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Controlling TCR in Thin Film Resistors

IP.com Disclosure Number: IPCOM000102692D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Bartush, TA: AUTHOR [+3]

Abstract

Laser trimming (cutting) 1 of thin film resistors 3 causes the thermal coefficient of resistance (TCR) to be reduced in SiCr resistors. Since the amount of total trimming length has a direct relationship to the amount of negative shift of the TCR, the precision of controlling both the resistance and the TCR becomes difficult. This becomes a process tolerance concern for resistors which require tight matching character istics, since the matching of the various resistors requires trimming to a different degree and, therefore, will exhibit different TCR values.

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Controlling TCR in Thin Film Resistors

       Laser trimming (cutting) 1 of thin film resistors 3
causes the thermal coefficient of resistance (TCR) to be reduced in
SiCr resistors.  Since the amount of total trimming length has a
direct relationship to the amount of negative shift of the TCR, the
precision of controlling both the resistance and the TCR becomes
difficult.  This becomes a process tolerance concern for resistors
which require tight matching character istics, since the matching of
the various resistors requires trimming to a different degree and,
therefore, will exhibit different TCR values.

      Laser annealing, as opposed to laser trimming, will result in
an increase in the TCR values.  A combination of laser trimming 1 and
laser annealing 4 will result in achieving both the proper resistor
value (trimming) and minimal or no shift of the TCR value
(annealing).  The zero shift is realized by the offsetting effect of
the lower TCR due to trimming and of the higher TCR due to annealing.
The appropriate amount of trimming and annealing is determined from
calibration data.