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

By combining a 0.12-μm-long 1.2-V thin-oxide transistor with a 0.22-μm-long 3.3-V thick-oxide transistor in a 0.13-μm CMOS process, a composite MOS transistor structure with a drawn gate length of 0.34 μm is realized. Measurements show that at V/sub GS/=1.2 V and V/sub DS/=3.3 V, the composite transistor has more than two times the drain current of the minimum channel length (0.34 μm) 3.3-V thick-oxide transistor, while having the same breakdown voltage (V/sub 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.