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The Warsaw Voice » The Polish Science Voice » February 23, 2012
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Silicon Valves
February 23, 2012   
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Two types of valves designed to be used in microhydraulic devices have been built at the Institute of Electron Technology in Warsaw. The active components of the valves have been made of silicon, using advanced technology employed in the production of semiconductor systems.

The new microvalves can regulate the flow of liquids and gases under extremely high pressures.

Currently commercially available valves designed for microhydraulic systems are purely mechanical designs and do not provide the degree of precision necessary to efficiently regulate the flow of fluids under high pressure. “Our silicon microvalves provide water-tightness not exceeding several microliters per minute under pressures of the order of a few dozen atmospheres. We believe there is still some room for improvement,” says one of the designers, Paweł Kowalski, an engineer at the Institute of Electron Technology.

Two silicon microvalves have been built at the Institute of Electron Technology: an automatic check valve and a through-flow valve that is electronically controlled by means of a piezoelectric stack. The devices fall into a category known as Micro Electro-Mechanical Systems (MEMS). The key components of both of them are silicon membranes and specially shaped sockets made with micrometer accuracy.

In the check valve, pressure applied in the direction of the flow causes the silicon membrane to deform, allowing the liquid or gas to flow freely. Pressure applied in the opposite direction presses the membrane against an inlet opening, blocking it. The sensitivity of the valve and the pressure range depend on the thickness of the silicon brackets holding the membrane in place over the opening. “The main advantage of the valve is its extremely simple design,” says Kowalski.

In the electronically controlled valve, the silicon membrane is propped against a piezoelectric stack. Depending on the applied voltage, the stack expands or contracts, deforming the membrane and shutting off or allowing the flow of liquid. If the stack is powered by a voltage of 24 V, the valve will operate at pressures up to 50 atmospheres. In case of a voltage of 150 V, the pressures can reach up to 200 atmospheres. The pressure range can also be expanded without increasing the voltage, by increasing the size of the piezoelectric stack.

The silicon components of both valves are the result of consecutive processes of plasma etching, photolithography and the application of silicon and aluminum oxides. The advanced technologies used to produce the working parts of the valves are by no means cheap. Still, up to several dozen working parts can be produced from a single silicon plate in a single production cycle, which significantly reduces the cost per unit. The finished silicon components of the valves are then mounted in metal casings.

The Institute of Electron Technology carries out research in the field of electronics and solid-state physics. It develops, implements and popularizes state-of-the-art micro- and nanotechnologies in photonics and micro- and nanoelectronics. The institute focuses on optoelectronic detectors and radiation sources, state-of-the-art semiconductor lasers, micro- and nanoprobes, nuclear radiation detectors, microsystems and sensors for interdisciplinary applications, as well as application-specific integrated circuits (ASIC). To make it easier for industrial partners and research centers to access its technology, design and measurement services, the institute has established a Center of Nanophotonics, a Center of Nanosystems and Microelectronic Technologies, and a Laboratory for Multilayer and Ceramic Technologies.
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