| 摘要 |
PURPOSE:To improve high frequency properties, and also to enlarge capacity varying ratio by forming a diffusion layer, which nearly determines capacity ratio, in hollow columnar shape. CONSTITUTION:An N-conductivity type high resistivity epitaxial layer 2 is formed on a high impurity concentration N-conductivity semiconductor substrate 1. An N- conductivity type high impurity concentration circular hollow columnar diffusion layer 3 is formed to reach the substrate 1 from the main surface of the semiconductor base substance of this layer 2. A P-conductivity type high impurity concentration diffusion layer 4 is formed circularly by diffusion so that it may cover this layer 3, and by the layers 3 and 12, PN junction J2 is formed. An SiO2 film 51, which is the SiO2 film covering the center of an element formed in this diffusion process and covers the element main surface exposed part of PN junction and the element center, and an SiO2 film 5, which is formed on the periphery of the hollow column and covers the part where PN junction is exposed to the element main surface, are left as protective films. Next, the exposed part of the layer 4 and the film 51 are coated with a conductor film 6 so as to form an electrode. To this film 6, a gold wire 7 is force- bonded by heat. According to this constitution, it is possible to form the layer 4 extremely thin, and the capacity varying ratio can be enlarged. |
