To replace traditional DC I-V techniques, various implementations of high-speed (i.e., pulsed) I-V techniques have been developed for applications such as characterizing high-k dielectrics and Silicon-On-Insulator (SOI) isothermal testing. When testing SOI devices with traditional DC I-V techniques, their insulating substrates cause them to retain the self-heat generated by the test signal, skewing their measured characteristics;
Traditional High-Speed-Pulse/
Depending on the instruments and how well they were integrated, it could also place limitations on how short the pulses and their duty cycle could be. Despite these limitations, users of these earlier pulsed I-V test systems soon began applying them to a variety of other characterization tasks, including non-volatile memory testing, ultrafast NBTI reliability testing, and many other applications.
Given their somewhat limited dynamic range, these systems remained something of a specialty technology. In order to become a mainstream test technology, the next generation of ultra-fast I-V testing systems would have to provide a very broad source and measure dynamic range. That meant they had to be able to source sufficient voltage to characterize flash memory devices, as well as voltages low enough to handle the latest CMOS processes.
For example, consider an embedded flash device in a CMOS process—the flash device might require up to 40V to program, but the CMOS process is running on 2.5V, so the test system used must be able to supply voltages for both requirements. It also needed to have a broad enough current range to handle the newest technologies, and fast enough rise times and long enough pulse widths to cover a wide range of applications. It had to be simple to use, and have an interconnect system that would allow the system to deliver accurate results reliably.
The New Generation of Parameter Analyzers. Semiconductor parameter analyzers have evolved to solve many of these test problems. Now it’s possible to find test systems that combine DC I-V, C-V, and ultra-fast pulse I-V test capabilities. For example, in the Keithley Model 4200-SCS system, the Model 4225-PMU Ultra-Fast I-V Module has been added to the DC I-V and C-V measurement modules. Thus, all three required measurement types can be integrated in a single test system that’s optimized for advanced applications such as:
· Flash, PCRAM, and other nonvolatile memory tests
· Isothermal testing of medium-sized power devices
· Materials research testing for scaled CMOS, such as high-k dielectrics
· NBTI/PBTI reliability tests
· LDMOS testing
· Testing of III-V materials and devices such as GaAs
Naturally, the computerized operating system and test library of an integrated test system of this type must make it easy handle a broad range of test protocols, and quickly switch between the three different types of test. An example of this is the Keithley Test Environment Interactive (KTEI) operating software, which provides a single test environment that allows a user to combine measurements made with different instrument types into a single test sequence.
By using plug-in modules for the hardware chassis in a parameter analyzer, the test system can be readily optimized to address specific applications or sets of applications. Just as important, as new applications come along, a modular architecture allows for cost-effective system upgrades. For instance, in the Model 4200-SCS system, builders can choose from medium- and high-power Source-Measure Units for DC I-V measurements, an optional capacitance meter for C-V measurements, and an ultra-fast (pulsed) I-V module for high-speed pulse measurements.
Thus, the latest generation of parameter analyzers offers users a complete solution for an application like charge pumping, because the test system can be configured for the ultra-fast pulse generation and sensitive DC current measurements required. The test libraries include predefined tests for making most of the common charge pumping measurements, such as a pulsed base voltage sweep or a pulsed voltage amplitude sweep. In the case of solar cell testing, integrated I-V and C-V measurement capabilities make it possible to perform a wide range of measurements, including capacitance-
Pushing the Limits of Instrumentation. While it’s important for a test system to handle the day-to-day measurements of modern devices and materials, the development of leading edge technology often demands more. This makes parameter analyzers with open system architectures even more important. To address the needs of advanced technologies, Keithley’s Model 4200-SCS allows users to modify any of the measurements in its test libraries, such as C-V, C-t, and C-f measurements. This opens the door for more customized testing and analysis, such as that needed for solar cells; high- and low-k structures; MOSFETs; BJTs; diodes; III-V compound devices; carbon nanotube (CNT) devices; doping profiles, TOX, and carrier lifetime tests; as well as junction, pin-to-pin, and interconnect capacitance measurements.
System speed and hardware flexibility are equally important, including the ability to add external instrumentation without sacrificing throughput and measurement performance. Many of the new ultra-fast I-V tests that lab users wish to perform, such as charge pumping and NBTI testing, may require greater current sensitivity than a standard instrument module provides (e.g., the Keithley Model 4225-PMU). This may require the addition of an external preamp.
For such an application, the optional Model 4225-RPM Remote Amplifier/Switch for Keithley’s parameter analyzer offers additional low current ranges that extend the system’s current sensitivity down to tens of picoamps. It also reduces cable capacitance effects and supports automatic switching as needed between the system’s ultra-fast pulse module, C-V module, and SMU modules to perform different types of testing on the fly. There is no need to disconnect a module’s wiring then reconnect it to a different instrument. These features reduce test system latencies and help improve throughput.
Older parameter analyzers typically were designed for specific types of test within the current-sensitivity/
