Insight on the SU-8 resist as passivation layer for transparent Ga2O3–In2O3–ZnO thin-film transistors

Abstract

A nonvacuum and low temperature process for passivating transparent metal oxides based thin-film transistors is presented. This process uses the epoxy-based SU-8 resist which prevents device degradation against environmental conditions, vacuum or sputtering surface damage. The incorporation of SU-8 as a passivation layer is based on the ability of this polymer to provide features with high mechanical and chemical stability. With this approach, lithography is performed to pattern the resist over the active area of the device in order to form the passivation layer. The resulting transistors demonstrate very good electrical characteristics, such as μFE=61 cm2/V s, VON=−3 V, ON/OFF=4.4×109, and S=0.28 V/dec. Electrical behavior due to the SU-8/metal oxide interface characteristics is also reported on the basis of Fourier transform infrared analysis. In contrast, we demonstrate how sputtering of SiO2 as a passivation layer results in severely degraded devices that cannot be switched-off. In order to obtain proper working devices, it is shown that SU-8 should be hard baked at 200 °C for 1 h in order to obtain a highly cross-linked polymer network. The stability of SU-8 passivated devices over the time of storage, under current bias stress and vacuum conditions is also demonstrated.

Highly stable thin film transistors using multilayer channel structure

“…The HfO 2 acts as a passivation layer, which prevents the adsorption of water or oxygen molecules into the ZnO layer and hence improves the bias stability. 15,23,26 It is also noted that a single HfO 2 layer in the middle of two ZnO layers showed very similar trend of bias stress instability to that of TFT-A (results not shown here). Thus, a single HfO 2 layer at the top or in the middle of ZnO layer is not sufficient to effectively prevent the diffusion of water molecules toward the channel/dielectric layer interface.…”

Effects of Mg on the electrical characteristics and thermal stability of MgxZn1−xO thin film transistors

“…The active layer is fixed at a width/length ͑W / L͒ = 150 m / 5 m. To prevent ambient absorption/desorption during the electrical testing, a SU-8 resist is coated on top of the TFT channel, serving as a passivation layer. 12 All the electrical tests are conducted in the dark using an HP-4156C electrical testing system with a temperature controlled chuck. Figure 1͑c͒ shows the hard saturation behavior in the I DS -V DS curve.…”

Improving positive and negative bias illumination stress stability in parylene passivated IGZO transistors

“…3 To protect oxide TFTs from atmosphere, different materials have been used as passivation layers, such as Al 2 O 3 , 4 SiO x , 5 polyimide, 5 SU-8, 6 SiN x , 7 and parylene. 8 Parylene specifically has also been widely used as an encapsulation layer on printed circuit boards and in biomedical applications using other semiconductor technologies.…”