Printhead integrated circuit with planar actuators

1. A printhead integrated circuit for an inkjet printhead, the printhead integrated circuit comprising

a wafer substrate that defines a plurality of ink inlet channels;

drive circuitry positioned on the wafer substrate;

a plurality of nozzle chamber structures positioned on the wafer substrate, each nozzle chamber structure defining a nozzle chamber in fluid communication with a respective ink inlet channel and an ink ejection port aligned with the respective ink inlet channel; and

a plurality of elongate, planar actuators positioned in respective nozzle chambers to overlie respective ink inlet channels, each actuator being connected to the drive circuitry to be displaceable towards and away from the ink ejection port on receipt of an electrical signal from the drive circuitry to eject ink from the ink ejection port.

2. A printhead integrated circuit as claimed in claim 1 , in which the drive circuitry is defined by CMOS layers formed on the wafer substrate.

3. A printhead integrated circuit as claimed in claim 1 , in which each nozzle chamber structure is rectangular in plan and includes side walls and a roof positioned on the substrate to define the nozzle chamber, the roof defining the ink ejection port and the actuators spanning a plan cross-sectional area of the respective nozzle chambers.

4. A printhead integrated circuit as claimed in claim 3 , in which each actuator includes a heater layer that comprises an electrical heating circuit that is connected to the drive circuitry at one end of the actuator and at least one expansion layer that is fast with the heater layer, the heater layer being positioned so that the expansion layer experiences thermal expansion when the heater layer receives an electrical signal from the drive circuitry layer and the actuator is displaced.

5. A printhead integrated circuit as claimed in claim 4 , in which each actuator includes a first expansion layer positioned between the heater layer and the substrate and a second expansion layer positioned between the heater layer and the roof.

6. A printhead integrated circuit as claimed in claim 5 , in which each actuator is spaced a predetermined distance from the substrate to define a gap between the actuator and the substrate.

7. A printhead integrated circuit as claimed in claim 6 , in which the first expansion layer has a hydrophobic surface such that an air bubble is formed in the gap subsequent to the ejection of ink from the nozzle chamber.

8. A printhead integrated circuit as claimed in claim 6 , in which the second expansion layer has a hydrophilic surface.