A.B. Frazier

Electric impedance spectroscopy using microchannels with integrated metal electrodes

Microelectric impedance measurement systems containing microchannels with integrated gold electrodes were fabricated to enable EI measurements of femtoliter (10/sup -15/) volumes of liquid or gas. The microinstruments were characterized using samples of air, partially deionized water, and saline solutions with various ionic concentrations over the frequency range of 100 Hz to 2 MHz. Resulting spectral patterns varied systemically as a function of ionic concentration. In addition to industrial sensing applications, this technology may prove to be beneficial in monitoring microsystems utilizing on-chip fluid chemistry, measuring the dielectric dispersion of polymer solutions, and determining the electrical properties of isolated biological materials.

Metallic microstructures fabricated using photosensitive polyimide electroplating molds

A polyiimide-based process for the fabrication of thick (1-150 mu m), sharp-sidewall, high-aspect-ratio electroplated microstructures is presented. This process is a low-cost alternative to the LIGA process for microstructure fabrication. Although this process cannot match the performance of the LIGA process, it uses ordinary optical masks and ultraviolet light exposure, resulting in simple and inexpensive equipment requirements. Using this technology, structures made of a variety of electroplated metals can be fabricated. Vertically integrated structures that exploit the multilayer ability of the polyimides used can also be realized. Surface micromachining with this process can be used to fabricate movable electroplated microactuators. >

Surface micromachined metallic microneedles

In this paper, a method for fabricating surface micromachined, hollow, metallic microneedles is described. Single microneedle and multiple microneedle arrays with process enabled features such as complex tip geometries, micro barbs, mechanical penetration stops and multiple fluid output ports were fabricated, packaged and characterized. The microneedles were fabricated using electroplated metals including palladium, palladium-cobalt alloys and nickel as structural materials. The microneedles were 200 mm-2.0 cm in length with a cross-section of 70-200 /spl mu/m in width and 75-120 /spl mu/m in height, with a wall thickness of 30-35 /spl mu/m. The microneedle arrays were typically 9.0 mm in width and 3.0 mm in height with between 3 and 17 needles per array. Using water as the fluid medium, the average inlet pressure was found to be 30.0 KPa for a flow rate of 1000 /spl mu/L/h and 106 KPa for a flow rate 4000 /spl mu/L/h.

The miniaturization technologies: past, present, and future

Microelectromechanical systems (MEMS), micro systems technologies (MST, primarily in Europe) and micromanufacturing have become synonymous with the design, development, and manufacture of very small devices and systems. This paper overviews the history of the major technologies that are utilized in this field. After this brief historical overview of the technologies, a short description of MEMS technologies is presented. The status of the MEMS effort worldwide is reviewed with emphasis on the United States, Japan, and the European Community with particular emphasis placed on Germany, the Netherlands, and Switzerland. The future for the technology along with technology transfer and management is discussed from the standpoint of market pull. Bulk and surface micromachining of silicon, X-ray micromachining using the LIGA process, and the complementary processes such as laser and focused ion beam micromachining are reviewed. >

High aspect ratio electroplated microstructures using a photosensitive polyimide process

A polymide-based process for the fabrication of high-aspect ratio microstructures is presented. The process exploits the sharp-sidewall characteristics of photosensitive polyimide to create the electroplating form through which the high-aspect-ratio structures are electroplated. Although the resolution of this process is inferior to the synchrotron-based process, this process has several advantages: it is simple and can be carried out using commercially available materials and common clean room equipment; the excellent chemical and thermal resistance of polyimide allows plating to take place in a variety of environments; and multiple coats of polyimide can be used to fabricate vertically integrated structures which have variation in the third dimension. The process is completely compatible with surface micromachining sacrificial layer techniques to create released electroplated microstructures.<<ETX>>

A low-temperature IC-compatible process for fabricating surface-micromachined metallic microchannels

In this paper, a low-temperature integrated-circuit (IC)-compatible process for fabricating metallic microchannels is described. Arrays of 1-100 metallic microchannels have been fabricated on silicon and glass substrates. The process can be extended to many planar substrate materials including polymers and ceramics. The microchannels are formed using microelectro-formed metals. The microchannels demonstrated in this paper use nickel as the structural material and gold as the surface coating on the inside walls of the microchannels. The inner dimensions of the individual microchannels fabricated to date range from 30 /spl mu/m to 1.5 mm in width, 0.5 mm to several centimeters in length, and 5-100 /spl mu/m in thickness. The wall thickness ranges from 5 to 50 /spl mu/m. The microchannel fabrication technology enables the fabrication of surface microchannels with a relatively large cross-sectional area. The metallic microchannels can be fabricated to extend from the substrate edge. Interfacing schemes are given for attaching external pressure feeds.

Two dimensional metallic microelectrode arrays for extracellular stimulation and recording of neurons

An inexpensive and reproducible technique for realizing metallic microelectrode arrays is presented. Arrays of sixteen microelectrodes have been fabricated using bulk silicon etching technology and photosensitive polyimide processing. The arrays are fabricated on a silicon substrate using nickel as the structural material and gold as the exposed material at the neural recording sites. Silicon nitride serves as the insulating material for the shaft of the electrodes. Individual electrodes are 15- mu m thick, 25- mu m wide, and 1.1 mm in length, and have a probe-to-probe spacing of 75 mu m. The process used to fabricate the microelectrode arrays is compatible with standard integrated circuit fabrication technology. The arrays have successfully undergone repeated insertion into the olfactory bulb of laboratory rats.<<ETX>>

Whole-Cell Impedance Analysis for Highly and Poorly Metastatic Cancer Cells

A micro electrical impedance spectroscopy (muEIS) system has been developed and implemented to analyze highly and poorly metastatic head and neck cancer (HNC) cell lines with single-cell resolution. The microsystem has arrays of 16 impedance analysis sites, each of which is capable of capturing a single cell and analyzing its whole-cell electrical impedance spectrum. This muEIS system was used to obtain the electrical impedance spectra of the poorly metastatic HNC cell line 686 LN and the highly metastatic HNC cell line 686 LN-M4e over a frequency range of 40 Hz - 10 MHz. The 686 LN cells had higher impedance phase compared to that of 686 LN-M4e cells at frequencies between 50 kHz and 2 MHz. This result demonstrates that the metastatic state of HNC cells can be distinguished using the developed muEIS system. This system is expected to serve as a powerful tool for future detection and quantification of cancer cells from various tumor stages.

Diamagnetic capture mode magnetophoretic microseparator for blood cells

This paper presents the characterization of a continuous diamagnetic capture (DMC) mode magnetophoretic microseparator for separating red and white blood cells from diluted whole blood based on their native magnetic properties. The DMC microseparator separated the blood cells using a high-gradient magnetic separation (HGMS) method without the use of additives such as magnetic beads. The microseparator was fabricated using microfabrication technology, enabling the integration of microscale magnetic flux concentrators in an aqueous microenvironment. Experimental results show that the DMC microseparator can continuously separate out 89.7% of red blood cells (RBCs) from diluted whole blood within 5 min using an external magnetic flux of 0.2 T from a permanent magnet. Monitoring white blood cells (WBCs) probed with a fluorescence dye show that 72.7% of WBCs were separated out within 10 min in the DMC microseparator using a 0.2 T external applied magnetic flux. Consequently, the DMC microseparator may facilitate the separation of WBCs from whole blood in applications such as a genetic sample preparation and blood borne disease detection. [1574].

Micromachined needle arrays for drug delivery or fluid extraction

Micromachined needle arrays have been designed, fabricated, and characterized. The design includes arrays of 25 needles with fluid coupling channels and dual structural supports. Numerical modeling of fluid flow characteristics was performed, demonstrating that the needle coupling channels redistribute flow when the input or output ports are fully restricted. Micromachining technologies have been used to batch fabricate hollow metallic fluid coupled needle arrays. The significance of this work includes the development of the hollow metallic micromachined needle arrays for biomedical applications, as well as a discussion of structural, fluidic, and biological design considerations. The micromachined needle array has many advantages, including (a) reduced trauma at penetration site (small size), (b) greater freedom of patient movement (minimal penetration), (c) a practically pain-free drug delivery device (distribution of force), (d) precise control of penetration depth (needle extension length), and (e) they can be stacked and packaged into a 3-D device for fluid transfer.