Reliability and MMIC Technology Development and Production

A key aspect of MMIC technology development and production is reliability. At Northrop Grumman Space Technology (NGST), reliability assessment and improvement are incorporated into the formative stages of technology development and continue through process qualification and manufacturing. Key components of this approach include: multi-temperature accelerated life testing; other accelerated life testing; determination of failure mechanisms using both device parametric changes and destructive physical analysis; investigation of anomalous behavior or unexpected failures; and the use of long-term, low-temperature testing. The importance of each of these components will be illustrated using the results from GaAs HEMT MMIC technology. Multi-temperature testing projects GaAs HEMT MMIC life times in excess of 10 hours at a junction temperature of 125°C or less. Investigation of the reliability test failures demonstrates the primary failure mechanism for thermally accelerated failures is gate-sinking. In addition, hot-carrier induced degradation can limit MMIC life times and must be tested for differently than thermally-accelerated mechanisms. Investigation of anomalous behavior led to the identification a previously unidentified failure mechanism related to movement/loss of the ohmic metal. Long-term, low-temperature testing displays excellent stability and provides confidence in the inherent reliability of technology. INTRODUCTION A comprehensive approach to ensuring MMIC reliability, shown schematically in Figure 1, involves incorporating reliability assessment and improvement into the formative stages of technology development and continuing those activities throughout process qualification and manufacturing. Key components of this approach include: multi-temperature accelerated life testing; other accelerated life testing; determination of failure mechanism using both device parametric changes and destructive physical analysis; investigation of anomalous behavior or unexpected failures; and the use of long-term, low-temperature testing. The importance of each of these components will be illustrated using the results from GaAs HEMT MMIC technologies. Figure 1. NGST’s approach to MMIC reliability. GAAS HEMT TECHNOLOGY The GaAs HEMT technology described in this paper uses a 0.15 um Ti/Pt/Au T-gate [1]. The epitaxial structure contains an In0.22Ga0.78As channel clad on both sides with Al0.3Ga0.7As barriers as shown in Figure 2. SiNx passivation n+ GaAs AlGaAs Schottky barrier layer Si planar doping AlGaAs InGaAs channel GaAs substrate Drain Gate Source Figure 2. 0.15 um GaAs HEMT. MULTI-TEMPERATURE LIFE TEST High-temperature life testing is the primary method for estimating MMIC life times at operating conditions. This is CS MANTECH Conference, April 14-17, 2008, Chicago, Illinois, USA typically a 3 temperature life test with ambient temperatures at 200°C and above. This method is described in various industry standards documents, including MIL-STD-883 and JEP118 (where a 4th temperature requirement is outlined). An excellent test vehicle for this testing is a 2-stage, 40 GHz GaAs HEMT amplifier MMIC. This MMIC provides both RF output characteristics and aggregate DC device parametric data (for example, Gm and Id versus Vg, as shown in Figure 3). During life test the parts are stressed while biased at maximum voltage and current allowed (5V and 250 mA/mm). Between stress intervals, the MMICs are characterized for both RF performance and aggregate DC device parameters. 0.00 0.05 0.10 0.15 0.20 0.25 0.30 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 Vg (V) Id (A ) 0.00E+00 5.00E+01 1.00E+02 1.50E+02 2.00E+02 2.50E+02 3.00E+02 3.50E+02 4.00E+02 4.50E+02 5.00E+02 G m (S /m ) Estimated Tj = 313°C