4616P-R2R-503 datasheet(58/62 Pages) BOURNS

58 / 62 page

Specifications are subject to change without notice.

334

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

19.608K

+1M

-1M

LT1012A

975K

25K

20K

-9V

OUT

50K

OPTIONAL

CMRR

TRIM

TYPICAL PERFORMANCE:

COMMON MODE REJECTION RATIO

WITH OPTIONAL TRIM

OUTPUT OFFSET (TRIMMABLE TO ZERO)

OUTPUT OFFSET DRIFT

INPUT RESISTANCE

BANDWIDTH

BATTERY CURRENT

= 74dB (RESISTOR LIMITED)

= 130dB

= 500µV

= 10µV/°C

= 1M (CM)

2M (DIFF)

= 13KHz

= 370µA

±250V Common Mode Range Instrumentation Amplifier (Av=1)

Thin Film Applications

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