A Stored Charge Model for Integrated Injection Logic (I2L) Structures using Si/SiGe Material

This work describes the development of a charge control model that is used in the design and optimisation of the Si/SiGe heterojunction bipolar transistors (HBTs) used in I²L circuits. The devices are divided into discrete charge storage regions associated with quasi-neutral and depleted regions. The difference between the charge in the discrete regions for terminal potentials of logic 1 and logic 0 is used to calculate the switching times of an inverter. D.C. design criteria for inverting action are considered in the model which place constraints on the optimisation for dynamic performance. The inclusion of spreading resistances in the model is seen to be very important in the design. Our technique has the advantage of providing good physical insight into the limiting factors on performance.