| 摘要 |
PURPOSE:To attain the low noise execution without enlarging extremely the chip area of an initial step transistor by diffusing or implanting further impurities to a p-type semiconductor with a high concentration and forming a base layer, in the base forming area of the initial transistor of an input signal. CONSTITUTION:To initial step transistors Q1 and Q2 of a preamplifier to amplify a fine signal of a magnetic head, etc., a base diffusing layer composed of a p<+> diffusion layer 7 of the high concentration is introduced. As this result, the base expanded resistance of the transistors Q1 and Q2 can be widely decreased. Namely, a base expanded resistance rbb' comes to be rbb' alpha1/Na (provided that impurities concentration of Na:p diffusion), and therefore, by making a p<+> diffusion layer 7 of a high concentration into a base diffusion layer, the rbb' can be decreased even when the pattern size is a standard size as it is. Consequently, even the thermal noise of the transistor can be decreased.
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