Measuring leakage current in RF power transistors: Page 3 of 6

October 26, 2011 // By William R. Murphy, Richardson RFPD
Around the globe, engineers and technicians using RF power devices have had many concerns regarding the specifications for leakage current, what the specifications mean in terms of the part's performance in the field, and most importantly, how to properly test/verify that a given part is meeting its printed leakage current specification...
current specification, absolute care must be taken to properly test and evaluate the device.

Proper Conditions

  1. Always test per the manufacturer’s specifications (temperature, voltages, shorts, etc.).
  2. The device itself must be free of foreign substances, dirt, dust, and other contaminants.
  3. Isolate the DUT. The device cannot be properly isolated and tested when soldered into a board with other parts connected. These other parts will alter the test results because they are indeed part of the test. Also, the leakage current attributed solely to contaminants on the board (even solder flux and fingerprints) can be higher than the leakage current through the DUT itself.
  4. Always use properly calibrated laboratory-grade test equipment.
  5. Never use a battery operated “multimeter” to test leakage current.
  6. Extreme care must be taken with regard to the testing environment itself and the procedures employed in performing the tests as well. Each must:
    • Comply with all industry Electrostatic Discharge (ESD) requirements.
    • Employ proper lab grounding techniques (equipment and technician).
    • Ensure that technicians are trained properly for the task.
    • Ensure that isolation techniques are employed for the DUT…
    • Use a proper, calibrated test fixture and shielded test leads.
    • Providing shielding from light (for the DUT) and some filtering/shielding from other noise sources (AC line, RF, etc.) may be necessary to detect low nA currents.

Proper testing methods

There are at least three acceptable methods for testing leakage current in RF power transistors:

  1. Calibrated lab power supply and calibrated (µA or nA) ammeter. (Good)
  2. Calibrated programmable semiconductor tester. (Better)
  3. Calibrated curve tracer. (Best)

Figure 3: Calibrated curve tracer (the best overall choice for measuring one device).

Current conditions in “Real World” leakage current testing

Engineers and technicians know that a working transistor with too much leakage current, that is to say a working transistor with “out-of-spec” leakage current, can indeed be a problem in the field. Such a device can cause early field failures, exhibit poor performance, be an unnecessary drain

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