Printhead unit cell incorporating suspended looped heater element

1. A unit cell of a printhead, the unit cell comprising:

a multi-layer substrate defining an ink inlet;

one or more side walls extending from the substrate around the ink inlet;

a nozzle plate supported by the side walls to define a chamber in fluid communication with the ink inlet, the nozzle plate defining an aperture through which ink in the chamber can be ejected; and

a looped and elongate heater element suspended within the chamber, and which can be heated so that bubbles are generated in ink within the chamber and ink is ejected from the aperture,

wherein the heater element is configured to be heated for less than 1 millisecond to generate a thermal pulse sufficient to cause the ejection of the ink.

2. A unit cell as claimed in claim 1 , wherein the heater element is configured so that the bubbles merge to form a single elongate bubble extending transverse to the side walls.

3. A unit cell as claimed in claim 1 , wherein the nozzle plate defines a protruding rim bounding the aperture.

4. A unit cell as claimed in claim 3 , wherein the nozzle plate further defines a well in which the rim is located.

5. A unit cell as claimed in claim 4 , wherein the well has an endless wall surrounding the rim that is corrugated.

6. A unit cell as claimed in claim 1 , wherein the elongate heater element terminates in a peripheral well in which the side walls are received.