A technique to improve the drive current of high-voltage I/O transistors in digital CMOS technologies

By combining a 0.12-mu m-long 1.2-V thin-oxide transistor with a 0.22-mu m-long 3.3-V thick-oxide transistor in a 0.13-mu m CMOS process, a composite MOS transistor structure with a drawn gate length of 0.34 mu m is realized. Measurements show that at V-GS = 1.2 V and V-DS = 3.3 V, the composite transistor has more than two times the drain current of the minimum channel length (0.34 pm) 3.3-V thick-oxide transistor, while having the same breakdown voltage (V-BK) as the thick-oxide transistor. Exploiting these, it should be possible to implement 3.3-V I/O transistors with better combination of drive current, threshold voltage (V-T) and breakdown voltage in conventional CMOS technologies without adding any process modifications.