Carlos H. Mastrangelo

Mechanical stability and adhesion of microstructures under capillary forces. I. Basic theory

Strong capillary forces are developed in the fabrication process of surface micromachined structures during the wet etch of sacrificial layers. The magnitude of these forces is in some cases sufficient to deform and pin these structures to the substrate resulting in device failure. The deflection, mechanical stability, and adhesion of thin micromechanical structure under capillary forces are examined. These phenomena are divided into two separate stages of mechanical collapse and adhesion to the underlying substrate. The basic theory of collapse is described. Approximate conditions are computed to prevent contact to the substrate. >

Mechanical stability and adhesion of microstructures under capillary forces. II. Experiments

For pt.I see ibid., vol.2, p. 33 (1993). Strong capillary forces are developed in the fabrication process of surface micromachined structures during the wet etch of sacrificial layers. The magnitude of these forces is in some cases sufficient to deform and pin these structures to the substrate resulting in device failure. The deflection, mechanical stability, and adhesion of thin micromechanical structure under capillary forces are examined. Microstructure adhesion is considered and experimental data for polycrystalline silicon microstructures are presented. >

Adhesion-related failure mechanisms in micromechanical devices

Adhesion-related failures occur in microelectromechanical systems(MEMS) when suspended elastic members unexpectedly stick totheir substrates. This type of device failure is one of thedominant sources of yield loss in MEMS. This paper reviews thephysical mechanisms responsible for the failure from both the theoretical and practical stand point. In general, the failurerequires two different phenomena. First (a) the device must besubject to a force sufficiently strong to collapse the elasticmember thus bringing it in contact with the substrate. (b) Aftercontact is established and the force removed, the intersolidadhesion must exceed the elastic member restoring force hence keeping the device permanently pinned to the substrate. Both ofthese problems develop during the device fabrication as well asduring the device operation. Normalized elastic member dimensionbounds for prevention of collapse and pinning are presented. Thefailure rate can also be reduced using a wide variety ofprocessing, surface treatment, and physical schemes. These are discussed in regard to their practical applicability.

Microfabricated devices for genetic diagnostics

This paper presents a review of microfabricated devices for genetic diagnostics. Genetic diagnostics are powerful technology drivers and excellent candidate applications for miniaturization technologies because the demand for inexpensive genetic information is essentially unlimited, and the cost and time for the diagnostic decreases with sample volume. Genetic information is stored in long DNA molecules in solution. This information is processed and extracted using a series of enzymatic and other chemical reactions well known in molecular biology. Processing of DNA molecules in the microscale hence requires the implementation of microfluidic devices capable of handling, mixing, thermal cycling, separating, and detecting nano- and picoliter liquid samples. This paper discusses some of the fundamental macroscale protocols used for genetic analyses and how these processes scale down to microscopic volumes. The construction and performance of microfluidic devices of DNA amplification, separation, hybridization, and detection are discussed, showing that so far, no fundamental impediments exist for genetic diagnostics based on microelectromechanical systems. Some of the unresolved storage and packaging issues and future challenges for the practical implementation of these devices are also presented.

A simple experimental technique for the measurement of the work of adhesion of microstructures

A method to measure the interfacial work of adhesion, gamma /sub s/, between undoped polysilicon beams and a silicon substrate is presented. The method relies on the peeling and detachment of polysilicon cantilever beams. Values of surface energy of gamma /sub s/=140+or-70 mJ m/sup -2/ were found for both hydrophilic and hydrophobic samples. The technique used should also be applicable to the measurement of gamma /sub s/ for other micromechanical material systems.<<ETX>>

1-D POSITION SENSITIVE SINGLE CARRIER SEMICONDUCTOR DETECTORS

Abstract A single polarity charge sensing method has been studied using coplanar electrodes on 5 mm cubes of CdZnTe γ-ray detectors. This method can ameliorate the hole trapping problem of room-temperature semiconductor detectors. Our experimental results confirm that the energy resolution is dramatically improved compared with that obtained using the conventional readout method, but is still about an order of magnitude worse than the theoretical limit. A method to obtain the γ-ray interaction depth between the cathode and the anode is presented here. This technique could be used to correct for the electron trapping as a function of distance from the coplanar electrodes. Experimental results showed that a position resolution of about 0.9 mm FWHM at 122 keV can be obtained. These results will be of interest in the design of higher performance room-temperature semiconductor γ-ray detectors.

Thermal conductivity of heavily doped low‐pressure chemical vapor deposited polycrystalline silicon films

The lateral thermal conductivity of heavily doped low‐pressure chemical vapor deposited polycrystalline silicon films is measured using polycrystalline silicon microbridges elevated three micrometers above a silicon substrate. The bridges, lightly doped in their central regions and heavily doped elsewhere, are fabricated using a sacrificial silicon‐dioxide layer and phosphorus out‐diffusion from doped oxide. Voltage‐current characteristics measured on the bridges both under high vacuum and in silicone oil are used to calculate lateral thermal conductivity in the polycrystalline silicon. The experimental values for the thermal conductivity of heavily doped polycrystalline silicon range from 0.29 to 0.34 W cm−1 K−1 and average 0.32 W cm−1 K−1. These values agree closely with results obtained by a second method that employs uniformly doped polycrystalline silicon bridges. In the second method, high‐vacuum, voltage‐current characteristics are measured and the indicated thermal conductivities for two samples a...

Personal Navigation via High-Resolution Gait-Corrected Inertial Measurement Units

In this paper, a personal micronavigation system that uses high-resolution gait-corrected inertial measurement units is presented. The goal of this paper is to develop a navigation system that uses secondary inertial variables, such as velocity, to enable long-term precise navigation in the absence of Global Positioning System (GPS) and beacon signals. In this scheme, measured zero-velocity duration from the ground reaction sensors is used to reset the accumulated integration errors from accelerometers and gyroscopes in position calculation. With the described system, an average position error of 4 m is achieved at the end of half-hour walks.

Thermophysical properties of low-residual stress, Silicon-rich, LPCVD silicon nitride films

Abstract The thermal properties of low-residual stress, low-pressure chemical-vapor-deposited (LPCVD), silicon nitride (Si 1.0 N 1.1 ) have been extracted f

Electrothermally actuated inline microfluidic valve

A normally open electrothermally actuated inline microvalve that has been developed, fabricated and tested with liquids is presented. These actuators use high volumetric expansion of a sealed patch of Paraffin heated above its melting point, providing large displacements and forces while using low power. The inline valve is surface micromachined on top of preformed flexible microfluidic channels using a low temperature fabrication process; therefore it is suitable for integration with microfluidic networks requiring actuation of a large number of independent valves under electrical control. Complete closure of sealed microchannels has been observed with power as low as 40 mW. Response times of 15 ms have been measured. Breakdown of the inline valve occurs at an upstream pressure of 23 psig.