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PREVENTION OF THRESHOLD VOLTAGE DRIFT IN INTEGRATED THERMAL INK JET PRINTHEADS BY CHANNEL PLATE BIASING

IP.com Disclosure Number: IPCOM000027638D
Original Publication Date: 1998-Jun-30
Included in the Prior Art Database: 2004-Apr-08
Document File: 4 page(s) / 185K

Publishing Venue

Xerox Disclosure Journal

Abstract

It is observed that with at least certain types of (fully integrated) thermal ink jet printheads, drop ejection on some or all jets can cease when the operating voltage is continuously applied to the printhead over extended periods of time. The problem is attributed to an increase in the threshold voltage required for drop ejection, referred to as Vth drift. Recent experiments shed light on the root causes and mechanisms involved in Vth drift. This series of experiments relates the V, drift problem to an electric field (vbm) driven ion migration through the fluid in the printhead to critical interfaces in the integrated circuit. The source of the ions can be the constituents of the fluid itself as well as ionic species inherent in materials which comprise the printhead and come in contact with the fluid or are generated by interaction with the fluid. An anionic migration model is consistent with the experimental observation that a positive bias on the channel plate (which attracts anions) counteracts the positive Vbm potential on the heater wafer and prevents anionic migration to the integrated circuitry, thereby reducing/eliminating the Vth drift. There are two mechanisms which can explain the degrading circuit behavior in the presence of the ionic migration: (1) the interconnect layers are affected by shallow ionic migration and/or (2) the driver threshold can be affected by ionic migration. It is likely that both scenarios occur to some extent over the life of a printhead. In both cases, a reduction in switching capability of the driver is responsible. This is significant because the driver creates the power pulse at the heater. Any reduction in the amplitude or duration of the power pulse corresponds to a reduction in the energy delivered to the heater, and therefore, a reduction in the energy available for bubble nucleation at a given vbm.

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XEROX DISCLOSURE JOURNAL

PREVENTION OF THRESHOLD VOLTAGE DRIFT IN INTEGRATED THERMAL INK JET PRINTHEADS BY CHANNEL PLATE BIASING
Robert V. Lorenze, Jr.

Juan J. Becerra

Proposed Classification
U. S. C1.347/014 Int. C1. B41j 29/38

It is observed that with at least certain types of (fully integrated) thermal ink jet printheads, drop ejection on some or all jets can cease when the operating voltage is continuously applied to the printhead over extended periods of time. The problem is attributed to an increase in the threshold voltage required for drop ejection, referred to as Vth drift. Recent experiments shed light on the root causes and mechanisms involved in Vth drift. This series of experiments relates the V, drift problem to an electric field (vbm) driven ion migration through the fluid in the printhead to critical interfaces in the integrated circuit. The source of the ions can be the constituents of the fluid itself as well as ionic species inherent in materials which comprise the printhead and come in contact with the fluid or are generated by interaction with the fluid. An anionic migration model is consistent with the experimental observation that a positive bias on the channel plate (which attracts anions) counteracts the positive Vbm potential on the heater wafer and prevents anionic migration to the integrated circuitry, thereby reducing/eliminating the Vth drift. There are two mechanisms which can explain the degrading circuit behavior in the presence of the ionic migration: (1) the interconnect layers are affected by shallow ionic migration and/or (2) the driver threshold can be affected by ionic migration. It is likely that both scenarios occur to some extent over the life of a printhead. In both cases, a reduction in switching capability of the driver is responsible. This is significant because the driver creates the power pulse at the heater. Any reduction in the amplitude or duration of the power pulse corresponds to a reduction in the energy delivered to the heater, and therefore, a reduction in the energy available for bubble nucleation at a given vbm.

It is proposed that the Vth drift problem in integrated thermal ink jet printheads be avoided by incorporating a means of biasing the channel plate into the printhead fabrication process. This can be accomplished by several different methods. One method is to provide a conductive path between a high potential region on each die site on the heater wafer and the corresponding channel wafer site during the wafer-to-wafer bonding process. The high potential regions could be interconnect paths from the Vbm supply or separate high

XEROX DISCLOSURE JOURNAL - Vol. 23, No. 3 May/June 1998 117

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PREVENTION OF THRESHOLD VOLTAGE DRIFT IN INTEGRATED THERMAL INK JET PRINTHEADS BY CHANNEL PLATE BIASING (CONT'D)

voltage access locations incorporated in the heater wafer layout design specifically for this purpose. It...