This Small Business Technology Transfer (STTR) Phase I research project targets performance of GaAs-based heterojunction bipolar transistors (HBT). The high power and high frequency characteristics of these HBTs have led to their use as the power amplifier for several wireless applications such as cellular phones and wireless local area networks. The gain of a fabricated HBT increases by as much as a factor of four during the first few minutes of device operation, known as burn-in. The gain then continues to drift, which can be either up or down, over the span of tens of hours of operation. The drift in gain requires significant cost and resources in power amplifier design and production. The amplifier circuitry must be able to accommodate these variations in transistor gain requiring a significant performance compromise resulting in additional cost for circuit development and time to market. Individual devices must otherwise go through extensive testing to achieve stable operation. While well known, the burn-in and drift phenomena are poorly understood. Improved film deposition methods are needed to minimize the burn-in and drift. Previous investigations have linked these instabilities to point defects in the base.
With power amplifier production at hundreds of millions of units annually extended burn-in testing is expensive and necessary to avoid. If successful the development of low burn in heterojunction bipolar transistors for power amplifiers will be an important manufacturing development since it can ultimately lower the cost of the devices. Since these devices are used primarily in cell phones, for the transmitter, accomplishing a manufacturing methodology for low burn and drift devices would result in a lower cost to the consumer.
