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Laser-Trimmable, Serial Compensation Resistor Designs for Thermal Ink Jet Header Arrays

IP.com Disclosure Number: IPCOM000108617D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 8 page(s) / 270K

Publishing Venue

IBM

Related People

Eldridge, J: AUTHOR [+2]

Abstract

A method is described to achieve desirable resistance control in thermal ink jet resistive heater arrays. To this end, described is the use and design of serially-connected resistors, as shown schematically in Fig. 1. Automatic resistance probing is performed on every resistor "line" on each die on the wafer, after the wafer fabrication process is complete, including the addition of the inorganic and polyimide passivation layers and the terminal contact metallurgy. Each resistor "line" is comprised of the working resistor (the heater) and a "compensating resistor" whose value may vary from essentially zero (in the untrimmed, as-fabricated condition) to several ohms, as determinable by trimming.

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Laser-Trimmable, Serial Compensation Resistor Designs for Thermal Ink Jet Header Arrays

       A method is described to achieve desirable resistance
control in thermal ink jet resistive heater arrays.  To this end,
described is the use and design of serially-connected resistors, as
shown schematically in Fig. 1.  Automatic resistance probing is
performed on every resistor "line" on each die on the wafer, after
the wafer fabrication process is complete, including the addition of
the inorganic and polyimide passivation layers and the terminal
contact metallurgy.  Each resistor "line" is comprised of the working
resistor (the heater) and a "compensating resistor" whose value may
vary from essentially zero (in the untrimmed, as-fabricated
condition) to several ohms, as determinable by trimming.  During
probing, the controller computer measures the resistor "line"
resistance and determines the value that the auxiliary resistor must
have to produce a constant energy density per pulse on the heater
resistor.  This is then accomplished by laser trimming of the
compensating resistor to the appropriate value. Trimming damage to
the compensating resistor clearly cannot impact the reliability of
the working resistor.  In addition, the compensating resistor does
not undergo substantial heating by its design, is also protected by
the polyimide layer, as well as the two inorganic overcoats, may well
lie outside the ink-covered region of the die, and, thus should have
excellent reliability.

      There are two essential requirements that must be met in the
design and fabrication of the compensating resistor:
   1.   The resistance must be small, relative to that of the heater
in order to provide a proper distribution of useful power and an
optimal electrical drive efficiency.
   2.   The energy density must be very low to minimize its heating.

      Other desirable guidelines for the compensating resistor are:
   1.   The geometry should be simple and compact (small and/or
narrow) and located away from the ink-covered substrate so that any
small defects generated during trimming cannot reduce device
reliability.
   2.   The design should provide sufficient geometric resolution to
allow adequate control of resistance by trimming.
   3.   It should be fabricated with the same (or, fewer) processing
steps used to make the active heater so as to not raise process
complexity and costs.

      A proposed heater network having a serial trim resistor for
each resistor heater is shown in Fig. 2, and an example of a
practical design  is illustrated by the plane view in Fig. 3.  Note
that this trim resistor can be fabricated using the same process
steps constructing the heater resistor array with only photomask
modifications.  The following example illustrates how this device
functions:

      Suppose we want to manufacture arrays of heaters on substrates
where the resistance of each heater is nominal 83 + 0%/- 20%. ...