K0900E70 Datasheet, PDF (153/224 Pages) Teccor Electronics – Thyristor Product Catalog

AN1006
6
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 (V_TM) 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.
©2002 Teccor Electronics
Thyristor Product Catalog
AN1006 - 1
http://www.teccor.com
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