Inkjet printhead nozzle arrangement having non-coincident low mass electrode and heater element

1. An inkjet printhead nozzle arrangement comprising:

side walls provided on a wafer substrate and a roof layer deposited on said side walls to define an ink chamber, the roof layer defining a nozzle aperture;

an inlet defined in the substrate to supply the ink chamber with printing fluid; and

at least one heater element having two opposite sides parallel to a plane of the nozzle aperture, the heater element adapted to generate a gas bubble at both of said opposite sides, wherein

the heater elements and associated electrodes are arranged in the chamber to be non-coincident and have an annular shape facilitating a point of collapse of the bubble near a centre thereof, and

the heater element has a mass of less than 10 nanograms.

2. The printhead of claim 1 , wherein the heater element is in the form of beams suspended from the side walls so that the point of collapse is between the beams.

3. The printhead of claim 1 , wherein the heater element is configured such that activation energy of less than 500 nanojoules (nJ) is required to be applied to the element to produce the bubble in the fluid.

4. The printhead of claim 1 , wherein the heater element is substantially covered by a conformal protective coating applied to all sides of the heater element simultaneously such that the coating is seamless.

5. The printhead of claim 1 , wherein the fluid inlet is 100 to 400 microns in length and 8 to 24 microns in diameter.