A thin film transistor (TFT) structure includes a gate electrode, a gate dielectric layer on the gate electrode, a channel layer including a semiconductor material with a first polarity on the gate dielectric layer. The TFT structure also includes a multi-layer material stack on the channel layer, opposite the gate dielectric layer, an interlayer dielectric (ILD) material over the multi-layer material stack and beyond a sidewall of the channel layer. The TFT structure further includes source and drain contacts through the interlayer dielectric material, and in contact with the channel layer, where the multi-layer material stack includes a barrier layer including oxygen and a metal in contact with the channel layer, where the barrier layer has a second polarity. A sealant layer is in contact with the barrier layer, where the sealant layer and the ILD have a different composition.