Many engineers recognize Keithley Instruments’ sourcemeters (source-measure units, or SMUs) as extremely handy bench instruments. SMUs can be a great alternative to test systems configured with separate programmable power supplies and digital multimeters. However, what’s been missing in Keithley’s SMU lineup is a model optimized for low-voltage test. The model 2401 SourceMeter plugs that hole with a 1-A/20-V range (see the figure).
The 2401 is derived from the existing 2400 SourceMeter lineup but is borne of Keithley’s recognition of the growth in photovoltaic applications. The instrument proves its worth in applications such as I-V characterization of solar cells, high-brightness LEDs, testing of low-voltage materials and other semiconductor devices, and resistance measurements.
In building the 2401, Keithley’s engineers removed some of the cost that comes with its higher-voltage models but managed to retain all of the features of those models. The only thing missing is a 200-V range. Consequently, the instrument costs about 25% less than the high-voltage models. Additionally, rear-panel ports were deactivated because the 2401 will be used more as a bench instrument and less in high-volume manufacturing test applications.
In operation, the model 2401 is just like its siblings in the 2400 SourceMeter family, with programming performed in similar fashion. It’s a GPIB-operated (general-purpose interface bus) instrument into which you can pre-load about 100 commands. The instrument integrates a highly stable dc power source with a highly accurate 6.5-digit multimeter.
To supplement its SourceMeter products, Keithley has answered customers’ calls for a line of programmable power supplies. Of course, an SMU is a programmable power supply and can be used as one, but it’s a costly power supply.
Keithley’s Series 2200 programmable supplies are offered in five variants with maximum output voltages from 20 V to 72 V and maximum currents from 5 A down to 1.2 A. These single-output, linear supplies (multi-output models are in the works) can deliver the maximum current at the maximum voltage.
Keithley considers the supplies to be a natural extension of its four-quadrant 2400 SourceMeter family. Often, devices under test (DUTs) require precision dc sourcing at some pins or inputs but not at others. A single-quadrant supply such as the Series 2200 models will be sufficient for those inputs.
Specifications include basic voltage/current accuracy of 0.03% and 0.05%, respectively. Resolution is to 1 mV/0.1 mA. A remote-sense capability on the rear panel eliminates the effects of lead resistances for a more accurate voltage at the DUT. Users can store and run up to seven test sequences with up to 80 steps in each one.
The supplies’ displays show more information than is usually found on programmable supplies. For instance, the display shows both the programmed settings and the actual output settings at once. This enables quick identification of unexpected DUT conditions. And, in addition to a knob, a keypad permits fast, convenient, and direct entry of settings. The supplies also offer GPIB and USB ports as standard equipment.
Additionally, Keithley has released Keithley Test Environment (KTE) 5.3 software for its S530 parametric test systems. The S530 systems can address all of the dc I-V and C-V measurements required in process-control monitoring, process reliability monitoring, and device characterization.
“A parametric tester is really a collection of SMUs, all intended to massage and exercise test structures on a wafer,” says Chuck Cimino, Keithley’s marketing director. The S530 monitors those test structures to determine whether anything is going awry in a fab.
What Keithley has done is migrate its older KTE platform to run on the S530 testers. This means that test engineers who had test recipes coded up in KTE for the older environment can migrate their code over to the new hardware platform.
Earlier versions of KTE were Unix-based. The new version is Linux-based and runs on PCs. Among the key features of the new software is a 1-kV capability to any pin. This is useful for testing the three-phase voltage controllers found in today’s hybrid vehicles, power ICs, display-driver ICs, and other high-voltage requirements.