A source measure unit (SMU) is a type 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 ...

which, as the name indicates, is capable of both sourcing and measuring at the same time.

Overview

The source measure unit (SMU), or source-measurement unit as it is sometimes called, 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

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. They are also commonly used in

automatic test equipment Automatic test equipment or automated test equipment (ATE) is any apparatus that performs tests on a device, known as the device under test (DUT), equipment under test (EUT) or unit under test (UUT), using automation to quickly perform measurements ...

and usually are equipped with an interface such as

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USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...

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 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 ...

or as a constant

voltage source A voltage source is a two-terminal device which can maintain a fixed voltage. An ideal voltage source can maintain the fixed voltage independent of the load resistance or the output current. However, a real-world voltage source cannot supply unli ...

, 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.

References

External links

Video of Keithley 2450 SMU Review and Experiments

Source Measurement Unit solutions from National Instruments

Source Measure Unit

GS610 Single channel Source Measure Unit from Yokogawa

GS820 Two channel Source Measure Unit from Yokogawa
{{DEFAULTSORT:Source-measurement unit Electronic test equipment