Kalin V. Lazarov

Analytical model for analysis and design of V-shaped thermal microactuators

An analytical solution of the thermoelastic bending/buckling problem of thermal microactuators is presented. V-shaped beam actuators are modeled using the theory of beam-column buckling. Axial (longitudinal) deformations including first-order nonlinear strain-displacement relations and thermal strains are included. The resulting nonlinear transcendental equations for the reaction forces are solved numerically and the solutions are compared with a nonlinear finite element (FE) model. A test actuator has also been fabricated and characterized. The obtained accuracy of the prediction is within 1.1% of the nonlinear FE solution and agrees well with the experimental data. A corresponding one-dimensional (1-D) heat transfer model has also been developed and validated against experimental i-V measurements at various temperatures. The developed analytical models are then used to analyze maximum stress and the heat transfer paths. It has been confirmed that the heat flux toward the substrate is a dominant heat dissipation route in sacrificially released devices.

PCB-integrated metallic thermal micro-actuators

The development of thermal micro-actuators on printed circuit boards is described. The fabricated metal actuators are shown to have similar displacement characteristics when compared with silicon-based devices described in the literature. The actuators are benchmarked with respect to power consumption, stroke, and response time. It is further demonstrated that simple analytical estimates for the response time are in good agreement with the experimental measurements and finite element analysis. The thermal cooling transient times are captured using a two-step constant-current excitation method. The fabrication process and potential application areas of the developed device are also provided.

Optically transparent gripper for microassembly

Production of complex Micro-Opto Electro-Mechanical Systems (MOEMS) often requires assembly of a system from individual components built by mutually incompatible processes. This fabrication step also constitutes the largest portion of the total cost (about 80%), and is one of the major roadblocks to successfully implementing a complex microsystem. Our previous experience with such systems shows, that gripping and manipulation of microparts significantly differs from the assembly of macroscopic devices. The main difference stems from the increased role of the surface electrostatic forces and the reduced influence of body forces such as gravity. This paper describes one possible use of the surface forces in the development of a novel optically transparent electrostatic microgripper. The principle of operation, design and simulation of the new device are described. Several models describing the gripping force are also presented. The out-of-plane and in-plane holding (frictional) forces are measured as a function of the applied voltage for two common materials - silicon and nickel. The fabrication sequence and the materials used are discussed.

Microelectrical Mechanical Systems Actuator Array for Tactile Communication

Tactile perception of alpha-numerics is possible using a tactile illusion (TI). The illusory sensation of motion is produced by mechanical actuators applying points of pressure on the skin. Vibrating points induce a nonveridical perception of motion from point to point. Intact lemniscal and parietal cortex are necessary for perception of the TI and can be used as a neurophysiological testing tool and an additional human-machine communication channel. We describe a 4 × 5 actuator array of individual vibrating pixels for fingertip tactile communication. The array utilizes novel micro-clutch MEMS technology. Individual pixels are turned ON and OFF by pairs of microscopic thermal actuators, while the main vibration is generated by a vibrating piezo-electric plate. Physiological parameters required for inducing TI and the fabrication sequence for the thermal micro-actuators along with actuation results are presented. Fingertip perception of micro-actuators could be built into a variety of data acquisition interfaces for handicapped persons.

An optically transparent gripper for micro-assembly

This paper describes the development of a novel optically transparent electrostatic microgripper for assembly of micro-electromechanical systems (MEMS). The principle of operation, design and tests of the new device are described. Fabrication sequence and the materials used are also provided. The resulting gripping force is measured as a function of the applied voltage and compared with a parallel pate capacitor model. The frictional (in-plane) force was also determined for two common materials, silicon and nickel. As expected, a small amount of trapped interfacial charge was observed and characterized via scanning potential microscopy (SPM). The present work provides experimental data on the magnitude of the residual charge, the corresponding force, as well as charge decay data. Although undesirable, in the assembly of high-aspect-ratio interconnects, the part release can be achieved via path planning, since the parts are inserted into micro-machined slots. A simple demonstration assembly cell with image- and laser-based position-sensing modalities has also been described.

Composite Thermal Micro-Actuator Array for Tactile Displays

Tactile perception of complex symbols through tactile stimulation is an exciting application of a phenomenon known as tactile illusion (TI). Sensation of motion on the skin can be produced by a limited number of discrete mechanical actuators applying light pressure over the skin. This phenomenon can thus be used as a neurophysiological testing tool to determine central and peripheral nervous system injury as well as providing an additional human-machine communication channel. This paper describes the development of a 4 x 5 actuator array of individual vibrating pixels for fingertip tactile communication. The array is approximately one square centimeter and utilizes novel micro-clutch MEMS technology. The individual pixels are turned ON and OFF by pairs of microscopic composite thermal actuators, while the main vibration is generated by a vibrating piezo-electric plate. The physiological parameters required for inducing tactile illusion are described. The fabrication sequence for the thermal micro-actuators along with actuation results are also presented.

Hybrid micro-meso mechanical switch array for tactile displays

Traditional MEMS actuators have limited stroke and force characteristics. This paper describes the development of a novel hybrid actuation solution, which utilizes a micro-machined actuator array to provide switching of mechanical motion of a larger meso-scale piezo-electric actuator. One motivating application of this technology is the development of a tactile display, where discrete mechanical actuators apply vibratory excitation at discrete locations on the skin. Specifically, this paper describes the development fabrication and characterization of a 4 × 5 micro-actuator array of individual vibrating pixels for fingertip tactile communication. The individual pixels are turned ON and OFF by pairs of microscopic thermal actuators, while the main vibration is generated by a vibrating piezo-electric plate. A thermo-electric and non-linear thermo-elastic models have been developed to account for the temperature dependence of the electrical resistance and the lateral buckling of the hot, respectively. Comparison between analytical and finite element models indicated very good agreement, confirming that the buckling of the hot arm has most significant impact in the overall actuator performance. The fabrication sequence and the actuation performance of the array are also presented.Copyright

Metallic Microactuators Based on Sacrificial Layer SU8 Release

Thermal micro-actuators are a promising solution to the need for large-displacement, low-power MEMS actuators. Potential applications of these devices are micro-relays, tunable impedance RF networks, and miniature medical instrumentation. In this paper the development of thermal microactuators based on SU8 is described. A polymeric sacrificial layer allows the removal of the SU8 mold to occur without the use of harsh etching conditions. In addition to silicon non-traditional for MEMS substrates such as RF-printed circuit boards have also been successfully utilized to fabricate the devices. The PCB-based devices exhibited similar characteristics, thus opening the possibility of integrating RF MEMS directly on PCBs. The actuators were benchmarked with respect to power consumption, stroke, and response time. The fabricated nickel actuators are shown to be robust with displacements in the range of 76 micrometers using 80 mW of power. Actual cooling transients were captured using a two-step constant-current excitation method. It is further demonstrated through analytical models that the thermal cooling times limit the bandwidth of these devices below 1KHz. Several commercially relevant applications of the developed actuators are also discussed. One such application is a vibro-tactile display for disabled individuals.Copyright

MEMS actuator array as a neuro-physiological testing tool

Tactile perception of complex symbols through tactile stimulation is an exciting application of a phenomenon known as tactile illusion (TI). Sensation of motion on the skin can be produced by a limited number of discrete mechanical actuators applying light pressure over the skin. This phenomenon can thus be used as a neurophysiological testing tool to determine central and peripheral nervous system injury as well as providing an additional human-machine communication channel. This paper describes the development of a 4/spl times/5 actuator array of individual vibrating pixels for fingertip tactile communication. The array is approximately one square centimeter and utilizes novel micro-clutch MEMS technology. The individual pixels are turned ON and OFF by pairs of microscopic thermal actuators, while the main vibration is generated by a vibrating piezo-electric plate. The physiological parameters required for inducing tactile illusion are described. The fabrication sequence for the thermal microactuators along with actuation results are also presented.

Design of Electro-Thermal Micro-Actuators: Mechanics and Electronic Position Detection

This chapter is devoted to the design of electro-thermal micro-actuators with capacitive position feedback. Analytical and finite element solutions of the electro-thermal and thermo-elastic problems are presented. A separate section is devoted to the challenging problem of displacement determination using charge sensitive amplifiers for high-precision capacitance measurements. These are illustrated with examples of electronic measurement circuits tested by the authors.