science

Source measure unit

Source measure unit is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Source measure unit rather than just read about it. In short: A source measure unit (SMU) is a type of electronic test equipment which can source voltage and current and measure them as it does so. Overview The source measure unit (SMU), or source-measurement unit, is an electronic instrument that is capable of both sourcing and measuring at the same time.

Key takeaways

Source measure unit belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Source measure unit to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Source measure unit from memory before moving on to harder problems.

Reference excerpt

A source measure unit (SMU) is a type of electronic test equipment which can source voltage and current and measure them as it does so.

Overview The source measure unit (SMU), or source-measurement unit, is an electronic instrument that is capable of both sourcing and measuring at the same time. It can precisely force voltage or current and simultaneously measure precise voltage and/or current.

SMUs are used for test applications requiring high accuracy, high resolution and measurement flexibility. Such applications include I-V characterizing and testing semiconductors and other non-linear devices and materials, where sourcing voltage and current source span across both positive and negative values. To accomplish this, SMUs have four-quadrant outputs. For characterization purposes SMUs are bench instruments similar to a curve tracer. They are also commonly used in automatic test equipment and usually are equipped with an interface such as GPIB or USB to enable connection to a computer.

History Semiconductor characterization led to the development of source measure units. The HP4145A semiconductor parameter analyzer introduced in 1982 was capable of a complete DC characterization of semiconductor devices and materials. It consisted of four independently controlled source monitor units (the precursor to source measure units) enclosed in a mainframe. The Keithley 236 introduced in 1989 was the first stand-alone SMU and allowed system builders to integrate one or more SMUs with a separate PC control. Over time stand-alone SMUs have evolved to offer a broader range of current, voltage, power level and price points for applications beyond semiconductor characterization. Smaller form factors made possible through the use of modern computing technologies have allowed system builders to integrate SMUs into rack and stack systems for larger scale production test applications.

Operation A SMU integrates a highly stable DC power source, as a constant current source or as a constant voltage source, and a high precision multimeter. It typically has four terminals, two for source and measurement and two more for kelvin, or remote sense, connection. Power is simultaneously sourced (positive) or sinked (negative) to a pair of terminals at the same time as measuring the current or voltage across those terminals is done.

SMU vs. power supply A power supply is mainly intended to provide appropriate power for a particular application. Due to this, the majority of power-supplies are one-quadrant (source only, with fixed polarity), and in most cases constant-voltage operation. Bench power supplies might add constant-current operation as well as providing limited measurement capabilities, but these are in many cases still one-quadrant only and with margins of errors acceptable for coarse lab-work. Some high-end lab power-supplies will have two- or four-quadrant operation (source and sink, with fixed or dual polarity), which is an essential feature of a SMU. However, many of these still have a main focus on providing power to an application, where eventual measurement capabilities has secondary priority. These may have advanced capabilities of controlling the power output, but might lack things like specialized test-modes or monitoring-options tailored for precise and easy power-characterization. This particular class of power-supplies can be regarded as the predecessor for the SMU, where the SMU differs in that it adds features particularly aimed towards characterization.

SMU vs. DMM The built-in sourcing capabilities of an SMU work with the instrument's measurement capabilities to reduce measurement uncertainty and support low current and more flexible resistance measurements. In voltage measurements system-level leakage can be suppressed more easily than with separate instruments. In current measurements, the SMU's design reduces voltage burden. For resistance measurements, SMUs provide programmable source values, useful for protecting the device being tested.

Significant features

Notable features of SMUs include the following:

I and V sweeping—Sweep capabilities offer a way to test devices under a range of conditions with different source, delay and measure characteristics. These can include fixed level, linear/log and pulsed sweeps. On-board processor—Some SMUs further improve instrument integration, communication and test time by adding an on-board script processor. User-defined on-board script execution offers capabilities for controlling test sequencing/flow, decision making, and instrument autonomy. Contact check—SMUs can verify good connections to the device under test before the test begins. Some of the problems this function can detect include contact fatigue, breakage, contamination, corrosion, loose or broken connections and relay failures.

See also Semiconductor curve tracer Voltage source Current source Digital multimeter Power supply Electrometer Electronic load

References

External links Video of Keithley 2450 SMU Review and Experiments Source Measurement Unit solutions from National Instruments SMMU07 Source Measurement Multiplex Unit from FRANK Germany Source Measure Unit GS610 Single channel Source Measure Unit from Yokogawa GS820 Two channel Source Measure Unit from Yokogawa Aim-TTi SMU4000 series PowerFlex SMU

Illustrations

Worked examples

Example 1 — a first encounter with Source measure unit

Start with the simplest possible case. Write down what Source measure unit claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Source measure unit before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Source measure unit ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Source measure unit

In research: Source measure unit appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Source measure unit in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Source measure unit is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electronic test equipment, so understanding it makes those chapters shorter.
In everyday life: Look for Source measure unit outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Source measure unit in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Source measure unit means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Source measure unit out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Source measure unit in simple terms?

A source measure unit (SMU) is a type of electronic test equipment which can source voltage and current and measure them as it does so. Overview The source measure unit (SMU), or source-measurement unit, is an electronic instrument that is capable of both sourcing and measuring at the same time.

Why does Source measure unit matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Source measure unit?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Source measure unit.