Inkjet unit cell with dual heater elements

1. A unit cell for an inkjet printhead, the unit cell comprising:

a multilayered substrate defining an ink inlet passage;

walls extending from the substrate;

a nozzle plate supported by the walls to define a nozzle chamber in fluid communication with the ink inlet passage, the nozzle plate having a nozzle rim defining an aperture in fluid communication with the nozzle chamber; and

dual looped and elongate heater elements suspended within the nozzle chamber which, when heated, cause ink in the nozzle chamber to be output through the aperture,

wherein the nozzle plate defines a well surrounding the rim to impede the spread of any spilled ink.

2. A unit cell as claimed in claim 1 , wherein the heater elements are of different sizes relative to each other and are electrically connected together in series.

3. A unit cell as claimed in claim 1 , wherein each heater element terminates in a pair of electrodes which are thicker than the element so that more electrical resistance is provided by the element than the electrodes.

4. A unit cell as claimed in claim 1 , wherein each heater element is connected to a current supply configured to generate pulse currents.

5. A unit cell as claimed in claim 1 , wherein each heater element is embedded in the walls.

6. A unit cell as claimed in claim 1 , wherein each heater element extends substantially entirely across the nozzle chamber.

7. A unit cell as claimed in claim 6 , wherein each heater element has a plurality of concentric portions.