A method includes providing a substrate having an N+ type layer; forming a P type region in the N+ type layer disposed within the N+ type layer; forming a first deep trench isolation structure extending through a silicon layer and into the N+ type layer to a depth that is greater than a depth of the P type layer; forming a dynamic RAM FET in the silicon layer, forming a first logic/static RAM FET in the silicon layer above the P type region, the P type region being functional as a P-type back gate of the first logic/static RAM FET; and forming a first contact through the silicon layer and an insulating layer to electrically connect to the N+ type layer and a second contact through the silicon layer and the insulating layer to electrically connect to the P type region.