Thin film transistors with raised source and drain contacts and process for forming such

A device, comprising:

• a source contact and a drain contact in a source contact trench and a drain contact trench;
• a channel layer under the source contact and the drain contact, the channel layer having a first depression in a source region beneath the source contact, and the channel layer having a second depression in a drain region beneath the drain contact;
• a first spacing layer on a bottom of the source contact and in the first depression in the channel layer, and a second spacing layer on a bottom of the drain contact and in the second depression in the channel layer, wherein the first spacing layer and the second spacing layer are on a surface of the channel layer and line sidewalls of the source contact trench and the drain contact trench each of the first spacing layer and the second spacing layer having a central deeper portion laterally between outer shallower portions, each of the source contact and the drain contact having an upper portion wider than a bottom portion in the respective source contact trench and the drain contact trench;
• a gate electrode below the channel layer;
• and
• a dielectric above the gate electrode and underneath the channel layer;
• and
• wherein the first spacing layer and the second spacing layer extend a distance of 15 to 30 nm up along sides of the source contact trench and the drain contact trench.