Characteristics of a new isolated p-well structure using thinepitaxy over the buried layer and trench isolation

An isolated p-well structure for deep-submicrometer BiCMOS LSIs is proposed. The structure consists of a retrograde p-well in an n-type thin epitaxial layer over an n⁺ buried layer, and trench isolation. Latchup characteristics in this CMOS structure and breakdown characteristics of the shallow p-well are studied on test devices. Excellent latchup immunity and sufficient voltage tolerance are obtained with a thin 1-μm epitaxial layer. A CMOS 1/8 dynamic-type frequency divider using this well structure functions properly up to 3.2 GHz at a 2-V supply voltage