In some embodiments, as shown in the left and middle portions of FIG. 7, the ILD layer 180 fills up the gaps/spaces G between the portions 135B, 136A and 136B in the isolating region IR. As shown in FIG. 7 & FIG. 12A, the portions 135B, 136A and 136B located on the isolation structure(s) 110 and the ILD layer 180 filled between the portions 135B, 136A and 136B constitute a capacitor structure 10C. In FIG. 12A, the ILD layer 180 fills between the heavily doped portion 135B and the ring-shaped structure that includes the lightly doped portions 136A and heavily doped portions 136B. As shown in FIG. 12A through FIG. 12C, the capacitor structure 10C is a horizontal structure overlying on the top surface 111 (as the horizontal plane) of the isolation structure 110. In certain embodiments, when the semiconductor material is polysilicon, the capacitor structure 10C includes the portions 135B, 136A and 136B as the polysilicon parts and the ILD layer 180 filled between the portions 135B, 136A and 136B as the insulator part (ID) of a polysilicon-insulator-polysilicon (PIP) capacitor structure arranged along the horizontal plane. In some embodiments, the interface IF1 between the lightly doped portion 136A and the insulator part ID (the ILD layer 180) is substantially perpendicular to the horizontal plane of the top surface 111 of the isolation structure 110. In some embodiments, the interface IF2 between the heavily doped portion 135B and the insulator part ID (the ILD layer 180) is substantially perpendicular to the horizontal plane of the top surface 111 of the isolation structure 110. If considering the portions 135B, 136B and 136A packed with the insulator portion ID are arranged at the same level (same horizontal level) and directly on the isolation structure 110, such configuration of the capacitor structure 10C is very different from the vertically stacked three layered capacitor structure. That is, the capacitor structure 10C may be considered as a horizontal-type capacitor.