Charge-coupled transistor with different-dielectric-thickness structure

A device comprising:

• a substrate;
• a first transistor over the substrate and comprising:
• a dielectric structure comprising a first portion and a second portion over the first portion and having a thicker thickness than the first portion, wherein the first portion of the dielectric structure laterally extends across opposite sidewalls of the second portion of the dielectric structure, and the first portion of the dielectric structure is in contact with an entirety of a bottom surface of the second portion of the dielectric structure;
• a drain electrode penetrating through the second portion of the dielectric structure, wherein a bottommost surface of the drain electrode is in direct contact with a top surface of the first portion of the dielectric structure;
• and
• a gate electrode having a first T-shaped pattern from a cross-sectional view, the first T-shaped pattern having a horizontal linear portion above a topmost position of the dielectric structure and a vertical linear portion penetrating through the second portion of the dielectric structure and being in contact with the top surface of the first portion of the dielectric structure;
• and
• a second transistor over the substrate and comprising:
• a channel portion in the substrate;
• a source/drain feature adjacent to the channel portion;
• and
• a gate structure over the channel portion, wherein a bottom surface of the gate structure is lower than the top surface of the first portion of the dielectric structure of the first transistor.

A method, comprising:

• forming a dielectric structure over a substrate, wherein the dielectric structure comprises a first portion, a second portion, and a third portion laterally surrounding the first and second portions and having a thicker thickness than the first and second portions;
• forming a drain electrode over the substrate, wherein from a cross-sectional view, the drain electrode has a stepped sidewall structure having an upper sidewall, a lower sidewall horizontally set back from the upper sidewall, a first horizontal surface connecting the lower sidewall to the upper sidewall, and a second horizontal surface connecting the lower sidewall at a side of the lower sidewall opposing the first horizontal surface, the second horizontal surface is a bottommost surface of the drain electrode in direct contact with a top surface of the first portion of the dielectric structure, and the first horizontal surface is in contact with a top surface of the third portion of the dielectric structure, and from a top view, the drain electrode and the first portion of the dielectric structure are concentric circles;
• and
• forming a gate electrode over the dielectric structure, in contact with the second portion of the dielectric structure, and spaced apart from the first portion of the dielectric structure.