Pulse/Waveform Generation with Integrated Measurement Capability

The ability to perform current or voltage measurement at any point along a voltage pulse or arbitrarily generated voltage waveform has long been a highly desired measurement capability. In many measurement applications, especially those involving cutting-edge materials and devices, not only the DC current versus voltage (IV) characteristics but also the AC characteristics (such as pulsed IV, stepped IV or ramped IV) are required for accurate characterization. In addition, the ability to perform noise current analysis in both the time and frequency domains continues to take on increased importance for advanced device characterization in a variety of applications.

Previous pulsed measurement solutions have consisted of user-configured instrument setups, usually consisting of a pulse or function generator, a current to voltage convertor, and an oscilloscope (or voltage sampler). However, these types of measurement solutions have difficulty producing stable and consistent measurement results. This is mostly due to poorly calibrated components and to the lack of calibration of the entire system. In addition, measurement solutions constructed from multiple instruments can easily generate substantial measurementerrors due to their complicated cabling and the overall error arising from the cumulative errors of the individual instrument components. Therefore, in order to acquire consistent data, an off-the-shelf, self-contained solution with guaranteed specifications is highly desirable.

To meet these needs Keysight Technologies, Inc. developed the B1530A waveform generator/fast measurement unit (WGFMU) module for the B1500A semiconductor device analyzer. The WGFMU module combines pulsing and arbitrary linear waveform generation (ALWG) capabilities with current and voltage measurement functions in a single unit. The WGFMU module can measure current or voltage at sampling rates up to 200 Mega-samples/s and it possesses a 16 MHz bandwidth. Its ALWG function has a minimum programmable timing resolution of 10 ns and its bandwidth is about 45 MHz. These features enable the WGFMU to meet the measurement challenges posed by advanced materials and devices mentioned above.

In this product note, the key features of the WGFMU are introduced first. Then the measurement applications are explained based on practical examples with some technical hints to use it more efficiently. This product note includes the following contents:

• Key features of the WGFMU
• ALWG function
• Fast I/V measurement
• Software for ease of use and data handling
• Other B1500A measurement capabilities

Overview

Figure 2 shows a simplified circuit diagram of the WGFMU and the remote-sense and switch unit (RSU). The waveforms created using the WGFMU’s ALWG voltage generation capability output through the RSU. The RSU is also where the actual current or voltage measurement is performed. The WGFMU has two operation modes: PG mode and Fast IV mode. The PG mode combines a very fast voltage measurement capability with 50 ohm output impedance to minimize waveform reflections. The Fast IV mode has a slightly slower measurement speed and slower waveform rise/fall times than the PG mode, but it can measure both current and voltage. In fast IV mode five fixed current measurement ranges (from 1 μA to 10 mA) are available, and you can dynamically switch between ranges during a measurement.

Using the WGFMU module, a conventional pulsed or transient measurement can be made very easily as shown in Figure 3 on page 5.

The conventional system has difficulty producing stable and consistent measurement results due to poorly calibrated, user-created components and to a lack of calibration of the entire system. In addition, measurement solutions constructed from multiple instruments can easily generate measurement errors due to their complicated cabling and the overall error arising from the cumulative errors of the individual instrument components. In contrast, the WGFMU is a single module with guaranteed specifications. By placing the RSU close to the device under test (DUT), the WGFMU’s cabling is also kept very short and simple.

The key features and specifications of the WGFMU module that are relevant to pulsed or transient measurement are described below.

ALWG function

The ALWG function of the WGFMU can generate waveforms as a series of linear segments of variable length (from 10 ns to 10,000 ns with 10 ns resolution). The memory depth of the waveform vector is 2,048, and the WGFMU has a sequence memory that

allows it to create an output sequence consisting of up to 512 waveforms. In addition, a burst counter with a burst count of up to 1012 is available for each waveform included in the output sequence that supports the generation of long-duration AC signals. These capabilities allow the WGFMU to generate waveforms of long duration yet also support sections with very rapid changes (please see Figure 4).

The WGFMU module supports the following output voltage ranges: ±3 V, ±5 V, -10 V to 0 V and 0 V to +10 V. The resolution of the output voltage is also much better than conventional pulse and function generators: 96 μV for the ± 3 V range and 160 μV for the other ranges; this supports the creation of the very precise stimuli that are required to observe subtle device responses.

As previously mentioned, the WGFMU has a sequence memory that allows it to create an output sequence consisting of up to 512 waveforms (please see Figure 5). The sequence memory allows waveform data to be reused, thereby minimizing waveform memory consumption.

In this product note the key features of the B1500A WGFMU module have been explained. The WGFMU can be used for a wide variety of measurement applications due to its unique combination of pulsed and arbitrary waveform generation functions and high speed current/voltage measurement capabilities. A number of practical measurement examples utilizing these features have been discussed. The WGFMU is a self-contained, off-the-shelf measurement solution providing accurate and repeatable analysis capabilities that can be used to evaluate state-of-the-art devices constructed from the most advanced materials.

The Keysight B1500A semiconductor device analyzer uses the same precision SMU technology as its predecessor, the Keysight 4155/56 series semiconductor parameter analyzer. However, SMUs are not fast enough to meet the needs of many modern devices and process technologies. The B1500A WGFMU module is available to cover the measurement areas that SMUs cannot, permitting the B1500A to become the next de facto industry standard tool for semiconductor parametric test.