Edward S. Kolesar

Review and summary of a silicon micromachined gas chromatography system

A miniature gas chromatography (GC) system has been designed and fabricated using silicon micromachining and integrated circuit (IC) processing techniques. The silicon micromachined gas chromatography system (SMGCS) is composed of a miniature sample injector that incorporates a 10 μl sample loop; a 0.9-m long, rectangular-shaped (300 μm width and 10 μm height) capillary column coated with a 0.2-μm thick copper phthalocyanine (CuPc) stationary-phase; and a dual-detector scheme based upon a CuPc-coated chemiresistor and a commercially available, 125-μm diameter thermal conductivity detector (TCD) bead. Silicon micromachining was employed to fabricate the interface between the sample injector and the GC column, the column itself, and the dual-detector cavity. A novel IC thin-film processing technique was developed to sublime the CuPc stationary-phase coating on the column walls that were micromachined in the host silicon wafer substrate and Pyrex cover plate, which were then electrostatically bonded together. The SMGCS can separate binary gas mixtures composed of parts-per-million (ppm) concentrations of ammonia (NH3) and nitrogen dioxide (NO2) when isothermally operated (55–80 °C). With a helium carrier gas and nitrogen diluent, a 10 μl sample volume containing ammonia and nitrogen dioxide injected at 40 psi (2.8 × 105 Pa) can be separated in less than 30 min.

The lateral instability problem in electrostatic comb drive actuators: modeling and feedback control

Comb drives inherently suffer from electromechanical instability called lateral pull-in, side pull-in or, sometimes, lateral instability. Although fabricated to be perfectly symmetrical, the actuator’s comb structure is always unbalanced, causing adjacent finger electrodes to contact each other when voltage–deflection conditions are favorable. Lateral instability decreases the active traveling range of the actuator, and the problem is typically approached by improving the mechanical design of the suspension. In this paper, a novel approach to counteracting the pull-in phenomenon is proposed. It is shown that the pull-in problem can be successfully counteracted by introducing active feedback steering of the lateral motion. In order to do this, however, the actuator must be controllable in the lateral direction, and lateral deflection measurements need to be available. It is shown herein how to accomplish this. The experimentally verified dynamic model of the comb drive is extended with a lateral motion model. The lateral part of the model is verified through experimental results and finite element analysis and is hypothetically extended to accommodate both sensor and actuator functionalities for lateral movement. A set of simulations is performed to illustrate the improved traveling range gained by the controller.

Silicon-micromachined gas chromatography system used to separate and detect ammonia and nitrogen dioxide. II. Evaluation, analysis, and theoretical modeling of the gas chromatography system

A miniature gas chromatography (GC) system was designed and developed using silicon micromachining and integrated circuit (IC) processing techniques. The MMGC system can separate parts-per-million (ppm) ammonia and nitrogen dioxide concentrations in less than 30 minutes when isothermally operated (80/spl deg/C) at 40 psi. The heat of adsorption of nitrogen dioxide (0.38 eV) on a CuPc thin film (0.2 /spl mu/m thick) was also independently established. As a result of the MMGC systems performance evaluation, several of the assumptions invoked in the initial design were re-investigated, and a refined technique for optimizing the MMGC systems operation and performance was developed. >

Thermally-actuated cantilever beam for achieving large in-plane mechanical deflections

Abstract The design, finite-element analysis, and experimental performance evaluation of a microelectromechanical systems (MEMS) device known as a thermally-actuated beam is presented. A MEMS polysilicon thermally-actuated beam is a device that uses resistive (Joule) heating to generate thermal expansion and movement. To be a useful MEMS device, a thermally-actuated beam needs to produce incremental in-plane mechanical beam tip deflections that span 0–10 μm, while generating force magnitudes on the order of 10 μN. The thermally-actuated beam design was accomplished with the L-Edit software program, and the devices were fabricated using the Multi-User Microelectromechanical Systems (MEMS) Process (MUMPs) foundry at the Microelectronics Center of North Carolina (MCNC). Finite-element modeling analysis was accomplished with the IntelliCAD computer program. This CAD software incorporates an MCNC fabrication process description file that generates a 3-D solid model of the thermal beam. The resulting thermo- and electro-mechanical finite-element analyses predicted beam tip deflections and forces consistent with experimental observations. For example, when the drive voltage was varied between 0 and 6.5 V DC (corresponding to currents spanning 0–4.5 mA), tip deflections on the order of 0–13 μm were observed and calculated. When the ‘hot’ arms temperature was modeled to be 200°C (Joule heating), the resulting beam tip deflection was calculated to be 4.55 μm. The resonant frequency associated with in-plane motion, without damping, was calculated to be 75.16 kHz. The average resonant frequency measured in ambient air was 69.73 kHz. The average tip force generated by the thermal beam was measured to be 8.5 μN. A relative measure of the reliability of the thermal beam was established to be greater than 3 million cycles when continuously operated with a 30 Hz, 3-volt amplitude square wave with a 1.5-V DC offset.

In-plane tip deflection and force achieved with asymmetrical polysilicon electrothermal microactuators

Abstract Several microactuator technologies have recently been investigated for positioning individual elements in large-scale microelectromechanical systems (MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion are the most common modes of microactuator operation. This research focuses on the design and experimental characterization of two types of asymmetrical MEMS electrothermal microactuators. The motivation is to present a unified description of the behavior of the electrothermal microactuator so that it can be adapted to a variety of MEMS applications. Both MEMS polysilicon electrothermal microactuator design variants use resistive (Joule) heating to generate thermal expansion and movement. In a conventional electrothermal microactuator, the ‘hot’ arm is positioned parallel to a ‘cold’ arm, but because the ‘hot’ arm is narrower than the ‘cold’ arm, the electrical resistance of the ‘hot’ arm is higher. When an electric current passes through the microactuator (through the series connected electrical resistance of the ‘hot’ and ‘cold’ arms), the ‘hot’ arm is heated to a higher temperature than the ‘cold’ arm. This temperature increase causes the ‘hot’ arm to expand along its length, thus forcing the tip of the device to rotate about a mechanical flexure element. The new thermal actuator design eliminates the parasitic electrical resistance of the ‘cold’ arm by incorporating an additional ‘hot’ arm. The second ‘hot’ arm results in an improvement in electrical efficiency by providing an active return current path. Additionally, the ‘cold’ arm can have a narrower flexure than the flexure in a conventional single-‘hot’ arm device because it does not have to pass an electric current. The narrower flexure element manifests improved mechanical efficiency. Deflection and force measurements of both actuators as a function of applied electrical power have been presented in this work.

Method for Determining a Dynamical State–Space Model for Control of Thermal MEMS Devices

A method is presented for determining lumped dynamical models of thermal microelectromechanical systems (MEMS) devices for purposes of feedback control. As a case study, an electrothermal actuator is used. The physical properties and a set of assumptions are used to determine the basic structure of the dynamical model, which requires the development of the electrical, thermal, and mechanical dynamics. The importance of temperature-dependent parameters is emphasized for dynamical modeling for purposes of feedback control. To confront temperature dependence in a practical yet effective manner, an average temperature is introduced to preserve the energy balance inside the structure. This allows the development of a practical method that combines structure of the model, through the average body temperature, with finite element analysis (FEA) in novel way to perform system identification and identify the unknown parameters. The result is a lumped dynamical model of a MEMS device that can be used for the design of feedback control systems. We compare computer simulated results using the dynamical model with experimental behavior of the actual device to show that our procedure indeed generates an accurate model. This dynamical model is intended for further synthesis of driving signal and control system but also gives a qualitative insight into the relationship between devices geometry and its behavior. The method enables fast development of the model by conducting relatively few static FEA and is verifiable with dynamic experimental results even when temperature measurements are not available.

Control issues for microelectromechanical systems

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Single- and double-hot arm asymmetrical polysilicon surface micromachined electrothermal microactuators applied to realize a microengine

This paper highlights some microelectromechanical systems (MEMS) control issues and provides an overview of MEMS control.

Implementation of micromirror arrays as optical binary switches and amplitude modulators

The design, finite-element analysis, and experimental performance evaluation of a microelectromechanical systems (MEMS) device, known as a thermally actuated beam, is presented. The behavior of the thermal beam has been characterized so that it can be considered as an actuator in future MEMS applications. A MEMS polysilicon thermally actuated beam uses resistive (Joule) heating to generate thermal expansion and movement. To be a useful MEMS device, a thermally actuated beam will need to produce in-plane tip deflections that span 0–10 μm; while generating force magnitudes on the order of 10 μN. The thermally actuated beam design was accomplished with the L-Edit® software program. The devices were fabricated using the Multi-User Microelectromechanical Systems Process foundry service at the Microelectronics Center of North Carolina. The finite-element modeling analysis was accomplished with the IntelliCAD® computer program. These analyses predicted thermal beam tip deflections (0–13 μm) consistent with exper...