TECHNOLOGICAL AND CONSTRUCTIVE METHODS FOR REDUCING THE LEVEL OF LOW-FREQUENCY NOISE IN n-p-n TRANSISTORS

Abstract

The article provides an analysis of the components of the low-frequency noise of bipolar transistors, developed constructive and technological methods that allow to reduce the amount of  low-frequency noise, and provide data on the noise figure on experimental samples of transistors. Bipolar low-noise transistors are used in the input stages and stages of preliminary amplification of small input signals in electronic equipment for various purposes, which reduces signal distortion at the output and increases the sensitivity at the input. The lower the noise level of the used transistors, the higher the quality of the electronic equipment. In addition to the well-known components of low-frequency noise, which are calculated according to known expressions, the article contains additional noise components that, due to random factors in each specific case, cannot be calculated. Analysis of all noise components in a bipolar transistor has shown that it is possible to reduce the noise level both by constructive for some noise components and by technological methods for other components. In the process of work, the design and technology of a bipolar silicon planar n-p-n transistor with a low level of low-frequency noise were developed. The manufacture of experimental samples and the measurement of their electrical parameters were carried out on standard equipment used for the manufacture of low-noise silicon transistors of the KT3102 series, taken as an analogue. To reduce the noise level in the constructive sense, it is advisable to use the strip geometry of the emitters, and in the technological plan, it is advisable to form the base of the transistor with a small dose of impurity, but with an increased base thickness, and also to use additional diffusion layers of p-type conductivity with an increased value of the surface concentration under the base contacts. The averaged values ​​of the low-frequency noise factor on the experimental transistors were obtained by about 30% less than those of the KT3102 series transistors similar in electrical parameters and characteristics, which proves the possibility of reducing low-frequency noise by both constructive and technological methods.