A semiconductor curve tracer (also known as a semiconductor parameter analyzer) is a specialised piece of
electronic test equipment
Electronic test equipment is used to create signals and capture responses from electronic devices under test (DUTs). In this way, the proper operation of the DUT can be proven or faults in the device can be traced. Use of electronic test equipmen ...
used to analyze the characteristics of discrete
semiconductor device
A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivity li ...
s such as
diode
A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.
A diode ...
s,
transistor
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
s, and
thyristor
A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current ...
s. Based on an
oscilloscope
An oscilloscope (informally a scope) is a type of electronic test instrument that graphically displays varying electrical voltages as a two-dimensional plot of one or more signals as a function of time. The main purposes are to display repetiti ...
, the device also contains voltage and
current source
A current source is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it.
A current source is the dual of a voltage source. The term ''current sink'' is sometimes used for sources f ...
s that can be used to stimulate the
device under test A device under test (DUT), also known as equipment under test (EUT) and unit under test (UUT), is a manufactured product undergoing testing, either at first manufacture or later during its life cycle as part of ongoing functional testing and calibra ...
(DUT).
Operation
The function is to apply a swept (automatically continuously varying with time) voltage to two terminals of the device under test, and measuring the amount of current that the device permits to flow at each voltage. This so-called V-I (voltage versus current) graph is displayed on an oscilloscope screen. Configuration includes the maximum voltage applied, the polarity of the voltage applied (including the automatic application of both positive and negative polarities), and the resistance inserted in series with the device. The main terminal voltage can often be swept up to several thousand volts, with load currents of tens of amps available at lower voltages.
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 leakage current in a semiconductor device is the current from that semiconductor device when the device is reverse biased.
When a semiconductor device is reverse biased it should not conduct any current, however, due to an increased barr ...
, 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
In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it.
This is in contrast to an ordi ...
devices (such as
tunnel diode
A tunnel diode or Esaki diode is a type of semiconductor diode that has effectively "negative resistance" due to the quantum mechanical effect called tunneling. It was invented in August 1957 by Leo Esaki, Yuriko Kurose, and Takashi Suzuki ...
s) can also be seen. This is a method for finding electrically damaged pins on
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
devices.
For three-terminal devices (such as
transistors
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
and
field effect transistors
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs control ...
(FET),) a connection to the control terminal of the device being tested is used, such as the Base or Gate terminal. For transistors and other current based devices, the base or other control terminal current is stepped. For FETs, a stepped voltage is used instead. By sweeping the voltage through the configured range of main terminal voltages, for each voltage step of the control signal, a group of I-V curves is generated automatically. This group of curves makes it very easy to determine the gain of a transistor, or the trigger voltage of a thyristor or
TRIAC
A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised tradem ...
.
Test Device Connection
Curve tracers usually contain convenient connection arrangements for two- or three-terminal devices, 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 amplifier
A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs V_\text^- and V_\text^+ and one outpu ...
s) which depend upon the close matching of device parameters. This can be seen in the adjacent image 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.
Kelvin sensing
Curve tracers, especially high-current models, are usually supplied with various semiconductor device test fixture adapter
that have
Four-terminal sensing, Kelvin sensing.
Capacitive balance control
Some analog curve tracers, especially sensitive low-current models, are equipped with a manual control for balancing a capacitive
Bridge circuit
A bridge circuit is a topology of electrical circuitry in which two circuit branches (usually in parallel with each other) are "bridged" by a third branch connected between the first two branches at some intermediate point along them. The bridge ...
for compensating ("nulling") the stray capacitances of the test setup. This adjustment is performed by tracing the curve of the empty test setup (with all required cables, probes, adapters and other auxiliary devices connected, but without the DUT) and adjusting the balance control until the I curve is displayed at a constant zero level.
I-V Curve Tracing
I-V curve tracing is a method of analyzing the performance of a
Photovoltaic system
A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and co ...
, ideal for testing all the possible operating points of a PV module or string of modules.
History
Before the introduction of semiconductors, there were
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied.
The type kn ...
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
Tektronix, Inc., historically widely known as Tek, is an American company best known for manufacturing test and measurement devices such as oscilloscopes, logic analyzers, and video and mobile test protocol equipment.
Originally an independent ...
model 575 curve tracer shown in the gallery was a typical early instrument.
Nowadays, curve tracers are entirely
solid state 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.
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.
[Semiconductor Characterization Software offers parametric testing. (October 1, 2011) ThomasNet News. http://news.thomasnet.com/fullstory/Semiconductor-Characterization-Software-offers-parametric-testing-584774]
Safety
Some curve tracers, specifically those designed for high voltage or current or power devices, are capable of generating lethal voltages and currents and so pose an
electrocution
Electrocution is death or severe injury caused by electric shock from electric current passing through the body. The word is derived from "electro" and "execution", but it is also used for accidental death.
The term "electrocution" was coined ...
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. Inexpensive curve tracers cannot test such devices and are less likely to be lethally dangerous.
Image:Transistor curve tracer detail1.jpg, ''Transistor-curve tracer'' (detail 1)
Image:Transistor curve tracer detail2.jpg, ''Transistor-curve tracer'' (detail 2)
Image:Transistor curve tracer parts.jpg, ''Transistor-curve tracer'' (parts)
References
{{Reflist
External links
The Museum of Tektronix ScopesAll manufacturers of curve tracers.A homebrew Curve Tracer.
Electronic test equipment
Laboratory equipment
Electronics work tools