Semiconductor curve tracer

The Type 575 Transistor-Curve Tracer displays the dynamic characteristic curves of both NPN and PNP transistors on the screen of a 5-inch cathode-ray tube. Several different transistor characteristic curves may be displayed, including the collector family in the common-base and common emitter configuration. In addition to the transistor characteristic curves, the Type 575 is used to display dynamic characteristics of a wide range of semiconductor devices." (Tektronix, Catalog, 1967)

A semiconductor curve tracer is a specialised piece of electronic test equipment used to analyse the characteristics of discrete semiconductor devices such as diodes, transistors, and thyristors. Based on an oscilloscope, the device also contains voltage and current sources that can be used to stimulate the device under test (DUT).

Operation

The basic operating principle of the device is to apply a swept (automatically varying) voltage to the main terminals of the device under test while measuring the amount of current that the device permits to flow. This so-called V-I (voltage versus current) graph is displayed on an oscilloscope screen. The operator can control the maximum amount of voltage applied to the device, the polarity of the voltage applied (including the automatic application of both positive and negative polarities), and the load resistance inserted in series with the device.

For two terminal devices (such as diodes and DIACs), this is sufficient to fully characterize the device. The curve tracer can display all of the interesting parameters such as the diode's forward voltage, reverse leakage current, reverse breakdown voltage, and so on. For triggerable devices such as DIACs, the forward and reverse trigger voltages will be clearly displayed. The discontinuity caused by negative resistance devices (such as tunnel diodes) can also be seen.

The main terminal voltage can often be swept up to several thousand volts with load currents of tens of amps available at lower voltages.

Three-terminal devices require an additional connection; this is usually supplied from a stepped voltage or current source attached to the control terminal of the DUT. By sweeping through the full range of main terminal voltages with each step of the control signal, a family of V-I curves can be generated. This family of curves makes it very easy to determine the gain of a transistor or the trigger voltage of a thyristor or TRIAC. For most devices, a stepped current is used. For field effect transistors, a stepped voltage is used instead.

Curve tracers usually contain convenient connection arrangements for two- or three-terminal DUTs, often in the form of sockets arranged to allow the plugging-in of the various common packages used for transistors and diodes. Most curve tracers also allow the simultaneous connection of two DUTs; in this way, two DUTs can be "matched" for optimum performance in circuits (such as differential amplifiers) which depend upon the close matching of device parameters. This can be seen in the image to the right where a toggle switch allows the rapid switching between the DUT on the left and the DUT on the right as the operator compared the respective curve families of the two devices.

I-V curves are used to characterize devices and materials through DC source-measure testing. These applications may also require calculation of resistance and the derivation of other parameters based on I-V measurements. For example, I-V data can be used to study anomalies, locate maximum or minimum curve slopes, and perform reliability analyses. A typical application is finding a semiconductor diode’s reverse bias leakage current and doing forward and reverse bias voltage sweeps and current measurements to generate its I-V curve.^[1]

Kelvin sensing

Curve tracers are usually supplied with various semiconductor device test fixture adapters [1] that have Kelvin sensing.

History

Before the introduction of semiconductors, there were vacuum tube curve tracers (e.g., Tektronix 570). Early semiconductor curve tracers themselves used vacuum tube circuits, as semiconductor devices then available could not do everything required in a curve tracer. The Tektronix model 575 curve tracer shown in the gallery was a typical early instrument.

Nowadays, curve tracers are entirely solid state (except for the CRT, if used) and are substantially automated to ease the workload of the operator, automatically capture data, and assure the safety of the curve tracer and the DUT.

Recent developments in semiconductor curve tracer systems now allow three core types of curve tracing: current-voltage (I-V), capacitance-voltage (C-V), and ultra-fast transient or pulsed current-voltage (I-V). Modern curve tracer instrument designs tend to be modular, allowing system specifiers to configure them to match the applications for which they will be used. For example, new mainframe-based curve tracer systems, can be configured by specifying the number and power level of the Source Measure Units (SMUs) to be plugged into the slots in the back panel of the chassis. This modular design also provides the flexibility to incorporate other types of instrumentation to handle a wider range of applications. These mainframe-based systems typically include a self-contained PC to simplify test setup, data analysis, graphing and printing, and on-board results storage. Users of these types of systems include semiconductor researchers, device modeling engineers, reliability engineers, die sort engineers, and process development engineers. ^[2]

In addition to mainframe-based systems, other curve tracer solutions are available that allow system builders to combine one or more discrete Source-Measure Units (SMUs) with a separate PC controller running curve tracer software. Discrete SMUs offer a broader range of current, voltage, and power levels than mainframe-based systems permit and allow the system to be reconfigured as test needs change. New Wizard-based user interfaces have been developed to make it easy for students or less experienced industry users to find and run the tests they need, such as the FET curve trace test. ^[3]

List of curve tracer models

Although many of the older analog type curve tracers are no longer manufactured, they may be available on the used equipment market. Modern chassis-based systems, like Keithley Instrument’s Model 4200-SCS Semiconductor Characterization System and Scientific Test's 5000 Series of Curve Tracers, are more generally commercially available. Scientific Test additionally offers other curver tracer systems including the 5000E and 5300HX semiconductor testers; and Keithley also offers other curve tracing solutions, including the ACS Basic Edition package and the Series 2400 and Series 2600A SourceMeter instruments.

ABI Electronics Ltd

• CircuitMaster 4000M (main function circuit analysis, available as of 2011^[update])
• Counterfeit IC Detector[2], available as of 2011^[update]
• System 8 Range of V-I Testers (main function board fault-finding, available as of 2011^[update])

http://www.abielectronics.co.uk

Agilent Technologies

• B1505A [3], available as of 2011^[update]

B&K Precision

• 501A

Heathkit

• IT-1121
• IT-3121

Keithley Instruments

• Model 4200-SCS Semiconductor Characterization System [4]
• Series 2400 SourceMeter instruments [5]
• Series 2600A System SourceMeter instruments [6]
• ACS Basic Edition [7]

Leader Electronics

• LTC-905

Scientific Test, Inc.

Series 5000 Curver Tracers [8] and [9]

• Model 5000C1 Curve Tracer: 50A, 1Kv
• Model 5000C2 Curve Tracer: 50A, 2Kv
• Model 5000C2-1 Curve Tracer: 100A, 2Kv
• Model 5000C2-5 Curve Tracer: 500A, 2Kv
• Model 5000C2-10 Curve Tracer: 1000A, 2Kv
• Curve Tracer Software [10]

Tektronix

• 570 - vacuum tube curve tracer, discontinued
• 575, discontinued
• 576, discontinued
• 577, 577D1, 577D2, discontinued

Telequipment

• CT71, c1974, discontinued. CT71 Manual

Sony/Tektronix

• 370, 370A and 370B[11], discontinued
• 371, 371A and 371B (high power)[12], discontinued

Safety

Curve tracers are capable of generating lethal voltages and currents and so pose an electrocution hazard for the operator. Modern curve tracers often contain mechanical shields and interlocks that make it more difficult for the operator to come into contact with hazardous voltages or currents. Power DUTs can become dangerously hot during testing.

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  Transistor-curve tracer (detail 1)

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  Transistor-curve tracer (detail 2)

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  Transistor-curve tracer (parts)

References

1. ^ http://www.microwaves101.com/encyclopedia/curvetracer.cfm
2. ^ Keithley Instruments, Inc. The Challenge of Integrating Three Critical Semiconductor Measurement Types into a Single Instrument Chassis. http://www.keithley.com/data?asset=52840
3. ^ Semiconductor Characterization Software offers parametric testing. (October 1, 2011) ThomasNet News. http://news.thomasnet.com/fullstory/Semiconductor-Characterization-Software-offers-parametric-testing-584774

External links

• The Museum of Tektronix Scopes
• All manufacturers of curve tracers.
• A homebrew Curve Tracer.