TriQuint: Company / Quality & Reliability / FAQs

Activation Energy is a number that indicates how temperature affects the rate of progression of a failure mechanism. Different failure mechanisms have different activation energies and in general, those for gallium arsenide are higher than the ones appropriate for silicon devices. The activation energy number is determined by life testing devices at more than one temperature, and quantifying the difference in the resulting lifetimes by using a relationship called the Arrhenius Equation. Activation energies have units called electron Volts, abbreviated eV. Since each structure on a GaAs IC has a different failure mechanism and each design has different configurations of structures, there is not a single activation energy that applies to all ICs manufactured at TriQuint. The predominant wearout failure mechanism involves gate metal "sinking" into the channel of MesFETs and has an activation energy of about 2.5eV. However, activation energies as low as 0.4eV have been measured for failure mechanisms causing nichrome resistor wearout. Life tests on ICs (involving an interaction of all structures operating over an range of temperatures present at the die surface) have resulted in activation energies from 1.6eV to 2.4eV. Examples of IC activation energies are shown on the Arrhenius Graph in Figure 1. Based upon this data, the most conservative estimate for an appropriate activation energy is 1.6eV. From a reliability standpoint, there is no difference in activation energies or expected failure rates between any of the TriQuint processes. Our historical data base on IC life test results are is shown on the Graph in Figure 2.

What's the Temperature?

Once the operating temperature of the IC is known, median lifetimes and failure rates can be predicted. A complete thermal analysis involving liquid crystal transition temperature measurements and infrared scanning is the best approach for measuring temperatures empirically. TriQuint has also developed software that performs simple thermal modeling for temperature estimation. An infrared thermal scan can sometimes provide average temperature information accurate enough to estimate reliability. For digital devices utilizing standard cell designs, we have generally found that the thermal resistance from the die hotspot to the case is less than 10°C/Watt. With a special heat-spreader package design and solder die attach, a thermal resistance as low as 2°C/Watt has been demonstrated. Temperatures of microwave, linear, and special digital designs are much more difficult to predict. Thermal resistances as high as 65°C/Watt have been measured.

Making a Prediction

Our data shows that all devices fabricated at TriQuint meet the goal of having failure rates less than 100 FIT during the first 20 years of operation at the maximum channel temperature of 150°C. This goal translates to a minimum MTBF of 10 million hours. These FIT and MTBF estimates are conservative for four reasons:

Operating temperatures are usually less than the maximum rating (using an activation energy of 1.6 eV, a 6.4°C drop in operating temperature will double the expected lifetime),
Actual MTBFs in early life will be much higher since failure rates increase in time (Figure 1),
Measured lifetimes exceed the goal, and
Activation energies are usually higher than 1.6eV.

FAQ 12: What Activation Energy is Correct?