A 20nm thick gate oxide is grown on top.
This process has 120-angstrom gate oxide that did not tolerate 5.0 V operation.
For the traditional gate oxide, silicon dioxide, the former barrier is approximately 8 eV.
Since metal 2 is not built yet, there is no diode connected to the gate oxide.
If the diode is connected to metal near the gate(s), it can protect the gate oxide.
Another implantation is then completed using a different dopant type, with ions penetrating the gate oxide.
The gate oxide is very thin (100 nm or less), so it can only sustain a limited voltage.
Overstressing the gate oxide can lead to stress-induced leakage current.
That layer is sometimes called the "gate oxide."
The thickness of the gate oxide and the active layer is below one micrometer.