An Investigation of Process Variations and Mismatch Characteristics of Vertical Bipolar Junction Transistors

Abstract

Bipolar junction transistors (BJT) are widely used integrated devices for analog circuits. For most of analog applications, the process variation and the match performance of BJT pairs are critical for the circuit design. Vertical BJT device has advantages of current gain stability and high carriers collect efficiency over lateral BJT device. This work investigates the process variation, mismatch characteristics and related data distribution of $0.11~\mu \text{m}$ process vertical BJT devices throughly. Experiment data indicates that bigger devices have smaller electrical dispersion and better match characteristics than smaller devices of the same type. The distribution of electrical parameters does not conform with the typical Gaussian distribution. The standard deviation of the electrical parameter difference of matched device pairs is inversely proportional to the square root of emitter area. Generally, the matching properties of $\mathrm {3.3~V}$ BJT devices are better than their $\mathrm {1.5~V}$ counterparts, the PNP BJT devices matches better than their NPN counterparts with the same operating voltage and geometry size. The mismatch ratio is not located at the exact zero point but slightly deviates from the center zero point. The die location does not show significant impact on the statistical performance of vertical BJT devices. Electrical parameters of the same type and different bias point have strong statistical correlations. These investigated properties of process variation and mismatch characteristics is helpful for the analog circuit design which requires high accuracy matched vertical BJT device pairs.

Keywords

• Bipolar junction transistor (BJT)
• process variation
• mismatch