Scaling of bipolar transistor analog properties for mixed analog/digital BiCMOS

The analog performance of polysilicon emitter transistors for small-geometry bipolar and biCMOS technologies is discussed. It is shown that under optimized processing conditions, high-performance analog transistors are obtained. The choice of interface treatment, emitter drive, and contact technology influence the overall performance. The transistors exhibit high gain, high Early voltage, and a low intrinsic base sheet resistance. Constant gain over eight decades of collector current is obtained. Temperature dependence of the gain is less than for implanted emitter transistors. The HF transistors have lower noise levels and smaller emitter resistances than RCA transistors with which they are compared. A 1.5-μm transistor is shown to exhibit better overall performance with a polysilicon emitter than with an implanted, metal contacted emitter