AC08FSM datasheet(153/223 Pages) TECCOR

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Testing Teccor Semiconductor Devices

Using Curve Tracers

Introduction

One of the most useful and versatile instruments for testing semi-

conductor devices is the curve tracer (CT). Tektronix is the best

known manufacturer of curve tracers and produces four basic

models: 575, 576, 577 and 370. These instruments are specially

adapted CRT display screens with associated electronics such

as power supplies, amplifiers, and variable input and output func-

tions that allow the user to display the operating characteristics of

a device in an easy-to-read, standard graph form. Operation of

Tektronix CTs is simple and straightforward and easily taught to

non-technical personnel. Although widely used by semiconductor

manufacturers for design and analytical work, the device con-

sumer will find many uses for the curve tracer, such as incoming

quality control, failure analysis, and supplier comparison. Curve

tracers may be easily adapted for go-no go production testing.

Tektronix also supplies optional accessories for specific applica-

tions along with other useful hardware.

Tektronix Equipment

Although Tektronix no longer produces curve tracer model 575,

many of the units are still operating in the field, and it is still an

extremely useful instrument. The 576, 577 and 370 are current

curve tracer models and are more streamlined in their appear-

ance and operation. The 577 is a less elaborate version of the

576, yet retains all necessary test functions.

The following basic functions are common to all curve tracers:

•

Power supply supplies positive DC voltage, negative DC volt-

age, or AC voltage to bias the device. Available power is varied

by limiting resistors.

•

Step generator supplies current or voltage in precise steps to

control the electrode of the device. The number, polarity, and

frequency of steps are selectable.

•

Horizontal amplifier displays power supply voltage as applied

to the device. Scale calibration is selectable.

•

Vertical amplifier displays current drawn from the supply by

the device. Scale calibration is selectable.

Curve tracer controls for beam position, calibration, pulse opera-

tion, and other functions vary from model to model. The basic

theory of operation is that for each curve one terminal is driven

with a constant voltage or current and the other one is swept with

a half sinewave of voltage. The driving voltage is stepped

through several values, and a different trace is drawn on each

sweep to generate a family of curves.

Limitations, Accuracy, and Correlation

Although the curve tracer is a highly versatile device, it is not

capable of every test that one may wish to perform on semicon-

ductor devices such as dv/dt, secondary reverse breakdown,

switching speeds, and others. Also, tests at very high currents

and/or voltages are difficult to conduct accurately and without

damaging the devices. A special high-current test fixture avail-

able from Tektronix can extend operation to 200 A pulsed peak.

Kelvin contacts available on the 576 and 577 eliminate inaccu-

racy in voltage measured at high current (VTM) by sensing voltage

drop due to contact resistance and subtracting from the reading.

Accuracy of the unit is within the published manufacturer’s speci-

fication. Allow the curve tracer to warm up and stabilize before

testing begins. Always expand the horizontal or vertical scale as

far as possible to increase the resolution. Be judicious in record-

ing data from the screen, as the trace line width and scale resolu-

tion factor somewhat limit the accuracy of what may be read.

Regular calibration checks of the instrument are recommended.

Some users keep a selection of calibrated devices on hand to

verify instrument operation when in doubt. Re-calibration or

adjustment should be performed only by qualified personnel.

Often discrepancies exist between measurements taken on

different types of instrument. In particular, most semiconductor

manufacturers use high-speed, computerized test equipment to

test devices. They test using very short pulses. If a borderline

unit is then measured on a curve tracer, it may appear to be out

of specification. The most common culprit here is heat. When a

semiconductor device increases in temperature due to current

flow, certain characteristics may change, notably gate character-

istics on SCRs, gain on transistors, leakage, and so on. It is very

difficult to operate the curve tracer in such a way as to eliminate

the heating effect. Pulsed or single-trace operation helps reduce

this problem, but care should be taken in comparing curve tracer

measurements to computer tests. Other factors such as stray

capacitances, impedance matching, noise, and device oscillation

also may create differences.

AN1006

AC08FSM Datasheet(PDF) 153 Page - Teccor Electronics

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