TC700/702 Traveling Wave Amplifier Environmental Data

This application note provides information regarding the operation and performance of the TC700 and TC702 traveling wave amps under a variety of environmental conditions. Included in this application note are:

• TC700, TC702 reliability data.
• Test results in humid and condensing environments.
• Electrostatic discharge damage thresholds.
• RF input power damage.
• Thermal resistance measurements.
• Environmental test check list.

The data is intended to aid the designer in determining the necessary guard bands and precautions required (on reliability, thermal, and environmental issues) to insure a successful end product. This data is supplemental and does not imply any guaranteed specifications.

1.0 High Temperature Operating Life (HTOL) Test Results

High Temperature Operating Life (HTOL) Test Results The TC700 and TC702 TWAs have been subjected to HTOL life tests at the test and bias conditions shown in Table 1. The failure criteria was defined as ±1 dB drift in S21 measured at 26.5 GHz. The results from these tests show that the failure rate of both the TC700 and TC702 TWAs will be less than 100 FITS (or .01% failure/1000 hours.), after one year of continuous operation at the bias and temperature conditions listed in the following table.

2.1 Unbiased Humidity Test

Over 50 TWA wafers have been subjected to a three day (72 hour) 65 °C/95% R.H. soak. S–parameters were measured before and after the humidity soak. S21 was the only parameter exhibiting a measurable drift. The change in S21 was on the average –0.17 dB, with a standard deviation of .08 dB. The cumulative distribution is shown in Figure 1. This drift is recoverable when the wafers are “baked out” at 150 °C for 8 hours.

2.2 Biased Humidity Tests

Performance of TWAs under bias, in humidity, was investigated on several wafers. Two bias conditions were tested: high dc power dissipation bias, and low dc power dissipation bias. In standard, or high dc power dissipation bias, the TC700 is dissipating approximately 1 watt of dc power (2 watts for the TC702). In the low bias state the current in the TWA is adjusted, using an externally applied second gate voltage, to approximately 20% of Idss (or ~.2 to .4W Pdc dissipation). See Figures 2 and 3.

The low bias state is of particular interest to customers, providing external bias to the second gate of the TWA for AGC or pulse modulation applications. The results of these tests (see Table 2) indicate that TWAs biased at standard or high bias conditions will exhibit the same level of humidity sensitivity, measured by changes in S21, as in the unbiased 65 °C/95% R.H. test (i.e., approximately –.2 dB drift in S21). In the low bias state, catastrophic failures have resulted after several days of exposure to humidity.

It is postulated that the low bias state does not generate enough “self heating” to drive the moisture away from the active areas of the TWA FETs. The combination of high humidity, high voltage differentials and low dc power dissipation can significantly degrade TWA performance and ultimately lead to catastrophic failure. As a result, hermetic packaging is strongly recommended for any TWA applications where operation at low dc power dissipations in humid environments is likely. This is not a problem in non–humid environments.

3.0 RF Input Power

There are two maximum input power ratings on the TC700 and TC702 TWAs. The Absolute Maximum Input Power rating should be interpreted as the damage level. Applied power equal to or greater than the quoted Absolute Maximum Input Power rating may result in immediate, non–recoverable damage to the IC. The continuous RF Input Power rating represents the maximum input power that can be continuously applied to the device without degradation.1 For both cases the power limiting element on the TWA is the 50 thin film termination resistor. The power ratings are shown in Table 3.

5.0 Thermal Resistance

The thermal resistance of the TC700 and TC702s was measured using liquid crystal thermography. Thermal resistance measurements are very dependent on the assembly technique and thermal environment surrounding the IC. The assembly technique and materials used for these measurements are shown in Figure 6. The results are shown in Table 5

6.0 Microcircuit Environmental Qualification Checklist

Most microcircuits designed at Keysight Technologies are subjected to a series of environmental qualification tests. These tests are intended to evaluate how the microcircuit will function under the specified environment. The results will be a complex function of bias condition, thermal design, internal microcircuit components and other application- specific variables. As a result, the performance of a microcircuit under a specific set of environmental conditions can not always be predicted from environmental tests performed on an isolated component used in the microcircuit.

With this qualification in mind, Table 6 lists a number of tests a typical microcircuit is subjected to during production qualification.2 Performance of the TC700 and TC702 TWAs is noted for each test as: Passed (in device form), Will Not Pass, or Not Tested.