Characterize Your Devices in Depth Using Curve Tracers
Key takeaways:
- The complex nonlinear behaviors of semiconductor devices and materials require instruments like curve tracers to characterize them through wide ranges of voltages and currents.
- Curve tracers are extensively used in the semiconductor industry both during design for modeling and simulations and during fabrication for automated verification.
- Curve tracers are also used in power electronics and electric vehicle industries.
The electrical behaviors of a lot of semiconductor devices can't be modeled using simple linear relationships. They exhibit complex nonlinear dynamic responses under various operating conditions. However, understanding these behaviors comprehensively is crucial because these devices have tremendous technical and business advantages if used properly.
Curve tracers are the instruments that facilitate such in-depth understanding. In this article, get to know what curve tracers are, what they can measure, how they're used in different industries, and how they work.
What is a curve tracer?
Figure 1. Semiconductor device characteristics
In electronics, curve tracers help engineers and designers measure important direct current (DC) characteristics of semiconductor devices and materials that exhibit complex behaviors like multiple regions of operation, nonlinearity, and asymmetry.
Such characteristics have traditionally included current-voltage (I-V) curves. However, modern curve tracers like the Keysight B1505A go far beyond them with advanced capacitance measurements, gate charge measurements, current collapse measurements, and characterization of cutting-edge wide bandgap (WBG) semiconductors like silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga2O3).
Understanding these complex behaviors is critical to the design and testing of circuits and devices in several industries, like semiconductor manufacturing, electric vehicles, and power electronics. Since they don't exhibit simple linear relationships, they are best understood by visualizing the responses to a range of inputs and operating conditions.
Are curve tracers instruments or instrument software?
Traditionally, curve tracers were dedicated electronic test instruments similar to analog oscilloscopes.
Nowadays, engineers use curve tracer software running on multi-purpose versatile instruments like source measure units (SMUs) and power deviceanalyzers that can simultaneously function as both current sources and sinks.
Specialized curve tracers called semiconductor deviceanalyzers help with the characterization of semiconductor materials and integrated circuits.
What are some differences between a curve tracer and a standard multimeter?
Some key differences between curve tracers and standard multimeters are outlined below:
- A curve tracer has both source and measure capabilities and supports wide current and voltage ranges. A multimeter has only measurement capabilities.
- A curve tracer can do both spot and sweep measurements and display them as graphs. But a multimeter supports only spot measurements and displays them as values without the useful graph views.
- A modern curve tracer like the Keysight B1500A comes with software like the Keysight EasyEXPERT group+ that provides powerful data analysis functions to accelerate device development and testing. Multimeters don't have such data analysis capabilities.
- A curve tracer typically has a rotary knob that enables intuitive and interactive sweep control to check the device characteristics in real time. A multimeter doesn’t have such easy-to-use controls for sweeping.
Are there any common problems or limitations with curve tracers?
Traditional I-V curve tracers are often capable of only current-voltage measurements which are not sufficient to understand the complex operational behaviors of modern semiconductor devices.
Keysight curve tracers overcome such limitations by providing not only high-precision I-V measurements but also C-V, gate charge, and current collapse characterization.
What devices and materials can be tested with curve tracers?
The devices and materials that are tested with curve tracers include:
- N-channel and P-channel field effect transistors (FETs)
- metal-oxide-semiconductor FETs (MOSFETs)
- negative-positive-negative (NPN) and positive-negative-positive (PNP) bipolar junction transistors (BJTs)
- insulated-gate bipolar transistors (IGBTs)
- diodes
- thyristors
- wafers and wafer-level devices as well as modules and packages during integrated circuit (IC) fabrication
- discrete devices during their automated bulk testing
- semiconductor materials, including WBG ones like SiC, GaN, and Ga2O3
What characteristics can a modern curve tracer measure?
Curve tracers can measure and analyze a variety of device parameters as listed below:
- Voltages and currents: They can measure source-drain outputs of MOSFETs (Id-Vds) and collector-emitter outputs of BJTs (Ic-Vce).
- Breakdown voltages: Beyond the breakdown voltages (BVds and BVce), excessive current flow and thermal runaway occur.
- Threshold voltages: For a FET, the threshold voltage is the minimum gate-to-source volts (Vth) to create a conductive channel between the source and the drain. For an IGBT, it's the gate-to-emitter voltage (Vgeth) at which the device starts to turn on.
- On resistance: This is the resistance of a FET while in the on state (Rds-on).
- Gate charge parameters: These are crucial for understanding the switching performance of N-channel MOSFETs and IGBTs. They include the total gate charge to turn on the device (Qg), the gate charge at the threshold voltage Qg(th), the gate-source charge (Qgs), the gate-drain charge (Qgd), the gate charge during switching (Qsw), and more.
- Leakage currents: The output leakage currents (Idss and Ices) and gate leakage currents (Igss and Iges) are crucial for characterizing power losses.
- Capacitances: The key capacitances include capacitances at the input (Ciss), output (Coss), reverse (Cres), gate-source (Cgs), gate-drain (Cgd), and others.
How are curve tracers used in different industries?
Curve tracers are essential for design and testing in multiple critical industries as outlined below.
Semiconductor industry
Figure 2. On-wafer I-V and C-V measurements using the B1500A curve tracer
Curve tracers are extensively used in integrated circuit (IC) and system-on-chip (SoC) design as well as manufacturing.
IC design
During the IC design process, simulations are heavily used to predict a chip's behavior. These simulations use device models that are either theoretical models derived from physics principles or empirical models based on measurements taken from similar devices. Curve tracers are widely used to obtain these measurements.
For example, Angelov-GaN is a widely used empirical model for GaN devices that uses I-V and C-V measurements from curve tracers. Similarly, the DynaFET artificial neural network model for GaN devices is trained on measurements from curve tracers.
IC manufacturing
Curve tracers are widely used for automated device testing and verification in certain stages of IC manufacturing like research and development, wafer fabrication, and final product testing.For on-wafer testing, curve tracers are integrated with wafer prober machines. The wafer prober consists of probes on one side that make contact with key points on each die. The other side of the prober has terminals that connect to the curve tracer through an appropriate accessories. This way, the curve tracer is brought into electrical contact with each die. As the wafer prober positions each die under the probe, it instructs the curve tracer to take the relevant measurements.
Similar tests are carried out at the pre-packaging and post-packaging stages using curve tracers.
Electric vehicles
Curve tracers are used for various tests in the electric vehicle (EV) industry as follows:
- Component testing: Curve tracers can test semiconductor devices used in EV components like inverters, converters, and other high-voltage systems.
- Research: Curve tracers can be used to study new materials or technologies for batteries and other electronic components.
Power electronics
Curve tracers are used in power electronics and power device testing as follows:
- Characterize device: Curve tracers, like the B1506A Power DeviceAnalyzer, enable the failure analysis and characterization of a wide range of essential power device parameters like breakdown voltages, on-resistance, and capacitances. This helps engineers select devices that will perform adequately under operational conditions.
- Automate accurate measurements: Automated I-V measurements reduce the test time and effort of manual rewiring. Pulsed current measurements minimize self-heating effects to ensure that the device's true performance characteristics are captured.
- Test thermal behavior: Curve tracers enable fast thermal tests across wide temperature ranges (-50 °C to +250 °C). This is crucial for understanding device behaviors under different real-world thermal conditions.
- Analyze power losses: Curve tracers help analyze conduction, switching, and driving losses, which is integral for optimizing design and enhancing efficiency in power converters and drivers.
- Extract accurate models: Using curve tracers, designers can gather data to develop accurate models of power devices, which can be used in simulations to predict circuit behavior accurately.
- Support advanced device types: Modern power devices based on GaN and SiC require precise measurement for optimal design.
- Facilitate digital control: With digital control becoming prevalent in power converters and power supplies, curve tracers assist engineers in modeling and assessing various devices in tightly packed arrays to capture transient behaviors accurately. This is essential for mitigating voltage and current surges during operation.
How does a curve tracer work?
A curve tracer supplies a varying direct current (DC) voltage or current to a device under test (DUT) and plots the corresponding current or voltage response curve on a screen.
The working of the signal variation can differ as outlined below.
Continuous sweep curve tracers
Figure 3. Continuous sweep input signal
The tracer sweeps through all the voltages or currents in a set range and continuously records the resulting response current or voltage.
However, such continuous inputs can result in higher power consumption by the device, subsequent thermal effects, and possibly affect the accuracy of the response.
Pulsed curve tracers
Figure 4. Pulsed input signal
To avoid the unwanted effects of continuous inputs, the input voltages and currents can be supplied in short pulses with microsecond to millisecond durations. These are called pulsed or spot measurements.
Such curve tracers enable the DUTs to remain in thermal equilibrium throughout the duration of the test. Pulsing also matches the typical operational environments of semiconductor devices where fast switching and clock signals are common.
Double-pulse test (DPT) curve tracers
Figure 5. Double-pulse test input signal
In power electronics, engineers need to accurately characterize energy losses between device turn-on and turn-off during fast switching. This is done using double-pulse testing where two pulses of different currents and adjustable durations are fired and the responses are measured using DPT-capable curve tracers like the Keysight PD1500A.
What are some key features to look for in a curve tracer?
Good curve tracers must have the following capabilities:
- Wide voltage and current ranges: Curve tracers must support a wide range of input values. Since some devices work as amplifiers with very high gains or switch very high currents, curve tracers must be able to measure a wide range of output currents and voltages too.
- Low current measurements: To analyze the leakage from devices in their turned-off states, curve tracers must be able to measure very low currents. For example, the Keysight B1500A can measure ultra-low currents in the femto-ampere range.
- Wide application coverage: Curve tracers must support built-in configurations for the diverse applications that different devices are used for. These include transistor amplifier applications, memory devices, power devices, nanodevices, reliability testing, and more.
- Ease of use: The curve tracer must facilitate easy setup, configuration, measurements, and analyses. Curve tracers are widely used for bulk component verification as well as automated test equipment (ATE) setups where ease of use and speed are critical. Conveniences like touch screens and on-device graphical user interfaces greatly streamline such verification.
- Simultaneous capacitance measurements: C-V measurements are critical to semiconductor modeling and testing. A curve tracer that can simultaneously measure I-V and C-V at different frequencies dramatically speeds up automated testing in fabs.
How do you calibrate a curve tracer?
For accurate measurements, modern curve tracers like Keysight's have advanced features like module self-calibration and SMU current offset cancel capabilities.
Note, however, that to satisfy all the test specifications shown in their data sheets, annual calibration at a Keysight service center is required.
Keysight curve tracers streamline every industry
Keysight's curve tracer hardware includes power device analyzers for power electronics as well as precision current-voltage analyzers and mainframes integrated with wafer probers for semiconductors.
These instruments run a variety of useful curve tracing software like:
- PathWave IV Curve Measurement Software to conduct synchronous I-V measurements on up to 20 channels of SMUs and analyze the results without any programming
- EasyEXPERT group+ for in-depth characterization
- Device Modeling WaferPro for automating on-wafer measurements
- Device Modeling IC-CAP for creating empirical models from curve tracer measurements
Contact us for in-depth recommendations on selecting the right curve tracers for your projects.