4608X-102-102 Datasheet, PDF (58/62 Pages) Bourns Electronic Solutions – Resistor Networks Product Selection Guide

Thin Film Applications
Thin film is the preferred generic description for the field of
micro-electronics in which conductive, resistive, and/or insulat-
ing films are deposited or sputtered on a ceramic or other insu-
lating substrate. The films can be deposited either in a required
pattern or as a complete film layer and photoprocessed and
etched to form the required pattern.
The term “thin film” is derived from the fact that the deposited
films are of the order of a few micrometers in thickness com-
pared with the 10 to 50 micrometers for thick film. Often, thin
film conductors are plated to improve conductivity.
Thin Film Applications
Thin film resistor networks typically find application in the ana-
log world. The number one use of thin film is in controlling the
gain on operational amplifiers. Some other applications are as a
stable reference, stable voltage division, stable feedback loops
and analog to digital or digital to analog conversion. These net-
works may also be used for “wire-OR” pull-up, ECL output pull-
down, TTL input pull-down, power down pull-up, open collector
pull-up, digital pulse squaring, current summing amplifiers, TTL
unused gate pull-up, TTL/MOS interfacing, coding and decod-
ing, and telemetry.
Thin film resistors in a network form offer additional benefits in
performance. The resistors in a network are more closely
matched in resistance and TCR and actually see reduced differ-
entials of temperature in the end use application. These com-
bine to provide improved tracking in networks. This improved
tracking would be an advantage to the instrumentation and
industrial control markets.
Potential target markets for thin film include harsh environmen-
tal conditions as well as the need for precision resistors. The
improved ability to be stable at extended temperatures and the
increased ability to handle moist environments are both benefits
of the thin film offering. Target applications such as automotive
and telecommunications will benefit from these capabilities.
Thin Film Vs. Thick Film
The basic distinction between thick film and thin film is the
method of deposition of the metallization. In thick film, specially
formulated pastes are applied and fired onto a substrate. The
pastes are usually applied with a silk screen method and the
substrate is of 96% alumina ceramic. In thin film, a layer of met-
allization is sputtered onto a substrate and then a pattern is
etched into the previously applied metal layer, the substrates are
often 99.5% alumina ceramic, silicon, or glass. Thick film is an
additive process where layers of termination and resistor materi-
al are added to the substrate, while thin film is a subtractive
process where the unwanted material is etched away in a suc-
cession of selective photoetching processes. The use of photo-
lithographic processes to form thin film patterns produce much
finer lines and traces than thick film processes. Thin film is very
appropriate for high density and high frequency applications.
Thick and thin film technologies are well suited for low to medi-
um volume custom circuits. Thick film has the advantages of
lower cost (both of tooling up new designs and of production
runs), of being able to handle more power, and of being able to
service a higher range of ohmic values. Thin film has the advan-
tages of tighter absolute and ratio tolerances and more environ-
mentally stable components with lower noise and tighter TCR
than thick film.
Thin film technology is used wherever precision resistors are
needed.
Differential Op-amp Input
Differential Op Amps are needed in electrically dirty environ-
ments to reject noise transients that are picked up by wires. The
differential Op Amps subtracts the noise out of the two signal
wires.
Thin film tracking capabilities are needed in these circuits to
ensure that the input resistors do not affect the contents of the
incoming signal.
COMMON
MODE
INPUT
±250V
-1M 3
+1M 7
R1
1M
4
R5
975K
1
R2
20K
R3
1M
9V
R6
25K
2-
7
2
6
LT1012A
6 ³⁺
4
R4
19.608K
5
-9V
50K
OPTIONAL
CMRR
TRIM
OUT
TYPICAL PERFORMANCE:
COMMON MODE REJECTION RATIO = 74dB (RESISTOR LIMITED)
WITH OPTIONAL TRIM = 130dB
OUTPUT OFFSET (TRIMMABLE TO ZERO) = 500µV
OUTPUT OFFSET DRIFT = 10µV/°C
INPUT RESISTANCE = 1M (CM)
2M (DIFF)
BANDWIDTH = 13KHz
BATTERY CURRENT = 370µA
±250V Common Mode Range Instrumentation Amplifier (Av=1)
334
Specifications are subject to change without notice.