Paul C. Galambos

Electrical and Fluidic Packaging of Surface Micromachined Electro-Microfluidic Devices

Microfluidic devices have applications in chemical analysis, biomedical devices and ink-jets1. An integrated microfluidic system incorporates electrical signals on-chip. Such electro-microfluidic devices require fluidic and electrical connection to larger packages. Therefore electrical and fluidic packaging of electro-microfluidic devices is the key to the development of integrated microfluidic systems. Packaging is more challenging for surface micromachined devices than for larger bulk micromachined devices. However, because surface micromachining allows incorporation of electrical traces during microfluidic channel fabrication, a monolithic device results. A new architecture for packaging surface micromachined electro- microfluidic devices is presented. This architecture relies on two scales of packaging to bring fluid to the device scale (picoliters) from the macroscale (microliters). The architecture emulates and utilizes electronics packaging technology. The larger package consists of a circuit board with embedded fluidic channels and standard fluidic connectors. The embedded channels connect to the smaller package, an Electro-Microfluidic Dual-Inline-Package (EMDIP) that takes fluid to the microfluidic integrated circuit (MIC). The fluidic connection is made to the back of the MIC through Bosch2 etched holes that take fluid to surface micromachined channels on the front of the MIC. Electrical connection is made to bond pads on the front of the MIC.

Combined field-induced dielectrophoresis and phase separation for manipulating particles in microfluidics

Experiments were conducted in microfluidics equipped with dielectrophoretic gates arranged perpendicular to the flow. Under the action of a high-gradient ac field and shear, flowing suspensions were found to undergo a phase separation and to form a distinct front between the regions enriched with and depleted of particles. We demonstrate that this many-body phenomenon, which originates from interparticle electrical interactions, provides a method for concentrating particles in focused regions and for separating biological and nonbiological materials. The evolution of the particle patterns formation is well described by a proposed electrohydrodynamic model.

Design and Analysis of a Surface Micromachined Spiral-Channel Viscous Pump

A new viscous spiral micropump which uses the surface micromachining technology is introduced. We outline the design of a spiral pump fabricated in five levels of polysilicon using Sandias Ultraplanar Multilevel MEMS Technology (SUMMiT), and presents an analytical solution of the floss field in its spiral channel. The pump characteristics are obtained experimentally for a scaled-up prototype

Development of surface micromachining technologies for microfluidics and bioMEMS

In the last decade, examples of devices manufactured with SUMMiT(TM) technology have demonstrated the capabilities of polysilicon surface micromachining. Currently we are working on enhancements to this technology that utilize additional structural layers of silicon nitride to enable Microfluidics and BioMEMS applications. The addition of the silicon nitride layers allows the fabrication of microfluidic flow channels that are transparent (allowing observation of cellular motion) and insulating (allowing the placement of polysilicon electrodes at arbitrary locations in the flow channels). The goal of this technology development effort is to ultimately provide functionality that is not feasible with other microfabrication technologies. The enhancements build on the key features of surface micromachining: manufacturability and compatibility with CMOS processing, which allow us to leverage the investment already made in the microelectronics processing technology. In this paper we will present examples of devices fabricated using this new enhanced surface micromachining technology. These devices include pumps, valves, and a cell manipulator.

Monolithic surface micromachined fluidic devices for dielectrophoretic preconcentration and routing of particles

We describe a batch fabrication process for producing encapsulated monolithic microfluidic structures. The process relies on sacrificial layers of silicon oxide to produce surface micromachined fluid channels. Bulk micromachined interconnects provide an interface between the microchannels and meso-scale fluidics. The full integration of the fabrication processing significantly increases device reproducibility and reduces long-term costs. The design and fabrication of dielectrophoresis (DEP) gating structures configured in both batch-flow and continuous-flow modes are detailed. Highly efficient microparticle preconcentration (up to ~100× in 100 s) and valving (97% particle routing efficiency) are demonstrated using ac DEP and an accompanying phase separation. The low aspect-ratio fluid channels with integrated microelectrodes are well suited for µm and sub-µm particle manipulation with electric fields.

High-efficiency magnetic particle focusing using dielectrophoresis and magnetophoresis in a microfluidic device

We describe a novel technique that utilizes simultaneous implementation of dielectrophoresis (DEP) and magnetophoresis (MAP) to focus magnetic particles into streams for optical analysis of biological samples. This technique does not require sheath flow and utilizes a novel interdigitated electrode array chip that yields multiple streams of flowing magnetic particles in single-file columns. The MAP force placed particles in close proximity to the microelectrodes where they were subjected to a strong DEP force that generated the particle focusing effect. Particle focusing efficiency was improved using this combination DEP–MAP technique compared to DEP alone: particle stream widths were reduced ~47% and stream width variability was reduced 80% for focused streams of 8.5 µm diameter magnetic particles. 3 µm diameter magnetic particles were strongly focused with DEP–MAP (~4 µm wide streams with sub-µm variability in stream width) while DEP alone provided minimal focusing. Additional components of a prototype detection system were also demonstrated including an integrated magnetic pelleting component, a hand-held MHz frequency signal generator and a bench-top near-confocal microscope for optical analysis of flowing particles. Preliminary testing of a sandwich assay performed on the surface of magnetic particles showed 50 ppb detection levels of a surrogate biotoxin (ovalbumin) in a raw milk sample.

Active MEMS Valves for Flow Control in a High-Pressure Micro-Gas-Analyzer

We present active electrostatic MEMS gas valves for Micro-Gas-Analyzer (MGA) flow control. These unique valves enable extremely low dead volume, highly integrated flow control chips for the MGA application, and potentially others (e.g., propulsion, pneumatic, and thermodynamic microsystems). We have demonstrated low leak rates ( <; 0.025 sccm, <; 0.0025 sccm on a similar passive valve design), high operating pressures 6.9×105 N/m2 (100 psig), a high-pressure record for valves of this size and type, and high flow rates (>; 25 sccm) using control voltages on the order of 100 V. The valve designs presented eliminate charge build-up issues associated with insulating materials and are closely tied to a base-lined microfabrication process (SUMMiT), allowing mass production. Using this process, which incorporates only CMOS compatible materials, eliminates outgassing and absorption problems inherent to microvalve designs that incorporate elastomers or organic bonding layers, and reduces contamination when the valve is part of the chemical analysis flowpath. The results obtained indicate that even higher performance level valves (>; 1.4 × 106 N/m2 or 200 psig operating pressure, at similar control voltage, flow rates, and leak rates) are possible.

A Surface Micromachined Electrostatic Drop Ejector

Ejectors have applications ranging from ink-jet printing to drug delivery. A novel electrostatic ejector was surface micromachined; and satellite-free, 2 pl drops were ejected at 10 m/s using an electrostatic field (E-field) of 20 V/µm. The E-field is applied across the ejected liquid, which simplifies device design, but allows the possibility of dielectric breakdown and electrolysis in the liquid. These challenges were overcome in the prototype described herein.

Passive MEMS Valves With Preset Operating Pressures for Microgas Analyzer

In this paper, we present integrated disk-in-cage poppet valves with tuned spring stiffness for gas flow control of a microgas analyzer. The valves require zero power and close at preset offset pressures (0-35 psig) to switch from gas sample loading onto a preconcentrator to concentrated constituent sample injection into a microgas chromatograph. Air flow rates of 4.5 mL/min at pressures of - 2.5--5 psig (vacuum sample loading) were measured. Hydrogen leak rates of 0.1 muL/s (0.006 mL/min) were measured with valves closed at 15 psig. Analytical and numerical modeling was used to guide design of valve spring constants (ranging from 10 to 1500 N/m) that control the valve open position, flow rate, and closing pressure. The parameter design space is limited to a range of seat overlap, valve size, and spring stiffness that will allow adequate flow rate, sealing, and closing at predictable pressures. A linear curve defining closing pressure as a function of spring constant, valve gap, valve size, and seat overlap fit measured closing pressure data and can be used to predict closing pressure for future designs.

Surface Micromachined Cell Manipulation Device for Transfection and Sample Preparation

We have designed and fabricated a micromachined cell manipulation device using Si surface micromachining technology [1]. The device is designed to mechanically disrupt the cellular membrane of a cell, allowing the delivery of large molecules (for example DNA, RNA, proteins or fluorescent molecules) into the cytoplasm without completely lysing the cells. To deliver large molecules into cell, electroporation or chemical permeabilization methods are typically used [2], as well as some recent utilization of micromachined parts [3]. This device is designed to mechanically disrupt the cellular membrane in a controlled and repeatable manner (Figs. 1–3) and operates in a continuous flow mode. The cells flowing through the device are engaged by the manipulator which is operating in a reciprocating motion, powered by high performance comb drives and a compliant displacement multiplier. The mechanical features of the manipulator and the opposing structure are designed to effectively permeabilize the cellular membrane. A third port for addition of chemicals is immediately downstream of the cellular disruption chamber (Fig. 2). Mechanical membrane disruption effectively decouples the membrane disruption process from the chemical addition or electrical manipulation processes, allowing a wider range of chemicals and electrical signals to be used and broadening the field of potential applications for cellular manipulation devices. This device can also be used to lyse cells with a known and repeatable physical mechanism, enabling simplified, highly uniform and consistent cellular sample analysis. To our knowledge this is the first example of a continuous flow, mechanical cellular membrane disrupter to be reported and it is intended to be a capable demonstration tool for the unique integration of mechanical, optical and microfluidic components possible using this fabrication technology. Open image in new window Fig. 1 Mask layout of the micromachined cell manipulation device - and SEM close-up of the fabricated mechanical probe which is designed to disrupt the cellular membrane and allow delivery of large molecules into the cellular medium. Open image in new window Fig. 2 The high performance comb drive and the displacement multiplier that are driving the manipulator are visible in this SEM. The close-up shows the piston that is coupled into the microfluidic chamber, the manipulator is visible inside the silicon nitride channel. The chamber is formed during the process and no bonding steps are necessary to from the cavity. Open image in new window Fig. 3 Red blood cells flowing through the device. The manipulator was run from sub-Hz to kHz range with varying displacements. Current characterization efforts are aimed at delivery of fluorescent material into the manipulated cells. In this picture, material flow is from right to left.