Source Measure Unit – An Unsung Hero on Your Workbench

Article By : Tektronix

There’s a powerful tool - the SourceMeter SMU Instrument - that can help you do all these things beside your oscilloscope and a DMM. Let's check it out!

If a new instrument can help you quickly and safely find all of the subtle problems that were overlooked during the design phase as well as the manufacturing problems, then why not use it? There’s a powerful tool – the SourceMeter SMU Instrument – that can help you do all these things and should be within easy reach beside your oscilloscope and a good digital multimeter (DMM).

Perhaps you know a bit about SMU instruments and may even be considering buying one. You may already have a power supply and a DMM on your bench and are wondering how an SMU or SourceMeter instrument can make you more productive. A closer look at the SourceMeter instrument may help you convince your manager that you need one!

A source measure unit (SMU) instrument is a five-in-one tool. It combines the useful features of a digital multimeter (DMM), power supply, current source, electronic load and pulse generator, all in a compact form factor.

This empowers you to:

Fig: MOSFET ID vs VD graph

• Precisely source and measure voltage and/or current at the same time
• Measure resistance vs. current/voltage directly or indirectly
• Source and measure across a very broad range of current (100 aA to 50 A) and voltage (100 nV to 3 kV) with 6½ digits of measurement resolution
• Run production tests 60% faster and gain up to 10X more throughput
• Save time, maximize speed and get jobs done quickly

Here are some of the typical applications which the Keithley SMU can address your needs.


LED, HBLED and OLED Testing

Visible high brightness light emitting diodes (HBLEDs) have gained a reputation for high efficiency and long lifetimes, which has led to their use in a growing list of applications, including automotive displays and exterior lights, backlighting for televisions and video monitors, streetlights, outdoor signs, and interior lighting. HBLEDs are advancing at an incredible pace.

Manufacturers require accurate, reliable, and repeatable source and measurement equipment with the power and flexibility to adapt to their ever-changing testing needs.

Innovative features like the graphical user interface, real-time I-V curve plotting, and the 7A, 100 watt analog capability allow the Keithley SMU to make repeatable measurements accurately, making it the perfect choice for testing HBLEDs. Download our resources today.


VSCEL and Laser Diode Testing

Laser diodes are capable of outputting a narrow and coherent light beam. Two common types of laser diodes are edge emitter laser (EEL) and the fast-growing VCSEL (vertical cavity surface emitting laser).

Fig: Simplified VSCEL Structure

VCSEL combines the advantage of low-cost manufacturability, optical efficiency, temperature stability, and large 2D arrays for increased power. Wavelength stability over the entire operating temperature of these devices is critical to maintaining precision and minimize noise in received signals.

Electrical efficiency measurement through precision trigger and synchronization of pulse width and duty cycle further optimize the required intensity and resolution of illumination. These directly impact the heat dissipation, power consumption, and battery life of the end system.

Keithley has an extensive portfolio of instruments for electrical tests, including light intensity, forward voltage, lasing threshold current, quantum efficiency, dark current, the presence of “kink” or kink test, slope efficiency, thermistor resistance, temperature, capacitance, and the full spectrum of L-I-V pulse testing of laser diodes. Download our resources today.


High Power Semiconductor Device Characterization

New compound materials, including silicon carbide (SiC) and gallium nitride (GaN), are increasingly being used to create these high-power semiconductor devices because they offer much higher power density, smaller size, better high temperature performance, higher frequency response, and lower ON resistance than silicon. All of these advantages add up to greater operating efficiency. These compound semiconductor devices are also far less leaky than silicon, so testing demands a combination of greater current measurement sensitivity and higher voltage sourcing. Characterizing these new devices at current levels barely above the noise floor typically requires special triaxial cabling.

Compound semiconductor materials are more difficult to work with and control than traditional silicon simply because the underlying technologies are less mature. The engineers responsible for designing and characterizing these devices, as well as those involved in quality assurance, failure analysis, and process monitoring, face significant and expensive technical challenges. These challenges make these devices more expensive than their silicon equivalents, which puts pressure on the cost of test, especially final test. However, given their end-user customers’ reliability requirements, these manufacturers can’t afford to skimp on testing.

Keithley Model Series 2651A and 2657A SMUs combine the capabilities of a semiconductor parametric analyzer, precision power supply, true current source, DMM, low-frequency ARB, pulse generator, electronic load, and trigger controller – all in one full-rack, four-quadrant instrument. Download our resources today.


Solar Cell and Photovoltaic Cell Testing

Solar or photovoltaic (PV) cells are devices that absorb photons from a light source and then release electrons, causing an electric current to flow when the cell is connected to a load. Solar panels are just a collection of solar cells connected in series and parallel that provide more power than just a single, smaller cell.

Fig: Typical forward bias I-V characteristics of solar cell.

Researchers and manufacturers of PV cells and panels strive to achieve the highest possible efficiency with minimal losses. As a result, electrical characterization of the cell as well as PV materials is performed as part of research and development and during the manufacturing process.

The current-voltage (I-V) characterization of the cell is performed to derive important parameters about the cell’s performance, including its maximum current (Imax) and voltage (Vmax), open circuit voltage (Voc), short circuit current (ISC), and its efficiency (η). You can simplify the I-V characterization of the solar cells and panels using the Keithley SMU. Download our resources today.

In summary, Keithley pioneered the development of these individual, compact, bench-top instruments and is the leader in SMU instrument technology today. This integrated I-V instrument is a sound investment for the future that’s affordable. Keithley, enabling you to have a greater measure of confidence.

Leave a comment