Characterizations and Micro-assembly of Electrostatic Actuators for 3-DOF Micromanipulators in Laser Phonomicrosurgery.

International audienceThis paper presents a design of electrostatic actuators for 3-DOF micromanipulators in robot-assisted laser phonomicrosurgery. By integrating three sets of electrostatic actuators in a vertical configuration, scanning micro-mirror canbe used as a manipulator for laser source. Key enable technology for these miniaturized actuators is microfabrication processes for microelectromechanical systems (MEMS) because the processes can create submicron features with high precision, mass productive, and low cost. Based on precise micromachined electrostatic actuators, the platform is assembled using micro assembly approach. With sizes less than 5 mm x 5 mm x 5 mm, the proposed design has three degree-of-freedom: two rotational motions around the in-plane axis and one out-of-plane translational motion. Static and dynamic analysis of the device is simulated by Finite Element Analysis (FEA) and compared to theoretical calculations. This system preserves outstanding characteristics of electrostatic actuators for fast response and low power consumption. By micro-assembly of the scanning micromirror, the endoscopic systems can be created with a high range of motion and high scanning speed. The target applications of this system include laryngeal microsurgery, optical coherence tomography (OCT), and minimally invasive surgeries (MIS)

Electrostatic microactuators with integrated gear linkages for mechanical power transmission

In this paper a surface micromachining process is presented which has been used to fabricate electrostatic microactuators that are interconnected with each other and linked to other movable microstructures by integrated gear linkages. The gear linkages consist of rotational and linear gear structures and the electrostatic microactuators include curved electrode actuators, comb drive actuators and axial gap wobble motors. The micromechanical structures are constructed from polysilicon. Silicon dioxide has been used as a sacrificial layer and silicon nitride was used for electrical insulation. A cyclohexane freeze drying technique is used to prevent problems with stiction. The actuators, loaded with various mechanisms, have been driven successfully by electrostatic actuation. The work is a first step towards mechanical power transmission in micromechanical system

A fabrication process for electrostatic microactuators with integrated gear linkages

A surface micromachining process is presented which has been used to fabricate electrostatic microactuators. These microactuators are interconnected with each other and linked to other movable microstructures by integrated gear linkages. The gear linkages consist of rotational and linear gear structures, and the electrostatic microactuators include curved electrode actuators, comb-drive actuators, and axial-gap wobble motors. The micromechanical structures are constructed from polysilicon. Silicon dioxide was used as a sacrificial layer, and silicon nitride was used for electrical insulation. A cyclohexane freeze drying technique was used to prevent problems with stiction. The actuators, loaded with various mechanisms, were successfully driven by electrostatic actuation. The work is a first step toward mechanical power transmission in micromechanical system

Improving controllability in RF-MEMS switches using resistive damping

An efficient way to control the impact velocity in order to achieve soft landing and fewer bouncing phenomena is the resistive damping. This control method is also referred as charge drive and presented for first time by Castaner and Senturia [1]. Under charge control the Pull-in phenomenon of the Constant Voltage controlled electrostatic actuators does not exist and if the current drive is ideal, any position across the gap is stable. The main reason for this behavior is that the electrostatic force applied is always attractive and independent of the remaining gap of the actuator. Charge drive control incorporating constant current sources is mostly preferred to extend the travel range of electrostatic micro-actuators [2], [3], [4], [5]. Nevertheless there are very few references in the literature about charge drive control on RF MEMS. Recently published work based on numerical simulations for capacitive RF-MEMS, [6] and [7] present a learning algorithm in order to reduce fabrication variability using resistive damping for the pull-down phase. Nevertheless none of them present any details on how to implement resistive damping and any results of such kind of applications. This work presents in detail the entire procedure in calculating the bias resistance of an RFMEMS switch controlled under resistive damping

Design of a charge injection compensation system for MEMS electrostatic actuators

Projecte final de carrera realitzat en col.laboració amb Technical University of LodzThe main goal of this project is to implement and experimentally verify various control algorithms for MEMS electrostatic actuators. Those algorithms include a charge injection compensation subsystem. The hardware platform consists of some MEMS electrostatic actuators, a front-end sensing system (comprising a full-custom mixed-signal integrated circuit designed at UPC and a highspeed A/D converter) and a Xilinx FPGA for algorithm coding. The work involves the following: o Understanding the working principle of the hardware platform and the issues related to MEMS electrostatic actuators. o Improve the hardware platform, if required by the control algorithm. This might involve some simple PCB design and test with laboratory instrumentation. o Algorithm implementation in VHDL. This includes the signal-processing algorithms and also the ancillary routines for I/O data extraction and signal visualization. Capacitance of MEMS electrostatic actuators were measured under different voltages conditions. It was found that positive voltage stress caused negative charging of the dielectric whereas negative voltage stress caused positive charging of the dielectric. This is consistent with the nature of traps in the silicon oxynitride dielectric used for the switches. Report is divided into three parts, the first chapter is devoted to the description to the MEMS word. The chapter is devoted a small multiplexing board design description. And finally chapter 3 introduce a development of a VHDL code to control all system

Dielectric charging effects on Parylene electrostatic actuators

We report here the first characterization of dielectric charging effects on Parylene electrostatic actuators. High-resistivity Parylene in-between air gaps can cause undesirable charging effects due to air ionization when operating as electrostatic sensors/actuators at voltages as low as tens of volts. This undesirable effect can either lower the sensitivity of the sensor or increase the pull-in voltage of the actuator. It is further observed that Parylene actuators operating at high voltage could even show "bounce-back" and "pull-in voltage drift" problems. It is concluded that even for MEMS, attention must be paid to the operating voltages and the resistivity of the dielectrics

Resistive damping implementation as a method to improve controllability in stiff ohmic RF-MEMS switches

This paper presents in detail the entire procedure of calculating the bias resistance of an ohmic RF-MEMS switch, controlled under resistive damping (charge drive technique). In case of a very stiff device, like the North Eastern University switch, the actuation control under resistive damping is the only way to achieve controllability. Due to the short switching time as well as the high actuation voltage, it is not practical to apply a tailored control pulse (voltage drive control technique). Implementing a bias resistor of 33 MΩ in series with the voltage source, the impact velocity of the cantilever has been reduced 80 % (13.2 from 65.9 cm/s), eliminating bouncing and high initial impact force during the pull-down phase. However, this results in an affordable cost of switching time increase from 2.38 to 4.34 μs. During the release phase the amplitude of bouncing has also been reduced 34 % (174 from 255 nm), providing significant improvement in both switching operation phases of the switch. © 2013 Springer-Verlag Berlin Heidelberg

A Large-Stroke Electrostatic Micro-Actuator

Voltage-driven parallel-plate electrostatic actuators suffer from an operation range limit of 30% of the electrostatic gap; this has restrained their application in microelectromechanical systems. In this paper, the travel range of an electrostatic actuator made of a micro-cantilever beam above a fixed electrode is extended quasi-statically to 90% of the capacitor gap by introducing a voltage regulator (controller) circuit designed for low-frequency actuation. The voltage regulator reduces the actuator input voltage, and therefore the electrostatic force, as the beam approaches the fixed electrode so that balance is maintained between the mechanical restoring force and the electrostatic force. The low-frequency actuator also shows evidence of high-order superharmonic resonances that are observed here for the first time in electrostatic actuators