-sized parts, yet the reproducibility of critical feature size and location dimensions is difficult as the sources of variation in micro-fabrication processes are chemical/diffusion-based in nature and not as easily controlled, (3) The design and integration of actuators, sensors and electronics is complicated due to the need to ensure process compatibility between the types of devices which are fabricated on the same wafer, (4) Lack of reliable, low cost metrology equipment for characterizing the multi-axis performance and stiffness of MEMS devices (although interferometer-based systems have started to appear in recent years) and (5) difficulty fabricating robust precision contact bearings and motion constraints in MEMS devices. This is not an exhaustive list of problems and the preceding points do not represent ubiquitous problems, rather they reflect the types of challenges which the precision engineer is likely to face when adjusting their methods to adapt to the constraints which will be placed on their thinking, and therefore the machines can design, at the small-scale. This document is mean to (1) provide a collection of references on MEMS technologies which have promise for use in precision alignment equipment/manipulators with nanometer-level accuracy/precision and (2) provide a brief introduction to the technologies which show promise for practical application in small-scale precision machines. Within the 4 page limit of this document, we have decided to separate the text into roughly 2/3 explanation of the basic technologies and 1/3 references which we believe will be of interest to precision engineers.