Long Que

Bent-beam electro-thermal actuators for high force applications

This paper describes in-plane microactuators fabricated by standard microsensor materials and processes that can generate forces up to about a milli-newton. They operate by leveraging the deformations produced by localized thermal stresses. Analytical and finite element models of device performance are presented along with measured results of fabricated devices using electroplated Ni, LPCVD polysilicon, and p/sup ++/ Si as structural materials. A maskless process extension for incorporating thermal and electrical isolation is outlined. Test results show that static displacements of /spl ap/10 /spl mu/m can be achieved with power dissipation of /spl ap/100 mW, and output forces >300 /spl mu/N can be achieved with input power <250 mW. It is also shown that cascaded devices offer a 4/spl times/ improvement in displacement. The displacements are rectilinear, and the output forces generated are 10/spl times/-100/spl times/ higher than those available from other comparable options. This performance is achieved at much lower drive voltages than necessary for electrostatic actuation, indicating that bent-beam thermal actuators are suitable for integration in a variety of microsystems.

Microfluidic electrodischarge devices with integrated dispersion optics for spectral analysis of water impurities

This paper reports a microfluidic device that integrates electrical and optical features required for field-portable water-chemistry testing by discharge spectroscopy. The device utilizes a dc-powered spark between a metal anode and a liquid cathode as the spectral source. Impurities are sputtered from the water sample into the microdischarge and characteristic atomic transitions due to them are detected optically. A blazed grating is used as the dispersion element. The device is fabricated from stacked glass layers, and is assembled and used with a charge-coupled device (CCD) sensing element to distinguish atomic spectra. Two structural variations and optical arrangements are reported. Detection of Cr and other chemicals in water samples has been successfully demonstrated with both devices. The angular resolution in terms of angular change per unit variation in wavelength (/spl part//spl theta///spl part//spl lambda/) is experimentally determined to be approximately 0.10 rad//spl mu/m, as opposed to the idealized theoretical estimate of 0.22 rad//spl mu/m. This is because the microdischarge is uncollimated and not a point source. However, this is sufficient angular resolution to allow critical spectra of metal impurities to be distinguished.

Pulse and DC operation lifetimes of bent-beam electrothermal actuators

This paper reports on lifetime studies of polysilicon and p/sup ++/ Si electrothermal actuators designed for rectilinear displacements. Measurements show that degradation patterns for displacement amplitude can be linked to design variables and operating conditions. At low power levels (which result in average operating temperatures of 300-400/spl deg/C), both types of devices provide continuous DC actuation for >1400 min. and pulse actuation for >30 million cycles without change in amplitude. A model similar to that used for fatigue in steel is used to fit pulse test data for p/sup ++/ Si actuators. The model parameters are explored as functions of operating conditions and device geometry.

Microfluidic discharge-based optical sources for detection of biochemicals

This paper reports a discharge-based optical source for fluorescence of biochemicals in microfluidic systems. Its efficacy is demonstrated using a stacked microchip that integrates a microfluidic wavelength-tunable optical source, a biochemical sample reservoir and optical filters. It is shown to excite fluorescence in l-tryptophan and DNA samples labeled by SYBR green dye. The discharge is struck in ambient air, between a metal anode and a cathode cavity that is filled with an aqueous solution, which is doped with a metal salt selected for its emission characteristics. The characteristic line spectra, which arise from energetic transitions of the metal ions that are sputtered into the glow region of the discharge, are optically filtered and guided to the biochemical sample that resides in a separate on-chip reservoir. For DNA fluorescence, a barium chloride solution is used to emit light at 454 and 493 nm. For tryptophan fluorescence, the cathode contains lead (ii) nitrate solution to provide a 280 nm emission. The resulting fluorescence from the DNA and tryptophan samples is compared to reference data. This technique can also be used to excite other fluorophores by using appropriately doped liquid cathodes having the desired emission characteristics.

A bi-stable electro-thermal RF switch for high power applications

This paper reports on the development of a bi-stable electro-thermal RF switch which can be operated with zero standby power (and bias) in either latched state. The device includes a bi-stable structure, which electrically shorts the input and output signal lines. Two electro-thermal actuators are used to switch it on and off. The entire structure is fabricated from 27 /spl mu/m thick electroplated Cu, suspended 3 /spl mu/m above a glass substrate. Typical actuation of the driving engine is performed by a 20 ms single pulse, corresponding to power and energy consumption of 33 mW and 662 /spl mu/J, respectively. Bursts of pulses of 0.1 ms width, used in sets of various durations, can reduce the total switching energy to <210 /spl mu/J. Measurements show that at 2.2 GHz, the device offers -0.5 dB insertion loss and -38 dB isolation, whereas at 3.5 GHz it offers -1 dB insertion loss and -30 dB isolation. Power handling capability tests for cold switching show that the device can be easily switched even after flowing >1 W RF power, suggesting that any micro-welding that may occur does not impede switching.

Reliability studies of bent-beam electro-thermal actuators

This paper reports on the first lifetime studies of the recently developed bent-beam electro-thermal microactuators. Measurements of p/sup ++/ Si bulk micromachined devices under varying operating conditions reveal that device lifetimes and degradation patterns are linked to actuation conditions as well as certain dimensional parameters. Device lifetimes in excess of 30 million cycles are observed. A model similar to that used for fatigue of steel is shown to be very suitable for predicting performance degradation. The model parameters are explored as a function of operating conditions.

Lifetime studies of electrothermal bent-beam actuators in single-crystal silicon and polysilicon

Microsystems using electrothermal bent-beam microactuators have been demonstrated for a variety of applications including optical attenuators, RF switches, and micro positioners, thus creating a need for information on the longevity of these devices. This paper reports on the dc and pulse mode lifetime testing of this class of actuators constructed using polysilicon and p/sup ++/ doped single crystal silicon. The relative temperature profile along the top surface of an actuator is experimentally verified by scanning probe microscopy. Displacement measurements are used to explore links between aging behavior and the design variables and operating conditions. At low power levels (which result in average operating temperatures of 300-400/spl deg/C) both polysilicon and p/sup ++/ Si devices provide continuous dc operation for >1400 min, in air without change in amplitude. While some types of p/sup ++/ Si devices show monotonic loss of amplitude in pulse tests, others have been operated up to 30 million cycles without degradation. The displacement for polysilicon actuators can either increase or decrease depending on the geometry of the device and operating conditions, both of which are related to temperature and stress of the structural members. Polysilicon grain transformations are observed over extended operation at high temperatures. Performance changes are correlated to material properties using SEM and TEM images.

A micromachined strain sensor with differential capacitive readout

This paper describes a laterally deflecting micromachined device that can be used to electronically monitor residual strain and Youngs modulus of microstructural materials. Residual strain is indicated by a change in the differential capacitance change, whereas the Youngs modulus is provided by the slope of a simple CV (capacitance vs. voltage) test. The device is suitable for automated wafer level as well as post-packaging readout. Typical strain sensitivities are 0.1-1 fF/MPa, and the CV slope essentially doubles (e.g. from 0.23 fF/V to 0.47 fF/V at 70 V bias) as the Youngs modulus changes from 220 to 130 GPa. Nickel plated and polysilicon strain sensors were fabricated by surface micromachining techniques and coated with self-assembled monolayers using an ODS-based process. Both stress and Youngs modulus measurements from these structures were found to closely match theoretical models.

A microfluidic ultra-violet emission source for direct fluorescence of tryptophan

This paper describes a fluidic microchip for observing the direct fluorescence of tryptophan and other amino acids, which are used in studying protein structure and dynamics. Since the excitation wavelengths of these are in the 250-290 nm ultra-violet range, it is a major challenge to find appropriate light sources that can be integrated onto micrototal analysis systems. This effort demonstrates that illumination from a microdischarge can be used to observe the direct fluorescence of tryptophan. The discharge is ignited across an air gap between an on-chip metal anode and a liquid cathode made of a saturated solution of lead nitrate. Atomic transitions in Pb atoms that are consequently sputtered into the discharge provide the wavelengths necessary to excite amino acids. Unwanted wavelengths are rejected by an optical filter that separates the microdischarge from the tryptophan sample. Measured results include the unfiltered and filtered spectral output of the microdischarge, as well as that of the resulting tryptophan emission, which has the characteristic broad peak from 300-450 nm.

A water spectroscopy microsystem with integrated discharge source, dispersion optics, and sample delivery

This paper reports a microsystem integrating the fluidic, electrical and optical elements required for field-portable water-chemistry testing by electric discharge spectroscopy. The device utilizes a DC microdischarge as a spectroscopic source. The discharge is created by applying a DC voltage between a metal anode and uses the water sample as the cathode. Impurities are sputtered from the water sample into the microdischarge. A blazed grating is used as the dispersion element, along with an aperture fabricated on a glass substrate. The microsystem is assembled and used with a CCD sensing element to distinguish atomic spectra. Two versions of the microsystem have been implemented: planar and a capillary tube-based device. Detection of Cr and other chemicals in water samples has been successfully demonstrated with both devices.