A NEW GENERATION of silicon bipolar transistors has recently been developed for microwave applications. The transistors provide state-of-the-art performance up to the 5-GHz region. Within this family a power transistor, having excellent linearity at high frequencies, has also been developed. This transistor is especially well suited for linear power applications in communications systems, microwave radar, and ECM systems in the 2 to 5-GHz region. The designs afford a combination of linear power output, gain, low distortion and ease of broadband matching.The power transistor chip, designed to maximize linear performance in the 2 to 5-GHz region, uses a new transistor process which includes ion implantation, local oxidation and self-aligning techniques'. The interdigitated design can be fabricated with excellent uniformity. Each of the transistor's 34 emitter sites has its own Ta2N ballast resistor contacted with the highly reliable Ti/Pt/Au metal system as shown in Figure 1 (a). The resulting device has a uniform temperature distribution over its active area which enhances device reliability and linear power performance.When a microwave power transistor chip is packaged without any internal matching, the resulting input and output impedances are often far from 50 $2 and quite difficult to manage. The high reflection coefficients of these impedances present challenges to the designer who is trying to achieve flat power and power gain over more than 200 MHz with the packaged device. To increase the transistor's bandwidth capability when packaged, an MIS capacitor was incorporated into the package as shown in Figure 1 ( b ) to match partially the transistor's input. Figure 2 shows the effect of internal matching on the optimum source and load impedances. The reduction of the source reflection coefficient is apparent. An additional effect of the internal matching was additiopal realizable gain as demonstrated in Figure 3. For the data in Figure 3, internally matched and non-matched units were measured under optimum power matched conditions for linear output power. The resultant matched power gain, including the circuit losses, was generally higher for the internally matched unit than for the unmatched. The gain difference was approximately 1 dB at 4 GHz and, as expected, increased with frequency.For the internally matched device, the linear output power and associated power gain at the 1 d B gain compression point __ 1 Snapp, C.P., Hsu, T.H., Wong, R.W., "Process Technology and Modeling of a Low-Noise Silicon Bipolar Transistor with Sub-Micron Emitter Widths", International Microwave S y mposium; June, 1976. 'Mellor, D.J., Linvill, J.G., "Synthesis of Interstage Networks of Prescribed Gain Versus Frequency Slopes", IEEE Trans. Microwave Theory Tech., Vol. MTT-23, p. 1013-1020; Dec., 1975.are typically 850 mW with 11 dB gain at 2 GHz, and 500 mW with 7 dB gain at 4 GHz, which correspond to power-added efficiencies of 39% and 20%, respectively. The transistor is usable t o 5 GHz where 250 mW of linear output power with ...
