Nozzle arrangement with an electrically heated actuator

1. A micro-electromechanical fluid ejection mechanism, the fluid ejection mechanism comprising

a substrate that incorporates drive circuitry;

a nozzle chamber structure arranged on the substrate to define a nozzle chamber and a fluid ejection port in fluid communication with the nozzle chamber; and

an actuator that is fast at one end with the substrate and that extends into the nozzle chamber, the actuator comprising

an actuating member that is connected to the drive circuitry and anchored at one end to the substrate, the actuating member being displaceable between a quiescent position and an active position to eject fluid from the ejection port, at least a portion of the actuating member being of an electrically conductive material which is configured so that, when the electrically conductive material is electrically heated, the actuating member is displaced between the quiescent and active positions, the actuating member being connected to the drive circuitry so that the electrically conductive material can be heated on receipt of an electrical signal from the drive circuitry.

2. A micro-electromechanical fluid ejection mechanism as claimed in claim 1 , in which the actuating member incorporates a heating circuit of the shape memory alloy, the heating circuit being connected to the drive circuitry of the substrate.

3. A micro-electromechanical fluid ejection mechanism as claimed in claim 2 , in which the actuating member is a laminated structure, with the heater circuit defining one layer of the actuating member.

4. A micro-electromechanical fluid ejection mechanism as claimed in claim 2 , in which the actuating member includes a pre-stressing layer positioned on, and mechanically fast with, the heating circuit, the shape memory alloy having a generally planar form when in the austenitic phase and the pre-stressing layer serving to curl the actuating member away from the ejection port, when the shape memory alloy is in the martensitic phase, such that, when heated, the shape memory alloy drives the actuating member into a planar form, thereby ejecting a drop of ink from the ejection port.

5. A micro-electromechanical fluid ejection mechanism as claimed in claim 4 , in which the shape memory alloy is a nickel titanium alloy.

6. A micro-electromechanical fluid ejection mechanism as claimed in claim 4 , in which the pre-stressing layer is high stress silicon nitride.

7. A micro-electromechanical fluid ejection mechanism as claimed in claim 4 , in which the heating circuit is interposed between the pre-stressing layer and a stress reference layer for the pre-stressing layer.

8. A micro-electromechanical fluid ejection mechanism as claimed in claim 1 , in which the nozzle chamber structure is defined by the substrate as a result of an etching process carried out on the substrate, such that one of the layers of the substrate defines the ejection port on one side of the substrate and the actuator is positioned on an opposite side of the substrate.