Inkjet printhead comprising printhead integrated circuits

1. An inkjet printhead comprising a plurality of printhead integrated circuits, each integrated circuit comprising:

a substrate;

drive circuitry arranged on the substrate; and

a plurality of micro-electromechanical devices positioned on the substrate, each device comprising:

an actuator connected to the drive circuitry, the actuator including a free end reciprocally displaceable along a path relative to the substrate, and an arm that is expandable when heated by an electrical current received from the drive circuitry, said expansion causing displacement of the free end along said path.

2. The inkjet printhead as claimed in claim 1 , wherein each micro-electromechanical device includes a fluid ejection member positioned on the free end of the actuator, the integrated circuit device including a plurality of fluid chambers positioned on the substrate, with the substrate defining fluid flow paths that communicate with the fluid chambers, each fluid ejection member being positioned in a respective fluid chamber to eject fluid from the fluid chamber on displacement of the actuator.

3. The inkjet printhead as claimed in claim 2 , in which a sidewall and a roof wall define each fluid chamber, the roof wall defining an ejection port, with the fluid ejection member being displaceable towards and away from the ejection port to eject fluid from the ejection port.

4. The inkjet printhead as claimed in claim 3 , in which each fluid ejection member is in the form of a paddle member that spans a region between the respective fluid chamber and the respective fluid flow path so that, when the heating circuit receives a signal from the drive circuitry, the paddle member is driven towards the fluid ejection port and fluid is drawn into the respective fluid chamber.

5. The inkjet printhead as claimed in claim 4 , in which each paddle member has a projecting formation positioned on a periphery of the paddle member, the formation projecting towards the ejection port so that the efficacy of the paddle member can be maintained while inhibiting contact between the paddle member and a meniscus forming across the ejection port.

6. The inkjet printhead as claimed in claim 1 , in which each actuator includes a heat sink that is positioned on the arm, intermediate ends of that arm, to provide generally uniform heating along the length of the arm.