A modified inverted-staggered TFT structure suitable for a fully wet etch fabrication process for high performance low and high voltage a-Si:H TFTs

We designed an inverted staggered structure suitable for a completely wet etching process which also allows integration of many other a-Si:H based devices and circuits, using the same TFT fabrication process, with no need for any extra step. This structure lends itself to a fully wet etch fabrication technology which is simple, reproducible, completely compatible with positive photo-resist lithography techniques, and suitable for mass production of amorphous silicon TFT based circuits. Our wet etch method, unlike conventional dry etch methods, does not cause bulk and surface damage to the devices. Using this process, we fabricated high performance TFTs with a typical effective mobility of 1.2 cm²/V.s, threshold voltage as low as 1 V and on/off current ratio of 10⁷. With the same process and utilizing our novel soft contact TFT (SCTFT), we managed to fabricate high performance, high voltage TFTs which extend the working voltage range of our TFTs to above 100 V. Our high voltage SCTFTs, unlike conventional high voltage TFTs (HVTFTs), do not suffer from a low on-current V_x shift and a huge curvature in its output characteristic. The soft contact structure also improves the yield and reliability