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characterisation  industry


Keithley has introduced a new tester that is suitable for scrutinizing the performance of LEDs and high-power semiconductors. Test is clearly an important part of the manufacturing process, but many manufacturers see it as an annoying additive to the process. Should they view it in that manner?


Q A


It’s long past time for device manufacturers to start thinking about test as much more than ‘a necessary evil’. The growing demand for higher efficiency semiconductors is driven in part by the push for more energy-efficient devices. One of the goals for end products that employ lots of power semiconductors, such as power supplies for servers, must be reducing their energy consumption. When the power supply is in standby/off mode, leaky semiconductors in the inputs will waste a lot of electricity, especially when that leakage is multiplied by the number of power supplies in a big server farm.


To improve energy efficiency, IC manufacturers are constantly exploring ways to create more efficient silicon devices, as well as those based on compound semiconductors like SiC and GaN, which are inherently more efficient than silicon. All of that means greater testing challenges: ‘more efficient’ means materials and devices that are less leaky, ‘less leaky’ means IC makers need to be able to characterise ever-lower leakage currents, which is especially challenging in production.


Older instrumentation designed for characterizing relatively leaky silicon is typically not up to the challenge. The ability to characterise power semiconductors with pulsed measurements is also critical to ensuring accuracy because pulsed measurements let you test using high current levels without creating the self-heating problems that would occur if you were sourcing high DC currents.


High-brightness (HB) LEDs also present some critical testing challenges. For the types of applications that these devices serve, the colour of the light they output must be highly consistent from device to device because they’re typically packaged with multiple LEDs in a module, and multiple modules in a single end product. Any significant colour variation is immediately obvious and would be unacceptable to the consumer. Ensuring high colour consistency requires the ability to test these devices with extreme accuracy.


Here, too, high-throughput pulse testing is essential because HBLEDs are very susceptible to self-heating, which will affect the colour of the light they output. And, of course, in production, test throughput is equally critical. And those are the big issues the Model 2651A High Power System SourceMeter instrument was designed to address.


Many companies highlight the generic capacities of their tools over a number of areas but with this tool Keithley have deliberately focused on the specialities the tester provides. What motivates such a decision and what process advantages does it provide the manufacturer?


Q A For some of our customers, all we have to say is


‘We’ve got a terrific new 50A SMU’ and they’ll know exactly how to use it in their applications. But for the rest, we feel that test vendors have a big responsibility to their customers to help them choose and use their products effectively. You’re right, this product is designed to address a specific set of applications, but it’s undoubtedly the fastest growing area of the semiconductor industry. Power semiconductors are used throughout more industries every year: in the auto industry for hybrid and electric vehicles, electric grid applications, solar and wind power generation, power supplies for PCs and consumer electronics, and many more. Just about every segment of the electronics industry and their downstream customers are using power semiconductors and HB LEDs in some way. And we want to serve all of them.


Test has become an ever increasing part of the manufacturing process but also an ever increasing part of the cost. In industries where margins are so tight how does this new tool help manufacturers with cost? And when they see specific tool requirements, should they assume that the cost will also be higher?


Q A


Until recently, manufacturers of power semiconductors had to rely on what we call ‘big-iron’ ATE functional testers. And those systems were pretty expensive – typically hundreds of thousands of dollars each. Even more important, those systems aren’t really optimised to characterise modern power semiconductor materials and devices with their lower leakage currents and higher power levels.


In contrast, the Model 2651A is designed for exactly those characterisation challenges – and it costs about one-tenth as much. From a production test perspective, it not only dramatically lowers the cost of ownership, but provides higher-accuracy, better-quality measurements without a loss of throughput. That’s because the combination of the Test Script Processor (TSP) embedded in the Model 2651A, and the TSP-Link virtual backplane that system integrators can use to link multiple instruments together, makes it easy to scale a system as large as they need while ensuring high throughput. TSP makes embedded scripting and execution of commands possible, in contrast with line-by-line execution of commands over GPIB as in traditional instrumentation.


October 2011 www.compoundsemiconductor.net 27


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