o provide the pulse characteristic data needed to
optimize the design and implementation of ESD protection circuits. As transistors in IC's continue
to decrease in size and operating voltage, the design of efficient sub-micron protection structures
requires an accurate measurement tool to optimize the design and minimize the amount of silicon
real estate used for ESD protection.


ESDA Standard Practice for TLP
Many home-made TLP systems have been made since the TLP method was first described in
1985.[1] Since then, a large number of technical papers have described test results of many
structures designed with different types of TLP systems. However, the precision of these TLP
systems has not been determined so that users can determine test data accuracy. Over time,
operators of different TLP testers learn how to interpret the results in each system to minimizing
measurement errors inherent in each system. This process takes significant engineering skill and
time to be able to use the test data to speed their designs. Acquiring such experience is costly.
To assist TLP users in the industry, the ESDA has recently formed a new Working Group to
create a "Standard Practice Document" for TLP. Many different ESD designers experienced in
TLP are combining their knowledge into suggested operating parameters for this document. Their
experience learned in collecting test data from their systems is bringing together a wide base of
different operating parameters learned during the use of many different homemade and
commercial systems. When this document is completed, it will inform the ESD community how to
best use a TLP system and interpret the data for their particular needs. It will hopefully also be
able to describe a process that can "standardize" the reporting of TLP data and provide a method
to identify the level of accuracy.

Until the ESDA Standard Practice Document is finished, we suggest the following Evaluation
Procedure to provide detailed methods and technical guidance for new TLP users, and for those
who are considering its use. This TLP evaluation procedure explains methods that can identify
the basic accuracy characteristics of different measurement systems. When these "testing the
tester" procedures are used throughout the industry, the accuracy of data collection will be
known. We provide a method for TLP system analysis, which can be trusted to determine the
accuracy of data collection. This fundamental information is important and useful to ESD
protection designers.

The evaluation procedures described here can be performed on any commercial or homemade
TLP system. The goal of this evaluation process is to provide a well-defined measurement
method that we use as the tool to determine the accuracy of a TLP system. It also provides
knowledge of TLP test data consistency, and a basic understanding of how these test procedures
evaluate the capabilities of time domain measurement equipment. This information is helpful for
TLP users or buyers alike, because it was developed to measure the accuracy and capabilities of
the system. This is important because it will be used to measure how well their circuits meet the
electrical parameter designs. Knowing the precision of the measurement data provided by any
system allows the designer to more precisely gage the effectiveness of each silicon circuit
produced. Because each revision to a wafer is very expensive, accurate and repeatable test data
can minimize the number of revisions, which is critical to produce cost effective designs.
Achieving the best possible test data on each revision minimizes the effort and number of steps
required to create high levels of ESD protection. Performing this type of evaluation of a TLP 2
system is valuable either when considering purchase of a TLP system, or when verifying the
operation, precision and measurement drift of an operating TLP system.


SOLZ testing
The most precise method to evaluate a TLP system is to measure known electrical elements with
precise electrical characteristics. A simple analysis of this TLP data provides clear information on
the amount of deviation from known electrical values. Each reference element is placed at the
"device test terminals" and the test data from each is recorded. These reference elements "test
the tester" to determine how closely the measured test data matches the reference element.
During our development of the first commercial system, we found four reference elements that
are stable, repeatable, and affordable, for these tests. These elements are a "Short", "Open",
"Load", and "Zener" diode. The SOLZ acronym is made from these four TLP test elements. To
encourage making these tests on all TLP systems by any ESD designer at any laboratory, we are
providing a kit of these four elements in a handy DIP package, with an instruction sheet and the
measured parameters, free of charge to any one who requests it.


Short and Open Circuit Testing of a TLP System
The following plots are similar to what you will find when evaluating a TLP system:




Raw I-V "Short" measurement data plot
Raw I-V "Open" measurement data plot.

Notice that the raw data from a TLP system when measuring a zero ohm (Short Circuit), in the
left plot shown above, measures the internal series resistance in the TLP system. The resistance
derived from the slope of the line (V/I) in this case shows an internal loss in the system of about
0.2 ohms. Variations from a straight line is the amount of "noise" inherent in any system. The
voltage scale here is magnified greater than that used for device testing to clearly identify the
system errors. We correct for that internal series resistance by removing its value in the data
reduction and software analysis plots. These measured points should be a vertical line with
minimum voltage deviations, because no voltage can exist across a Short Circuit. The corrected
Short Circuit measurement is shown below on the left plot.

Notice also that in the raw data when using a TLP system to measure an infinity ohm (Open
Circuit), in the right plot shown above, there is some small amount of internal shunt resistance
losses in the TLP system. In this case, the shunt resistance calculated from the resistance slope
is approximately 12 K ohms or about 86 micromhos. We also correct for that internal shunt
resistance by removing it in the software so that the measured points of an Open Circuit 3
becomes as close to a horizontal line with minimal current deviations as possible. The corrected
Open Circuit measurement is shown below on the right.


Corrected I-V Short Circuit data plot Corrected I-V Open Circuit data plot.

Load Resistor Testing of a TLP System
The purpose of measuring the Load element, or Load resistor, is to compare the voltage to
current data by analyzing the slope of the plotted data. It should be a straight line with the V/I
slope determining the measured value of resistance. For TLP testing of ESD protection on
integrated circuits, it is best to use a low value resistor, which simulates the "on" resistance of a
modern protection device. Other resistance values can be measured; but testing the slope of a 50
ohm resistor in a 50 ohm system is hardly meaningful because ESD protection circuits rarely
produce dynamic resistance values above 10 ohms at high current levels. Also, measuring the V/I
slope of a resistor that is equal to the TLP system impedance is the least demanding test possible
for any TLP system. Measuring a 2 ohm, or 5 ohm resistor provides a much better evaluation of a
TLP system because these values are much closer to those found in modern protection circuits.
Evaluating this resistance region in a TLP system where most of the test data on ESD protection
devices will be measured also provides information on the linearity of the system that will not be
demonstrated with short or open tests. The three resistance values of zero ohms, infinity ohms
and 2, or 5 ohms provide the maximum amount of information on any TLP system capabilities. An
example of the I-V data plot for a 5 ohm Load resistor after the Short and Open correction
values are included in the software analysis, is shown below.


5.00 ohm resistor slope for an A/V and V/A corrected TLP system 4

Zener Diode Testing of a TLP System

The final element to use when evaluating a TLP system is the Zener diode. It provides a precisely
defined voltage point on the voltage axis to identify the accuracy of the TLP voltage data.




Corrected TLP data plot of 10 Volt

Corrected TLP data plot of 10 Volt
Zener diode at low currents


Zener diode at high currents

The Zener (voltage) calibration combined with the Load (resistor) plot can provide information on
the accuracy of the TLP current data. Two I-V plots of the same Zener diode are shown above at
two different current and voltage levels. The left plot is shown at low current levels where the
average Zener voltage can be computed by averaging a number of data points. This Zener diode
had an average voltage of 7.32 volts from 0.3 mA to 30 mA. Comparing this to the measured DC
Zener voltage at 1 mA of 7.342 volts shows the exceptional accuracy of the pulsed voltage
measurement was better than 1% at this amplitude.

Continuing the testing too much higher current levels