**5.4 Dual-gate metal-oxide technology**

**Figure 14** (a) depicts the cross section of the dual-gate self-aligned metal-oxide (MO) technology on a 15-μm-thick polyimide film [25, 26]. The metal-oxide (IGZO or ITZO) TFTs are fabricated with two metal gates (M0, M1) and sourcedrain metal contacts (M2). An additional metal layer (M3), not shown in the cross section, is beneficial for footprint but also for performance and noise. The CSA experimental results shown in the following sections are designed with an extra metal layer, also used as anode layer.

**Figure 14(b)** shows the distribution of the extracted on-current (ION) from the measured transfer characteristics of 480/20 (μm/μm) IGZO (red) and ITZO (orange) dual-gate TFTs. The IGZO TFTs exhibits a median ION of 54.4 μA, whereas

#### **Figure 14.**

*(a) Cross section of dual-gate self-aligned metal-oxide technology on flexible polyimide substrate and (b) extracted on-current (ION) from experimental data of 480/20 (μm/μm) dual-gate self-aligned ITZO (red) and IGZO (orange) TFTs.*

the ITZO dual-gate TFT exhibits a median of 250.4 μA. Although the ION of the ITZO TFT is 5 times larger, the normalized spread of ION to the median over the wafer is double (15.4% for ITZO and 8.8% for IGZO). Threshold voltage is also extracted from the same measurements, yielding 1.16 V (and σVt = 242 mV) for ITZO and 1.77 V (and σVt = 94 mV) for IGZO TFTs. The 480/20 TFT is the largest footprint TFT used in the implemented designs. In **Figure 15**, microphotos of the (a) ADC and (b) the L = 3 μm CSA are shown.
