Two silicon microvalves have been built at the Institute of Electron Technology in Warsaw, Poland: a check valve, which does not require any control, and a through-flow valve, electronically controlled by means of a piezoelectric stack.

The devices belong to a category of micromechanical systems known as MEMS (Micro Electro-Mechanical Systems).

The key elements of both of them are silicon membranes and specially shaped sockets made with micrometre accuracy.

In the check valve, pressure applied in the direction of the flow causes the silicon membrane to deform, allowing 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 silicon brackets holding the membrane in place over the opening. “The main advantage of the valve is its extremely simple construction,” argues Pawel Kowalski, an engineer at the institute and one of the designers.

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 elements of both valves are the result of consecutive processes of plasma etching, photolithography and deposition of silicon and aluminium oxides.