Electronics

Conductivity of a liquid solution provides valuable information about the solution, but commercially available conductivity probes are costly and have diameters greater than 1cm, limiting their potential applications. Microscale thin-film liquid conductivity sensors are a novel application of semiconductor processing methodology and are capable of measuring ion concentrations in nanoliter size samples of liquid. The devices can be readily commercialized for small volume sample analysis or for in-vivo measurement in chemical or biological processes and mesoscale machines. Sensors can be fabricated as part of an integrated circuit and may be integrated with other sensors for multiparameter measurements. These robust, low-cost sensors also have potential for a wide range of commercial and industrial monitoring and control applications.

Current, commercially available liquid conductivity sensors are bulky, expensive and unable to measure small sample volumes or to be used for in-vivo and in-situ applications. A newly developed surface and bulk micromachining technique enables the fabrication of low cost, robust sensor probes with temperature compensation and improved packaging on silicon wafers.

From 200 to 2000 devices (depending on desired size) can be fabricated on a 4" silicon wafer, greatly reducing fabrication cost. Pt-black electroplating reduces the electrode/solution interfacial impedance, maintaining measurement accuracy while significantly reducing operation frequency. Reduction of operation frequency eliminates dependence on expensive measurement electronics.

With the new process and 4-electrode measurement, sensor probes can be fabricated with tip widths much less than 100 microns. To improve device accuracy, an RTD temperature sensor can be integrated on the sensor probe tip to provide local temperature compensation. The bulk micromachining method also allows the thermal mass of the sensor to be reduced, thus improving the response time of the probe.

Applications

• Analysis of chemical and biological fluids.
• In-vivo and in-situ measurements for medical testing.
• Controls for washing machine and dishwasher rinse cycles.
• Monitors to improve the performance and safety of water and ice dispensers and water purifiers.
• Devices for monitoring ultrapure water and measuring seawater salinity.

Benefits

• Sensors can measure electrical conductivity in nanoliter size samples over a wide range of solution conductivity.
• The sensor tip accommodates an integrated temperature sensor that enhances sensor accuracy by measuring local temperature.
• A four-electrode design provides independent measurement of current and voltage.
• The device is hundreds of times smaller than commercially available conductivity probes; future devices may be miniaturized to 100 micron tip width.
• Sensors can be operated at very low current and power consumption and are ideal for low-power or battery-operated applications.
• Sensors can be driven at relatively high electric currents, with the resulting high temperature acting to de-foul the electrodes.
• Because of low fabrications costs, sensors can be disposable.

This technology is a method to eliminate voltage overshoot in cables used to connect AC electric motors and pulse width modulation (PWM) inverters. As a function of cable length and voltage rise time, voltage overshoot occurs when high frequency currents reflect between the motor and source ends of a cable. University of Illinois researchers have devised a compensator that shapes the output of the PWM inverter in order to eliminate these reflections; the method only requires knowledge of the transmission line characteristic impedance and propagation delay. This technique extends the life of motor insulation and protects voltage-sensitive devices.

Voltage overshoot occurs when high frequency currents reflect between the motor and source ends of an electrical cable. Reflective waves of current can build up, causing motor insulation failure as well as damage to voltage-sensitive devices. While there have been techniques developed to compensate for voltage overshoot, many are complex, need load characteristics, and often require the use of bulky and expensive equipment.

The University of Illinois technique provides a mathematically exact solution that modifies the output of the PWM inverter in order to eliminate wave reflection. This technique is designed to eliminate voltage overshoot in the cable that connects alternating current (AC) electric motors to pulse width modulation (PWM) inverters that use insulated gate bipolar transistors (IGBT). IGBT motor drive cables are particularly susceptible to voltage overshoot due to their extremely fast switching speeds. The compensator, which attaches to either the source or motor end of a cable, is a filter that uses an appropriate linear combination of voltages and currents to transform the transmission line into a pure delay transfer. This prevents wave reflection and thus voltage overshoot. Users do not need to know the motor or drives characteristics; however, they do need to know the transmission line impedance and the propagation delay in order to use this device.

This invention improves on existing solutions to voltage overshoot by providing an exact solution rather than approximation. 

Applications:

The range of applications that use AC motors is vast, examples include:

• Heavy Industrial Machines or Manufacture: Heavy industries including automotive, materials handling, mining operations, plastic and rubber production, ceramics, textile, and utilities.
• Workshops: Metalworking, printing and woodworking shops.
• Chemical Industries: Chemical refining, pharmaceutical production, and plastic fabrication.

Benefits

• Cost-Effective: Eliminates damaging wave reflection, prolonging the usefulness of motors and voltage-sensitive devices.
• Low-Cost and Small: No large or expensive equipment is needed to implement this technology.
• Self-Adapting: Modifies waveform as transmission cable properties change over time.
• Versatile: Can be implemented at either the motor or source side of a cable, allowing users to select the side that is easier to maintain.

This technology describes a fabrication method for multi-channel, multi-layered microfluidic devices, with numerous functional characteristics capable of integration into a lab-on-a-chip platform. The chip allows broader analytical capabilities in point-of-use microfluidic technology than previously possible, and it does so with exceeding strength and stability.

Fabrication of this chip is made possible by a transfer process of labile membranes and the development of a contact printing method for a thermally curable epoxy-based adhesive. This adhesive has bond strengths that prevent leakage, channel rupture and delamination to nearly 6atm. Channels on the chip - 100 m wide and 20 m deep - are contact printed without the adhesive entering the microchannel.

The chip is characterized in terms of resistivity measurements along the microfluidic channels, electroosmotic flow (EOF) measurements at differing pH levels and laser-induced-fluorescence (LIF) detection of green-fluorescent (GFP) plugs injected across the nanocapillary membrane and into a microfluidic channel. The resulting product is a mixed-polymer micro-nanofluidic multilayer chip, which has the electrical characteristics necessary for use in microanalytical systems.

Applications:

• Solution sample clean-up and preparation: Prepare materials for research faster than ever before.
• Automated lab-on-a-chip: Develop high-throughput, fully-automated systems for life sciences research and drug discovery investigation.
• Laboratory-tests-on-a-card or "Lab Cards": Analyze blood and tissue samples on the spot with portable and hand-held devices.

Benefits:

• Built-in NCAMs: The NCAM (nanocapillary-array membranes) acts as an electrostatic "gateway," permitting only compounds of a particular size and charge to pass through. Integration of NCAMs into microfluidic devices increases the chips' sophistication and analytical capabilities by permitting simultaneous sample streams, multiple molecular manipulations, and controlled reactions and optical verification.
• Vertical nanocapillary interconnects: Sandwiching the NCAMs between layers of nanocapillary interconnects increases both scalability and complexity by allowing unique operations such as the separation of analytes based upon molecular size, channel isolation, enhanced mixing, and sample concentration.
• Optically transparent: Inspect fluids within the channels in the near UV and visible light spectrum.
• Incorporate numerous layers: With large arrays of NCAMS and nanocapillary interconnects, the fabrication method enables a wide degree of functional complexity because each layer can be optimized to a particular task.
• Reliable structure: Strong bonding during fabrication produces a high-test chip, whose nanocapillary arrays maintain stability up to nearly 6atm of pressure, even when several arrays are stacked together.

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A method of plasma etching Ga-based compound semiconductors includes providing a process chamber and a source electrode adjacent to the process chamber. The process chamber contains a sample comprising a Ga-based compound semiconductor. The sample is in contact with a platen which is electrically connected to a first power supply, and the source electrode is electrically connected to a second power supply. The method includes flowing SiCl.sub.4 gas into the chamber, flowing Ar gas into the chamber, and flowing H.sub.2 gas into the chamber. RF power is supplied independently to the source electrode and the platen. A plasma is generated based on the gases in the process chamber, and regions of a surface of the sample adjacent to one or more masked portions of the surface are etched to create a substantially smooth etched surface including features having substantially vertical walls beneath the masked portions.