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A G R E AT E R M E AS U R E O F CO N F I D E N C E
Accurate, Cost-Effective
converted to a current that's measured using
an ammeter or one channel of a source-
measure unit (SMU).
High Brightness LED Reverse Breakdown Voltage Test
A negative bias current applied to an HBLED
Testing Starts with Device
allows probing for its reverse breakdown volt-
age (VR). The test current should be set to a
level where the measured voltage value no
Fundamentals
longer increases significantly when current
is increased slightly. At higher voltages, large
increases in reverse bias current produce
insignificant changes in reverse voltage. The
VR test is performed by sourcing a low-level
Mark Cejer, Marketing Director reverse bias current for a specified time, then
Keithley Instruments, Inc. measuring the voltage drop across the HBLED.
Results are typically in the tens of volts.
H
igh brightness light emitting speed system setup and enhance throughput. Leakage Current Testing
diodes (HBLEDs) combine high Testing can be done at the die level (both Moderate voltages are normally used to mea-
output and high efficiency with wafer and package), or the module / subas- sure the current that leaks across an HBLED
long lifetimes. Manufacturers are sembly level. At the module/subassembly when a reverse voltage less than breakdown
developing devices that offer level, HBLEDs are connected in series and/or is applied (IL). In production testing, it's
higher luminous flux, longer lifetimes, parallel; therefore, higher currents are typi- common practice to ensure only that leakage
greater chromaticity, and more lumens per cally involved, sometimes up to 50A or more, doesn't exceed a specified threshold.
watt. Ensuring their performance and reli- depending on the application. Some die-level
ability demands accurate, cost-effective testing can be in the range of 5 to 10 amps, Boosting HBLED Production
testing at every phase of production. depending on die size. Test Throughput
The electrical I-V curve of a typical diode Once, a PC controlled all aspects of HBLED
is illustrated in Figure 1. Although a com- Forward Voltage Test production test. In other words, in each
plete test sequence could include hundreds Understanding how new building-block element of a test sequence, the sources and
of points, a limited sample is generally suf- materials like graphene, carbon nanotubes, instruments had to be configured for each
ficient to probe for the figures of merit. Many silicon nanowires, or quantum dots will test, perform the desired action, and then
HBLED tests require sourcing a known cur- perform in the electronic devices of tomor- return the data to the PC. The controlling
rent and measuring the resulting voltage or row demands instrumentation that can PC evaluated the pass/fail criteria and deter-
vice-versa. Instruments that combine syn- characterize resistance, resistivity, mobility, mined where to bin the DUT. Significant
chronized sourcing and measurement can and conductivity over wide ranges. Often, time was consumed by passing commands
this requires the measurement of very small from the PC and results back to it.
currents and voltages. The ability to create The latest generation of smart instruments,
accurate and repeatable measurements at the including Keithley's new High Power 2651A
nanoscale level is critical to engineers seek- System SourceMeter, boost throughput sub-
ing to develop and commercialize these next stantially by minimizing communications
generation materials. traffic. The majority of the test sequence is
embedded in the instrument in a Test Script
Optical Tests Processor (TSP