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There are many reasons why gallium arsenide devices exhibit good reliability, but the primary factor is that quality and reliability is built into the process. Each GaAs manufacturer has different processes for the fabrication of devices, and thus each manufacturer has different strengths and weaknesses. There are several clear advantages for devices manufactured at TriQuint.

First of all, the metallizations used are all primarily composed of gold. Gold is more conductive than aluminum used in conventional silicon device processing, and is also less susceptible to electromigration. Gold also is much less susceptible to corrosion than aluminum. Gold eliminates the potential for Au/Al intermetallic problems during assembly since gold bond wires are typically available. From a reliability standpoint, gold is clearly superior to aluminum metal for integrated circuit reliability.

Secondly, the active device used in mature GaAs ICs is the MesFET. Unlike the MOSFET, the gate is formed by a Schottky metal contact to the channel, instead of using a gate oxide. This eliminates the primary failure mechanisms found in MOS devices. Because of this Schottky configuration, the MesFET is relatively immune to surface effects and ionic contamination which plague silicon devices. Newer GaAs active devices, pHEMTs and HBTs, also have advantages over MOS devices and similar immunity to typical silicon surface problems.

Next, the use of dielectrics is fundamentally different in TriQuint GaAs than in typical silicon implementations. As we mentioned, the MesFETs, HBTs, and pHEMTs eliminate the need for gate oxide. The airbridge interconnect or low K planarizing dielectrics ease the requirements for cross-over, or inter-layer, dielectrics. The most stringent requirements for dielectrics are within capacitors. TriQuint is a GaAs leader in offering high capacitance structures, but even those have much thicker dielectric layers than MOS gates. Another function of dielectrics in GaAs is for environmental protection. Although the dielectric requirements are much less stringent for GaAs devices than silicon, a high quality plasma-deposited nitride or oxide is used for all the dielectric layers. The thinnest capacitor layers are 500 Angstroms thick, with breakdown voltages typically exceeding 40 Volts.

The last major component of the process is the bulk wafer material itself. GaAs is actually a semi-insulator except in areas where it is implanted with silicon or in epitaxial layers. Because of its higher bulk resistivity, roughly 1,000 times more resistive than silicon, GaAs is much less sensitive to the isolation and latch-up problems associated with silicon and silicon CMOS. There are other GaAs properties that lend themselves to better reliability, like lower electric fields at peak electron velocity, but they are minor compared to the four major groups that have been discussed.