(A) high-resolution monolithic thermal inkjet printhead

Abstract

A monolithic fabrication process to implement a thermal inkjet printhead is proposed. The monolithic printhead is fabricated by direct growing of nozzle plate on the silicon substrate. A multi-exposure and single development (MESD) process is used for the formation of photoresist mold for nozzle-plate electroplating. Electrochemical etching method as a back- end process is used for ink feed hole formation. The ink feed hole can be formed with a tolerance of 2 ㎛ without any backside mask. The proposed structure is simple and the fabrication process is highly controllable and batch process-orientated. Ink ejection results with the fabricated 300-dpi printhead show the ink dot diameter of 100-140 ㎛ for current pulses of 0.3 A and 4-8㎲. Ink droplets are ejected up to the operating frequency of 11 kHz. Reliability characteristics of Ta-Al alloy thin film heating resistor, which determines the printhead life, against current pulse stress are investigated. The lifetime of the heating resistor is affected strongly by the power density of current pulse. Heat treatment (450℃ 1 hr) of Ta-Al is effective and 15- 20 at.% of Al contents are recommended for formation of robust heating resistors. A monolithic thermal inkjet printhead for high-resolution and high-speed printing is proposed and fabricated. The printer performance can be enhanced by increasing the number of nozzles or the operating frequency as well as decreasing the nozzle size. Two-dimensional nozzle arrangement is proposed for high-resolution and high-speed printing. Nozzle arrangement schemes for high-speed printing are also designed. A 2400×2400 dpi inkjet printhead with 3600 nozzles on a chip (a chip size of 1/2``\times\frac1/2``$) is fabricated. Ink ejection results show ink dot diameter of 10-15 ㎛ for current pulses of 30 mA and 2-12㎲. Printed ink dots are suitable for 2400 dpi printing. For the first time in the world, ink ejection for 2400-dpi inkjet printing is achieved with a nozzle of 10 ㎛ dia...