| 摘要 |
PURPOSE:To realize a charge detecting circuit having a high sensitivity and a superior linearity, by partially decreasing the density of P type or N type impurity for decreasing the junction capacity in the electrostatic capacity of a P-N coupled charge detecting layer. CONSTITUTION:A P<-> type layer 17 having the same type of conductivity as a substrate 1 and a sufficiently low density of impurity is provided adjacent to an N<+> type diffused layer 2. The region surrounded by broken lines 18 is a depletion layer. Since the P<-> type impurity layer 17 surrounding the diffusion layer 2 has a low density, the thickness Xd of the depletion layer is increased. The junction capacity CFV is decreased and the total electrostatic capacity CFD is also decreased, whereby the sensitivity of detecting charge is improved. When it is assumed that the P<-> type impurity layer 17 has the density of impurity corresponding to 1/16 of that of the substrate 1, the capacity CFV is decreased to 1/4 if the density of N type impurity layer >> the density of the P type impurity layer. Further, the decrease in the non-linear junction capacity improves the linearity of the charge detecting characteristics. |
