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In-situ Monitoring of Heater Failure in Thermal Ink Jet Devices

IP.com Disclosure Number: IPCOM000121352D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 4 page(s) / 133K

Publishing Venue

IBM

Related People

Eldridge, JM: AUTHOR [+4]

Abstract

Simple detection devices can be built into the thin film structure of a thermal ink jet printhead to detect in-situ impending failures of the resistive heating elements. Such failures can develop as the thin film passivating overcoats are gradually removed by erosion and/or corrosion processes. Typically, device passivation is accomplished using one or more chemically inert, dielectric layers; for example, silicon nitride covered by silicon carbide. More durable devices now employ an additional metallic overcoat of Ta deposited on the top dielectric layer. In this invention, the detection methods are basically electrical such as those standard schemes used to monitor impedance changes across two electrodes in a composite electrical circuit.

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In-situ Monitoring of Heater Failure in Thermal Ink Jet Devices

      Simple detection devices can be built into the thin film
structure of a thermal ink jet printhead to detect in-situ impending
failures of the resistive heating elements.  Such failures can
develop as the thin film passivating overcoats are gradually removed
by erosion and/or corrosion processes. Typically, device passivation
is accomplished using one or more chemically inert, dielectric
layers; for example, silicon nitride covered by silicon carbide.
More durable devices now employ an additional metallic overcoat of Ta
deposited on the top dielectric layer.  In this invention, the
detection methods are basically electrical such as those standard
schemes used to monitor impedance changes across two electrodes in a
composite electrical circuit.

      Fig. 1 shows a thermal jet heater structure having a metallic
Ta overcoat on top of a typical silicon nitride/carbide duplex
overcoat.  The Ta layer is extended to an electrical contact pad on
the perimeter of the substrate and can thus serve as the top
electrode of a capacitive, resistive, inductive (RLC) circuit where
the resistive, bottom-layer film acts as the second electrode with
the duplex dielectric layers sandwiched in between.  The bottom
electrode is connected to the electrical common of the structure.
Standard impedance measuring electronics (typically, a low-voltage AC
circuit) can then be applied using both the top Ta and the bottom
common to monitor the impedance of the sandwiched structure.  Since
the Ta electrode and common electrode are common to all heater
channels (usually several tens or more per substrate), such
measurements will effectively monitor the total composite impedance
of the entire printhead utilizing this substrate. An initial
characterization of the total impedance will include resonance
frequency, phase angle, and amplitude and will serve as the base
reference.  As the overcoat layers (above one or more heaters)
deteriorate during device operation (due to mechanical and/or
chemical attack by the ink and bubbles therein), changes in the
characteristic impedance parameters can be detected using electronic
comparator circuitry.  In many instances, the resona...