Inkjet printer with unit cells having suspended heater elements

1. An inkjet printer having a printhead with a plurality of unit cells each comprising:

a wafer substrate having a layer of micro-electromechanical drive circuitry, with a dielectric layer on the drive circuitry layer, and a passivation layer on the dielectric layer, the passivation layer defining a plurality of vias;

sidewalls located on the passivation layer with a nozzle plate so that the nozzle plate and the sidewalls together form an ink chamber; and

a heater element suspended from the sidewalls in said ink chamber, the heater element electrically connected to the drive circuitry layer through the vias, the unit cell having an ink channel defined through the wafer substrate ending in an ejection nozzle in the nozzle plate, wherein the vias through the passivation layer corresponds with contact electrodes defined on the heater element, the vias forming a grid of apertures through said passivation layer.

2. The inkjet printer of claim 1 , wherein each heater element has a bubble nucleation section with a smaller cross section than the remainder of the element.

3. The inkjet printer of claim 1 , wherein the dielectric layer includes four metal layers, which together form a seal ring for the ink channel defined through said dielectric layer, the metal seal ring configured to prevent ink moisture from seeping into the dielectric layer when the inlet passage is filled with ink.

4. The inkjet printer of claim 1 , wherein the heater element includes a monolayer of titanium-aluminum-nitride (TiAlN).

5. The inkjet printer of claim 1 , wherein the passivation layer is the product of a plasma-enhanced chemical vapour deposition process.

6. The inkjet printer of claim 1 , wherein the ink channel and ink chamber are treated to be hydrophilic.

7. The inkjet printer of claim 1 , wherein an outer surface of the nozzle plate is treated to be hydrophobic.