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A G R E AT E R M E A S U R E O F C O N F I D E N C E etries, new materials, and more complex
designs are having a tremendous impact on
device lifetimes due to increased fragility,
higher power density, and new failure mech-
anisms. This need is driven in part by the
higher operating speeds of today's electronic
circuits. The higher operating speed requires
test equipment that can produce simulated
clock and data signals at the rate that the cir-
cuit will actually perform.
Also, analog components used in these
circuits behave differently at higher speeds,
so they can't be characterized at DC using
traditional DC methods. Because pulse sizes
can be made extremely small, on the order
of a few nanoseconds, pulse testing over-
comes the problems inherent in DC testing
techniques. Therefore, pulsed test signals are
needed to characterize these components.
A Feel for the Pulse
In addition, as components have become
smaller, the need for pulsed testing tech-
niques becomes more critical. Smaller DUTs
are more susceptible to self-heating, which
Todd Stocker, Keithley Instruments, Inc. can destroy or damage the part or change
its response to test signals, masking the re-
Understanding your test requirements will Pulse or pattern generators are used in a sponse the user is seeking. Pulse testing is
helpyouselecttherightpulsegeneratorfor wide variety of applications in both the lab commonly used when characterizing nano-
thejob. and on the production line. Researchers often electronic devices.
need to stimulate a device under test (DUT) Advanced IC technologies incorporate
Introduction with a pulse, series of pulses, or known data new materials and failure mechanism that
Rapidly changing and advancing technol- patterns at specified rates in order to char- traditional DC testing techniques may not
ogy continually challenges test equipment acterize device performance. Pulse or pat- be powerful enough to uncover. The limits
manufacturers to develop new systems for tern generators are often configured into of DC methods are apparent in charge-trap-
testing the latest generation of electronic de- test systems that also include SMUs, digital ping behavior in gate dielectrics in semicon-
vices and materials. Industries such as semi- multimeters, voltmeters, switches, and oscil- ductor devices. The issue is the relatively
conductor and communication technology, loscopes. long periods of time required for these DC
with rapid development of new standards, techniques.
often require cutting-edge device testing and Need for Pulse Testing During device development, structures
new source and measurement capabilities. The need for pulse sources has been like single electron transistors (SETs), sen-
In recent years, new testing techniques growing over time. Shrinking device geom- sors, and other experimental devices often
have been developed to meet these chal-
lenges. One such technique is pulse testing.
The uses for instruments with pulse capabili-
ties are many. For instance, testing advanced
semiconductor devices as well as RF devices
such as high-speed serial communications
links.
Pulse Testing
Pulse testing involves delivering a single
pulse to an output. This pulse is used to test
a variety of things, such as for transient test-
ing of a device to determine its transfer func-
tion and thereby characterize the material Figure 1. Keithley's Series 3400 Pulse/Pattern Generators feature a frequency range from 1mHz to
under test. 165MHz with programmable rise and fall times down to two nanoseconds.
A Feel for the Pulse August2006
display unique properties. Characterizing parameters can reduce the flexibility of the such as rise-time or fall-time are specified at
these properties without damaging one-of-a- instrument. It is important to understand either 10% to 90% or 20% to 80%. Using
kind structures requires systems that provide that if you adjust one parameter, that another 20%-80% allows a slower pulse to appear
tight control over sourcing to prevent device parameter does not change. For example if to have a faster rise-time. Additionally using
self-heating. you adjust the rise-time of the pulse, does the looser specification, the actual fidelity of
Voltage pulsing can produce much nar- the pulse amplitude change? This extensive the pulse could be significantly lower.
rower pulse widths than current pulsing, so control over key signal parameters makes the Ease of use is another factor to consider,
it's often used in experiments such as thermal instrument flexible and useable in many dif- which often times gets overlooked. For ex-
transport, in which the timeframe of interest ferent applications. ample, an intuitive user interface makes in-
is shorter than a few hundred nanoseconds. The second key item to look for is pulse struments simple to use for both experienced
High amplitude accuracy and program- fidelity. The amount of overshoot, or droop test engineers as well as novice users instru-
mable rise and fall times are necessary to in a pulse can make the instrument not suit- mentation for the first time.
control the amount of energy delivered to a able for your application. These undesirable
device. effects can be worsened by the setup and Conclusion
cabling that your application requires. Using Facilities involved in testing semiconduc-
What to Look For an instrument that minimizes these effects tor devices and nanotechnology devices and
The three key items to keep in mind while will help reduce these setup challenges. In- high speed components are faced with in-
evaluating a pulse/pattern generator are flex- struments that can deliver an extremely short tense budget and time-to-market constraints.
ibility, fidelity and ease of use. duration pulse, on the order of a few nanosec- However, they cannot compromise on meas-
Flexibility is key to a good pulse genera- onds wide, with tight control of critical sig- urement quality, valuable rack or bench-top
tor. It lets users control the critical signal pa- nal parameters, are highly useful for testing space, or ease of use. These designers have a
rameters such as amplitude, offset, rise and sensitive devices. Also related to the fidelity need for test instruments such as pulse gen-
fall times, pulse widths, and duty cycle of of the pulse is to look carefully at the speci- erators that satisfy their needs for current as
the output signal. Interdependency of these fications of the unit. Often times parameter well as future testing.
Specifications are subject to change without notice.
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