Evolution from MEMS-based Linear Drives to Bio-based Nano Drives

Abstract

The successful extension of semiconductor technology to fabricate mechanical parts of the sizes from 10 to 100 micrometers opened wide ranges of possibilities for micromechanical devices and systems. The fabrication technique is called micromachining. Micromachining processes are based on silicon integrated circuits (IC) technology and used to build three-dimensional structures and movable parts by the combination of lithography, etching, film deposition, and wafer bonding. Microactuators are the key devices allowing MEMS to perform physical functions. Some of them are driven by electric, magnetic, and fluidic forces. Some others utilize actuator materials including piezoelectric (PZT, ZnO, quartz) and magnetostrictive materials (TbFe), shape memory alloy (TiNi) and bio molecular motors.This paper deals with the development of MEMS based microactuators, especially linear drives, following my own research experience. They include an electrostatic actuator, a superconductive levitated actuator, arrayed actuators, and a bio-motor-driven actuator. I started the investigation of MEMS in 1886. The study on microactuators has been one of the major activities in my laboratory. The development of novel micromachining technology has been conducted intensively in order to realize microactuators. The first fully micromachined actuator in my laboratory was an electrostatic comb drive. An example of a comb drive is shown in Fig. 1. The actuator utilized electrostatic pulling force between two interdigited comb-like fingers, one set was fixed to the substrate and the other set was attached to the moving part. The actuator typically generated the force of 10-100 micro-N and the displacement of 1-10 micrometers.The cilialy motion conveyor mimics the motion of cilia in living organisms. We fabricated an array of microactuators which are thermally driven bimorphic cantilevers. When Joule heating in the heater relaxes the thermal stress, the curled cantilever becomes flat. Thus the tip goes up and down. The dimensions of the cantilever are: 500 micrometers in length, 100 micrometers in width Linear bio motors consisting of two proteins, i.e. kinesin and microtubule, were attached to MEMS structures and substrates, respectively. Thus, we could build a transportation device driven by bio motors. When kinesin-coated structures are placed on the microtubule, kinesin generates force and convey those objects (Fig. 2). The energy for bio motors is supplied by ATP molecules in water. On and off control of the motion of micro beads was successfully demonstrated by adding ATP molecules and removing them from the solution. We also succeeded the aligned immobilization of microtubules on the substrate or in the micro channel. It was possible to convey objects in the pre-determined direction with this technology.When micromachining technology and microactuator design were established, the applications were pursued. A needle attached to a microactuator was brought into the close vicinity (less than a few nanometers) from the stationary electrode;...