Thermal ink jet printhead with drive circuitry offset from heater elements

A printer system which incorporates a printhead, the printhead comprising:

• a plurality of nozzles, formed on a wafer substrate by lithographic etching and deposition techniques, each of the nozzles having a chamber for holding ejectable liquid, an ejection aperture in one wall of the chamber, and inlet for the ejectable liquid formed in a wall opposing that of the ejection aperture, a heater element suspended in the chamber for thermal contact with the ejectable liquid, the heater element having a planar structure configured parallel to that of the ejection aperture;
• drive circuitry corresponding to each of the nozzles for controlling the operation of the heater element;
• such that,
• heating the heater element to a temperature above the boiling point of the ejectable liquid forms a gas bubble that causes the ejection of a drop of the ejectable liquid through the ejection aperture corresponding to that heater element;
• wherein,
• the drive circuitry is formed in an area of the wafer substrate, the area having a centre point that is offset from a center point of the corresponding ejection aperture by less than 200 microns.

A method of ejecting drops of an ejectable liquid from a printhead, the printhead comprising a plurality of nozzles, formed on a wafer substrate by lithographic etching and deposition techniques, each of the nozzles having a chamber for holding ejectable liquid, an ejection aperture in one wall of the chamber, and inlet for the ejectable liquid formed in a wall opposing that of the ejection aperture, a heater element suspended in the chamber for thermal contact with the ejectable liquid, the heater element having a planar structure configured parallel to that of the ejection aperture;

• drive circuitry corresponding to each of the nozzles for controlling the operation of the heater element;
• wherein,
• the drive circuitry is formed in an area of the wafer substrate, the area having a centre point that is offset from a center point of the corresponding nozzle by less than 200 microns;
• the method comprising the steps of:
• heating the heater element to a temperature above the boiling point of the ejectable liquid to form a gas bubble that causes the ejection of a drop of the ejectable liquid from the nozzle;
• and
• supplying the nozzle with a replacement volume of the ejectable liquid equivalent to the ejected drop.