We experimentally prove that amorphous IGZO FET can be scaled down by connected dual-gate design with enhanced electrostatic control. By connected dual-gate operation and scaled dual stacks, the short channel device (LCH=30 nm) achieves near ideal SS of 63 mV/dec and ultra-high on-state current (ION) of 615 µA/µm at VGS-VTH=2 V&VDS=1 V. By this design, record-high transconductance (Gm) of 559 µS/µm at VDS=1 V and record-low drain-induced-barrier-lowering (DIBL) of 10 mV/V are achieved, to our best knowledge, among all the a-IGZO transistors with sub-100 nm channel length reported so far.