Team:Yale/Our Project/Applications

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Applications: Engineering Design

Nano/Micro scale circuits have been instrumental development of new concepts and technologies like the lab-in-a-chip. The wire deposition technique invented by the Yale team can be used to fabricate such circuits by depositing copper wire a substrate in a controlled fashion: [[Image:Example.jpg]]

First, a mould can be created on a silicon/silicon dioxide substrate using conventional techniques like photolithography or etching. The mould cane then be inundated with copper sulphate solution containing the engineered bacteria. The liquid withdraws out of the channels as the copper is deposited. The final product is a copper wire etched on a a substrate that can be processed further to work as a circuit. The case study illustrate how such wires can used to make a micro-sized thermocouple temperature sensor.

A similar approach can be used to make micro metallic structures. Complex moulds can be made using conventional manipulation techniques and deposited with metal. This approach allows for some degree of mass production as the same mould can be used to fabricate multiple parts unlike other common methods. For instance the commonly used Atomic Force Microscopy probe that ac pull, push, and indent surfaces to assemble nano/micro structures, does not allow to visualize the object and manipulate it at the same time, so requires a series of ‘look and move’ operations that make manipulation cumbersome.

A mould based system can simplify/eliminate the need for such manipulation by constraining deposition to the space inundated by the growth solution. This approach also allows for formation of complex geometries. However, this strategy requires efficient mould-part separation techniques (expand).

Specific Application Case Study: Micro Temperature Sensors
A simple thermocouple device can be made on an appropriately etched substrate. A thermocouple consists of two wires of dissimilar metals joined together at a junction. An electromotive force is induced across the wires when the junction is exposed to an external temperature. The EMF is proportional to the temperature, so the relationship can be used to deduce the temperature using the voltage. A more complete circuit for this sensor includes two junctions (J1 and J2). J1 is kept at a known temperature, while J2 is exposed to the unknown temperature. The voltage Vab is directly proportional to the difference of these temperatures. Fig 1 shows the equivalent circuit of such a thermocouple.

The CAD models illustrate how such a device can be assembled on a micro-scale. Two channels can be etched on a substrate and inundated with copper sulphate and iron sulphate solutions containing the engineered bacteria. Deposition leads to two embedded wires connected interfaced at a junction. Further support electronics will be required to make the device functional and will add complexity, nevertheless, the fabrication technique is an important step towards such a device.

Broad Application Case Study: Micro-Robots