Patent ID: 7431431

Claim:
An inkjet printhead comprising: a plurality of nozzles; a bubble forming chamber corresponding to each of the nozzles respectively, the bubble forming chambers adapted to contain ejectable liquid; a heater element disposed in each of the bubble forming chambers respectively, the heater element configured for heating some of the ejectable liquid above its boiling point to form a gas bubble that causes the ejection of a drop of the ejectable liquid from the nozzle; a print engine controller to control the ejection of drops from each of the nozzles such that it actuates any one of the heaters to eiect a keep-wet drop if the interval between successive actuations of that heater reaches a predetermined maximum; wherein, the heater element is formed from a transition metal nitride with an additive whose oxidation is thermodynamically favored above all other elements in the transition metal nitride, such that the heater element is self passivating, and during use, the density of dots on the media substrate from the keep-wet drops, is less than 1:250 and not clustered so as to produce any artifacts visible to the eye.